That won't load in my version of MathCAD (2001).  Print it in PDF form and repost it.  Maybe I can help.  

John D
 

I have changed some things in the original file I sent and now it's a bit more plain and simple. the program is shown in the attached PDF file. I want to plot S21_0(f) and P0(f) as shown in the new file I have attached but I could not do so. Any ideas where the problem is? Could you help me to plot it and say where my error is?

Many thanks,

Ganiu.
 

• http://files.engineering.com/getfile.aspx?folder=638fed90-dca0-435c-8e02-f8

Try making S21_0 a function of f and n:  S21_0(f,n).  Then plot for discrete values of n (not range variable).  For instance S21_0(f,1) vs f, S21_0(f,2) vs f, etc.

Dear pstuckey,

I have tried what you asked me to do but it didn't work. The system displays "Mathcad Application has stopped working - close program" and then shuts down. What do you think is responsible for this? Do you think my program is not correct somewhere? I've tried to figure out where but couldn't. Please help me.

I have made good progress, thanks man! But there's one or two things left. I have done for one mode as you will see in my program (attached). How do I make more than one mode appear. You will see that I manually put Q0(1) in the equation S21_0(f) and that's why I have only one peak representing Q0(1). How do I do it for Q0(n) to give n number of peaks?

Secondly, P(0)f is not plotting. The program automatically closes when I try to plot it. Why do you think this is happening? It's saying "this value must be a matrix of scalar elements".

Thanks in advance,

Sheeni.

• http://files.engineering.com/getfile.aspx?folder=3cf6ccc1-c488-40e4-a668-88

Looking back at your original xmcd file, the problem with P0(f) is that you are taking the determinate rather than absolute value.  Unfortunately, Mathcad uses vertical bars for both so you can't tell which it's doing by looking at a printout.  Point the mouse at the S21_0 term in P0(f) and right click, if the box for determinate is checked, change it to absolute value.  Note that both the matrix toolbar and the calculator toolbar have a button for vertical bars, matrix toolbar is determinate, calculator toolbar is absolute value.

For your question about Q0, it will be easiest to work with the xmcd file.  Please attach that to your next post.

Peter

 

Hi Peter, I must confess you are a GURU! LOL! I have been able to plot my P0(f) after following your advice, thanks. Though both S21_0(f) and P0(f) look alike, which I don't think should be, I should be able to figure it out easily. What I need now is the Q0. I have attached the xmcd file as you asked me to. I used MathCAD version 14 now so I hope you'll be able to open it from your side this time. Thanks once again, I look forward to hearing from you soon.

Regards,

Sheeni.

• http://files.engineering.com/getfile.aspx?folder=2e4c0117-2d44-4de4-8056-0e

Sheeni,

Take a look at the alternate graph and let me know if that is what you had in mind.

Regarding P0 and S21_0, 10log(P0) is equal to 20log(S21_0) due to the square term in the definition of P0.

Peter
 

• http://files.engineering.com/getfile.aspx?folder=b27b52d8-bc6e-49e6-960a-05

Thanks Peter for your effort. This not exactly what I have in mind. If you look at my code, I designed the resonant frequency of my resonator to length 83.8 mm which resonates at a fundamental frequency (f0) of 1.25 GHz. So what I have in mind is to plot S21 for 6 modes and have peaks for S21 at 1.25 GHz, 2.5 GHz, 3.75 GHz, 5 GHz, 6.25 GHz, and 7.5 GHz. In your plot, there is only one peak for different values of f. The first peak on my plot and yours are not at 1.25 GHz (should be around 1.8 GHz) and that's what I've been trying to fix. Can you do that for me?

Thanks.

Hi Peter,

I have attached a word document too maybe you'll understand better what I want to achieve. I have modelled a resonator used for broadband measurement. The fundamental frequency is 1.25 GHz and has other modes as shown in the file attached. What i want to do is to reproduce what is in the attachment in MathCAD using the equation S21 which I have developed. I think you'll understand better if you view the attached file. Thanks.

• http://files.engineering.com/getfile.aspx?folder=d424b138-ec36-4054-8e14-b5

Sheeni,

Thanks that does help.  I can tell you the form that the solution must take at least.  For each peak in the response, you need one 'zero' in the denominator.  The way your current equation is written the location of the zero is determined by (f-f0).  since f0 is a constant, the zero is always at the same frequency irregardless of the value of Q0.

I've attached a worksheet to demonstrate the form the equation must take.  The caveat being that this is SOLELY to demonstrate the form of the equation - see the explanation in the xmcd file.

Peter
 

• http://files.engineering.com/getfile.aspx?folder=bf677a98-8d7a-4dbd-98d0-f7

Hi Peter
I have a lower version of mathcad so i can't view your document. Please can you save it with a lower version and resend it? thanks.

Saved as MathCad v11.

Peter
 

• http://files.engineering.com/getfile.aspx?folder=cee1155d-72d3-4361-ae97-93

This looks very interesting Peter. I will have a deeper look into it and see what I can make out. Thanks.