Guoyong Zhang

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.

Design and performance of a compact forward-coupled HTS microstrip filter for a GSM system

A practical design technique for a compact forward-coupled microstrip bandpass filter structure is introduced based on a computer-aided simulation and optimization software TUMIC. The structure consists of a parallel array of fully aligned half-wavelength resonators. Aimed at the application in the front-end receiver of a GSM base station, a 9-pole high-temperature superconductor filter with 2.6% fractional bandwidth at 1732.5 MHz was designed and fabricated using double-sided YBCO thin films on a 30-mm/spl times/30-mm/spl times/0.5-mm LaAlO/sub 3/ wafer. The S-parameter measurements show a good agreement with the simulated results. At 30 K, the filter has less than 0.4-dB insertion loss, 0.3-dB passband ripple, and better than 12-dB return loss.

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.

HTS subsystem formed by 12-pole filter for GSM1800 mobile communication

Abstract High temperature superconductor (HTS) microwave filter was designed for Global System for Mobile Communication (GSM)1800 system. The center frequency and the transmission fractional bandwidth of the 12-pole micro-strip line filter were designed as 1750 MHz and 4.3% respectively. The filter was fabricated on 30 mm ×19 mm ×0.5 mm LaAlO 3 wafer that was double side coated with YBCO thin films. At the temperature of 70 K, the filter has the insertion loss less than 0.48 dB, and the out-band rejection higher than 65 dB. Assembled with a low noise amplifier, the 12-pole filter formed the receive front of GSM1800 base station. The HTS receive front was tested by Datang’s lab and showed the good performance. The gain of the receive front is 22.5 dB and the noise figure of the receive front is less than 0.6 dB.

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.

Low Loss Tunable Superconducting Dual-Mode Filter at L-Band Using Semiconductor Varactors

This letter presents a superconducting continuously tunable bandpass filter with dual-mode resonator and Gallium arsenide (GaAs) varactors. The even- and odd-modes of the dual-mode resonator can be tuned simultaneously using a single bias voltage. The interstage and external couplings are realized with interdigital coupling structure to enhance the coupling strength. A four-pole dual-mode superconducting filter at L-band with a fractional bandwidth of approximately 20% is successfully designed. Two transmission zeros are generated in the upper stopband to increase the stopband rejection. The tuning range of the filter is 16% from 784.92 to 918.23 MHz. The insertion loss at 918.23 MHz is 0.69 dB with a reverse bias voltage of 9 V. The measurements of the filter match well with the simulated ones.

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.

A Miniature Wideband VHF Superconducting Filter Using Double-Surface Quasi-CPW Spiral Structures

Double-surface quasi-coplanar-waveguide spiral structures to attain strong couplings in low-frequency wideband filter designs are presented. Such structures yield coupling coefficients of up to 0.86 at the VHF band. A compact four-pole high-temperature superconducting filter centered at 112 MHz with a 38% fractional bandwidth, 0.03 dB insertion loss, and 17.5 dB return loss is demonstrated. The simulated and measured results show excellent agreement.

Superconducting Varactor Tunable Filter With Constant Bandwidth Using Coupling Line

This letter presents a superconducting tunable filter with a constant bandwidth using semiconductor varactors. A coupling line is introduced to adjust the inter-resonator coupling to meet the requirement of constant bandwidth. The external couplings are designed to remain a good passband shape with the tunable frequency. With the proposed method, a superconducting tunable filter with constant bandwidth is successfully implemented. The measured results of the filter agree well with the simulated ones. It shows a frequency tuning range of 11% from 924.5 MHz to 1030.8 MHz, a 1 dB bandwidth of 23.8 ± 0.3 MHz, and an insertion loss of 0.16 to 1.41 dB.