Broadband superheterodyne tracking circuits for millimeter-wave measurements

Superheterodyne stimulus-response measurements can be made with high dynamic range, but are often sensitive to oscillator frequency drift and noise. The usual techniques for reducing this sensitivity often become impractical at millimeter-wave frequencies and above. This paper describes a feedforward tracking technique and its application to single frequency millimeter-wave interferometry and Doppler-shift scattering measurements on tokamak plasmas. Swept frequency transmission measurements can also be made with high dynamic range using this technique.