Abstract: In this paper, a microstrip monopulse antenna is designed and fabricated in the Ku band, featuring low sidelobes and compact structure. A stripline power distribution network of series-fed and parallel-fed stripline is designed. Based on the requirement of equal-phase but unequal-amplitude excitation for each antenna element, a multi-layer microstrip board process is adopted, and the antenna elements are fed through aperture coupling. This feeding method not only broadens the antenna′s operating bandwidth, but also effectively suppresses the parasitic radiation of the power distribution network, achieving the goal of low sidelobes. Combined with the proposed novel stripline-waveguide-microstrip line transition structure, the antenna is miniaturized and has a low profile. The microstrip monopulse antenna array has 52 elements, a diameter of 90 mm, a total thickness of 12 mm, and an operating bandwidth of 14.8 GHz to 15.2 GHz. Test results show that the antenna array′s S₁₁ is less than -10 dB, the sidelobes in both E-plane and H-plane are better than -20 dB, and the null depth of the difference beam is better than -22 dB, meeting the design expectations. It has broad application prospects in some special platforms that require low sidelobe, low profile, and lightweight for monopulse antennas.