Measurement of Noise Figure of an X-Band Waveguide Mixer with Tunnel Diode

摘要

Noise-figure measurements of an X-band tunnel diode mixer must be carried out with extreme care, since spurious responses can often produce incorrect results. At microwave frequencies, a waveguide system with a plunger at one side of the diode is used and it is important that one terminal of the diode be isolated from the waveguide wall when the bias voltage is applied. The output of the mixer containing the difference frequency is connected to the input of an amplifier with a series combination of bias components. This series combination contains additional inductance and capacitance other than that of the 30 Mcps amplifier and can produce resonance effects when the tunnel diode is operated in the positive region close to the peak current, thereby leading to an error in the noisefigure measurement. Correct and incorrect noise figures are compared. A noise figure of 3 db, free of spurious responses, has been measured for a tunnel diode (D4168D) operated at a pump frequency of 9.205 Gc and a difference frequency of 30 Mcps in an X-band waveguide mixer. (Author)