. The Bell System technical journal . - may indeed just manage to produce a desirablebeam. A little analysis shows however that an appreciable phase variationfrom element to element, e\en though linear, will introduce a serious ex-tra lobe. To get around this difiKulty elements with some end lircdirec-livity must be used. RADAR ANTENNAS 281 A simple end fire element, and one that has been used in practice, is thepolyrod (Fig. 38). A polyrod, is as its name implies, a rod of rod, if inserted into the open end of a waveguide, and if properly pro-portioned and tapered, will radia
. The Bell System technical journal . - may indeed just manage to produce a desirablebeam. A little analysis shows however that an appreciable phase variationfrom element to element, e\en though linear, will introduce a serious ex-tra lobe. To get around this difiKulty elements with some end lircdirec-livity must be used. RADAR ANTENNAS 281 A simple end fire element, and one that has been used in practice, is thepolyrod (Fig. 38). A polyrod, is as its name implies, a rod of rod, if inserted into the open end of a waveguide, and if properly pro-portioned and tapered, will radiate energy entering from the waveguidefrom points which are distributed continuously along its length. If the Fig. 38—A l>x[)erimental Polyrod Array. wave in the polyrod travels approximately with free space velocity it willproduce a radiation maximum in the direction of its axis. The radia-tion pattern of the polyrod will have a shape which is characteristic of endfire arrays, narrower and flatter topped than the pattern of a side fire arraywhich occupies the same lateral dimension. This elementary pattern canbe fitted in well with the array factor of a scanning array. Such a scanning array is shown in Fig. 39 and will be described in 282 BELL SYSTEM TECH NIC A L JOURNA L greater detail in section Each element of this array consists of a fixedvertical array of three polyrods. This elementary array provides the re-quired vertical pattern and has appropriate horizontal of these elements are arranged in a horizontal array with a spacingbetween neighbors of about two wavelengths. Energy is distributed amongthe elements with a system of branching waveguides. Thirteen rotar
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