WAVEGUIDE TESTING WITH MILLIMICROSECOND PULSES 



47 



other echoes are associated with the parts of the system from which 

 they came by the dashed Hues and arrows on the figure. A clamped 

 joint in the line gave the reflection shown next following the initial 

 overloaded pulse. A well made threaded coupling in which the ends of 

 the pipe butted squarel,y is seen to have a very much lower reflection, 

 scarcely observable on this trace. Since there is ahvays reflection from 

 the mouth and upper reflector parts of this kind of antenna, it is not 

 possible to measure a throat transition piece alone by conventional CW 

 methods, as the total reflected power from the system is measured. 

 Here, use of the resolution of this short pulse equipment completely 

 separated the reflection of the transition piece from all other reflections 

 and made a measurement of its performance possible. In this particular 

 case, the reflection from the transition is more than 50 db down from 

 the incident signal which represents very good design. As can be seen, 



OPEN APERTURE 



FIBERGLASS COVER 

 OVER APERTURE 



REFLECTION APPEARS 

 -^TO COME FROM 16 FT 

 N FRONT OF HORN MOUTH 



DIRECTIONAL TRANSDUCER CLAMPED THREADED ROUND-TO 

 COUPLER JOINT COUPLING SQUARE 



TRANSITION 



Fig. 11 — Waveguide and antenna arrangement with trace photos showing re- 

 flections from joints, transition section, and cover. 



