Extremely low-profile, wideband spiral antenna with absorbing material

The radiation efficiency for an Archimedean spiral (ARCS) antenna backed by a cavity is investigated, together with other antenna characteristics, where the antenna height is chosen to be extremely small (0.07 wavelength at the lowest analysis frequency of 3 GHz) in order to realize an extremely low-profile antenna. Deterioration in the axial ration and input impedance due to the close proximity of the cavity is ameliorated by applying a very thin ring-shaped absorber (0.07 wavelength thickness) to the cavity wall. The radiation efficiency increases with frequency and reaches approximately 100% at the highest analysis frequency of 10 GHz. It is also observed that the radiation efficiency at low frequencies increases as the maximum radius of the ARCS (r_maxSP) is increased; a radiation efficiency of 38% for r_maxSP = 34 mm at 3 GHz increases to 55% for r_maxSP = 66 mm.