Synthesis of cosecant-squared pattern in substrate integrated waveguide leaky-wave antennas

Abstract

A synthesis procedure for realizing a cosecant-squared pattern in leaky-wave antennas (LWAs) is presented. In this method, the antenna is divided into a number of sections, each with an appropriate phase constant, length and leakage rate. The phase constant of the radiating sections is obtained such that their beam pointing angles would arrange on an appropriate layout in the shaped region. The two latter parameters are determined such that the radiation intensity of each section would decay with a cosecant-squared profile. Finally, using an optimization algorithm, i.e., a genetic algorithm (GA) optimization, the initial values of the leakage rate are adjusted to achieve the desired shaped region. The synthesis procedure is applied to a slotted substrate integrated waveguide (SIW) LWA, and a prototype of the antenna is designed to achieve the cosecant-squared pattern within the range of 10° to 30°. The results show that the antenna has low ripples (≤2 dB) in the shaped region with a low level of sidelobes (≤-18 dB) outside the region. The antenna is fabricated and measured. Measurements show a good agreement with the simulation results. The obtained results reveal that the proposed synthesis procedure can be utilized in designing cosecant-squared pattern LWAs to use in air-surveillance radar systems.