L-probe proximity-fed annular ring microstrip antennas

A broadband single-layer annular ring microstrip antenna fed by an L-shaped probe is studied. It achieves, for the TM/sub 11/ mode, an impedance bandwidth of about 24% [standing wave ratio (SWR) /spl les/2], a 3-dB gain bandwidth of 33%, and a maximum gain of 7.5 dBi. For the TM/sub 12/ mode, an impedance bandwidth of about 27% (SWR /spl les/2), a 3-dB gain bandwidth of 15.5% and a peak gain of 10.3 dBi are obtained. A foam substrate of thickness around 10% of the operating wavelength in free-space is used as the supporting substrate. The far-field radiation patterns are stable across the passband.