Electronically Reconfigurable Uniplanar Antenna With Polarization Diversity for Cognitive Radio Applications

A uniplanar, polarization diversity antenna with wideband/narrowband (WB/NB) switching capability is presented. The design utilizes an open annular slot with an orthogonal feeding mechanism to achieve polarization diversity performance across the operating bands. To attain high isolation between the ports, a strip is incorporated in the ground plane. Electronically reconfigurable slot resonator-based filters are also precisely embedded in the feedlines for the WB/NB switching. A fully functional prototype was fabricated, and the results were validated. The antenna provides a wide bandwidth mode from 3.4 to 8.0 GHz and a narrow bandwidth mode from 4.7 to 5.4 GHz with interport isolation better than 15 dB. Moreover, the design delivers polarization diversity with a low envelope correlation coefficient, a nearly omnidirectional radiation pattern, and a moderate gain while operating in WB and NB modes. These characteristics make the proposed antenna suitable for next-generation cognitive radio systems, where the WB antenna is used for spectrum sensing and the NB antenna for communication.