Far Field Radiation Patterns from Open Ended Oversized Circular Waveguides and Identification of Multimode Outputs of Gyrotrons

摘要

The far field radiation patterns of TEmn-modes and TMmn-modes from openended circular multimode waveguides in the E-plane and H-plane are calculated. The possibility and convenience of identifying the operating mode mixture of high power gyrotrons with multimode output and analyzing the mode conversion properties of overmoded waveguide components by measuring the far field radiation pattern are studied. At certain angles radiated power is contributed only by one mode from every series of modes with the same m number. This character is very convenient for mode identification. Mode mixtures in overmoded waveguides might also be identified by directional couplers, each being prepared for the selective pick up of a particular mode. Measurements of the voltage traveling wave ratio in the waveguide by small probes can be related to the composition of the modes inside the multimode waveguide, but not at high powers.