4-Element Concentric Pentagonal Slot-Line-Based Ultra-Wide Tuning Frequency Reconfigurable MIMO Antenna System

In this communication, a novel, compact, ultrawideband tuning, concentric pentagonal slot-line-based frequency-reconfigurable multiple-input-multiple-output (MIMO) antenna system is presented. It consists of a four-element antenna design on a commercially available FR-4 substrate with the dimensions of $60\times 120\times 1.56$ mm3. All the antenna elements are planar in structure, which are etched out from ground plane. Frequency reconfigurability is achieved using varactor diodes by reactively loading the antennas. Each capacitance value of the varactor diode results in the triband operation. Proper capacitive reactance loading enables the antenna to resonate over a wide frequency band. The proposed MIMO antenna system is tuned over an ultrawide frequency band, and a smooth variation of the resonance frequencies is observed from 1.32 to 1.49 and 1.75 to 5.2 GHz. Moreover, the unique feature of the proposed antenna system is the effectiveness of reactively loading the slot over all the resonating bands. The proposed antenna system is compact and suitable to be used in wireless handheld devices and mobile terminals for cognitive radio applications. The envelope correlation coefficient did not exceed 0.186 in the entire operating band of the MIMO antenna operation. The maximum measured gain of the MIMO antenna is 4.5 dBi with a maximum efficiency of 81%.