Low-Profile Wideband Metasurface Antennas Using Characteristic Mode Analysis

A metasurface (MTS) antenna is proposed for low-profile and wideband operation based on characteristic mode analysis (CMA). An MTS radiator formed by a diamond-slotted patch is fed by a microstrip line at its bottom through a slot centered on a ground plane. The CMA is used for the modeling, analysis, and optimization of the proposed antenna in order to reveal the underlying modal behaviors of the MTS and to guide the mode excitation. It is found that an extraordinary quisiTM30 MTS mode and a slot mode both with wideband broadside radiation are formulated and well excited simultaneously, leading to a broadband operation. Empirical equations are outlined for speeding up design. To verify the concept, a 2 × 2 array with the overall size of 1.78λ ₀ × 1.78λ ₀ × 0.07λ ₀ (λ ₀ is the free-space wavelength at 5.5 GHz) is designed and prototyped at 5-GHz Wi-Fi bands. The achieved impedance bandwidth for 10-dB return loss is 31% with the gain of 13-14.5 dBi over the operating bandwidth.