Effects of slotted and photonic bandgap ground planes on the characteristics of an air-substrate annular-ring patch antenna at TM/sub 21/ mode

This paper presents an experimental study on the characteristics of annular-ring patch antennas with slotted and photonic bandgap (PBG) ground planes for operating at the higher-order mode of TM ₂₁ for conical-pattern radiation. The antenna studied is with an air-layer substrate and is fed using a probe feed. Experimental results show that, for the case with a slotted ground plane, greatly lowered resonant frequency and enhanced impedance bandwidth can be obtained, compared to the case with a regular ground plane. However, the front-to-back radiation ratio is greatly lowered. As for the case with a PBG ground plane, the impedance bandwidth is also enhanced. On the other hand, the resonant frequency is slightly increased, and the front-to-back radiation ratio is greatly improved. Details of the experimental results are presented and discussed.