Explain the twisted coupling to me?


I have a background in high power radar and am currently working in radio communications.

Normally when two waveguide meet (in my experience) they must line up perfectly. 

Recently I have noticed with several PTP microwave links that the coupling isnt true vertical or true horizontal, but on some angle in between!

I am happy to report that I know it works, but I would like to know why the offset angle in the coupling between the ODU and the Antenna?

Can anyone help?

Excellent question!

Rather than have one mediation device change the polarity by 90°, and the rest of the mediation devices act as a "pass-through" (i.e., not changing the polarity at all), each of the mediation devices contributes to changing the polarity of the signal.

When all of the mediation devices are connected, any vertical signal is vertically polarized, and any horizontal signal is horizontally polarized.

You might ask, "Wait just a minute. I gave you pictures for a 6 GHz PTP 820S. I'm planning to connect it directly to an antenna. What other mediation devices are changing the polarity?"

There is a disc (with a rectangular hole) that fits into the antenna--this changes the polarity just a bit. The antenna mount (the metal thing between the ODU and antenna) also changes the polarity just a bit as well.


Without the twister plate, the PTP820 radio antenna port output is not 100% aligned with the rectangular shape of the waveguide yet. The twist plate will help finish the rest adjustment and make it fully aligned. That's why you will need to adjust the twist for your installation.



I'm sorry but I still don't understaned how this works.  I'm also confused if this is the ONLY thing that needs to be done at installation time to configure a PTP820S for horizontal polarization.  Does the radio also need to be somehow rotated 90 degrees on the antenna?  That would have the glands facing to the side, that doesn't seem right.  Does the antenna need to be assembled differently?  I'm talking about the Cambium branded Radiowaves 2 ft dish, I only see one way to attach the radio to the dish.  Not like some other brands of licensed radio where you rotate the radio 90 degrees and the glands are at 45 degrees rather than straight down.

Can a customer who has done this offer some clarification, I'm not finding the Cambium documentation or the answers from Cambium support very clear or helpful.

Unfortunately we already installed the radios and dishes, I do have a backordered dish coming maybe Monday that I can look at.  But I get the impression there is either a feedtube with a rectangular waveguide interface, or maybe just a rectangular window, on the back of the antenna that needs to be rotated 90 degrees.  Probably 4 Phillips head screws?  In addition to switching the "twister" plate on the radio.  Neither the Cambium nor Radiowaves documentation explains this or has any photos.

If my guess is correct, we shouldn't have to unmount the dish, just take the radio off the back of the dish, maybe have one climber hold it while another fiddles with some gizmo on the back of the dish.

there are two things you need to set.

1. Depends on horizaontal or vertical, you may need to adjust the flange at antenna size. Normally the antenna by default is set to horizontal polarity. In the case you need change to horizontal, please follow hte instruction guide to make the necessary change.

2. Adjust the twist on the radio antenna ports. There are two position the twist shall be, one V and one H. Please adjust it according to the PTP820S installation guide.

3. Attach the radio with the antenna. You will find the twist port not 100% coupled with the rectangular waveguide port at antenna, this is completely normal and OK. The radio is design in such way, and there is no problem with it.

with all that, you shall have a good installation and all polarity is aligned. hopefully that helps.


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