A Low Profile Bidirectional Broadside Coupled Spiral Antenna

A low-profile twin arm broadside coupled spiral antenna is proposed, and its performance is compared to a conventional twin arm spiral of the same size. Different size reduction techniques have been examined, and their effect on impedance and far-field radiation performance is analysed. A compact spiral of
$0. 28\lambda$
diameter and
$0. 09\lambda$
height at the lowest frequency of operation is fabricated and characterised. Good performance in terms of VSWR bandwidth of 147% (<2) and an axial ratio bandwidth of 142% (largely below 3dB) has been achieved.