group delay filter modeling matlab

[rizias]

Hello everyone,
I have the measurements of filter’s Group delay and S-parameters.
The S-parameters are of the following form presented in a touchstone file
!Agilent Technologies,N5242A,MY49421489,A.09.33.09
!Agilent N5242A: A.09.33.09
!Date: Thursday, March 22, 2012 19:50:06
!Correction: S11(Full 2 Port(1,2))
!S21(Full 2 Port(1,2))
!S12(Full 2 Port(1,2))
!S22(Full 2 Port(1,2))
!S2P File: Measurements: S11, S21, S12, S22:
# Hz S dB R 50
1450000000 -0.44925556 132.79056 -43.664959 42.970737 -43.609634 45.291161 -0.41757283 131.60133
1450100050.025 -0.44976574 132.81039 -43.738403 42.790764 -43.597622 44.620411 -0.40801486 131.61304
1450200100.05 -0.45033455 132.82925 -43.531742 44.20499 -43.862129 44.206757 -0.40980196 131.49973
(The S-parameters are of the following format S11,angle(db), S21,angle(db), S12,angle(db), S22,angle(db))
The filter’s Group delay data are like the demonstrated bellow:
!CSV A.01.01
!Agilent Technologies N5242A MY49421489 A.09.33.09
!Agilent N5242A: A.09.33.09
!Date: Thursday March 22 2012 19:57:00
!Source: Standard
BEGIN CH1_DATA
Freq(Hz) S21 Delay(s)
1.45E+09 -2.02E-08
1.45E+09 -1.32E-08
1.45E+09 -1.77E-08
1.45E+09 -1.70E-08
1.45E+09 -1.56E-08
1.45E+09 -1.36E-08
1.45E+09 -1.20E-08

That i want to do is to simulated the impact that the group delay will have on a particular waveform using MATLAB.
I tried to use the fdesign.arbgrpdelay in order to insert my group delay data and somehow observe how that would impact on a waveform but i am getting the following error:
Error using fdesign.abstracttype/superdesign (line 96)
Design options must be specified as a structure or as parameter-value
pairs.

Error in fdesign.abstracttype/design (line 11)
varargout{1} = superdesign(this, varargin{:});

Error in allpassfilterarbitrarygrpdly (line 413)
Hgd = design(hgd,'iirlpnorm','Weights','MaxPoleRadius',0.95);

I also tried to use fdatool but i couldn't find a way of designing a filter by changing its group delay.The group delay was flat in all the available designs.

 

[GregLocock]

Frankly I'd use simulink for this job. Failing that did you read through the examples on filter design and simulation? I am no expert but it looks to me like you didn't structure your data correctly.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[hacksaw]

Seems that you may need to look at the frequency resolution of your csv file

when the correct frequency data are used, you should be getting more detailed results from matlab see attached

 

[rizias]

Hello and thank you fro your reply,
I know that it could be better modelled on Simuling but it should be bone on MATLAB.
The frequencies used are scaled from 0 to one,it is the default method for the fdesign.arbgrpdelay.So that it must me done is the group delay to be inserted.@hacksaw Can you expand a bit more on that you suggested me?
Thank you in advance for your reply.

 

[hacksaw]

your data shows that the group delay is anything but constant
here it is in tabular form

frequency time delay
1450000000 -2.02E-08
1450100050 -1.32E-08
1450200100 -1.77E-08
1450300100 -1.70E-08
1450400100 -1.56E-08
1450500100 -1.36E-08
1450600100 -1.20E-08

beyond that only an ideal transmission line will show a constant group delay, not a filter where the phase shift and the group delay is frequency dependent

good luck