A transmission line decoupling technique for enhancement of port isolation of dual-band MIMO antennas

Abstract

In this paper, a transmission line decoupling network (TLDN) technique is presented to enhance the isolation of a dual-band multiple input and multiple output (MIMO) antenna. The MIMO antenna with enhanced isolation is designed by the following steps: Firstly, each port of an initial 2-port MIMO antenna is connected with an admittance transformer formed by two transmission line sections. The length and the width of the admittance transformer are designed to retrieve mutual admittance between ports having only imaginary part. The two ports are then connected in parallel electrically with the proposed TLDN to cancel the resultant imaginary mutual admittance. At the final stage, a simple dual-band matching network is added to each port to improve matching performance. The proposed method is applied to two designs of dual-band printed MIMO antenna working at 2.45 GHz/5.25 GHz and 1.8 GHz/3.5 GHz. For the purpose of verification, the two designs were fabricated and measured. The measured results are in good agreement with the simulation ones. Both designs yielded a high isolation, low envelop correlation coefficient, simple structures for design and fabrication. These features demonstrated the feasibility of the technique in implementing MIMO antennas.