Design of a low-profile wideband spiral antenna

Abstract

It is a long time research on designing wide band antennas of low profile that can be used in satellite communications and military systems. Nowadays,the demand for antenna is significantly increased. Spiral antenna is a kind of radio frequency antenna which operates over a wideband frequency and radiates circularly polarizedwave. It can be shaped as single-arm, double-arm, or more arms.

The purpose of this final year project is to design a circularly polarizedspiral antenna with a good VSWR and a good axial ratiothat can operate over a wideband frequency from 3GHZ to 10GHZ. In order to increase the antenna’s radiation efficiency, an Artificial Magnetic Conductor (AMC)is designed in this project to replace the convention ground plane. In addition, extensive simulations are conducted to optimize the antenna performance.

The first part of this final year project involves designing a wideband Single-Arm Spiral (SAS) antenna with a small disc backed by a cavityanda ring-shaped AbsorbingMaterial (ABS). By placing a conducting cavity behind an SAS with a disc, the circularly polarized bidirectional beam isconvertedinto unidirectional beam. The simulation results showthe SAS antenna has a good VSWR and a good axial ratio when the operation frequency varies from 3GHz to 10GHz.

The second part of this final year project is to design a low-profile wideband spiral antenna by replacing conventionground plane with the Artificial Magnetic Conductor (AMC). The purpose of this AMC surface is to reduce the antenna’s profile and increase the antenna’s radiation efficiency. Besides, a microstrip to parallel strip transition is introduced to form the matching network between the antenna impedance and the subminiature version A(SMA) connector impedance. The simulation results show that the low-profile spiral antenna with AMC could be used for the wideband frequency.