Why not use an open waveguide to achieve a pure standing wave state

The influence of external electromagnetic field distribution. The standing wave coefficient of the open-circuit waveguide is affected by the distribution of electromagnetic fields in the outside world, and the actual experiment is not the ideal open-circuit, and other objects next to the opening will also affect the standing wave data, so that the standing wave coefficient of the open-circuit waveguide is not equal to infinity. When the terminal load is short-circuited or open-circuited, the transmission line is pure standing wave, and all the energy is reflected.