# freqresp

Frequency response of rational object and `rationalfit` function object

## Syntax

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

## Description

example

````[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`.```

## Examples

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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)))`

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

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

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

Data Types: `double`

## Output Arguments

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

Data Types: `double`

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

Data Types: `double`

## Version History

Introduced before R2006a