taking fft for singal having different angles in degree

hello everyone I am not very much expert in taking FFT analysis, i have a signal which have 3 different angles (30,45,75) i want to plot a fft which will show the peaks for the angles in the signal at these values

sind(30)=0.5, sind(45)=0.707, sind(75)=0.965;

clear all
close all
clc

th(1:400,1)=30;
th(401:600,1)=45;
th(601:1000,1)=75;

N=length(th); %number of samples
n=0:N-1;
L=(500*10^-6); %length of the wedge
lambda=2*10^-6;
dx=n*(L/N);  %spacing
dx=dx';
t=1/lambda;

signal1=exp(1i*(2*pi/lambda)*dx .* sind(th));
Zs=fft(signal1,length(signal1));

xx=linspace(0,1,N);
figure(1)
plot(xx,signal1,'r');

figure(2)
plot(xx,Zs,'r')

thanks for your support.