Abstract: Aiming at the demand of Ka-band high-throughput satellites for antennas, a Ka-band broadband circularly polarized microstrip antenna is designed. The antenna element is mainly composed of a circular radiating patch and a slot-coupled feed structure, where broadband circular polarization is achieved through the combination of two T-like slots. The antenna has only three metal layers and the structure is simple. The simulation results show that the relative impedance bandwidth of the antenna element is 31.5%(25.1−34.5 GHz), and the relative 3 dB axial ratio bandwidth is 20.3%(26.5−32.5 GHz). Due to the small size of the element, it is inconvenient to verify the performance of the designed antenna element, so it is used to form a 2×2 antenna array, and the processing test is carried out. Simulation and test results show that the antenna array impedance bandwidth and 3 dB axial ratio bandwidth can cover the 25.6−33.1 GHz frequency band, and the measured results are in good agreement with the simulation results.