L-probe proximity-fed annular ring microstrip antennas

A broad-band single-layer annular ring microstrip antenna fed by an L-shaped probe is studied. It achieves, for the TM11 mode, an impedance bandwidth of about 24% [standing wave ratio (SWR) less than or equal to 2], a 3-dB gain bandwidth of 33%, and a maximum gain of 7.5 dBi, For the TM12 mode, an impedance bandwidth of about 27% (SWR less than or equal to 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.