How shield patch antenna to reduce range? (2.4GHz)

[TriggerHappy]

I want to partially shield bluetooth antennas so that their ranges are reduced. My motive is that I want to use reception or non-reception as a means of measuring indoor location (of my mobile phone with simple software for that purpose) with a room by room resolution. Bluetooth is by standard far too powerful for that, easily penetrating walls and floors.

Here is an image of a bluetooth hands free device opened:
https://imageshack.us/photo/my-images/267/bt95switchlarge.jpg/
I suppose that the zigzag pattern to the left (about 12mm by 4 mm) is a bluetooth patch antenna.

QUESTIONS:
1) Roughly how are the radio waves propagated from such an antenna (2.4 GHz)? For example, stronger in its plane or perpendicular to it? On the bottom side of such patch antennas, I've read that there should be a ground plane. Does that mean that it doesn't transmit at all directly through that plane? (Reception in that direction would then be explained by reflections)

2) Is it feasible, as imagine, that it suffice to gradually cover it with metal until the range is optimal. I imagine for example twining thin insulated wires around it. 1-4 rounds would gradually cover it and provide sufficient degrees of range choice. Or covering it completely on three sides, and cutting partially covering aluminium foil patterns to stick onto its front with some adhesive. (I'm on a low budget concept testing level).

3) Would there be any better way to reduce signal strength than to partially shield the antenna? I have no real documentation about the bluetooth chip, but the signal strength seems to be very low level hard coded. And breaking the commercially mass produced standards could require very expensive new chip development. Or is there a short cut?

I have achieved optimal range by covering the entire device with steel wool in even and measured thickness. But it is flimsy, and I want to get up close to the antenna itself now, in hope of making range adjustments tidy, sturdy and repeatable with precision.

(And any feed back on my project idea as a whole is always very welcome!)

 

[enjunear]

Bluetooth devices are generally meant to operate in any orientation (like a headset, relative to a cellphone), so their radiation pattern is "relatively" omnidirectional. You'd probably end up having to make a 5-sided box around the antenna/device, so that it can only radiate out one side (like a cube with one end open).

If you could find a way to break into the feeding transmission line, you could make and connect up a real microstrip patch antenna, which is rather directional by design.

 

[ferdows]

shield help you to increase efficiency so it may be help you to reduce power but i think power in same in this condition for read more about shield u can read the papers of andre alu

 

[E Kafeman]

I use rubber mat of this type: **broken link removed** to "calm down" hot spots in a chamber but you can use almost any rubber mat at BT freq for gradually absorbing RF signal. Partly metal shielding is very unpredictable.
Somewhat more controlled test proposal: Place the phone in a fixed position in a complete shielded box with a metallic mesh as a window. Drill a hole in the box for a chassi mount SMA connector. Solder a short wire at SMA connector, inside the box. Make an external BT antenna soldered at a second SMA connector.
Now can you add SMA attenuators between box mounted SMA connector and the external antenna until you reach a critical radiation level. This setup is a bit more repeatable compared to wrapping phone in undefined amount of shielding material.

 

[Mark W. Ingalls]

I want to partially shield bluetooth antennas so that their ranges are reduced. My motive is that I want to use reception or non-reception as a means of measuring indoor location (of my mobile phone with simple software for that purpose) with a room by room resolution. Bluetooth is by standard far too powerful for that, easily penetrating walls and floors.

Here is an image of a bluetooth hands free device opened:
https://imageshack.us/photo/my-images/267/bt95switchlarge.jpg/
I suppose that the zigzag pattern to the left (about 12mm by 4 mm) is a bluetooth patch antenna.

QUESTIONS:
1) Roughly how are the radio waves propagated from such an antenna (2.4 GHz)? For example, stronger in its plane or perpendicular to it? On the bottom side of such patch antennas, I've read that there should be a ground plane. Does that mean that it doesn't transmit at all directly through that plane? (Reception in that direction would then be explained by reflections)

INGALLS: What you have shown is not a patch, but a meandered 'thin wire' antenna (I believe). It also appears to be loaded so as to have more than one band of operation. As to how the signal propagates, that is a very complicated question that depends not only on the meandered trace itself, but also everything around it.

2) Is it feasible, as imagine, that it suffice to gradually cover it with metal until the range is optimal. I imagine for example twining thin insulated wires around it. 1-4 rounds would gradually cover it and provide sufficient degrees of range choice. Or covering it completely on three sides, and cutting partially covering aluminium foil patterns to stick onto its front with some adhesive. (I'm on a low budget concept testing level).

INGALLS: I like the conductive rubber idea, as proposed by Kafeman. You may produce the opposite of your intended effect with wires.

3) Would there be any better way to reduce signal strength than to partially shield the antenna? I have no real documentation about the bluetooth chip, but the signal strength seems to be very low level hard coded. And breaking the commercially mass produced standards could require very expensive new chip development. Or is there a short cut?

INGALLS: Depending on where you live, you might find this site helpful: https://www.sparkfun.com/. Also, look into ZIGBEE, perhaps.

I have achieved optimal range by covering the entire device with steel wool in even and measured thickness. But it is flimsy, and I want to get up close to the antenna itself now, in hope of making range adjustments tidy, sturdy and repeatable with precision.

INGALLS: My first suggestion would have been steel wool. Carbon paper also works. Also conductive paint.

(And any feed back on my project idea as a whole is always very welcome!)

INGALLS: Best of luck with your project!