New results of experimental investigations of the possibility and conditions of initiation of electric breakdown of air in a quasi-optical microwave beam with a subcritical field level are described. The breakdown is initiated by a linear electromagnetic (EM) vibrator placed in a traveling EM wave on the surface of the dielectric sheet facing toward the wave vector k, on its opposite surface and near it. Simultaneously, theoretical calculations of the induced electric field near its ends were carried out for all variants of the vibrator location considered in the experiments. Numerical estimates and experimental results have shown that the placement of the vibrator on the surface of a dielectric plate can initiate a breakdown of air at significantly lower levels of the EM field in the microwave beam compared to the case of placing the vibrator in “free space”, i.e.at the absence of any dielectric plates

The results of experimental studies of combustion of propane–air gaseous mixture when it was ignited by a microwave discharge have been described. The mixture with different propane content fills a sealed radio-transparent tube placed along the axis of a focused linearly polarized quasi-optical microwave beam at atmospheric pressure. Multi-point ignition of the mixture is carried out near one end of the tube by a pulsed microwave discharge with a surface-developed streamer structure. The growth of gas pressure in the tube as propane burned was recorded in the experiments. The microwave pulse energy being invested in high-temperature discharge plasma has been estimated in them. The minimum percentage of propane in the mixture at which the microwave discharge ignites it has been determined in experiments. The time dependence of the pressure increase in the tube as the propane burns determines the combustion process dynamics.