PROPAGATION STUDIES AT MICROWAVK FREQUENCIES 



99 



ing sweep expansion so that succeeding pulses fell on proper parts of 

 the scale and by keeping this expansion constant, it was possible to ob- 

 tain a calibration. 



TWO-PATH SIMULATOR 



.\s an aid to interpreting the results obtained from the above experi- 

 ment, particularly when the two pulses overlap and interfere, a circuit 

 was set up in the laboratory to simulate two-path transmission. The 

 equipment, as shown on Fig. 9, consisted of a wave guide hybrid junction 

 with the r-f pulse energj^ being fed into the E plane arm. To each side 

 arm was connected a ^•ariable attenuator in series with a few feet of wave 

 guide fitted with a short circuiting plunger. Waves reflected from these 

 two plungers recombine in the H plane arm where the detector is located. 

 There are two separate paths through the hybrid as follows: (1) Input, 

 side arm A, reflecting plunger A, side arm A to output. (2) Input, side 

 arm B, reflecting plunger B, side arm B to output. By adjusting the 

 attenuator in either branch the amplitude of the signal transmitted bj" 

 way of that branch could be adjusted. In the same way by adjusting 

 the position of the reflecting plunger in either branch the distance 

 traveled b}^ a signal in traversing that branch could be varied. 



If the path lengths were made the same and the amplitudes adjusted 

 to be equal there would be perfect cancellation due to a phase turn-over 

 in the hybrid junction and hence no output from the detector. If one 

 plimger were now left fixed in the above position and the other mo\-ed by 

 a quarter wavelength (to produce a total shift of half wavelength or 180°) 





AUG 2 6 1950 1l:03-2SP.M. ^UG. 2 6 1950 1l : 9 - 4 5 P.M 



Fig. 8 — Received pulses and calibrating pulses. 



