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- Pridružio: 17 Sep 2010
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Neke karakertiristike radara AN/SPY-1 u ulozi anti-bal. odbrane
Citat:The focus of the description here is on the 1B/D versions, and on their physical characteristics relevant to BMD use.
Frequency and Bandwidth:
Citat:The Aegis system operates in S-band, from about 3.1 to 3.5 GHz (λ = 8.6 to 9.7 cm). Early descriptions indicated that the system reportedly had a “sustained coherent bandwidth” of 10 MHz and instantaneous bandwidth of 40 MHz. An early paper on the SPY-1 radar discusses three sub-bands, FL, FC, and FH, each 40 MHz wide, in the context of measuring antenna gain. However, data was also collected over much wider bands than the defined ones — 160 MHz at broadside, and 120 MHz at a 60 degrees scan angle.
The Aegis system’s bandwidth was apparently subsequently increased, perhaps up to its maximum frequency extent of 400 MHz. The 4.0.1 version of the Aegis Ballistic Missile Defense system, which is now entering service, added an adjunct BMD Signal Processor that, among other things, allows the formation of two-dimensional inverse synthetic aperture images with better resolution than had previously been possible, which implies a wideband capability. A 1999 Lincoln Laboratory briefing slide shows a “Wideband Waveform Concept for AN/SPY-1 Radar” using a 400 MHz wideband waveform constructed from ten 40 MHz bandwidth pulses frequency jumping from 3.1 to 3.5 GHz. A 2002 paper cites a bandwidth of 300 MHz for Aegis. Such a bandwidth would likely permit a range resolution of about 0.5-1.0 meters.
Antennas and Beamwidths:
Citat:Each Aegis radar system has four radar antenna faces. Starting with the SPY-1B, a new antenna was introduced, that although outwardly similar in appearance to the antenna of the SPY-1A, incorporated significant improvements. In particular, it has improved peak and average sidelobes relative to the 1A version and eliminates grating lobes within the antenna scan angles. These improvements were accomplished by subdividing the antenna into many more subarrays (2,175, each with two elements, for a total of 4,350 elements) than the 1A antenna (68 subarrays of 64 elements each, for a total of 4,352 elements) and by improved machining tolerances and alignment techniques.
The antenna face physical structure is octagonal, with a height of 4.06 m and a width of 3.94 m. In the 1A version, the antenna elements themselves are contained within a similar hexagonal shape with dimensions of roughly 3.84 m in height and 3.67 m in width. The area populated by the antenna elements appears to be about 12 m2. In the 1B/D version, the antenna face itself (the area occupied by the elements) is more nearly circular than in the 1A antenna, but since the number of elements is essentially the same, it is likely that its aperture area is also about the same.
The Aegis radar reportedly has a gain of G = 42 dB (= 15,800) and a beamwidth of 1.7˚x 1.7˚. This gain figure is consistent with G = ρ(4πA/λ2) with A =12 m2 and λ = 9.1 cm, only if ρ = 0.87 (which seems too high). Moreover, a gain of 42 dB appears to be inconsistent with the stated beamwidth of 1.7˚, which indicates a lower gain of about G =9,000.
Emitted Power:
Citat:As noted above, the 1B and 1D versions are nearly identical except that the 1B version uses two transmitters for each pair of two antenna faces, whereas the 1D version has one transmitter for all four faces. However, since a transmitter can apparently be used with only one face at a time, the maximum power that can be put out of any antenna face should be same for both versions.
The original SPY-1A version reportedly has a peak power of up to 5 MW and an average power of 32 kW. The SPY-A’s transmitter output is provided by 32 crossed field amplifiers (CFAs), each with peak power of 132 kw, which would give a combined peak power of 4.2 MW. This seems to indicate that reported peak and average powers for the radar are the transmitter power, not the power actually emitted, which will be less due to losses between the transmitter and antenna.
The SPY-1B reportedly has an average power of 58 kW with a peak power of 4-6 MW. This is roughly consistent with reports that the 1B version had the same peak power but twice the average power (that is, its duty cycle was doubled) of the 1A, and that, more specifically, the SPY-1B/D used a new CFA with a doubled duty cycle.
According to a 2004 Defense Science Board Report, “the average radiated power aperture for the Aegis System is 485 kwm2.” Assuming that statement applies to the SPY-1D (since the SPY-1D(V) version was not yet operational) and an antenna area of 12 m2, this would give an average emitted power of about 40 kW.
Pulse Lengths:
Citat:The Aegis radar (1B version) can produce pulses with lengths of 6.4, 12.7, 25 and 51 microseconds, with a pulse compression ratio of 128. This 51 μs maximum pulse length is consistent with a 1997 study that stated that the electromagnetic interference produced by an Aegis radar pulse would last for at most 52 microseconds. However, given the many upgrades to the Aegis system, including the BMD upgrades, these pulse lengths may have changed significantly.
A 1978 paper states that the noise figure for the Aegis SPY-1A receiver was about 4.25 dB = 2.66.
Detection Range:
Citat:The only public numerical figure on Aegis detection range against a specific target (that I have seen) is that the SPY-1D “can track golf ball-sized targets at ranges in excess of 165 kilometers.” A golf ball-size (1.68 inches diameter) sphere corresponds to radar cross section of about 0.0025 m2 at 3.3 GHz. This statement was made in the context of the soon-to-be deployed SPY-1D(V) radar to detect mortar and artillery shell and small-caliber rockets against a clutter background, so presumably it applies to the D(V) version. Scaling to a radar cross section more typical of a ballistic missile warhead (0.03 m2 at 3.3 GHz) gives a range of at least 310 km.
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