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RF Probe and Pigtail

Discussion in 'Electronic Design' started by Brian Chan, Aug 6, 2007.

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  1. Brian Chan

    Brian Chan Guest

    Hey Guys,

    I am designing a circuit with a 2.4 GHZ printed antenna, I would like to
    probe the antenna for S11 parameters without sticking an SMA jack on the
    PCB. It seems to me that the only way to accomplish this is to put an RF
    Probe point on the PCB. Can someone direct me to a resource that specifies
    how to place the probe point?

    I would like some information on what the probe point should look like, I
    suspect this depends greatly on the type of probe that is being used. What
    types of probes exist? I have heard of the use of pigtails as cheap RF
    probes but I am not so sure about the details (and pitfalls) of doing this.


  2. Joel Kolstad

    Joel Kolstad Guest

    Well, there are plenty of other connectors besides SMA jacks -- MMCX is not
    uncommon for 2.4GHz stuff. But I'm assuming you didn't want to put *any*
    connector on the PCB?
    Unless you have more money than you know what to do with (in which case you
    can give, e.g., Cascade Microtech a call), you'll find yourself using just
    straight 50 ohm coax or FET probes. FET probes are meant more for
    troubleshooting, however, and this is really the core of your problem: At
    2.4GHz, to get accurate *measurements*, you need a mechanically repeatable
    interface to the board for your signal and ground reference. After that, you
    need some amount of transmission line (preferably many tens of degrees at a
    minimum) to de-embed whatever your mechanical interface is... and you need to
    make yourself a a open/short/through/load (or similar) calibration board with
    the same amount of transmission line.

    Now, if you're just after *relative* measurements (i.e., just trying to find
    resonances or maixmize return loss, etc.), you probably don't need any of
    this: Just solder down some short pigtail leads off of a coax cable to your
    board, and call it good.

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