2.10 Design Guidelines for a Linearly Polarized Rectangular Microstrip Antenna

There are a number of antenna performance trade-offs with respect to substrate dielectric constant and thickness to consider when designing a linear rectangular microstrip antenna. ^[58] Clearly if one needs to feed a patch with a coaxial transmission line, then a probe feed is a good choice. If the design a requires a microstrip feed, a non-radiating edge feed can make sense, but the patch needs to be narrow enough to decrease any excitation of a secondary mode. A narrower patch has slightly decreased bandwidth compared with a wide patch. If the impedance bandwidth requirement is greater than a narrow patch can provide, then one can turn to a feed along a radiating edge. A quarter wave transformer feed on a radiating edge produces the least amount of perturbation of the patch radiation, but if the design constraints do not allow for enough area to implement the transformer, an inset feed can be utilized. In either case, if the patch is fed in the center, the driving point impedance presented by the next dominant mode is along a shorting plane for that mode and mismatched even if the patch is square.

A useful beginning patch width for a linear microstrip antenna is:

Patch thickness is an important parameter to consider. If the patch thickness is too thin, the efficiency and impedance bandwidth are decreased. When the patch is too thick it can efficiently generate surface waves. The lowest order...