Design and fabrication of a slant polarized monopulse antenna array with a cosecant squared beam for tracking applications

This paper presents the design and fabrication of a slant-polarized monopulse array antenna featuring a cosecant-squared radiation pattern for accurate target tracking. The proposed 2 × 8 microstrip array employs a modified proximity coupling scheme and incorporates metallic walls to reduce mutual coupling. A strategically placed ground plane enhances the gain, suppresses the back lobe, and improves isolation from the surrounding environment. The amplitude and phase excitations are optimized with a genetic algorithm that accounts for mutual coupling to synthesize the desired cosecant-squared pattern. A rectangular 180-degree hybrid coupler is integrated to enable monopulse operation in the azimuth plane, thereby improving tracking performance. Measurement results of the fabricated prototype demonstrate a 34% impedance bandwidth (3.8-5.4 GHz), a peak gain of 13.05 dBi, a sidelobe level of 13 dB, a null depth of 24 dB, and an elevation plane beamwidth of 24° at the center frequency, all of which align closely with simulation results. The measured radiation pattern accurately follows the ideal cosecant-squared curve.