JPS5778201A - High frequency filter - Google Patents

Abstract

PURPOSE:To reduce the insertion loss in the pass band, by providing plural resonators having the resonance mode, where the current is maximum near the center part, on distributed constant lines which are about <=1/4 wavelength long and have both ends terminated by capacities. CONSTITUTION:An earth conductor 13 is provided under a dielectric substrate 12, and end parts of the earth conductor 13 are extended to the upper face of the substrate 12. On the upper face of the substrate 12, distributed constant lines 10 consist of plural microstrip MST lines which are 2l (about 1/8 wavelength) long face to one another through gaps which form capacities together with the end part of the earth conductor 13. Input and output energizing lines 11 consisting of MST lines are provided to interpose lines 10 on the upper face of the substrate 12, and one ends of these lines 11 are connected to the earth conductor 13. By this constitution, since a current is a maximum and a voltage is 0 in a middle point AA' of lines 10, the middle point AA' is regarded as an earth point equivalently, and thus, the conductor loss of the earth end face is eliminated, and consequently, the insertion loss in the band is reduced, and a small-sized high frequency filter is obtained.