This chapter systematically explains the structure and working principle of patch antennas. Firstly, the structural advantages of planar, low profile, and easy integration of patch antennas were introduced, as well as their application value in 5G millimeter wave communication, consumer electronics, aerospace, and other fields. Next, explain the essence of radiation achieved by patch antennas relying on microstrip circuit electromagnetic leakage, and analyze the structural characteristics, performance differences, and applicable scenarios of different types of antennas from three dimensions: patch shape, feeding method, and polarization mode. Subsequently, an in-depth analysis was conducted on the key roles of the three core components of conductor patch, dielectric substrate, and ground plane in antenna performance. Furthermore, taking the rectangular microstrip patch antenna as an example, the mechanism of radiation through the gap between the radiation patch and the metal floor and the principle of equivalent magnetic current radiation field formation are revealed. The applicability and advantages and disadvantages of the transmission line model, cavity model, and full wave analysis method are systematically sorted out. In addition, the physical significance, calculation methods, and engineering compliance requirements of key performance parameters such as input impedance, voltage standing wave ratio, return loss, bandwidth, radiation pattern, gain, and axis ratio were analyzed. Finally, looking ahead to the application prospects of patch antennas in 5G/6G communication, IoT, automotive electronics, medical electronics, and other fields, it is pointed out that material, design, and manufacturing process innovation will drive their performance optimization to meet a wider range of technological needs.