Microwave kinetic inductance detectors (MKIDs) are playing an increasingly role in THz astronomy. Superconducting coplanar waveguide (CPW) lines are commonly adopted in MKIDs for the resonators as well as the readout through line. It is therefore of particular interest to characterize the transmission properities of superconducting CPW lines at low temperatures. A cryogenic through-line method based on two cryogenic RF switches is proposed to characterize Nb and TiN superconducting CPW lines. On-chip calibration has been successfully carried out. Detailed results and analysis will be presented.
A novel wavefront-based algorithm for the beam simulation of both reflective and refractive optics in a complicated quasi-optical system is proposed. The algorithm can be regarded as the extension to the conventional Physical Optics algorithm to handle dielectrics. Internal reflections are modeled in an accurate fashion, and coating and flossy materials can be treated in a straightforward manner. A parallel implementation of the algorithm has been developed and numerical examples show that the algorithm yields sufficient accuracy by comparing with experimental results, while the computational complexity is much less than the full-wave methods. The algorithm offers an alternative approach to the modeling of quasi-optical systems in addition to the Geometrical Optics modeling and full-wave methods.
A 100GHz Schottky diode mixer based on quartz substrate is presented, which will be used as the detector for the millimeter imaging. The Schottky diode is modeled based on its physical dimension thus its high frequency parasitic parameters can be fully taken into consideration. The measured conversion loss is better than 10dBm over 95~105GHz with 8dBm LO pump at 49.53GHz. The measured result is also in excellent accord with the simulated model.
This paper presents the design and characterization of a novel quasioptical subharmonically pumped GaAs Schottky diode mixer at 375 GHz. It features the use of two off-axis twin-slot antennas fed by CPW to receive the RF and LO signals respectively. The mixer circuits together with the antennas are integrated on a silicon extended elliptical lens. Conventional harmonic balance simulations in combination with 3D fullwave simulations in HFSS are carried out to analyze the performance of the mixer. Optimal conversion loss is obtained after impedances of the LO and RF ports are matched.Final simulation results show that the mixer achieves a DSB conversion loss of 10 dB and a noise temperature of 2900 K.