# Regarding Polarization in Waveguide

• kathir1983
In summary, while waveguide can theoretically produce a polarized wave, it is not always the case due to the lack of a central conductor.
kathir1983
Hi members, am new to antenna field.I would like to know more about polarization in waveguide.As per book,it is stated that TEM wave cannot travel in waveguide.If that is the case how come horizontal or vertical polarization can be achieved.If am wrong,please correct me.Thanks in advance.

I'm not expert on tranmission lines but know a little about fibre optics. A horizontally or vertically polarised wave just has the field variation in one direction (although the E and M fields are orthoganal which makes it a bit difficult to visualise, just consider one).

Maybe if you just consider it from the point of view of the wave rather than thinking about the path of propogation?

Persoanlly, I find it hard to see how a waveguide doesn't introduce some sort of polarisation...

The electric and magnetic fields in the fundamental mode are both perpendicular to the direction down the guide. That sounds pretty transverse to me.

...So I did a little research. The fundamental mode for a waveguide is TE_{1,0}.

TEM requires that there be no magnetic or electric field components in the direction of propagation. Down the geometric center of the guide P, E and M are all perpenducular. Toward the edges, the magnetic fields have longitudinal components.

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I will put my question clear...we are connecting the output of magnetron to DDC through rectangular waveguide.The output of magnetron is TEM wave (both magnetic & electric field perpendicular to the direction of propagation) but the rectangular waveguide dominant mode is TE10 (electric field perpendicular to the direction of propagation & not magnetic field).In such case how will be my electic field orientation.whether it will be horizontal or vertical w.r.t to direction of propagation.

Query Regarding Polarization

whether the electric & magnetic field should be perpendicular to direction of propagation or is it electric or magnetic field alone is perpendicular to direction of propagation (Linear polarization)

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OK. Assuming your guide is matched to the magnetron frequency so the guide is conducting in the fundamental mode, the electric field will stretch across the shorter dimension of the guide. Looking down at the wider side, the magnetic fields will obtain as regions of alternating circulation, strung along the length of the guide. In each region the magnetic field circulates, alternately clockwise, then counter clockwise. The loops of field lines get more rectangular in shape on the outside of these regions as the field lines get closer to the walls and the adjacent loops.

Still looking down on the widest side of the guide, along the longitudinal centerline the magnetic field is transverse to the Poynting vector along the length of the guide. But close enough to the walls the magnetic fields have a larger longitudinal component, than transverse, because of the looping business.

(I suppose this means the Poynting vector ducks in and out of the guide wall-I hadn't thought about it.)

So these loops of field, and electric field too, race down the guide at some velocity greater than c, that is a function of the guide width.

The same field patterns are obtained as the interferance from a multiple source array, spaced a little more than half(?) a wavelength apart--as can be shown using boundry conditions.

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sorry...i didn't get you...

See figure 1:2. It's close enough to correct.

http://www.swedetrack.com/waveguid.htm"

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I thought TEM required a centre conductor making it a coaxial cable rather than a waveguide.

For propagation in a waveguide there will be either a transverse magnetic (TM) or transverse electric (TE) mode.

If the z-axis points down the length of the waveguide, then in a TM mode wave the magnetic field will not have a z component but the electric field will. In a TE mode wave the electric field will not have a z component but the magnetic field will.

In Griffiths' "Introduction to Electrodynamics" he shows in an interesting and surprisingly simple way how a solution for a TEM wave (transverse electromagnetic wave) does not exist for the wave equation in the case of a waveguide.

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For TEM, all the magnetic field across the wavefront is perpendicular to the direction of propagation, and all the electric field is perpendicular to the direction of propagation.

I hope this lends some clarity.

## 1. What is polarization in waveguide?

Polarization in waveguide refers to the direction in which an electromagnetic wave oscillates as it travels through the waveguide. It can be either linear or circular, and is determined by the orientation of the electric field with respect to the direction of propagation.

## 2. How does polarization affect wave propagation in a waveguide?

The polarization of a wave in a waveguide can affect its transmission, reflection, and attenuation. If the polarization of the wave does not match that of the waveguide, it may experience higher levels of loss and reflection, leading to decreased signal strength.

## 3. What are the different types of polarization in waveguides?

The two main types of polarization in waveguides are TE (transverse electric) and TM (transverse magnetic). In TE polarization, the electric field is perpendicular to the direction of propagation, while in TM polarization, the magnetic field is perpendicular to the direction of propagation.

## 4. How is polarization controlled in waveguides?

Polarization can be controlled in waveguides through the use of polarization filters and mode converters. These devices manipulate the electric and magnetic fields of the wave to achieve the desired polarization, allowing for more efficient transmission and reception of signals.

## 5. What are some applications of polarization in waveguides?

Polarization in waveguides is used in a variety of applications, such as in microwave communication systems, radar systems, and optical fibers for telecommunications. It is also important in the design and optimization of antennas and other waveguide components.

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