diff --git a/chapter_01/main_chapter01_04.py b/chapter_01/main_chapter01_04.py
new file mode 100644
index 0000000..f9db6b2
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+++ b/chapter_01/main_chapter01_04.py
@@ -0,0 +1,59 @@
+# -*- coding: utf-8 -*-
+"""
+Created on 26 January 2018
+
+Chapter 1 example on power aperture product
+Mahafza book
+
+@author: Ashiv Dhondea
+"""
+import math
+import numpy as np
+
+import RadarBasics as RB
+import RadarConstants as RC
+
+# ------------------------------------------------------------------------- #
+def fn_Calc_SearchVolume(az,el):
+    """
+    az,el in deg
+    eqn 1.61 in Mahafza book
+    """
+    return az*el/(57.296**2) # steradians
+    
+def fn_power_aperture(snr,tsc,rcs,rho,te,nf,loss,az_angle,el_angle):
+    """
+    implements Listing 1.5. MATLAB Function “power_aperture.m”
+    % This program implements Eq. (1.67)
+
+    """
+    Tsc = RB.fn_Power_to_dB(tsc); # convert Tsc into dB
+    Sigma = RB.fn_Power_to_dB(rcs);# convert sigma to dB
+    four_pi = RB.fn_Power_to_dB(4.0 * math.pi); # (4pi) in dB
+    k_B = RC.boltzmann_constant;
+    k_db = RB.fn_Power_to_dB(k_B); # Boltzman’s constant in dB
+    Te = RB.fn_Power_to_dB(te) #noise temp. in dB
+    range_pwr4_db = RB.fn_Power_to_dB(rho**4); # target range^4 in dB
+    omega = fn_Calc_SearchVolume(az_angle,el_angle) # compute search volume in steradians
+    Omega = RB.fn_Power_to_dB(omega)# search volume in dB
+    # implement Eq. (1.67)
+    PAP = snr + four_pi + k_db + Te + nf + loss + range_pwr4_db + Omega - Sigma - Tsc;
+    return PAP
+    
+    
+
+# ------------------------------------------------------------------------- #
+T_sc = 2.; # [s]
+noise_fig_dB = 8. ;# [dB]
+
+losses_dB = 6.;
+rho=75e3; # [m]
+snr_req_dB = 20.; # [dB]
+
+T_e = 290; # [K]
+rcs = 3.162; # [m^2]
+
+az = 180.;
+el = 135.;
+PAP = fn_power_aperture(snr_req_dB,T_sc,rcs,rho,T_e,noise_fig_dB,losses_dB,az,el)
+print('power aperture product = %.1f dB' %PAP)
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