Waveguide is a metallic-sheathed physical transmission medium; unlike a cable, waves propagate along it without an inner conductor.
Microwave energy travels through guided media in different modes. A microwave waveguide with a single conductor is a high pass filter; these structures have a cutoff frequency.
Single-conductor options include:
• Rectangular waveguide
• Circular waveguide
• Elliptical waveguide
• Ridged waveguide
• Corrugated waveguide
Attenuation in waveguide can be caused by dielectric loss, if the waveguide is full of dielectric, or by conductor loss due to the metal structure’s finite conductivity. The various modes of operation available depend on the desired frequency, as well as the size and shape of the waveguide itself.
The maximum attenuation values—measured in decibels per meter (dB/m)—are published by the International Eletrotechnical Commission based in Switzerland (IEC). Waveguide attenuation is published by manufacturer.
For example, an EWP52 elliptical waveguide (attenuation: 3.93 dB/100 m (1.2 dB/100 ft) @ 6.175 GHz will attenuate 2.4 dB over a 61 m (200 ft) length. Microwave waveguides are maintained under dry air or dry nitrogen pressure to avoid moisture condensation that would impede their performance.
