PROPAGATION OF RADIO WAVES 
should be understood that the portion of the optical 
region near the earth is not included. It must be 
considered instead as part of the diffraction region. 
The diffraction region, accordingly, designates a 
layer in the optical region as well as the region below 
the line of sight (see Figure 3 in Chapter 5). Below 
the line of sight the field falls off exponentially. 
Within the diffraction region, fields are strengthened 
by raising the receiver or transmitter antennas. 
Typical Radio Gain Curves 
Three types of graphical representation of radio 
gain in a vertical plane through the transmitter 
antenna are possible, namely, (1) at a specified 
distance, radio gain against height; (2) at a specified 
height, radio gain against distance; and (3) a set of 
contour lines representing constant radio gain. 
In Figure 7, curves of type (1) are exhibited for 
various frequencies. The transmission is over sea 
water with horizontally polarized waves. It may be 
observed that the higher the frequency the lower the 
: 
= 1000 FTRANSMITTER HEIGHT 9M 
z DISTANCE 80KM 
= SEA WATER 
£ 
é 100 ee 
# 
-160 
20 LOG A IN DB 
140 “120 -100 -80 
Figure 7. Radio gain vs receiver height for horizontal 
polarization. 
>> -100 DE 
Kilometers 
> ua 
mp Oo 
— 
Kilometers 8 
Frequency !00Mc 
Horizontal Polarization 
Antenna Height 9.14 meters 
k:473 
- 
333 
10,000 
FREQUENCIES 
---- 3000MC 
—— 100,200,500mc 
VERTICAL POLARIZATION 
a TRANSMITTER HEIGHT 9M 
2 DISTANCE 80 KM 
wi SEA WATER 
5 1000 
= 
= 
a LINE OF SIGHT 
he 
x= 
° 
Fy 
~ 100 
Ww 
= 
w 
o 
Ww 
c 
re) 
=240 
-200 
-180 -I60 -I40 
20 LOG A IN DB 
—120 -100 -80 
Ficure 8. Radio gain vs receiver height for vertical 
polarization. 
first maximum and the narrower the lobe. Figure 8 
gives similar information for vertically polarized 
waves. Note that the minima are not so deep with 
vertical polarization. Curves of type (2) exhibit 
similar characteristics (see Figure 6 of Chapter 5). 
In Figures 9 to 12*, vertical coverage diagrams of 
type (8) are given. These illustrate the effects of 
frequency, polarization, and transmitter height. 
A comparison of Figures 9 and 10 shows the effect 
of frequency. As the frequency increases, the lobes 
become more numerous, narrower, and lower. 
Another effect is exhibited along the surface. For 
the higher frequency the corresponding decibel lines 
come in closer to the transmitter. This illustrates the 
fact that for the higher frequency the shadow effect 
is more pronounced along the surface of the earth. 
A comparison of Figures 10 and 11 shows that 
for horizontal polarization the nulls are deeper but 
the lobes extend out farther. Along the line of sight, 
® Figures 7 to 12 have been adapted from Radiation Lab- 
oratory Report C-6. 
Ficure 9. Contours of constant radio gain factor for horizontal polarization on 100 mc over sea water. 
