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The main drawback of the transmissive focusing metasurface (TFM) is its low operational bandwidth and low aperture efficiencywhich usually the simultaneous increase of these two radiation characteristics is a major challenge in these structures. Thispaper introduces a novel multi-state coding metasurface with an enhanced frequency bandwidth and efficiency exploitingsystem-level and element-level synthesis approaches. Unlike most of the TFMs proposed in this concern, the proposed novelelement consists of only two dielectric layers. The system-level synthesis approach is implemented by the well-establishedbroadband technique named multi-frequency phase synthesis (MFPS) using an optimization algorithm to balance the phaseerror in the whole band in terms of gain and aperture efficiency. At the element design level, a wideband technology based onthe polarization conversion technique (PCT) is adopted and implemented by a subwavelength non-resonant element which iscomposed of three C-shape metallic patterns. The metal layers are printed on two sides of two identical dielectric layers withoutusing any metalized via in the configuration. Eight states of phase quantization are realized by simply changing the angle of arccurves in all layers. The amplitude of the transmitted wave with rotated polarization is larger than 0.9 from 12.3 GHz to 16.5GHz. A 25×25-element TFM is designed, fabricated, and tested by the above broadband technique. The measurement resultsdemonstrate that the 1-dB gain bandwidth of the antenna is 12.3-16.5 GHz which is equal to 29%. The maximum measuredaperture efficiency is 53.6%, which occurs at 12.8 GHz. The proposed metasurface is classified in the group of broadbandhigh-efficiency TFM. |
