magnetron microwave launcher design 2

[ProfDrK]

I plan to direct the output from an oven magnetron from a launcher/horn combination to dry wet soil as efficiently as possible. I have played with a couple of launchers, but despite an auto tuner showing no reflections, the (aircooled) magnetron overheats (over 100 C in a couple of minutes). When mounted back into the oven, it levels at 90 C. I think airflow is not an issue in my configurations. I noted two launchers have a grid of small holes and a dimple opposite the emitter on the sidewall of the waveguide..for what benefit? I will make another launcher and want to know besides the 1/4 wavelength back standoff, is there a trick I am missing that prevents overheating? Should the exit flange be placed at 1/2 wave from the emitter or is 1 lambda better? or is some other fraction better? All hardware is W284 size and I wonder if it shouldn't be bigger?

 

[logbook]

wow, that termite killer looks well dodgy !