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Why I can't have a right simulation result for antenna by HFSS

kent5566007

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Hello all,

I just want to compare the antenna characteristic between simulation, processed by HFSS 13, and real sample purchased from market. I learned the simulation step by step from forum, YouTube and HFSS helper.

But it comes up with huge different result. I try very hard to get a matched simulation, but keep fail and fail.


Is anyone could point out the wrong procedure I processed? Here is the simulation details as following,
  • Draw the outline of antenna on XY plane with +-0.1mm deviation.
step1.png
  • Add substrate and air space.
step2.png
  • Draw an IC input and two inductor patch on each sides of IC.
step3.png
  • Setup the material for copper antenna with 1.4mil thickness and 0.4mm for FR-4 epoxy substrate.
step4.png
  • Apply Solution Type as Driven Terminal. Setup Perfect E for inductors patches and lumped port input with 28.31+204.1j impedance, which is Alien H3 chip with 28.31-204.1 impedance.
step5_.jpg
  • Setup boundary radiation for air space.
step6.png
  • Setup the max number of passes and Delta. S.
step7.png
  • Setup the sweep.
step8.png
  • Validate and run the analyze.
  • Finally, I open the Terminal S parameter result, it turns totally wrong.
result.png
Note: all the dimension was measured by microscope with +-0.1mm variation.


According to this result, this RFID can’t even be read from 1 meter away. I run the test by Voyantic test bench to compare the real situation, it shows the conjugate frequency around 940MHz with read range over 5 meter away. And according to my experience, there is no way to come up with such difference with slightly dimension variation.


Please help to give me a hint, I stuck with this problem for two months, and just can’t figure it out.

Thanks,
 

PlanarMetamaterials

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Hi @kent5566007,

I think we need some more information. You said the simulation result was "totally wrong"; what were you expecting? If you plot ReZ11 and ImZ11, what values do you see?
 

kent5566007

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Hi @PlanarMetamaterials ,
The main purpose of this simulation is I want to make sure I use correct processes before I make a design. Therefore, I just simulate a real sample and compare with its performance by Voyantic test bench.
As I know, if test bench shows the longest read range at specified frequency, test from 800MHz to 1GHz. Which means the conjugate impedance would happen around that frequency.

Now I get the result, which is 940MHz as the longest read range. So I assume that the conjugate impedance would happen around 940MHz.
impedance.png

Thanks,
 

kent5566007

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To avoid misunderstanding with port impedance definition, I would use a test case to see if HFSS requires the conjugate impedance or the device impedance.
Hi @volker@muehlhaus ,
sorry to my confusion, I am not sure the meaning of device impedance. Does this means antenna impedance with 50Ohms input?
If not, would you like to help to give more details?

Many thanks,
 

volker@muehlhaus

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I meant that you can try with opposite sign for the imaginary part.

Or do a test case to verify that you get S11=0 in HFSS when the port impedance is conjugate match. It is a bit fuzzy in RF simulators what to specify as port impedance for complex loads, so you better double check the sign of the imaginary part.
 

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