A Highly Efficient and Low-Mutual Coupling Partial $\pi /8$ SIW Cavity-Based 8-Port MIMO Antenna

A sector-shaped compact
$\boldsymbol{\pi}/\mathbf {8}$
partial substrate-integrated waveguide cavity antenna from the
$\rm {\mathbf{TM}}_{\mathbf{220}}$
diagonal mode of the SIW cavity is presented. A 61
$\%$
size miniaturization is achieved compared to the SIW rectangular cavity in its complete mode configuration. The compact cavity radiator is used as an element of a compact 8-port multiple-input–multiple-output (MIMO) antenna. The 8-port MIMO antenna occupies the entire full cavity with slots loaded on the top and bottom layers. The fabricated prototype has a
$-$
10 dB impedance bandwidth (BW) from 6.006 to 6.143 GHz. The mutual coupling within the BW is less than
$-$
21 dB. The presented MIMO antenna has an envelope correlation coefficient (ECC) less than 0.0027, and a percentage diversity gain reduction below 1.73
$\%$
, which makes it a suitable candidate for use in MIMO-based wireless communications.