Tunable Filtenna With DGS Loaded Resonators for a Cognitive Radio System Based on an SDR Transceiver

This paper introduces the design of a filtenna for cognitive radio systems. Four varactor diodes, which are inserted in the bandpass filter, are used to achieve the desired tunability. The proposed bandpass filter is integrated with a wideband monopole antenna. The bandpass filter is achieved by using two coupled defected ground structure (DGS) resonators and two coupled microstrip lines ended with two stubs. The monopole antenna is designed to operate in a frequency band from 1.3 GHz to 3 GHz. The four varactor diodes are used to tune the antenna resonance frequency from 2.7 GHz to 2 GHz when the capacitance increases from 1.55 pF to 2.67 pF. The performance of the proposed filtenna is validated by simulation and measurements from a fabricated prototype. Finally, the proposed filtenna is tested using the Software Defined Radio (SDR) platform bladeRF. This transceiver can transmit and receive in a wide frequency range of 0.3 GHz up to 3.8 GHz, which makes it suitable for testing the proposed reconfigurable filtenna.