High-power microwave (HPM) beams are used in space science for transferring energy from Earth-to-space, space-to-Earth, and space-to-space. Increase of the power of the microwave beam of a high-power microwave pulse compression system (HPMS) without any changes in its weight and size characteristics is currently an urgent task. Losses in a plasma of gas discharge tube of microwave switch of a HPMS may reach up to 50% at output energy. Understanding the process of microwave frequencies interaction with plasma, as well as microwave frequencies parameters, will reduce the losses in the gas-discharge tube of the switch during energy output. This will increase the power of the HPMS microwave beam at the same weight and size characteristics, which will reduce the cost of deploying the microwave energy in the Earth orbit. This paper presents results of an experimental study of H11 wave switching in interference microwave switches based on TE-tees made from S-band circular waveguides made for energy output devices in resonant microwave compressors. The switching is carried out by the plasma of a gas microwave discharge initiated in a quartz tube located along the diameter of the waveguide. The simulation experiments at high-power levels helped to determine the basic conditions for effective switching. It is shown that the use of S-band circular waveguide switches made from circular waveguides in resonant microwave compressors makes it possible to switch a wave with power up to 0.5 GW and form stable nanosecond microwave pulses with power up to 1 GW and a repetition rate up to 100 Hz.