question about "attenuation pad"...

In my opinion,the attenuation pad is used as an impedance transfer tool.(Am I right?) And I ever saw several types such as cross-section pad(from Z-comm AN),pi-section pad(National EVM) and L-section pad(maxim AN) that are attached in this post. My questions are:

1) what is the difference of these 3 type of pad?
2) how to calculate equivalent impedance of the pad? Is there any tools or tutorials?
3) If I want to use attenuation pad(resistor network) to do impedance match and at the same time, I want to get a bias voltage for the next stage. How to consider the resistor value especially?
4) Why not use L and C to do impedance match on PCB instead of the resistor network? Because the L and C will not consume any energy.
5) In the attached picture,there are always AC coupling capacitors. I am afraid that this cap will also influence the impedance.Is it necessary to consider it when select the resistor's value?

thank you very much.

>the attenuation pad is used as an impedance transfer tool.(Am I right?)

A pad will not improve power transfer. If the load is not at the nominal
characteristic impedance a pad will make the source see an impedance closer
to the nominal value.

>what is the difference of these 3 type of pad?
Not much. The cross section pad may be better at high frequencys where resistor
parasistic impedance and ground impedance is more significance.

>2) how to calculate equivalent impedance of the pad?
This is very basic mathematics. Read a basic electronics book about resistors
in series and in parallel.

>4)Why not use L and C to do impedance match on PCB instead of the resistor network?

A pad will reduce reflected power from a mismatched load.

>5) In the attached picture,there are always AC coupling capacitors.
>I am afraid that this cap will also influence the impedance.

The value of the coupling capacitor is sometimes chosen to be large enough
that it's impedance is small at the frequencys of the signals passing
through it. Sometimes the capacitance is canceld by load inductance at
the operating frequency.

>Is it necessary to consider it when select the resistor's value?

Depends on the application.

1. The cross section is really a TEE. For High Frequency I prefer this once since the layout is very balanced from an EM point of view. The L may not give you a perfect match in both directions.
2. Simple impedance calculation. Use your calculator or Rf simulator.
3. I've never done this. The resistor values will probably be too high (too large a voltage drop).
4. Resistive (min-loss) pad match is extremely broadband and very predictable. You can't do that with L/C since the Q is much higher.
5. The cap is probably a DC blocking cap. You have to take it's effect into account but it is not part of the matching network.

There are what are called "minimum loss pads" which have different impedances at each port. If you have more than enough signal level these can be used to do "matching."

One common one goes between 50 and 75 ohms. These are commercially sold for use in testing 75 ohm systems with 50 ohm test equipment.

Here are some equations for their design **broken link removed**

flatulent toonafishy throwaway18
Thank you very much.

Hi throwaway18
Would you recommend me any references for "If the load is not at the nominal
characteristic impedance a pad will make the source see an impedance closer
to the nominal value"?
I ever want to understand the role of attenuator pad via google,however I can not find a good reference. Thank you for your help.