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A wide-band compact antenna combining a rectangular dielectric resonator (DR) with a grounded and inverted L-plate is proposed. Two different impedance matching circuits, a vertical T-shaped strip attached to one side of the DR and a microstrip stub terminated into a T-branch, are introduced to enhance the impedance matching and to economize the space utilization by the matching circuits. A two-step procedure is applied to design the radiation element and the feed structure of the antenna. Approximate formulas are used to obtain initial estimation of the antenna dimensions. Then finite-difference time-domain method (FDTD) with the help of fast Fourier transform/Pade method is used for fine-tuning these dimensions to obtain satisfactory resonant frequency and quality factor. Next, the feed structure is designed and adjusted to obtain the optimal impedance matching. Since the radiation element and the feed structure are designed separately, the design process is simplified and both their performances are optimized within the frame of design restrictions. Two antennas, for 2.4 and 5.8 GHz Bluetooth and wireless local-area network applications, are designed as examples. The -10 dB bandwidths between 210 and 240 MHz are obtained. The antenna gains are 1.0 and 1.5 dBi, respectively. Index Terms--Dielectric antennas, finite-difference time-domain method (FDTD) methods, microstrip antennas.

In this paper, a new representation for the space domain Green's function of general multilayer media is presented. This approach is based on an efficient plane wave expansion of the source incident field. Using the transmission line model for the multilayer medium, the effect of the layered medium on the incident plane waves is determined by a transmission coefficient, and the amplitude and phase of each plane wave at the field point are obtained. The total field is evaluated by summing the resultant plane waves at the field point. The main advantage of the proposed method is that the spatial domain Green's function of multilayer media can be obtained easily as a summation of simple exponential functions, without the need for Sommerfeld integration or complex image approximation. The plane wave approximation is independent of the parameters of the medium and is valid over a wide frequency range. Furthermore, the exponential form of the plane wave solution makes it possible to compute the method of moments matrix elements analytically for most important types of basis functions in multilayer problems. Index Terms--Green's function, method of moments (MoMs), multilayer medium, plane wave expansion.

The concurrent complementary operators method (C-COM) is extended to simulate microwave planar circuits with the finite-difference time-domain (FDTD) method for the first time. The dispersive boundary condition (DBC) and its complementary operator are used to truncate the FDTD lattices and the fields in the boundary layers are calculated, respectively. Then these two simulations are averaged to annihilate the first-order reflections. Numerical error analysis shows that the performance of the DBC is improved greatly due to the implementation of complementary operators, and the setup of its parameters becomes easier and more robust. A flexible and high-performance absorbing boundary condition is thus obtained through the combination of the DBC and C-COM. This method has been successfully used to simulate a variety of planar circuit structures. Simulations of a microstrip low-pass filter, coupled-line bandpass filter, modified microstrip transmission lines, and dielectric resonator antenna, are presented in this paper. Index Terms--Absorbing boundary conditions (ABCs), dielectric antennas, finite-difference time-domain (FDTD) methods, microwave circuits.

A steady-state photoresponse analysis of thin superconducting film is described, based on the Bardeen, Cooper and Schreiffer (BCS) theory. The analysis is helpful for designing superconducting optoelectronic devices based on photo-excited superconducting film, and for designing optically controlled superconducting microwave devices.

A response by Y.L. Chow, R. Faraji-Dana and S. Safavi-Naeini to the article 'Analysis of Superconducting Microwave Structures: Application to Microstrip Lines' is presented. They allege that the contrasting results of the author is caused by the application of a quasi-TEM approximation where a proportionality relation between axial current distribution and stored charge density is strongly suggested.

Optical-microwave interaction in high-[T.sub.c] superconductors is investigated for performing basic optoelectronic functions in cryogenic environment. A fast bolometric photoresponse in conjunction with the unique electrical properties of high-temperature superconductor (HTS) materials allows us to explore a series of novel optoelectronic devices with low-noise/low-power and high-speed/high-frequency characteristics. After reviewing the HTS photoresponse categories, we describe the fast bolometric photoresponse and its condition with heat transfer analysis. The analytical solution of heat diffusion equation for an HTS strip mounted on a substrate will be presented for three different type of optical sources. Then the effect of optical irradiation will be incorporated in the two-fluid model by thermomodulation concept in order to model the interaction of optical radiation with electrical signal. The current-field relationship and the supercurrent response time are evaluated in the presence of both optical and electrical signals. Our numerical simulations for YBaCuO film will demonstrate the possibility of RF harmonic generation when the laser beam is modulated by the RF signal in the presence of dc bias current and RF signal mixing when the HTS film is fed by a time-harmonic microwave source. The developed model can also be used to study optical control and tunability techniques for HTS microwave devices for analog signal processing. Index Terms--High-temperature superconductors, microwave-photonics, superconducting films, superconducting microwave devices, superconducting optoelectronics.