74 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



picture is the metal-lens antenna used for making the angle-of-arrival 

 observations. Its half -power beamwiclth is 0.12 degree at the operating 

 frequency of 24,000 mc. The focal length of the lens is 48 feet and its 

 feed is located in the little cupola on top of the building. The feed is 

 held fixed, while the lens is moved vertically by a motor-driven mecha- 

 nism; thus the antenna beam also moves vertically. The antenna scans a 

 total angle of two degrees in ten seconds. It is fed by a 24,000-mc radar 

 set which is gated to receive only the pulses reflected from a corner 

 reflector located at the distant terminal of the transmission path. The 

 spot on the radar cathode ray tube moves vertically in synchronism 

 with the scanning antenna, and the horizontal deflection is proportional 

 to the amplitude of the pulse received from the corner reflector. The 

 display thus shows amplitude of the various incoming signal components 

 as a function of their angles of arrival. 



The antenna installation on Southard Hill is shown in Fig. 5. At the 

 left is the transmitting paraboloid for the 4195-mc continuous wave 

 transmitter, the radar corner reflector is in the center, and on the right 

 is the horn-reflector antenna used in the frequency-sweep experiments 

 described below. Similar equipment is located at the Murray Hill termi- 

 nus. The corner reflector is 5.5 feet on a side, and at 24,000-mc has 

 sufficient gain to override reflections from other nearby objects, and 

 thus becomes easily identifiable on the radar screen. 



The radar oscilloscope for typical propagation conditions is shown in 

 Fig. 6. These pictures were obtained by leaving the camera shutter open 

 during the ten-second interval required for the antenna beam to scan 

 through the angular range of 2°. All of these representative photographs 

 were taken on the Murray Hill-Crawford Hill path although similar 

 results were obtained on the Southard Hill-Crawford Hill path with the 

 exception of Fig. 6(f). The normal daytime transmission is shown in Fig. 

 6(a) to consist of a single path arriving at an angle of —0.2° with respect 

 to a fixed reference angle. The horizontal lines represent intervals of 

 0.1°, so that changes of 0.05° can be estimated. The other pictures in 

 Fig. 6 were all taken during fading conditions. 



Figs. 6(b) and 6(c) are good examples of the multiple-path condition 

 shown in Fig. 3(a) in which the individual components are almost equal 

 in amplitude and Avell separated in angle. In Fig. 6(b) there are two 

 components arriving at angles of 0.1° and 0.6° above the normal line-of- 

 sight while in 6(c) there are three components with angles of 0.05°, 0.35° 

 and 0.7° above the normal angle. The position and amplitude of the 

 signal components may change radically in a matter of minutes, and 

 often there is no component that can be identified as the "normal" one. 



