Spiral Antenna with a Two-Layer Circular HIS Reflector Sandwiched by Ring-Shaped Absorbers

A two-layer circular high-impedance surface reflector (TL-CirHISR) sandwiched by ring-shaped absorbers (R-ABSs) is proposed to realize a low-profile wideband spiral antenna. The antenna height is 0.092 wavelength at the lowest design frequency of 2.4 GHz. It is found that the proposed antenna has almost constant input impedance, axial ratio of less than 3 dB, and gain of more than 5 dBi, across a frequency range of 2.4–10 GHz (a fractional bandwidth of 122.6%).