How can I set up a linear FM signal with triangular modulation?

I am trying to set up an fmcw signal model with following parameters: Carrier freq: 24e9 Hz Baseband freq: 1e3 Hz (meaning the period of the whole triangle is 1e-3 sec) Bandwidth: 150e6 Hz (Signal must change from 24e9 to 24.15e9 Hz and back down) Modulation: triangle (not sawtooth)

I tried this code:

%
B = 150*10^6; %Bandwidth
f0=24*10^9; %carrier
%f0 = 200e6; %debug carrier
Ampl=B/2;
w0=2*1000*pi;
W=0.5;
t=0:Tm/2000000:(Tm)-Tm/2e6;
tri=B/2+Ampl*sawtooth(w0*t,W);
Stx=cos(2*pi*f0.*t+tri*0.5.*(t.^2)); %transmitted signal
figure;
plot(t,Stx);
figure;
pspectrum(Stx,2000000,'spectrogram','TimeResolution',1e-3);

I intended to see the freq changing up and down on the spectrogram, according to the triangle parameters, but something assymmetric or even linear comes out. Tried using Carrier freq = 200MHz for debug purposes, didn't cause much changes except for computation time. For f0=24e9 Hz I used

%
t=0:Tm/2.5e7:(Tm)-Tm/2.5e7;
% and
pspectrum(Stx,4.84e11,'FrequencyResolution',10000000,'FrequencyLimits',[0 24.2e9]);

Answer 1

[Dayalan Nair]

Hi,

Try this: https://www.mathworks.com/help/phased/ref/phased.fmcwwaveform-system-object.html

[NoYeah]

how to set the carrier in that toolbox? I cannot set carrier or starting frequency

[Dayalan Nair]

Hi, you would set the carrier when creating other simulation objects. For example:

channel = phased.FreeSpace('PropagationSpeed',c,...

'OperatingFrequency',fc,'SampleRate',fs,'TwoWayPropagation',true);