1  import numpy as np
 2  from numpy.fft import fft, ifft
 3  import matplotlib.pyplot as plt
 4  
 5  
 6  fs=125*pow(10,6) #sampling frequency
 7  Ts=1/fs # sampling time
 8  Tb=0.5*pow(10,-6) # burst time
 9  Tau=900*pow(10,-6) # pulse repetition time
10  fmax=30*pow(10,6) # maximum frequency on ramp
11  fmin=10*pow(10,6) # minimum frequency on ramp
12  n=int(Tb/Ts) # number of samples per ramp
13  N = np.arange(0, n, 1)
14  theta_n= 2*np.pi*(pow(N,2)*pow(Ts,2)*(fmax-fmin)/(2*Tb)+fmin*N*Ts) # instantaneous phase
15  
16  y = 1 + np.sin(theta_n) # ramp signal in time domain
17  
18  t = Ts*np.arange(0,n,1)
19  Y = fft(y)
20  M =len(Y)
21  m = np.arange(M)
22  T = M*Ts
23  freq = m/T
24  
25  
26  plt.figure(figsize = (12, 6))
27  plt.subplot(121)
28  plt.stem(freq, np.abs(Y), 'b', \
29           markerfmt=" ", basefmt="-b")
30  plt.xlabel('Freq (Hz)')
31  plt.ylabel('FFT Amplitude |Y(freq)|')
32  plt.xlim(0, (1.3*fmax))
33  plt.ylim(0, 60)
34  
35  plt.subplot(122)
36  plt.plot(t, ifft(Y), 'r')
37  plt.xlabel('Time (s)')
38  plt.ylabel('Amplitude')
39  plt.tight_layout()
40  
41  plt.show()