Hieng Tiong Su

HTS Quasi-Elliptic Filter Using Capacitive-Loaded Cross-Shape Resonators With Low Sensitivity to Substrate Thickness

The design and implementation of a four-pole quasi-elliptic filter for X-band radar applications using high-temperature superconductors is presented. The resonators used consist of cross-shape ring resonators with additional interdigital capacitive loads that allow miniaturization with reduction of sensitivity to substrate thickness. The experimental and simulated results are shown together with the power dependence of the filter

Measurement of YBCO Thin Film Surface Resistance Using Coplanar Line Resonator Techniques From 20 MHz to 20 GHz

The surface resistances of YBCO thin films are measured over a wide and continuous frequency range from 20 MHz to 20 GHz, by characterizing more than 1000 harmonics of two 20 MHz high-temperature superconductor resonators. One resonator is based on the conventional coplanar waveguide (CPW) and the other based on the conductor-backed CPW (CBCPW). The quality factors and resonant frequencies are measured. The attenuation and group-delays of the coplanar lines are estimated and surface resistances of the superconductors are extracted using a transmission-line model. The wideband frequency-dependence of the surface resistance is investigated. The sources of experimental errors are analyzed. This paper also reports some temperature-dependent and power-dependent measurement results.

A novel compact quadruple-mode microstrip bandpass filter with low harmonic response

A novel compact quadruple-mode resonator is presented in this paper. The quadruple-mode resonator consists of a pair of quarter-wavelength resonators and a pair of L-C type resonators connected to each other through a grounded via. The new resonator has the same size as a dual mode square open-loop resonator published earlier, but has four modes and better harmonic response. The resonator filter has a centre frequency of 0.99 GHz and passband insertion loss of 1.2 dB. The selectivity of the filter and stopband response can be improved by implementing different feed structures. Simulated and measured results are in good agreement.

An Aperture-Backed H-Ring Ultra-Wideband Bandpass Filter with Floating Conductor for Spurious Suppression

Abstract This article presents analyses of and design procedures for a compact quintuple-resonance aperture-backed ultra-wideband bandpass filter. First, a one-wavelength H-ring resonated at 6.85-GHz center frequency is coupled with open stubs at both sides to produce a triple-resonance filter characteristic. To increase the resonances of the filter to five, stepped-impedance feed lines are then implemented to introduce two extra transmission poles at each side of the center frequency. The filter, which has a structure that is both horizontally and vertically symmetrical, simplifies the analysis to a quarter of the structure while enabling the stepped-impedance feed lines to be designed analytically. A wide aperture is then etched on the ground plane directly below each interdigital line to achieve strong coupling. This results in wider coupling gaps to enable in-house fabrication. A floating strip conductor is then added at the center of each ground aperture to suppress the spurious harmonic appearing at twice the fundamental frequency of the ring resonator. The filter is fabricated on an RT/Duroid 6010.2LM substrate (Rogers Corporation, Rogers, Connecticut, USA). The simulated and measured responses are in good agreement.

Compact microstrip bandpass filters using triple-mode resonator

Step-by-step procedures for designing a third order bandpass filter and a sixth order bandpass filter using a triple-mode resonator are described in this paper. The triple-mode resonator is a square open-loop resonator with an open circuited stepped-impedance stub and a grounding via located at the symmetrical plane of the resonator. The equations for approximating the resonant frequencies of the resonator are obtained from odd and even mode analysis. To design a filter, first, the theoretical resonant frequencies for the filter are calculated. Then the basic dimensions of the resonator are approximated using the equations. The filter layouts are fine-tuned by simulation and verified by experiment to conclude the paper. The first spurious response occurs at about 3 times the center frequency of the first passband in both filters. The simulated and measured results are in good agreement.

BaxSr1-xTiO3 Thin Films for Tunable Microwave Devices in Cryogenic and Room Temperature Application

The microwave properties of YBCO/Ba 0.05 Sr 0.95 TiO 3 (BST5) and Ag/Ba 0.5 Sr 0.5 TiO 3 (BST50) films were characterized at 80 K and 290 K. At zero bias, the BST5 had a permittivity of 400 and a loss tangent of 0.02; the BST50 had a permittivity of 900 and a loss tangent of 0.1. The respective tunabilities at 3.6 V μ m− 1 were 15% and 44%. Analysis of the performance of phase shifters and tunable filters based on these films showed that both conductor and dielectric losses need to be considered in the selection of materials for devices. A high tunability alone does not guarantee good performance.

A Modified Hair-Pin Resonator for the Design of Compact Bandpass Filter with Suppression of Even Harmonics

A new design consideration is explored for a hair-pin resonator. A grounding via at the mid-point of the resonator acts as a perturbation to split the resonant frequencies. The via also suppresses even harmonics of the fundamental. The principle operation of the hair-pin resonator with a via is analyzed and verified by measurement. It is shown that such a hair-pin resonator can be made more compact using stepped impedance line. A compact 4-pole bandpass filter using the modified compact hair-pin resonator with a via is demonstrated. Simulation and measured results showed good agreement.

Circuit modeling for the design of Composite Right/Left-handed ring resonator

A desirable feature of a Composite Right/Left-handed (CRLH) dual-mode ring resonator is the suppression of the second harmonic. This paper presents the results of an investigation of the CRLH dual-mode ring resonator filter by using circuit modeling approach. The circuit approach shows that one can use a single capacitor unlike three capacitors in previous design. It also provides an initial design which can then be fine tuned by simulation. A fourth order Chebyshev filter is then implemented using two CRLH dual-mode ring resonators. The design and implementation agree reasonably well.

An aperture-backed sextuple-mode ultra-wideband bandpass filter

In this paper, a sextuple-mode ring resonator ultra-wideband bandpass filter is presented. The objective is to enhance the selectivity of a quintuple-mode filter by introducing an additional transmission pole within the passband. The extra pole comes from two open stubs inserted symmetrically inside the ring resonator. Analysis of the filter is done to show the relationship between the six resonant frequencies, and characteristic impedance and electrical length of the stubs. The filter is designed, fabricated and measured. The measured responses are in good agreement with simulations. The filter exhibits 108.02% 3dB fractional bandwidth at 6.85GHz centre frequency.

Investigating the Performance of RF MEMS Switches

The performance of micro-electro-mechanical system (MEMS) metal switches were investigated at wide temperature range. Measurements were carried out using cryogenic probe station and S-parameters were taken using a network analyser for frequencies up to 20 GHz. A total of 28 switches were evaluated. The investigation shows a 50% increase in the actuation voltage and a decrease in the percentage of operational switches as the temperature was reduced to 10 K. At room temperature the best isolation (when open) was 30 dB at 10 GHz with an insertion loss of 0.14 dB (when closed). Measurement accuracy was reduced at low temperature, however, isolations and insertion losses were similar to room temperature values.