4.0 Broadband Microstrip Antennas

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), or adding additional 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. Recently, Kumar and Ray have compiled a considerable number of microstrip antenna design variations which utilize these approaches ^[1] as has Wong. ^[2]

The use of a groundplane slot excited with a microstrip line which in turn couples to a microstrip patch can be adjusted to produce an elegant matching network which provides a broadband input impedance match. One implementation of this type of antenna is called SSFIP for Strip Slot Foam Inverted Patch by Z rcher and Gardiol in the mid 1990s. The design of these antennas is experimental in nature. The parameters which may be used to guide this type of design are found in the literature. ^{[3] [4] [5]}