The environment within a waveguide is under positive pressure. This pressurization serves to ensure that the waveguide leaks out rather than in and prevents vapor, dust, and other particulates from entering the waveguide. Particulates in the waveguide can cause reflection, which can be measured as VSWR (voltage standing wave ratio), and cause signal loss or attenuation. In most communication applications, a dehydrator will maintain a clean, dry, particulate-free environment within the waveguide.