In this work, a 2-layer frequency reconfigurable Yagi-like multiple-input–multiple-output (MIMO) antenna system is proposed based on a closed pentagonal slot-loop excitation. The MIMO system consists of 4 identical active antenna elements reactively loaded with varactor diodes to achieve frequency reconfigurability over a band from 1.5 to 2.1 GHz. The distinguishing feature of the proposed work is achieving Yagi-like directional characteristics over a very wide frequency band. The conventional omni-directional pattern of a slot antenna is made directional by using a parasitic metallic reflector layer below the substrate. By using the reflector element, the back-lobe radiation is highly suppressed and a front-to-back ratio of 5–13 dB is achieved within the entire frequency band of operation. The proposed design is compact with an overall size of $100 \times 100\times 20\,{\rm mm}^3$100×100×20mm3 , and a reflector size of $110 \times 110\,{\rm mm}^2$110×110mm2 . A single element has a maximum peak gain of 4 dBi and total measured radiation efficiency of 76%. The antenna system also shows good MIMO performance with high port isolation of 11.3 dB and very low envelope correlation coefficient values within the operational band.

中文翻译：

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堆叠式频率可重配置的八木类MIMO天线系统

在这个 在工作中，基于封闭的五边形缝隙环激励，提出了一种两层频率可重构的八木类多输入多输出（MIMO）天线系统。MIMO系统由4个相同的有源天线元件组成，这些有源天线元件反应性地装有变容二极管，以实现1.5至2.1 GHz频带上的频率可重构性。拟议工作的显着特征是在非常宽的频带上实现类似八木的定向特性。通过使用基板下方的寄生金属反射层，可以将缝隙天线的常规全向图案定向。通过使用反射器元件，可以高度抑制后瓣辐射，并在整个工作频带内实现5-13 dB的前后比。拟议的设计紧凑，总尺寸为$ 100 \ times 100 \ times 20 \，{\ rm mm} ^ 3 $100×100×20毫米3 ，并且反射器尺寸为 $ 110 \ times 110 \，{\ rm mm} ^ 2 $110×110毫米2 。单个元件的最大峰值增益为4 dBi，测得的总辐射效率为76％。该天线系统还具有良好的MIMO性能，端口隔离度高达11.3 dB，工作频带内的包络相关系数值非常低。