Wideband Sidelobe-Level Reduced $Ka$ -Band Metasurface Antenna Array Fed by Substrate-Integrated Gap Waveguide Using Characteristic Mode Analysis

substrate-integrated gap waveguide (SIGW)-fed metasurface antenna (metantenna) array with nonuniform excitation is proposed for wideband operation and sidelobe-level (SLL) reduction at millimeter-wave Ka-band. To achieve wideband and low profile, a 2 × 2 square patch-based metasurface is introduced based on characteristic mode analysis (CMA). The ridged microstrip-fed slot is employed to excite the metasurface, while the mushroom-like patches are positioned around feeding lines to operate as the SIGW for suppressing the undesired modes. Due to the compactness of the proposed SIGW, the amplitude of each element is controllable using unbalanced T-junctions. A nonuniformly excited 4 × 4 antenna array is designed and fabricated for validation. The measured results show an impedance bandwidth (IS11I <; -10 dB) of full Ka-band with a 3 dB gain bandwidth of 28-40 GHz (35.3%) and SLLs less than -12.1 and -15.6 dB in the Eand H-planes, respectively.