Wideband Power Combining of Four Microfabricated W-Band Traveling-Wave Tubes

Wideband power combining of four W-band microfabricated traveling-wave tubes (TWTs) is presented. The proposed TWTs are based on a planar helix slow-wave structure (SWS) with straight-edge connections (PH-SEC) that can be microfabricated with stripline input-output feed. A novel 1:4 WR-10 waveguide-to-stripline power divider- combiner is designed that covers the frequency range of 92-104 GHz. The simulation results show that S
₁₁
is less than -20 dB and the magnitude and phase differences among the four output signals are less than 0.01 dB and 0.41°, respectively, indicating a power combining efficiency as high as 99.9%. The power divider, four PH-SEC SWSs, and the power combiner are assembled and the performance of the overall assembly is checked by simulation. The overall S
₁₁
is better than -15 dB in the frequency range of 91.7-100.7 GHz and S
₂₁
is better than -12.3 dB. Effects of power and phase variation of individual TWTs have also been considered. With four 5-kV and 10-mA sheet electron beams, particle-in-cell simulations show that the combined TWTs can give 25-W saturation peak power at 94 GHz with a gain of 18 dB.