A Time-Modulated Polarization-Rotating Frequency-Selective Surface

Modulation of electromagnetic (EM) waves can be realized by modulating the transmission or reflection coefficient of a frequency-selective surface (FSS) with time. The modulation produces multiple sideband frequency components. Polarization manipulation is another interesting application of FSSs, which can rotate the EM wave polarization by 90° upon reflection. In this article, for the first time the time modulation and polarization-rotation are used simultaneously in single structure as a countermeasure to Radar detection. Initially, a p-i-n diode-based, switchable polarization-rotating FSS that switches between co-polarized and cross-polarized reflection is designed. Then, an EM wave modulation scheme is planned where the polarization state of the FSS is switched using a periodic signal. When a linearly polarized EM wave of single frequency component is incident upon the surface, it is reflected back as two orthogonally polarized waves. Both the reflected waves have several sideband frequency components besides the incident frequency component. Two additional modulation scheme are also proposed where one of the co-polarized or the cross-polarized reflected wave is dominant. A prototype was prepared and its response was measured. The time-modulated polarization-rotating FSS operates in the 2–3 GHz frequency range.