Capacitive loading comb-shaped tri-polarized MIMO slot antennas

Design of three orthogonal polarized slot antennas with capacitive loading is presented. The elements are identical slot antennas with slits on both sides of the slot. The radiating slot is loaded with capacitor that becomes step impedance resonator (SIR) structure to miniaturize the antennas. The size of the antennas can be reduced to 61.4%. Simulations and measurements show they work at 2.45GHz with a 150MHz bandwidth. The radiation characteristics of the size-reduced antennas are almost similar to the unloaded slot, with the low cross-polarization levels. The antennas can be used in multi-polarized MIMO system.