Dual-Band Dual-Circularly Polarized Holographic Metasurface Antenna With Mode-Selective Electromagnetic Band Gap

This paper presents a dual-band holographic meta-surface antenna capable of generating steered beams with both right-hand (RH) and left-hand (LH) circular polarization (CP). The proposed unit cell consists of three stacked layers above a ground plane. The first layer features a mode-selective electro-magnetic bandgap structure that effectively isolates transverse magnetic (TM) and transverse electric (TE) surface-wave modes. Such isolation allows independent operation at distinct frequencies for various beam directions, while maintaining radiation efficiency comparable to single-mode designs. The second layer employs split-ring elements designed for the TE mode, and the third layer utilizes split-patch patterns for the TM mode. The dual-port configuration provides distinct polarization control: the TM mode at 11 GHz, excited by a vertical monopole, achieves RHCP, while the TE mode at 14 GHz, excited by a horizontal dipole, produces LHCP. Each port supports directional beam radiation at 30° and 20°, respectively, with measured gains of 17.47 dBi and 18.01 dBi, and corresponding axial ratios of 0.53 dB and 0.43 dB.