Passive FSS based polarization converter integrated microstrip antenna

A reflection mode linear to circular polarization converter (PC) with high angular stability up to 60 degrees is proposed in which no metallic backing is required, like the conventional PCs. Two distinct frequency selective surfaces (FSS1 and FSS2) are designed to block TE and TM waves, respectively, across the same frequency band (6.8-13.6 GHz). While the top layer (FSS1) and bottom layer (FSS2) are kept at an air gap of lambda/8 between them, a phase quadrature in orthogonal components of the reflected wave is realized. An axial ratio <= 3 dB is obtained by designing the FSS layers such that the magnitude of reflection coefficient (S-11) under TM polarization for FSS2 is equal to that of FSS1 under TE polarization. As a proof of concept, this PC is integrated with a linearly polarized (LP) microstrip antenna (MSA) and tested. It converts the LP waves into circularly polarized (CP) waves at three different frequency bands and also enhances antenna gain by 4.5 dB. Further, by varying only the altitudinal position of the top FSS layer manually, reconfigurability in CP bands can be accomplished without using any active elements and electronic tuning systems. A prototype is fabricated and validated by proper measurements.