Post subject: Impedance matching attenuator Posted: Mon
Aug 15, 2005 12:02 pm
I'm trying to impedance match
a non-50Ohm DUT to a 50Ohm VNA. I've seen an explanation of how
to do this using minimum loss pads (see "Spectrum and Network Measurements"
by Robert A. Witte), but any commercial attenuators I see are simply
rated in dB attenuation. Do I need a special 'impedance match' attenuator,
or can I use any which attenuate more than the theoretical minimum
loss? Thanks for your help.
Post subject: Posted: Mon Aug 15, 2005 1:03 pm
Joined: Mon Jun 27, 2005 2:02 pm
element has an attenuation. Therefore, an attenuator that is based
on resistors will have an attenuation. This kind of attenuator will
decrease (improve) the return loss by 2dB for each dB of attenuation.
The only type of matching networks without loss (theoretical)
are reactive matching networks i.e networka that are based on capacitors
and inductors. However, practically, these network are lossy due
to the Q of its components -especially the inductors.
Post subject: Min loss PadsPosted: Mon
Aug 15, 2005 2:58 pm
Yes, you do need special matching attenuators
for this task. Most standard attenuators are 50 ohm in and out.
If you are looking to match from 50 to 75 ohms there are
some sources out there. I have used a relatively inexpensive source
in the past. The insertion loss is 5.7dB.
You can also make your own for any impedance
combination using 1 series and 1 shunt resistor.
K=SQRT(Z1/Z2) + SQRT(Z1/Z2 - 1)
Post subject: Posted: Tue Aug 16, 2005 7:16 am
Thanks for the replies.