Microstrip patch antennas

The basic geometry of a microstrip patch antenna (MPA) consists of a metallic patch which is either printed on a grounded substrate or suspended above a ground plane. The antenna is usually fed either by a coaxial probe or a stripline. In the coaxial case, the center conductor is directly connected to the patch and the outer conductor to the ground. In the stripline case, energy is coupled to the patch in several ways: by direct connection, by proximity coupling, and by aperture coupling. The patch antenna idea appeared to be originated in the early 1950s, but there was little activity for almost two decades, mainly due to its inherent narrow bandwidth. It began to attract the serious attention of the antenna community in the 1970s, as antenna designers began to appreciate the advantages offered by this type of antennas, which include low profile, conformability to a shaped surface, ease of fabrication, and compatibility with integrated circuit technology. In the last three decades, extensive studies have been devoted to improving the bandwidth and other performance characteristics. This chapter begins with a brief description of the modeling techniques and basic characteristics of the MPA. Methods for broadbanding are then discussed, followed by dual- and multiband designs, size reduction techniques, circularly polarized patch antennas, and frequency-agile and polarization-agile designs. The chapter ends with some concluding remarks.