I need to design a coaxial balun for 2.4GHz application.

Discussion in 'Wireless & RF Design' started by donut, Dec 5, 2012.

  1. donut

    Thread Starter Member

    May 23, 2012
    I have a test board that has a TI reference design for a Lattice type balun (see attached). The lattice balun on one side is assumed to be matched to the cc2540 at 70 +30j (obtained from TI's spec sheet). And the other side of the lattice balun is assumed to be matched to 50 ohms (obtained from TI's spec sheet).

    What I want to do is measure the impedance of the TI referenced design lattice balun on the differential side for now but the problem is that my VNA does not support differential inputs.

    Since my VNA does not support differential inputs I need to make a coaxial balun that allows me to connect the differential side of the TI reference design lattice balun that exist on my test board.

    So my questions are:

    1) How do I design a coaxial balun for 2.4GHz applications? Any notes, application notes, white papers, links, calculators available that are good resources that can help me with this design?

    2) Will the coaxial balun convert from differential to single ended without changing the assumed differential impedance of 70+30j? Or will the coaxial balun change my impedance on the differential side from 70+30j to 50 ohms?

    3) Is it feasible/possible to connect my TI reference design test board that has the Lattice type balun on it to my vna through the coax balun without changing the assumed impedance of 70+30j?

    4) Is my approach ok?
    Last edited: Dec 5, 2012
  2. Adalberto Amorim FH

    New Member

    Mar 11, 2015
    hello there... do you still remeber of this project?? i don´t have the answer for your question, but have you noticed that one of the legs of the lattice balun does not match? i know that they must be equal values for phase goal, but i can´t understand
    how they use it , the second leg will not match, at least is what i found... using 35+15j you can just match one leg if you use same values for cap and inductor using smith chart. can you give me any tip?
  3. Papabravo


    Feb 24, 2006
    It has been six months since the OP(Original Poster) has logged in. I would not hold out much hope of a reply.