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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.