PURPOSE: To improve the characteristics at a blocking band having a large insertion loss, by providing a metallic shield plate in a metallic case so as to separate an input and an output line between the input and the output line of the titled filter and preventing an irradiated wave from propagating in the metallic case.

CONSTITUTION: The whole part of a band-pass filter 4 the input and outut lines 3 of which are coupled to a half wavelength microstrip line resonator 2 provided on a dielectric base 1, is made to contain in the metallic case 5. In figure, 6, 7 are the metallic shield plates and provided in the metallic case 5, and arranged on the dielectric base 1 so as to separate the input and output lines 3 and to bridge over the resonator 2. The insertion loss versus frequency characteristics in figure show an example of the characteristics of a band-pass filter having about 12.2GHz of center frequency f0 and comprising four-stage half wavelength microstrip line resonators and input and output lines, and solid lines indicate a conventional characteristic and dotted lines depict that of this invention. As seen clearly from figure, the insertion loss at the out-band at frequencies lower than fa(11.2GHz) is improved to about 50dB, in case of this invention providing the metallic shield plates.