A 3-D Analysis of a Microfabricated Ladder Slow-Wave Structure for a Millimeter-Wave Traveling-Wave Tube

The design and the analysis of a ladder slow-wave structure (SWS) operating at 50 GHz is presented. A 3-D particle-in-cell (PIC) modeling of a ladder SWS is presented for the first time. Compared with a conventional helix circuit, the ladder SWS provides wide bandwidth, high interaction impedance, and ease of manufacturing at millimeter wavelengths. A small-signal code based on Pierce's theory was developed to determine the dimensions and the small-signal characteristics of the device. Cold- and hot-test simulations were performed using High Frequency Structure Simulator

and VORPAL

codes. VORPAL, a 3-D PIC simulator that makes use of the conformal finite-difference time-domain method, predicts a small-signal gain of 15 dB and an instantaneous bandwidth of 6% for a 68-period ladder SWS that is driven by a 22-kV and 196-mA electron beam. Dispersion characteristics, large-signal characteristics, and nonlinear-beam dynamics are investigated.