Which waveguide mode is preferred for efficient power transmission?

Hello,

I have a general question concerning modes in waveguides. A waveguide is, simply put, a high pass filter with the dominant mode (cut off frequency) determined by the smallest allowed m & n integers. Each mode has its own cut-off frequency. My question is what happens if the frequency of the wave you’re transmitting is above the cut-off of several different modes. To illustrate, assume a 3 GHz wave that can be transmitted by a rectangular waveguide with the following modes: TE_10, TE_11, TE_21, TE_22.

Does it make a difference if there are many (compared to few) more modes suitable for transmission of a wave at a frequency?

Which mode is preferred for efficient power transmission?

How do you excite a single mode, if possible?

My textbook mainly solves the wave equations and uses m &n as eigenvalues. Physically, is there a difference between a TE and a TM waveguide?


TIA

In general, the lowest order mode, (m + n = 1), is preferred. This is intentionally excited in the guide with a probe or loop at the point where the electric or the magnetic field is maximum.

This is why there are a standard set of different sizes so that you can select the one for your frequency and it will have only one mode.