1. O. Buneman, inCrossed Field Microwave Devices, edited by E. Okress (Academic Press Inc., New York 1961), Chap. 5.
2. R. W. Gould, Electron Tube and Microwave Laboratory, California Institute of Technology, Technical Report No. 3 (1955).
3. W. Knauer, Hughes Research Laboratory, Research Report 332 (1960).