Loop-shaded strip line dual mode multistage filter in which the strip

Abstract

A strip dual mode filter consists of a strip line ring resonator having an electric length equivalent to a resonance wavelength .lambda..sub.o for resonating microwaves at the resonance wavelength .lambda..sub.o according to a characteristic impedance thereof, an input coupling capacitor for transmitting the microwaves from an input terminal to a coupling point A of the ring resonator, an output coupling capacitor for outputting the microwaves resonated in the ring resonator from a coupling point B of the ring resonator to an output terminal, and a phase-shifting circuit connected to a coupling point C and a coupling point D of the ring resonator for changing the characteristic impedance of the ring resonator by shifting a phase of the microwave by a multiple of a half wavelength of the microwaves. The coupling point B is spaced a quarter wavelength of the microwaves apart from the coupling point A, the coupling point C is spaced the half wavelength of the microwaves apart from the coupling point A, and the coupling point D is spaced the half wavelength of the microwaves apart from the coupling point B.