Waveguides 2

ECE357 / Prof. S. V. Hum

Rectangular Waveguide

•  Metal-walled “tube” of dimensions a × b

•  Transverse field variation in both x and y directions possible

•  Modes supported? q TEM? q TE? q TM?

ECE357 / Prof. S. V. Hum

Transverse Field Components of TM Modes

ECE357 / Prof. S. V. Hum

TM Transverse Field Distributions

TM21

TM11

ECE357 / Prof. S. V. Hum

TE Mode Field Solutions

ECE357 / Prof. S. V. Hum

TE10 Mode

•  This mode is the dominant mode of a rectangular waveguide with a > b

•  Most useful mode used in rectangular waveguide equipment – Has the lowest attenuation of all modes (not

proved here) – Electric field polarized purely in one direction

(practical importance)

ECE357 / Prof. S. V. Hum

TE10 Transverse Field Distribution

ECE357 / Prof. S. V. Hum

ECE357 / Prof. S. V. Hum

Higher Order Modes

•  Defined as those other than the dominant (TE10) mode – All have cutoff frequencies higher than (fc)10

•  A waveguide can support multiple modes at a time

•  If there are modes propagating along a waveguide in addition to the dominant mode, the waveguide is overmoded

ECE357 / Prof. S. V. Hum

H.O.M. Transverse Field Distributions

ECE357 / Prof. S. V. Hum

H.O.M. Transverse Field Distributions

ECE357 / Prof. S. V. Hum

Rectangular Waveguide Summary

Rect. Waveguide Applications Loss-loss TX lines for base stations

Antenna feed systems for satellites

ECE357 / Prof. S. V. Hum

Rect. Waveguide Applications

52 GHz receiver, NRAO Output multiplexer, satellite systems

ECE357 / Prof. S. V. Hum

ECE357 / Prof. S. V. Hum

Closing Remarks on RWG

•  Waveguide is heavily used in high-power applications (e.g. microwave ovens, satellite transmitters) – Higher power handling capability and lower

loss than planar and coaxial lines – Size of waveguide (cutoff frequency) chosen

to minimize losses •  All waveguide modes are dispersive --

designer needs to be aware of this for wideband applications