Design and Analysis of Compact Quad-Element MIMO Antenna with Asymmetrical Ground Structures for Ultra-Wideband Communication

This paper presented a compact quad-element flower-shaped (FS) multiple-input multiple-output (MIMO) antenna for ultra-wideband (UWB) communication. The designed antenna exhibits ultra wideband characteristics whose impedance bandwidth (for S 11 ≤ − 10 dB) ranges from 3.1 to 11.7 GHz and the inter-port isolation is better than − 14 dB over operating frequency without any decoupling structure. The proposed electrically small (32 × 32 mm 2 ) FS quad-element MIMO antenna is printed on a low-cost FR4 substrate. An FS radiating element is formed by merging four same dimension ellipses at 45° to each other. The top layer of the proposed structure comprises four FS radiating elements, which are positioned orthogonal to each other. The bottom layer consists of asymmetrical ground structures which offer good impedance matching and low mutual coupling between radiating elements at the desired operating frequency band. Besides, the proposed quad-element MIMO antenna with the shared ground is also designed and tested. Its simulated results show satisfactory inter-port isolation of around − 10 dB over frequencies 3.08–11.48 GHz. The antenna provides a low envelope correlation coefficient (ECC < 0.03) and appreciable other diversity parameters. Moreover, the measured 2D radiation patterns confirm the pattern diversity, which will help to mitigate the multipath fading. Also, the simulation study of the MIMO antenna in the actual environment is carried out. Finally, the numerical result of both proposed antennas with the isolated and shared ground is verified experimentally and found suitable for UWB-MIMO applications.