Defining and plotting a function using symsum

Hello

I am trying to plot the array factor for a uniform linear antenna array using this code:

syms k
psi = -pi: .05: pi;

AF = symsum(exp(1i*(k-1).*psi), k, 1, 10)

AF_dB = 10.*log10(AF);

figure(1)
plot(psi, AF_dB)

I can tell that something is wrong with the way I am defining the summation for AF because when k is 1, AF is evaluated to be 0 when it should be 1.

I am trying to figure out how to define a function, in this case AF, as a summation so that I can define more complicated array factors and do things like determine side lobe level by using findpeaks, etc. Is there a better way to do that than what I have tried to implement here?

Thank you