A filter-antenna consisting of a monopole antenna and a conical frequency selective surface (FSS) radome was designed and investigated. A coupled-resonator spatial filter (CRSF) was used to design an FSS array with stable performances, and then a specific geometrical layout was proposed to construct a conical FSS radome. We technically investigated the combination of a monopole antenna and the conical FSS radome. Both the simulated and measured results show that the proposed filter-antenna keeps the input reflection coefficient, radiation pattern of the monopole antenna within the designed passband, and reflects out-of-band signals. Such properties of the filter-antenna will exhibit anti-interference capability and low RCS, which can be widely used in military applications.

In this work, we propose a multiband linear-polarization (LP) conversion and circular polarization (CP) maintaining reflector using a symmetric anisotropic metasurface. The anisotropic metasurface is composed of a square array of a two-corner-cut square multiring disk printed on a grounded dielectric substrate, which is a symmetric structure with a pair of mutually perpendicular symmetric axes $u$ and $v$ along the $\pm 45°$ directions with respect to the $y$-axis direction. The simulated results show that the reflector can realize LP conversion in five frequency bands at both $x$- and $y$-polarized incidence, the first four bands all have a certain bandwidth, and the fourth one, especially, is an ultrawideband. In addition, because of the symmetry of the reflector structure, the polarization state of a CP wave can be maintained after reflection, and the magnitude of the copolarized reflection coefficient at the CP incidence is just equal to that of the cross-polarized reflection coefficient at the $x$- and $y$-polarized incidence. We analyze the root cause of the multiband LP conversion and CP maintaining reflection, and carry out one experiment to verify the proposed reflector.

In this work, an ultra-wideband and high-efficiency reflective linear-to-circular polarization converter based on an anisotropic metasurface is proposed, which is an orthotropic structure with a pair of mutually perpendicular symmetric axes u and v along 45 directions with respect to the vertical y axis. The simulated and experimental results show that the polarization converter can realize ultra-wideband linear-to-circular polarization conversion at both x- and ypolarized incidences, its 3dB-axial-ratio-band is between 5.8 and 20.4 GHz, which is corresponding to a relative bandwidth of 112%; moreover, the polarization conversion efficiency (PCE) can be kept larger than 99.6% in the frequency range of 6.1-19.8GHz. In addition, to get an insight into the root cause of the LTC polarization conversion, a detailed theoretical analysis is presented, in which the conclusion is reached that in the case of neglecting thelittle dielectric loss, the axial ratio (AR) of the reflected wave can be completely determined by the phase difference between the two reflection coefficients at u- and v-polarized incidences, and any anisotropic metasurface can be used as an effective LTC polarization converter when the phase difference is close to o 90 .

In this work, a dual-band and high-efficiency reflective cross-polarization converter based on an anisotropic metasurface for linearly polarized electromagnetic waves is proposed. Its unit cell is composed of an elliptical disk-ring mounted on grounded dielectric substrate, which is an anisotropic structure with a pair of mutually perpendicular symmetric axes u and v along $\pm 45°$ directions with respect to y-axis direction. Both the simulation and measured results show that the polarization converter can convert x- or y-polarized incident wave to its cross polarized wave in the two frequency bands (6.99–9.18 GHz, 11.66–20.40 GHz) with the conversion efficiency higher than 90%; moreover, the higher frequency band is an ultra-wide one with a relative bandwidth of 54.5% for multiple plasmon resonances. In addition, we present a detailed analysis for the polarization conversion of the polarization converter, and derive a formula to calculate the cross- and co-polarization reflections at y-polarized incidence according to the phase differences between the two reflected coefficients at u-polarized and v-polarized incidences. The simulated, calculated, and measured results are all in agreement with the entire frequency regions.