Michael J. Lancaster

Couplings of microstrip square open-loop resonators for cross-coupled planar microwave filters

A new type of cross-coupled planar microwave filter using coupled microstrip square open-loop resonators is proposed. A method for the rigorous calculation of the coupling coefficients of three basic coupling structures encountered in this type of filter is developed. Simple empirical models are derived for estimation of the coupling coefficients. Experiments are performed to verify the theory. A four-pole elliptic function filter of this type is designed and fabricated. Both the theoretical and experimental performance is presented.

Theory and experiment of novel microstrip slow-wave open-loop resonator filters

This paper presents the theory and experiment of a new class of microstrip slow-wave open-loop resonator filters. A comprehensive treatment of capacitively loaded transmission line resonator is described, which leads to the invention of microstrip slow-wave open-loop resonator. The utilization of microstrip slow-wave open-loop resonators allows various filter configurations including those of elliptic or quasi-elliptic function response to be realized. The filters are not only compact size due to the slow-wave effect, but also have a wider upper stopband resulting from the dispersion effect. These attractive features make the microstrip slow-wave open-loop resonator filters promising for mobile communications, superconducting and other applications. Two filter designs of this type are described in detail. The experimental results are demonstrated and discussed.

Microstrip bandpass filter using degenerate modes of a novel meander loop resonator

A novel type of dual-mode microstrip bandpass filter using degenerate modes of a meander loop resonator has been developed for miniaturization of high selectivity narrow-band microwave bandpass filters. A filter of this type having a 2.5% bandwidth at 1.58 GHz was designed and fabricated. The measured filter performance is presented. >

Thin-film ferroelectric microwave devices

When an electric field is applied to a ferroelectric material, the microwave permittivity undergoes a substantial change. This change in permittivity can be utilized in microwave devices to produce frequency-agile functions. This paper is a comprehensive review of the work on ferroelectric materials; this includes models of the ferroelectric permittivity and loss tangent, as well as methods of measurement of these properties. New measurements are presented on thin-film strontium titanate and single-crystal strontium barium titanate substrates. These results are compared with the model. A brief discussion is given of the applications of ferroelectric material in microwave devices.

Aperture-coupled microstrip open-loop resonators and their applications to the design of novel microstrip bandpass filters

The rapid growth of wireless and mobile communications has stimulated the development of multilayer filter technology. In this paper, two types of aperture-coupled microstrip open-loop resonators in a multilayer structure are proposed and investigated for the applications to the design of a new class of compact microstrip bandpass filters. The new filter configuration consists of two arrays of microstrip open-loop resonators that ran be coupled through the apertures on the common ground plane. Depending on the arrangement of the apertures, different filtering characteristics can easily be realized. Electromagnetic modeling of the aperture couplings is presented. Three experimental filters of this type with Chebyshev, elliptic function, and linear phase response respectively, are described together with theoretical and experimental results. The filter asymmetric responses associated with frequency-dependent couplings are investigated.

On the development of superconducting microstrip filters for mobile communications applications

This paper presents recent developments of an eight-pole planar high-temperature superconducting (HTS) bandpass filter with a quasi-elliptic function response. A novel planar filter configuration that allows a pair of transmission zeros to be placed at the band edges is described. The miniature HTS filter has a fraction bandwidth less than 1% and is designed for mobile communication base-station applications to increase sensitivity and selectivity. Design considerations including filter characteristics, design approach, sensitivity analysis and unloaded quality factor of resonators are addressed. The filter was fabricated using double-sided YBCO thin film on an MgO substrate of size 0.3/spl times/22.5/spl times/39 mm. Very good experimental results were obtained with the filter cooled using liquid nitrogen. The minimum passband loss was measured to be approximately 1 dB. The passband width at points 1 dB down from the minimum loss point was 12.8 MHz for a center frequency of 1738.5 MHz. High selectivity was achieved with a 30-dB rejection bandwidth of 16 MHz.

Development of new microstrip pseudo-interdigital bandpass filters

A new type of miniaturized microstrip bandpass filter with pseudo-interdigital structure without via hole grounded resonators is described. A very compact filter of this type, having a size smaller than quarter-wavelength by quarter-wavelength at a midband frequency of 1.1 GHz was designed and fabricated. The measured and simulated results are presented. >

The coplanar resonator technique for determining the surface impedance of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films

We describe how coplanar microwave resonators fabricated from patterned thin films of YBa/sub 2/Cu/sub 3/O/sub 7/(-/spl delta/) (YBCO) can he used to measure the ab-plane microwave surface impedance Z/sub s/=R/sub s/+jX/sub s/ of the films, in particular the absolute value and temperature dependence of the magnetic penetration depth /spl lambda/. The current distribution of the resonator is calculated by modelling the resonator as a network of coupled transmission lines of rectangular cross-sections; this is then used to estimate the ab-plane /spl lambda/(T) from the measurements of resonators of different geometries patterned onto the same film. We obtain values of /spl lambda/(0) in the range 150-220 nm. The unloaded quality factors of the linear resonators at 7.95 GHz are around 45000 at 15 K and around 6500 at 77 K. We estimate the corresponding values of the intrinsic R/sub s/ at 7.95 GHz to be 23 /spl mu//spl Omega/ and 110 /spl mu//spl Omega/ at 15 K and 77 K, respectively. These values are comparable with those of other high quality unpatterned YBCO films reported in the literature. Z/sub s/ for the best optimised films appears to be insensitive to the effects of patterning. >

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).

WR-3 Band Waveguides and Filters Fabricated Using SU8 Photoresist Micromachining Technology

This paper demonstrates a two-layer SU8 photoresist micromachining technology that has similar performance to conventionally machined metal. The technology is demonstrated in the WR-3 band (220-325 GHz). Three different WR-3 band circuits, namely a WR-3 band straight through waveguide, a bandpass filter and a dual-band filter are demonstrated. For the measurements, a conventionally precision machined metal block was used for the WR-3 band waveguide and the bandpass filter to achieve good calibration and accurate interconnection with standard waveguide flanges; whereas, for the dual-band filter, two back-to-back right-angle bends are added in order to achieve accurate, reliable waveguide interconnection without using the metal block. A measured average insertion loss of 0.03 dB/mm has been achieved for the 14.97 mm long straight through waveguide. This is comparable to the loss of around 0.02 dB/mm for a standard metal waveguide at this frequency. The fifth-order waveguide filter exhibits an 8% 3 dB bandwidth at a central frequency of around 300 GHz. The minimum passband insertion loss was measured to be around 1 dB and the return loss was better than 10 dB throughout the passband. The filter results showed a notable improvement over those obtained from the separate SU8 layer technique that was also used to make the same devices for comparison. To further demonstrate the advantages of the new two-layer SU8 micromachining technique, the dual-band filter included isolated regions in the waveguide channels that would have not been possible for micromachining using the previous separate single layer technique. The performance of the micromachined dual band filter was excellent in terms of very low insertion losses on both passbands.