Spectral breaking of high power microwave pulse propagating in a self-generated plasma

Summary form only given, as follows. It is shown that a high power microwave pulse may cause the breakdown of background gas and generate a plasma which varies rapidly in space and time. Such a plasma can effectively modify the spectral content of the pulse, producing both frequency upshift and downshift. Both experimental evidence and theory are presented to demonstrate this phenomena. The experiment is conducted in a Plexiglas chamber filled with dry air. A microwave pulse is fed into the chamber through an S-band horn at one side. A second S-band horn, placed at the opposite side of the chamber, is used to receive the transmitted pulse. The power of the incident pulse is held at a fixed level. By varying the background air pressure, the collision frequency and ionization frequency are changed accordingly. The background pressure is always operating in the region below that giving the Paschen breakdown minimum. Thus, as the pressure is increased to a certain level, the ionization becomes too fast and the spectrum of the transmitted pulse breaks up into two peaks, one has an up shifted frequency and the other a down shifted frequency. The results show that the amount of frequency upshift and downshift are correlated to the ionization frequency and the loss of the wave in the self-generated plasma, respectively. Using the theoretical model developed in the previous work, the experiments are also simulated numerically. It is shown the numerical results agree well with the experimental observations.