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The U-slot patch antenna, a single-layer single-patch antenna on a relatively thick substrate (~ 0.08 [lambda].sub.o), is a wide-band antenna with an impedance bandwidth in a range of 20%-30%, which is about an order of magnitude larger than that of the regular patch antenna. Recently, it was shown that a half U-slot patch antenna, with half of one of the dimensions of the U-slot patch, maintains similar wide-band behavior. The half-structure was also successfully applied to the U-slot with shorting wall. In this paper, new results on half structures, not previously published, are presented. First, the shorting pin technique is used to reduce the size of the half U-slot patch antenna. By both simulation and experimental studies, it is concluded that the impedance bandwidths, radiation patterns, radiation efficiencies and gains of the half-structures are comparable to the corresponding full structures. Bandwidth of 28.6% and radiation efficiencies exceeding 90% are obtained for the half U-slot patch with shorting pin. Radiation patterns are stable across the matching band. Second, it is shown that a structure obtained from halving the E-shaped patch, which is a derivative of the U-slot patch, also maintains its wide-band behavior. Index Terms--Broadband antennas, microstrip antennas.

Novel compact parallel-coupled microstrip bandpass filters are proposed by using additional lumped inductors to realize K-inverters between coupled-line sections to achieve an equivalent to the quarter-wavelength ([lambda]/4) resonator filters. As a resuit, the filter order can be doubled without increasing the circuit area, and no repeated passband is observed at twice the center frequency. In addition, by introducing the cross-coupling effect, two transmission zeros at upper and lower stopbands may be created. Simple equivalent-circuit models are also established as effective design tools. Specifically, several compact fourth-order microstrip bandpass filters with good stopband rejection are implemented and carefully examined. Index Terms--Bandpass filter, coupled line, lumped element, microstrip.

Quadruplet microstrip filters with source-load coupling are proposed to achieve similar skirt selectivity and/or in-band flat group delay as that of a sixth-order canonical form or an extracted pole microstrip filter. The diagnosis method of unwanted effects such as asynchronous resonant frequencies and unwanted couplings, which often occurs in the microstrip's open environment, is described in detail. A systematic design flow to implement a quadruplet microstrip source-load coupled filter with proper filter response is also provided. Two trial filters exhibited quasi-elliptical and flat group-delay response are designed and fabricated. Both theoretical and experimental results are presented. Index Terms--Diagnosis, flat group delay, microstrip quadruplet filter, source-load coupling.

The development and testing of a two-dimensional (2-D) prototype detector based on a microstrip gas chamber (MSGC) are reported. The second coordinate is obtained by utilising a plane of wires as pick up electrodes. The detector is operated with the wire plane at such a potential so as not to induce any gain around the wires. This means that the high tolerances normally associated with wire planes in multiwire proportional counters are not necessary, making the manufacture and repair of such a device relatively easier. The detector comprises of 48 individually instrumented channels in both X (MSGC strips) and Y (transverse wire plane). A specially designed encoding module has been constructed which feeds digital addresses for each event to the ISIS data acquisiton electronics (DAE) system. (ISIS is the spallation neutron source at the Rutherford Appleton Laboratory.) An intrinsic detector resolution of ~ 0.5 mm full-width at half-maximum (FWHM) has been measured for both dimensions which is degraded slightly by the digital resolution for the overall system. This readout method is shown to be very tolerant of a poor signal-to-noise ratio in the readout channels (unlike traditional analogue wire chamber readout systems) and permits the operation of the MSGC at moderate avalanche gains (~ 1000) which helps to maximize the rate and lifetime performance of the detector as well as permitting data capture rates in the MHz range. Index Terms--Gas microstrip detector, MSGC, X-ray imaging detector.

This paper presents the design of a novel branch-line coupler that can operate at two arbitrary frequencies. The proposed circuit also features compact size and planar structure. Explicit design formulas of the proposed dual-band coupler are analytically derived. Moreover, practical issues such as the realization of branch-line impedance and optimum choice of circuit topologies are addressed. For verification purposes, both simulated and measured results of a microstrip branch-line coupler operating at 900/2000 MHz are included. Index Terms--Couplers, dual band, planar circuits.

A capillary plate (CP) comprising an assembly of fine glass tubes was applied as a pre-gas-amplification device for a microstrip gas chamber (MSGC) operating under a gas pressure of 3 atm of helium-3 for use in neutron detection. The collection efficiency of the electrons between the CP and MSGC was maximally 17% using neutrons. The effective gas gain of the detector system was ~600 at a gas pressure of 3 atm with a 10% mixture of ethane with helium-3, confirming the feasibility of the CP as a pre-gas-amplification device. Moreover, we demonstrated that the coincidence measurement of the signals between the CP and the anodes of MSGC decreased the background levels of electronics noise, electronic discharges, and gamma-rays, indicating that a detector system with a low background can be constructed using the CP. Index Terms--Capillary plate (CP), gas gain, microstrip gas chamber, neutron detector.

Bandpass filters with an optimal rejection bandwidth are designed using parallel-coupled stepped impedance resonators (SIRs). The fundamental ([f.sub.o]) and higher order resonant harmonics of an SIR are analyzed against the length ratio of the high-Z and low-Z segments. It is found that an optimal length ratio can be obtained for each high-Z to low-Z impedance ratio to maximize the upper rejection bandwidth. A tapped-line input/output structure is exploited to create two extra transmission zeros in the stopband. The singly loaded Q([Q.sub.si]) of a tapped SIR is derived. With the aid of [Q.sub.si], the two zeros can be independently tuned over a wide frequency range. When the positions of the two zeros are purposely located at the two leading higher order harmonics, the upper rejection band can be greatly extended. Chebyshev bandpass filters with spurious resonances up to 4.4 [f.sub.o], 6.5 [f.sub.o], and 8.2 [f.sub.o] are fabricated and measured to demonstrate the idea. Index Terms--Microstrip, microwave filter, spurious response, stepped impedance resonator (SIR), transmission zero.

A two-port ring resonator is used to characterize the microwave properties of a microstrip line printed on Ferro A6-S low-temperature co-fired ceramic. The ring and its coupling gaps are simulated using a simple lumped-element model. The coupling gaps are modeled as capacitors, the values of which are extracted using a commercial two-and-one-half-dimensional electromagnetic simulator. The validity of the lumped-element model is assessed by comparing the simulated and experimental resonant frequencies and, for the first time, the simulated magnitudes of both the reflection and transmission coefficients are also compared with those obtained experimentally. A correction for the frequency pushing due to the capacitive loading of the coupling gaps is also presented. The resulting model is then shown to predict the resonant frequencies to within 0.11% from 5 to 40 GHz. The simulated and experimental reflection magnitudes are within 0.5 dB across the band, whereas the transmission magnitudes are within 3.5 dB up to 22 GHz. Experimental results indicate that the loss of the microstrip ranges from approximately 0.11 to 0.42 dB/cm across the band and that the relative permittivity of the substrate is nearly constant versus frequency with an average value of 6.17. Index Terms--Attenuation and permittivity measurements, equivalent lumped elements, resonant frequency, ring resonator.

This paper presents a new impedance matrix interpolation algorithm, in the context of method of moments, for planar microstrip structures. Three different interpolating functions are implemented depending upon the distance between the basis and testing functions. To demonstrate its efficiency, the technique is applied to several planar microstrip structures, viz. a patch antenna fed by microstrip line and a 4 x 4 planar patch array. It is demonstrated that the use of the proposed impedance matrix interpolation scheme can result in significant savings in the computation time with little or no compromise in the accuracy of the solution. Index Terms--Impedance matrix interpolation, method of moments (MOM), microstrip patch antenna, probe-fed square patch array.

This paper describes a full-wave moment-method analysis of an aperture-coupled microstrip coupler using a resonant cavity (rectangular or circular) between the substrate ground planes. Structures of this type are useful for millimeter-wave integrated circuits and phased arrays, as they allow the use of a relatively thick central ground plane to provide isolation, as well as heat dissipation. Both four-port coupler geometries and two-port transitions are treated. Equivalent circuits are derived for each of these problems, and computed results are validated with data from the literature and with independent calculations from commercial computer-aided design (CAD) packages and measured data. These comparisons show that the solutions derived here are accurate and computationally efficient, and have the added advantage over commercial CAD packages in that equivalent-circuit parameters can be obtained directly. The vector Bessel transform is used to derive the required Green's function for the circular cavity. Index Terms--Aperture coupling, cavity coupling, microstrip couplers.

A high dynamic control system for the Alspa VDM 7000 medium-voltage drive was implemented, which provides fast torque response times of a few milliseconds despite the typically low switching frequency of gate-turn-off thyristors which is necessary to achieve high efficiency. The drive system consists of a three-level voltage-source converter with active front end and a synchronous motor. The drive has most recently been applied to a main strip mill. It provides a maximum of 8.3-MW mechanical power with a rated motor voltage of 3 kV. Besides motor torque as the main control objective, the control system has to comply with a number of additional objectives and constraints like dc-link voltage regulation and balancing, current and torque harmonics, motor flux, and excitation. Index Terms--Adjustable-speed drives, converter control, drives, highly dynamic drives, industrial applications, multilevel converters, variable-speed drives, vector control.

A novel double-layer coupled stripline resonator structure is introduced to realize miniature broadband bandpass filters. Filters with relative bandwidth up to 60% and size less than λ/8 × λ/8 × h (λ is wavelength at the midband frequency; h is the substrate height, which is much smaller than λ/8) can be fulfilled using such resonators. Two possible filter configurations are proposed in this paper: combline and interdigital. The filter synthesis procedure follows the classical coupling matrix approach that generates very good initial responses. Optimization by the mode-matching method and fine tuning in Ansoft's High Frequency Structure Simulator are combined to improve the filter performance. Two filter design examples are given to validate the feasibility. Low temperature co-fired ceramic (LTCC) technology is employed to manufacture the filters. Experimental results of the two manufactured filters are presented. The effects of LTCC manufacturing procedure on the filter performance are also discussed. [ABSTRACT FROM AUTHOR]