Abstract: The specification discloses a low noise parametric amplifier for use with a radar receiver. A Gunn diode oscillator is provided to generate a pump frequency. A bandpass filter filters the pump frequency and applies the pump power through a waveguide having a reduced height portion employing a multisection Chebycheff transformer. A coaxial signal input line connects through the waveguide to a coaxial idler section which is provided to terminate the signal input line and to match the signal and idler frequencies. A varactor diode assembly is mounted on the center conductor of the signal input line and the idler section. A cup member is attached to the diode assembly for matching the parallel resonance of the diode assembly to the pump frequency.