(19)
(11) EP 0 818 883 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
09.09.1998 Bulletin 1998/37

(43) Date of publication A2:
14.01.1998 Bulletin 1998/03

(21) Application number: 97304719.4

(22) Date of filing: 30.06.1997
(51) International Patent Classification (IPC)6: H03H 9/72
(84) Designated Contracting States:
AT BE CH DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE

(30) Priority: 11.07.1996 FI 962815

(71) Applicant: LK-PRODUCTS OY
SF-90440 Kempele (FI)

(72) Inventors:
  • Närhi, Harri
    90460 Oulunsalo (FI)
  • Niiranen, Erkki
    91100 Ii (FI)

(74) Representative: Haws, Helen Louise et al
Nokia Mobile Phones, Patent Department, St. Georges Court/St. Georges Road, 9 High Street
Camberley, Surrey GU15 3QZ
Camberley, Surrey GU15 3QZ (GB)

   


(54) Duplex filter


(57) The invention relates to a radio-frequency filter with a good temperature stability and power handling capacity. The invention can be applied in the pre-stages of portable mobile telephone apparatuses, for example. The receiver branch (2) of the filter construction according to the invention employs two filter stages (3, 4), the first of which (3) attenuates the signal connected to the second filter stage, said second filter stage being a SAW filter (4). Said first filter stage (3) can be realized with a helix or dielectric resonator, for example. In a second embodiment of the invention, said first filter stage (3) is used to compensate for changes caused by the temperature dependence of the frequency response of the SAW filter (4).






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