The rectangular patch antenna is very probably the most popular microstrip antenna geometry implemented by designers. The Chapter begins by discussing the transmission line model and the cavity model before going on to look at the radiation pattern of a linear rectangular patch, quarter-wave microstrip antennas, efficiency, dielectric cover microstrip antennas' design, circularly polarized antennas, EM coupled antennas, ultra-wide antennas, and cross-polarization.

Microstrip antennas are inherently narrow band. The typical bandwidth of a microstrip antenna is around 4%-7%. A considerable number of experimental approaches have been undertaken to develop microstrip antennas which have a broader impedance bandwidth than a single microstrip element achieves without external matching. The methods employed to increase impedance bandwidth are essentially variations of three approaches: (a) Increasing the antenna volume. This is accomplished by geometry changes which increase the volume under the patch (e.g. increasing the thickness h), decreasing the substrate dielectric constant, or adding additional coupled resonators. (b) The implementation of a matching network. (c) Perturbing the antenna geometry to create or relocate resonances using shorts and slots in the antenna. Kumar and Ray (2003) have compiled a considerable number of microstrip antenna design variations which utilize these approaches, as has Wong (2002). One approach is the use of a groundplane slot, which is excited by a microstrip line below the groundplane, which in turn couples to a microstrip patch which is above the groundplane. This configuration can be adjusted to produce an elegant matching network, low dielectric constant substrate for the patch, and maximized substrate thickness, which provides a broadband input impedance match, and a large impedance bandwidth. One implementation of this type of antenna is called SSFIP for Strip-Slot-Foam-Inverted Patch by Zürcher and Gardiol in the mid-1990s. The design of these antennas is experimental in nature. These researchers state: “Since the various parts of the antenna interact, determining the best design is a long and tedious process, even when carried out systematically.” The parameters which may be used to guide this type of design are found in the literature. Some possible alternatives to the SSFIP matching-network/thick patch design are explored in this Chapter.

A single microstrip antenna utilizing an air dielectric substrate (ε_r ≈ 1) is able to provide a maximum gain of nearly 10 dBi. When larger gain is required, and a microstrip antenna solution is the best choice, a number of microstrip elements may be connected together to form an array of antennas. The array of elements provides a much larger effective aperture and therefore gain compared to a single microstrip element. This Chapter will discuss elementary methods used to design microstrip antenna arrays.

The MM-wave frequency spectrum between 30 and 300 GHz is referred to as the extremely high frequency (EHF) band. Within and near to this, commercial millimeter wave frequencies are from 20 to 80 GHz approximately. Also, automotive collision avoidance radars operate at 24 and 77 GHz. The Chapter considers general millimeter wave design and goes on to discuss corporate-fed patch arrays, giving examples at 28 GHz and 60 GHz.

This Appendix discusses numerical methods relevant to the study of antennas. These include numerical integration, evaluation of sums, fixed-point iteration, bisection algorithm, and MSA Q-efficiency calculation.

This Appendix discusses various topics associated with antennas, including: the Friis transmission formula, wireless link range versus power input, decibels, antenna gain and directivity, attenuation and voltage standing wave ratio, return loss and reflection loss, and attenuators.

The Chapter begins with a discussion of transmission line theory. It describes the mismatch that can occur between two TEM transmission lines which have identical characteristic impedance, but mismatched fields. When examined in terms of distributed circuit analysis, it is clear that a mismatch can occur. Transmission line theory rests on a number of assumptions which are well described by Chipman (1968), and these assumptions are considered next. The Chapter goes on to look at the L-C lattice balun, the coupled microstrip transmission line balun, the microstrip transmission line Marchand balun, and the microstrip branchline (ladder ) balun.