English: Far field radiation pattern of 0.25 wavelength monopole antenna over a perfectly conducting infinite ground plane. The radial axis is relative signal strength (peak electric field magnitude) and the circumferential axis is in degrees. The distance of the line from the origin in any direction is proportional to the signal strength of the radio wave radiated in that direction. Made with:

  
#   GNU Octave program
#   Using dipole directivity equation in 
#   Balanis 2005 Antenna Theory, 3rd Ed, p.172, eq. 4-62a and 
#   Johnson 1993 Antenna Engineering Handbook, 3rd Ed, eq.4-6
#--------------------------------------------------------------------
function mpole( length )		#length of monopole in wavelengths
kl = 2.*pi.*length;			#length of monopole in radians
theta = linspace(-pi./2,pi/2,100);	
rho = (cos(kl .* cos(theta)) - cos(kl)) ./ sin(theta); 	#directivity eq
rhomax = max( abs( rho ) );		#scale rho so graph is relative to 1.0
handle = polar( theta + pi./2, abs( rho )./rhomax ); 	#draw graph 
set(gca, "rtick", 0.2:0.2:1.0, "ttick", 0:15:180);	#axis properties
set(gca, "fontsize", 10, "linewidth", 1 );		#axes properties			
set(handle, "color", 'b', "linewidth", 1.5);	#change color and width of plot
str = sprintf("%g wavelengths", length );
htitle = title(str);			#lists wavelength of antenna in title at top
set(htitle, "fontsize", 15 ); 		#set fontsize of title
print -dpng mpolepattern.png;		#save image in file
endfunction;