Why don’t VHF or UHF antennas use waveguides as feed lines?

VHF (Very High Frequency) and UHF (Ultra High Frequency) antennas typically do not utilize waveguides as feed lines primarily because the dimensions required for waveguides become impractical at these wavelengths. Waveguides function by confining and guiding electromagnetic waves, but their internal dimensions need to be compatible with the wavelengths being transmitted or received.

As the frequency increases, the wavelengths decrease, which implies that the dimensions of the waveguide must also decrease. However, at VHF and UHF frequencies, the dimensions can become quite small, which can lead to manufacturing challenges and difficulties in handling, connecting, and installing these components. Smaller waveguides might also be less robust, potentially affecting performance.

In contrast, coaxial cables and other types of transmission lines are more versatile and easier to work with for these frequency ranges. They are capable of being produced in practical sizes while maintaining efficiency. Thus, while factors like cost, weight, and efficiency at lower frequencies can play a role in the choice of transmission line, the impracticality of waveguide dimensions at VHF and UHF frequencies is the primary reason they are not used in this context.