. The Bell System technical journal . 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 360 350 340 330 320 310 300 290 280 270 260 250 240 230 220 210 200 190 180 ANGLES OF INCIDENCE (6) — DEGREES Fig. Sd—Relative Directional Receptivity of Cupar, Scotland—Antenna No. 1 The reason for this can be appreciated by reference to Fig. 7, where itis shown that the far end of the long antenna is at the top of a rockyhill; while after shortening, the far end is in a swamp, at the same 334 BELL SYSTEM TECHNICAL JOURNAL average elevation as the remainder of the antenna. The eHminationof t
. The Bell System technical journal . 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 360 350 340 330 320 310 300 290 280 270 260 250 240 230 220 210 200 190 180 ANGLES OF INCIDENCE (6) — DEGREES Fig. Sd—Relative Directional Receptivity of Cupar, Scotland—Antenna No. 1 The reason for this can be appreciated by reference to Fig. 7, where itis shown that the far end of the long antenna is at the top of a rockyhill; while after shortening, the far end is in a swamp, at the same 334 BELL SYSTEM TECHNICAL JOURNAL average elevation as the remainder of the antenna. The eHminationof this sharp rise over rocky ground serves principally to remove anirregularity in the constants of the wave-antenna near the end, sothat the entire antenna may be considered more nearly a smooth makes the antenna function more satisfactorily as a unit of anarray in connection with other antennas constructed Fig. 9. 6. Wave-Antenna Arrays. Since 1899, when S. G. Brown ^^ proposedthe use of two vertical antennas, separated in space by an appreciableportion of a wave-length and excited at a half-period phase difference,as a means of directional transmission, the use of arrays of antennas 1^ R. M. Foster, Directive Diagrams of Antenna Arrays, Bell System , 5, 292; April, 1926. Also see references listed in Fosters paper. TRANSATLANTIC RADIO TELEPHONY 335 for directional transmission and reception has become increasinglyimportant. Antenna arrays may be divided into two general classes:(1) arrays of antennas having dissimilar directional characteristics,and (2) arrays of antennas the directional characteristics of which areidentical. The array formed by the use of a loop and a verticalantenna to form the familiar cardioid is representative of the firstclass of antenna arrays. Foster^ has pointed out that the idealwave-antenna may be considered as an array of an infinite number ofloop
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