passive Sum difference method for finding bearing
Following code finds the bearing or Direction of arrival of signal passively. Its doesnt transmit any signal between bearing is find out on basis of sum and difference signal.
clc
clear all
close all
fs=20e7;
T=1/fs;
t=0:T:0.0000002;
f=10e6;
scanagle_deg=60; % Range covered by seeker antenna
step_deg=6;
% for ploting original arrays of sum, diff and ratio
theta=-deg2rad(scanagle_deg):deg2rad(step_deg):deg2rad(scanagle_deg);
for i=1:length(theta);
ant1=1*sin(2*pi*f*t); %Antenna 1
ant2=1*sin(2*pi*f*t+theta(i)); %Antenna 2
[my,mx]=max(ant1);
sum_ant(i)=ant1(mx)+ant2(mx); %Sum of antennas
diff_ant(i)=ant1(mx)-ant2(mx); %diff of antennas
ratio_ant(i)=diff_ant(i)/sum_ant(i); %ratio
end
% subplot(311)
% plot(t,ant1,t,ant2)
% subplot(211)
% plot(rad2deg(theta),sum_ant,rad2deg(theta),diff_ant)
% subplot(212)
% plot(rad2deg(theta),ratio_ant)
%
% figure
% subplot(211)
% plot(rad2deg(theta),sumn_ant,rad2deg(theta),diffn_ant)
% subplot(212)
% plot(rad2deg(theta),ration_ant)
%%%%%%%%%%%%%%%%Recieved signal at antenna for DOA%%%%%%%%%%%%%%%%%%%%%%%%%%
A_ant1=2; % Amplitude of antenna 1
A_ant2=3; % Amplitude of antenna 2
DOA_angle_target=20; % DOA of TARGET
sim_ant11=A_ant1*sin(2*pi*f*t); % Simulated antenna 1
sim_ant22=A_ant2*sin(2*pi*f*t+deg2rad(DOA_angle_target)); % Simulated antenna 2
sim_ant1=sim_ant11/max(sim_ant11); %normalization
sim_ant2=sim_ant22/max(sim_ant22);
[smy,smx]=max(sim_ant1);
%%%%also take for same sample value of data
sim_sum_ant=sim_ant1(smx)+sim_ant2(smx);
sim_diff_ant=sim_ant1(smx)-sim_ant2(smx);
sim_ratio_ant=sim_diff_ant/sim_sum_ant;
%%%%%%%%%%%%% Polynomial fitting of ratio_ant of 6th order%%%%%%%%%%%%
% Error in DOA is obtained because of this
% if polynomial fitting is removed or more accurate results are obtained
% DOA of target can be found with greater accuracy
% Polynomial was obtained though curve fitting toolbox
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
p1 = 1.047e-008;
p2 = -6.907e-007;
p3 = 2.383e-005;
p4 = -0.0004914;
p5 = 0.008555;
p6 = -0.09626;
p7 = 0.4215;
x=0;
for ii=1:2200
x=x+0.01;
fitted_model_rat_ant(ii) = p1*x^6 + p2*x^5 + p3*x^4 + p4*x^3 + p5*x^2 + p6*x + p7;
end
theta_new=-scanagle_deg:.0545:scanagle_deg; % Theta for ploting fitted model
figure
plot(theta_new(1:2200),fitted_model_rat_ant)
c1=ceil(sim_ratio_ant*7000); % For comparison of sim_ratio ant and model
c2=ceil(fitted_model_rat_ant*7000); % Different threshold Threshold can be chosen
[r,c,v]= find(c2==c1);
detected_theta=(c.*0.0545)-60 %theta from curve fitting model
if(A_ant1>A_ant2) % condition for checking which angle was correct
correct_theta=detected_theta(1)
elseif(A_ant1<A_ant2)
correct_theta=detected_theta(2)
else
correct_theta=detected_theta
end