clc
clear?all
close?all
N=7;
f0=20*1000;
fs=20*f0;
T=0.05;
t=0:1/fs:T;
%?st=exp（j*2*pi*f0*t）;
%?St=st*st‘/length（st）;
c=1500;
lamda=c/f0;
d=lamda/2;
theta0=degtorad（0:0.01:60）;
for?theta=degtorad（0:1:180）
????sum=0;
????sum2=0;
????for?i=0:N-1
????????v0=exp（j*2*pi*0