Why are waveguides preferred over conventional coaxial transmission lines at microwave frequencies?

Waveguides are preferred over conventional coaxial transmission lines at microwave frequencies primarily because they have considerably less loss. At microwave frequencies, the attenuation of signals can become significant in coaxial cables due to dielectric losses, skin effect, and other factors. Waveguides, being hollow structures, do not rely on dielectric materials in the same way that coaxial systems do, which minimizes dielectric loss and leads to improved efficiency in the transmission of high-frequency signals.

Additionally, waveguides support the propagation of electromagnetic waves in specific modes, which can help to reduce losses associated with unwanted radiation and reflections. Their design allows them to handle higher power levels without significant voltage standing wave ratio (VSWR) issues, which is particularly advantageous in microwave applications.

While the other statements highlight certain benefits of waveguides, they do not address the primary reason that makes them preferable at microwave frequencies. Waveguides may indeed be smaller and easier to handle, lighter due to their hollow construction, and potentially less affected by moisture, but these characteristics are secondary to the critical factor of lower loss in signal transmission.