Broadband Electrically Small Circularly Polarized Directive Antenna

A broadband electrically small antenna with directive circularly polarized radiation is presented. It is composed of a compact single-feed crossed dipole driver, which is backed by a near-field resonant parasitic (NFRP) reflector to achieve the directive radiation pattern. The NFRP reflector is designed to generate extra resonances and minimum axial ratio (AR) points in the antenna system. These features are combined with those resulting from the driver to broaden the operational bandwidth. The proposed antenna was fabricated and measured. The antenna prototype, with a low profile (0.066 lambda(o) at 1.45 GHz) and an electrically small size (ka = 0.71 at 1.45 GHz), has a measured |S-11| < -10 dB bandwidth of 25.66% (1.362-1.763 GHz) and a 3-dB AR bandwidth of 10.56% (1.390-1.545 GHz). Additionally, the measurements resulted in a broadside gain of 2.31 +/- 0.4 dBic and an average radiation efficiency of 80% within the operational bandwidth.