%  Smart Antennas Figure 4.8   plotting the directivity vs. steering angle for 
%  N element array
set(0,'defaultfigurecolor','w')
N=4;
F=inline('(sin(.5*N*pi*(cos(x)-cos(theta0)))./(.5*N*pi*(cos(x)-cos(theta0)))).^2')
delta=.0013;
x=delta:delta:pi;
figure
n=0;
for i=0:30:90
 n=n+1   
    theta0=i*pi/180+.01;
    den=trapz(x,F(N,theta0,x).*sin(x));
D(n,:)=2.*F(N,theta0,x)./den;
end
y=x*180/pi;
plot(y,D(1,:),'k',y,D(2,:),'k',y,D(3,:),'k',y,D(4,:),'k')
axis([0 180 0 2*N+1])
grid on
xlabel('\theta')
Ylabel('D_o')
%legend('End-Fire','30^0','60^0','Broadside')