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 pseudosparksourced 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 S11 (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 × 107 A/m2, obtaining a high output power (max. 190 kW) over an ultrawide tuning band of 38 GHz (75–113 GHz) due to enhanced coupling impedance.