Isolation enhancement of MIMO antennas using shorting pins

This paper provides an effective technique to reduce the mutual coupling between two adjacent probe-fed microstrip antenna elements operating at 3.5 GHz in multiple input multiple output (MIMO) configurations. The required reduction in the mutual coupling is achieved via loading of six metallic pins near the adjacent edges of two square patch radiators to ground the radiating elements in order to alter the polarization of the antennas. The two radiating elements are closely spaced with an edge-to-edge separation of 0.012λo and a centre-to-centre separation of 0.027λo. The idea is to make the two antennas orthogonal in terms of polarization via loading of shorting pins at appropriate locations. In order to validate the proposed technique, a two-element MIMO antenna is designed, fabricated, and measured. A good agreement between measurement and simulation is observed. Simulated and measured results are used to analyse the performance of the proposed technique in terms of mutual coupling between the two ports, radiation pattern, and realized peak gain. The measurement results show that the isolation between the two elements is enhanced from 2.8 dB to 20 dB at around 3.5 GHz.