Abstract: In response to the demand of low profile, wide band, and high efficiency of antennas in monopulse radar systems in recent years, a circular aperture low profile monopulse antenna based on ridge gap waveguide is designed. The bandwidth is expanded by removing the traditional back cavity layer and introducing double ridge shaped radiation slots to replace the traditional rectangular slots. Compared to the traditional four layer or more structure of the traditional wide edge longitudinal slot series feeding and back cavity slot parallel feeding monopulse antenna, the entire antenna has only three layers, making it more compact in structure. At the same time, a broadband unequal power divider is designed to reduce antenna sidelobes. The center frequency of the antenna is 35 GHz, covering a frequency range of 32. 6 GHz~ 37. 4 GHz, approximately 4. 8 GHz. The relative impedance bandwidth reaches 13. 7%, the sidelobe is less than -20 dB, the zero depth is better than -35 dB, and the antenna efficiency is greater than 60%. It meets the requirements of current monopulse radar systems for antennas and has broad application prospects.