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Need small directional antenna for bluetooth

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michcfr

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Hello,

For my project I would like to acquire directional small (few cm) narrow beam antennas of width of 30°, 45° or 60° max for bluetooth frequency.
I googled around but found nothing to buy and even to build by myself (like microstrip antenna or else).
Can you please help me.

In advance thank you,
Michel
 


Thx Biff44
But the purpose is not to get gain but to measure angle of arrival with phases using many narrow beam antennas.
I really need small antennas.
 

You can simply consider gain and directivity interchangeable in this context. You need multiple wavelength antenna size to implement the intended directivity.
 

FvM said:
You can simply consider gain and directivity interchangeable in this context. You need multiple wavelength antenna size to implement the intended directivity.
Click to expand...

Thank you for your reponse, so where can I order these kind of antennas at reasonable size? Thx
 

Bluetooth is in the same band as wifi. Just look for directional wifi antennas. There are thousands.
 

Thank you hagster
Already checked directional wifi antennas, but found only big antennas. I'm looking for small (few cm) antennas.

Regards
 

The wavelength is ~12cm. Thus you cant have good directionality without an antenna thats at least a good proportion of that size.

You can have an array of lots of inefficient small antennas, but the overall array spacing still needs to be large. If the elements are close together they basically receive signals with very similar phases and hence no angle discrimination.
 

Thank you hagster for your information,

Yes, I want to build an array of antennas and I've been told that interspace should be half of the wavelength: 6.25cm and beam width of 45 degree ideally.
So, 4-5 antennas of around 12cm and with 6.25cm interspace is enough for me but...I wish I can find directionnal antennas of 12cm or little more but Google do not propose any link :-(

Can someone help me?


Regards
Michel
 

Around 15cm of depth
 

in order to measure angle of arrival, you use 4 or 5 OMNIDIRECTIONAL antennas in a ring (sometimes with one in the center as a reference), and measure the time delay (or phase delay) to each element with parallel receivers.

the antenna element does not determine anything. it is the processing electronics that does that.
 

Small and directional do not usually go together. Pick one or the other. The only real way to get both is to go very high in frequency and there the electrical size can be large while the physical size is "small". In reality that is not really a real solution but rather a word game.
 

Hello

Thank you for your contribution.

A dielectric filled helix antenna have been suggested to reduce the size and also because it can be easily realized.
I have found many websites providing helix antenna calculator but not for dielectric filled (with ABS or Teflon/PTFE).

Can someone provide me some help, links or references to calculate dielectric filled antennas?


Thx
Michel
 

michcfr said:
Hello

Thank you for your contribution.

A dielectric filled helix antenna have been suggested to reduce the size and also because it can be easily realized.
I have found many websites providing helix antenna calculator but not for dielectric filled (with ABS or Teflon/PTFE).

Can someone provide me some help, links or references to calculate dielectric filled antennas?


Thx
Michel
Click to expand...

The Helix is good and is a pretty efficient use of space. I don't think there are any calculators that will work out the sizes with dielectrics (other than the expensive EM software like HFSS). Trial and error is your best bet, but you obviously need a reasonable way of measuring your performance. Personally I would print several formers of different sizes on a 3D printer and select the best.

But I think you will loose beamwidth as you make it smaller in this way, and to hit your 30° requirement you would be starting with a fairly big antenna anyway. Using this calculator tells me it needs to be 12 turns and 37cm long. https://www.daycounter.com/Calculators/Helical-Antenna-Design-Calculator.phtml
 

Thank you hagster for your response.
Since I make trials, how can I measure performance of the antenna? in particular dbi and beamwidth?
The calculator says normal helix would be 4cm diameter. So when dielectric filled, may I try with half diameter?
I can go up to 45 degrees beam width. Of course 30 is the best.


Thx
Michel
 

michcfr said:
how can I measure performance of the antenna? in particular dbi and beamwidth?
Click to expand...

What RF test equipment do you have available to you? You can do crude measurements with a wifi card and some free software such as INSSIDER, but it will be crude.

michcfr said:
The calculator says normal helix would be 4cm diameter. So when dielectric filled, may I try with half diameter?
Click to expand...

Yep, you can start there. If you have the right test gear you can do a frequency sweep and see where your best performance is (gain and vswr) is and scale appropriately. I.e if your best frequency is 50% too low then decrease the size by 50% and try again. Two or three iterations like that will get you pretty close to optimal. Without the right kit you just need to build more variants iterate more.
 

Thank you again hagster. Nice methodology!
Concerning RF test equipment, I found it can also be done with a network analyzer. I suppose it is an alternative you had thought about. It is better but expensive...maybe should I rent one.

Are there better alternatives to ABS and PTFE as dielectric?


thx
 

Better in what respect? If you want directivity then using high dielectrics to reduce the size will probably be counter productive. There are other alternatives such HIPS of you are 3D printing like i suggested.

Yes a descent network analyser is ideal, or a sig gen and SA, or a SA with a tracking generator can be used too.

The bigger picture though is exactly what exactly you are trying to acheive? I dont think its particularly clear. As Biff44 said, if you are trying obtain the direction by comparing phases then you dont need highly directional antennas in the first place. In fact you want something with a very well defined phase centre such as an omni monopole.
 

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