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  1. #1
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    Simulation of CPW Patch Antenna using HFSS

    I am trying to simulate a CPW antenna using HFSS. It has a resonance at 2.45 GHz but for some reason, S11 is positive at most of the frequency range!
    The attached response is plotted using Zpi. Zpv gives me 0 for all frequencies.
    Could you please give me any hints or suggestions to fix it.
    Thank you.

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  2. #2
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    Re: Simulation of CPW Patch Antenna using HFSS

    Hi abuzaid10,

    I took a look at your simulation. Look at the fields on the wave port -- when I ran your simulation, the fields produced were not that of a CPW mode. I would surmise your port is the incorrect size. You might want to play around with adjusting its height and width. If it still doesn't work, you may need to use lumped ports instead.

    Good Luck!


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  3. #3
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    Re: Simulation of CPW Patch Antenna using HFSS

    Hi PlanarMetamaterials,

    Thank you very much.
    I followed the steps in HFSS manual (link is below), pages 270 - 271, to implement the lumped port. This example about CPW Fed Bowtie Antenna.
    http://anlage.umd.edu/HFSSv10UserGuide.pdf

    I am attaching the S11 response which is negative now but without resonance at 2.45 GHz.
    The strange thing is that when I plotted Z of the port, it varied between 25 to 200 Ohms as in the attached image.
    Since I am assigning full port impedance of 50 ohms, it should be 50!
    Do you know the reason?
    Thanks again.



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  4. #4
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    Re: Simulation of CPW Patch Antenna using HFSS

    You have S11 < -10dB (VSWR better than 2:1) between 2.1GHz and 2.6GHz, so the antenna resonates on the desired 2.4GHz frequency.
    Bow-tie antennas are wideband antennas, but placed in a 4x1 array configuration, the electrical length of the feed line segments would affect the overall S11 frequency response.
    For example if the feed line segment is λ/4 at 2.4GHz, will not be the same at 2.2GHz.
    Have to evaluate also a single antenna element (part of the array) and the coupling between antenna elements (which may need to be adjusted for desired directivity and minimum side lobes).


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  5. #5
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    Re: Simulation of CPW Patch Antenna using HFSS

    Quote Originally Posted by abuzaid10 View Post
    The strange thing is that when I plotted Z of the port, it varied between 25 to 200 Ohms as in the attached image.
    Since I am assigning full port impedance of 50 ohms, it should be 50!
    Do you know the reason?
    Yes, Z(1,1) is not port impedance. It's the input impedance seen at the port.


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  6. #6
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    Re: Simulation of CPW Patch Antenna using HFSS

    Thank you very much vfone.

    Quote Originally Posted by PlanarMetamaterials View Post
    Yes, Z(1,1) is not port impedance. It's the input impedance seen at the port.
    I see. Thanks a lot for clarification.
    I think this means the feedlines are not designed correctly to match the 50 Ohms connectors, correct?



  7. #7
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    Re: Simulation of CPW Patch Antenna using HFSS

    It appears from the S11 that there are many mismatches, yes.

    As a caveat, I have *heard of* people having issues with these lumped port feeds indicating responses that were not observed in measurement. I think to verify, you should try simulating an attached connector, and feeding that instead of the transmission line directly.


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  8. #8
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    Re: Simulation of CPW Patch Antenna using HFSS

    Quote Originally Posted by abuzaid10 View Post
    I think this means the feedlines are not designed correctly to match the 50 Ohms connectors, correct?
    No, not correct!


    Zin= 5o Ohm requires that your antenna is 50 Ohm also. But of course, your antenna is NOT perfect matched over the complete simulation range.


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