A highly efficient X band BWO with an inhomogeneous slow wave structure

We present a novel, 3 stage inhomogeneous slow wave structure (SWS) to enhance the efficiency of a high power backward wave oscillator. The design features 3 sections of SWSs, each with different periods combined to form a single SWS. A new technique for increasing both the interaction impedance and phase velocity of the TM₀₁ mode in each section is introduced. An eigen mode analysis of a single SWS cell is carried out to establish the optimum operating point for an X band BWO. Finally we present simulation results of an X band BWO generating 6.44 MW of power at 8.47 GHz with 70% peak power efficiency.