Two port frequency reconfigurable antenna for cognitive radios

A two port frequency reconfigurable antenna for cognitive radios is presented. It is composed of a disc monopole with two ports that excite at opposite sides; one port is very wideband and consists of a coplanar feed line and the other port is tunable narrowband and consists of a microstrip feed line with defect slots in its ground plane. The slots act as a filter that suppresses frequencies outside the desired band, its operating frequency band can be tuned by varying the length of the slots. The two ports are decoupled by at least 10 dB through the considered frequency range. It is believed that the proposed antenna can be a good candidate for cognitive radios in generic small base stations where the narrowband port is used for operation and the wideband one is used for sensing the spectrum. For accuracy, it is important that the sensing (measurement of the interference noise) is made with the same polarisation as the operation and the proposed antenna achieves this by having the two collinear ports. To examine the presented approach, simulated and measured results are presented and good agreement is reported.