A theory on the broadbanding of a patch antenna

The aim of this paper is to understand the cause of the narrow band in a microstrip patch antennas. The paper points out that the cause is due to heavy reactance cancellation. The cause is the same regardless how the patch is fed, by a coaxial probe or through a short slot by a microstripline under the ground plane. With the cause known, one can confidently design broadband patches with extra slot cuts on the patch or on the ground plane. Two specific examples are given.