A novel compact antenna of radio altimeters based on bi-layer substrate technology

In this paper, a novel compact antenna of radio altimeter based on bi-layer substrate is presented, which is composed of bi-layer microwave circuits. A palisade-shaped conductor is placed on the upper substrate to enhance purity of the linear polarization, while a two-unit parallel-fed microstrip antenna array and its feeding network are laid on the lower substrate. This new kind of radio altimeter antenna may be installed on certain air vehicle with small scale. The bi-layer substrate has a size of 56mm×36mm×3mm, and the outline of the antenna is of 65mm×60mm×6mm.The simulated and measured results indicate that the half-power beamwidth of this novel altimeter antenna is about ±33° × ±37°, and the 2∶1 voltage standing wave ratio(VSWR) bandwidth is about 210MHz, with a 8 dB max gain. Also we measured the isolation between two antennas of radio altimeter with a distance of 500mm, and the final isolation value is more than 50dB in its working frequency range. As the altimeter antenna has good performance in beamwidth, bandwidth, and isolation, together with a compact structure, it will have promising future for application.