What is used as a dielectric in waveguide?

In waveguides, dielectric materials are used to separate conductive elements and influence the propagation of electromagnetic waves. Common dielectric materials include air, plastics, ceramics, and glass, depending on the frequency range and application. These dielectrics help maintain the waveguide's operational efficiency by reducing signal loss and controlling the wave's mode structure. The choice of dielectric affects the waveguide's characteristics, such as its cutoff frequency and bandwidth.