What is First Null Return Loss?

[si14]

nulled return loss

Hi all,

What is the First Null Return Loss (FNRL)? I think it's applications are in Low pass filters.
Does any one know anything about this? Is it a criteria for LP filters?

Thanks.

 

[kspalla]

Null in other words is zero response, means it can be for any filter or antenna.
If it is LPF then the RL at corner freq is the FNRL.

 

[si14]

Many Thanks for the help.
Could you please tell me the amount of FNRL for the filter I've attached?

The (3-dB)cut off frequency is about 4.5 GHz.
The red plot is S21 and the blue one is S11.
What's the FNRL? (-40dB @ 4.2GHz or -15dB@3.8GHz)

**broken link removed**

 

[kspalla]

I am confused with the result. It shows two results of RL. One may be from schematic and the other from sonnet EM simulator.

From the graph, I estimate that( as it is not table)
FNRL from one case is it is at 4.8GHz and 3.6GH in other case. Both are at -40dB.

 

[si14]

Thanks for the help. I got it.