PART I 
SUMMARY 
Chapter 1 
STANDARD PROPAGATION 
INTRODUCTION 
B’ STANDARD PROPAGATION is meant radio wave 
propagation through an atmosphere free from 
irregular stratifications, particularly of vertical dis- 
tributions of water vapor and temperature. With 
irregular stratification the propagation is said to be 
nonstandard and will be treated extensively in the 
Jater chapters. 
In this chapter the fundamental general relations 
between transmitted and received power is first re- 
viewed; then the main factors influencing the trans- 
mission of electromagnetic waves such as refraction, 
diffraction, and dielectric properties of the ground 
are surveyed; and finally the computation of the 
field at the receiver for various heights of transmitter 
and receiver above a homogeneous smooth earth of 
given electromagnetic properties is very briefly dis- 
cussed. The last subject divides naturally into the 
determination of the field above the line of sight and 
the determination of the field below the line of sight 
in the earth’s shadow. 
The text of the present chapter largely follows the 
book, issued by the Columbia University Wave 
Propagation Group [CUDWR WPG] under the title 
Propagation of Radio Waves through the Standard 
Atmosphere 
POWER TRANSMISSION 
Certain relations occur so frequently in wave 
propagation problems that it is convenient to 
summarize them here before entering into a descrip- 
tion of the characteristic features of short wave 
propagation. Some of these are mere definitions; 
some are consequences of electromagnetic theory. 
It is convenient to use, as a standard antenna, one 
which has a length which is small compared to the 
wavelength, designated as “doublet.’’ Such doublets 
may be used for both the transmitting and receiving 
antennas. In the latter case it is assumed that the 
load resistance is matched to the output resistance 
of the antenna. In free space, optimum transmission. 
is achieved when the two doublets are parallel to 
each other and perpendicular to the line connecting 
their centers. If their distance apart, d, is large com- 
pared to the wavelength, the ratio of power trans- 
mitted to maximum useful power received is found 
from electromagnetic theory to be 
Ba ONG 
p-(S): @) 
where \ and d are measured in the same units. Here 
P, is the power delivered to a matched load at the 
output terminal of the receiver and A, the power fed 
to the transmitting antenna. 
The gain G of any directive antenna is the ratio of 
the power transmitted by a doublet to the power 
transmitted by the antenna in question, to produce 
the same response in a distant receiver, when. both 
transmitting antennas are adjusted for maximum 
transfer of power. The gain of a receiving antenna is 
similarly the ratio cf the power delivered to the 
transmitting antenna when a doublet receiving an- 
tenna is used to the power delivered to the transmit- 
ting antenna to produce the same response when the 
antenna in question is used at the receiver. 
Two methods of expressing antenna gain are in 
common use: the one just indicated where the gain 
is measured as the ratio of the power in the optimum 
direction relative to that of a doublet, and the other 
where the gain is that relative to a hypothetical iso- 
tropic radiator which is one assumed to radiate the 
same power density in all directions. Simple geomet- 
rical considerations show that the gain of a doublet 
over that of an isotropic radiator is 3/2 so that the 
gains expressed in the former system are converted 
into the latter system by multiplying them by 3/2. 
Tn the equations below, the gain is expressed relative 
to the doublet. 
If transmission takes plaze, not in free space, but 
over a conducting ground, in a refracting atmosphere, 
etc., the power ratio will be expressed as 
Po _ Br) 42 
p= G25) 40, @) 
