fft of breath signal

I got this result from this code, but the plot should be sth like this below image, how can I make it more smooth?

phi = atan2(Q_ch, I_ch);
phi = unwrap(phi);
time_taken = length(I_ch)/Fs;
t_array = linspace(0, time_taken, length(I_ch));

Range = (c.*phi)/(4*pi*fc);

min_range = min(Range);
adjusted_range = Range - min_range;

Range = ((c.*phi)/(4*pi*fc));
figure;
plot(t_array, -adjusted_range);
title("Respiratory Rate CW");
xlabel("Time");
ylabel("Amplitude");

%fft
range_fft = abs(fft(abs(Range)));
range_fft_half = range_fft(1:length(range_fft)/2);
%DB Value
fft_db_norm = 20*log10(range_fft_half);
fft_db_norm = fft_db_norm(1:100) - max(fft_db_norm(1:100));
fft_db_norm(fft_db_norm < -60) = -60;
fft_db_norm(fft_db_norm > 0) = 0;
%Plot
f_array = linspace(0, 2, length(fft_db_norm));
figure;
plot(f_array, fft_db_norm);
title("Heart Rate (FFT)");
xlabel("Frequency (Hz)");
ylabel("Amplitude (dB)");

Answer 1

[Image Analyst]

Looks like it has a lot more sample points, hence it can follow that curve better. Yours has fewer points so it looks choppy. See if you can sample Q_ch and I_ch at higher sampling rates to get more resolution (more elements in your vectors). Otherwise you'll just have to handle what you've got.

Give context: why do you think you need it to be smoother anyway? Maybe it doesn't need to be.