Which dimension determines the frequency range of a waveguide?

The "a" dimension in a waveguide refers to the larger of the two dimensions of the rectangular waveguide cross-section, which plays a critical role in determining the cutoff frequency and the frequency range through which the waveguide can effectively operate. When establishing the mode of propagation for electromagnetic waves in a rectangular waveguide, this dimension directly influences the wavelength and therefore the frequency range that can be transmitted. The fundamental mode, typically the dominant mode, can propagate as long as the frequency of the signal exceeds the cutoff frequency, which is dictated by this "a" dimension.

Understanding this concept is crucial in waveguide design, as the selected dimension will ensure that the desired frequencies can travel with minimal attenuation and distortion. It is key to maintaining effective signal integrity in high-frequency applications, such as radar and microwave communications often utilized in aviation and military contexts.