New compact bandpass filter using microstrip /spl lambda//4 resonators with open stub inverter

A novel bandpass filter using microstrip quarter-wavelength resonators is proposed. The proposed filter consists of the open stub inverter between quarter-wavelength resonators, which results in a compact design as well as low loss. The tapped open stub not only works as a K-inverter but also introduces an attenuation pole. The attenuation pole can be located at the upper or lower side of the passband by adjusting the open stub length. A two-pole Chebyshev bandpass filter is designed and tested at 1.99 GHz. A four-pole bandpass filter of elliptic-type performance is also designed and tested at 2.015 GHz.