In this paper, a new frequency tunable filtering-antenna (so-called filtenna) is inspired by a Defected Ground Structure (DGS) band-pass filter for the fifth generation picocell base stations. It is intended for use in Cognitive Radio (CR) communications within the European Union Sub-6 GHz spectrum, which ranges between 3.4 and 3.8 GHz. Firstly, a Wideband (WB) monopole antenna is proposed where the operational frequencies cover 3.15-4.19 GHz, taking the 10-dB return loss level as a threshold. A band-pass filter of a Semi-Square Semi-Circle shape is integrated into the WB antenna ground to obtain the communicating filtenna. The narrowband frequency tunability is achieved by changing two varactor diode capacitances located on the filter slots. The antenna is prototyped occupying a total space of 60 x 80 x 0.77 mm3, then tested to verify the simulated results. Three operating frequencies 3.4, 3.6 and 3.8 GHz of the filtenna are studied in terms of return loss, realized gain and radiation patterns which verify that the frequency shift has almost no effect on the antenna performance. The filtenna has a maximum gain of 4.5 dBi in measurements and 3.47 dBi in simulations. The obtained results have proved their efficiency for CR communications.
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