Efficiency Improvement of High-Directivity Fabry-Perot Resonator Antenna Array

In this paper, a method of efficiency improvement is presented for high-directivity Fabry-Perot (F-P) resonator array antennas. Firstly, an F-P resonator antenna unit with a high tapered efficiency of 91.78% and a directivity of 20.16dB is achieved. A nonuniform frequency selective surface (FSS) is used as the superstrate and the aperture near-field with almost uniform amplitude and equal phase is realized. Then, a $2\\times 2$ FP resonator array antenna is constructed with the high-efficiency units. To keep the almost uniform aperture near-field, metal strips are placed on the substrate, just between the F-P resonator units. The original field near-field is superposed with the one generated by the metal strips, so that the aperture field of the entire F-P resonator array antenna is also nearly uniform. Finally, the $2\\times 2$ FP resonator array antenna is optimized with a side length of $5.75\\boldsymbol{\\lambda}\\times 5.75\\boldsymbol{\\lambda}$ ( $\\lambda$ is free-space wavelength) corresponding to the frequency of 15GHz. A directivity of 25.98dB has been achieved, the tapered efficiency is 95.43%. The maximum side lobe is −14.25dB. The proposed method can be used to construct much larger array with almost uniform aperture near-field to ensure the high directivity and high efficiency. With this method, antennas can be designed in the millimeter wave band and applied in biomedicine.