In this paper cognitive radio is described, discussed and compared with software defined radio (SDR). The two types of cognitive radio are presented and examples on both spectrum interweave and spectrum underlay cognitive radio antenna systems are detailed. Reconfigurable filtennas are proposed as communicating antennas in a MIMO setting for both cases of cognitive radio. The benefits of resorting to filtennas as well as to MIMO configuration is shown and discussed herein. The various antenna examples are designed, tested and compared with each other. Conclusions are drawn based on the presented results.