Investigation of Parallel and Quadrature MIMO Antennas with Double-Notched Structure for UWB Applications

In order to solve the interference of narrowband communication system to ultra-wideband (UWB) system and meet the design requirements of high isolation of multiple-input multiple-output (MIMO) antenna, two MIMO antennas with double notch structures are designed. Firstly, a two-element antenna was placed symmetrically in parallel, and two rectangular branches were loaded to improve the isolation. U-shaped slots and inverted U-shaped slots are etched on the radiating patch and feeder to achieve notch characteristics in WIMAX and ITU band, respectively. Then, in order to meet more application scenarios, a four-element MIMO antenna is designed, where each element is placed orthogonally to each other, and the isolation is improved by loading a cross-shaped branches in the middle of elements. Both antenna samples are tested to verify the design. Measured results show that the working bandwidth of the two-element UWB MIMO antenna is 2.45-14.88 GHz, the isolation is greater than 17 dB, the peak gain is 5.7 dB, the maximum radiation efficiency can reach 96%, the envelope correlation coefficient (ECC)is less than 0.02. Meanwhile, the working bandwidth of the four-element antenna is 2.14-14.95 GHz, the isolation is greater than 20 dB, the peak gain is 5.9 dB, the maximum radiation efficiency can reach 95%, the ECC is lower than 0.05. They both are with very good omnidirectional characteristic, and meet the requirements of the UWB application.