The unimode magnetron

A new kind of multicavity anode is used to solve the moding problem in the magnetron. The anode consists of two or more sections of coupled resonators with dissimilar frequency phase shift characteristics but with a common mode point. At this common mode point the 2nπ reentrant condition is satisfied and therefore it is the only fundamental mode of oscillation that can be supported by the structure. Several versions of unimode anodes were cold tested with successful results. Uniform field patterns were obtained at the mode desired while the patterns corresponding to other modes were distorted to various degrees. The most thoroughly tested anode was one which consisted of cavities of three different sizes arranged in random order. These cavities were tuned by non-uniform straps to a common frequency at π-mode. This anode structure was incorporated into a high power magnetron. Measured under actual operating conditions, the unimode tube showed a slight increase in power output and efficiency over the unmodified tubes and the third harmonic power output was reduced by 30 db.