AN EXPERIMENTAL DUAL POLARIZATION ANTENNA FEED 



401 



Capacitive rods form a periodic structure in the rectangular guide, as 

 shown in Fig. 8, that creates a rejection band in the 6-kme region. Fig. 9 

 illustrates how effectively the rejection band increases the transfer loss 

 in the 6-knic region. Phase velocities are made e(iual in the rectangular 

 and round guides at the center of the 500-mc wide 4-kmc band to secure 

 a low transfer loss. Due to the rejection bands and the difference of phase 

 constants, high transfer losses result in the 6- and 11-kmc bands. To 

 prevent unconti'olled coupling the round guide size is chosen so that no 

 modes cut off in the three bands. Details of the design are covered in 

 Appendix II. Figs. 10 and 11 show the measured transfer and insertion 

 losses in the 4-kmc band. 



MEASURED CHARACTERISTICS OF ARRAY 



The three pairs of couplers were assembled in a tandem array with 

 linear taper sections between them. In the discussions that follow the port 

 designations of Fig. 1 will be used. Transfer loss measurements indicate 



_i 



111 



18 



17 

 16 

 15 

 14 

 13 



U 



uj 



Q 12 



m 1 1 



in 



O 



_i 



tr 



UJ 



to 



z 



6 

 5 



3600 



3700 3800 3900 4000 4100 4200 



FREQUENCY IN MEGACYCLES PER SECOND 



4300 



4400 



Fig. 11 — Insertion loss of 4-kmc coupler in 4-kmc baud. 



