freqresp

Frequency response of rational object and rationalfit function object

Syntax

[response, outputfreq] = freqresp(fit,inputfreq)

Description

[response, outputfreq] = freqresp(fit,inputfreq) calculates the frequency response, response of the fit of a rationalfit function object or a rational object at the specified input frequencies, inputfreq.

Note

There is limited control over how the freqresp function extrapolates outside the input data's frequency band because the rational object creates a rational-function fit to frequency-domain data . The high-frequency limit of the response is determined by the TendsToZero property of the rational object: if the TendsToZero is set to true, the response will approach zero at high frequencies; otherwise, it will follow the best-fitting that is predicted by the rational object.

Examples

Frequency Response of Data Stored In File

Create a sparameters object from a file and use rfparam to extract the ${\mathit{S}}_{21}$parameters.

S = sparameters('passive.s2p');
S21 = rfparam(S,2,1);

Fit a rational function to the data by using rationalfit.

freq = S.Frequencies;
fit_data = rationalfit(freq,S21);

Compute the frequency response by using the freqresp method and plot the magnitude and angle of the frequency response.

[resp,freq] = freqresp(fit_data,freq);
plot(freq/1e9,20*log10(abs(resp)))

plot(freq/1e9,unwrap(angle(resp)))

Frequency Response of S-Parameters Object

Perform rational fitting on a S-parameters object by using rational object.

S = sparameters('passive.s2p');
fit_data = rational(S);

Compute the frequency response by using the freqresp function.

freq = S.Frequencies;
[resp,freq] = freqresp(fit_data,freq);

Plot the magnitude of the frequency response of the ${\mathit{S}}_{21}$data.

plot(freq/1e9,20*log10(abs(squeeze(resp(2,1,:)))))
xlabel('Frequency (Hz)');
ylabel('Magnitude of Frequency Response');

Plot the angle of the frequency response of the ${\mathit{S}}_{21}$data.

plot(freq/1e9,unwrap(angle(squeeze(resp(2,1,:)))))
xlabel('Frequency (Hz)');
ylabel('Angle of Frequency Response');

Input Arguments

fit — Rational fit object

rfmodel.rational object | rational object | M-by-N array

Rational fit object, specified as a rfmodel.rational or rational object. The size of this object is M-by-N array.

inputfreq — Input frequency

real positive vector

Input frequency to compute and plot the frequency response, specified as a vector of positive frequencies in Hz.

Data Types: double

Output Arguments

response — Computed frequency response

vector

Computed frequency response of each M-by-N fit, specified as a vector.

Data Types: double

outputfreq — Frequency values same as input frequencies

real positive vector

Frequency values same as input frequencies, returned as a real positive vector.

Data Types: double

Version History

Introduced before R2006a