Frequency-Reconfigurable Antenna With Wide- and Narrowband Modes for Sub-6 GHz Cognitive Radio

This letter presents a frequency-reconfigurable antenna for cognitive radio application in sub-6 GHz 5G band. The proposed antenna consists of a wideband (WB) monopole integrated with a narrowband microstrip patch in a single-layer substrate. Two PIN diodes are employed to switch between the WB sensing mode and narrowband (NB) communication mode. Three varactor diodes are implemented on the patch to continuously tune the operating frequencies in the NB mode. The proposed antenna produces a wide bandwidth of 54.2% (3.19–5.56 GHz) for the sensing mode and a continuously tunable bandwidth of 44% (3.4–5.32 GHz) for the communication mode. Both modes present good radiation characteristics with peak measured realized gains of 6.02 and 5.37 dB, respectively.