A duplexer comprising: a first high-frequency filter, the first high-frequency filter comprising: - basic elements connected in series with an electroacoustic resonator each, - impedance converters connected in series between the basic elements, wherein - the impedance converters are impedance inverters, - the resonators of the basic elements are only series resonators, and - at least one of the resonators is tunable; a second high-frequency filter, the second high-frequency filter comprising: - basic elements connected in series with an electroacoustic resonator each, - impedance converters connected in series between the basic elements, wherein - the impedance converters are admittance inverters, - the resonators of the basic elements are only parallel resonators, and - at least one of the resonators is tunable; characterised in that the first high-frequency filter is used as a transmit filter for a transmit frequency band, and the second high-frequency filter is used as a receive filter for a receive frequency band when the transmit frequency band is below the receive frequency band, or the first high-frequency filter is used as a receive filter for a receive frequency band, and the second high-frequency filter is used as a transmit filter for a transmit frequency band when the transmit frequency band is above the receive frequency band. a first high-frequency filter, the first high-frequency filter comprising: - basic elements connected in series with an electroacoustic resonator each, - impedance converters connected in series between the basic elements, wherein - the impedance converters are impedance inverters, - the resonators of the basic elements are only series resonators, and - at least one of the resonators is tunable; - basic elements connected in series with an electroacoustic resonator each, - impedance converters connected in series between the basic elements, wherein - the impedance converters are impedance inverters, - the resonators of the basic elements are only series resonators, and - at least one of the resonators is tunable; a second high-frequency filter, the second high-frequency filter comprising: - basic elements connected in series with an electroacoustic resonator each, - impedance converters connected in series between the basic elements, wherein - the impedance converters are admittance inverters, - the resonators of the basic elements are only parallel resonators, and - at least one of the resonators is tunable; characterised in that the first high-frequency filter is used as a transmit filter for a transmit frequency band, and the second high-frequency filter is used as a receive filter for a receive frequency band when the transmit frequency band is below the receive frequency band, or the first high-frequency filter is used as a receive filter for a receive frequency band, and the second high-frequency filter is used as a transmit filter for a transmit frequency band when the transmit frequency band is above the receive frequency band. - basic elements connected in series with an electroacoustic resonator each, - impedance converters connected in series between the basic elements, wherein - the impedance converters are admittance inverters, - the resonators of the basic elements are only parallel resonators, and - at least one of the resonators is tunable; characterised in that the first high-frequency filter is used as a transmit filter for a transmit frequency band, and the second high-frequency filter is used as a receive filter for a receive frequency band when the transmit frequency band is below the receive frequency band, or the first high-frequency filter is used as a receive filter for a receive frequency band, and the second high-frequency filter is used as a transmit filter for a transmit frequency band when the transmit frequency band is above the receive frequency band. the first high-frequency filter is used as a transmit filter for a transmit frequency band, and the second high-frequency filter is used as a receive filter for a receive frequency band when the transmit frequency band is below the receive frequency band, or the first high-frequency filter is used as a receive filter for a receive frequency band, and the second high-frequency filter is used as a transmit filter for a transmit frequency band when the transmit frequency band is above the receive frequency band.