Main Content


Set axis type for rfplot in RF Toolbox

Since R2019b



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.


collapse all

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 object and another object of type uitoolbar. The axes object with title s21 vs. Frequency, xlabel Frequency (kHz), ylabel Magnitude (dB) 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

collapse all

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

Version History

Introduced in R2019b

See Also