Spiral Antenna with a Circular HIS Reflector Sandwiched by Ring-shaped Absorbers

A spiral antenna with a circular high-impedance surface (HIS) reflector (CirHISR) sandwiched by ring-shaped absorbers (R-ABSs) is investigated. To improve the variation of the gain in a specific frequency region for a spiral antenna with a CirHISR, we propose a new structure where the CirHISR is sandwiched by two R-ABSs. The antenna height is 0.096 wavelength at 2.5 GHz (the lowest operating frequency). The antenna characteristics are analyzed using a commercially available method of moment software. It is found that the CirHISR sandwiched by two R-ABSs contributes to the enhancement of the gain variation (more than 5.0 dBi across a frequency range of 2.5 GHz to 9 GHz), compared to the gain of the CirHISR without R-ABSs. Other antenna characteristics, including input impedance and axial ratio, are also analyzed and presented here.