1254 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 



oscillators which has already resulted in 5 to 6 mm oscillators and which 

 appears suitable for use at shorter wavelengths.* Recently, E. D. Reed 

 produced a 5 to 6 mm reflex klystron.* 



R. S. Ohl has continued his pioneering work on point-contact crystal 

 converters and has made units for use at 6 mm having conversion losses 

 of less than 8 db and output noise ratios on the order of three times basic 

 thermal noise. Ohl also made point contact silicon units for use as har- 

 monic generators to permit the conversion of 24,000 mc power to 48,000 

 mc power. His harmonic generators have proven invaluable as a source 

 of millimeter wave power — essentially all of the radio research work 

 done to date has been carried out using them. 



In order to evaluate crystals and millimeter wave oscillators, it is 

 essential to have an absolute power reference in the millimeter region, 

 and work* has been done by W. M. Sharpless to establish such 

 a reference. 



Up to the present time all of the amplifiers, oscillators and other 

 circuit elements have employed dominant-mode rectangular waveguides 

 in order to simplify the circuit design. Therefore, it is of importance to 

 know how to transform a signal from a dominant-mode rectangular guide 

 to the circular electric wave in round pipe. The first circular-electric- 

 wave transducer made in these Laboratories was designed by A. P. King 

 and had the form sketched in Fig. 27. This transducer is of the general 

 type in which the metallic boundary of the waveguide is shaped to force 

 the field lines in the cross section of the guide into the pattern character- 

 istic of the desired output wave. In Fig. 27 the dominant-mode rectan- 

 gular guide at the left end is gradually tapered to the sector of a circle; 

 the size of this sector is small enough so that only one wave type can 

 exist at this point, and the electric field lines are arcs of a circle. Next, the 

 angle of the sector is gradually increased along the axis of propagation 

 until at one point a cross section of the guide has the shape of a half 

 circle. The size of the sectoral angle is continually increased, however, 

 until finally the metallic sector of the circle disappears as a radial vane. 

 When the taper is done gradually (an overall length of approximately 

 10 to 15 wavelengths) the electric field lines remain ares of a circle as 



Fig. 27 — Circular-olectric wave transducer (due to A. P. King). 



* A portion of this work was carried out under Office of Naval Research Con- 

 tract Nonr 687(00). 



