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Set axis type for rfplot in RF Toolbox



setrfplot(axistype) applies or removes the use of engineering units on the X-axis of rfplot. By default, engineering units are always applied in the X-axis and persist across all MATLAB sessions.

setrfplot(axistype,persist) controls the persistence behavior of the units on the X-axis plot across MATLAB sessions.


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This example shows how to design a low-pass Butterworth filter with passband frequency of 3 kHz, stopband frequency 7 kHz, passband attenuation of 2 dB, and stopband attenuation 60 dB. Display the filter order of such a designed filter and determine the passband frequency at 3.0103 dB. See [2] in rffilter object page.

Filter Parameters

Fp = 3e3;          % Passband frequency, Hz
Ap = 2;            % Passband attenuation, dB
Fs = 7e3;          % Stopband frequency, Hz
As = 60;           % Stopband attenuation, dB

Design Filter

r = rffilter("FilterType","Butterworth","ResponseType","Lowpass","Implementation","Transfer function","PassbandFrequency",Fp,     ...

Filter Order of Designed Filter

N = r.DesignData.FilterOrder;
sprintf('Calculated filter order is %d',N)
ans = 
'Calculated filter order is 9'

Frequency at 3.0103 dB

F_3dB = r.DesignData.PassbandFrequency/1e3;
sprintf('Frequency at 3.0103 dB is %d kHz',F_3dB)
ans = 
'Frequency at 3.0103 dB is 3.090733e+00 kHz'

Visualize Magnitude Response

frequencies = linspace(0,2*Fs,1001);
rfplot(r, frequencies)

Figure S-Parameters 21 contains an axes and another object of type uitoolbar. The axes with title s21 vs. Frequency contains an object of type line.

Note: To use rfplot and plot on the same figure use setrfplot. Type 'help setrfplot' in command window for information.


  1. Larry D. Paarmann, Design and Analysis of Analog Filters: A Signal Processing Perspective, Kluwer Academic Publishers

Input Arguments

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Units on rfplot X-axis, specified as 'engunits' or 'noengunits'.

Data Types: char | string

Units on rfplot X-axis across MATLAB sessions, specified as true or false.

Data Types: logical

See Also

Introduced in R2019b