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How to calculate stopband attenuation for Chebyshev bandpass filter

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Monzerje

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Hi
I have designed a Chebyshev microstrip bandpass filter for frequency range (27.5 - 31.2)GHz and according to my specifications the stopband attenuation should be higher than 30 dB. May I know how to obtain that from the graph?

Capture.PNG
 

Well, you don't show enough of your frequency range but it looks like your stopband attenuation is about -19 db.
 

Stop-Band attenuation is given by an offset frequency.For instance..
-30dB att. 1GHz off-set from center frequency..
 

barry said:
Well, you don't show enough of your frequency range but it looks like your stopband attenuation is about -19 db.
Click to expand...

May I know how you find it -19dB?
Capture.PNG

- - - Updated - - -

BigBoss said:
Stop-Band attenuation is given by an offset frequency.For instance..
-30dB att. 1GHz off-set from center frequency..
Click to expand...

Can you be more precise please?, or if you have links explaining that would you provide them please.
 

Great, now you don't show the out of band signal; it's somewhere off the bottom of the chart. Maybe it's 70 dB, maybe it's 1000000000 dB. But you can see it's greater than 30 dB.
 

barry said:
Great, now you don't show the out of band signal; it's somewhere off the bottom of the chart. Maybe it's 70 dB, maybe it's 1000000000 dB. But you can see it's greater than 30 dB.
Click to expand...

Is the label position correct? and how it is grater then 30dB since the obtained value is -66dB?
Capture.PNG
 

Monzerje said:
Is the label position correct? and how it is grater then 30dB since the obtained value is -66dB?
Click to expand...

Why did you place the marker at that frequency? To evaluate the stopband attenuation value, you need a specification for the stopband frequency range first.
 

Before using a tool whose output you don't understand, it would be better to study some technical literature.
The terms used to specify a filter can be found in every good filter book. Or read the user manual of the software.
 
volker@muehlhaus said:
Why did you place the marker at that frequency? To evaluate the stopband attenuation value, you need a specification for the stopband frequency range first.
Click to expand...

That's why I am asking about it, because I do not know how to find it from the graph

- - - Updated - - -

niki said:
Before using a tool whose output you don't understand, it would be better to study some technical literature.
The terms used to specify a filter can be found in every good filter book. Or read the user manual of the software.
Click to expand...

I already checked, most of them are using the transfer function method which is very long process if I want to do it for many graphs
 

Hi,

That's why I am asking about it, because I do not know how to find it from the graph
Click to expand...
stopband attenuation are two values:
* the (expected, given) attenuation
* the frequency.

You need to have one value to find the other.
It´s impossible to find both.

Read through this:
https://www.dsprelated.com/showarticle/164.php
and see the graphs that describe the terminology.

Klaus
 

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