Miniaturization of a circularly-polarized, uni-directional, ultra-wideband spiral antenna

A low-profile, miniaturized ground-plane backed spiral antenna with a wideband circularly-polarized response is presented. This antenna is a multilayer structure composed of a center-fed modified Archimedean spiral antenna that includes a novel loading structure, a ring shaped absorber, and a feeding network. The loading structure possesses both inductive and capacitive characteristics, which increase the equivalent electrical length of the antenna while maintaining its maximum dimensions. Using this structure, the volume occupied by a conventional uni-directional Archimedean spiral antenna is miniaturized by a factor of 78%. This antenna is integrated into the multilayer structure along with its differential feeding network. An optimized ring-shape absorber is used to reduce the ground effects on the antenna performance. The measured peak realized gain of the antenna with the feeding network is 2.62 dBiC. The measured 3-dB axial ratio (CP) bandwidth is 2.5:1. The size of the antenna with the feeding network is 0.24λ_min × 0.24λ_min × 0.10λ_min, where λ_min is the wavelength at the lowest frequency of operation. The design process, simulation, and the measurement results of the antenna are presented and discussed.