848 



BELL SYSTEM TECHNICAL JOURNAL 



5. Construction and Operational Details 



Figure 10 shows a production model of a polyrod for 3000 megacycles, 

 with means for matching it to a rectangular waveguide.^^ A two-iris 

 transformer is used with a resulting width of 4% between the 1 db standing 

 wave points. The clamping illustrated is designed to maintain a firm grip 

 on the rod despite tendencies of the polystyrene to cold flow. 



Another type of coupling is indicated in Fig. 11. Here the polyrod is 

 still fed from a waveguide but this is in turn transformed to a coaxial line. 

 The composite can thus be regarded as a coaxial to polyrod coupling. The 

 coaxial line taps at point b onto the short-circuited antenna a-b-c at a point 



POLYSTYRENE 

 ROD 



COAXIAL 

 FEED 



Fig. 11 — Coaxial feed for polyrod. 



chosen to match the characteristic impedance of the coaxial line. The back 

 end of the waveguide is short circuited by a metal cap a quarter wavelength 

 behind the transverse wire antenna. A movable coaxial plunger provides 

 tuning. This arrangement has a bandwidth of 1% to the 1 db standing 

 wave points. 



The frequency response of a polyrod is inherently broad. The directive 

 pattern varies slowly with both phase velocity and amplitude distribution 

 along the axis. As shown in Figs. 1 and 2, these quantities are slowly vary- 

 ing functions of X over a considerable range of polyrod proportions. At 



" Developed by Mr. D. H. RiiiR. 



