8.1 INTRODUCTION

This chapter deals with the radiation characteristics of slot antennas and includes the effects of finite and curved surfaces, dielectric coatings, cavity backing, and single slots fed by waveguides. The simplest example of such an antenna consists of a rectangular slot cut in an extended thin flat sheet of metal with the slot free to radiate on both sides of this sheet, as shown in Figure 8-1. The slot is excited by a voltage source such as a balanced parallel transmission line connected to the opposite edges of the slot or a coaxial transmission line connected to the opposite edges of the slot or a coaxial transmission line.

Figure 8-1: Rectangular slot

The electric field distribution in the slot can be obtained from the relationship between the slot and complementary wire antennas, as established by Booker.1 It has been shown that the electric field distribution (magnetic current) in the slot is identical to the electric current distribution on the complementary wire. In the illustrated rectangular slot, the electric field is perpendicular to the long dimension, and its amplitude vanishes at the ends of the slot.

The electric field is everywhere normal to the surface of the slot antenna except in the region of the slot itself. The theoretical analysis of this configuration shows that the radiation of the currents in the sheet can be deduced directly from the distribution of the electric field in the slot. Consequently, the radiated field of an elementary...