RADAR ANTENNAS 



281 



A simple end fire element, and one that has been used in practice, is the 

 'polyrod' (Fig. 38). A polyrod, is as its name implies, a rod of polystyrene. 

 This rod, if inserted into the open end of a waveguide, and if properly pro- 

 portioned and tapered, will radiate energy entering from the waveguide 

 from points which are distributed continuously along its length. If the 





Fig. 38— A Polyrod. 



l'>x[)erimental Polyrod Array. 



wave in the polyrod travels approximately with free space velocity it will 

 produce a radiation maximum in the direction of its axis. The radia- 

 tion pattern of the polyrod will have a shape which is characteristic of end 

 fire arrays, narrower and flatter topped than the pattern of a side fire array 

 which occupies the same lateral dimension. This elementary pattern can 

 be fitted in well with the array factor of a scanning array. 



Such a scanning array is shown in Fig. 39 and will be described in 



