Patent ID: 7034630

Claim:
Balun transformer ( 100 ) for converting an unbalanced signal into a balanced signal or vice versa and having a bandpass characteristic for bandpass-filtering the signal being converted, comprising: a first electronic circuit, including a first tuning unit ( 110 ) being connected to a first coupling element (CPL 1 ), for transceiving the unbalanced signal; and a second electronic circuit, including a second tuning unit ( 120 ) being connected to a second coupling element (CPL 2 ), for transceiving the balanced signal; wherein the first and the second electronic circuit are coupled via the first and the second coupling element (CPL 1 , CPL 2 ); characterized in that both the first and the second electronic circuit are embodied as individual resonance circuits ( 100 - 1 , 100 - 2 ) being operated at their individual resonance frequencies f R1 , f R2 representing the centre frequencies of the bandpass filter characteristic, respectively; each of the individual resonance frequencies is set-up by adjusting the tuning unit ( 110 , 120 ) and/or at least one dimension of the coupling element (CPL 1 , CPL 2 ) of its co-ordinated resonance circuit ( 100 - 1 , 100 - 2 ) under the consideration that the length of each of the coupling elements (CPL 1 , CPL 2 ) must be shorter than λ/4 with λ representing the wavelength of the signal to be converted and/or by adjusting the spacing between the coupling elements ( 110 , 120 ) of said two resonance circuits; and the resonance frequencies set up in the first and second resonance circuit ( 100 - 1 , 100 - 2 ) are identical and represent one single centre frequency of the bandpass filter characteristic.