A Wideband Circularly Polarized Conical Spiral Antenna based on Multistage Nested Cavity Structure

A wideband circularly polarized spiral antenna with conical and cylindrical surfaces is proposed. The two-arm spiral, whose line width and pitch change gradually with frequency, achieves a wide beam and improves the gain of low elevation. The wound cylindrical spiral and resistance loading improve the radiation performance of low frequency. In order to further increase the low elevation gain and make full use of the backward radiation, a wideband stepped reflector cavity is designed. Its height and diameter vary with frequency, and it is equipped with a choker groove. A spherical dielectric radome loaded at the front end of the antenna reduces beam jitter and makes the radiation pattern smoother. The volume of the antenna is 20.6×20.6× 20.25mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>, operates at 8-18GHz, VSWR <2, axial ratio <3dB. Moreover, it has a gain value greater than 0.19dBi in the axial ± 60° range and a gain value greater than -6dBi in the axial ±90° range. The antenna proposed in this paper has good radiation performance in the upper half space.