Analysis and Performance of Waveguide-Hybrid Rings 

 for Microwaves 



By H. T. BUPENBOM 



This paper presents an analytical treatment of waveguide hybrid rings for 

 microwaves, considered as re-entrant transmission lines. The resulting lines 

 are transformed into equivalent "T" or "lattice" network sections, and deter- 

 minantal methods are applied in analyzing these equivalent network assemblies 

 for their transmission properties. Some experimental results obtained from a 

 carefully constructed sample of each of two specific types are given. A satis- 

 factory agreement is obtained between the values predicted by theory and 

 experimental results. 



Introduction 



TN A recent paper^, Mr. W. A. Tyrrell has described two general types of 

 -^ waveguide or waveguide/coaxial structures whose properties include 

 bridge or null balance characteristics analogous to those of the hybrid coil 

 common in voice-frequency communication practice. One type, the hy- 

 brid junction, is a particular orthogonal junction of four rectangular wave- 

 guides. Certain properties of the hybrid junction, notably its impedance 

 characteristics, have been the subject of a British publication^. The present 

 paper presents a method for detailed analysis of the other general struc- 

 ture described by Tyrrell, the hybrid ring. This latter structure is essen- 

 tially an annular ring or annulus of waveguide, at present usually an in- 

 tegral number of quarter wavelengths in circumference, and fitted with an 

 appropriate number of series or shunt branch taps. In this article, phrases 

 such as "quarter wavelength," etc., describing tap spacing or mean annulus 

 perimeter, refer to wavelength in the guide, not to free space wavelength. 



The method of analysis employed herein is essentially to treat the tapped 

 annulus as a re-entrant transmission Hne. Certain circuit equivalences and 

 quarter wave impedance transformations were used by Tyrrell in his paper 

 to develop, with the aid of the reciprocity theorem, many basic properties 

 of hybrid circles and hybrid junctions. In the present paper "T" or "lat- 

 tice" equivalents (neglecting dissipation) are developed for each section of 

 the annulus, and the method of determinants is applied. 



The hybrid junction (known also as the "magic tee") came into use in the 

 newer radars in the latter part of the war. One of its uses, that of providing 



1 "Hybrid Circuits for Microwaves," W. A. Tyrrell, Proc. I. R. E., November 1947. 



2 "The Theory and Experimental Behaviour of Right-Angled Junctions in Rectangular- 

 Section Wave Guides," /. E. E. Jour., September 1946, p. 177. 



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