ABSTRACTS OF TECHNICAL ARTICLES 511 



Domain Properties in BaTiOz. W. J. Merz^ Letter to the Editor. 

 Phys. Reu., 88, pp. 421-422, Oct. 15, 1952. 



Notes on Methods of Transmitting the Circular Electric Wave Around 

 Bends. E. S. Miller^. LR.E., Proc, 40, pp. 1104-1113, Sept., 1952. 

 (Monograph 2037). 



The tendency for energy to be converted out of the circular electric wave in 

 bent round pipe may be avoided by one of three general approaches: (1) by re- 

 moving the degeneracy between TEoi and TMn, (2) by converting to a normal 

 mode of the bent guide at both ends of the bend, and (3) by utilizing dissipation 

 in the unwanted modes to prevent power transfer to them. All three approaches 

 are discussed. Normal attenuation in round pipe should be effective in moderat- 

 ing straightness requirements. Elliptical guide and special waveguide structures 

 may be used to negotiate intentional bends; bending radii in the range one to 

 1,000 feet appear acceptable at 50,000 mc for waveguides %-uich to 2 inches in 

 diameter, respectively. 



Multi-Element Directional Couplers. S. E. Miller^ and W. W. Mum- 

 FORD^ I.R.E., Proc, 40, pp. 1071-1078, Sept., 1952. (Monograph 2038). 



It is shown that the backward wave in a directional coupler is related to the 

 shape of the function describing the coupling between transmission lines by the 

 Fourier transform. This facihtates the design of directional couplers for arbitrary 

 directivities over any prescribed frequency band. Tightly coupled directional 

 couplers are analyzed in simple terms, and it is shown that any desired loss ratio, 

 including complete power transfer between lines, may be achieved. The theories 

 are verified using waveguide models operating at 4,000, 24,000 and 48,000 mc, 

 and it is indicated that the work is appUcable to many types of electrical and 

 acoustic transmission lines. 



Transistor Noise in Circuit Applications. H. C. Montgomery^. I.R.E.y 

 Proc, 40, pp. 1461-1471, Nov., 1952. 



Linear circuit problems involving multiple noise sources can be handled by 

 famihar methods with the aid of certain noise spectrum functions, which are 

 described. Several theorems of general interest dealing with noise spectra and 

 noise correlation are derived. The noise behavior of transistors can be described 

 by giving the spectrum functions for simple but arbitrary configurations of 

 equivalent noise generators. From these, the noise figure can be calculated for 

 any desired external circuit. 



Transistor Noise in Circuit Applications. H. C. Montgomery^ I.R.E.y 

 Proc, 40, pp. 1314-1326, Nov., 1952. 



The invention of the transistor provided a simple, apparently rugged device 

 that could amplify — an abihty which the vacuum tube had long monopoHzed. 

 As with most new electron devices, however, a number of extremely practical 

 hmitations had to be overcome before the transistor could be regarded as a 



^ Bell Telephone Laboratories. 



