The use of coaxial cable as a transmission line becomes increasingly detrimental as the operating frequency increases. Microwave and mmWave communication technologies employ waveguide transmission lines between the radio and antenna to overcome the electrical limitations of coaxial cable.

A waveguide is a type of physical structure that directs electromagnetic waves from one point to another. It functions as a conduit for these waves, ensuring they travel in a specific direction without loss of signal strength. Common waveguide shapes include:

  • Rectangular: Characterised by a rectangular cross-section, this type of waveguide is widely used due to its simplicity and ease of manufacture. It supports a broad range of frequencies and allows for efficient transmission of electromagnetic waves.
  • Circular: This waveguide shape features a circular cross-section. It is typically used in applications where rotational symmetry is required, such as in radar systems. The circular shape allows for the transmission of waves in multiple modes.
  • Double Ridge: The double ridge waveguide has two ridges extending along the length of the guide. This design increases the bandwidth of the waveguide, making it suitable for applications that require a wide range of frequencies.
  • Elliptical: An elliptical waveguide has an elliptical cross-section. It offers a compromise between the rectangular and circular designs, providing low attenuation and supporting multiple modes.

Each waveguide shape offers unique advantages and is chosen based on the specific requirements of the communication system, such as the frequency range, power handling capacity, and physical constraints.

Internationally Standardised Waveguide Sizes
IEC / EIA / UK Designation Type Frequency Width Height
R3 / WR2300 / WG00 Rectangular 0.32 to 0.49 GHz 584.2 mm 292.1 mm
R4 / WR2100 / WG0 Rectangular 0.35 to 0.53 GHz 533.4 mm 266.7 mm
R5 / WR1800 / WG1 Rectangular 0.41 to 0.62 GHz 457.2 mm 228.6 mm
R6 / WR1500 / WG2 Rectangular 0.49 to 0.75 GHz 381 mm 190.5 mm
R8 / WR1150 / WG3 Rectangular 0.64 to 0.98 GHz 292.1 mm 146.05 mm
R9 / WR975 / WG4 Rectangular 0.76 to 1.15 GHz 247.65 mm 123.82 mm
R12 / WR770 / WG5 Rectangular 0.96 to 1.46 GHz 195.58 mm 97.79 mm
R14 / WR650 / WG6 Rectangular 1.13 to 1.73 GHz 165.1 mm 82.55 mm
R18 / WR510 / WG7 Rectangular 1.45 to 2.2 GHz 129.54 mm 64.77 mm
R22 / WR430 / WG8 Rectangular 1.72 to 2.61 GHz 109.22 mm 54.61 mm
R26 / WR340 / WG9A Rectangular 2.17 to 3.3 GHz 86.36 mm 43.18 mm
R32 / WR284 / WG10 Rectangular 2.6 to 3.95 GHz 72.14 mm 34.04 mm
R40 / WR229 / WG11A Rectangular 3.22 to 4.9 GHz 58.17 mm 29.08 mm
R48 / WR187 / WG12 Rectangular 3.94 to 5.99 GHz 47.549 mm 22.149 mm
R58 / WR159 / WG13 Rectangular 4.64 to 7.05 GHz 40.386 mm 20.193 mm
R70 / WR137 / WG14 Rectangular 5.38 to 8.17 GHz 34.849 mm 15.799 mm
R84 / WR112 / WG15 Rectangular 6.57 to 9.99 GHz 28.499 mm 12.624 mm
R100 / WR90 / WG16 Rectangular 8.2 to 12.5 GHz 22.86 mm 10.16 mm
R120 / WR75 / WG17 Rectangular 9.84 to 15 GHz 19.05 mm 9.525 mm
R140 / WR62 / WG18 Rectangular 11.9 to 18 GHz 15.799 mm 7.899 mm