A Low-Profile, Wideband Antenna With Vertically Polarized Directional Radiation

A low-profile, compact, and wideband vertically polarized antenna demonstrating directional radiation characteristics in both the azimuth and the elevation planes is presented. The antenna is composed of four bent-diamond-shaped half-loops placed on a ground plane. The half-loops are fed at their centers and short-circuited to the ground at their ends. Two of the half-loops are fed in phase, while the other two are fed with 180 ° phase difference generating omnidirectional and figure-eight-shaped radiation patterns, respectively. Coherent combination of these radiation patterns generates a cardioid-shaped directional pattern. A prototype of the antenna was fabricated and characterized. The antenna has electrical dimensions of 0.54λ
_min
× 0.4λ
_min
× 0.116λ
_min
at its lowest frequency of operation and operates over a 2:1 bandwidth.