Reconfigurable Compact Wide-Band Quad-Port Antennas Based on a Varactor Diode for Sub-6 GHz 5G Communications.

The rapid expansion of wireless communication systems has spurred a growing demand for adaptable multiple-input multipleoutput (MIMO) antennas capable of accommodating diverse frequency bands and operational environments. This paper presents a compact quad-port wide-band tuning-reconfigurable MIMO antenna tailored specifically for 5G applications operating within the sub-6 GHz spectrum. The proposed design enhances isolation levels (> 18 dB) and augments pattern diversity by utilizing four orthogonal radiating elements. Integrating a C-shaped monopole element with a matching stub facilitates frequency tuning via a varactor diode, ensuring a consistent radiation pattern. The lower and upper resonant bands could be fine-tuned by adjusting the varactor diode's reversebiased voltage within the allowed range of 0.5 to 10 V. These bands are 4 to 5.18 GHz and 5.45 to 6.65 GHz, respectively. The proposed antenna system's four C-shaped elements are placed on a 40 × 40 mm2 ground plane and mounted on a Rogers RT5880 substrate that is 0.8 mm thick with a relative permittivity of 2.2. This design is well suited for various wireless applications and cognitive radio networks due to its compatibility with sub-6 GHz frequency bands and wide-band tuning capabilities. [ABSTRACT FROM AUTHOR]