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.

中文翻译：

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小型化频率可调谐自四工MIMO天线系统

我们提出了一种具有频率捷变能力的自四工的四元素多输入多输出（MIMO）天线系统。从同一个腔中切出四个单独馈入的正交U形槽，以定位辐射贴片。通过将四个变容二极管插入辐射结构中来实现频率调谐。金属化的通孔用于天线的小型化并减少辐射元件之间的耦合。同样，天线利用在其接地平面上实现的缝隙来进一步提高隔离度。的确，同时调谐时，元件之间的隔离度从8 dB增强到16 dB。天线系统的附加优点是可以分别调谐每个元件，以激发四个具有自四倍频功能的不同工作频率。测量表明，可以在4.67至5.84 GHz范围内一起调谐频带或单独调谐频带，而不会互相影响。测得的峰值增益和效率分别为3.73 dBi和65％。所提出的MIMO天线被印刷在一个基片层上，具有最小化的尺寸，具有良好的分集性能，最大包络相关系数为0.11，并且可以分别重新配置这四个元件，而无需额外的四路复用器，因此是通信系统的有希望的候选人电路。