Bisong Cao

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.

Design of a High-Power Superconducting Filter Using Resonators With Different Linewidths

This paper presents a design method to develop a high-power superconducting microstrip filter with different linewidth resonators. The linewidth of every resonator is optimized using this method to meet the same maximum current density. Thus, the power-handling capability of the five-pole filter on a limited substrate size can reach a maximum value. The design method is verified by the electromagnetic simulation of the current density distribution. The high-power superconducting filter is designed and fabricated on a 38 mm times 30 mm times 0.505 mm LaAlO3 substrate. The maximum resonator linewidth is 7 mm, and the minimum one is 1.6 mm. The filter has a center frequency of 2006 MHz and a narrow bandwidth of 1.0%. The measured power level is up to 35 dBm at 65 K without an evident change in insertion loss.

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.

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.

Design and Performance of an Ultra-Narrowband Superconducting Filter at UHF Band

A stepped impedance spiral resonator suitable for high-temperature superconducting (HTS) filter with bandwidth narrower than 0.5% is presented. An eight-pole demonstration HTS filter is developed with a central frequency of 650 MHz and a bandwidth of 0.3%. The measurements show that the insertion loss is less than 0.3 dB, and the return loss is better than 16 dB. The filter has out-of-band rejections of 65 dB at 2 MHz below the passband and 80 dB at 2 MHz above the passband, respectively.

Superconducting Ultra-Wideband (UWB) Bandpass Filter Design Based on Quintuple/Quadruple/ Triple-Mode Resonator

This paper analyzes the coupling modes when multiple hairpin resonators are coupled. Three kinds of current distribution and direction states exist in the coupled hairpin resonators: the current along the clockwise direction, the current along the counterclockwise direction, and no current density distribution. Different combinations of these current states lead to different coupling modes. In order to distinguish these modes, auxiliary lines are introduced between each two coupled resonators to denote each coupling mode, and this method is theoretically based on the analysis of the eigenvector of the coupling matrix. A simple and effective technique to construct multi-mode resonators (MMRs) is then proposed. An n-mode resonator can be constructed by connecting n hairpins with small patches. Resonant modes of this class of MMRs were analyzed in detail using the proposed auxiliary lines method. Single stage and four stages of quintuple-mode resonators were used to design high-temperature superconducting ultra-wideband (UWB) filters by properly allocating the first five resonant peaks. Two UWB filters based on quadruple-mode and triple-mode resonators are also given. Parallel-coupled three lines were used to provide tight external couplings, which also generated two transmission poles. Measured results are in good agreement with the simulated ones without any tuning.