Circularly polarized wideband EQSP antenna backed by a cavity with arc-shaped strip absorbers

An equiangular spiral antenna backed by a cavity is investigated using the electric and magnetic fields obtained using Yeepsilas FDTD method. Strip absorbers are placed inside the cavity. Antenna configuration parameters other than the cavity height H_cav are fixed throughout this paper, where the cavity diameter D_cav is chosen to be 120 mm (slightly larger than the antenna diameter of 113 mm). The investigation is performed for frequencies from 2 GHz to 10 GHz. The cavity height H_cav is chosen to be small and varied from 3.5 mm = 0.035lambda₃ to 10.5 mm = 0.105lambda₃, where lambda₃ is the wavelength at 3 GHz. It is found that, as the cavity height H_cav is increased, (1) variation in the input impedance becomes smaller over a wide frequency range, i.e., the input impedance characteristic becomes relatively constant, (2) the axial ratio at low frequencies improves, and (3) the gain at low frequencies increases.