%  Figure 3.19   plotting the directivity vs. loop circumference in wavelengths

F=inline('(a*sin(x)/2).^2.*sin(x)')
delta=.001;
x=0:delta:pi;
for i=1:100
    a=i/5;
    A(i)=a;
den=trapz(x,F(a,x));
num=2*max((a*sin(x)/2).^2);
temp2=num/den;
q(i)=temp2;
end
figure;
plot(A,10*log10(q),'k')
hold on
plot(A,10*log10(.682*A),'k:')
axis([0 20 0 15])