This PDF file contains the front matter associated with SPIE Proceedings Volume 9462, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Within the European Commission’s Seventh Framework Programme (FP7), the CONSORTIS project will design and fabricate a stand-off system for the detection of objects concealed on people. This system operating in the sub-millimetre wave part of the spectrum will scan people as they walk by the sensor. The aim of the project is to produce a system which has a high probability of detection, low false alarm rates, is non-invasive and respects privacy. The top level system design for CONSORTIS brings together both passive and active sensors and the simulation tools developed to evaluate the design are described. The passive system will operate in two or three bands between 100 and 600GHz and will be based on a cryogen free cooled focal plane array sensor whilst the active system will be a solid-state 340GHz radar. This will maximize the probability of detection and reduce false alarms. A ‘systems engineering’ approach was adopted with performance modeling being used to develop the system specifications. A modified version of OpenFx is used to model the passive system and SE-RAY-EM for the active system. Both of these tools are capable of rendering imagery which is electromagnetically correct and account for the properties of the sensor. Furthermore this imagery can be animated to give moving images similar to those observed in the real system. Targets can be embedded under clothing so that performance can be estimated. False alarms can be introduced in a similar way to understand if their signatures can be rejected.

In the frame-work of the European project CONSORTIS, a stand-off system for concealed object detections working at submillimeter-wave frequencies is being developed. The system is required to perform real-time image acquisition over a large field of view at a short range using both an active and a passive sensor operating in the frequency range from 250 to 600 GHz. In this contribution, the main trade-offs associated with the quasi-optical system design are presented. The imaging distance is from 2 m to 5 m range with a spatial resolution lower than 2 cm. Focal plane arrays will be used to achieve high imaging frame rates. Two configurations are considered in CONSORTIS: a sparse array of active transceivers and incoherent passive staring array with a large number of elements. Both cases use mechanical scanning to achieve the required field of view. This paper presents an in-depth analysis of the different trade-offs driving the quasi-optical design: from the mechanical scanner considerations to the optical beam quality required over the whole field of view. This analysis starts from the fundamental limitations of the quasi-optical mechanical systems. The limitations of the optics are discussed considering a canonical elliptical reflector as a reference. After this fundamental analysis, we compare the performances of several practical standard implementations, based on dual-reflectors and lenses, with canonical geometries. It is shown that, at short ranges, the main limitation of the optical system is the poor beam quality associated with the wide angular field of view and none of the standard implementation fulfills the requirements. In the last section, a technique to overcome this limitation is investigated. In particular, the use of optics with oversized reflectors can significantly improve the performance over a larger field of view if the coma aberrations are limited by a good angular filter.

Near field radar imaging systems are used for demanding security applications including concealed weapon detection in airports and other high-security venues. Despite the near-field operation, phase noise and thermal noise can limit performance in several ways. Practical imaging systems can employ arrays with low gain antennas and relatively large signal distribution networks that have substantial losses which limit transmit power and increase the effective noise figure of the receiver chain, resulting in substantial thermal noise. Phase noise can also limit system performance. The signal coupled from transmitter to receiver is much larger than expected target signals. Phase noise from this coupled signal can set the system noise floor if the oscillator is too noisy. Frequency modulated continuous wave (FM-CW) radar transceivers used in short range systems are relatively immune to the effects of the coupled phase noise due to range correlation effects. This effect can reduce the phase-noise floor such that it is below the thermal noise floor for moderate performance oscillators. Phase noise is also manifested in the range response around bright targets, and can cause smaller targets to be obscured. Noise in synthetic aperture imaging systems is mitigated by the processing gain of the system. In this paper, the effects of thermal noise, phase noise, and processing gain are analyzed in the context of a near field 3-D FM-CW imaging radar as might be used for concealed weapon detection. In addition to traditional frequency domain analysis, a time-domain simulation is employed to graphically demonstrate the effect of these noise sources on a fast-chirping FM-CW system.

In this presentation we will discuss the performance and limitations of our 220 channel video rate passive millimeter wave imaging system based on a distributed aperture with optical upconversion architecture. We will cover our efforts to reduce the cost, size, weight, and power (CSWaP) requirements of our next generation imager. To this end, we have developed custom integrated circuit silicon-germanium (SiGe) low noise amplifiers that have been designed to efficiently couple with our high performance lithium niobate upconversion modules. We have also developed millimeter wave packaging and components in multilayer liquid crystal polymer (LCP) substrates which greatly improve the manufacturability of the upconversion modules. These structures include antennas, substrate integrated waveguides, filters, and substrates for InP and SiGe mmW amplifiers.

The millimeter-wave (MMW) radar is a promising candidate for high-precision imaging because of its short wavelength and broad range of available bandwidths. In particular in the frequency range of 92-100 GHz, which is regulated for radiolocation, an atmospheric attenuation coefficient less than 1 dB/km limits the imaging range. Therefore, a combination of MMW radar and distributed antenna system directly connected to optical fiber networks can realize both high-precision imaging and large-area surveillance. In this paper, we demonstrate a multi-channel MMW frequency-modulated continuous-wave distributed radar system connected to an analog radio-over-fiber network.

Combination of superconductive and semiconductor technologies on the one substrate in any case will give birth to principal trends of critical electronic technologies, including the realization of superconductive Josephson junction near the gate of a semiconductor transistor. Further development will allow us to realize passive imaging systems with main advantage - electronic tuning of the receiving frequency.

Preliminary design considerations for an image quality tool to complement millimeter wave imaging systems are presented. The tool is planned for use in confirming operating parameters; confirmation of continuity for imaging component design changes, and analysis of new components and detection algorithms. Potential embodiments of an image quality tool may contain materials that mimic human skin in order to provide a realistic signal return for testing, which may also help reduce or eliminate the need for mock passengers for developmental testing. Two candidate materials, a dielectric liquid and an iron-loaded epoxy, have been identified and reflection measurements have been performed using laboratory systems in the range 18 - 40 GHz. Results show good agreement with both laboratory and literature data on human skin, particularly in the range of operation of two commercially available millimeter wave imaging systems. Issues related to the practical use of liquids and magnetic materials for image quality tools are discussed.

A method for extracting dielectric constant from free-space 18 - 40 GHz millimeter-wave reflection data is demonstrated. The reflection coefficient is a function of frequency because of propagation effects, and numerically fitting data to a theoretical model based on geometric optics gives a solution for the complex dielectric constant and target thickness. The discriminative value is illustrated with inert substances and military sheet explosive. In principle, the measurement of reflectivity across multiple frequencies can be incorporated into Advanced Imaging Technology (AIT) systems to automatically identify the composition of anomalies detected on persons at screening checkpoints.

The Army Research Laboratory (ARL) has developed a polarimetric frequency-modulated continuous-wave (FMCW) instrumentation radar that has been used to study the polarization and backscatter properties of in-situ rain in the 220 GHz atmospheric window. A summary of the preliminary measurements is presented in this work including an analysis of the co-polarization backscatter and attenuation characteristics measured at 216 GHz. A marginal detection of the copolarization backscatter signature of rain was made during a series of fast-moving, heavy downpour thunderstorm events. A detection limit of -40±3 dB[m²/m³] was found for the VV-polarization cross section per unit volume for rain rates up to 150 mm/hr. Co-polarization (VV- and HH-polarization) attenuation characteristics measured at high rain rates (< 20 mm/hr) were well described by a Joss thunderstorm drop distribution in the high frequency limit, where drop size is much greater than the observation wavelength. Observations at 216 GHz suggest attenuation levels of 8-10 dB/km at rain rates above 20 mm/hr, strengthening previous evidence that attenuation through rain is independent of frequency under high rain rate conditions. Attenuation measurements at lower rain rates (< 20 mm/hr) were qualitatively consistent with both Laws and Parsons and Joss thunderstorm distributions.

With the demand for larger bandwidths and faster data speeds, wireless communication systems are expanding into the millimeter wave and terahertz region of the electromagnetic spectrum. Successful transition to higher frequencies, particularly for systems located in urban or indoor environments, will require a thorough understanding of the reflection, transmission, absorption, and scattering of a wide variety of materials. For this study, the co-polarization and crosspolarization backscattering coefficients of several dielectrics were measured in compact radar ranges operating from 160 GHz to 1.55 THz. These structures consisted of dielectric disks with various rough surfaces. The backscattering measurements of these disks were compared as a function of polarization, incident angle, roughness, and frequency.

Passive millimeter-wave imaging systems can play a significant role in security applications. Especially, the detection of hidden threats for border security is a growing field. In this paper we propose a novel approach for automatic threat detection using multiple 94 GHz passive millimeter-wave images. Herein, we discuss four steps essential to solving the task: pre-processing, region-of-interest extraction, threat extraction in each frame and, finally, intelligent fusion of the results from all frames. Besides, showing that the proposed method works reliably for the data-set at hand, we also discuss the advantages of using this method in contrast to state-of-the-art methods.

In this article we present preliminary results for the combination of two interesting fields in the last few years: 1) Compressed imaging (CI), which is a joint sensing and compressing process, that attempts to exploit the large redundancy in typical images in order to capture fewer samples than usual. 2) Millimeter Waves (MMW) imaging. MMW based imaging systems are required for a large variety of applications in many growing fields such as medical treatments, homeland security, concealed weapon detection, and space technology. Moreover, the possibility to create a reliable imaging in low visibility conditions such as heavy cloud, smoke, fog and sandstorms in the MMW region, generate high interest from military groups in order to be ready for new combat. The lack of inexpensive room temperature imaging sensors makes it difficult to provide a suitable MMW system for many of the above applications. A system based on Glow Discharge Detector (GDD) Focal Plane Arrays (FPA) can be very efficient in real time imaging with significant results. The GDD is located in free space and it can detect MMW radiation almost isotropically. In this article, we present a new approach of reconstruction MMW imaging by rotation scanning of the target. The Collection process here, based on Radon projections allows implementation of the compressive sensing principles into the MMW region. Feasibility of concept was obtained as radon line imaging results. MMW imaging results with our resent sensor are also presented for the first time. The multiplexing frame rate of 16×16 GDD FPA permits real time video rate imaging of 30 frames per second and comprehensive 3D MMW imaging. It uses commercial GDD lamps with 3mm diameter, Ne indicator lamps as pixel detectors. Combination of these two fields should make significant improvement in MMW region imaging research, and new various of possibilities in compressing sensing technique.

The transmission characteristics of millimeter waves (mmWs) make them suitable for many applications in defense and security, from airport preflight scanning to penetrating degraded visual environments such as brownout or heavy fog. While the cold sky provides sufficient illumination for these images to be taken passively in outdoor scenarios, this utility comes at a cost; the diffraction limit of the longer wavelengths involved leads to lower resolution imagery compared to the visible or IR regimes, and the low power levels inherent to passive imagery allow the data to be more easily degraded by noise. Recent techniques leveraging optical upconversion have shown significant promise, but are still subject to fundamental limits in resolution and signal-to-noise ratio. To address these issues we have applied techniques developed for visible and IR imagery to decrease noise and increase resolution in mmW imagery. We have developed these techniques into fieldable software, making use of GPU platforms for real-time operation of computationally complex image processing algorithms. We present data from a passive, 77 GHz, distributed aperture, video-rate imaging platform captured during field tests at full video rate. These videos demonstrate the increase in situational awareness that can be gained through applying computational techniques in real-time without needing changes in detection hardware.