Well, I can tell you how I do it. I usually work
at 900 MHz, so I don't know how well this method
will scale with frequency, though it should if
you use the right cables.
First of all,
you need a vector network analyzer. The 8753D or
later model from HP/Agilent is a nice choice.
The important thing when using a VNA is to
calibrate the ports. More on that later.
On your board, you need a way to disconnect the
DUT (device under test) from the rest of the
circuitry. Normally, there is a DC blocking cap
in line with most parts of an RF circuit, so the
easiest thing to do is to remove the DC blocking
capacitor. Next, take a short section of RG174
cable with a SMA connector on one end and strip
back the other end to expose the shield and
center conductor. You will also need a complete
SMA RG-174 cable with SMA connectors on both
ends for calibration.
Solder the shield
of the test cable to a ground point very close
to the antenna, filter, or whatever you are
testing. Solder the center conductor to the pad
of the DC block you just removed so that the
cable is now electrically connected to the DUT.
Now, connect the other cable (the one we are
using for calibration) to one of the ports of
the VNA; Lets use port 1 for this example. Using
the instructions for the VNA, perform a 1-port
calibration on port 1. THis will involved you
connected calibration standard loads to the end
of the cable; there will be a 50-ohm, a short,
and an open standard. Once complete, the VNA is
now calibrated, including the length of cable
you are using with the DUT.
now be able to connect the cable soldered to the
DUT to port 1 of the VNA and perform your
You can do the same trick
with 2 cables if you need to do 2 port analysis
Please post any questions
you have if this isn't clear enough.
The RF Troubleshooter