tf

Converts rffilter to transfer function

Syntax

[numerator,denominator] = tf(filter)

Description

[numerator,denominator] = tf(filter) returns numerators of S-parameters, S_ij 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

Generate Transfer Function of Butterworth Filter

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

filter — RF filter

rffilter object

RF filter, specified as an rffilter object.

Output Arguments

numerator — Numerators of S-parameters

cell array

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

denominator — Denominator of coefficients

row vector

Denominator of coefficients, returned as a row vector.

Version History

Introduced in R2019b