A Low Profile Circularly Polarized Microstrip Antenna with Pattern Diversity

This paper presents a low profile circularly polarized antenna which use an antiphase and in-phase hybrid feed network to realize its pattern diversity property. The antenna contains two square ring patches as radiators that are excited by two coupling slots on the ground, when the two radiators are excited by two antiphase signals, the antenna realizes its broadside pattern mode, when the two radiators are excited by two in-phase signals, the antenna can radiate dual beam. Thus, we use a hybrid feed network to produce two antiphase signals or two in-phase signals, the thickness of the antenna is only 0.045λ0 (λ0 is the free-space wavelength of the center frequency). Besides, a perturbation is introduced by the radiator to achieve circularly polarized radiation. The simulation results show the coincident operating bandwidth
$(\vert \mathrm{S}_{11}\vert < 10\text{dB}$
and AR<3dB) is 1.7% (3.52-3.58GHz).