Topic: Electromagnetics
The EM wave which does not propagate through a rectangular waveguide with $a=30$ mm and $b=15$ mm is
- A. EM wave of frequency 4.5 GHz
- B. EM wave of frequency 5.5 GHz
- C. EM wave of frequency 50 GHz
- D. EM wave of frequency 300 GHz
Answer: A. EM wave of frequency 4.5 GHz
Explanation: Critical frequency for the dominant mode $TE_{10}$ is $f_{c}=\frac{v_{0}}{2a}=\frac{3\times10^{8}}{2\times30\times10^{-3}}=5~GHz$. So, the waves having the frequency above cut-off frequency will only pass. So, the EM wave of frequency 4.5 GHz will not pass.