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BELL SYSTEM TECHNICAL JOURNAL 



the electric force vector in traversing the waveguide run. The path from 

 the r.f. unit is in rectangular guide (TEi, o mode) through the right angle 

 bend, to the base of the rotary joint. A transducer which forms the base 

 portion of the joint converts to the TMoi mode in circular pipe. For this 

 mode, the electric held has radial symmetry, much as though the wave- 

 guide were a coaxial line of vanishingly small inner conductor diameter. 



PIPE CONTAINING 

 SPIRAL SEPTUM 



TE. 



INDICATES DIRECTION 

 OF ELECTRIC VECTOR. 

 INDICATES VECTOR 

 LIES X TO PLANE OF 

 PAPER. 



REFLECTOR 



ROTARY JOINT 

 I AND CHOKE 



TEio 



Fig. 43 — SL Radar Antenna — Wave Guide Path. 



The energy passes the rotary joint in this mode; choke labyrinths are pro- 

 vided at the joint to minimize radio frequency leakage. The energy then 

 flows through another transducer, from TMoi mode back to TEio mode. 

 The lower horizontal portion of the feed pipe immediately tapers to round 

 guide, the mode being now TEn. Ne.xt the energy transverses a 90° elbow, 

 which is a standard 9i)° pipe casting, and enters the vertical section im- 



