Gain and Bandwidth Enhancement of a Spiral Antenna Using a Circularly Symmetric HIS

A circularly symmetric high-impedance surface (HIS) is used as a ground plane in the design of a low-profile two-arm spiral antenna. It is shown through simulations that an HIS with circular periodicity provides 16% and 11.3% greater operational and fractional bandwidths, respectively, for spiral antennas compared to canonical rectangular HISs. It is also observed that with the aid of a circular HIS ground plane, the gain of the spiral antenna increases for 2.5 dB compared to when a rectangular HIS is used as a ground plane. Measurements are performed to validate the simulations; a very good agreement is indicated.