Qirong Li

A Compact Superconducting Bandpass Filter at 360 MHz With Very Wide Stopband Using Modified Spiral Resonators

This paper proposes a modified spiral resonator with a tight three-turn spiral and inner/outer tails. The resonator has good spurious response because the mutual inductances between the three turns at the fundamental mode are positive and thus reduce the fundamental resonant frequency f0, whereas those at the first spurious mode are negative and increase the first spurious resonant frequency fS. By further optimizing the lengths of the spiral and inner/outer tails of the proposed resonator, a spurious resonant frequency fS up to 3.4 f0 is obtained. Moreover, the couplings between such resonators at spurious modes are much weaker than that at the fundamental mode, which is helpful to suppress the spurious response of bandpass filters consisting of such resonators. Furthermore, three dissimilar types of resonators with the same fundamental frequency but with different spurious resonant frequencies are used to compose a bandpass filter and further suppress the spurious response in the stopband. With these methods, a ten-pole superconducting filter at 360 MHz with a 15-MHz bandwidth is successfully designed and fabricated on a LaAlO3 substrate. The overall measurements show a high performance and agree very well with the simulations. The maximum insertion loss is 0.15 dB, the return loss is greater than 19 dB, and the rectangle coefficient (the ratio between the 40-dB bandwidth and the 3-dB bandwidth) is 1.35. Moreover, the out-of-band rejection is higher than 76 dB up to 2030 MHz, which is 5.64 f0. The ten-pole filter occupies a compact area of 33 mm × 15 mm, which amounts to only 0.15 λg0 × 0.07 λg0, where λg0 is the guided wavelength of the 50-Ω line on the substrate at f0.

Design and Optimization of a Compact Superconducting Quadruplexer at VHF-Band With an Accurate Equivalent Circuit Model

This paper presents the modeling and optimization of a manifold-coupled superconducting quadruplexer at VHF-band. The quadruplexer consists of four individually designed channel filters with a bandwidth of 400 kHz centered at 216, 224, 232, and 240 MHz, respectively, connected to a common manifold. The complex interactions between the channel filters make the design and optimization of the quadruplexer difficult and even impossible. An equivalent circuit for the manifold and the capacitive external couplings of the four channel filters in the quadruplexer is presented. The parameters of the equivalent circuit are accurately extracted from electromagnetic simulations. Afterward, the equivalent circuit is optimized to compensate for the interactions between the channel filters and obtain a good common-port return loss and channel transfer characteristics. Thereafter, the design of the individual channel filters is improved according to the optimized parameters of the equivalent circuit. The superconducting quadruplexer is successfully designed and fabricated. The measurements show high performance and match well with the simulations. The experimental insertion losses of the four channels are less than 0.45 dB, the center frequency discrepancies of the four channels are less than 40 kHz, the common-port return loss is greater than 16.3 dB, and the out-of-band rejection is higher than 90 dB. Moreover, a high isolation greater than 75 dB between the channels is achieved.

An Ultra-Low Loss 2 B Reconfigurable Superconducting Filter at P-Band

A superconducting resonator, consisting of a microstrip spiral and a 2 b interdigital capacitor array, is proposed. The resonator has a measured unloaded Q over 51 000 in all four states. A two-pole reconfigurable superconducting filter at P-band with a fractional bandwidth of 1% is designed with this resonator and fabricated. The measurements show that the tuning range of the center frequency is from 499.4 to 484.9 MHz with insertion losses of less than 0.1 dB in all four states, and are in good agreement with the simulations.