Superconducting on-chip spectrometers have both imaging and spectroscopic capabilities. In general, the broadband signal coupled from an antenna goes through frequency dispersion via a series of filters that are connected with superconducting detectors like kinetic inductance detectors or bolometers. The filters have the same relative bandwidth, which determines the frequency resolution of the spectrometer. We here present the design and simulations on the twin-slot antenna, CPW-to-microstrip transition, and a ten-channel filter-bank of a verification-stage terahertz spectrometer chip at 350 GHz. The simulation results of the antenna and transition showed low return loss, and the simulation results of the ten-channel filter-bank show that each channel has good readout independence and coupling strength. These designs and simulations can provide assistance for the future development of terahertz on-chip spectrometer.
Lens integrated twin slot antennas have been widely used in superconducting transition edge sensor (TES) detectors due to its high directivity and low cross-polarization. In this paper, we present the design and simulation of a 210 GHz dual-polarized twin slot antenna for TES detectors. We used Ansoft HFSS to simulate the return loss and isolation of the dual-polarized twin slot antenna. The results show that the return loss of the dual-polarized twin slot antenna is less than -15 dB and the isolation is great than 10 dB in the frequency range from 170 GHz to 230 GHz. We also used FEKO to simulate the beam pattern of the dual-polarized twin slot antenna integrated with a silicon lens with a diameter of 5 mm. After optimizing the extended length of the silicon lens, a near Gaussian beam with a half power beam width (HPBW) of 19.4 degrees and a side lobe level of 17.3 dB was obtained. In addition, we designed and simulated an air bridge that is used to transmit the signals received by the twin slot antennas in the orthogonal directions. We find that the transmission coefficient of the air bridge is close to 0 dB and the isolation in the orthogonal directions exceeds 35 dB.
Conventional coherent and non-coherent techniques such as quasi-optical vector network analyze (VNA) and Fourier transform spectroscopy (FTS) can be employed to measure the exhaustive properties of dielectrics in the terahertz band. However, the VNA can only cover a narrow frequency range, and the FTS takes a relatively long period of time for measurement. By contrast, the terahertz time domain spectroscopy (TDS) allows the measurement of material properties such as dielectric constant and loss tangent in a wide frequency range and in a short period of time. Using a terahertz TDS, we characterize the complex properties of some materials commonly used in terahertz superconducting receivers, including high density polyethylene (HDPE), single crystal magnesium oxide (MgO), single crystal quartz, single crystal sapphire, single crystal silicon (S.C. silicon), high resistance silicon (H.R. silicon), and ultra-high molecular weight polyethylene (UHMWPE). The measurements at room temperature have finished yet. The measurements at cryostat temperature are in progress and will be published later.
Phased array feeds (PAF) are playing an increasingly important role in low-frequency radio astronomy, but less explored at THz wavelengths. Here we present the design of a 0.35-THz planar array antenna, which consists of an array of twinslot antennas, a coplanar waveguide (CPW) feed network and airbridges. The planar array antenna is based on a silicon substrate without any lens as well as anti-reflection coating. The airbridges are used to improve the performance of the CPW T-junctions and the transmission efficiency of the feed network. Simulation results show that the substrate thickness can change the power distribution on both sides of the substrate. With an appropriate substrate thickness and some airbridges, the total gain of a 16-element array can reach 15.3 dB and the main-beam efficiency is about 54%. This kind of planar array antenna can be easily integrated with a terahertz detector such as hot electron bolometer (HEB) and kinetic inductance detector (KID), based on photolithographic fabrication.
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