In this study, novel compact filtennas with large tunable frequency band are proposed for cognitive radio (CR) applications. Tunability is achieved by integrating a tunable T‐shaped and H‐shaped bandpass filter with a planar ultra‐wideband monopole antenna. The T‐shaped filter consists of a microstrip resonator loaded with a stub. The H‐shaped filter is composed of two connected microstrip resonators. The proposed tuning technique for both filters is based on centrally loading the stub and the H‐shaped with only a single varactor for miniaturisation. Increasing the varactor capacitance results in decreasing the even resonant mode of the resonator without affecting the dominant odd mode. Measurements results show that the proposed T‐shaped and H‐shaped filtennas are capable of tuning over a wide operating band of 1.68 and 1.73 GHz covering continuous bands for CR communication with 32.9% frequency tuning range (TR) from 4.26 to 5.94 GHz and with 36.7% frequency TR from 3.85 to 5.58 GHz, respectively. Moreover, the radiation patterns are stable over the operating frequency ranges. The frequency characteristics and radiation performance are successfully optimised using 3D full‐wave electromagnetic simulator. The fabricated designs are measured for verification purposes. Good agreements are found between simulated and measured results.

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In this article, a new wireless power transfer (WPT) design is proposed for improving the efficiency of the system. The suggested system contains two spiral defected ground structure (DGS) resonators coupled back-toback. A band-pass filter is then to be designed for the wireless power to be transferred from the transmitter unit to the receiver unit. The DGS resonators are loaded through chip capacitors for miniaturization. The proposed structures are fabricated and tested. The proposed system has the highest efficiency of 97.7% at a transmission distance of 10 mm which is suitable for biomedical applications. Both simulated and experimental results are in good concurrence.

In this paper, a new miniaturized frequency agile filter-antenna with a wide reconfigurable frequency band is proposed for interweave cognitive radios (CRs). A tunable bandpass filter (BPF) composed of a symmetrical ring resonator is cascaded to the feed line of an ultra-wideband planar antenna. The structure of the proposed ring resonator BPF is simple and compact so that the total size of the proposed filter-antenna is smaller than that of a conventional system made of a separate antenna and BPF. The reconfigurability of the proposed filter-antenna is achieved by changing the operating frequency of the BPF by loading the ring resonator with a single varactor diode at its center. The fabricated prototype has successfully achieved a wide operational bandwidth of 1.43 GHz which covers continuous narrow bands from 4.65 to 6.08 GHz. Moreover, the operating tunable narrow bands have stable radiation characteristics. Good agreement between measurement and simulation results is demonstrated.