Modelisation of Probe Feed Excitation Using Iterative Method

This paper presents an implementation of an iterative method based on the waves concept for analyzing patch antennas fed by coaxial probes. This method includes a two-dimensional fast Fourier transform (FFT-2D) in a wave guide environment. The method has the advantage of simplicity in that it does not involve basis functions and inversion of matrices, as used in other calculation methods. Therefore, it is capable of analyzing larger bodies than other classical techniques. An implementation of the iterative calculation is shown for the extraction of S parameters of microwave components and antennas. The good agreement between simulation results and experimental published data justifies the design procedure and validates the present analysis approach. INDEX TERMS : Iterative method, fast Fourier transform in waveguide environment, probe feed. IINTRODUCTION Microstrip patch antennas are widely used in wireless communication because of their advantages, such as being low profile, light weight, and conformal. Different numerical electromagnetic analysis techniques such as the method of moments [1], the finite elements method [2], and the finite difference time domain method can be used to accurately simulate the microstrip antenna [3]. In most cases those numerical techniques are not practical to use directly in CAD software for design and optimisation purposes, due to the enormous amount of computer time required. Circuit simulators on the other hand are very fast. However, models of microwave integrated circuits used in circuit simulators are often inaccurate or even invariable. To overcome these difficulties, the use of the iterative method, which is based on the concept of waves, has been proposed. It consists of generating a recursive relationship between incident waves and reflected waves at the interface containing the circuit which is divided into cells [4]. A high computational speed has been achieved by using 2D fast Fourier Transform in wave-guide environment [5]. In this paper, a general implementation of the iterative method is proposed to treat microstrip patch antennas. The theory as well as its procedure implementation is described. The numerical results are compared to measured data [8] to establish the validity and usefulness of the iterative method given in this study. IIGENERAL FORMULATION OF ITERATIVE METHOD We consider the shielded microstrip circuit, assumed to be loss-less, presented in Fig. 1. The air-dielectric interface π is divided into cells denoted by three sub-domains corresponding to metal, source and dielectric. 198 1054-4887 © 2004 ACES ACES JOURNAL, VOL. 19, NO. 3, NOVEMBER 2004