US 5,717,368 AGranted

Varactor tuned helical resonator for use with duplex filter

AssigneeLK-Products Oy

InventorErkki Niiranen

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Abstract

A radio frequency filter comprising several resonator circuits, such as duplex filter, is provides with a given passband. Signal frequencies generating spurious response, mirror frequencies, etc. can be effectively attenuated so that the filter comprises one more resonator circuit connected as a bandstop circuit. That comprises a transmission line resonator (Res), a series connection of an inductive element (MLIN2) and a capacitance diode (D), one end of the series connection being couples to a coupling point in the transmission line resonator, dividing it into two parts (TLIN1, TLIN2), and the other end being couples to the output connector (1) of the radio frequency filter. In addition, means are provided for carrying the direct voltage (V+) to the cathode of the capacitance diode, whereby the series resonance frequency changes according to the control voltage.

Claims11

Dependent claims

A duplex radio frequency filter having pass bands, comprising:

a receiving part with a plurality of resonators defining a receiving pass band region, said receiving part being connected between a receiving branch of a radio telephone at an output connector and an antenna;
a transmitting part with a transmission pass band region, said transmitting part being connected between a transmitting branch of a radio telephone and the antenna;
and
a tunable bandstop filter coupled to the receiving part of the radio telephone at the output connector, the tunable bandstop filter including an electrically tunable resonator which is tunable to attenuate signals in the pass bands of said duplex radio frequency filter, the electrically tunable band stop resonator being disposed in the duplex filter structure at a distance remote from the antenna of the radio telephone such that at least one of said plurality of resonators is situated between said electrically tunable bandstop resonator and the antenna.

1 more element

Dependencies are inferred from the claim text.