Patent ID: 6614328
Filing Date: 2003-09-02
Classification: H01P

Abstract:
In a radio frequency filter of a combline structure including an input terminal, an output terminal, transmission lines arranged in a pair, each of the transmission lines having a desired width and being connected to a capacitance compensating circuit through a via hole, whereby the radio frequency filter has a predetermined frequency bandwidth, a frequency cut-off circuit for cutting off a specific frequency from a frequency band having the predetermined frequency bandwidth, the frequency cut-off circuit comprising:an inductive transmission line extending from the output terminal by a length determined to provide an approximate inductance corresponding to a calculated value approximate to an inductance for obtaining the specific frequency; and a capacitive element coupled to the approximate inductance provided by the inductive transmission line, the capacitive element having a capacitance for obtaining the specific frequency; wherein the inductive transmission line is connected to the capacitive element through a via hole formed at an end of the transmission line opposite to the output terminal, from which the transmission line extends.