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Home-Brew Compact 6dBi 5.1 to 5.8 Collinear Antenna

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Home-Brew Compact 6dBi 5.1 to 5.8 Collinear Antenna

Does anyone have a design for a home-brew compact 5.6 to 5.8GHz collinear antenna that they could share. I have seen the one on the internet for the Home-brew Compact 6dBi Collinear Antenna 2.4GHz. Just looking for something similar.

Steve KF7WGL

A colinear is generally
A colinear is generally vertically polarized. If you are going to deploy a single polarity antenna it is recommended that it be horizontaly polarized which is normally a slot waveguide format.

In both cases the tolerances are so tight that it is hard to produce at home. At 5.8GHz 10% error is just 5mm IIRC.

On top of that dual polarity is even better as it can significantly increase the link quality and speed.
kg9dw's picture
As someone that has played
As someone that has played with single polarity antennas with the ubiquiti gear, I'd recommend avoiding this trap and sticking with MIMO antennas and radios. We aren't running a simple FM analog signal at 5GHz. While RF antenna theory holds true, you do need to understand how the radios are working and what they expect to see. 

k1ky's picture
There are so many options....
Why bother with building something when you can order 12+ dbi antennas from E-Bay for around $3 - $10?  I have a Rocket M2 that I am playing with a pair of co-liinear "duckie" antennas - reverse SMA connectors, about 1.5 feet long. One Vertical and the other Horizontal.  Jury is still out, but it does work!

I have also played with some commercial co-linear antennas on the Bullet M5 and M2.   They work and we used them this past week for a communications exercise over an area the size of a small college campus.
Just a FYI running two omni's

Just a FYI running two omni's like this isn't a great MIMO setup. You would be better with a cheap sector or NanoStation.

First off the antennas may not share the same radiation pattern because of how they are built and installed when putting a vertical omni on its side you end up with a forward back pattern on that antenna and omni on the vertical.

Secondly and more importantly the isolation between antennas is likely not there, the antennas are so close together that the fields can be interacting.

True MIMO antennas generally have a 20-30db or more isolation between antennas, this is power that is not returning to the transmitters to interfere and more importantly the isolation between the two allows the individual signals to be captured better while rejecting the opposite polarity.

k1ky's picture
Good Point!
And good info too!
Home-Brew Compact 6dBi 5.1 to 5.8 Collinear Antenna
WOW. Great information and thank you for your input. It seems that I need to educate myself on dual polarity (circular ?) antennas. 

Technically it just means two
Technically it just means two distinct polarities, but in the case of mesh it is usually Horizontal(-) and vertical (|) especially since that's what the NanoStations ship with and may networks use those as user access devices.

It could easily be Cross(X) as they make antennas for this (same as a horizontal and vertical but internally the antennas are electrically rotated 45 degrees off the vertical axis.

I haven't ever seen a dual polarity circular polarized antenna but that doesn't mean it can't be done but would be a speciality item and would be needed on both sides of the link.
KE2N's picture

Right hand and left hand circular would seem like a great way to get two spacial streams for MIMO. The problem is that when a RHCP signal reflects off of something it becomes LHCP (and vice versa) thereby destroying the isolation between streams.   Linear polarized signals (V/H/X) tend to remain linearly polarized  even after reflections.

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