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n.biniossek
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ZOR Antenna shift resonnance frequency

Dear Sir or Madam,

 Currently we develop a first prototype of a new Bluetooth device. Therefore we used the example ZOR Antenna (document AN-B-027 Z,  5.4 ZOR Antenna, 1.6 mm Substrate). Attached you can see the Layerstack of our circuit board.

Unfortunately the resonance frequency of our antenna is around 2,8Ghz.

Could you please explain me how to shift the resonance frequency to 2.4Ghz (like in  figure 20 in AN-B-027).

I am looking forward to your answer! Many thanks in advance.

 

Best,

Nik

Attachment: 
Device: 
PM_Dialog
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Hi n.biniossek,

Hi n.biniossek,

Thanks for your question. I’ve escalated it internally to our RF team. I’ll get back to you shortly.

Thanks, PM_Dialog

PM_Dialog
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Hi n.biniossek,

Hi n.biniossek,

Please note that an offset of 400 MHz is quite significant. Could you indicate if you are using the top and bottom layer to implement the ZOR antenna? In the provided layout view, we can see layers, that should be empty.  What is placed on those layers? (see attached)

Thanks, PM_Dialog

Attachment: 
n.biniossek
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Last seen: 1 year 7 months ago
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Hi Dailog Team,

Hi Dailog Team,

yes I am using the top and bottom layer for the ZOR antenna. Attached I send you the different layers. In the middle layers is nothing placed. The purple area which do you marked only shows area without solder maske. Please see the attchead file.

From my point of view, a connection between the 4 small copper areas on the bottom layer would be necessary. Please the the dxf files for more details.

I am looking forward to your answer!

Best,

Nik

 

Attachment: 
PM_Dialog
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Hi Nik,

Hi Nik,

The 4 small copper areas on the bottom layer should not be connected. What antenna matching did you use for the shared |S11| measurement? Was the matching placed close to the antenna? Did you try to match the antenna without success?

Thanks, PM_Dialog

PM_Dialog
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Hi Nik,

Hi Nik,

Could you please let us know if there is any update on this? What antenna matching did you use for the shared |S11| measurement?

Thanks, PM_Dialog

n.biniossek
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Hi Dialog Team,

Hi Dialog Team,

finally I got much better result. For the matching I use a 3,3nH series inductor.

Strangely,  whenever I place a shut capacitor (regardless of the farad size) the antenna matching is destroyed.

 

Best

Nik

PM_Dialog
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Hi Nik,

Hi Nik,

The antenna matching is not only influenced by the antenna structure, but the ground plane of the PCB, the plastics around the antenna and any conductive element close by (screw, etc.). The matching in the application note is only valid for the test board we used.

https://www.dialog-semiconductor.com/sites/default/files/an-b-027_designing_printed_antennas_for_bluetooth_low_energy_2v2.pdf

This means, that you should check the matching of the antenna for optimal performance. The matching should be done with a S11 measurement and the matching components should be chosen to get an optimal (low) reflection in the wanted band. A shunt capacitor to ground is shifting the curve on the smith chart down the constant conductance circle. If the matching gets worse with a capacitor to ground the input impedance imaginary part might be already negative.

A matching based on range experiments and placement of different components is quite cumbersome and might lead to suboptimal results. Our suggestion would be to use a network analyzer to perform an optimal matching.

Thanks, PM_Dialog

PM_Dialog
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Hi Nik,

Hi Nik,

Thanks for accepting my answer. Can you please let me know if you have any other follow up questions/

Thanks, PM_Dialog