Wideband power combining of Ka-band microfabricated traveling wave tubes

Wideband power combining of two Ka-band traveling wave tubes (TWTs) is reported. The TWTs are based on a configuration of planar helix slow-wave structure (SWS) with straight-edge connections (PH-SEC) that can be microfabricated. WR-28 waveguides are used as the input and output ports. A wideband transition between waveguide and PH-SEC enables wideband power division and power combining. Transient simulations of two 150-period SWSs with waveguide power divider and combiner show that in the frequency range 26.5 GHz ∼ 35.5 GHz, S11 is less than −20 dB and S21 is better than − 5.5 dB. Using two 3.7 KV and 10 mA electron beams, the PIC simulation results show that the gain can reach 31 dB at 30 GHz, with a 3-dB bandwidth of 23 % centered at 30.5 GHz.