376 BELL SYSTEM TECHNICAL JOURNAL 



Space-Charge and Transit-Time Effects on Signal and Noise in Microwave 

 Tetrodes}^ L. C. Peterson. Signal and noise in microwave tetrodes are 

 discussed with particular emphasis on their behavior as space-charge condi- 

 tions are varied in the grid-screen, or drift, region. The analysis assumes 

 that the electron-stream velocity is single-valued . For particular conditions 

 the noise figure may be substantially improved by increasing the space- 

 charge density in the grid-screen region until an entering electron encounters 

 a field of a certain magnitude. The noise reduction is largely due to the 

 cancellation in the output of the noise produced by the random cathode 

 emission. The method of noise reduction described is applicable only when 

 the transit angles of both input and drift regions are fairly long. 



In a forthcoming paper, H. V. Neher describes experimental results which 

 broadly agree with the theory. 



"Cloverleaf" Antenna for F. M. Broadcasting.^^ Phillip H. SmxH. The 

 radiation requirements and general design considerations for transmitting 

 antennas suitable for f.m. broadcoasting are briefly discussed, and an ex- 

 planation of the design and operation of the arrangement of radiating ele- 

 ments and associated feed system employed in the ''cloverleaf" antenna is 

 given. Both calculated and measured data are included, showing field-in- 

 tensity distribution, gain, impedance-frequency characteristics, etc. De- 

 sign features which are discussed include a simple coaxial impedance-match- 

 ing transformer developed initially for microwave application, and the 

 method and facilities provided for the removal of sleet. 



Hybrid Circuits for Microwaves}^ W. A. Tyrrell. The fundamental 

 behavior of hybrid circuits is reviewed and discussed, largely in terms of 

 reciprocity relationships. The phase properties of simple wave-guide tee 

 junctions are briefly considered. Two kinds of hybrid circuits are then 

 described, the one involving a ring or loop of transmission line, the other 

 relying upon the symmetry properties of certain four-arm junctions. The 

 description is centered about wave-guide structures for microwaves, but the 

 principles may also be applied to other kinds of transmission lines for other 

 frequency ranges. Experimental verification is provided, and some of the 

 important applications are outlined. * 



" Proc. /. R. £., November 1947. 



" Proc. L R. E.— Waves and Electrons Section, December 1947. 



w Proc. L R. £., November 1947. 



