Broadband Metasurface Antenna Optimized for High‐Frequency Radiation Patterns Using Characteristic Mode Analysis

The radiation pattern of the broadband metasurface (MTS) antenna often has large sidelobe and large H‐plane cross‐polarization (cross‐pol) at high frequencies because both the fundamental mode and the higher order modes (HOMs) have large sidelobe at these frequencies. However, as for the above two reasons that leading to deterioration of high‐frequency radiation of MTS antennas, the out‐of‐phase current and the sidelobe of the fundamental mode at the high frequency have not been discussed in detail in the previous references. In this paper, a MTS antenna optimized for high‐frequency radiation patterns using the characteristic mode analysis (CMA) method is proposed. The unwanted HOMs are moved out of the desired frequency band by loading parallel slots at parts of patches. Especially, the large sidelobe of the fundamental mode at high frequency is optimized by cutting off the out‐of‐phase currents. Because of these two improvements, the high‐frequency radiation patterns of the broadband MTS antenna are optimized. Subsequently, the simulated and experiment results show that the proposed antenna achieved a −10 dB bandwidth of 43.5% (5.8–9.02 GHz) and the flat realized gain of 5.6–8.4 dBi. In particular, the main lobe magnitude at the high frequency 9 GHz is enhanced from 3.2 dBi to 7.8 dBi, and the sidelobe is reduced about 9 dB. The maximum H‐plane cross‐pol levels improve about 13.17 dB compared with the reference antenna before optimization. Therefore, the proposed MTS antenna is experimentally validated with consistent radiation pattern across the entire operating band of 5.8–9.02 GHz by optimizing the radiation pattern at 9 GHz.