TESTING from DEV1

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

Derren Oliver is director of business development for the Microwave Systems unit at CommScope. He has nearly 20 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.

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Comments

16 comments for "Back to Basics in Microwave Systems: Polarization"
Prajna Sunday, March 06, 2016 9:12 PM

Sir, What do u mean by Dual circularly Polarization?

Derren Oliver Thursday, July 07, 2016 1:15 PM

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

BELL Tuesday, November 01, 2016 5:01 AM

Hi. How do you cutover/deinstallation a microwave link

Derren Oliver Tuesday, November 01, 2016 10:54 AM

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.

bell Friday, January 13, 2017 4:42 AM

Thanks Derren for responding my question is how do you upgrade a microwave link?

Donald Gardner Tuesday, January 17, 2017 10:38 AM

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.

Rakesh grewal Thursday, February 02, 2017 9:20 PM

Hllo sir i am confused about polarization of RFS's OMT NMT 820-01

Donald Gardner Friday, February 03, 2017 11:38 AM

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.

Yaseen Khalid Friday, March 03, 2017 1:49 PM

Hi Darren Sir, can you please explain why & when to use vertical & when horizontal polarizations ...? Does it depend on the terrestrial characteristics or what ?

Donald Gardner Tuesday, March 07, 2017 7:21 AM

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/.

Samaj Poudel Thursday, March 30, 2017 8:17 AM

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?

Donald Gardner Monday, April 03, 2017 3:37 AM

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/.

Michael Tuesday, August 15, 2017 4:59 PM

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.

Donald Gardner Friday, August 18, 2017 10:53 AM

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.

Naga Prakash.K Monday, August 28, 2017 7:59 AM

Hi Mr.Micheal,
I am working with 1.2 Diameter antennas for Vodafone network in India ,I am regularly facing High tension lines passing through LOS path ,what will be the impact on RSL.Second point we are using 5-8 year old antennas and radios for implementing transmission paths how ageing of this equipment will impact on planned RSL.Kindly help me.

Derren Oliver Monday, September 04, 2017 10:55 AM

Dear Prakash,
Thanks for your comment. With regard to your first point - this is something your network planners should account based on information from the initial site survey. Typically power lines are at very low frequency so you wouldn't expect them to interfere with a microwave frequency link. However it is possible that if there are a lot of power lines or they are supported by large structures (eg Pylons) then reflections could occur which may impact RSL. Best to avoid if possible or have your network planners ensure the link is operable with such an obstruction. For point 2. I cannot comment on the Radio equipment as the manufacturers each have their own specification. For a CommScope antenna 5-8 years old should not cause problems if the antenna has been regularly maintained and has not been damaged by poor installation or vandalism. We have seen instances of antennas from other manufacturers starting to deteriorate after only a short time due to improper or inferior build processes, design or materials so please make sure you are buying your antennas from a reputable supplier

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