piclist 2002\07\06\111429a >
Thread: Directional couplers & T/R test sets
face BY : Bill Colville email (remove spam text)

I have never heard of using a 90 degree hybrid for making S
parameter measurements. They are usually used for comparing
impedences. I don't see any practical way to do it.

Lacking a proper S parameter test set, as described by another
poster, the hook-up for using a separate power splitter and
directional coupler is as follows:

The RF output from the network analyzer goes to the input of the
power splitter. One output from the power splitter goes to the
Reference input of the analyzer. When measuring an active device,
such as your preamp, the other output from the power splitter goes
through an attenuator to the input of the directional coupler and the
non-coupled output goes to the input of the DUT. The coupled
output of the directional coupler goes to either the A or B input on
the analyzer. The attenuator is to reduce the input voltage so it will
not overload the DUT while still providing sufficient Reference signal
for the analyzer. The other, A or B, input of the analyzer goes to
the output of the DUT, might require an attenuator depending on
the gain of the device. This set-up will measure S-11 and S-21, to
measure S-12 and S-22 reverse the DUT. Make sure there is no
DC voltage on the input and output connectors of the DUT, if there
is, a DC block or bias T must be used to isolate it from the
analyzer detectors.

Bill, W3NMK

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In reply to: <046901c22467$e21ae500$199f42d8@czhang>
See also: www.piclist.com/techref/index.htm?key=directional+couplers
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