. The Bell System technical journal . rength couplings (as described above) and theexact discrimination plotted using (13) and (14). The results are givenin Figs. 13 and 14. The original continuous coupling function yields dis-criminations greater than 38 db for all values of ^/tt greater than 2; the40-point simulation approximates this well in the region of Q/-K = , but thereafter begins to fail. The 12-point simulation (Fig. 13) nevermatches the original but does best in the region of small Q/t. It is more efficient to seek high discriminations by tapering thestrength of equally spa
. The Bell System technical journal . rength couplings (as described above) and theexact discrimination plotted using (13) and (14). The results are givenin Figs. 13 and 14. The original continuous coupling function yields dis-criminations greater than 38 db for all values of ^/tt greater than 2; the40-point simulation approximates this well in the region of Q/-K = , but thereafter begins to fail. The 12-point simulation (Fig. 13) nevermatches the original but does best in the region of small Q/t. It is more efficient to seek high discriminations by tapering thestrength of equally spaced couphngs than by tapering the spacing be-tAveen equal strength couplings. However, when Ioav discriminations areacceptable, the relative efficiency of tapering the spacing between con- [|I L I U a503L A I U >l I ME Fig. 13 — Discrimination for 12 oqiial-strcngth point couplings arranged tosimulate the continuous distribution of Fig. 4, line 2. 676 THE BELL SYSTEM TECHNICAL JOURXAL, MAY 1954. Fig. 14 — Discrimination for 40 equal-strength point couplings arranged tosimulate the continuous distribution of Fig. 4, line 2. < 20 r ^2 V ^2 Xi = LX2 = L X3 = LX4 = L 1 1 M i 1 [ \j\ l\j 1 f / , / I / \ / J V y V -^ 40/7T Fig. 15 — Discrimination function for 8 equal strength couplings arranged tomaximize the bandwidth (e/ir range) for moderate discrimination. COUPLED WAVE THEORY AND WAVEGUIDE APPLICATIONS C)77 stant strength couplings is much greater than when high discriminationsare required. Fig. shows a (hstribution wliich i)ro(hi(es about 20 dbdiscrimination from QJ-k = 1 to Eight coujolings arranged with theTchebjsheff amplitude taper for 20 db discrimiuation would i)roducethat discrimination from 6/w = to It is possible to obtain directivity or mode discrimination at smallerd/ir values than made available with uniform coupling. This situation isanalogous to the superdirectivity problem in antenna design, w
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