Balun transformer and transceiver

The invention relates to a balun transformer for converting an unbalanced signal into a balanced signal or vice versa and having a bandpass characteristic for bandpass filtering the signal being converted. Such balanced transformers are substantially known in the art and comprise a first electronic circuit for transceiving the unbalanced signal and a second electronic circuit for transceiving the balanced signal wherein the first and the second electronic circuit are non-galvanically coupled via coupling elements. It is the object of the present invention to reduce the size of such known balun transformer. This object is achieved by embodying both electronic circuits as individual resonance circuits 100 - 1, 100 - 2 being operated at their individual resonance frequencies representing the centre frequencies of the bandpass filter characteristic. Each of the individual resonance frequencies is preferably set-up by adjusting a 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 lambda/4. The invention further relates to a transceiver 400 comprising such a balun transformer 100.