. The Bell System technical journal . characteristics of the portion of the wave frontwhere it is located. Its effect is to subtract from the undisturbedpattern a shadow pattern component which is broad in angle. Thisdecreases the gain and increases the minor lobes as indicated in Fig. 21.^ \ V-FEED Fig. 20—Offset Parabolic Section. 2. Return of reflected energy into the feed introduces a standing waveof impedance mismatch in the feed line which is constant in amplitudebut varies rapidly in phase as the frequency is varied. A mismatch atthe feed which cancels the standing wave at one frequency
. The Bell System technical journal . characteristics of the portion of the wave frontwhere it is located. Its effect is to subtract from the undisturbedpattern a shadow pattern component which is broad in angle. Thisdecreases the gain and increases the minor lobes as indicated in Fig. 21.^ \ V-FEED Fig. 20—Offset Parabolic Section. 2. Return of reflected energy into the feed introduces a standing waveof impedance mismatch in the feed line which is constant in amplitudebut varies rapidly in phase as the frequency is varied. A mismatch atthe feed which cancels the standing wave at one frequency will add toit at another frequency. A mismatch which will compensate over aband can be introduced by placing a raised plate of proper dimensionsat the vertex of the reflector as indicated in Fig. 22, but such a jilateproduces a harmful effect on the pattern. In an antenna which mustoperate over a broad band it is consequently usually better to match Figures 21, 22, and 23 arc taken from V. C. Cutler, loc. cit. J RADAR ANTENNAS 257. Fig. 21- -5 0 5 DEGREES OFF AXIS-Effect of Shadow on Paraboloid Radiation Pattern.
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