A Ka-Band Radial Beam Oscillator With Phase-Velocity Tapering

This research article presents a high-power radial oscillator in the Ka-band equipped with a radial sheet electron beam. Radial beam devices outperform traditional devices by offering more extensive interaction spaces and reduced space charge effects. This advantage eliminates the necessity for external magnetic fields, efficiently solving the efficiency issues. The design parameters of the presented device for efficient operation in pi mode within the Ka-band frequency spectrum are identified through numerical analysis. The baseline model with a constant period is simulated using particle-in-cell (PIC) solver, and importantly, without an external magnetic field. The simulation features a radial beam cathode with an emission area of 2 pi x 107.5 x 0.7 mm, generating a current density of 444.37 A/cm(2). At 160- and 170-kV beam voltage, the device achieves efficiencies of 31.05% and 38.5%, with peak powers of 104.3 and 137.8 MW, respectively, while maintaining stable signal frequencies around 34.6 and 34.62 GHz. The baseline model's performance is further enhanced through various phase-velocity tapering techniques, including linear, exponential, and logarithmic methods. The impact of these velocity tapering approaches on beam-wave interaction is analyzed. Linear tapering, in particular, improves output power to 190.61 MW and efficiency to 53.39%, exceeding the constant period model's 137.8 MW power and 38.5% efficiency. Although exponential and logarithmic methods also boost efficiency, they are less effective than the linear approach. These tapering techniques lead to minor frequency shifts, indicating their structural influence on the oscillator's performance.