How to find the start and end coordinates of main-lobe of rectangular window spectrum.

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Palguna Gopireddy
Palguna Gopireddy 2022-12-28
编辑： Palguna Gopireddy 2022-12-28
The rectangular window spectrum is found like
M=66;
r=rectwin(M);
n=512;
r_fft=fft(r,n);
r_fft2=fftshift(r_fft);
r_fftdB=20*log10(abs(r_fft2));
figure
plot(1:n,r_fftdB)
title(M)
The spectrum of the rectanular window spectrum (r_fftdB) is given by r_fftdB.
The plotted spectrum is
The spectrum is symmetrical about the peak of main-lobe. The starting of main-lobe is at coordinate 249. The ending of the main-lobe is at 265, The peak of main-lobe is at 257.
How to find the values of staring and ending coordinates of main-lobe (249,265 respectively)?

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回答（1 个）

Palguna Gopireddy
Palguna Gopireddy 2022-12-28
编辑：Palguna Gopireddy 2022-12-28
Ran in:
I have tried this
M=66;
r=rectwin(M);
n=512;
r_fft=fft(r,n);
r_fft2=fftshift(r_fft);
r_fftdB=20*log10(abs(r_fft2));
[Max,I_max] = max(r_fftdB);
for i=I_max:-1:1
if r_fftdB(i)>r_fftdB(i-1)
start=i-1;
else
break;
end
end
for i=I_max:n
if r_fftdB(i)>r_fftdB(i+1)
ending=i+1;
else
break;
end
end
disp(start);
249
disp(ending);
265
Is there anyway we can get both the values in the same loop, so that the code-length and runtime minimizes?
Or
is there any other method to get these values?

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