Broadband variations of a proximity fed circular microstrip antenna gap-coupled with narrow annular sectoral patches are proposed. The gap-coupling of pairs of parasitic annular sectors along the x- and y-axes of the fed patch tunes the spacing in between the fundamental modes on the respective patches that yields wider bandwidth. A maximum bandwidth of 728 MHz (55%) offering peak gain of nearly 9 dBi is obtained in the circular patch gap-coupled with four pairs of annular sectors along the x-axis. This bandwidth is around 13% larger than the bandwidth offered by a single circular microstrip antenna. Instead of using multiple sectoral patches, a gap-coupled design of circular patch with a stub loaded annular sectoral patch is presented. The stub tunes TM02 mode frequency with reference to the fundamental modes on the circular and sectoral patches that yields bandwidth of 660 MHz (51%). Resonant length formulation and subsequent design methodology for all the proposed gap coupled configurations are presented, which helps in the re-designing of similar antennas at the given fundamental mode frequency. All the optimum and re-designed antennas are fabricated, and the measured results shows close agreement with the simulations.
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