# Problem with measuring resistance of circular antenna..

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#### varunrvarun

##### Newbie level 5
Hi all,

I am trying to simulate a circular antenna with Momentum in ADS. It has 20 turns and the its a 2 layer PCB, where the top layer has the antenna.

I measured the antenna with the LCR Meter and Network analyzer and got the Resistance to be around 9.3 Ohms and impedance around 6.6 uH.

But, when simulating with ADS, i am not getting correct resistance value. I have used 1 oz copper
layer desc..
top - 1.37 mil thickness
prepreg - 59.05 mil thickness
bottom - 1.37 mil thickness
Also model: Sheet
material:conductivity (sigma): 5.7e7 siemens/m is given as input to ADS

Whereas the inductance value is accurate as measured in those meters.

Can someone please guide me why this mistake would have happened?

#### MobiNaz

##### Full Member level 3
Your antenna is attached to an SMA connector (for sure). The length of the connector shifts the phase of the measured S parameter of antenna (amplitude is not that affected and can be neglected). If the design in simulation did not include the connector you will definitely get diff measured results.

Here is what you can do.
With network analyser , measure the phase of the connector only first.

Subtract this phase from the phase of the measured antenna S parameters and get new S parameter phase.

Calculate Z now.

This should match your simulated result now.

Hope it helps!

#### varunrvarun

##### Newbie level 5
Hi MobiNaz,

I understand your point with network analyzer. But, i get the same impedance value in the LCR meter even without the sma connector.
but in the simulation i could not get the correct resistance value (which was proved to be the same by both LCR meter and Network analyzer). Inductance value matches and there is no issue with that.

Also, i would like to know the impact that will be caused to the coil antenna because of resistance... can we omit the resistance since we get accurate inductance values in LCR meter, network analyzer and ADS simulation?

V

#### volker_muehlhaus

##### Guest
I understand that LCR meter and network analyzer agree, and give the same series resistance at the operating frequency. (13MHz?)
I understand that Momentum gives a different (lower?) series resistance.

How did you model the conductor metal in Momentum? Did you simulate with edge mesh, to allow high edge current?

#### zxcv123

##### Newbie level 6
on behalf of varunrvarun:

Yes...The simulation is run with edge mesh..The frequency of simulation is (2 MHz).
The conductor we gave expansion up along with the corresponding conductivity of copper.

The other thing is our system showed out of memory for full 20 turns.
So we segmented the turns to four 5 turn coils and added the resistance..

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