An Aperture Efficiency Enhancement Method for Transmitarray Antenna by Exploiting Dual Metasurfaces Modulation

This letter presents a systematic method for improving the aperture efficiency (AE) of transmitarray antenna (TA) without increasing the profile through modulation of dual metasurface transmitarrays. The first metasurface transmitarray intercepts more energy from the feed source and redistributes the intercepted energy over the second transmitarray through phase modulation, thereby improving spillover and taper efficiencies simultaneously. The phase efficiency is improved through the modulation of second metasurface transmitarray. The method overcomes mutual constraint between spillover efficiency and taper efficiency in traditional TA with single metasurface TA (TA-SM). To demonstrate the effectiveness of the method, two TAs [termed as TA-SM and dual metasurface TA (TA-DM)] with identical focal-length-to-diameter (F/D) of 0.625 are designed, fabricated, measured, and compared. The TA-SM with single transmitarray is a traditional TA with optimal AE, and the TA-DM with dual transmitarrays is designed based on the proposed method. Finally, at 14 GHz, the TA-DM realizes peak AE of 67.8$\%$ with low profile (F/D=0.625) and achieves maximum AE improvement of 20.6$\%$ compared to TA-SM (realized AE of 47.2$\%$). Besides, the TA-DM has 1 dB gain bandwidth of 22.9$\%$. The proposed method is a good candidate for the design of high gain and low profile antenna in long-distance communication.