Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

fmcw radar range doppler info of the target

Status
Not open for further replies.

hoz

Junior Member level 3
Joined
Dec 22, 2006
Messages
26
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,455
Hello everyone,

I am trying to plot range-doppler diagram for an fmcw radar.
Here is how I generate transmitted,received and video signal;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

clear all;
close all;
clc

c=3e8; %speed of light
fc=8e9; %carrier freq
deltaF=32e6; %sweep freq
T=1e-3; %one period
alph=deltaF/T; %sweep rate

R=500; %initial distance of the target
td=2*R/(c); %initial delay of returned signal

v=2; %speed of the target (give some value between 0 and 10)
D=64; % #of doppler cells OR #of sent periods
N=2^10; %for length of time

t=linspace(0,D*T,D*N); %total time

n=0;
nT=length(t)/D; %length of one period
a=zeros(1,length(t)); %transmitted signal
b=zeros(1,length(t)); %received signal
r_t=zeros(1,length(t));
ta=zeros(1,length(t));
r1=R;
f0=fc;
for i=1:length(t)

r_t(i)=r1+v*t(i); % range of the target in terms of its velocity and initial range
ta(i)=2*r_t(i)/c; % delay for received signal

if i>n*nT && i<=(n+1)*nT % doing this for D of periods (nt length of pulse)

a(i)=sin(2*pi*(f0*t(i)+.5*alph*t(i)^2-alph*t(i)*n*T)); %transmitted signal
b(i)=sin(2*pi*(f0*(t(i)-ta(i))+.5*alph*(t(i)-ta(i))^2-alph*(t(i)-ta(i))*n*T)); %received signal

else

n=n+1
a(i)=sin(2*pi*(f0*t(i)+.5*alph*t(i)^2-alph*t(i)*n*T)); %transmitted signal
b(i)=sin(2*pi*(f0*(t(i)-ta(i))+.5*alph*(t(i)-ta(i))^2-alph*(t(i)-ta(i))*n*T)); %received signal

end

end

mixed1=(a.*b); %video signal OR IF signal (output of mixer)

m1=reshape(mixed1,length(mixed1)/D,D); %generating matrix ---> each row % showing range info for one period AND each column showing number of periods

[My,Ny]=size(m1');

win=hamming(Ny);
m2=conj(m1).*(win*ones(1,My)); %taking conjugate and applying window for %%sidelobe reduction (in time domain)

Win=fft(hamming(My),D);
M2=(fft(m2,2*N)); %First FFT for range information

M3=fftshift(fft(M2',2*D)); %Second FFT for doppler information

[My,Ny]=size(M3);
doppler=linspace(-D,D,My);
range=linspace(-N,N,Ny);

figure;contour(range,doppler,abs(M3));grid on;
xlabel('Range');
ylabel('Doppler')

figure;mesh(range,doppler,abs(M3));
xlabel('Range');
ylabel('Doppler')


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

There are a few thing I am not sure if I am doing right.
First, while defining the received signal (b) is that the correct way to do it for every period.
Second, I am applying window for the video signal for range sidelobe reduction.
Do I need to do it for doppler sidelobes also?
Third, I am not sure if I am using 'fftshift' function right. Because when I increase the speed of the target, for example from 0 to 1,
peak's position shifts to negative value (below zero).
Forth, how do I define range and doppler resolutions and use them for x and y axis while plotting.

Please give comments and give me some direction.
Thanks!
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top