New design of UWB-MIMO antenna with enhanced isolation and dual-band rejection for WiMAX and WLAN systems

In this work, a new design of wide-band multiple-input multiple-output (MIMO) antenna with improved isolation and dual-band rejection is proposed for wireless systems operating over the entire ultra-wide-band (UWB), X-band, and Ku-band (3-18GHz). The proposed four-element UWB-MIMO antenna is fabricated on Rogers RT/Duroid-5880 substrate with dimension of 73x73x0.79mm(3). It achieves high isolation (>20dB) between antenna elements without using any decoupling structures. In order to prevent interference problems from nearby WiMAX (3.3-3.8GHz) and WLAN (5.1-5.8GHz) systems, a C-shaped stub is embedded in the radiating patch and a pair of U-shaped parasitic strips is inserted beside the feed line in the single element design. The effectiveness of the proposed design is demonstrated by investigating measurement and simulation results, and comparing them with other existing designs. The results show that the proposed design has an input reflection coefficient <-10dB, a mutual coupling <-20dB, and an omnidirectional radiation pattern across the bandwidth of interest (3-18GHz) excluding the two rejected bands. Also, the proposed design exhibits high diversity performance in terms of envelope correlation coefficient (ECC <0.0015) and channel capacity loss (CCL<0.3bits/s/Hz). This reveals the effectiveness of the proposed design in wide-band wireless applications such as satellite communications and microwave medical imaging.