A reconfigurable monopole MIMO antenna with wideband sensing capability for cognitive radio using varactor diodes

A cognitive radio multiple-input-multiple-output (MIMO) antenna is presented in this paper. The proposed antenna consists of two reconfigurable printed monopole antennas and a coplanar waveguide (CPW) fed wideband sensing antenna located between the two antennas. The structure is specially designed for antenna miniature. Furthermore, the wideband antenna at the middle is utilized as a structure to enhance the isolation of two monopoles. When properly designed, the MIMO antenna can be electronically tuned over the lower ultrawideband (UWB) frequency band (2300-6300 MHz) using two pairs of varactor diodes. The wideband sensing antenna is used to cover a wide range frequency band from 2.2 GHz to more than 7 GHz. The proposed antenna elements develop a complete antenna platform for cognitive radio (CR) applications. The overall size of the antenna is set to be 60 × 40 mm².