Design of a High-Efficiency Ka-Band TWT Power Amplifier for Radar Applications

The design of a high-efficiency traveling-wave tube (TWT) based on a nonconventional folded waveguide slow wave structure (FW-SWS) operating over 34–36 GHz for naval and ground Ka-band radars is presented. The ridge-vane-loaded FW structure allows a good compromise between high interaction impedance and wide bandwidth along with a low weight required for aircraft radar applications and a simple planar manufacturing process structure. Small-signal simulations are performed with a custom interaction impedance evaluation program. The CST suite 2021 3-D electromagnetic simulation code is used for the prediction of the dispersion diagram. Starting from a sensitivity analysis of the FW in terms of width, a high electronic efficiency value of 14.6% is obtained with a reduction in the width of 0.1 mm. To further improve electronic efficiency, a negative phase-velocity step tapering technique is applied and a value of 15.4% from 34 to 36 GHz is obtained. Finally, under an optimized beam voltage and a current of 21 kV and 550 mA, respectively, a peak value of the output power of approximately 1.7 kW and an output power of 800 W with a duty cycle of 12% over the frequency band are obtained. Measurement results of the interaction impedance of a ridge-vane-loaded FWG structure composed of a ten-period high-conductivity oxygen-free copper carried out according to the Langerstrom perturbation method confirm the goodness of the simulation results.