The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> RF Design >> About reflection coefficient and ripple coefficient
https://designers-guide.org/forum/YaBB.pl?num=1216996857

Message started by gaom9 on Jul 25^th, 2008, 7:40am

Title: About reflection coefficient and ripple coefficient
Post by gaom9 on Jul 25^th, 2008, 7:40am

Hi,
I have a question about the relation between reflection coefficient and ripple coefficient in filter design in rf circuit.
I have read two kind of relationship of them as shown by the following pictures.
Can anyone tell me which one is right?

And I want to where is the relationship from, and how to calculate it, for an example, when we want to get a -10dB reflection coefficient, we should make the ripple coefficient below -0.46dB, can anyone show me the process of this calculation and what unit should we take in calculation, dB or others, please?

Thank you!
Best regards!

Title: Re: About reflection coefficient and ripple coefficient
Post by buddypoor on Jul 25^th, 2008, 8:50am

I think that the second equation is correct. But the following definitions are important - also because of the units.

1.) The ripple coefficient must be used in the equation as an absolute number - and in contrast to you I call this "a" .
2.) Γ is the reflection coefficient (absolute), when multiplied by 100 >>> in %
3.) a is the "ripple coefficient" (absolut) : a=Amax/Amin (absolut) and with your terminology ρ=20log(a).
4.) This leads to the result Γ=0 if Amax=Amin (no ripple) which makes sense.
5.) Your example: ρ=0.46 dB (positive sign !) >>> a=1.0544
Γ²=1-1/1.0544²=1-1/1.111=0.1005024 >>>Γ=0.317 >>> -10 dB.

I think it suits.
Regards

Title: Re: About reflection coefficient and ripple coefficient
Post by gaom9 on Jul 25^th, 2008, 7:42pm

LvW,
Thank you very much!
This question has puzzled me a long time.

Best regards!