POLY ROD ANTENNAS 



843 



its operation involves the solution of Maxwell's equations subject to the 

 boundary conditions appropriate to the configuration. An analysis of this 

 sort is not available because of its mathematical complexity. However, a 

 satisfactory explanation of polyrod operation, especially for engineering 

 purposes, can be obtained by establishing analogies with array theory, 

 coupled with existing knowledge about transmission in uniform dielectric 

 wires. In this treatment by analogy, we remain essentially ignorant of the 

 local fields in the vicinity of the dielectric, the role played by the discon- 

 tinuities at both ends of the antenna, and other detailed features. We do 

 have, however, a working theory which predicts closely the features of the 

 radiation as observed at a distance. Under these circumstances, insistence 

 upon a rigorous field solution has not so far appeared necessary. 



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DEGREES OFF AXIS 



Fig. 6 — Data on polyrods of uniform rectangular cross-section gX by ^X. 



Experimental data have been obtained at frequencies in the vicinity of 

 3000 megacycles except for Fig. 9, representing work at 9000 megacycles. 

 For the sake of generality, these results are presented in dimensions of X, 

 the free space wavelength. In all cases, polyrods have been energized from 

 a dielectric filled metal guide whose conducting sheath is abruptly termi- 

 nated, the dielectric continuing on as the radiator. 



The earliest form of polyrod^ was a polystyrene rod of uniform rectangular 

 cross-section, about |X by §X. Figure 6 shows the gains and directional 

 patterns measured for such rods in three different lengths. In a plane 

 normal to the axis, the radiation is approximately isotropic. The observed 

 gains are proportional to length. They are greater than 4p by a factor of 



»The earliest work on polyrods was done in 1<M1 hv Dr. G. C. Southworth. C:f. his 

 r. S. Patent 2,206,923 issued in 1940. 



