The National Radio Astronomy Observatory is proposing to upgrade and expand the Very Large Array (VLA). This project, known as the VLA Expansion Project, will transform the VLA into the Expanded Very Large Array (EVLA) -- a new telescope whose observational capabilities will be at least an order of magnitude better than those of the VLA in every key instrumental parameter: sensitivity, frequency flexibility, spectral resolution, and spatial resolution. These improvements will be obtained at less than one third the investment cost of the VLA because the antennas, array design and infrastructure will be retained, while most of the electronics signal transmission system, and signal processing will be replaced with modern systems. The EVLA will be utilized by scientists from around the world for cutting-edge research throughout astronomy, providing unique information in such diverse areas as magnetic fields, cosmic sources in dusty regions, transient phenomena, and the formation of stars and galaxies.

The 1HT will be a large area telescope whose novel characteristics will be a wide field of view, continuous frequency coverage from .500 - 11 Ghz, multibeam capability, and provision for RFI mitigation built in. Its scientific motivation includes deep SETI searches, pulsar detection and investigation, galactic magnetic field mapping through many Zeemann transitions, mapping of the decrement in the cosmic background radiation seen toward galaxy clusters, observation of HI absorption toward quasars at redshifts up to z equals 2, and deep mapping of the HI distributions in the Milky Way and nearby galaxies. The array will use economies of scale to keep the costs down. It will consist of 500 - 1000 dishes of diameters in the range 3.6 m - 5 m. The dishes will be TV satellite style with wideband MMIC chip front-end amplifiers. Substantial prototype activity is under way. The feed, dish, and front-end MMIC designs are well along. A seven element test array is nearing completion. It will be used for studying RFI mitigation. By 2002, a 12 element array (PTA) which will be made up of all the final components will be operational. Final construction of the full array is expected by 2005.

The LOw Frequency ARray (LOFAR) is the Digital Software Radio Telescope that has been under study by the NFRA and the NRL for the last two years. A scaleable configuration is presented for an aperture synthesis array operating in the frequency range from the ionospheric cut off at about 10 MHz to about 160 MHz where existing telescopes are confusion limited. Both the array and the antenna station have a fractal structure following an exponential scaling law, which by appropriate weighting can provide a field of view and a synthesized resolution pattern of almost constant angular size independent of frequency. The processing architecture is scaleable as well and allows optimum distribution of the total processing power over signal and data processing tasks, by trading processed bandwidth in beam-formers and correlators for advanced processing like interference rejection, multi-beaming, pulsar processing, decade-wide chirp processing. The phased array antenna station provides a set of beams, which extends about a steradian on the sky and can be configured such that all relevant science objects are covered simultaneously. The pipelined self-calibration processing provides a clean image every third of a day, improving the sensitivity by a factor eight after two month of repeated observing. Based on the fast expansion of high performance processing technology, it is only after 2003 that signal and data processing will no longer dominate the cost of LOFAR in producing a confusion limited sky survey at sub mJy level.

The Large Adaptive Reflector (LAR) is a concept for a low- cost, large aperture, wideband, radio telescope, designed to operate over the wavelength range from 2 m to 1.4 cm. It consists of a 200-m diameter actuated-surface parabolic reflector with a focal length of 500 m, mounted flat on the ground. The feed is held in place by a tension-structure, consisting of three or more tethers tensioned by the lift of a large, helium-filled aerostat -- a stiff structure that effectively resists wind forces. The telescope is steered by simultaneously changing the lengths of the tethers with winches (thus the position of the feed) and by modifying the shape of the reflector. At all times the reflector configuration is that of an offset parabolic antenna, with the capability to point anywhere in the sky above approximately 15 degree Elevation Angle. At mid-range wavelengths, the feed is a multi-beam prime-focus phased array, about 5 m diameter; at meter wavelengths, it is a single-beam phased array of up to 10 m diameter. Simulations have shown that in operating wind conditions (10 m/s average speed with 2.5 m/s gusts), the position of the feed platform can be stabilized to within a few cm over time scales of approximately 20 s. Research indicates that the telescope concept is feasible and that an order of magnitude improvement in cost per m² of collecting area over traditional designs of large parabolic antennas can be achieved.

The collecting area of a radio telescope is a figure of merit of that instruments's capability. A Five hundred meter Aperture Spherical Telescope (FAST) is proposed to be built in the unique karst area of southwest China, and will act, in a sense, as a prototype for the Square Kilometer Array (SKA). It will be over twice as large as Arecibo coupled with much wider sky coverage. Some results from site surveys for such a SKA concept are briefly reported. Technically, FAST is not simply a copy of the existing Arecibo telescope but has rather a number of innovations. Firstly, the proposed main spherical reflector, by conforming to a paraboloid of revolution in real time through actuated active control, enables the realization of both wide bandwidth and full polarization capability while using standard feed design. Secondly, a feed support system which integrates optical, mechanical and electronic technologies will effectively reduce the cost of the support structure and control system. With an overall diameter of 500 m and radius of its spherical surface of 300 m, FAST will be the world's largest single dish.

We are proposing a very large FX correlator system as an enhanced ALMA correlator. Maximum bandwidth per IF is 4096 MHz. Spectral channels per baseline per IF is 128 X 1024. The possible number of correlation is a few thousands per IF. This correlator system realizes both high spectral resolution (< 0.1 km/s at 100 GHz) and wideband (> 1000 km/s at 850 GHz) observations up to 850 GHz. We have started the design and development of a minimum test system of the very large FX correlator in order to overcome several technical issues. This test system consists of two 2-bit A/D converters and one FX spectro-correlator. This correlator system has the bandwidth of 2048 MHz, 'half' bandwidth of the final specifications. But the spectral resolving point is the same as the final one. For the A/D converter, we are now measuring the sampling performance of high-speed sample-hold circuit at the clock of 8 GHz. For the FX correlator, we have finished the coefficient error estimation for the finite word length of FFT. More than 9-bit FFT calculation will make the coefficient error less than 3%. We also apply a new function, re-quantization. It reduces the number of connection between F and X parts with almost keeping the sensitivity.

An 8 X 8 equals 64 element digital interferometer was developed at Waseda University (1989 - 1995). It was an equally spaced two dimensional array of 2.4 m dishes at 10.6 GHz, and a 2D FFT processor was used for Nyquist rate imaging. Recently a spatial-temporal (2 + 1)D FFT processor has been developed for pulsar survey (1996 - 2000), in which a first 2D spatial FFT transforms the electric fields of coordinate represented to those of momentum represented. We obtain the electric fields in each 64 direction at Nyquist rate by the 2D spatial Fourier transform. The following temporal 1D FFT gives the spectrum of 64ch or 256ch to 64 directions respectively also at Nyquist rate. The total bandwidths of each direction are 20 MHz and the resulting frequency resolutions are 20/64 MHz or 20/256 MHz. For sensitive pulsar survey, we also have developed an interferometric array of 20 m spherical dishes in Nasu flat, 160 km north of Tokyo. Five dishes are completed at present. Normal temperature receivers of high electron mobility transistors (HEMT) are used at 1.4 GHz observation and the receiver noise temperatures are below 40 K. Expected rms detection limit (Delta) T is about 10^-2K under the condition of 20 MHz band widths and 1s integration time. Preliminary results of zenith survey at (delta) equals 40 deg using a single dish show (Delta) T equals 0.03 K without switching. Sub-reflectors and feed horns were designed so as to observe 5 deg off directions from zenith and they rotate around Az axis. It enable us to survey the declination zone of 32 <EQ (delta) <EQ 42 deg.

New digital spectrometers for the 25-BEam Array Receiver System (BEARS) of the Nobeyama 45-m telescope are described. A commercial digital oscilloscope is used as a digitizer. The digitizer samples analogue data with 2 bits (4 levels). Data of 512 MHz bandwidth are processed for four beams at the same time. The data-formatting unit demultiplexes 2 bits 8 data in parallel to 32 parallels and sends outputs to LSIs. General purpose LSIs for autocorrelation read the digital data with a clock rate of 32 MHz. Thirty-two LSIs of 32 lags connected in cascades calculate 1024-lag autocorrelation, and output a 1024-channel power spectrum of 512 MHz bandwidth. The bandwidth of 32 MHz is achieved by picking up the data in a rate of 1/16 in the front part of the autocorrelator module. The total performances have been demonstrated by long-term integration of noise signals from receivers and observations of the Galactic star-forming region W51 in CO line.

The technical evolution of the correlators of the Plateau de Bure interferometer since the first fringes, 14 years ago, is shortly presented. The progressive addition of antennas over this period has allowed the Grenoble correlator group to undertake several 'start-from-scratch' designs, which have replaced on-site equipment as it came obsolete. The tradeoff between design cycle time and lifetime of such equipment is discussed. The latest design is described in detail. The new correlator can be set to analyze up to eight simultaneous windows, adjustable in size and center frequency, thanks to a 2 X 220 MHz image rejection mixer. Advantages of analog IF processing are presented. The frequency plan of the IF processor has been designed to be fully compatible with MarkIV VLBI recording. The correlator is then used to sum up the signals of the 6 antennas over 256 MHz. The digital section mainly uses an IRAM-designed low-power, low-cost ASIC. Delay lines use FPGA's and phase rotators use DDS's. Surface-mount technology is used everywhere. A commercial CPU module runs the real-time software under Linux. A 21-slot VME chassis hosts the hardware. Test results and measurements of performance on the full-size machine are presented. The difficulties encountered in achieving this kind of machine within schedule in today's industrial environment are retrospectively analyzed.

A digital filter being developed by the National Radio Astronomy Observatory (NRAO) for the Atacama Large Millimeter Array (ALMA) is presented here. The filter is designed using field programmable gate array (FPGA) integrated circuits and has an equivalent clock rate of 4 GHz. The ALMA radio astronomy array being developed by the NRAO in cooperation with several European scientific agencies will consist of up to 64 twelve-meter diameter antennas to be used for observing astronomical sources at millimeter and submillimeter wavelengths. This instrument is to observe with bandwidths up to 16 GHz per antenna in eight unbroken RF bands of 2 GHz each. Bandwidth-resolution trade-offs are done in ALMA by providing each of the eight 4-Gsample/s digitizers per antenna with a programmable Finite Impulse Response (FIR) digital filter. The filter can be selected to perform 1/1, 1/2, 1/4, . . ., 1/64 band filtering and sample decimation. In the 1/2 band mode, the filter has the equivalent of 128 tap weight multiplications. Tap weights increase by factors of two to the limit of 2048 tap weights when the filter is programmed to be a 1/32 band low-pass or high-pass filter. The filter is designed to process the output of a four-bit digitizer. The filter utilizes RAM look-up tables for tap weight multiplications. The output of the tap weight multiplications drive an adder tree which has 10-bit precision in the early stages and 7-bit precision in latter stages. Output quantizing of the adder tree output is done in look-up table RAM to 2- bit, 4-level precision. The filter is implemented on a 280-mm, 6-U, Euro card using FPGA ICs running with a system clock rate of 125 MHz.

A new Auto-Correlation Spectral Imaging System (ACSIS) for the James Clerk Maxwell Telescope (JCMT) is being developed at the National Research Council of Canada, in collaboration with the Joint Astronomy Centre and the United Kingdom Astronomy Technology Centre. The system is capable of computing the integrated power-spectra over 1-GHz bandwidths for up to 32 receiver beams every 50 ms. An innovative, multiprocessor computer will produce calibrated, gridded, 3-D data cubes so that they can be viewed in real-time and are in hand when an observation is over. When connected to arrays of receivers at the Nasmyth focus of the telescope, the system will be able to rapidly make large-scale images with high spectral resolution and map multiple transitions. The ACSIS system will be mated initially with the multibeam 350-GHz receiver system. Heterodyne ARray Program (HARP), under development at the Mullard Radio Astronomy Observatory in Cambridge, England. In this paper we describe ACSIS, how it is designed and the results of key performance tests made.

New radio telescope arrays are currently being contemplated which may be built using hundreds, or even thousands, of relatively small antennas. These include the One Hectare Telescope of the SETI Institute and UC Berkeley, the LOFAR telescope planned for the New Mexico desert surrounding the VLA, and possibly the ambitious international Square Kilometer Array (SKA) project. Recent and continuing advances in signal transmission and processing technology make it realistic to consider full cross-correlation of signals from such a large number of antennas, permitting the synthesis of an aperture with much greater fidelity than in the past. In principle, many advantages in instrumental performance are gained by this 'large-N' approach to the design, most of which require the development of new algorithms. Because new instruments of this type are expected to outstrip the performance of current instruments by wide margins, much of their scientific productivity is likely to come from the study of objects which are currently unknown. For this reason, instrumental flexibility is of special importance in design studies. A research effort has begun at Haystack Observatory to explore large-N performance benefits, and to determine what array design properties and data reduction algorithms are required to achieve them. The approach to these problems, involving a sophisticated data simulator, algorithm development, and exploration of array configuration parameter space, will be described, and progress to date will be summarized.

The 100-m NRAO Green Bank Telescope will be completed in early 2000. The GBT is the most ambitious, single radio telescope ever constructed and has a large number of unique design and performance features. This paper will review those features, which include an offset feed (clear aperture) design, an active surface, a closed-loop laser metrology system for surface figure and pointing control, broad frequency coverage from approximately 100 MHz to 115 GHz, a versatile receiver selection mechanism, and a new multi-input, 256k-channel autocorrelation spectrometer. The status of the project, the commissioning schedule, plans for early operations, the initial instrumentation suite, and plans for future instrumentation will be reviewed. Through most of its frequency range, the GBT will offer a considerable advance in sensitivity and image fidelity compared with exiting telescopes. Scientific areas for which the GBT will have a large impact will be discussed.

The Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT/GTM) is a joint project of the Instituto Nacional de Astrofisica Optica y Electronica, Tonantzintla, Mexico and the University of Massachusetts, Amherst, USA. The telescope will have an aperture of 50 m diameter with a surface accuracy of 75 micrometer and a pointing accuracy of 1.0 arcsec. The telescope is under construction on Cerro La Negra, Orizaba, Puebla, Mexico. The telescope is exposed to the severe environment at 4600 m altitude, will operate in up to 10 m/sec wind speed during sunshine or cold night and must survive thunderstorms, snow, ice etc. We describe the design features of the telescope and its subsystems, as the isostatic support of the carbonfiber reflector panels, the reflector backup structure and the thermal control system, the servo system including main axis drives and active surface control, the alidade with the large receiver rooms and excellent access to the science instruments, and the foundation on the volcanic summit of Cerro La Negra. The active deformation compensation system is described in a separate paper at this conference.

The Academia Sinica, Institute for Astronomy and Astrophysics (ASIAA) is building two antennas to be added to the six antennas of the Sub-Millimeter Array (SMA) of the Smithsonian Astrophysical Observatory (SAO). The antennas have been designed at SAO and are currently under construction at Mauna Kea. ASIAA's two antennas are made in Taiwan from parts manufactured locally and imported from Europe and from the USA. This report will focus on the manufacturing and testing of 2 major components: the alidade and the reflector. We will emphasize the work done on the composite parts used in the 6- meter reflectors, namely the carbon fiber tubes for the backup structure, the carbon fiber legs of the quadrupod and the composite central hub. We will discuss the modal testing and pointing tests of the antennas. Finally this report will show how the Taiwanese industry was able to respond to the high manufacturing standards required to build sub-millimeter antennas. The design and manufacturing capabilities of the Aeronautical Research Laboratories and China Shipbuilding Corporation have made possible the construction of the telescopes in Taiwan.

A 10-m submillimeter telescope designed for interferometric observations at bands from 3 to 0.3 mm has constructed at Nobeyama Radio Observatory. The telescope is an engineering model for a large millimeter and sub-millimeter array, and will be operated for developments of sub-millimeter observation techniques at a remote site. We have fabricated lightweight machined aluminum panels (15 kg m^-2) that have a surface accuracy of 5 micrometer rms. They have a typical size of 0.8 m X 0.6 m, and are supported with three motorized screws. The back-up structure is constructed of a central hub of low thermal expansion alloy, and CFRP honeycomb boards and tubes. Holography measurements will be made with a nearby transmitter at 3 mm. The overall surface accuracy is expected to be < 25 micrometer rms; the goal being 17 micrometer rms. We have achieved an accuracy of 0.03' rms for angle encoders. The drive and control system is designed to achieve a pointing error of 1'.0 rms with no wind and at night. Under a wind velocity of 7 m s^-1, the pointing error increases to 2'.0 rms. An optical telescope of 10-cm diameter mounted on the center hub will be used to characterize pointing and tracking accuracy. Thermal effects on the pointing and surface accuracy will be investigated using temperature measurements and FEM analyses. The fast position switching capability is also demanded to cancel atmospheric fluctuations. The antenna is able to drive both axes at a maximum velocity of 3 deg s^-2 with a maximum acceleration of 6 deg. s^-2. The telescope is currently equipped with SIS receivers for 100, 150, 230, and 345 GHz and a continuum backend and an FX-type digital autocorrelator with an instantaneous bandwidth of 512 MHz and 1024 channel outputs.

The Mt. Fuji submillimeter-wave telescope has been operated since November 1998 to survey neutral atomic carbon (CI) toward the Milky Way. It has a 1.2 m main reflector with a surface accuracy of 10 micrometer in rms. A dual polarization superconductor-insulator-superconductor (SIS) mixer receiver mounted on the Nasmyth focus receives 810/492/345 GHz bands in DSB simultaneously. An acousto-optical spectrometer (AOS) has 1024 channels for 0.8 GHz bandwidth. The telescope was installed with a helicopter and bulldozers at the summit of Mt. Fuji (alt. 3725 m) in July 1998 after a test operation at Nobeyama for a year. It has been remotely operated via a satellite communication from Tokyo or Nobeyama. Atmospheric opacity at Mt. Fuji was 0.4 - 1.0 at 492 GHz in 30% of time and 0.07 - 0.5 at 345 GHz in 60% of time during winter five months. The system noise temperature was typically 1200 K (SSB) at 492 GHz and 500 K (DSB) at 345 GHz. The beam size was measured to be 2.'2 and 3.'1 at 492 and 345 GHz, respectively. We have conducted a large-scale survey of the CI (492 GHz) and CO (3 - 2: 345 GHz) emission from nearby molecular clouds with total area of 10 square degrees. We describe the telescope system and report the performance obtained in the 1998 winter.

We discuss the various evolution phases of radioheliography, the incompatibility between its achievements and the requirements of modern solar physics and the physics of solar- terrestrial relationships, and the trends of and approaches to solving the challenging information problems. Further, we substantiate and outline the program of the creation of a multiwave radioheliograph on the basis of upgrading the Siberian Solar Radio Telescope (SSRT) -- an essentially new- generation radioheliograph.

The Institute of Space and Astronautical Science (ISAS) launched the first space VLBI (Very Long Baseline Interferometry) satellite, HALCA, in February 1997. After completing a series of engineering experiments to verify space-VLBI observations, the first VLBI fringes and images were obtained in May and in June, respectively. HALCA has now been operated for science observations at 1.6 and 5 GHz for the VSOP (VLBI Space Observatory Programme) project in cooperation with many organizations and radio telescopes around the world. In this paper the current science activities of the mission are reviewed and results presented.

The Far Infrared and Submillimeter Telescope (FIRST), is an ESA cornerstone mission, that will be used for photometry, imaging and spectroscopy in the 80 to 670 micrometer range. NASA, through the Jet Propulsion Laboratory (JPL), will be contributing the telescope and its design to ESA. This paper will discuss the work being done by JPL and Composite Optics, Incorporated (COI), the developer of the primary mirror technology. Optical and mechanical constraints for the telescope have been defined by ESA and evolved from their trade studies. Design drivers are wave front error (10 micrometer rms with a goal of 6 micrometer rms), mass (260 kg), primary mirror diameter (3.5 m) and f number (f/0.5), and the operational temperature (less than 90 K). In response to these requirements a low mass, low coefficient of thermal expansion (CTE) telescope has been designed using carbon fiber reinforced polymer (CFRP). This paper will first present background on the JPL/COI CFRP mirror development efforts. After selection of the material, the next two steps, that are being done in parallel, are to demonstrate that a large CFRP mirror could meet the requirements and to detail the optical, thermal and mechanical design of the telescope.

The Atacama Submillimeter Telescope Experiment (ASTE) is a Japanese development program for the large millimeter and submillimeter array (LMSA/ALMA). The new 10-m submillimeter- wave telescope is a prototype telescope for the LMSA project and to be installed in Chile in 2001. The telescope will be equipped with submillimeter-wave SIS mixer receivers and a submillimeter-wave direct detector camera. The submillimeter- wave camera based on superconducting direct detectors (SIS photon detectors) are under development to realize very wide field observations in submillimeter-wave. Niobium tunnel junctions with low leakage current coupled to antenna structures can be sensitive submillimeter-wave detectors when high quantum efficiency and low leakage current is realized. Inhomogeneous distributed junctions coupled to log-periodic antennas can be used to realize this. Input coupling of more than 50% is calculated using 5-element and 10-element inhomogeneous distributed junctions. With leakage current of less than 100 pA, noise equivalent power can be less than 10^-16 W/Hz^0.5 under shot noise limited operation. Submillimeter-wave camera of 100 pixels is now under design and will be installed on ASTE 10-m telescope in 2002 or later.

A large focal plane array receiver system for the NRO 45 m telescope (SIS 25-BEam Array Receiver System, or BEARS) is described. This new array receiver uses SIS junctions and has 25 elements. It can operate at the frequency range of 82 - 116 GHz. The development of this new system is almost complete. We describe about the whole system in detail, which includes the receiver, the IF systems, the new spectrometers and the remote control systems. We also describe about the performances and the uniformity of the system and show the astronomical result.

This is to report on our progress and current status of the Sub-Millimeter Array (SMA) project in Taiwan. In particular, we will describe the development of the SMA receiver systems. The SMA is the first major instrumentation project in the Taiwanese astronomical research community. The primary design and development of the SMA receiver system has been carried out in the receiver laboratory at the Smithsonian Astrophysical Observatory (SAO). We have undertaken the system assembly, integration and testing, and the task to fabricate the superconductor-insulator-superconductor (SIS) mixers used for our SMA receivers. The system will be initially equipped with two SIS receiver modules to cover 176 - 256 GHz and 250 - 350 GHz bands, followed with a third band of 600 - 720 GHz. The receiver system will be installed in the antenna in the mid-2000. The major milestone for this project is to ship the antennas to Mauna Kea, Hawaii to join the rest of the SMA for testing interferometric observation before the end of the year 2000.

In this paper, we present the design and construction of DesertSTAR, a seven pixel heterodyne receiver for the 345 GHz atmospheric window for operation on the Heinrich Hertz Telescope located at Mt.Graham, Arizona. The seven beams are arranged in a hexagonal close-packed pattern with one beam spacing. The instrument uses fixed tuned split-block, half- height waveguide mixers with Nb SIS junctions. The mixers have an instantaneous bandwidth of 2 GHz, centered on 5 GHz. The cryostat uses a NRAO Joule-Thompson refrigerator to cool the mixers, isolators, amplifiers and optics to 4K. The computer controlled bias system allows automated bias optimization and monitoring both locally and remotely. The instrument will take full advantage of the good 345 GHz weather at the HHT and dramatically increase scientific throughput. We expect to have first operations with seven pixels in November, 2000.

Heterodyne Multibeam receivers will boost the mapping performances of millimeter and submillimeter telescopes. The IRAM 30 m telescope will be equipped with an 18 channel SIS receiver for frequencies between 210 to 270 GHz. In this paper we discus the receiver system design and give arguments for the specific technological choices and their impacts on various observing modes. The electrical and cryogenic design of the receiver is presented and we discuss the theoretical and experimental performance of the receiver optics.

The Large Binocular Telescope (LBT) will consist of two, 8.417 m, spin-cast, optical quality primary mirrors on a common azimuth-elevation mount. The center-to-center distance between the primaries is 14.417 m. The LBT is being constructed on a site known to have relatively low atmospheric opacity at submillimeter wavelengths. In this paper we describe a unique 350 micrometer heterodyne receiver system designed for use on the LBT. The optical quality of the primaries and their size will give the LBT a light gathering power more than twice that of existing submillimeter-wave telescopes.

We have an on-going observation project of the Sunyaev- Zel'dovich (S-Z) effect using a 40 - 50 GHz focal-plane array SIS receiver installed in the Nobeyama 45-m telescope in order to measure Hubble constant. The receiver have 6 beams located at 2 X 3 grids of 90' interval and have a typical receiver noise temperature of 40 K. We are improving the array receiver to increase the observing efficiency by reducing of the receiver noise temperature and increasing of the IF bandwidth. The direct connection of IF amplifier and SIS mixer should realize these performances. However, this may introduce impedance mismatch and heat flow from the IF amplifier to the SIS mixer. We tested a SIS mixer with an one-stage HEMT IF amplifier. There was no severe temperature increase in the SIS mixer. The impedance mismatch may make some undulations in the IF output character. The SIS receiver were operated with equivalent performance to the original SIS mixer in LO frequency range of 42.5 to 48.5 GHz and in IF frequency range of 1.1 to 2.5 GHz.

As part of the development of a new international radio- telescope SKA (Square Kilometer Array), an outdoor phased- array prototype, the THousand Element Array (THEA), is being developed at NFRA. THEA is a phased array with 1024 active elements distributed on a regular grid over a surface of approximately 16 m². The array is organized into 16 units denoted as tiles. THEA operates in the frequency band from 750 to 1500 MHz. On a tile the signals from 64 antenna elements are converted into two independent RF beams. Two times 16 beams can be made simultaneously with full sensitivity by the real-time digital beam former of the THEA system. At the output of each tile the analog RF signal from a beam is converted into a 2 X 12-bit digital quadrature representation by a receiver system. A double super-heterodyne architecture is used to mix the signal band of interest to an intermediate frequency of 210 MHz. The IF-signal is shifted to baseband by means of a partly digitally implemented I/Q mixer scheme. After a quadrature mixer stage, the I and Q signals are digitized by means of 12 bit A/D converters at 40 MS/s. Implementing a part of the mixing scheme digitally offers the flexibility to use different I/Q architectures, e.g. Hartley and Weaver mixer setups. This way the effect of RFI in different mixing architectures can be analyzed. After the digital processing, the samples are multiplexed, serialized and transported over fibers to the central adaptive digital beam former unit where the signals from all tiles are combined giving 32 beams. This paper focuses on the design choices and the final implementation of the THEA system. In particular, the receiver architecture is addressed. A digital solution is presented, which enables switching between Hartley and a Weaver based mixer scheme.

The One Centimeter Receiver Array (OCRA) will be an approximately 100-element close-packed horn array mounted at the secondary focus of a large paraboloidal radio telescope. With its large number of simultaneous beams OCRA will be able to carry out unbiased surveys of the radio sky at sensitivity levels which are currently impractical; it therefore offers the potential for making new astronomical discoveries. OCRA will use conventional waveguide horns and the radio frequency technology will be based on that being developed for the Low Frequency Instrument (LFI) on the Planck Surveyor satellite. The principal design problems to overcome are fluctuations in the atmospheric transmission during the observations and the intrinsic 1/f noise in the wide-band (approximately 10 GHz) receivers. The baseline design concept involves approximately 50 paris of horns with each pair connected to an independent correlation receiver. An alternative concept involves approximately 100 total power receivers with moving tertiary mirror to modulate their beam patterns on the sky at a rate faster than either the fluctuations in the atmosphere or the 1/f noise. The relative advantages and disadvantages of these different approaches are under investigation.

Phased array feeds offer the possibility of more efficient use of large radio astronomy reflector antennas by providing more closely spaced beams over a wide field of view and higher aperture efficiency in each beam than have been realized with horn feeds. This paper examines the array design constraints imposed by complete sampling of the fields near the reflector focus. In particular, array element spacing must be less than 1 (lambda) for large F/D reflectors and less than about 0.7 (lambda) for F/D < 0.5. This rules out conventional horns as array elements and sets a limit on the array bandwidth. The receive-only case of radio astronomy permits the use of number of signal combining techniques that do not degrade system sensitivity. Because practical arrays are of finite extent, and unwanted noise from the antenna surroundings is largely coherent between the elements, neither field conjugate nor maximal-ratio diversity methods of array weight optimization can be used. A modified form of field matching is a good starting approximation, however. Correction of reflector errors is examined briefly.

The increasing use of the electromagnetic spectrum and the need for more sensitive radio telescopes spurs wide interest in adaptive RFI suppression techniques, such as spatial filtering. We study the effect of spatial filtering techniques on radio astronomical image formation. Current deconvolution procedures such as CLEAN are shown to be unsuitable to spatially filtered data, and the necessary corrections are derived. To that end, we reformulate the imaging (deconvolution/calibration) process as a sequential estimation of the locations of astronomical sources. This leads to an extended CLEAN algorithm and gives estimates of the expected image quality and the amount of interference suppression that can be achieved. Some of the effects are shown in simulated images.

The next generation of radio telescopes designed to work at centimeter wavelengths may have collecting areas of up to one million square meters, and in principal will be able to reach radio sources as weak as 100 nanojanskys in 12 hours or a few tens of nanojansky in a few hundred hours integration time. However, special care will be needed to achieve the high angular resolution needed to study individual sources and to reduce the effects of confusion and spurious responses below the thermal noise level. This will require array dimensions up to one thousand kilometers to achieve noise limited performance at 1.4 GHz (20 cm) and up to ten thousand kilometers at 300 MHz (1 meter). But, even then, the performance may be limited by the finite extent of the sources and the consequential blending of their images. A scenario is presented for the gradual implementation of a Square Kilometer Array with global dimensions to give submicrojansky sensitivity over a broad range of angular scales and surface brightness.

Traditional calibration methods based on scalar self- calibration rely on a linearized quasi-scalar approximation. Several underlying assumptions will no longer hold for the phased-array telescopes being considered in this conference. The reason is that the element antennas will show a strong instrumental polarization, that is moreover strongly dependent on the pointing of the array. Scalar selfcal cannot be used for calibrating such an array. This paper offers a rigorous description, based upon 2 X 2 matrices, that fully accounts for polarization phenomena in an interferometer. It then translates the traditional selfcal algorithm into this matrix language by exploiting the analogies between scalar and matrix multiplications. It is shown that the matrix algorithm does not yield a complete calibration: It only aligns all antenna- based error by suppressing the scattering of radiation away from source components to places in the image that should be empty. In doing so, it satisfies the requirement for a high dynamic range. However, it admits an unknown uniform in-place transformation, the poldistortion, of the matrix brightness. In terms of Stokes brightness parameters, the polvector (Q,U,V) in Stokes-vector space is rotated in an unknown way and there is an unknown mutual polconversion between Stokes I and the polvector. One must eliminate this poldistortion to make the image a faithful rendition of the source. Unpolarized sources can be used as calibrators to suppress the polconversion effect, after which prior statistical knowledge about the orientations and ellipticities of the antenna elements serves to eliminate most of the polrotation, much in the same way as in the quasi-scalar method. For homogeneous arrays of identical elements, one supplementary phase measurement of some sort is required; for heterogeneous arrays this is not even necessary. In the absence of unpolarized calibrators, polconversion must be eliminated by other means. There are no obvious ways of achieving this: Developing suitable calibration techniques will be a major challenge for the new generation of telescopes. In the concluding section, the consequences of my findings for the design of phased-array aperture-synthesis telescopes are explored.

Calibrating SKA comes down to removing the effects of the many bright sources in the field. This can only be done in a closed-loop system, using a model of the observed brightness distribution. This implies an extension of the well-known 'self-calibration' technique to solve for 'image-plane' effects, i.e. instrumental effects that depend on the position in the field. In other words, we have to start solving for the detailed shape of the voltage beams of the individual stations. A distinction must be made between the treatment of the main lobe, and of the sidelobes of these beams. This paper investigates some of the boundary conditions of this approach, and formulates requirements for the accuracy and stability of SKA hardware.

In order to upgrade existing large radio telescopes or develop new ones, it is necessary to employ sophisticated active controls to meet the higher requirements on surface precision and pointing accuracy. However, in order for these high- performance controllers to maintain stability, they require an accurate characterization of the telescope structure. A finite element model (FEM) is sufficient to prove controller concepts, but does not have the level of accuracy required for final controller implementation. This results in a need for experimental characterization of the structure. A significant problem is that the structural behavior of the telescope is typically measured at the encoders, while the critical performance is the actual pointing on the sky. Conventional pointing measurements are excellent for obtaining the actual pointing direction, but are insufficient for structural characterization. Conversely, conventional physical measurements are excellent for determining structural behavior, but are not suitable for high accuracy calculation of the final pointing. We describe a new method for taking pointing measurements to quantify the static and dynamic tracking errors in the telescope. This is accomplished by combining pointing measurements at a high sample rate with simultaneous data taken from sensors on the structure. In the simplest form, the method allows improvement of the telescope controller and some indication of the relative importance of static and dynamic effects. More complete implementations of the approach can provide information about the major contributors of pointing error, improvements to the FEM, and extraction of the force distribution history on the structure. Such data will be essential if future telescope upgrades and designs are to take advantage of complex control and metrology.

We have carried out Fourier Transform Spectrometer (FTS) measurements of the millimeter and submillimeter-wave (150 - 1500 GHz or 2 mm - 200 micrometer) atmospheric opacity at Pampa la Bola, 4800 m above sea level in northern Chile on September 1997 and June 1998. One of the best transmission spectra show up to approximately 67% transmission at well- known submillimeter-wave windows. Supra-terahertz windows (located around 1035 GHz, 1350 GHz, and 1500 GHz) were identified in the same spectrum. The observed spectra can be well modeled by newly developed radiative-transfer calculations. Correlations between 220 GHz opacities and those of the center of submillimeter-wave windows or even those of the supra-terahertz windows are obtained using the entire data set. Good correlations were obtained except for the periods affected by the liquid water opacity component. We succeeded to separate the total opacity in two parts: the water vapor opacity and the liquid water opacity, using two frequencies, one in the millimeter domain and another one in the submillimeter. The separated water vapor opacity component shows good correlation with the 183 GHz pure water vapor line opacity which is also covered in the measured spectra, but the liquid water opacity component shows no correlation. The liquid water opacity component also shows no correlation with the phase fluctuation measured with the 11 GHz radio seeing monitor. Modeling of this component is currently under way. Combined with a statistical study of the 225 GHz opacity data of the Chajnantor site (approximately 7 km apart from Pampa la Bola), it is estimated that submillimeter-wave observations can be done with zenith opacity less than 1.0 (at the most transparent frequency in those windows) for about 50% of the winter season, assuming no presence of liquid water absorption.

Radio seeing shows up on filled-aperture telescopes as an apparent displacement of a radio source from its true position, known as anomalous refraction (AR). The magnitude of this effect, as a fraction of the beam width, is bigger on larger telescopes. Here we report the partial results of systematic AR measurements conducted with the 14 m telescope of the Five College Radio Astronomy Observatory. The measured values range from approximately equals 2' (winter) to approximately equals 20' (summer). These data indicate that the pointing accuracy of large telescopes will be limited by tropospheric turbulence. We therefore discuss the basic concept and preliminary design of a tip-tilt compensation system at millimeter wavelengths that would use a 183 GHz radiometer as a wave front sensing device, capable of recovering most of the turbulence-induced pointing error.

It is argued that an antenna element based around the Luneburg lens best meets the electromagnetic requirements of the proposed Square Kilometer Array. There are a number of practical difficulties in implementing such an antenna element which are addressed with means of overcoming them suggested. Some initial calculations on the electromagnetic performance of selected lens configurations are presented.

Various unique concepts are studied for the Square Kilometer Array expected to be operational between 2010 and 2015. We compare telescopes in operation today with the SKA requirements and among these concepts, emphasize the active adaptive aperture antenna. This electronic concept for aperture synthesis has intrinsic capabilities that may widen avenues of new astronomical research with SKA even further and is topic of active R & D within NFRA. Within the program, technology demonstrators are built with increasing complexity. As desirable side effect of the ongoing studies for SKA, new albeit smaller telescopes are coming into operation earlier. Of these, a new generation low frequency array to be operational in 2005 may result with close ties to the exploration of new technologies in our R & D program together with firm scientific push from the U.S. and Holland. Experience gained with this telescope are relevant for SKA's mainstream development and in particular the electronic array. Results of these and other research aspects of the R & D program are presented.

The emerging technology of large (approximately 10,000 pixel) submillimeter-wave bolometer arrays presents a novel optical design problem -- how can such arrays be fed by diffraction- limited telescope optics where the primary mirror is less than 100,000 wavelengths in diameter? Standard Cassegrain designs for radiotelescope optics exhibit focal surface curvature so large that detectors cannot be placed more than 25 beam diameters from the central ray. The problem is worse for Ritchey-Chretien designs, because these minimize coma while increasing field curvature. Classical aberrations, including coma, are usually dominated by diffraction in submillimeter- wave single dish telescopes. The telescope designer must consider (1) diffraction, (2) aberration, (3) curvature of field, (4) cross-polarization, (5) internal reflections, (6) the effect of blockages, (7) means of beam chopping on- and off-source, (8) gravitational and thermal deformations of the primary mirror, (9) the physical mounting of large detector packages, and (10) the effect of gravity and (11) vibration on those detectors. Simultaneous optimization of these considerations in the case of large detector arrays leads to telescopes that differ considerably from standard radiotelescope designs. Offset optics provide flexibility for mounting detectors, while eliminating blockage and internal reflections. Aberrations and cross-polarization can be the same as on-axis designs having the same diameter and focal length. Trade-offs include the complication of primary mirror homology and an increase in overall cost. A dramatic increase in usable field of view can be achieved using shaped optics. Solutions having one to six mirrors will be discussed, including possible six-mirror design for the proposed South Pole 10 m telescope.

The Low Frequency Array (LOFAR) will be a radio telescope that opens up a hardly explored part of the spectrum range for astronomy. LOFAR will operate between at least 10 MHz and 150 MHz. Due to its advanced concept using among others active antenna arrays, adaptive interference cancellation and calibration techniques, it will provide unique arc second resolution and milliJansky sensitivity. Key element for this instrument is a compact active, broadband antenna and this will be the main topic of presentation. Information will be provided on the basic design and performance of both antenna structure and integrated low noise amplifier. The antenna element is optimized in terms of beam pattern, while the associated amplifier is optimized for very low noise performance and high dynamic range. Insight is given how the antenna design is systematically tailored to the system requirements. Both simulated and measure performance regarding among others beam pattern and noise performance will be presented. The active antenna technology developed for LOFAR is the first application of this technology in radio astronomy and will be an important step towards future large radio telescopes.

A Superconductor-Insulator-Superconductor (SIS) mixer using parallel array of N junctions have been studied. It has been shown by theoretical analysis that the performance of this type of device is excellent and that nearly quantum-limited performance of the mixer can be obtained. It has been demonstrated that the double sideband (DSB) noise temperature of a receiver employing parallel array of twin junctions, which is the most simplest case in the parallel array of N junctions, was approximately 3 to 5 times as large as the quantum limited photon noise up to the gap frequency of Nb (approximately 700 GHz). It has been also shown that the bandwidth performance of parallel junction arrays can be improved significantly with a large number of SIS junctions even if SIS junctions with a relatively low current density or a large (omega) R_NC_J product are adopted in the arrays.

Next generation radio telescope designs face two serious technical challenges in pointing accuracy. The first is that improved resolution requires more precise pointing, and the second is that increased size makes that pointing accuracy even harder to achieve. New telescopes, such as the 50 m LMT/GTM, require sub-arcsecond pointing in significant wind, whereas current large radio telescopes point only to a couple of arcseconds without wind. A commonly proposed solution to the pointing problem is laser metrology. In this approach, structural deformations are measured, enabling correction of the resulting pointing errors. These measurements are typically slow, allowing only quasi-static effects to be removed. However, the low natural frequencies of large structures allow a significant response to the frequency content of the wind. This effect is difficult to calculate accurately because of both the limited knowledge of the actual wind power spectrum and the complex interaction of the wind with the structure. To investigate the dynamic behavior of large radio telescope in the wind, we conducted pointing measurements with the Nobeyama Radio Observatory (NRO) 45 m telescope. We measured the pointing error in elevation and cross-elevation as a function of time and wind speed, and examined the frequency content of the results. We present results which confirm that the dominant wind effects are at low frequencies, suitable for elimination via a laser-based system. However, the resonant behavior of the telescope is clearly visible in the data, and these dynamic errors are the dominant effects above about 0.1 Hz, even in modest (approximately 4 m/s) wind. As a result, an understanding of this dynamic behavior will be essential for the design of future large telescopes and metrology systems.

The Large Adaptive Reflector (LAR), currently being developed at the National Research Council Canada, is a low-cost, large- aperture, wide-band, cm-wave radio telescope designed for implementation in the Square Kilometer Array (SKA). The LAR consists of a 200 m diameter, actuated-surface, parabolic reflector with a feed located at a 500 m focal length. Since the feed must be positioned on a 500 m hemisphere centered about the reflector and between a zenith angle of 0 degree(s) to 60 degree(s), an innovative method for feed positioning is required. This feed positioning will be achieved using a high- tension structure consisting of a 4100 m³ helium aerostat supporting an array of tethers. The length of each tether can be controlled through the use of winches, resulting in accurate control of the feed position. The feasibility of the tethered aerostat feed-positioning system is of critical importance to the success of the LAR. Extensive steady-state analyses of the multi-tethered aerostat have been completed and provide strong evidence that this feed-positioning system will operate reliably in moderate weather conditions (10 m/s constant wind velocity with 2.5 m/s wind gusts). The framework of these analyses and the corresponding results will be presented.

The 50 m LMT/GTM is exposed to the climatic conditions at 4,600 m height on Cerro La Negra, Mexico. For operating the telescope to the challenging requirements of its millimeter objective, an active approach for monitoring and compensating the structural deformations (Flexible Body Compensation FBC) is necessary. This system includes temperature sensors and strain gages for identifying large scale deformations of the reflector backup structure, a laser system for measuring the subreflector position, and an inclinometer system for measuring the deformations of the alidade. For compensating the monitored deformations, the telescope is equipped with additional actuators for active control of the main reflector surface and the subreflector position. The paper describes the verification of the active deformation system by finite element calculations and MATLAB simulations of the surface accuracy and the pointing including the servo under the operational wind and thermal conditions.

Corrugated feedhorns are commonly used with reflector antennas, either for emission or reception purposes, because of their very low side lobe beam patterns, their very good E-H plane symmetry and their important bandwidth. Unfortunately, the electroforming technique that is generally used to fabricate them requires the machining of single-use mandrel. Direct milling of the horn is also possible, either in a single block or in a split block, but this also requires to machine each desired horn. At submillimeter frequencies, machining of small corrugations in a mandrel or in a block is costly. We present in this paper a cost-effective technique to fabricate helicoidal corrugated feed horns, which consists in machining one reusable mandrel and to mold as many horns as needed.

We are developing high quality reflector panels for the new 10-m telescope for millimeter/sub-millimeter waves, which is to be a prototype antenna for LMSA/ALMA. The telescope consists of 205 reflector panels, and is expected to achieve the surface accuracy of 17 micrometer for the entire telescope. Each reflector panels are machined from a single block of aluminum in size of 80 cm X 80 cm and weighs 15 kg/m². The panel surface needs to be processed not to focus the sun-light on to the sub-reflector and the support structure to protect them from heating up. We have examined several methods for surface processing, including scratching the surface by a steel-wool or a sandpaper, and to blast sand like small particles against the panel surface. As a result, we found the sand-blast process to be the acceptable solution. The scattering width for the sun-lights were measured to be 86 degree(s) (FWHM), which feeds less than 1% of the incident sun- light to the sub-reflector, and causes temperature increase of only 45 degree(s)C. The sub-millimeter reflectivity of the sand- blasted panel was measured with the Fourier transform spectrometer which showed that the sand-blast process does not affect the reflectivity for the sub-millimeter waves up to 1.5 THz. The reflector panel mounted on the telescope is yet to be processed for scattering the sun-light in the near future.

High accuracy, light-weight carbon fiber reinforced plastic (CFRP), membrane reflectors have been demonstrated by Composite Optics, Inc. (COI) for applications in ground based, millimeter wave radio astronomy. The surface figure of a semi- rigid membrane can be significantly improved by adjustment with an array of passive adjusters the support the membrane. A factor of ten contour improvement is possible. First, the surface is measured and analyzed for distortion from the desired shape. Then adjustment instructions are calculated by a customized software program and applied to the adjusters. This process is repeated to produce dimensionally stable reflectors, several meters in diameter at or below 25 micrometers RMS.

A real-time VLBI (Very Long Baseline Interferometer) system using conventional telephone lines is proposed. This system enables us to check if the VLBI network is alive by on-line manner, which is useful to reduce the loss of observation time caused by system malfunctions. In this system, a beacon of satellite or the emission from cosmic maser sources is received. The narrow-band spectral profile of the received signal leads us to compress the data up to the size less than the capacity of transmission rate on conventional telephone lines, that is to say a few tens of kbps. Additional devices for the real-time operation are A-D converters, PCs and modems, which are not special ones. As the link between the VLBI stations is performed by the conventional way, the system is applied not only to domestic VLBI networks, but also to international VLBI networks, in which a part of the VLBI stations is located in rural place. It has been confirmed that the cross-correlation is clearly detected for the compressed beacon wave data.

We have carried out the experiment of real-time space VLBI by using a high-speed ATM network. A space VLBI program is carried out with the HALCA satellite, which has an 8-m diameter radio telescope. Downlink data is transmitted to Usuda station, which is a Japanese data link station. And Usuda 64-m telescope is used as a ground radio telescope. They were used for this experiment. It is the first experiment that an optical fiber network was applied for a real-time space VLBI. The ATM optical-fiber network has 2.4 Gbps transmission capability. For the real-time space VLBI experiment, 128 Mbps data are transmitted. The VLBI correlator at NAOJ is used, which is usually used for the tape based ground and space VLBI observations. And we have succeeded to detect fringes using this network with a satellite downlink station and a ground radio telescope by test data, which are play-backed with recorded tapes. Unfortunately we have not tested actual observations because of a serious trouble of the satellite.

The National Astronomical Observatory has just started the VERA project, VLBI Exploration of Radio Astrometry. The VERA aims at obtaining very high accurate position of galactic maser sources by referencing the position to nearby quasars. The maser position is to be measured with the accuracy in an order of 10 micro arc-seconds that means the distance to the source beyond 10-kilo parsec could be measured by monitoring the annual parallax motion. The measuring range of the VERA is about 100 times greater than that of the HIPPARCOS. To achieve such high positional accuracy, the VERA first introduced a dual beam telescope. Simultaneous observations of a maser object and a quasar closely separated makes possible to remove a large phase fluctuation induced in the paths of each direction. The closer separation, however, decreases possibility of finding a bright quasar near the target. The insufficient strength of the quasar may increase thermal phase fluctuation. The optimal compromising is necessary to be studied. In this article the authors show a brief outline of the VERA observing system and present results of the error analysis in considering statistical property of the atmospheric phase fluctuation and discuss the time required to complete the measurements of 500 maser sources in our galaxy.

We present a unique hexapod platform array for the new Taiwanese AMIBA project. AMIBA is a 90 GHz radio interferometric array consisting of 19 elements mounted on a roughly 10 m diameter platform. A hexapod mount is used to steer this platform. The resulting design is lightweight in comparison to a more conventional mount. The design goals of pointing stability, platform accuracy and reduced cost can be met with this design. A metrology system for pointing is proposed for inclusion in the design.

The FIRST telescope will be made of carbon fiber reinforced plastic. The optics follow a two mirror near-classical Ritchey-Chretian design, but deviates from that in two respects. The secondary mirror defines the pupil of the system, and the primary mirror is uncommonly fast at f/0.5. After presenting the optical design, the sensitivities will be presented. Current work in progress will be described in the following areas; (1) secondary mirror figure correction (2) stray light (3) primary mirror gaps (4) standing wave impact on the heterodyne instrument for FIRST (HIFI).

Single sideband fixed-tuned design, 8 GHz intermediate frequency band per polarization and state-of-art noise performance are the specifications for the SIS mixers to be used for receiver of Atacama Large Millimeter Array (ALMA). A quadrature sideband-separating scheme that uses two identical SIS mixers with the input signal divided equally between the mixers pumped by a local oscillator with 90 degree phase difference, is a good candidate to fulfill these requirements. This side-band separating mixer technology has been successfully demonstrated for mm-wave band. We introduce a new sideband separation mixer aimed for the ALMA instrument, band 7 (275 - 370 GHz). In the design we use a novel fixed-tuned waveguide-to-microstrip double-probe coupler structure that provides a broadband low-loss distribution of the input RF signal between the two quadrature SIS mixers. We present results of HFSS simulations and scale model measurements at 10 and 100 GHz for this key component of the new receiver, the double-probe coupler. The SIS mixers can be placed on the same substrate with their respective integrated tuning circuitry directly coupled to the waveguide via the probes.

In millimeter and submillimeter wave band, radio telescopes' observing efficiency and weak signal detecting capability have been greatly raised in the past tens of years, due to the application of the SIS mixers as their receiver front-ends. However general local power injection methods for a heterodyne receiver usually result in additional insertion loss which degrades sensitivity of SIS receivers. Based on the extremely small local power requirements of SIS quantum mixing, we developed a novel LO path built-in SIS mixer, in which an additional waveguide was built for LO power injection. Without any of traditional external LO diplexers (e.g., crossguide- couplers or beamsplitters), LO power is provided to SIS junctions through the LO waveguide and the junction chip which connects both LO- and signal waveguides. There is no RF signal lost due to coupling LO power since LO- and RF signal take different paths before arriving at junctions, resulting in a compact, stable and lower loss SIS receiver system. Experiments at 110- and 230 GHz bands show that there is no any problem to couple sufficient pumping power to SIS junctions from general LO sources for present LPB mixer, and the receiver sensitivities have a further improvement of about 10 K compared to our previous beamsplitter LO power coupling receiver system. We expect this LPB SIS mixer can be also applied into submillimeter wave band.

The first, serendipitous, radio-astronomical observations by K. Jansky were at decametric wavelengths. However, after the initial pioneering work, long-wavelength radio astronomy was largely abandoned in the quest for higher angular resolution because ionospheric structure was thought to limit interferometric imaging to short (< 5 km) baselines. The long-wavelength (LW, 2 - 20 m or 15 - 150 MHz) portion of the electromagnetic spectrum thus remains poorly explored. The NRL-NRAO 74 MHz observing system on the Very Large Array has demonstrated that self-calibration techniques can remove ionospheric distortions over arbitrarily long baselines. We describe the scientific justification and initial technical design of the Low Frequency Array (LOFAR) -- a fully electronic, broad-band antenna array operating in the 15 - 150 MHz range with a collecting area of 1 km² at 15 MHz. The longest baselines may be 500 km, providing an angular resolution of 10' at 15 MHz and 1' at 150 MHz. The combination of large collecting area and high angular resolution will enable LOFAR to produce images with sensitivities of order 1 mJy at 15 MHz and 300 (mu) Jy at 150 MHz. As such LOFAR will represent an improvement of 2 - 3 orders of magnitude in resolution and sensitivity over the state of the art. A key operational goal of LOFAR will be solar observations -- both passive imaging and radar imaging. In the latter mode LOFAR will serve as the receiver for bi-static observations of the Sun, with particular emphasis on the imaging of coronal mass ejections. LOFAR will serve as an astrophysical laboratory to study the origin, spectrum, and distribution of the Galactic cosmic ray electron gas and as an instrument to probe the high-redshift Universe.

Laser micromachining is a powerful alternative to the conventional fabrication of waveguide structures, feedhorns and backshorts designed to operate at frequencies greater than 800 GHz. Computer controlled laser etching permits the direct scaling and fabrication of successful waveguide designs to THz frequencies with micrometer tolerances in just a few hours. Laser micromachining can also be used to produce quasi optical components such as anti-reflection (AR) grooved silicon lenses, and local oscillator (LO) phase gratings. In these proceedings we describe the specifics of the laser micromachining facility being completed at the Steward Observatory Radio Astronomy Laboratory and its potential for the fabrication of THz imaging array receivers.

Tropospheric phase fluctuation due to the water vapor content is one of difficult problems which degrades imaging performances of radio interferometry. One of the potential solutions is differential radiometry observations to measure the differential water vapor content along the line of sights. We developed a 22-GHz-line radiometer to be mounted on a ground data-link antenna which supplies the timing reference signal for a space VLBI satellite, HALCA. This system will allow us to compare directly the atmospheric phase fluctuation with the water vapor content along a single line of sight measured by the radiometer.

For millimeter wavelength antennas, solar radiation is a very important source of serious surface, phase, and pointing distortions. To reduce these distortions, carbon fiber composites are widely used in some existing and newly designed millimeter wavelength antennas. However, carbon fiber reinforced composites (CFRP) are different from other isotropic structural materials. Their properties are direction dependent; in the fiber direction, very favorable; perpendicular to the fibers, less favorable. Carbon fiber composite joints are also complex and costly. This paper discusses the properties of carbon fiber structure members, such as: tubes, beams, cones, thin plates, and honeycomb sandwiched thick plates. Comparisons are provided both from the structural and thermal points of view. The paper also gives the stress distribution of a simple composite glued joint.

We present a plan of heterodyne receivers for Atacama Submillimeter Telescope Experiment (ASTE), which is one of Japanese R&D project of Large Millimeter Submillimeter Array (LMSA) and Atacama Large Millimeter Array (ALMA). A new 10 m submillimeter-wave telescope has been pre-installed at Nobeyama since February 2000 and will be installed at Pampa la Bola (el. 4800 m) in northern Chile. The telescope has four receiver layouts: (1) A shaped Cassegrain optics was designed for the Nobeyama operation to achieve high beam-efficiency at millimeter-wave bands. (2) Normal Gaussian optics will be replaced for the Chile operation to optimize submillimeter- wave bands up to 850 GHz. (3) It is possible to install an ALMA prototype receiver at the focus of secondary reflector. (4) An optics for submillimeter SIS photon camera. We describe the 350 GHz receiver which noise temperature was around 55 K in the frequency band of 330 - 360 GHz. The temperature ripple at the 4 K stage of two stages Gifford-McMahon refrigerator has been reduced to be less than 10 mK by employing a He-pot temperature stabilizer.

The design of the new 5 X 5 SIS focal plane array receiver for the 45-m telescope at the Nobeyama Radio Observatory (NRO) is described. It is called BEARS (SIS 25-BEam Array Receiver System). This receiver has 25 elements. It covers the frequency range from 82 to 116 GHz. The array uses SIS junctions mounted in fixed tuned mixer blocks. The mean DSB receiver noise temperature is about 75 K at all the LO frequencies. The standard deviation of the receiver noise temperature is about 20 K. The receiver was installed on the telescope and has been used for observations and measurements since April 1998. The design of the receiver system, the optics and the heat model will be presented in this paper.

VERA (VLBI Exploration of Radio Astrometry), being promoted by National Astronomical Observatory of Japan in collaboration with several Japanese universities, is a new VLBI array for phase referencing astrometry approved to start its construction in 2000. VERA, the first VLBI array dedicated to phase referencing VLBI, has a dual beam antenna system which enables us to observe a Galactic maser source and a nearby reference source simultaneously to remove the atmospheric fluctuation, and will measure positions of Galactic maser sources relative to reference sources (QSOs and radio galaxies) with 10 microarcsec level accuracy. With that accuracy, VERA will be able to determine parallaxes and proper motions of maser sources in the whole Galaxy. The major science targets of VERA will include 3D structure of the Galaxy and the distribution of dark matter, physics of outflow in star forming regions and stellar envelopes, precise calibration of the period-luminosity relation of Mira-type stars, and structure an evolution of QSOs and radio galaxies.

This document gives an overview of the pointing model (PM) at the IRAM 30 m Telescope and the parameters used in its determination. We describe recent improvements achieved by the installation of an inclinometer to measure the tilt of the azimuth axis. The use of the inclinometer allows to determine two of the PM parameters in a reliable way. As a consequence, the pointing observations can be carried out faster, and the PM can be partly updated, if necessary, independently of astronomical observations.

The gigabit digital filter prototype has been developed with the FPGA (FIeld Programmable Gate Array) for the radio astronomical observation. The digital filtering techniques enables a variety of observing modes defined on the data acquisition system, even with a fixed sampling frequency A/D converter. In this study, the principle of gigabit digital filter design is described in detail, parallel processing design of a FIR (Finite Inpulse Response) filter is presented, and the results of the test manufacturing are shown.

Interferometric fringes of giga-bit VLBI was successfully detected in 1998 on the off-line processing base using an 1- Gbit recorder. Though an 8-Gbps VLBI system, an 8-Gbps sampler and an 8-Gbps correlator are now available, the highest possible observing rate has been limited at 2-Gbps or slower by a limitation of an available data recording system. That is a reason the authors have started the developments of a realtime VLBI system in which 2-Gbps or higher rate of observing data is transferred to the correlator through an optical fiber link now established in the data transmission mode of STM-16. The authors and the Communications Research Laboratory, Japan (CRL) have already succeeded the realtime VLBI on STM-1, at 155-Mbps data rate, and proceeds trial manufacturing for the higher data rate than 2-Gbps by considering a fact that an 100-Gbps or higher data rate is already achieved on the most advanced optical data transmission link by using high speed devices for MUX and DEMUX logics. National Astronomical Observatory, Japan (NAO) now promotes the OLIVE project, Optical LInked VLBI Experiment, which directly connects VLBI observation stations, the Usuda 64-m and the Nobeyama 45-m radio telescopes, to a central correlator in Tokyo through an optical fiber link in realtime. Now 256-Mbps data transmission and correlations have been succeeded. The authors have an experimental plan to transmit 2-Gbps data of the Usuda 64-m telescope to the Kashima correlator about 200-km apart with each other at 2.4- Gbps data rate through an optical fiber link of a STM-16 mode. The authors are developing the ultra-high-speed ATM transmitter (TX) and receiver (RX), and the experiments of 2.4-Gbps transmission rate was made with the OLIVE network. The data transmission line is the Nobeyama-Musashino-Nobeyama with the data rate of 2 Gbps in February, 2000. After this communication successfully tested, the authors can expect great improvement on the VLBI sensitivity to observe more dark and compact object.

The Atacama Large Millimeter Array (ALMA), a joint project between Europe and the U.S. and at present in its design and development phase, is a major new ground based telescope facility for millimeter and submillimeter astronomy. Its huge collecting area (7000 m²), sensitive receivers and location at one of the driest sites on Earth will make it a unique instrument. We present preliminary design concepts for the overall receiver configuration. Optics and cryostat design concepts from OSO, OVRO, RAL, IRAM, NRAO and SRON and their main features are described.

MERLIN (Multi Element Radio Linked Interferometer Network) is a cornerstone of the UK's ground-based astronomical facilities, providing sub-0.1 arcsecond radio imaging, polarimetry, spectroscopy and astrometry. It consists of six telescopes distributed over central England with a maximum baseline length of 217 km. The sensitivity of MERLIN is currently limited by the narrow-band of the microwave links used to transmit data from the remote telescopes to the correlator situated at Jodrell Bank. At the heart of the MERLIN upgrade will be the replacement of these links with broad-band optical fibers transmitting data at up to 10 Gbps. In addition, new receivers in the 12 - 15 GHz band will be installed, the old low-frequency telescope at Defford will be replaced and a new broad-band correlator will be constructed. The result will be an array transformed, with a sensitivity of up to a factor of 30 greater than that of the current array, which will give the capability of new science at high frequency and high resolution.

Astronomers use the 1612 MHz OH spectral line emission as a unique window on properties of evolved stars, galactic dynamics, and putative proto-planetary disk systems around young stars. In recent years, experiments using this OH line have become more difficult because radio telescopes are very sensitive to transmissions from the GLONASS satellite system. The weak astronomical signals are often undetectable in the presence of these unwanted human generated signals. In this paper we demonstrate that GLONASS narrow band signals may be removed using digital signal processing in a manner that is robust and non-toxic to the weak astronomy signals, without using a reference antenna. We present results using real astronomy data and outline the steps required to implement useful systems on radio telescopes.