Frederick Huang

Ultra-compact superconducting narrow-band filters using single- and twin-spiral resonators

Superconducting filters using spiral resonators have been demonstrated. Compared with meander lines, errors in track width have a smaller effect on the total inductance; fabrication tolerance, simulation accuracy, power handling, and quality factor are consequently improved. The coils do not require air bridges, which are difficult to produce in superconductors. The devices can be designed using a standard procedure based on the coupling coefficients between resonators and coupling to source and load. Fourth- and sixth-order Chebyshev filters employing single and twin spirals are demonstrated for 0.86% bandwidth filters with center frequency of approximately 1750 MHz. A new coupling structure has been introduced for the single-spiral resonators. Despite the very small size of approximately 1.7/spl times/1.7 mm, the resonators have a quality factor of approximately 30000 at 77 K and the filters can handle approximately 20 mW.

Miniature superconducting filters

Because of the intrinsic low loss of high temperature superconductors at microwave frequencies it is possible to reduce the size of filters while still retaining excellent performance. In order to accomplish this reduction in size new filter geometry is required. Under this theme of miniaturization a number of new and novel types of microwave filter are discussed, this includes delay line filters, lumped element filters and filters based on slow wave structures. Each of the filters are constructed out of high temperature superconductors (HTS).

Coplanar quarter-wavelength quasi-elliptic filters without bond-wire bridges

This paper presents the design and experimental results of two coplanar quarter-wavelength microwave filters operating at a frequency of approximately 3 GHz. Coplanar designs are of particular interest because they are less sensitive to the thickness of the dielectric substrate than other transmission-line types such as a microstrip. One of the designs has a quasi-elliptic frequency response. In addition, the design also eliminates problems with unbalancing of the ground planes normally present in coplanar structures. Bond wires between the ground planes are not required. This paper describes in detail the structure of the resonators and how they are coupled together to form a filter.

Superconducting spiral filters with quasi-elliptic characteristic for radio astronomy

To produce a filter small enough to fit a 2-in wafer at 408 MHz while maintaining high-quality performance, half-wavelength single spiral microstrip resonators are introduced. New coupling structures make both positive and negative coupling available by changing the directions of spiral winding. An eight-pole high-temperature superconducting bandpass spiral filter with 3.7% bandwidth at 408-MHz band is presented for radio astronomy applications at the Jodrell Bank Radio Observatory, Macclesfield, Cheshire, U.K. A quasi-elliptic characteristic with four transmission zeros is realized by adding three cross-couplings to the standard Chebyshev filter. The filter shown is designed and fabricated on a 32 mm /spl times/ 18 mm /spl times/ 0.508 mm MgO substrate. The untuned measured results of the filter at 30 K show a maximum passband insertion loss 0.35 dB (ripple 0.27 dB), a minimum return loss 13.2 dB, and minimum out-of-band rejection of 65 dB, which have good agreement with its electromagnetic full-wave simulation results.

A high-temperature superconducting bandpass filter with microstrip quarter-wavelength spiral resonators

A high-temperature superconducting bandpass filter at 408 MHz using microstrip quarter-wavelength spiral resonators is demonstrated. The quarter-wavelength spiral resonators were shorted to ground, as in a combline filter, via a grounding strip that is attached to the box wall by a number of aluminum bonding wires. The introduction of the normal metal wires does not introduce a measurable attenuation. The filter achieves a symmetrical quasi-elliptic characteristic by using two cross-coupling links. The experimental results of the filter are in very good agreement with the simulated ones.

Micromachined Millimeter-Wave Rectangular-Coaxial Branch-Line Coupler With Enhanced Bandwidth

Wideband millimeter-wave branch-line couplers have been demonstrated using micromachined air-filled rectangular-coaxial lines supported by quarter-wavelength stubs. The coaxial lines are constructed by bonding five layers of gold-plated silicon or SU8 slices. The measured coupler shows an insertion loss of 3.2-4.0 dB in the coupled and thru ports between the frequencies 31.3-47.6 GHz. The isolation is better than 12.8 dB, and the return loss less than -10 dB. In addition to providing support, the stubs enhance bandwidth when properly placed.

HTS narrow band filters at UHF band for radio astronomy applications

High performance narrow-band High-Temperature Superconductor (HTS) filters at 610 MHz with very sharp cut-off response and low loss are needed for improving the observation of pulsars at the Jodrell Bank Observatory, UK. An eight-pole quasi-elliptic HTS filter using compact resonators has been designed for this purpose. The measured response of filter has an insertion loss of 0.3 dB (including a 0.2 dB ripple), and a return loss of 15 dB in the passband. Two transmission zeroes are realized to improve the steepness of the cut-off. The lowest harmonic is designed to appear at 1.79 GHz, about three times the center frequency. The out-of-band rejection is better than 85 dB up to this harmonic. The filter has been tested in the observatory with excellent results.

Superconducting microstrip filters using compact resonators with double-spiral inductors and interdigital capacitors

Novel resonators composed of double-spiral inductors and interdigital capacitors are developed, which not only are compact in size but also have no harmonics up to three times of the fundamental frequency. The center frequency is insensitive to the thickness of the substrate. A miniature seven-pole narrow-band HTS bandpass microstrip filter has been designed, fabricated and tested for an astronomy observation application, which requires a center frequency at 610 MHz and 0.82% fractional bandwidth. The computed and measured results are found in excellent agreement.

Wide-band superconducting coplanar delay lines

Two 25-ns high-temperature superconductor delay lines with novel double-spiral meander line structures were fabricated and measured, one based on the conventional coplanar waveguide (CPW) and the other based on the conductor-backed CPW. Compared with other published studies, the performance of the Conductor-backed CPW delay line is among the best in terms of the widest resonance-free band (2-18 GHz), low insertion loss (0.06 dB/ns at 60 K and 10 GHz), small ripple (<1 dB up until 16 GHz), and small dispersion (<2 ns in the variation of group delay between 2-18 GHz). This is also the first coplanar delay line successfully demonstrated without using wire bonding. The reflecting elements in the delay lines were identified through time-domain measurements. Full-wave simulations were performed to compare the double-spiral meander-line structure with conventional double-spiral line, and to identify the geometric factors restricting the bandwidth of the double-spiral meander line.

Superconducting microstrip wide band filter for radio astronomy

A ninth order wide-band bandpass filter is presented for radio astronomy applications. The filter, for Jodrell Bank Radio Observatory, is designed to have a fractional bandwidth of 26.14% and a center frequency of 1.53 GHz. It uses both straight and hairpin resonators in order to achieve the wide bandwidth. In addition, the filter is integrated with two spur-fine notch filters for second harmonic suppression. Good agreement between simulated and experimental results is obtained.