This paper explores the application of artificial magnetic conductor (AMC) surfaces to low-profile high-gain planar antennas. AMC surfaces, which behave as zero-degree reflection phase shifters for incident waves when placed on a grounded dielectric substrate, are studied using a resonant cavity model. The authors present a novel application of AMC surfaces as the ground plane in a high-gain microstrip patch antenna with a partially reflective surface (PRS) as the superstrate. This approach significantly reduces the antenna profile while maintaining high gain. The paper includes a detailed analysis of the AMC response using ray theory, full-wave analysis, and measurements. The resonant cavity model is validated through simulations and experiments, demonstrating that the AMC surface can reduce the antenna profile to approximately half its original thickness. The design guidelines and physical insights provided by the ray model are crucial for the successful implementation of AMC surfaces in high-gain antennas.This paper explores the application of artificial magnetic conductor (AMC) surfaces to low-profile high-gain planar antennas. AMC surfaces, which behave as zero-degree reflection phase shifters for incident waves when placed on a grounded dielectric substrate, are studied using a resonant cavity model. The authors present a novel application of AMC surfaces as the ground plane in a high-gain microstrip patch antenna with a partially reflective surface (PRS) as the superstrate. This approach significantly reduces the antenna profile while maintaining high gain. The paper includes a detailed analysis of the AMC response using ray theory, full-wave analysis, and measurements. The resonant cavity model is validated through simulations and experiments, demonstrating that the AMC surface can reduce the antenna profile to approximately half its original thickness. The design guidelines and physical insights provided by the ray model are crucial for the successful implementation of AMC surfaces in high-gain antennas.