Abstract: A millimeter wave circularly polarized monopulse antenna array featuring high gain and low axial ratio is proposed to meet the stringent requirements for self-tracking capability for downlink signal reception in the satellite communication system. A novel sequential rotation comparator network is devised, integrating the phase relationship between the traditional 2D monopulse comparator and the sequential rotation network to achieve low axial ratio radiation. Additionally, a low-profile left-handed circularly polarized subarray, comprising sixty-four radiators and a 1-to-64 feeder network, is designed. Four subarrays are arranged orthogonally and connected to the output ports of the sequential rotation comparator network. Simulation results demonstrate an operating bandwidth of 27.5 GHz ~ 30 GHz (return loss > −15 dB) for the 16×16 monopulse antenna array, with a sum beam main polarization gain reaching 33.2 dBic. The in-band axial ratio is less than 0.3 dB, and the zero depth is less than −25 dB. The developed monopulse antenna array exhibits high gain and circular polarization purity, rendering it suitable for satellite communication applications.