Four-Port MIMO Cognitive Radio System for Midband 5G Applications

In this paper, a multifunctional reconfigurable filter that can work in three operating modes has been presented. The three operating modes are: all-pass filter, tunable bandpass filter, and tunable band-reject filter. The developed filter has been integrated with an ultrawideband antenna that results in a reconfigurable filtenna. Such four filtennas are arranged on a single substrate, and sufficient isolation is maintained between them by using reflectors to form a four-port multiple-input multiple-output (MIMO) filtenna that can work for midband 5G cognitive radio (CR) applications. By controlling the operating modes of the filter, the final developed structure gives sensing and communicating antennas for spectrum-interweave and spectrum-underlay CRs. Simulated results have been validated by carrying out the measurement. MIMO performance of the proposed antenna has been evaluated by measuring an envelope correlation coefficient and found suitable for practical applications.