# Waveguides

GUIDE TYPETE11MODE
CUTOFF
[GHz]
MAXIMUM
FREQ. RANGE
[GHz]
ATTENUATION
[dB/100mt]
MAX POWER
[W]
VELOCITY FACTOR

EW 127 A 7.67 10.0 - 13.25 11.83 1.24 0.78
EW 132 9.22 11.0 - 15.35 15.84 0.85 0.78

WAVEGUIDE
A few basic facts about waveguide:
• The "WR" designation stands for "waveguide, rectangular"
• The wide inside dimension in inches is the "xxx" part of WRxxx; ie, WR650 is 6.50 inches, WR90 is 0.90 inches.
• The TE10 mode of propagation is the lowest mode that is supported.
• The waveguide width determines the lower cutoff frequency and is equal (ideally) to ½ wavelength of the lower cutoff frequency.
• The TE20, occurs when the width equals one wavelength of the lower cutoff frequency, and so on for higher modes.
• The TE01 mode occurs when the height equals ½ wavelength of the cutoff frequency, and so on to higher modes.
H-BendE-Bend An H-Bend is bent in the Hard direction (along the long side). This is the direction of the H-field in the TE10 mode. An E-Bend is bent in the Easy direction (along the short side). This is the direction of the E-field in the TE10 mode.

RECTANGULAR WAVEGUIDE
Cutoff frequency
The lower cutoff frequency (or wavelength) for a particular mode in rectangular waveguide is determined by the following equations: (Hz) (m)

where

a=
b=
m=
n=
e=
m=

Inside width
Inside height
Number of ½-wavelength variations of fields in the "a" direction
Number of ½-wavelength variations of fields in the "b" direction
Permittivity
Permeability
TE (Transverse Electric) Mode
The TE10 mode is the dominant mode of a rectangular waveguide with a>b, since it has the lowest attenuation of all modes.
Either m or n can be zero, but not both. End View (TE10) Side View (TE10) Top View (TE10)

____ Electric field lines
_ _ _ Magnetic field lines

TM (Transverse Magnetic) Mode
For TM modes, m=0 and n=0 are not possible, thus, TM11 is the lowest possible TM mode. End View (TM11) Side View (TM11)

____ Electric field lines
_ _ _ Magnetic field lines

CIRCULAR WAVEGUIDES
TE (Transverse Electric) Mode
The lower cutoff frequency (or wavelength) for a particular TE mode in circular waveguide is determined by the following equation: (m),

where p'mn is m p'm1 p'm2 p'm3
0 3.832 7.016 10.174
1 1.841 5.331 8.536
2 3.054 6.706 9.970
TM (Transverse Magnetic) Mode
The lower cutoff frequency (or wavelength) for a particular TM mode in circular waveguide is determined by the following equation: (m),

where pmn is

m pm1 pm2 pm3
0 2.405 5.520 8.654
1 3.832 7.016 10.174
2 5.135 8.417 11.620