The Rectangular Waveguide Cut-Off Frequency

When selecting an electrical component, designers should focus on the component’s specification or rating. While there are many specifications to consider, there are a few key ones to focus on in each component being used in a circuit. 

In RF and microwave circuits, the cut-off frequency is a significant specification for waveguides. In a rectangular waveguide being used to transfer energy, the rectangular waveguide cut-off frequency determines when the waveguide becomes obsolete, which is whenever it reaches below the cut-off frequency. A similar condition applies to circular waveguides, however, in this article, we will focus on the rectangular waveguide cut-off frequency.

Waveguide Cut-Off Frequency

Waveguides are hollow metallic structures that carry signals from one end to another. All the signals that propagate through a waveguide are above a certain frequency, called the cut-off frequency. Below the cut-off frequency, waveguides fail to transfer wave energy or propagate waves.

Cut-off frequency can also be described as the frequency above which the waveguide offers minimum attenuation to the propagation of the signal. Frequencies below the cut-off frequency are attenuated by the waveguide. The signal propagation through a waveguide is dependent on the signal wavelength as well. When a wavelength is too long, the waveguide stops carrying signals and becomes inoperative.