Polarization Insensitive Wideband Time-Modulated Frequency Selective Surface: An Approach for Radar Countermeasure of Microstrip Antenna

This manuscript presents a polarization-insensitive wideband time-modulated Frequency Selective Surface (FSS) for radar countermeasure applications in microwave antennas. The study investigates the out-of-band performance of the FSS relative to the operating frequency of a microstrip antenna. The proposed FSS operates in the L-band and part of the S-band, covering 0.8 GHz to 2.4 GHz with a 100% fractional bandwidth. The integrated antenna array is designed to function in the X-band at 8 GHz. Airborne antennas typically operate in the X-band, while ground-based detection systems commonly use the L and S bands to detect distant objects. To ensure operational security, the airborne antenna must remain concealed from enemy ground-based radar systems, without compromising its communication and functionality. This work presents the first experimental demonstration of a wideband time-modulated FSS operating in the L and S bands, designed to conceal a functioning X-band communication antenna. Initially, the wideband FSS is designed, followed by its integration with the antenna array to validate its performance. The structure is fabricated and experimentally tested, with measured results closely matching simulations. While the time-modulated FSS can completely cover the metallic body of an aircraft, the onboard communication antenna remains exposed to electromagnetic waves, which can provide precise information to adversary Doppler radar. To overcome this, the time-modulated FSS unit cell is designed with a transmissive top layer, ensuring seamless communication with the ground station while suppressing interference from out-of-band electromagnetic waves.