METALLIC DELAY LENSES 



71 



rods is very large, i.e., the dispersion is not very great. If it is desired to 

 have a highly dispersive material, this band can be considerably reduced 

 by the process of tilting the rods so that they are more nearly perpendicular 

 to the electric vector. They thereby become '' loosely coupled" to the 

 incident wave and acquire a higher Q. Some unsymmetrical arrangement 

 such as that shown in Fig. 14 is necessary to insure that the radiation 

 damping of the elements is actually reduced, since a uniform tilt of all the 

 elements would allow the array to radiate, unhindered, a wave polarized 

 parallel to the elements. Measurements of the index of refraction of a 

 dielectric made up of successive arrays of rods arranged as in Fig. 14 are 



Fig. 14 — Array of metal rods to produce a narrow dispersion band. 



F 

 rods 



ig. 15 

 of Fig. 14. 



4 400 4000 3600 3200 2800 

 FREQUENCY IN MEGACYCLES PER SECOND 



Measured index of refraction of a metallic dielectric comprising the tilted 



given in Fig. 15, and one observes a marked similarity to the behavior of the 

 index of refraction of dielectrics in the region of their anomalous dispersion. 

 Because of the rapid change of n with wavelength, such material may be 

 useful as a means of separating narrow band radio channels by the use of 

 prisms or by lenses having several feed horns located at the optimum focal 

 points for the various frequency bands involved. 



Microwave Repeater Antenna 

 For radio relay applications, there are three electrical characteristics 

 which antennas should possess. The first is high gain (effective area), as 

 this will reduce the path loss and accordingly the requirements on trans- 



