A Survey on Planar Antenna Designs for Cognitive Radio Applications

In recent years, the demand for spectrum continues to increase with the advent of various wireless communication applications. However, it is a limited resource and cannot be made available beyond a certain extent. Many of the times, licensed spectrum is free due to its inefficient utilization. So, it can be utilized for other applications to mitigate the problem of limited spectrum availability to some extent. Among the many ways of performing this task, one approach is to use the frequencies in statically licensed spectrum through continuous sensing, which is popularly known as cognitive radio technology. In this model, UWB antennas are employed to monitor the radio environment and narrow band (NB) antennas are adopted for communication. This paper discusses various kinds of planar monopole antennas for cognitive radio applications. They are divided into three categories on the basis of different antennas used in cognitive radio environment. In the first category two separate antennas, which include one UWB antenna and one frequency reconfigurable NB antenna are employed for spectrum sensing and communication, respectively. In the second category, a single port frequency reconfigurable UWB/NB antenna is used. However, it requires an appropriate switching mechanism to switch between the UWB and NB modes. The third category includes dual-port integrated antennas systems, in which one UWB antenna and one frequency reconfigurable NB antenna are integrated on a single substrate. Finally, this paper discuss an opinion of designing multi-port integrated UWB and NB antennas systems to overcome the drawbacks of reconfigurable antennas and to further enhance the spectrum utilization efficiency.