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tf

Converts rffilter to transfer function

Description

example

[numerator,denominator] = tf(filter) returns numerators of S-parameters, Sij contained in num(i,j) and the denominator of the filter object. This method only works for the 'Transfer function' implementation of rffilter object.

Examples

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Generate the transfer function of a low-pass fourth-order Butterworth filter for cut-off frequency of 1 rad/sec.

Create the rffilter object.

filtobj = rffilter('FilterType',"Butterworth",'ResponseType','Lowpass', ...
    'FilterOrder',4,'Implementation',"Transfer function",               ...
    "PassbandFrequency",1/(2*pi),"Zin",50,"Zout",50);

Use tf function to generate the transfer function.

[numerator,denominator] = tf(filtobj);

The numerator of the transfer function for S21 is:

numerator{2,1}
ans = 1×5

     0     0     0     0     1

The denominator of the transfer function for S21 is:

denominator
denominator = 1×5

    1.0000    2.6131    3.4142    2.6131    1.0000

The corresponding polynomials in factored form is:

filtobj.DesignData.Numerator21
ans = 2×3

     0     0     1
     0     0     1

filtobj.DesignData.Denominator
ans = 2×3

    1.0000    0.7654    1.0000
    1.0000    1.8478    1.0000

Input Arguments

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RF filter, specified as an rffilter object.

Output Arguments

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Numerators of S-parameters, returned as a cell array of Sij contained in num{i,j}.

Denominator of coefficients, returned as a row vector.

See Also

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Introduced in R2019b