A Helix-loaded Equiangular Spiral Antenna with Compact Structure

A broadband circular polarization antenna based on the composite structure of planar spiral and longitudinal helix is presented. Compared to single spiral antenna or helix antenna, proposed antenna has a better performance at low frequency by introducing two longitudinal helix arms connecting with the terminal of the planar spiral arms. As a result, the return loss, axial ratio (AR) and gain are both improved without increasing the antenna size. The antenna is designed to operate from 2 to 18 GHz and has a physical dimension of $\boldsymbol{\varphi} 50\times 45\ \mathbf{mm}^{3}$. A prototype was fabricated and tested, the results show that the proposed antenna can provide an AR of less than 2.5 dB, a return loss of less than −15 dB and a gain of greater than 0.5 dBi.