## passive Sum difference method for finding bearing

December 15, 2010 Coded in Matlab

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

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)
% subplot(212)

%
% figure
% subplot(211)
% subplot(212)

%%%%%%%%%%%%%%%%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_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``````