A Compact 2-Port QMSIW Cavity-Backed MIMO Antenna With Varied Frequencies Using CSRR-Slot Angles for WBAN Application

This paper presents a novel design of a compact, low-profile, Substrate Integrated Waveguide (SIW) based Multiple-Input Multiple-Output (MIMO) antenna operating at the 2.45 GHz Industrial, Scientific, Medical (ISM) band. The antenna consists of two quarter-mode (QM) SIW cavity resonators and one diamond-shaped complementary split ring resonator (CSRR) slot etched on each cavity. The unique feature of this geometry is the ability to tune the operating frequency of the dominant mode to a lower frequency range by rotating the slot in the range of 0°-180°. The excitation of both cavities is achieved using microstrip feedlines. By placing both cavities in an orthogonal configuration, a significant isolation level of around -28 dB between the two ports is achieved. MIMO metrics parameters, including the envelope correlation coefficient (ECC) and diversity gain (DG), mean effective gain (MEG), and channel capacity loss (CCL) have been investigated, validating the MIMO capabilities of the proposed design. Due to its compact dimensions, minimal profile, and alignment with the ISM band, the antenna lends itself seamlessly to integration with healthcare devices, facilitating its deployment within Wireless Body Area Network (WBAN) applications. The robust performance of the antenna in the vicinity of the human body has been verified by investigating the S11 against frequency on different body parts such as the arm, head, and chest of the voxel phantom. The proposed design has been experimentally tested, and the measured responses closely agree with the simulations. The antenna exhibits a front-to-back ratio better than 10 dB and peak measured gain values of 5.0 dBi.