An electromagnetic vibrator fixed on a screen initiates gas breakdown in the subcritical field of a microwave beam

Results of experimental investigation of the electric breakdown of air in a quasi-optical microwave beam with a deep subcritical field level are presented. The breakdown was initiated by a linear or $\Gamma$-shaped electromagnetic (EM) vibrator fixed on a screen. It is established that a vibrator positioned above the screen at a distance shorter than quarter-wavelength of the EM field can induce the electric breakdown of air at high pressures and relatively low field level. Using a $\Gamma$-shaped EM vibrator, it is possible to preset the spatial region of breakdown.