Rectangular waveguide vs Circular waveguide

This page on Rectangular waveguide vs Circular waveguide describes difference between Rectangular waveguide and Circular waveguide.

Both the waveguides are metal hollow structure to guide EM waves. Depending upon the shapes they are designated as rectangular or circular. Both types of waveguide behaves much like a High Pass Filter and is basically a passive microwave device. Cutoff frequency equations are mentioned below.

Rectangular waveguide

Figure depicts Rectangular waveguide with broad dimension and narrow dimension in the form of rectangular. Cutoff wavelength equation for rectangular waveguide is define below.

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

Following table mentions cutoff wavelengths and cutoff frequencies for various common modes in a rectangular waveguide.

Mode	Cutoff Wavelength(λ_c)	Cutoff Frequency(f_c)
TE₁₀	2*a, a=broad dimension	( 1/(με)^0.5 ) * (1/(2*a))
TE₁₁, TM₁₁	(2ab)/(a² + b²)^0.5	( 1/(με)^0.5 ) * ((a² + b²)^0.5/(2ab))
TE₂₀	a	( 1/(με)^0.5 ) * (1/a)
TE₀₁	2*b	( 1/(με)^0.5 ) * (1/(2*b))

Circular waveguide

Figure depicts Circular waveguide. Cutoff Frequency equation for circular waveguide fc is defined below , fc= (1.8412 * c /2*pi*a) Where, c is the speed of light within waveguide and a is the radius of the circular cross section.

Dominant mode in rectangular waveguide is TE10 and in circular waveguide is TE11.

Rectangular to circular waveguide transition convert dominant TE10 mode of rectangular waveguide to TE11 dominant mode of circular waveguide and vice versa.

Following table mentions cutoff wavelengths and cutoff frequencies for various common modes in a circular waveguide.

Mode	Cutoff Wavelength	Cutoff Frequency
TE₁₁	1.706d, d=diameter of the waveguide	( 1/(με)^0.5 ) * (1/(1.706*d))
TM₀₁	1.306d	( 1/(με)^0.5 ) * (1/(1.306*d))
TE₂₁	1.028d	( 1/(με)^0.5 ) * (1/(1.028*d))
TM₁₁	0.820d	( 1/(με)^0.5 ) * (1/(0.820*d))

WAVEGUIDE RELATED LINKS

RF Switch basics and applications along with manufacturers of RF switch refer following link:
RF Switch

For types of waveguide viz. rectangular & circular, waveguide propagation modes, impedance matching of waveguide read following waveguide tutorial.
waveguide basics tutorial

Manufacturers of waveguide components such as waveguide to coaxial adapter, coupler, flanges, gasket, tees, termination, shorts, isolator, circulator, horn antenna, attenuator, feed-thrus, bends, loads, twists, straights, pressure windows, transformers, sliding short circuits, fixed short circuits, sliding mismatches etc. visit following link.
Waveguide components manufacturer

Rectangular waveguide dimensions as per USA standard including frequency, broad dimension and narrow dimensions, visit following link.
Waveguide dimensions table

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