AN EXPERIMENTAL DUAL POLARIZATION ANTENNA FEED 395 



p. 0.6805XoV6 



-. - ..«y > - (ly /: - (3-^y <3) 



The quantities a and b are the large and small dimensions of the rec- 

 tangular waveguide and R is the round guide radius. The wavelength in 

 air is designated by Xn , and the radius of the coupling hole by r. A cor- 

 rection for the finite thickness of the wall is made by. considering the 

 circular coupling hole to be a mund wa\'eguide beyond cutoff. The ad- 

 ditional loss is 



where t is the wall thickness. Total coupling loss per hole is defined by 



20 1ogioa = 10 log :^' - A (5) 



The number of coupling holes n is found from the approximate coupling 

 length and hole spacing. Equation (2) is used to find a and then the hole 

 radius r is calculated from (3). 



Wa^'eguide dimensions must be corrected to allow for the perturba- 

 tion of the phase constants due to the coupling holes. The perturbed 

 phase constant* for the round guide is 



d 



where d is the hole spacing and p is the coupling between a pair of round 



guides 



(7) 



The perturbed phase constant for the rectangular guide is 



D _ ^D ,__ VP° 



/3p^ = /3" + -^ (8) 



P = 



9a%' 



[' - m 



(9) 



This correction is due to S. A. Schelkunoff as noted on page 708 in Reference 4. 



