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RF Probe and Pigtail

B

Brian Chan

Jan 1, 1970
0
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.

Thanks.

Brian
 
J

Joel Kolstad

Jan 1, 1970
0
Brian Chan said:
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.

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?
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?

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.

---Joel
 
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