. The Bell System technical journal . g hole by r. A cor-rection for the finite thickness of the wall is made by. considering thecircular 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 couplinglength and hole spacing. Equation (2) is used to find a and then the holeradius r is calculated from (3). Wa^eguide dimensions must be corrected to allow for the perturba-tion of the phase constants due to the cou
. The Bell System technical journal . g hole by r. A cor-rection for the finite thickness of the wall is made by. considering thecircular 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 couplinglength and hole spacing. Equation (2) is used to find a and then the holeradius 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 perturbedphase constant* for the round guide is d where d is the hole spacing and p is the coupling between a pair of round guides ^o p - R [l ( « Yl L \ J (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. 396 THE BELL SYSTEM TECHXICAL JOURNAL, MARCH 1957. n =28 EQUIVALENT UNIFORM HOLES T= °-^^° Fig. 2 — 11-kmc coupler sketch. _) UJ mo UJ o toin o _J rr UJ u. z^ L, 1 1 ■ sc—~ ^ FREQUENCY IN KILOMEGACYLES PER SECOND Fig. 3 — 11-kmc coupler transfer loss. AN EXPERIMENTAL DUAL POLARIZATION ANTENNA FEED 397 The perturbed phase constants are made etiual through a suitablechoice 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 theends of the array of identical holes to produce four reflections having therelative amplitudes of 1, , , 1. The modified binomial distributionwas chosen because impedance matching can be secured over a broader 20 1 & LU u Q 16 12 1 0 Z o I-tr
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