%  Smart Antennas  Figure 3.20   plotting the directivity vs. loop circumference in wavelengths

F=inline('(besselj(1,c*sin(x))).^2.*sin(x)')
delta=.01;
x=0:delta:pi;
for i=1:100
    c=i/5;
    C(i)=c;
den=trapz(x,F(c,x));
num=2*max(besselj(1,c*sin(x)).^2);
temp2=num/den;
q(i)=temp2;
end
figure;
plot(C,10*log10(q),'k')
axis([0 20 0 12])
xlabel('C/\lambda')
ylabel('D_o  (dB)')