Question

Difference between rectangular waveguide and circular waveguide

Answer 1

Rectangular waveguide and circular waveguide are metal hollow structure used to guide EM waves. Depending upon their shapes they are classified as rectangular or circular. They are basically a passive microwave device and acts like a High Pass Filter.

Rectangular waveguide :

It is the earliest kind of the transmission lines. 

It supports supports TM and TE modes.

It does not support TEM waves because it has only one conductor and  cannot define a unique voltage. 

Conductor is filled with a material that has material with permittivity e and permeability m. 

Cutoff wavelength equation for is define below.

λc = 2/$\sqrt{ ( \frac{m}{a})^{2} + ( \frac{n}{b} ) b^{2} }$

Here, m= number of half-wave along broad side dimension, 
N= number of half-wave along the shorter side. 

Circular Waveguide: 

It maintains a uniform circular cross section along their length. 

The cutoff frequency is unique for a specific waveguide  mode that is assumed to be propagating in a waveguide of a given diameter and determines the lower frequency of the waveguide’s operating frequency range.

The cutoff frequency  is calculated using the following formula:

$f_{c,m.n} = \frac{v}{2 \pi } \beta _{c,m,n}$