Design of a Broadband Omnidirectional Metasurface Antenna Using Characteristic Mode Analysis

A design of metasurface based antenna is presented for achieving broad bandwidth and wide beam. The characteristic mode analysis (CMA) is utilized to reveal the modal behavior of the antenna, as well as explore the potential resonating mode. The antenna is fed by an underlying microstrip line through a slot centered on the ground plane, which is located in the middle of two dielectric substrates. The radiation pattern is on the top. A single square radiator has been analyzed at very first. According to the eigenvalues from characteristic mode analysis, there are several modes which performed as broad bandwidth. However, the surface currents of these modes bring problems to the exciting structure design. To obtain an efficient surface current mode while keep its broadband feature, the square patch is optimized through slotting on the diagonal and then dividing into 4 little squares. Thereby a microstrip fed line is able to excite the expecting mode and obtain a broad bandwidth. Moreover, 4 triangle patches have been added to the corners of the slotted patch to increase the antenna gain and improve the omnidirectionality of radiation pattern. The back scattering has been effectively suppressed simultaneously. In order to obtain the optimal antenna geometrical parameters, parametric analysis have been performed using Ansys high frequency simulator structure (HFSS) software. The effects of parameters such as thickness of dielectric substrate and the geometries of radiation patch have been investigated and discussed. The simulation result shows that the achieved input reflection coefficient (below -10 dB) ranges from 25.2 GHz to 34.2 GHz (%30.3) with a profile of 0.125 lambda(0) (where lambda(0) is the free-space wavelength at 25.2 GHz), which is suitable to apply in 5G communication. Additionally, the radiation pattern shows a good omnidirectionality with achieved gain of 5.31-6.16 dBi.