Hello,

I have a question regarding Agilent AN 1287-8, and the references by Dr J. Dunsmore, using the time-domain tuning technique. My question is that when I try to get the simulated filter results presented in figure 2 on page 6, I cannot reach the same time-domain response shown on the right. I am using Matlab, taking inverse Fourier of the S11, for a range 2-5 times the bandwidth, with many points, say 1000.

I would appreciate if you could clarify how to exactly obtain the figure on the right hand side of figure 2, from the S-parameters. It seems that in this App note, ADS was used. I would highly appreciate if you could clarify how the plot is obtained, either using ADS or any other software. To me it looks like some sort of processing was done to obtain that figure in addition to the inverse fourier, which is probably mimicking the algorithms of the time-domain bandpass mode in VNA, or maybe certain conditions are followed which may have not been detailed in the app. note. I would appreciate if you could shed light on this.

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In Matlab:

Assume a S11 array with 1000 entries for a freq. span 2-5 times the bandwidth, centered at the center frequency of filter.

S11_t = IFFT (S11, 10000);

plot (1:10000,20*log10(abs(S11_t))) ;

--------------------------------------------------------

In ADS, for the simulated LC filter of Figure 1 having magnitude S as in Figure 2:

In the results window, I plot:

dB(ts(S(1,1),-10ns,50ns,10000))

-------------------------------------------------------------

I appreciate if you could let me know if these methods are at all correct or whether I should be taking a different approach,or whether some intermediate steps or settings are required.

Thank you.

I have a question regarding Agilent AN 1287-8, and the references by Dr J. Dunsmore, using the time-domain tuning technique. My question is that when I try to get the simulated filter results presented in figure 2 on page 6, I cannot reach the same time-domain response shown on the right. I am using Matlab, taking inverse Fourier of the S11, for a range 2-5 times the bandwidth, with many points, say 1000.

I would appreciate if you could clarify how to exactly obtain the figure on the right hand side of figure 2, from the S-parameters. It seems that in this App note, ADS was used. I would highly appreciate if you could clarify how the plot is obtained, either using ADS or any other software. To me it looks like some sort of processing was done to obtain that figure in addition to the inverse fourier, which is probably mimicking the algorithms of the time-domain bandpass mode in VNA, or maybe certain conditions are followed which may have not been detailed in the app. note. I would appreciate if you could shed light on this.

------------------------------------------------------------

In Matlab:

Assume a S11 array with 1000 entries for a freq. span 2-5 times the bandwidth, centered at the center frequency of filter.

S11_t = IFFT (S11, 10000);

plot (1:10000,20*log10(abs(S11_t))) ;

--------------------------------------------------------

In ADS, for the simulated LC filter of Figure 1 having magnitude S as in Figure 2:

In the results window, I plot:

dB(ts(S(1,1),-10ns,50ns,10000))

-------------------------------------------------------------

I appreciate if you could let me know if these methods are at all correct or whether I should be taking a different approach,or whether some intermediate steps or settings are required.

Thank you.

But, the filter tuning technique relies on "bandpass" time domain mode, so that is your first problem.

The IFFT is not at all the same as the Inverse Fourier Transform, because of bucketing limitations. You must use a discrete fourier transform to get sufficient resolution, so that is your second problem.

The plots in the application note were created by creating an ADS simulation, saving the data to CITI file, reading the CITI file into a PNA, computing the time domain trasform in bandpass mode, then saving the CITI file format of the result and reading it back into ADS for display. Not particularly elegant, but such is life.