In this article, a compact dual-band, 2-elements antenna-diplexer is investigated and extended to a 2×2 multi-input and multi-output (MIMO) antenna. The proposed design employs half-mode Substrate Integrated Waveguide (HMSIW) technology, which reduces the antenna footprint by 50%. To enhance the bandwidth, a rectangular slot is engraved at the center of each HMSIW cavity. The slot splits the dominant mode of the HM cavity into two odd-and even-half TE110 modes in a proximity, which leads to enhancement in the bandwidth by 50%. The antenna resonates around 3.4 GHz with a fractional bandwidth of 5% and around 4.3 GHz with a bandwidth of 4.7%, when corresponding ports are excited, respectively. Both the lower and upper frequency bands can be tuned individually, by simply altering the dimensions of each HMSIW cavity. This can be achieved in a common antenna, without employing filters, which satisfies the antenna-diplexer function. The isolation levels between any two radiating elements are obtained below -23 dB for the proposed MIMO antenna, and it occupies overall size of 1.0λg × 0.8λg. The peak gain of the antenna is obtained 5.35 dBi in the lower frequency band and 6.75 dBi in the upper frequency band while radiation efficiency is better than 80% in both frequency bands. The MIMO antenna properties have been evaluated and all found satisfactory. The envelope correlation coefficient (ECC) is obtained less than 0.13, DG around 9.9 dBi, and mean effective gain (MEG) around -3.05 dB. The 2×2 MIMO antenna is prototyped and experimentally verified. The measured results are closely following the simulation counterparts. The proposed 2×2 MIMO antenna is an appropriate alternative for LTE frequency bands in 5G wireless communication.INDEX TERMS Isolation, multi-input multi-output antenna (MIMO), half-mode substrate integrated waveguide (HMSIW), envelop correlation coefficient (ECC), mean effective gain (MEG).

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