A Wideband-to-Narrowband Rectangular Dielectric Resonator Antenna Integrated With Tunable Bandpass Filter

compact, frequency-reconfigurable dielectric resonator antenna (DRA) with wideband and continuously tunable narrowband states is presented. It is intended for the application scenario in the cognitive radio system. The wideband state is the sensing state and operationally covers 3.82–8.94 GHz. The narrowband states are intended to cover communications within the 5.14–5.98 GHz range, which completely covers the WLAN frequency bands. Three p-i-n diodes are employed to switch between wide and some narrowband operational states by selecting the corresponding path. A varactor diode is used to shift the operational frequencies continuously among the narrowband states. The proposed DRA consists of a rectangular dielectric resonator excited by microstrip feedline with a reconfigurable filter; it has a compact dimension: <inline-formula> <tex-math notation="LaTeX">$0.31\lambda _{L}\times 0.41\lambda _{L}\times 0.06\lambda _{L}$ </tex-math></inline-formula>, where the wavelength <inline-formula> <tex-math notation="LaTeX">$\lambda _{L}$ </tex-math></inline-formula> corresponds to the lower bound of its operating frequencies. The measured reflection coefficients, far-field radiation patterns, and realized gains for both operation states are in good consistent with their simulated values.