ANGLE-OF-ARRTVAL MEASUREMENTS 319 
6cer's HILL 
24,08 MILES 
) 2 3 4 3s 
BECRS HILL-NEW YORK PROFILE 
NEW YORK CIT’ 
(140 WEST 8T) 
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MILES 
Ficure 3. Propagation paths, (top) Beer’s Hill to New York and (bottom) Beer’s Hill to Deal. 
New York circuits. The maximum variation in the. 
vertical angle of arrival on the direct wave on the 
New York path has been 0.46 degree above that ob- 
served on a normal day, while the reflected wave has 
come in as low as 0.17 degree below the normal re- 
flected wave. (On a normal day the reflected wave on 
the New York path should be, by calculations, 0.33 
degree lower than the direct wave.) 
There does not seem to be any correlation between 
the variation in angle of arrival on the direct wave 
and the reflected wave. These variations do not as a 
tule occur together. At the time when the greatest 
deviation in the reflected wave was present the direct 
wave was coming in normally. Also, when the direct 
wave was up 0.46 degree, it was apparently being 
trapped, and at that time no reflected wave was re- 
ceived. The greatest spread observed between the 
direct and reflected wave was 0.75 degree (normal 
0.33 degree). At this time the direct wave was 0.35 
degree above normal while the reflected wave was 0.07 
degree below normal. The near proximity of Staten 
Island to the path normally taken by the reflected 
wave on the New York path has probably contributed 
to complexities of the results obtained on this circuit. 
The vertical angle of arrival on the Deal circuit has 
not varied as greatly as on the New York circuit. The 
degree in the direct wave angle of arrival. The reflected 
wave is not of sufficient magnitude to be observed on 
the Deal cireuit. 
Height run experiments were conducted to obtain a 
value for the effective coefficient of reflection for the 
Deal path. An oscillator was hoisted up and down the 
175-ft tower at Deal and the resulting received field 
recorded at Beer’s Hill. The field was found to vary 
3.6 db from maximum to minimum (3 maximum vyal- 
ues and 2 minimum values) as the oscillator changed 
height, which indicates an effective coefficient of reflec- 
tion of 0.2. This means that the received reflected wave 
is 5 times weaker than the direct or 14 db down. The 
distance above ground at which the maximum and 
minimum were obtained were noted on the receiver 
record, and from these the height of the effective reflec- 
tion layer was obtained. This height was found to be 
approximately 100 ft above average ground level. 
This experiment is to be repeated when leaves have 
fallen from the trees to determine if the effective re- 
flection coefficient or the height of the reflecting layer 
has changed. 
Rain has been found to influence the X-band cir- 
cuits in a manner such as to cause a lowering of the 
received fields. During very heavy downpours, we have 
experienced as much as 0.8-db attenuation per mile 
of path length on both the paths. We have no way of 
knowing how much rain was falling over an entire 
path, but the figure of 0.8 db per mile represents the 
maximum value of rain attenuation so far recorded on 
our circuits. 
Only part-time observations have been made on this 
project, and the results reported are based on such 
observations. It is not known, therefore, if more ex- 
treme conditions than those reported have existed at 
times when no observations were being made. 
METEOROLOGICAL ANALYSIS OF 
ANGLE-OF-ARRIVAL MEASUREMENTS» 
Purpose 
Recent experiments on propagation in the X band 
conducted by Bell Telephone Laboratories [BTL] 
have indicated that the angle of arrival of microwaves 
may be considerably at variance with that computed 
on the basis of rectilinear propagation. Deviations as 
large as 0.46 degree from true bearing® were measured 
during the summer season over a 24-mile path, partly 
over land and partly over water. The deviations found 
experimentally exceed considerably the tolerances spec- 
ified on angle of elevation, azimuth, and height deter- 
mination in present military characteristics on fire- 
control radar equipment. 
An analysis of propagation from the meteorological 
point of view has been undertaken to determine 
whether deviations from rectilinear propagation can 
bBy George D. Lukes, Signal Corps Ground Signal Agency. 
°The term ‘‘true bearing” as used in this paper refers to the 
vertical angle between the horizontal and a line perpendicular 
to the wave front at the receiving point. 
