1-10ANTENNA HEIGHT AND SPEED.—Another factor affecting radar range is antenna height. Thehigh-frequency energy transmitted by a radar system travels in a straight line and does not normally bendto conform to the curvature of the earth. Because of this, the height of both the antenna and the target arefactors in detection range. The distance to the horizon (in nautical miles) for a radar system varies withthe height of the antenna according to the following formula:For example, assume antenna height to be 64 feet in the following calculations:A target at a range greater than the radar horizon will not be detected unless it is high enough to beabove the horizon. An example of the antenna- and target-height relationship is shown in figure 1-7.Figure 1-7.—Radar horizon.The antenna-rotation rate also affects maximum detection range. The slower an antenna rotates, thegreater the detection range of a radar system. When the antenna is rotated at 10 revolutions per minute(rpm), the beam of energy strikes each target for just one-half the time it would if the rotation were 5 rpm.
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