Compact, Frequency-Reconfigurable Filtenna With Sharply Defined Wideband and Continuously Tunable Narrowband States

A compact, frequency-reconfigurable filtenna with sharp out-of-band rejection in both its wideband and continuously tunable narrowband states is presented. It is intended for use in cognitive radio applications. The wideband state is the sensing state and operationally covers 2.35-4.98 GHz. The narrowband states are intended to cover communications within the 3.05-4.39 GHz range, which completely covers the Worldwide Interoperability for Microwave Access (WiMAX) band and the satellite communications C-band. A p-i-n diode is employed to switch between these wide and narrowband operational states. Two varactor diodes are used to shift the operational frequencies continuously among the narrowband states. The filtenna consists of a funnel-shaped monopole augmented with a reconfigurable filter; it has a compact electrical size: 0.235λL× 0.392λL, where the wavelength λLcorresponds to the lower bound of its operational frequencies. The measured reflection coefficients, radiation patterns, and realized gains for both operational states are in good agreement with their simulated values.