Developing a Load-Line Concept to Study the Extended Interaction Oscillators

Extended interaction oscillators (EIOs) are millimeter-wave to terahertz vacuum electronic sources, based on the Smith-Purcell (Cerenkov) interaction between an electron beam of low to moderate voltage and a resonant slow-wave structure. They have been analyzed using the power-balance and Particle in cell (PIC) methods. In this paper, based on power-balance method, a load-line concept is introduced to investigate the EIOs. By this approach, the analysis of EIOs is much faster than the PIC method, and a wider quantitative and qualitative insight into the interaction process is obtained compared with the common power-balance method. To achieve the optimum RF power from an EIO, a region on the defined “beam-line” curve is assigned. A “frequency-shift line” curve is also derived to obtain the electronic tuning of the oscillator. In addition, the correct steady state in the multivalued solution conditions can be selected, which is not evident in the power-balance approach. A 94-GHz sheet-beam EIO is analyzed and optimized in this way, and the results are compared with those of a PIC solver.