A wideband power amplifier, comprising: a signal power divider configured to divide an input signal into first and second signals (S1, S2) by a predetermined signal power ratio; a set of amplifiers connected in parallel to amplify signals from input ports of the amplifiers, wherein the set of amplifiers comprises a main amplifier configured to receive and amplify the first signal and a peak amplifier configured to receive and amplify the second signal; a matching network configured to match the main amplifier and the peak amplifier with predetermined load values, the matching network having a first impedance frequency response as a monotonically decreasing function of frequency of the amplified signals in a target operation frequency range, wherein the matching network comprises a first output matching network configured to receive the amplified first signal and to output a third signal and a second output matching network configured to receive the amplified second signal and to output a fourth signal (S2'); a converter network configured to convert the third signal and the fourth signal (S2'), wherein the converter network comprises a first λ/4 impedance inverter, a second λ/4 impedance inverter and a node, wherein the first λ/4 impedance inverter is configured to receive the third signal and to output a fifth signal (S1'), wherein the node is configured to combine the fifth signal (S1') and the fourth signal (S2') as a sixth signal, and wherein the second λ/4 impedance inverter is configured to invert the sixth signal; and an impedance flattening network configured to have a second impedance frequency response as a monotonically increasing function of frequency of the amplified signals in the target operation frequency range, characterised in that the impedance flattening network is arranged in series between the converter network and an output port of the power amplifier, wherein the impedance flattening network includes a resonator having a parallel of an inductance L and a capacitance C, and wherein the resonator has a resonance frequency at a second harmonic frequency of an operation center frequency of the wideband power amplifier. a signal power divider configured to divide an input signal into first and second signals (S1, S2) by a predetermined signal power ratio; a set of amplifiers connected in parallel to amplify signals from input ports of the amplifiers, wherein the set of amplifiers comprises a main amplifier configured to receive and amplify the first signal and a peak amplifier configured to receive and amplify the second signal; a matching network configured to match the main amplifier and the peak amplifier with predetermined load values, the matching network having a first impedance frequency response as a monotonically decreasing function of frequency of the amplified signals in a target operation frequency range, wherein the matching network comprises a first output matching network configured to receive the amplified first signal and to output a third signal and a second output matching network configured to receive the amplified second signal and to output a fourth signal (S2'); a converter network configured to convert the third signal and the fourth signal (S2'), wherein the converter network comprises a first λ/4 impedance inverter, a second λ/4 impedance inverter and a node, wherein the first λ/4 impedance inverter is configured to receive the third signal and to output a fifth signal (S1'), wherein the node is configured to combine the fifth signal (S1') and the fourth signal (S2') as a sixth signal, and wherein the second λ/4 impedance inverter is configured to invert the sixth signal; and an impedance flattening network configured to have a second impedance frequency response as a monotonically increasing function of frequency of the amplified signals in the target operation frequency range, characterised in that the impedance flattening network is arranged in series between the converter network and an output port of the power amplifier, wherein the impedance flattening network includes a resonator having a parallel of an inductance L and a capacitance C, and wherein the resonator has a resonance frequency at a second harmonic frequency of an operation center frequency of the wideband power amplifier.