What is the primary lower-frequency limitation of waveguides?

The primary lower-frequency limitation of waveguides arises from their physical size. Waveguides operate by supporting specific modes of electromagnetic waves, which depend on their dimensions. They are designed to confine and direct the propagation of these waves; however, for effective guidance, the dimensions of the waveguide must be comparable to the wavelength of the signals being transmitted.

As the frequency of the signal decreases, the corresponding wavelength increases. For lower frequencies, if the physical dimensions of the waveguide are not sufficiently large relative to the wavelength, you may encounter issues such as mode cutoff, where the wave can no longer be guided effectively. This means that to operate at lower frequencies, a waveguide must be larger, which can lead to practical limitations in design and implementation.

This aspect of physical size plays a crucial role in determining the usable lower frequency limit, making it the key limiting factor for waveguide performance in lower frequency ranges.