A Compact 4-Ports UWB MIMO Antenna with WiMAX and WLAN Band Rejection Characteristics

Abstract

This study introduces a compact four-port UWB MIMO antenna featuring dual-band rejection capabilities aimed at suppressing interference from coexisting wireless services, specifically WiMAX at 3.5 GHz and WLAN at 5.5 GHz. The antenna employs an inverted C-slot etched into the radiator to achieve the WiMAX notch, while EBG structures are integrated to enable suppression of the WLAN band at 5.5 GHz. Fabricated on a low-cost FR4 substrate with dimensions 52 × 52 × 1.5 mm3 (εr = 4.5), the proposed design achieves high port isolation exceeding 15 dB across the 3.1–10.6 GHz UWB range. Simulated results show an operational bandwidth from 3 to 11 GHz, extending beyond 12 GHz in measurements, without the need for additional filters or decoupling structures. The antenna exhibits quasi-omnidirectional radiation patterns with a peak gain of 7.2 dBi and significant gain suppression at the notch frequencies (−1.5 dBi at 3.5 GHz and −1.2 dBi at 5.5 GHz). It maintains a VSWR below 2 across the UWB and achieves radiation efficiency above 90% outside the notched bands. The envelope correlation coefficient remains below 0.005, enabling a high diversity gain approaching 10 dB. The EBG structures effectively reduce mutual coupling, allowing a compact element spacing of just 2 mm (approximately λ/12.5 at 12 GHz). Both simulation and measurement results validate the proposed design’s suitability for mitigating co-channel interference in UWB-MIMO applications, including satellite communications in the S/C/X bands and high-speed wireless systems.