A compact feed network for wideband circularly polarized 2×2 spiral array antenna for GPS applications

A wideband feed network for a small-spiral 2×2 antenna array has been developed. The antenna is fed by a 4 port-network with a 90° sequential phase shift between the ports to provide circular polarization radiation. The feed is comprised of a balun and two multi-section quadrature hybrid splitters to provide an almost constant 90° differential phase shift across a 440 MHz bandwidth. The measurement results show maximum deviation of ±9° (off of the ideal 90°) over the entire frequency band and an amplitude imbalance of less than ±0.6 dB. The developed design is compact, simple, and has a relatively wide bandwidth and low loss over 1.16 GHz to 1.6 GHz.