Plane type strip line filter in which strip line is shortened and dual mode resonator in which two types microwaves are independently resonated

A strip line filter for resonating and filtering a microwave, comprising;

• a series of one-wavelength loop-shaped strip line resonators respectively having a uniform line impedance for respectively resonating and filtering a microwave according to a first resonance mode in which electric voltages at both a first coupling point and a second coupling point spaced 180 degrees in electric length apart from the first coupling point are maximized and respectively resonating and filtering the microwave according to a second resonance mode in which electric voltages at both a third coupling point spaced 90 degrees in electric length apart from the first coupling point and a fourth coupling point spaced 180 degrees in electric length apart from the third coupling point are maximized, each of the one-wavelength loop-shaped strip line resonators having a first parallel coupling line between the first and third coupling points and a second parallel coupling line between the second and fourth coupling points, the second parallel coupling line of a one-wavelength loop-shaped strip line resonator arranged in an N-th stage (N is an integral number) being electromagnetically coupled to the first parallel coupling line of another one-wavelength loop-shaped strip line resonator arranged in an (N+1)-th stage to transfer the microwave from the one-wavelength loop-shaped strip line resonator arranged in the N-th stage to the one-wavelength loop-shaped strip line resonator arranged in the (N.sub.1 1)th stage;
• four open-end transmission lines connected to the first, second, third and fourth coupling points of each of the one-wavelength loop-shaped strip line resonators for electromagnetically influencing the microwave resonated in each of the one-wavelength loop-shaped strip line resonators, the open-end transmission lines having the same electromagnetic characteristics;
• a microwave inputting element for inputting the microwave to the first coupling point of a one-wavelength loop-shaped strip line resonator arranged in a first stage, the microwave input by the microwave inputting element being resonated according to the first resonance mode by stages and being transferred to a one-wavelength loop-shaped strip line resonator arranged in a final stage;
• an inter-stage coupling circuit for transferring the microwave resonated according to the first resonance mode from the second coupling point of the one-wavelength loop-shaped strip line resonator arranged in the final stage to the third coupling point of the one-wavelength loop-shaped strip line resonator arranged in the first stage, the microwave resonator arranged in an (N+1)-th stage to transfer the microwave from the one-wavelength loop-shaped strip line resonator arranged in the N-th stage to the one-wavelength loop-shaped strip line resonator arranged in the (N+1)-th stage;
• four open-end transmission lines connected to the first, second, third and fourth coupling points of each of the one-wavelength loop-shaped strip line resonators for electromagnetically influencing the microwave resonated in each of the one-wavelength loop-shaped strip line resonators, the open-end transmission lines having the same electromagnetic characteristics;
• a microwave inputting element for inputting the microwave to the first coupling point of a one-wavelength loop-shaped strip line resonator arranged in a first stage, the microwave input by the microwave inputting element being resonated according to the first resonance mode by stages ad being transferred to a one-wavelength loop-shaped strip line resonator arranged in a final stage:
• an inter-stage coupling circuit for transferring the microwave resonated according to the first resonance mode from the second coupling point of the one-wavelength loop-shaped strip line resonator arranged in the final stage to the third coupling point of the one-wavelength loop-shaped strip line resonator arranged in the first stage, the microwave transferred by the inter-stage coupling circuit being resonated according to the second resonance mode by stages and being transferred to the one-wavelength loop-shaped strip line resonator arranged in the final stage;
• and
• a microwave outputting element for outputting the microwave resonated according to the second resonance mode in the one-wavelength loop-shaped strip line resonator arranged in the final stage.