I am simulating a FMCW radar (Ramp signal is used for transmission)and I have created the transmit signal from matlab FMCW model

hwav = phased.FMCWWaveform('SweepTime',sweep_time,'SweepBandwidth',radar_bandwidth,'SampleRate',Fs);
hchannel = phased.FreeSpace('PropagationSpeed',co,'OperatingFrequency',radar_startfreq,'SampleRate',Fs,'TwoWayPropagation',true);
htx = phased.Transmitter('PeakPower',1,'Gain',tx_gain);
hrx = phased.ReceiverPreamp('Gain',rx_gain,'NoiseFigure',1,'SampleRate',Fs);
hcar = phased.RadarTarget('MeanRCS',1,'PropagationSpeed',co,'OperatingFrequency',radar_startfreq);

x = step(hwav);    % Generate the FMCW signal
xt = step(htx,x);  % Transmitted FMCW signal

After the reflection from the target the reflected wave is : Some of the code delibrately missed.

xt = step(hrx,xt);  

and it comes after some delay and then its multiplied with the transmitted signal to get the beat signal.

Now the multiplication is done between the received signal and the transmitted signal to get the beat signal. The matlab uses dechirp method to perform this operation.

radar_return = dechirp((xt),x);

So the output look like:

enter image description here

So I want to ask some questions related to it: I came across the equation of mixed signal (Linear Frequency Modulated tx mixed with LFM Rx ) as (1/2)*cos(2*pi*(fctd+(4B*R/Tp)*t)) fc= center frequency td = delay time of pulse (From target reflection) B = Bandwidth R = Range Tp = pulse duration t = fast time (actual time) Is this equation of the same signal which I have plotted, I am confused due to leading zeros I am getting in my mixed signal but in equation if I put the values of t then no zeros I am getting.

Also If yes the plot and the equation after mixing (matlab dechirp) are same. Then how can I remove leading zeros and make it signal with continous time and phase shift in the equation. In the equation there is a phase shift


and In plotted signal received from mixing two Linear chirp signal I am getting zeros and the mix signal. How can I get the signal starting from t=0 with the same phase as in equation, since they both are same.


  • $\begingroup$ Your question isn't clear. First please rewrite it so it is understoodable even for CW radar non specialists. Is it linear or sinusoidal frequency modulation ? Please give each step of your system. You simulated a signal and you talk about delay, delay between what ? emiter-receiver, emiter-target-receiver ? why are you talking about ramp multiplication, mixer output ? What is this mixed signal equation, you don't give the variables's definitions. Please rewrite your question and give details about your system and your goals. I'm downvoting for now : your question is not answerable. $\endgroup$ – Antoine Bassoul Apr 27 '15 at 16:57
  • $\begingroup$ @AntoineBassoul Thanks for evaluating my post. Hope that now the question will be clear. $\endgroup$ – Mr. Khan Apr 28 '15 at 14:07

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