Xiaoke Song

Design of a Superconducting Ultra-Wideband (UWB) Bandpass Filter With Sharp Rejection Skirts and Miniaturized Size

This letter presents a superconducting ultra-wideband (UWB) bandpass filter (BPF) with sharp rejection skirts and miniaturized size using multiple-mode resonator (MMR). The MMR is formed by loading a stepped-impedance open-end stub in shunt to a modified stepped-impedance resonator (SIR). The modified SIR generates three resonant modes within the 3.1-10.6 GHz UWB band, whereas the stepped-impedance open-end stub creates two transmission zeros and two additional resonant modes improving the bandedge steepness. Interdigital coupled-lines are used for the external couplings to enhance the coupling strength. A superconducting UWB BPF is realized with a compact size of 20 mm × 11 mm. The measured results without any tuning show good performance. The insertion loss at the center frequency is 0.58 dB, the return loss is greater than 10.6 dB, and the group delay variation is less than 1.76 ns. Furthermore, the experimental results of the filter are in good agreement with the simulated ones.

Dual-Band Superconducting Bandpass Filter Using Stub-Loaded Resonators With Controllable Coupling and Feeding Structures

A four-pole dual-band bandpass filter is designed with stub-loaded resonators and dual-feeding structure. The stub-loaded resonator generates two resonant modes, and the interstage couplings between the resonators at the two modes can be controlled independently. A dual-feeding structure is proposed to meet the required external couplings of the two passbands simultaneously. The filter is successfully designed and fabricated on a MgO substrate with a compact size of 29.2 mm × 13.8 mm. The measured results show high performance and agree well with the simulations.

A UHF-Band Narrow-Band HTS Bandpass Filter With Wide Stopband Using Interdigital Structure

In this paper, a novel resonator with modified interdigital fingers and vertical meander line is proposed. This resonator has a high first spurious frequency and is suitable for the design of a narrow-band filter with a wide stopband. A compact narrow-band six-pole high-temperature superconducting filter at the ultrahigh-frequency band is successfully designed and fabricated with this resonator. The measured out-of-band rejection is better than 75 dB up to 2600 MHz, which is as high as 5.2 times of the fundamental frequency.

A Narrowband Superconducting Quadruplexer With High Isolation

A manifold-coupled microstrip superconducting quadruplexer with high isolation for S-band communications systems is presented. The problems of channel isolation and common-port impedance matching in the design of the quadruplexer are addressed and studied. An equivalent circuit model for a trial diplexer is built to analyze the isolation between two channel filters with Chebyshev responses. Analyses and simulations show that channel isolation is mainly determined by the resonators that are closest to the noncommon ports. A circuit layout is proposed for the quadruplexer to obtain high isolation. Moreover, a binary matching network is designed to minimize the undesired interactions between the four channel filters in the quadruplexer. The quadruplexer is successfully designed with the proposed methods and fabricated. The measured results show high performance and match well with the simulations.

Design and Optimization of a Superconducting Contiguous Diplexer Comprising Doubly Terminated Filters

This paper presents a simple and efficient method for the design of a microstrip contiguous diplexer comprising doubly terminated filters. The equivalent circuit for the channel filters is presented, which can accurately represent both the in-band and out-of-band characteristics of the channel filters. By analyzing and properly adjusting the input impedance of the channel filters, the equivalent circuit of the diplexer can be easily optimized. A high-temperature superconducting diplexer at S-band is successfully designed with this method and fabricated on a MgO substrate with a compact size of 32.6 mm × 18 mm. The measured results show high performance and agree well with the simulations.

Design of a High-Order Dual-Band Superconducting Filter With Controllable Frequencies and Bandwidths

This paper presents the design of an eight-pole dual-band bandpass high-temperature superconducting (HTS) filter with modified stub-loaded resonators (SLRs) and dual-feeding structures. The proposed modified SLRs are found to be advantageous because the even-mode and odd-mode couplings are separated from paths. The two bandwidths can be separately adjusted by two coupling paths. The proposed modified SLRs can conveniently be used to tune the two bandpass frequencies. Therefore, both the frequencies and bandwidths of each bandpass can be easily controlled. Moreover, the proposed modified SLRs can be also used to design high-frequency and high-order dual-band bandpass filters. A dual-feeding structure is adopted to match the external Q factor and internal couplings at two bandpass frequencies simultaneously. An eight-pole HTS dual-band bandpass filter operating at 2.55 and 3.53 GHz is designed and fabricated with a compact size of 18.14 mm × 9.36 mm to demonstrate the proposed design.

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.

A Compact Superconducting Filter at 6.5 MHz Using Capacitor-Loaded Spiral-in-Spiral-Out Resonators

Chip-capacitor-loaded spiral-in-spiral-out (SISO) resonators are proposed for superconducting filters at the HF band. Interdigital capacitors are used between resonators to provide large coupling values at the fundamental mode and small coupling values at harmonic modes. A compact four-pole high-temperature superconducting filter centered at 6.5 MHz is demonstrated, with a 8% fractional bandwidth, 0.13 dB insertion loss, and 14.3 dB return loss. The spurious response of the filter is below -40 dB up to about 13 times of the fundamental mode.