Amplitude modulated active method for plasma density measurements

An active system for plasma density measurement using an amplitude modulated microwave carrier signal is described. For plasmas of higher density, IR or visible carrier signals may be used. Adjacent-mode competition is avoided by choosing the wavelength of the modulating signal to be comparable to the active delay-line oscillator's feedback path length. Although the technique described is intended for use with plasma, it can be applied to measurements of other dielectrics