Dielectric filter of interdigital line type

Claim 1

An interdigital line type dielectric filter comprising: a dielectric block extending in a lateral direction and a longitudinal direction; a grounding electrode formed on the outer surface of the block; two parallel holes extending through the block in a lateral direction at an appropriate longitudinal interval to form exciter lines; a plurality of parallel electrode bodies between the two exciter lines extending through the block in the lateral direction substantially regularly spaced apart from one another in the longitudinal direction to form resonant lines, each electrode body being of a given cross-sectional width in the longitudinal direction and having one short-circuited end connected to the grounding electrode on one side of the dielectric block and the other end being an open end that is not connected to the grounding electrode on an opposite side of the dielectric block, the short-circuited end and the open end of any one of the electrode bodies being disposed on alternate sides of the dielectric block from those of an adjacent electrode body; and cutouts formed in the dielectric block in the vicinity of each respective one of the open ends of the electrode bodies, said cutouts being recessed laterally inward from the sides of the dielectric block, each cutout having lateral walls defining the recess which are lined by the grounding electrode extending inwardly in the direction to lateral a bottom part which is coaxial and coplanar with the open end of the electrode body and has a width in the longitudinal direction wider than the given width of the electrode body and along which the grounding electrode does not extend, whereby the open ends of the electrode bodies are exposed, no grounding electrode is facing opposite the open ends, each open end is isolated from the grounding electrode along the lateral walls of the cutout recess by the dielectric block which is exposed due to the bottom part of the cutout recess having the width wider than the width of the electrode body, and a fringing capacitance is established between the open end of the electrode body and the grounding electrode along the lateral walls of the cutout recess.