Design, Simulation, and Cold Test of a W-Band Double Nonparallel Staggered Grating Backward Wave Oscillator

A novel double nonparallel staggered grating (DNPSG) slow wave structure (SWS) is proposed to enhance the coupling impedance in a W-band backward wave oscillator (BWO) driven by a pseudospark-sourced sheet electron beam. The DNPSG SWS has been shown a broadband of 72-125 GHz and a higher coupling impedance compared with the traditional double staggered grating (DSG) SWS in simulation. The DNPSG BWO structure consisting of ten SWS units and a broadband output structure is designed and fabricated. In the cold test of the DNPSG BWO, the measured S-11 (double of the losses in the DNPSG BWO) is above -10 dB in most of the band, which is satisfactory in the pseudospark-driven high-power device. The hot-test performance of the DNPSG BWO is analyzed by particle-in-cell (PIC) simulation in a beam voltage range of 14-90 kV and a current density range of 1.5-5 x 10(7) A/m(2), obtaining a high output power (max. 190 kW) over an ultra-wide tuning band of 38 GHz (75-113 GHz) due to enhanced coupling impedance.