AN EXPERIMENTAL DUAL POLARIZATION ANTENNA FEED 



397 



The perturbed phase constants are made etiual through a suitable 

 choice of R and a, this choice being somewhat influenced by the coupUng- 

 hole radius r. 



Three coupling a{)ertures of successively reduced size are used at the 

 ends of the array of identical holes to produce four reflections having the 

 relative amplitudes of 1, 2.7, 2.7, 1. The modified binomial distribution 

 was chosen because impedance matching can be secured over a broader 



20 



1 & 



LU 



u 



Q 



16 



12 



1 



Z 



o 



I- 

 tr 



LU 



CO 



z 



6 



4 

 9.2 



9.6 10 10.4 10.8 n.2 11.6 



FREQUENCY IN KILOMEGACYCLES PER SECOND 



12 



Fig. 4 — 11-kmc coupler insertion loss. 



band (with minor degradation of the center-frequency match) when 

 compared to a standard binomial distribution. Amplitude reflections* 

 from the start of the coupling array are 



Ar = 



47rrf 



(10) 



where Q is the reflection from a single coupling hole. 



Fig. 2 is a sketch of the coupler with, the final design dimensions. 

 Fig. 3 shows the measured and theoretical transfer loss of an 11 kmc 

 coupler. Fig. 4 indicates the measured insertion loss for the same coupler. 



DESIGN OF 6-KMC COUPLER 



The 6-kmc coupler as shown in Fig. 5 utilizes a partially dielectric- 

 filled rectangular guide coupled to the circular guide. The use of dielectric 

 loading makes it possible for the phase velocities to be equal in the two 

 guides in the center of the 500-mc wide 6-kmc band, and unequal in 



* Information given to S. E. Miller by S. A. Schelkunoff in an informal com- 

 munication. 



