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Converts rffilter to transfer function



[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.


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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",               ...

Use tf function to generate the transfer function.

[numerator,denominator] = tf(filtobj);

The numerator of the transfer function for S21 is:

ans = 1×5

     0     0     0     0     1

The denominator of the transfer function for S21 is:

denominator = 1×5

    1.0000    2.6131    3.4142    2.6131    1.0000

The corresponding polynomials in factored form is:

ans = 2×3

     0     0     1
     0     0     1

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


Introduced in R2019b