Experimental Studies of an Overmoded Millimeter-Wave BWO

Experimental results are presented for a high power backward wave oscillator (BWO). An overmoded slow wave structure (SWS) with a relativistic hollow electron beam was used to increase the interaction impedance and to avoid RF breakdown. The results of experiments with this overmoded (D/λ ≈ 8) SWS successfully produced high power radiation at 78.5 GHz. The rectangular corrugation SWS can be fabricated more easily compared to a sinusoidal one. In order to select a higher order mode as the operating mode, a mode selection technique was utilized. In this work, the experimental results were compared with calculations performed using the MAGIC PIC code; the measured data are shown to agree favorably with simulations.