Efficient design of a wideband tunable microstrip filtenna for spectrum sensing in cognitive radio systems

Abstract This paper presents a novel design of a compact, wideband tunable microstrip filtenna system for effective spectrum sensing in cognitive radio (CR) applications. The proposed filtenna structure has a total bandwidth of $$1.63\,\text{GHz}$$ 1.63 GHz and flexible frequency scanning design throughout the frequency range from $$1.93\,\text{ to }\,3.56\,\text{ GHz}$$ 1.93 to 3.56 GHz with high selectivity and narrow bandwidths ranging from $$39.9\,\text{to}53\,\text{MHz}$$ 39.9 to 53 MHz . Frequency tuning is accomplished electrically via integrating a varactor diode into the filtenna construction. The filtenna is realized on a Rogers TMM4 substrate with $$h=1.52\,\text{mm}$$ h = 1.52 mm thickness and relative dielectric constant of $${\varepsilon }_{r}=4.5$$ ε r = 4.5 with dimensions of $$(25\times 35)\, {\text{mm}}^{2}$$ ( 25 × 35 ) mm 2 . The obtained gain and efficiency of the filtenna ranged from $$0.7$$ 0.7 to $$2.26\,\text{dBi}$$ 2.26 dBi and 49% to 60%, respectively, within the tuning range. Simple biasing circuitry, wideband operation, and compact planar structure are distinctive and appealing aspects of the design. For the manufactured prototypes, a significant level of agreement is found between the simulated and measured results in terms of scattering parameter $${\text{S}}_{11}$$ S 11 and radiation patterns at different operating frequencies.