Triple Band-Reject Functionality from a Four-Element, Offset-Fed Fractal UWB-MIMO Antenna Incorporated with Split-Ring Resonators and U-shaped Slot

In this work, a quad-port fractal MIMO antenna is configured, simulated, and experimented for ultra-wideband performance with the elimination of three interfering narrow bands. The antenna is assembled on dual 80 × 99.4mm² FR-4 dielectric substrates wherein the top substrate comprises four 2nd iterative Sierpinski gasket fractal patches and the bottom substrate incorporates a feeding arrangement. The aperture-coupled feeding approach is employed to activate the fractal radiators. The multi-frequency response produced by fractal antenna elements is transformed into a wide working range by modifying apertures (clipped from the ground surface) into spiral-shaped structures and offsetting the feedlines toward the right. The designed array effectively radiates in the 3.07–11 GHz range with 112.7% fractional bandwidth while maintaining minimal inter-element isolation of 16.19 dB. Additionally, each feedline is amalgamated with circular split-ring resonators, U-slots, and rectangular split-ring resonators to eradicate the interference emerging from the C-band (downlink satellite), WLAN, and radio-location band, respectively. Several diversity operation attributes are analyzed and are found to inhere to their admissible standards. The measured performance of the fabricated antenna design (with and without band-stop structures) depicts an agreeable similitude with the simulation results, thus validating the real-world operability of the proposed MIMO antenna in ultra-wideband communication devices.