Tianning Zheng

Design of a High-Power Superconducting Filter With Novel DGS Structures

A novel defected ground structure (DGS) resonator with improved power handling capability is proposed in this paper. The current density distribution of the DGS resonator is simulated and compared with that of the complete ground structure (CGS) resonator. Simulation shows that the maximum current density of the DGS resonator is lower than that of the CGS resonator. Two four-pole bandpass high-temperature superconducting filters centered at 2.9 GHz with a fractional bandwidth of nearly 1.5% are designed and fabricated using the DGS and CGS resonators, respectively. The measured maximum handling power is 37.3 dBm for the DGS filter at 77 K, which is higher than that of 34.1 dBm for the CGS filter.

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.

A Compact Dual-Band Bandpass Superconducting Filter Using Microstrip/CPW Spiral Resonators

A compact eight-pole dual-band bandpass filter is designed using a combination of microstrip and coplanar waveguide spiral resonators. To implement a coupling matrix with both large and small elements, four coupling paths are used to apply coupling coefficients varying from 0.001 to 0.3. The fabricated superconducting filter exhibits high performance and excellent agreement with simulations.

Compact Superconducting Diplexer Design With Conductor-Backed Coplanar Waveguide Structures

This paper presents a compact superconducting diplexer with conductor-backed coplanar waveguide (CBCPW) structures. The couplings of the CBCPW structure resonators are significantly weaker than those of traditional microstrip resonators. High isolations between two channels are therefore achieved by using the CBCPW structures because of their highly suppressed unwanted cross couplings. The CBCPW diplexer consists of two four-pole channel bandpass filters. The couplings in the CBCPW structures, in which the air layer below the substrate varies in height, are simulated and compared with the coupling simulations of microstrip structures. The comparison shows that the coupling intensities of the CBCPW structures are nearly one order of magnitude lower than those of the traditional microstrip structures. The fabricated diplexer exhibits high performance with a compact core size of only 20 mm x 14 mm, and its measurements agree well with the simulations. The measured insertion losses of both channels are less than 0.19 dB, and the isolations are over 53 dB.

Design of Compact Superconducting Diplexer With Spiral Short-Circuited Stubs

Three types of impedance-matching structures for diplexer design are analyzed and calculated in this paper. Calculations show that different matching structures should be selected for size reduction, depending on the input impedance of the channel filters in the diplexer. Two channel filters in the superconducting microstrip diplexer at the P-band are designed with spiral resonators and capacitively coupled feedlines. The diplexer is then constructed with an impedance-matching structure of spiral short-circuited stubs. The compact diplexer has a size of 22.9 mm × 21.7 mm on an MgO substrate, which amounts to only 0.101 λg0 ×0.096 λg0, where λg0 is the guided wavelength of the 50- Ω line on the substrate at the midband frequency. The fabricated device exhibits high performance, and its measurements match the simulations well. The experimental insertion loss of both channels is less than 0.13 dB. The common-port return loss is greater than 18.9 dB, and the isolation between the two channels is greater than 60 dB.