Left is one of the first patents on the multi-cavity magnetron, filed in Germany in November 29, 1935 by H.E. Hollmann. The patent explains in explicit detail how the cavity magnetron works and that it can have many configurations including any even number of cells. Also stated is that a fluid is used between the outer magnet and the inner cylinder to cool the device.

Below is the patent for split-anode magnetron and its controlling circuit. Other magnetron patents by Hollmann are shown below.