How the "attenuation pad" smooth out impedance mis

[trashbox]

The pi-section or Tee-section attenuation pad(or named attenuators) on PCB is used to smooth out any impedance bumps,and the greater the attenuation of the pad, the greater the degree of immunity to impedance changes.Furthermore, pi-section attenuator's leg resistors are equal in this case(please refer to: h**p://mrtmag.com/mag/radio_rf_attenuators_terminations/) What I can not understand is:

1)How the pi-section pad,whose leg resistors are equal,smooth out the impedance mismatch?(In fact,it is explained in the reference,but I can not see it since the lack of mentioned figures)

2)Some other articles also mentioned that the attenuation pad can act as an isolation? What is the principle?

Thanks for your comments.

 

[xtasa]

Re: How the "attenuation pad" smooth out impedance

Hello Trashbox,

If you putting Pi or Tee attenuator between two stages you will improve isolations between them . Bigger attenuation better isolation. Physical explanation is a very simple. ATT decrease useful signal but also unwanted reflections . Image for example that you have termination close to the open end useful power will be attenuate by ?dB value at the ATT and reflected power will be also attenuate before it arrived again to source at the ATT for the same value of ? DB. This mean if you have for the example ATT 6 dB you will have S11/S22 -12dB/to the both sides That is way how its work. Theoretically you will decrease impedance plane at the output/input where you can transform impedance of load .Open end will be never open also is the same situation with the short end.

GL XTASA

 

[toonafishy]

Re: How the "attenuation pad" smooth out impedance

Here is aother good reference

h**p://www.maxim-ic.com/appnotes.cfm/appnote_number/972

 

[jallem]

Re: How the "attenuation pad" smooth out impedance

There is an application note from Agilent(HP) when
the explanation of power measurement uncertainty
tells evrything about the attenuation and how that
affect the power measurement. How is that related?
The use of an atenuator decrease the amount of
MIsmatch uncertainty or in other words decrease the
amount of reflection seen by the power meter. it is
the same effect. Attenuation reduce the reflection
coeficient, consequently it looks as matching(smoothing)
device.