Abstract: A bias circuit for a Doherty amplifier, characterized by comprising: an input port with an input impedance, wherein the input port is configured to receive a bias signal from a power supply; a first output port configured to provide a bias signal to an amplifier; a second output port configured to provide a bias signal to an amplifier; a two port impedance transformer with an input connected to the first input port, and an output of the two port impedance transformer having an intermediate impedance; an in-phase N-port dividing impedance transformer with an input connected to the output of the two port impedance transformer, wherein the in-phase N-port dividing impedance transformer comprises: a first output connected to the first output port having a first output impedance; and a second output connected to the second output port having a second output impedance.

Abstract: A method and a system (13) for evaluating a lower filter part (2) of a cavity filter including a bottom plate from which wall portions and at least one resonating element extend in an upward direction, wherein the method comprises: —scanning the lower filter part using a laser scanning assembly (14) to collect data relating to shapes and dimensions of the lower filter part, —comparing the collected data with reference data to determine whether the lower filter part fulfils predetermined quality requirements. A method for manufacturing a cavity filter includes evaluating a filter body of the lower filter part prior to assembling the cavity filter, wherein the step of assembling the cavity filter is only carried out if the filter body fulfils the predetermined quality requirements.