We present a quasi-crystal metasurface that can simultaneously work as efficient cross-polarizer and circular polarizer for wide range of frequencies. The quasi-crystal technique benefits from individual resonant response of anisotropic patch and the coupled response due to periodic perturbations in the square lattice. It is shown that quasi-crystals offer broadband response for cross-polarization as well as high efficiency circular-polarization conversion of reflected fields. The quasi-crystal metasurface achieves cross-polarization (above −3 dB) for two broad frequency bands between 10.28–15.50 GHz and 16.21–18.80 GHz. Furthermore, the proposed metasurface can simultaneously work as high efficiency circular-polarizer from 10.15–10.27 GHz and 15.51–16.20 GHz. The metasurface design is also optimized to suppress co-polarization below −10 dB between 10.5–15.5 GHz. This metasurface can find potential applications in reflector antennas, imaging microscopy, remote sensing, and control of radar cross-section etc.

We present an anisotropic metasurface offering a simultaneous linear to cross-polarization conversion and linear to circular polarization conversion operations on large bandwidths of microwave frequencies. The proposed orthotropic structure consists of metallic bow tie shaped patches with embedded circular patches enabling diagonal structure symmetry. We demonstrate through numerical simulations and experiments that the metasurface can be used as a high efficiency linear to cross-polarization reflective converter within the two broad frequency bands of 7.48–10.55 GHz and 18.47–19.52 GHz with a polarization conversion ratio above 90%. Simultaneously, the designed metasurface acts as a circular polarizer for linearly polarized incident waves in triple frequency bands of 6.10–7.46 GHz, 10.55–18.42 GHz, and 19.60–22.39 GHz with an axial ratio below the 3 dB threshold. To the best of our knowledge, the second band from 10.55 to 18.42 GHz of circular polarization conversion “has the highest reported (to date) bandwidth of 54.3% for an axial ratio below 3 dB.” The designed metasurface remains angular stable up to 75° over most of the part of the above-mentioned operating bands for both transverse-electric and transverse-magnetic polarized wave incidences.

In a recent publication by Xiong et al. [J. Appl. Phys. 114, 064109 (2013)], a linear cross-polarizer is erroneously interpreted as a broadband absorber with a claimed absorptivity above 90% over a frequency range of 8.3721 GHz. In this article, the authors have presented an investigative study demonstrating that the structure proposed by Xiong et al. is actually an efficient cross-polarizer rather than a perfect absorber. If we consider both co- and cross-polarized components of the reflected electromagnetic wave, the subject absorber provides less than 20% absorption in the claimed band. In addition, the polarization conversion ratio of the structure is above 85% within the operating band, this makes the subject metasurface a potential candidate for applications where high-efficiency cross-polarization is desired.

In a recent article, Wang et al. [J. Appl. Phys. 116, 094504 (2014)] proposed an ultra-thin broadand microwave metamaterial absorber and claimed the absorption above 90% in the operating band of 8.85 GHz–14.17 GHz. In this comment, we argue that the authors have neglected the cross-polarized reflection in their calculation of absorption. The proclaimed anisotropic pentagon patch metamaterial is predominantly a cross polarizer for the normally incident electromagnetic wave. We demonstrate that the actual absorption of the metamaterial structure remain less than 40%. Hence, the proposed metamaterial is not a perfect broadband absorber; however, it can be used as an efficient cross-polarizer.

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