% Smart Antennas Figure 3.17   plotting the directivity vs. finite dipole length in wavelengths

F=inline('((cos(pi*ll*cos(x))-cos(pi*ll))./sin(x)).^2.*sin(x)')
delta=.01;
x=delta:delta:pi;
for i=1:120
    ll=i/40;
    L(i)=ll;
den=trapz(x,F(ll,x));
num=2*max(((cos(pi*ll*cos(x))-cos(pi*ll))./sin(x)).^2);
temp2=num/den;
q(i)=temp2;
end
figure;
plot(L,10*log10(q),'k')
xlabel('L/\lambda')
ylabel('D_o  (dB)')