In this chapter, several different types of antennas are discussed. The antennas presented are the reflector antenna, the lens antenna, the horn antenna, and the microstrip antenna. These antennas have distinct characteristics that make them suitable for a variety of applications.
5.1 Reflector antennas
Since World War II, when reflector antennas gained prominence due to their use with radar systems, reflector antennas have played an important role in communication systems. Love  has published a collection of papers on reflector antennas. Reflector antennas can have a variety of geometrical shapes and require careful design and a full characterization of the field system. Silver  presents the technique for their analysis based on aperture theory and physical optics. Other methods such as the geometrical theory of diffraction and the fast Fourier transform, along with various optimization techniques, are used more often for the accurate design of these antennas .
5.1.1 Plane and corner reflectors
The plane reflector, shown in Fig. 5.1(a), is the simplest type of reflector antenna . The polarization of the feed and its position can be adjusted to obtain the desired radiation properties. The analysis of the system can be done using image theory. The corner reflector has been investigated by Kraus , and the 90-deg corner reflector is found to be the most effective. The feeds for the corner reflector are generally dipoles, which are placed parallel to the vertex. These antennas can be analyzed in a rather straightforward manner using the method of images. In Fig. 5.1(b), the antenna 1, which is the feed, is shown along with three images. For corner reflectors with infinite sides, the gain increases as the angle increases.
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