4^2 BELL SYSTEM TECHNICAL JOURNAL 



the cavity, and the input and output couphng locations can then be appro- 

 priately chosen. On the basis that internal couplings are responsible for 

 mode crossing difficulties, one might hazard a guess that a real fin would 

 increase such couplings. 



Another application of fins might be in a wave guide feed in which it is 

 desired to establish only a TE Oni wave. In this case, Q is not so important 

 and larger fins can be used. If these extended virtually to the center and x 

 of them were present (with uniform angular spacing) all types of wave trans- 

 mission having / less than x/2, x even or / less than x, x odd, would be sup- 

 pressed. This use of fins is an extension of the wires that have been 

 proposed in the past. 



Conclusion 



It is hoped that the foregoing, which covers some of the theoretical work 

 done by the author during the war, will be of value to other workers in 

 cavity resonators. There is much that needs to be done and hardly time 

 for duplication of effort. 



Bibliography 



1. E. I. Green, H. J. Fisher, J. G. Ferguson, "Techniques and Facilities for Radar Test- 



ing." B.S.T.J., 25, pp. 435-482 (1946). 



2. I. G. Wilson, C. W. Schramm, J. P. Kinzer/'High Q Resonant Cavities for Micro- 



wave Testing" B.S.T.J., 25, pp. 408-434 (1946). 



3. J. R. Carson, S. P. Mead, S. A. Schelkunoff, "Hyper-Frequency Wave Guides — 



Mathematical Theory," B.S.T.J., 15, pp. 310-333 (1936). 



4. G. C. Southworth, " Hyperf requency Wave Guides — General Considerations and 



Experimental Results," B.S.T.J., 15, pp. 284-309 (1936). 



5. W. W. Hansen "A Type of Electrical Resonator," Jour. A pp. Phys., 9, pp. 654-663 



(1938). — A good general treatment of cavity resonators. Also deals briefly with 

 coupling loops. 



6. W. W. Hansen and R. D. Richtmyer, "On Resonators Suitable for Klystron Oscil- 



lators," Jour. A pp. Phys., 10, pp. 189-199 (1939). — Develops mathematical methods 

 for the treatment of certain shapes with axial symmetry, notably the "dimpled 

 sphere," or hour glass. 



7. W. L. Barrow and W. W. Mieher, "Natural Oscillations of Electrical Cavity Reso- 



nators," Proc. I.R.E., 28, pp. 184-191 (1940). An experimental investigation of 

 the resonant frequencies of cyhndrical, coaxial and partial coaxial (hybrid) cavities. 



8. R. Sarbacher and W. Edson, "Hyper and Ultrahigh Frequency Engineering," John 



Wiley and Sons, (1943). 



9. R. H. Bolt, "Frequency Distribution of Eigentones in a Three-Dimensional Con- 



tinuum," J.A.S.A., 10, pp. 228-234 (1939) — Derivation of better approximation 

 formula than the asymptotic one; comparison with calculated exact values. 



10. Dah-You Maa, "Distribution of Eigentones in a Rectangular Chamber at Low-Fre- 



quency Range," J.A.S.A., 10, pp. 235-238 (1939)— Another method of deriving an 

 a^jproximation formula. 



11. I. G. Wilson, C. W. Schramm, J. P. Kinzer, "High Q Resonant Cavities for Micro- 



wave Testing," B.S.T.J., 25, page 418, Table IK (1946). 



12. L. Brillouin, "Theoretical Study of Dielectric Cables," Elec. Comm., 16, pp. 350- 



372 (1938)— Solution for elliptical wave guides. 



13. L. J. Chu, "Electromagnetic Waves in EUiptic Hollow Pipes of Metal," Jour. App. 



Phys., 9, pp. 583-591 (1938). 



14. Stratton, Morse, Chu, Hutner, "Elliptic Cvlinder and Spheroidal Wave Functions," 



M.I.T. (1941). 



