HYBRID MUTUAL COUPLING REDUCTION TECHNIQUES IN MULTIPLE INPUT AND MULTIPLE OUTPUT ANTENNA FOR X-BAND APPLICATIONS

Abstract

In recent years, Multiple Input and Multiple Output antennas (MIMO) used for high-bandwidth communications where it's important to not have interference from microwave or RF systems. The MIMO antenna offers good matching with stable gain and desired radiation patterns but it suffers on mutual coupling effects. The spacing between antenna elements is less than half the wavelength, and then mutual coupling effects are more. This paper provides a review on different mutual coupling reduction techniques in MIMO antenna. In this letter, a hybrid mutual coupling reduction technique such as substrate integrated waveguide (SIW) and defected ground structure (DGS) in MIMO antennas for X-band applications. The developed MIMO antenna has dimensions as 25 x 36 mm over a FR4 1.6 mm substrate. The MIMO antenna has formed by combining two fractal-shaped structures.  Here, the antenna element spacing is taken as minimum of 5.62mm. To reduce the mutual coupling effect and enhance gain, hybrid techniques are used. By adding 24 hollow cylindrical SIW is placed in between a MIMO element and six rectangular DGS slots placed at the bottom of the antenna for reducing the mutual coupling and enhance the gain. The proposed antenna operates at resonating frequencies of 10.04 GHz, 11.14 GHz, and 11.69 GHz for measurement. The mutual coupling or isolation loss was observed around <-25 dB. The envelope correlation coefficient (ECC) and diversity gain (DG) of the proposed antenna are 0.0016 and >9 dB, respectively. The gain observed for the proposed design is 5.2 dB. The Ansys high-frequency structure simulator (HFSS) tool is used for antenna simulation.