Operation and optimization of gated field emission arrays in inductive output amplifiers

In an inductive output amplifier, an emission-gated electron beam induces high-frequency fields in an output circuit via displacement current, not convection current. Emission-gated electron beams experience strong interactions when traversing a resonant or synchronous electromagnetic field, and this strong interaction is responsible for both the interesting nonlinear physics and the attractive efficiency and compactness of emission-gated amplifiers. Field emission cathodes, due to their extremely low electron transit time and high transconductance, offer the opportunity to extend the advantages of emission gating into C and X band. This paper presents design criteria for the joint optimization of the field emission array (FEA) structure and the RF input and output circuits of inductive output amplifiers. We find that while output circuits yielding net efficiencies of 50% or greater are well within the state of the art, the gain is likely to be moderate (10-20 dB). With today's FEA performance, a desirable operating regime is achievable, yielding a new class of compact, highly efficient, and moderate gain power booster amplifiers.