A novel central-stub-loaded, dual-band bandpass filter for PCS and WiMAX application

A planar dual-band bandpass filter with large-bandwidth ratio, which is suitable in PCS and WiMAX applications, is presented. It possesses a compact and simple configuration, which includes a hexagon resonator and a central loaded stub. Benefiting from the introduction of loaded stub, additional mode is well excited and could operate between the first-order mode and the second-order mode of the hexagon resonator. By simply adjusting the central stub impedance, the fundamental mode of central stub could be shifted away from the first-order mode of the resonator (which operates in the lower frequency range covering PCS band), and close to the second-order degenerate modes of resonator, and thus form a second wide three-mode passband (which covers WiMAX band).