5-6 MM ATTENUATION FOR THE CIRCULAR ELECTRIC WAVE 1121 



Fig. 5 — Structure of waveguide switch. 



however, produce a power flow in the arm C to the balanced converter 

 of the receiver and an indication in the output meter. So far this set is 

 similar to a setup for measuring the round trip loss in a terminated 

 waveguide system. The impedance of the TE?o ^ TEoi wave trans- 

 ducer,^ taper section and mode filter connected as shown in the section 

 A-D of Fig. 3 can be matched to the rectangular waveguide at A by an 

 appropriate adjustment of the dielectric post tuner^ Ti whose structure 

 is shown in Fig. 4. Under these conditions a conical taper termination 

 placed in the round waveguide at D will again produce a balance and 

 again no power will flow in arm C. A ^vaveguide switch whose structure 

 is shown in Fig. 5 is connected between the point D and the line under 

 test. A movable short at the far end of the line completes the set-up. 



With the impedances matched as described above, the only reflection 

 which reaches the receiver wdll be from the far end of the line when the 

 switch S is open or, when shorted, from the switch itself. The round- 

 trip attenuation is the difference in attenuation measured for the two 

 positions of the switch. By means of a movable short at the far end of 

 the line, the line length can be varied to produce mode conversion and 

 mode reconversion effects, and the resultant variation in TEoi mode 

 transmission can be observed. This phenomena is described in some de- 

 tail elsewhere.^ 



" Reference 2, page 354, Fig. 14. 



■ C. F. Edwards, U.S. Patent 2,563,591, Aug. 7, 1951. The millimeter tuner 

 employs an adjustable dielectric post in place of a metallic tuning screw described 

 in the patent. 



* Reference 2, pp 356, 357. 



