[SI-LIST] Re: Rf measuring
- From: "McCoy, Bart O." <McCoy.Bart@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 11 Aug 2003 09:42:04 -0500
The most thorough method of measuring the reflection coefficient
of things like connectors is to use a vector network analyzer (VNA).
The VNA will give you a full magnitude and phase characterization
of the connector across a frequency band of interest. Theoretically,
a TDR has all of this information in it (usually with less bandwidth
information in it), but it can require lots of work to simulate
and extract the full reflection and VSWR characteristic as a function
of frequency (if you're doing broadband).
TDR measurements in the time domain are wonderful for measuring
impedance and reflection coefficients for structures that do not
have complex reflection coefficients (like microstrip lines and
small discontinuities) but if you want to understand VSWR of a
complicated connect across a band of frequencies and know what frequency
signals
will and won't work in your connector, the VNA is by far the most direct
method.
Unless you do a lot of model-hardware correlation, TDR will only give you
a single reflection coefficient for various physical points in your
structure.
That's great for debugging the structure itself. But if you want
CHARACTERIZATION of a connector, then you probably only want to know the
NET performance-- the final answer- of the connector itself. And for
that, you probably want to know-- not just a single reflection coefficient--
but the reflection characteristic across your entire frequency band of
interest.
You need a VNA for that.
e.g. Suppose you're doing narrow band signaling (for RF work) and a TDR
shows a certain
time-domain reflection characteristic. How much can you be off in your
TDR-derived
reflection coefficient? You will never know with a TDR. If your
connector is
a narrow band performer, your reflection coefficient could be great at the
frequency of
interest (the only place it matters) and be horrible elsewhere. Your VSWR
will be very low (near 1) and you can see all of that with a VNA at a
glance, but you
wouldn't necessarily know that from a TDR without lots of work.
It depends on what you want to know and understand about your circuits.
- Bart
-----Original Message-----
From: saeed keshavarz [mailto:saeed_keshavarz2002@xxxxxxxxx]
Sent: Saturday, August 09, 2003 12:03 AM
To: Si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Rf measuring
>> Hi all expert and amateurs
>> I'm looking for the most accurate & common method and procedure to
>> measuring the impedance and vswr and so the voltge reflection
cofficient of rf connectors of rf cables (ex: 2.5c-2v & 3c-2v connectors)
please
introduce some suitable rf equipments and the metods to do above
measuring.
>> thank you in advance.
>> Best
>> Saeed Keshavarz. E- MAIL saeed_keshavarz2002@xxxxxxxxx
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