SAR raw signal simulation from satellite with Radar Toolbox

Hi, I am trying to use the Radar Toolbox for SAR raw data simulation from satellite. I first copied the example from the Matlab tutorial https://es.mathworks.com/help/radar/ug/stripmap-synthetic-aperture-radar-sar-image-formation.html#SyntheticApertureRadarImageFormationExample-4

Particularizing it for the satellite case (697 km altitude) these is the input data I use. I want to simulate raw data first for point targets but ideally I would like to do it for a homogeneous distributed target (e.g. sea, rainforest, etc...) but I don't know how.

Note that truncrangesamples is very high, because the target to signal range is driven by the satellite altitude.

c = physconst('LightSpeed');
fc = 5.405e9;
rangeResolution = 5;  
crossRangeResolution = 5;
bw = 56.5e6;
prf = 1713; 
aperture = 12;  
tpd = 1/prf*0.09; 
fs = 62.15e6;
fs = round(fs/prf)*prf;

waveform = phased.LinearFMWaveform('SampleRate',fs, 'PulseWidth', tpd, 'PRF', prf,'SweepBandwidth', bw);
speed = 7.59e3;  
flightDuration = 1;
radarPlatform  = phased.Platform('InitialPosition', [0;697e3;0], 'Velocity', [speed;0;0]);
slowTime = 1/prf;
numpulses = flightDuration/slowTime +1;

maxRange = 800e3;
truncrangesamples = ceil((2*maxRange/c)*fs);
fastTime = (0:1/fs:(truncrangesamples-1)/fs);
%Rc = 1000; %%%%%%%%%%% Set the reference range for the cross-range processing.

antenna = phased.CosineAntennaElement('FrequencyRange', [5.4e9 5.5e9]);
antennaGain = aperture2gain(aperture,c/fc); 
transmitter = phased.Transmitter('PeakPower', 4368, 'Gain', antennaGain);
radiator = phased.Radiator('Sensor', antenna,'OperatingFrequency', fc, 'PropagationSpeed', c);
collector = phased.Collector('Sensor', antenna, 'PropagationSpeed', c,'OperatingFrequency', fc);
receiver = phased.ReceiverPreamp('SampleRate', fs, 'NoiseFigure', 2);
channel = phased.FreeSpace('PropagationSpeed', c, 'OperatingFrequency', fc,'SampleRate', fs,'TwoWayPropagation', true);

targetpos= [-40e3,0,400e3;0,400e3,0; 40e3,0,400e3]'; 
targetvel = [0,0,0;0,0,0; 0,0,0]';
target = phased.RadarTarget('OperatingFrequency', fc, 'MeanRCS', [1,1,1]);
pointTargets = phased.Platform('InitialPosition', targetpos,'Velocity',targetvel);

When I run the code I get the problem of truncrangesamples being too large. If I reduce it I only get simulated noise, no signal. Any ideas? Thank you!

refangle = zeros(1,size(targetpos,2));
rxsig = zeros(truncrangesamples,numpulses);
for ii = 1:numpulses
    ii
    % Update radar platform and target position
    [radarpos, radarvel] = radarPlatform(slowTime);
    [targetpos,targetvel] = pointTargets(slowTime);
    
    % Get the range and angle to the point targets
    [targetRange, targetAngle] = rangeangle(targetpos, radarpos);
    
    % Generate the LFM pulse
    sig = waveform();
    % Use only the pulse length that will cover the targets.
    sig = sig(1:truncrangesamples);
    
    % Transmit the pulse
    sig = transmitter(sig);
    
    % Define no tilting of beam in azimuth direction
    targetAngle(1,:) = refangle;
    
    % Radiate the pulse towards the targets
    sig = radiator(sig, targetAngle);
    
    % Propagate the pulse to the point targets in free space
    sig = channel(sig, radarpos, targetpos, radarvel, targetvel);
    
    % Reflect the pulse off the targets
    sig = target(sig);
    
    % Collect the reflected pulses at the antenna
    sig = collector(sig, targetAngle);
    
    % Receive the signal  
    rxsig(:,ii) = receiver(sig);
    
end