The source of the radiation used in the photographs was a permanent magnet magnetron. It operated at about 9.6 GHz, 3.3 cm. wavelength. The output was in the form of short pulses, 1 microsecond in length, at a repetition rate of about a thousand pulses a second. The peak power output was about 100 kilowatts, or an average power of 100 watts. In those days the radiation was handled in a manner that would bring criticism in later years when microwave ovens were being introduced and everyone became sensitized to the possible harm the radiation could cause to human biology. In later life I did not often use high power, that is, power above a few milliwatts. But when I did I always had to make sure I could justify the procedures I used did not allow the radiation to produce harmful affects on my colleagues.
The frequency I used was 4 times that used in microwave ovens today. The wave guide, the rectangular tube that leads the radiation from the magnetron to the horn antenna, is 1 inch by 1/2 inch in cross section.
Left click on photo to see it in its actual size.