In this paper, a miniaturized Planar Inverted-F Electromagnetic Protective Antenna is proposed, which achieves adaptive switching between the normal operation mode and the electromagnetic protection mode by loading a U-shaped protective structure on the planar inverted-F antenna. The U-shaped structure is connected to the antenna feed line via PIN diodes. Under normal operation, when the received signal power is below the threshold, the PIN diodes remain in the cutoff state, allowing the antenna to maintain its radiation characteristics without interference from the U-shaped structure. When under high-power microwave attacks, a strong induced electric field is generated across the PIN diodes in the U-shaped structure, causing them to rapidly switch to achieve a low-impedance conduction state. At this point, the U-shaped structure forms a closed loop with the feed line, effectively preventing high-power microwave signals from entering the backend electronic equipment, thereby achieving electromagnetic protection. By optimizing the geometric parameters of the U-shaped structure and the number of loaded diodes, the design maintains its compact size while delivering excellent radiation performance and protection capability. Measurement results show that the antenna achieves a relative bandwidth of 17.2%, with a gain of 2.36 dBi at the center frequency of 1.57 GHz. Simulation results demonstrate a protection level of 16.4 dB in the electromagnetic protection state. The radiator’s electrical dimension is only 0.25λ×0.06λ, realizing a miniaturized design for the electromagnetic protective antenna.