Removing broadside null of symmetric long‐slot antennas by using a coating layer

Abstract

This study presents a new concept in the design of symmetric long-slot leaky-wave antennas. Theoretically, a radiation null in the broadside direction of these antennas exists. The main idea of this study is to use a cover or coating layer to convert this null to a peak in the radiation pattern. The presence of the coating on the slot not only changes the leaked mode of the waveguide but also rotates its polarisation by 90°. As a proof of concept, a relatively small long-slot LWA is designed and fabricated on a C-band WR-159 waveguide, which is covered by an FR4 layer. The simulated relative broadside gain of the antenna with the coating over the antenna without the coating tends to infinity because of the presence of the null. Our simple measured results of the radiation pattern confirm the theory with more than 18 dB improvement. The realised gain of the antenna with a coating layer at broadside is 11.1 dBi with 9.8° half-power beam-width.