A low-noise directional amplifier includes a first port, a second port, a first coupler and a second coupler. The first port is coupled to a first coupler. The low-noise directional amplifier also includes at least two phase preserving amplifiers, a first phase preserving amplifier connected to the first coupler and a second coupler, and the second phase preserving amplifier connected to the first coupler and the second coupler.

Exemplary impedance matching circuit for an amplifier device comprises a broadband impedance transformer configured to transform, over a fundamental frequency range, an impedance associated with an input port or an output port of the impedance matching circuit; and to transmit RF signals having a fundamental frequency within the fundamental frequency range. The impedance matching circuit also includes a phase shifter circuit configured to transmit, with substantially matched impedance, the RF signals having a fundamental frequency within the fundamental frequency range, and to phase-shift higher-order harmonics of the RF signals. The impedance matching circuit also includes a high-pass impedance transformer configured to match an impedance of the RF signals having a fundamental frequency within the fundamental frequency range; and to transmit, with low reflection, second-order harmonics of the RF signals. Exemplary embodiments also include amplifier circuits comprising an RF amplifier and embodiments of the impedance matching circuit.

An impedance matching circuit be connected to a non-linear impedance including a superconductor, includes a first terminal designated first connection port to be connected to a first connector of the non-linear impedance, a second terminal designated second connection port to be connected to a second connector of the non-linear impedance, a third terminal designated input/output terminal to receive the signal to amplify and a fourth terminal designated supply terminal to be connected to a polarisation source and configured so that a voltage V is applied between the first connection port and the second connection port. The circuit further includes a plurality of passive electrical components.

An amplifier circuit includes an RF amplifier that is configured to amplify an RF signal between a first terminal and a second terminal across an RF frequency range. The amplifier circuit includes a multi-stage impedance matching network having a broadband impedance transformer, a phase shifter, and a high-pass impedance transformer connected in series with one another between a first port of the amplifier circuit and the first terminal. The broadband impedance transformer provides impedance transformation in the RF frequency range. The phase shifter shifts a phase output port reflection coefficient in a second order harmonic frequency range that overlaps with a second order harmonic of the fundamental RF frequency. The high-pass impedance transformer transmits an RF signal in the RF frequency range while providing impedance transformation in the RF frequency range and transmits RF signals in the second order harmonic frequency range with low impedance.

An impedance matching circuit be connected to a non-linear impedance including a superconductor, includes a first terminal designated first connection port to be connected to a first connector of the non-linear impedance, a second terminal designated second connection port to be connected to a second connector of the non-linear impedance, a third terminal designated input/output terminal to receive the signal to amplify and a fourth terminal designated supply terminal to be connected to a polarisation source and configured so that a voltage V is applied between the first connection port and the second connection port. The circuit further includes a plurality of passive electrical components.