FMCW

fmcw.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+import numpy as np
+import matplotlib.pyplot as plt
+import matplotlib as mpl
+plt.style.use('seaborn-ticks')
+
+def tx(F, Fs, alpha, tx_time):
+    freq = F + alpha * tx_time
+    signal = np.sin(2*np.pi*freq*tx_time/Fs)
+    return freq, signal
+
+def rx(F, Fs, alpha, rx_time, time, tau):
+    freq = 0 if time < tau else F + alpha * (rx_time - tau)
+    signal = 0 if time < tau else np.sin(2*np.pi*freq*(rx_time - tau)/Fs)
+    return freq, signal
+
+
+F = 77.e9
+B = 4.e9
+T = 40.e-6
+alpha = B/T
+
+R = 300
+c = 3.e8
+tau = 2.*R/c
+Fb = alpha*tau
+Fs = 2*(F+B)
+Ts = 1./Fs
+N = int(T/Ts)
+
+file1 = open('datafile1.txt', 'w')
+file2 = open('datafile2.txt', 'w')
+
+signal = []
+
+samples, spacing = np.linspace(0, T, N, retstep=True)
+time_sweep = spacing
+
+initial, final = 0, T
+tx_time, rx_time = 0, tau
+
+for n in range(2):
+    for time in np.linspace(initial, final, N):
+        tx_freq, tx_signal = tx(F, Fs, alpha, tx_time)
+        rx_freq, rx_signal = rx(F, Fs, alpha, rx_time, time, tau)
+
+        IF_signal = tx_signal * rx_signal
+        signal.append(IF_signal)
+
+        file1.write("%e \t %e \t %e \t %e\n" %(time, tx_freq, tx_signal, IF_signal))
+        file2.write("%e \t %e \t %e \t %e\n" %(time, rx_freq, rx_signal, IF_signal))
+
+        tx_time = tx_time + time_sweep
+        rx_time = tau if np.all(time < tau) else rx_time + time_sweep
+
+        tx_freq_ = "%.6e" %(tx_freq)
+        if float(tx_freq_) == F+B: tx_time = 0
+
+        rx_freq_ = "%.6e" %(rx_freq)
+        if float(rx_freq_) == F+B: rx_time = tau
+
+    initial += T; final += T
+
+file1.close()
+file2.close()
+
+data = signal
+data1 = np.loadtxt('datafile1.txt')
+data2 = np.loadtxt('datafile2.txt', skiprows=200)
+
+plt.plot(data1[:, 0], data1[:, 2], label='TX chirp')
+plt.plot(data2[:, 0], data2[:, 2], label='RX chirp')
+plt.gca().xaxis.set_major_formatter(mpl.ticker.ScalarFormatter(useMathText=True))
+plt.gca().yaxis.set_major_formatter(mpl.ticker.ScalarFormatter(useMathText=True))
+plt.ticklabel_format(style='sci', scilimits=(0, 0), axis='both')
+plt.show()