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Back to Basics in Microwave Systems: Polarization

Posted by Derren Oliver on May 22, 2014

ClassroomIn the microwave backhaul industry, many of us throw around terms and acronyms with the expectation that the person we are talking to knows exactly to what we’re referring. Recently Jim Syme told you that we are going “back to basics” by explaining some of the widely used phrases and parameters in the microwave antenna world. All of this information is contained in the Microwave Radio Antenna Link Fundamentals online course, available through the CommScope Infrastructure Academy.

In this blog post, I’d like to talk about polarization.

The radiowave is an electromagnetic waveform composed of both electric and magnetic fields. In free space, the fields are mutually perpendicular and are also perpendicular to the direction of propagation.

The term polarization commonly refers to the electric field component of the radiowave. In terrestrial microwave antennas, the polarization of the radio waves will be either horizontal or vertical. That is, the electric field will be either horizontal or vertically orientated.

The transmission characteristics of both polarizations are very similar at microwave frequencies. However, the effects of obstacles and reflections within the microwave link are more likely to degrade system performance in horizontal polarization than in vertical polarization and thus vertical polarization tends to be the first polarization of choice.

Microwave antennas will generally be either single polarized or dual polarized.

A single polarized antenna is one that responds only to one orientation of polarization – either horizontal or vertical. Thus radiowaves that are received or transmitted by a single polarized antenna will be either horizontal or vertical polarized.

A dual polarized antenna, however, can respond to both horizontally and vertically polarized radio waves simultaneously. The use of both polarizations in this way increases the traffic handling capacity of the system. For example, one transmitter/receiver combination can be set on vertical polarization, while a second independent transmitter/receiver combination can be set on horizontal polarization.

With our single polarized antennas there will be a single waveguide connection point, or port, at the customer interface. The polarization (vertical or horizontal) is sometimes denoted by an arrow placed adjacent to the port. The orientation of the waveguide cable will determine the polarization; if the broad wall of the guide is in the horizontal plane, the antenna is vertically polarized, and if the broad wall is in the vertical plane, the antenna is horizontally polarized.

The option to orientate the polarization in the desired direction is often facilitated by rotation either of the complete waveguide system or by a component of the waveguide system. The mechanisms for achieving this are explained in the microwave antenna installation bulletins.

For dual polarized antennas the customer interface will usually comprise two waveguide ports. Again, the polarization associated with each port will be explained in the antenna installation bulletin. Some antennas will also include polarization arrows to further assist identification.

That is a basic explanation of polarization. Any questions regarding this topic? Leave a comment if so, and I’ll be happy to reply.

About the Author

Derren Oliver 2

Derren Oliver

Derren Oliver holds dual roles as director of OEM sales and product line management, Microwave Systems. He is responsible for business development, technology road mapping, and management of sales of microwave antenna products. Derren has 16 years of experience in the telecoms industry, beginning in test and measurement for both wireless and wireline networking products at Hewlett Packard, Agilent Technologies and Ixia before joining CommScope in 2010. He holds a bachelor degree with first class honors in electrical and electronic engineering from the United Kingdom’s Heriot-Watt University and an MBA from Edinburgh Business School.

Comments

14 comments for "Back to Basics in Microwave Systems: Polarization"
Sunday, March 06, 2016 9:12 PM
Prajna says:
Sir, What do u mean by Dual circularly Polarization?
Thursday, July 07, 2016 1:15 PM
Derren Oliver says:
Dear Prajna, I don't believe I mentioned Circular polarisation in the article. however we do use circular polarisation in our antenna feeds before converting them to linear polarisation for transmitting or receiving from the radio. There are many references on the web which discuss the physics involved. Wikipedia has some good references here: https://en.wikipedia.org/wiki/Circular_polarization

I hope this helps.
Derren
Tuesday, November 01, 2016 5:01 AM
BELL says:
Hi. How do you cutover/deinstallation a microwave link
Tuesday, November 01, 2016 10:54 AM
Derren Oliver says:
Hello Bell, I'm not quite clear what your question means but I assume you are asking about the best way to install a new microwave link after de-installing another? For more details on microwave antennas, how to choose them and install them I recommend you register for the Microwave Radio Antenna Link Fundamentals [SP6105] course linked to in the above article. It should give you the information you require. Thanks for your interest.
Friday, January 13, 2017 4:42 AM
bell says:
Thanks Derren for responding my question is how do you upgrade a microwave link?
Tuesday, January 17, 2017 10:38 AM
Donald Gardner says:
Hi Bell, there are many ways of upgrading a microwave link. One of the easiest is to change to the antenna from a single polarized unit to dual polarized. This means that the link operates in both horizontal and vertical polarisations rather than just one. Depending on the antenna, this may be as simple as upgrading the antenna feed system. Of course, you will still require an additional radio to provide the traffic over the new polarization. For more information on the dual polarized antenna options please refer to CommScope’s electronic catalogue. Many thanks for your continued interest.
Thursday, February 02, 2017 9:20 PM
Rakesh grewal says:
Hllo sir i am confused about polarization of RFS's OMT NMT 820-01
Friday, February 03, 2017 11:38 AM
Donald Gardner says:
Hi Rakesh, I'm sorry but I can’t comment on other manufacturers products, however the OMTs that we use on our dual polarized ValuLine and Sentinel antennas are clearly labelled with the polarization orientation of each port. In addition, full installation instructions are supplied with the product.
Friday, March 03, 2017 1:49 PM
Yaseen Khalid says:
Hi Darren Sir, can you please explain why & when to use vertical & when horizontal polarizations ...? Does it depend on the terrestrial characteristics or what ?
Tuesday, March 07, 2017 7:21 AM
Donald Gardner says:
Hi Yaseen, In the first instance, the choice of whether to use vertical or horizontal polarization is down to what is available from the regulators in the country in which you wish to deploy the network – over a particular link one polarization may already have been used hence there may be alternative. At the lower frequencies there is little to choose, however at higher frequencies (say 30GHz and above), there is a general preference for vertical polarization since it is less susceptible to rain fade. For more information please refer to “Microwave Communication Basics eBook” - http://www.commscope.com/Resources/eBooks/.
Thursday, March 30, 2017 8:17 AM
Samaj Poudel says:
Hi Sir. We have MW Link with 1+1 ODU configuration(single antenna). One ODU in Vertical and other ODU in horizontal polarization directly mounted with antenna using coupler. So the receive signal level will be different or same in two ODUs(theoritically and practically)?If waveguide is also used will the RSL degrade?
Monday, April 03, 2017 3:37 AM
Donald Gardner says:
Hi Samej. In calm dry conditions there should be no difference in RSL between the horizontal and vertical polarizations. However, at higher frequencies, under rain fade conditions, there may well be a lower RSL in the horizontal polarization. Where there are additional waveguide runs (elliptical, flex-twists, or rigid waveguide) in the RF path, the RSL level will be reduced by the additional losses within the waveguide. For more information on waveguide performance please refer to “Microwave Communication Basics eBook” - http://www.commscope.com/Resources/eBooks/.
Tuesday, August 15, 2017 4:59 PM
Michael says:
Hi Darren,
while looking up your antenna RPE documentation I noticed the lack of cross-polarization discrimination sensitivity diagrams for rotational misalignment. So if our crew installs the antenna at let's say 2 degrees out of true vertical alignment(rotation not path alignment), what hit do we take to the discrimination between channels. Thank you for your help.
Friday, August 18, 2017 10:53 AM
Donald Gardner says:
Hi Michael
I’m guessing what you refer to a situation where one antenna is slightly misaligned rotationally to the other antenna across the link. In a correct installation, this should not happen – in addition to the antenna being aligned in elevation and azimuth, it should also be aligned rotationally to ensure optimum performance. Please refer to CommScope publication TP-108827; Path alignment and cross polarization procedure for parabolic microwave antennas for more details.

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