sector of ≈270 degrees. For the purposes of this report, the recommended doubled AN/TPY-2 radars are designated GBX radars.

More specifically, the recommended GBX radars would provide electronic scan coverage from the horizon to the zenith over a traverse angle sector of ±45 degrees from broadside. The traverse is a great circle angle passing through the broadside azimuth at the elevation of the scanned beam it covers: For example, ±45 degree azimuth at the horizon, ±93 degree azimuth at 45 degree elevation, and all azimuths at zenith.

The output of this “doubled,” over-and-under, dual-array GBX system would be combined coherently through a time-delay device that permits the full instantaneous signal bandwidth to be used for range Doppler imaging. The coherent combination produces an elevation beam width half that of the AN/TPY-2 radar, with twice the gain (four times the two-way gain) and twice the peak and average power. Duplicate power supply and cooling units would be required, but a single electronic equipment unit should suffice, with minimal added electronics to handle the combined signals.

It is recommended that these stacked GBX radars be located at the current UEWR (ballistic missile early warning system (BMEWS)) sites (Cape Cod, Massachusetts; Grand Forks, North Dakota; Thule, Greenland; and Fylingdales, United Kingdom). Additionally, as a result of its analysis, the committee recommends that a fifth GBX radar be added at Clear, Alaska, and that the SBX be moved permanently to Adak, Alaska.

Figure 5-8 shows the GBX architecture for homeland defense that was used for the analysis to support a multiple SLS firing doctrine: This architecture greatly increases system engagement effectiveness. Note in Figure 5-8 that the field of regard for the AN/TPY-2 radars is shown symbolically as 360 degrees. In fact, a rotational mounting would be needed to accomplish this 360-degree capability.

Scheduling of X-Band Radar for Multiple Engagements

The range at which acquisition and tracking of a target complex is possible can be increased when accurate cueing from external sensors permits the X-band radars to be pointed at the target without use of an acquisition scan. This allows the integration of multiple pulses. Without regard to the transmitted waveform, the time required to exchange a pulse with a target at 1,000 km range is equal to twice the range divided by the velocity of light, which is ≈7 ms, plus an allowance for reception of the entire echo, totaling ≈8 msec. For example, if integration of 10 pulses for acquisition and tracking were necessary, a beam dwell of approximately 80 msec at 1,000-km target range, or 160 msec at 2,000-km target range would be required. Accurate velocity measurement and range-Doppler imaging would typically require a sequence of these 10-pulse dwells over a period of approximately10 sec (for example, 4 dwells at 2.5 sec intervals). Thus, each target would consume a nominal 320-640 msec in 10 sec, or 3.2-6.4 percent of the radar’s time.

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