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Lumped-element superconducting resonators are a promising technology for their use in millimeter-wave observations and quantum computing applications that require large arrays of extremely sensitive detectors. Among them, lumped-element kinetic inductance detectors (LEKIDs) have shown good performance in the submillimeter band in several earth-based telescopes. In this work, LEKIDs for their use as millimeter-wave receivers of astronomical applications are presented. LEKID arrays using a thin bilayer of superconducting titanium/aluminum (Ti/Al), deposited on the silicon substrate, have been designed and fabricated. The design of a dual-polarization LEKID with the goal of detection at the $W$ -band for two orthogonal polarizations is described and a fabricated array has demonstrated absorption at ambient temperature. Also, an approximate design methodology of the coupling parameter for LEKIDs’ readout, essential for dynamic range optimization of the detector under millimeter-wave radiation, is proposed. In addition, the resonance characteristics and coupling factor of the fabricated superconducting resonators using high-quality internal factor $Q_{i}$ under cryogenic temperatures have been analyzed. The design guidelines in this work are applicable to other LEKID arrays, and the presented superconducting Ti/Al thin-film LEKIDs can be used in future receiver arrays in the millimeter bands. [ABSTRACT FROM AUTHOR]

A novel full-band (40% relative bandwidth) waveguide polar modulator (WPM) design based on a new architecture with two turnstile junctions and a nearly frequency-independent differential 180° phase shift between orthogonal arms is presented. The use of suitably designed turnstile junctions together with antiphase waveguide-coaxial-waveguide transitions in reduced-height waveguide technology enables the improvement of bandwidth over previous WPMs with a very compact and simple solution. This design enables continuous rotation about its central axis at 40 revolutions/s, which makes the modulator suitable for receivers with significant $1/f$ noise such as cryogenic radiometers. The polar modulator presented in this paper is designed to be cooled down to cryogenic temperatures in order to reduce its contribution to the receiver noise. This design is suitable for radio astronomy applications due to its cost-effective, compact design, and high quality performance as well as being readily scalable. A polar modulator in the Ka-band (26.5–40 GHz) has been designed to show a reflection better than −20 dB, an insertion loss around 0.3 dB, and a cross-coupling near −35 dB measured at room temperature ( $T = 298$ K). This insertion loss is reduced by 30%, while the phase difference and cross-coupling maintain similar values when the polar modulator is cooled to approximately $T = 80$ K. [ABSTRACT FROM AUTHOR]

In this paper, monolithic microwave integrated circuit (MMIC) broadband low-noise amplifiers (LNAs) for cryogenic applications based on a 100-nm metamorphic high-electron mobility transistor (mHEMT) technology in combination with grounded coplanar waveguide are reported. A three-stage LNA, operating in 4–12 GHz and cooled to 15 K exhibits an associated gain of 31.5 dB \pm 1.8 dB and average noise temperature of 5.3 K (NF=0.079\ \ dB) with a low power dissipation of 8 mW. Additionally another three-stage LNA 25–34 GHz cooled to 15 K has demonstrated a flat gain of 24.2 dB \pm 0.4 dB with 15.2 K (NF=0.22\ \ dB), average noise temperature, with a very low power dissipation of 2.8 mW on chip. The mHEMT-based LNA MMICs have demonstrated excellent noise characteristics at cryogenic temperatures for their use in radio-astronomy applications. [ABSTRACT FROM AUTHOR]