11.3 THE TRACKING RADAR

If we are to measure the echo from a target, we must point our instrumentation antennas toward it and set our range gate so as to maximize the sensitivity of our receiver to the captured echo pulse. While we may do this almost at leisure on a static test range, we must accomplish it from moment to moment in dynamic testing. Most of the time we rely on a tracking radar to provide antenna-pointing and range-gate-setting information to do so, assisted on occasion by a beacon or transponder (active echo enhancer) installed on the target under test. The tracking function may also be accomplished with telescopes and optical trackers, but we do not discuss them here.

It requires no fewer than three independent coordinates to specify the apparent target position relative to the radar site: azimuth angle, elevation angle, and range. The tracker radar therefore delivers three error signals to appropriate angle- and range-adjustment circuits, as shown in fig. 11.5. The signals are amplified, as necessary, and routed to devices that attempt to adjust the antenna-pointing direction and the receiver range-gate setting so as to force these error signals to zero. The angle-adjustment devices are circuits and motors that cause the antenna pedestal to be slewed in both azimuth and elevation. The range adjustment is activated by an electronic device that advances or retards the delay of the range-gate pulse delivered to both the tracker and instrumentation radar receivers. If the instrumentation antennas are...