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Low-profile antenna for 868 MHz with high directivity ? - RF Cafe Forums

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malvinas2
 Post subject: Low-profile antenna for 868 MHz with high directivity ?
Posted: Thu Feb 09, 2006 5:26 am 
Hello,

I'm searching for a low-profile antenne for 868 MHz, which possesses high directivity.

At the moment I don't have any idea how an antenna like this could be build. Normally if you want an antenna with directivity in this frecuency range, one would build something like a logarithmic antenna with a reflector and so on (Yagi etc.). But my antenna has to be nearly planar. Another possibility to achieve high directivity would be the use of an array, but for the frecuency required that would be quite big....
'High directivity' is not defined exactly until now, because I'm just searching for ideas, anything better than isotropic would be of help.

Any ideas ?


 
  
 
!AliG
 Post subject:
Posted: Mon Mar 27, 2006 5:52 pm 
I think you are right guys! :)


 
  
 
fred47
 Post subject: Directivity
Posted: Mon Mar 27, 2006 7:12 pm 
 
General
User avatar

Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
Hi!

You don't mention which is more important:
1. Transmission/reception from only one direction (narrow beam width), or 2. The ability to null out signals to/from one direction.

Also, what size range is acceptable? Your post seems a bit vague here.

Directivity is really only obtained by multiple radiators (the array approach, which can include driven and parasitic arrays) or by quasi-optical methods (parabolic dishes, lenses, etc.)

Good Luck!
Fred


 
   
 
nubbage
 Post subject: Low Profile Antenna for 868MHz
Posted: Wed Mar 29, 2006 4:58 am 
 
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User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Other info missing: do you wish to design the system or not?
If you wish to design it:
Using a corporate strip-line array of full-wavelength (in the dielectric) suggests an array of 4 full-wave dipoles would measure about 30cm high by 20cm wide for horizontal polar (or the other way round for vertical polarization), and would give a gain of about 12dBi

The dipoles are fed through 3dB strip-line T junction matched splitters

if you wish to purchase
Some companies manufacture such antennas as flat panel types for this part of the radio spectrum


Trev



Posted  11/12/2012