Frequency Conversion in a Microwave Discharge

One nonlinear property of a microwave discharge located between two closely spaced parallel plates whose dimensions are small compared to the wavelength is analyzed. This discharge geometry, with its small volume, permits the attainment of CW microwave power densities in the discharge of the order of 0.1 to 1 Mw/cm3. It is concluded that the high power density coupled with the high diffusion rate of the closely spaced parallel plates results in a modulation of the electron density at the microwave frequency. The source of this nonlinearity is postulated to be a modulation of the ionization frequency 𝒱i whose functional form is taken to be 𝒱i = α|vd| where vd is the ordered drift velocity and α is a proportionality factor constant in time. The theoretical analysis is compared to experimental results obtained by approximating the assumed geometry in an X-band and K-band frequency multiplier and in an X-band mixer. Harmonics up through the seventh at X band and up through the fourth at K band have been studied. Frequency mixing of 9- and 11-kMc signals to obtain a 20-kMc signal has yielded predictable results. Parametric amplification in a discharge is briefly considered.