Miniaturized frequency-tunable self-quadruplexing four-element MIMO antenna system

Abstract

We propose a self-quadruplexing four-element multiple-input-multiple-output (MIMO) antenna system with frequency agility. Four separately-fed orthogonal U-slots are cut from the same cavity to locate the radiating patches. The frequency tuning is realized by inserting four varactors into the radiating structures. Metalized vias are used for antenna miniaturization and to reduce the coupling between the radiating elements. Also, the antenna exploits the slits realized in its ground plane to further increase the isolation. Truly, the isolation between the elements is enhanced from 8 to 16 dB when they are tuned concurrently. The antenna system has the added merit of tuning each element separately to excite four different operating frequencies exhibiting the self-quadruplexing function. Measurements reveal that the frequency bands can be tuned together or individually from 4.67 to 5.84 GHz without affecting each other. The measured peak gain and efficiency are 3.73 dBi and 65%, respectively. The proposed MIMO antenna is a promising candidate for communication systems as it is printed on one substrate layer, has a miniaturized size, exhibits good diversity performance with a maximum envelope correlation coefficient of 0.11, and the four elements can be reconfigured separately without the additional quadruplexer circuit.