212 



ANGLE-OFARRIVAL EXPERIMENTS 



aud receiver (iueludiiig butli at^ceiit and descent of 

 the tower). Equipment limitations set tlie accuracy 

 of BTL angle of arrival measurements at ±0.04°. 

 It is believed that generalized, overall conclusions 

 for the entire period of comparison can be made as 

 follows : 



1. That occasions of true bearing and "near true 

 bearing-" (say — 0.11 to 0°) could have been pre- 

 dicted from the meteorological data. 



2. That the occurrence of extreme deviations from 

 true bearing would have been predicted from mete- 

 orological data nearest in time to the radio measure- 

 ments. 



3. That the magnitude of the most extreme meas- 

 ured deviation (0.46°) from true bearing can also tie 

 calculated from observed meteorological data, though 

 not simultaneously observed. 



^^^•* Conclusions 



The propagation path of microwave radiation can 

 be fairly well specified, given only a knowledge of the 

 temperature and water vapor pressure distribution 

 in the lower atmosphere and the positions in space of 

 transmitter and receiver. The equations of motion of 

 the propagation of the individual wave fronts have 

 been written in a form such that the angles of de- 

 parture from the transmitter and the angles of arrival 

 at the receiver can be evaluated directly from the 



meteorological stratification. Apjilicalion of the theory 

 to certain angle-of-arrival radio propagation experi- 

 ments conducted by Bell Telephone Laboratories dur- 

 ing the summer of 1911 has resulted in the following 

 conclusions : 



1. A surprisingly good correlation exists between 

 angles of arrival computed from meteorological and 

 survey data only and the angles of arrival deter- 

 mined experimentally. 



2. The extreme deviations (0.16°) from rectilinear 

 propagation measured experimentally by BTL are eon- 

 firmed as plausible on the basis of observed meteoro- 

 logical stratification. 



3. The meteorological analysis indicates that de- 

 viations from rectilinear propagation and the fluctua- 

 tion of the deviations about a mean value are as much 

 a function of position of transmitter and receiver 

 as they are a function of the existing meteorological 

 structure. 



It is strongly recommended that low-level meteoro- 

 logical soundings be considered an indispensable part 

 of any experimental angle-of-arrival measurements. 

 The good correlations secured between evaluation of 

 angles of arrival from meteorological data and angles 

 of arrival measured experimentally suggest that de- 

 viations from rectilinear propagation can be ac- 

 counted for by measurable atmospheric conditions 

 and that, further, these deviations can be reasonably 

 well predicted. 



