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CC2531EMK: CC2531EMK Meandered antenna impedance

Joaquim Martinez
Expert 1270 points
Part Number: CC2531EMK
Other Parts Discussed in Thread: CC2540, CC2511, CC2531

Hi all.

I am simulating the meandered antenna given in the CC2531EMK reference design. For this, I am following the AN043 "Small size 2.4GHz PCB antenna". The antennas layout are exactly, not the matching, but it s a good start point to understand how it works.

According to AN043 the impendance at the feed point is 50 Ohms. I imported the CC2531EMK gerbers and I simulated basically two different layouts: only the antenna, antenna + trace to balun. After several simulations the feed S11 params is +0.0020 dB at 2.45GHz, (impedance is 5KOhm  / 90º). I used different stackups for CC2540, CC2511, etc. but the results are always the same. Please refer to the attached images for an example.

The recommended balun is 2450BM15A0002, specially designed to match the CC2531 RF ports, which just need to see 50 Ohms at unbalanced port (antenna + track).

There is something special to consider in this design/simulation? 

  • 0
    TI__Genius 9215 points

    Hi,

    Since your S11 is close to 0 dB this means that almost all applied power is reflected back and nothing is radiated in the antenna.

    What simulation tool are you using? Are your simulation port setup correctly? You should see much lower impedance with this antenna at 2.45GHz than 5kohm if everything is setup and runs correctly (should be in the 50ohm area).

    Best Regards,

    R.M 

  • 0 in reply to R.M
    Expert 1270 points

    Hi R.M. 

    Thanks for your answer.

    I use ADS. 50 Ohms port is a Term port.

    I had a mistake in the Conductivity copper stakcup param. Now is fixed to 5.8e7 Siemens/m (by default) and I have "better" results but still far away from AN043 results. I am not sure if the problem can be the vias, but I think is OK. Please refer to the two 3D images vias (the first one is the via definition between layers, just to view the connection, and the the whole layout).

    Any idea about the problem?

    Thanks.