Compact Spiral Element for Wideband Beam-Steering Arrays

In this letter, a compact spiral element is proposed for wideband beam-steering arrays. The extremely limited element spacing and size to prevent the occurrence of grating lobes at high frequency range are the most critical issues in designing wideband phased arrays. Two miniaturization techniques are simultaneously applied to an Archimedean spiral radiator to reduce the area of the proposed spiral. This spiral radiator is designed with a reflector plane instead of an absorber and cavity to realize low-profile characteristics and achieve unidirectional pattern without power loss. A wideband balun that operates simultaneously as a wideband impedance transformer is also miniaturized to be integrated between the radiator and reflector plane. The proposed element consists of these three components, and its size is 0.25 lambda(L) x 0.25 lambda(L) x 0.13 lambda(L,) where lambda(L) is the wavelength at 2 GHz, the lowest frequency of interest. This compact spiral element with a simple structure and design procedure can achieve wideband beam steering without grating lobes and be employed in numerous applications, such as conformal arrays.