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Antenna design / joining two seperate outputs to one antenna

 
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fannta
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Joined: 24 Mar 2017
Posts: 1

PostPosted: Fri Mar 24, 2017 5:42 am    Post subject: Antenna design / joining two seperate outputs to one antenna Reply with quote

Dear Members

Recently I got hold of an antenna which uses dual inputs for my WRT54 router. As it has two external antennas the new antenna got attached to extend the range. As the antenna is inside a housing one could not tell from the outside whats inside.

Then I had to open the antenna housing to see whats inside, what made me wonder, because my assumption so far was that combining two outputs by simply joining then would be of no benefit it nor worse.

This is what was inside the housing:



The two solder blobs are actually the two antenna cores, simply soldered to the very same PCB. According to various comments simply cojoining antenna outputs to one antenna is not a good idea?



Basically the antenna element is being hold in place by the RPSMA connector itself and some tape. The plane of the antenna and the groundplate are not evenly parallel but twisted in various directions, furthermore the RC and Wifi elements axis are not parallel at all. The PCB is somewhat bent, I want to correct it but don't know what the distance between the ground plane and active element should be. Maybe someone can give me a hint?

Thanks[/img]
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hagster
Antenna Theory Regular


Joined: 09 May 2015
Posts: 27

PostPosted: Fri Mar 24, 2017 10:33 pm    Post subject: Reply with quote

The two antenna ports provide different polarisation. The WiFi router can exploit this using MIMO techniques to increase data capacity. I.e.You have 2 channels with polarisation divesity.
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hagster
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PostPosted: Sat Mar 25, 2017 7:26 am    Post subject: Reply with quote

Just to add a bit more to my last comment.

Its fairly normal to acheive dual polarisation this way. Although there is a DC short between the 2 feed pins at the operating frequency(looks like 5ghz to me) there is plenty of isolation between them. If you could visualise the voltage/current standing waves you would see that the secondary feedpoint would have a high impedence wrt the first feed point, and therefore just looks like an open cct.
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