# Waveguide of travelling waves

## Homework Statement

How to solve this problem?

An air-fi lled waveguide of rectangular cross-section (1 cm x 2 cm) is used to
carry EM waves at a frequency of 10 GHz.
Show that only the TE01 mode can be used?

I tried to find the cut-off frequency ( 7.5GHZ) and is that enough to prove that only TE01 can be used?

rude man
Homework Helper
Gold Member

## Homework Statement

How to solve this problem?

An air-filled waveguide of rectangular cross-section (1 cm x 2 cm) is used to
carry EM waves at a frequency of 10 GHz.
Show that only the TE01 mode can be used?

I tried to find the cut-off frequency ( 7.5GHZ) and is that enough to prove that only TE01 can be used?

The answer to your question is no. You haven't justified your answer mathematically.

Use the formula for cutoff frequency fc(m,n,a,b) where m,n are the mode descriptors Tmn and a and b are the waveguide dimensions. Then show that the only possible mode is TE01. Remember to distinguish between a and b with respect to the cutoff formula.

PS the TM01 mode requires one extra step beyond just using the fc formula.

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