PURPOSE: To provide a small filter which can be made flat with respect to the filter which is used in a communication equipment or the like in UHF to SHF bands and uses a single wavelength ring resonator.
CONSTITUTION: With respect to a single wavelength ring resonator 12, transmission lines 13, 14, 15, and 16 having front ends opened are connected at points A, B, C, and D, whose intervals are 90° electric length, to adjust the resonance frequency, and the inter-stage coupling circuit is made of parallel coupling lines 18 to make the filter small and flat. Since parallel coupling lines 18 between stages are coupled in a position off center of a propagation line, a notch can be generated near the pass band, and the filter superior in attenuation characteristic is realized with a small number of stages.
SAGAWA MORIKAZU
MAKIMOTO MITSUO
