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Radar System Engineering

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292 ANTENNAS, SCANNERS, AND STABILIZATION [SEC.9.13<br />

the guide width (and thereby the wavelength in the guide)’ periodically;<br />

this, in turn, varies the effective dipole phasing and moves the beam in<br />

azimuth.<br />

FIu. fl.18.-AN/.4P7-7<br />

antennahousingon a B-24.<br />

If all the dipoles are excited in the same phase, the beam is broadside<br />

to the array and directed straight ahead of the aircraft. With the dipole<br />

spacing actually used, this occurs when the inside width a of the guide<br />

is 1.200 in. Let us assume that the energy is propagated in the waveguide<br />

from left to right. Then, as the guide is narrowed to 0,660 in.,<br />

the beam moves 30° toward the left, that is, in the backfire direction.<br />

LSee Sec. 113.

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