Alternate cutoff radius criterion for probe-fed, circular microstrip patches

The effects of the patch size on probe-excited surface currents are relatively unknown. A simple yet rigorous criterion for selecting the cutoff radius of a circular microstrip patch is obtained from the contour integral representations of the infinite series terms of the probe-to-patch attachment mode current. This criterion predicts that by suitably selecting the patch dimensions and the substrate parameters, higher order terms may be suppressed. It is also shown that this criterion has remarkably similar features to earlier results, based on suppressing the lowest order TM/sub 01/ surface wave mode. Use of this result in optimizing patch radius for efficient feed and radiation performances is also suggested.