To investigate the potential damage caused by High-Power Microwave Weapons (HPMW) attacking radar systems through exposed cable backdoors, a cable model between radar units is established. The effects of different cable types, installation heights, electric field directions, and cable lengths on coupling signals are compared and analyzed. The characteristics of coupling signals are measured through irradiation experiments, and the impact of coupling signals on radar is analyzed. Corresponding protective circuits are designed, and other protective measures are discussed. Theoretical analysis and experimental results indicate that the peak voltage and waveform of the coupled signal are greatly affected by factors such as cable type, installation height, and electric field direction, while the resonant frequency of the coupled signal is greatly affected by cable length. The threat of coupling signals can be reduced through technical protection measures and reasonable cable layout.