L-probe proxity-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 TM₁₁ mode, an impedance bandwidth of about 24% (SWR⩽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⩽2), a 3-dB gain bandwidth of 15.5% and a peak gain of 10.3 dBi are obtained. A foam substrate of thickness ~0.1λ₀ is used as the supporting substrate. The far field radiation patterns are stable across the passband