A Compact Monopulse Antenna Array With Suppressed Mutual Coupling Using Broadband Schiffman Phase Shifters

This study presents the design, fabrication, and measurement of a compact microstrip monopulse antenna array for surveillance applications. The design process and limitations of the planar antenna structure are discussed, including the stacking of two radiating elements as a parasitic loaded patch antenna to increase bandwidth and suppress mutual coupling. A distributed feeding network for
$8\times 16$
elements with an integrated monopulse comparator, was designed and optimized, with the comparator placed in a separate layer to prevent spurious radiation. The operating frequency is 15.5-18 GHz, and the antenna exhibited a bandwidth of approximately 15%. The measurement results for the fabricated antenna array align with the simulations and design goals, with sidelobe levels of the beam better than 17 dB in both the E- and H-plane, and a null depth in the Delta pattern of less than −30 dB. The peak gain at the operating frequency is 22.3 dB and the total efficiency of the antenna array is approximately 55%.