Multi-mode filter

Abstract

The present invention relates to a multi-mode filter comprising a carrier on which is mounted a dielectric resonator having a covering of an electrically conductive material in which there is provided an aperture and a coupling structure for coupling input signals to the dielectric resonator or for extracting filtered output signals from the dielectric resonator. The carrier is provided with an enclosing formation of electrically conductive material, which enclosing formation is electrically coupled to the electrically conductive covering of the dielectric resonator, such that the covering and the enclosing formation together form an electrically conductive enclosure for the dielectric resonator. The enclosure formed from the covering of the dielectric resonator and the enclosing formation increases the isolation of the filter and reduces leakage. The filter of the present invention is particularly suitable for use in cascaded resonator filter arrangements, and in duplex/diplex filters.

1 . A multi-mode filter comprising;
 a carrier on which is mounted a dielectric resonator, the dielectric resonator having a covering of an electrically conductive material in which there is provided an aperture; and   at least one coupling structure for coupling input signals to the dielectric resonator or for extracting filtered output signals from the dielectric resonator,   wherein the carrier is provided with an enclosing formation of electrically conductive material, which enclosing formation is electrically coupled to the electrically conductive covering of the dielectric resonator, such that the covering and the enclosing formation together form an electrically conductive enclosure for the dielectric resonator.   
     
     
         2 . A multi-mode filter according to  claim 1  wherein the enclosing formation is electrically grounded. 
     
     
         3 . A multi-mode filter according to  claim 1  wherein the enclosing formation comprises a continuous or almost continuous formation of grounded electrically conducting material. 
     
     
         4 . A multi-mode filter according to  claim 3  wherein the carrier is provided with a trench of electrically conductive material which surrounds the resonator in a plane of the carrier, the trench being electrically grounded. 
     
     
         5 . A multi-mode filter according to  claim 4  wherein the trench comprises a side wall and a base portion, such that the enclosing formation comprises the side wall and the base portion of the trench. 
     
     
         6 . A multi-mode filter according to  claim 5  wherein the carrier is provided with conductive layer on which the dielectric resonator is mounted, the conductive layer being electrically coupled to the trench such that the enclosing formation comprises a portion of the conductive layer and the side wall and base portion of the trench. 
     
     
         7 . A multi-mode filter according to  claim 1  wherein carrier on which the dielectric resonator is mounted is a first carrier, the filter comprising a second carrier on which the first carrier is mounted, the second carrier having a groundplane layer to which the enclosing formation is electrically coupled to electrically ground the enclosing formation. 
     
     
         8 . A multi-mode filter according to  claim 1  wherein the enclosing formation has an aperture generally corresponding to the aperture of the covering of the dielectric resonator, the enclosing formation being electrically coupled to the covering of the dielectric resonator such that the aperture of the covering is aligned with the aperture of the enclosing formation. 
     
     
         9 . A multi-mode filter according to  claim 8  wherein the coupling structure is electrically coupled to a corresponding contact track provided within the aperture of the enclosing formation. 
     
     
         10 . A multi-mode cavity filter according to  claim 1  wherein the carrier is of a printed circuit board material, or a ceramic material, or glass. 
     
     
         11 . A cascaded resonator filter arrangement comprising:
 a first filter according to  claim 1 ; and   a second filter according to  claim 1 , wherein an output of the first filter is electrically coupled to an input of the second filter.   
     
     
         12 . A cascaded resonator filter arrangement according to  claim 11 , wherein the carrier of the first filter and the carrier of the second filter comprise a single carrier that is common to the first and second filters. 
     
     
         13 . A duplex or diplex filter comprising a transmit filter according to  claim 1  and a receive filter according to  claim 1 . 
     
     
         14 . A duplex or diplex filter according to  claim 13  wherein the carrier of the first filter and the carrier of the second filter comprise a single carrier that is common to the transmit and receive filters.