Four Elements Tapered Fed UWB MIMO Antenna Design Using Theory of Characteristic Modes

This paper represents a compact orthogonally placed four antenna elements with fractal ground ultra-wideband multiple-input multiple-output antenna along with isolation enhancement by analyzing the theory of characteristic modes. First, we analyze the characteristic modes of a circular radiator with a rectangular feed line where two significant modes are available. Then the circular radiator is replaced by a semicircle attached to an elliptical radiator and finds the three wideband significant modes. Later the rectangular feed line is replaced by a tapered feed to improve impedance. The fractal ground structure increases frequency bandwidth. Orthogonal placement of the antenna elements improves the isolation. The MIMO antenna has an impedance bandwidth (Sll $\lt-10$ dB) ranging from 2.3 to 13 GHz and a transmission coefficient of less than −19.5dB over the entire frequency bandwidth.