Application of simple subgridding technique for antenna radiation patterns

Abstract

By using Eqs. (2) and (3), the characteristic impedance Z 0 and electrical length h for fixed C out and L out can be obtained bywhere M ¼ 3 and the electrical length h is equal to p/6 or 30at the fundamental frequency when L out ¼ C out ¼ 0. CONCLUSIONSIn this article, a novel simple load network with harmonic tuning which is based on a stepped-impedance transmission line is presented. Based on effect of a spectrum narrowing when poles of the reactance function are approaching adjacent zeros with higher transmission-line impedance ratio, an open circuit at the second harmonic and a short circuit at the third harmonic are achieved, thus satisfying inverse Class F conditions. Design example of the load network with second and third harmonic tuning and effect of the device output shunt capacitance C out and series inductance L out with design equations are also described and analyzed. Because of its simplicity and versatility, the finite-difference time-domain (FDTD) method has been prevalently used in electromagnetic field problems. However, cell size is determined by the smallest part of the structure, stability, numerical dispersion, and simulation time, and memory problems limit the FDTD qualities in calculating radiation patterns of the antennas mounted on electrically large ground planes. Parallel FDTD algorithm can be an effective way to solve this issue [1], but the amount of calculation is not fundamentally reduced. Subgridding techniques have been the effective alternatives [2][3][4][5][6][7]. However, most subgridding techniques published in the literature have small ratios of space steps and suffered from late-time instability [2, 3]. In addition, some stable techniques have a drawback that time steps are the same in the two grids [4, 5]. A subgridding algorithm of separating spatial and temporal subgridding interfaces has been introduced in [6], but perfect electric conductor (PEC) bodies cannot traverse the grids boundary. Huygens subgridding (HSG) method, of which the ratio of the space steps of the two grids can be arbitrarily large and the ratio of the time steps is the same as the ratio of the space steps, has been presented in [2, 7]. However, the HSG method has a drawback of late-time instability. When dealing with the electrically large body, in addition to calculation time and memory saving, accuracy and latetime stability should be ensured. In this article, a simple method satisfying the above requirements is presented. The radiation pattern of an inverted-F antenna, which is mounted on a 600 Â 600 Â 4.5 mm 3 ground plane, is calculated from the proposed method. The calculated result is compared with the measured one, and the close correspondence is achieved. SIMULATED AND MEASURED RESULTSAn inverted-F antenna, of which resonance frequency is 2.42 GHz, is shown in Figure 1, and detailed dimension of the radiation element of the antenna is depicted in Figure 2. The size of the ground plane is 600 Â 600 Â 4.5 mm 3 , which is too large in comparison with the radiation element. As the lattice size...