Demonstration of the Electronic Cutoff Field in Millimeter-Wave Extended Interaction Oscillators

For extended interaction structure devices (EIDs), the determinants of field flatness are analyzed. It is found that the flatness of field distribution is determined by a cutoff condition existing in EIDs, which is based on the concepts of both resonant cavity and wave propagation. Such an analytical conclusion is verified by a novel scheme for the measurement of field distribution in an extended interaction oscillator (EIO) based on the perturbation technique. The sinusoidal-like axial field components with different flatness are obtained by utilizing the measured frequency shifts. Based on the cutoff condition, three field distribution patterns are established, including middle-concentrated, flat-distributed, and side-concentrated types. Particle-in-cell (PIC) simulations of a ${W}$ -band EIO show that three field distribution patterns have the advantages of low surface-loss power, high power-capacity, and low oscillating-threshold, respectively.