Overview

In this chapter we will discuss the most important and well-known relations and parameters of an array antenna which are relevant for the conception of a radar system [1 3]. Possible implementations for different applications will be summarised. We will start our discussion with a simple illustration, the basic principle of which is sketched in Figure 4.1. A set of antennas or an array of antenna elements is distributed on a metal ground plane, preferably on a regular grid. These antenna elements may be, for example, dipoles matched with the length of their arms to the operating wave-length ? of the radar system. In the case of transmission each antenna element is the source of a spherical wavefront. As a first step we assume waves of equal phase from each antenna element. Comparatively, we observe circular water waves if a group of persons standing at a linear sea wall are throwing stones at the same instant of time into a calm water. These waves superpose coherently according to the famous Huygens' Principle at each point in space. If all sources radiate in phase then at the boresight direction, orthogonal to the antenna plane, we have a linear or coherent summation of the field strength of all individual waves. That is if, at a certain distance from the antenna, the electrical field strength produced from one antenna element is E, then we would have with N antenna elements the field strength NE resulting at the boresight direction, or...