Compact Antennas for Wireless Communications and Terminals: Theory and Design

Chapter 3Cavity Model ¹

 

 

 

3.1. Introduction

The cavity model provides a formalism describing the fields in the antenna and the radiated fields. Contrary to the transmission line model which is limited to a rectangular patch, there is no a priori hypothesis regarding the shape of the radiating element. However, a didactic presentation is facilitated by the existence of analytical mode expressions, which can, for example, apply to either rectangular or circular patches. Here we will only examine the rectangular scenario and the reader should refer to existing literature [JAM 89] for other geometries.

The cavity model was developed at the end of the 1970s, at a time when the calculation power of computers did not allow for the possibilities offered by numerical resolution methods to be fully exploited. It is rich in a physical sense and will allow us to explain radiating fields analytically in Chapter 4. We have, however, used a purely numerical method in section 3.5 to trace the various modes of current and to highlight the influence of excitation.

3.2. Formulation of the electromagnetic problem

Let us consider the basic structure in Figure 3.1. The radiating element and the ground plane are assumed to be produced from a perfect metal and can therefore be seen as electric walls. On the surface of a perfect metal, we know that the tangential component of the electrical field and the normal component of the magnetic field cancel out or according to the conventions in Figure 3.1 ...