Wideband dual‐polarised SAW spiral antenna for monopulse system

Abstract

This study proposes a new technique for generating dual polarisation in spiral antennas. The proposed antenna is achieved by creating stair discontinuities in spiral antenna arms, entitled stair arm width (SAW) spiral antenna. Commonly, the spiral antenna is activated in direction finding systems, especially in wideband monopulse systems. Capability of generating sum and difference beams over a wide bandwidth is another feature of the proposed antenna. Radiation characteristics and generated modes of a wideband dual polarised four-arm SAW antenna in comparison with the modulated arm width (MAW) and conventional spiral antennas are presented. The cross-polarisation gain of SAW antenna, compared to MAW antenna, is decreased in difference pattern, which improves the antenna circular polarisation purity. Moreover, the input impedance of the proposed antenna with high n s is more stable than MAW antenna over a wide bandwidth due to gradual discontinuities. Finally, a prototype four-arm SAW spiral antenna is built and evaluated with an available beamformer for 5.8-10 GHz frequency bandwidth. Simulated and measured radiation characteristics proved dual circularly polarised and wideband properties of the antenna.