An analytical method of metal periodic slow-wave structure for rectangular cross-section Cerenkov maser

The dispersion characteristics of metal periodic slow-wave structure in rectangular cross-section Cerenkov maser have been analyzed. The effects of the geometrical parameters on the dispersion curves were investigated. In order to avoid the reflect oscillation induced by the changes at two ends of the slow-wave structure, the taper for matching the smooth waveguide and the slow-wave structure was analyzed by use of equivalent circuit method. Through comparing the linear, the two-piece linear and the exponential tapers, we know that the exponential taper gives the lowest total power reflection coefficient at the end, and the total change is mild. So the exponential taper can be used as an optimal solution for transition between slow and fast modes. The effects of frequency and fabrication error to the exponential taper were analyzed. The lower the frequency is, the lower the total power reflection coefficient is. Under the same frequency, the lower fabrication errors smooth the abrupt jumps of the total power reflection coefficient. With this analysis, an exponential taper with a total power reflection coefficient less than 0.01 was designed to attain a good match between the working mode and the fast wave mode. This method is more concise than the coupled mode theory, and the results of the two methods are consistent.