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3, DESCRIPTION Each face of the antenna is a metal plane l02 feet in diameter, from which a regular array of 5,354 antenna elements protrude (see Figures 2 and 3). Of these, 2,677 around the outer periphery are totally in- active, being provided now to allow for a possible increase in the size of the antenna and the power of the radar at some later date as yet undetermined. The 2,677 elements in the center of the array, a region 72 feet in diameter, constitute the antenna proper of the present system. Only l,792 of these elements are actively transmitting. Each is connected to its own solid state transmitter and receiver module. The remaining 885 electrically active elements do not connect to power sources; they serve only to improve control of the shape of the beam. The PAVE PAWS radar operates in the UHF band, using 24 different assigned frequencies in the range from 420-450MHz. Each of the l,792 active radiators is powered by its own solid state transmitting module, and couples to its own receiver. The nominal power radiated by one of these single transmitting modules is 322 watts. Total radiated power during a pulse is then about 580kW (580,000 = 320 x l,792). The pattern of pulses transmitted is complex. It depends, at any particular time, on the function being performed and on the number and location of targets under track. More details are discussed in Section 5. Averaged over a few second's time, the duty cycle of transmissions from one face cannot exceed 0.25; in any 54 millisecond period, the duty cycle does not exceed 0,30. Average total transmitted power is then about l45kW (0.25 x 580). For a discussion of "peak power" see Section 5, Table I summarizes major features of the PAVE PAWS radar, many of which will be referred to in later sections. The PAVE PAWS radar resembles two other major radars now operating in the U.S. One in Concrete, North Dakota, was deployed as part of the SAFEGUARD Anti-Ballistic Missile (ABM) System from which it acquired the acronymic PAR (Perimeter Acquisition Radar). Upon the dismantling of the ABM system, the PAR was retained and is now operated by the Air Force as part of the early warning network of which PAVE PAWS is a part. The other is the FPS-85, located at Eglin Air Force Base in western Florida. This too is a phased array radar controlled by a digital computer. It is operated by the Air Force as part of the Space Track network. 7
Figure 2 PAVE PAWS Radar (One Face) Showing an Array of Antenna Elements Courtesy of the United States Air Force
9 Figure 3 PAVE PAWS Radar Antenna Element Courtesy of the United States Air Force
10 Table I BASIC PARAMETERS - PAVE PAWS Antenna Gain Beamwidth, Deg (Transmit/Receive) Sidelobes Transmit lst S.L. Transmit Other Receive Polarization (Transmit/Receive) Array Diameter Face Tilt Azimuth Elevation Duty Cycle Capability Waveforms Search Track Sensitivity MTBF Inherent Availability 38.6dB Directive Gain 2.0/2.2 at Boresight Peak (dB) -20 -30 -30 Right Hand/Left Hand Circular 72.5 Ft (Utilized) 20 Degrees +_ 60°, 240° with Two Faces 3 - 85° 0.25 Each Face l00KHz (0.3 to 8ms) lMHz (0.25 to l6ms) S/N = l7.7dB at Boresight R = 3000 NMI T = l6ms a = l0m2 323 Hours ^ 0.9957 (Specification Requires >. 0.98)
ll The PAR transmits at l0MW (l07 watts) peak radiated power with a maximum duty cycle of .05. The FPS-85 transmits at 26MW peak radiated power with a maximum duty cycle of .005. Both have transmitting antennas of the order of l00 feet in diameter, somewhat larger than PAVE PAWS. Properties of the transmitters are compared with PAVE PAWS in Table II. The FPS-85 went into operation in l965, and the PAR about a decade later. PAVE PAWS follows the PAR by five years. These radars represent three different generations of microwave technology and of computer technology in their control systems. There has also been an evolution during this period in techniques for computer programming and antenna design. The basic principles embodied in the PAVE PAWS system are those that have been tried and demonstrated in the predecessor systems. The design itself, based on these principles, has been supported by extensive calculations using the powerful computers that are today available to the designers. The design itself exploits the simplicity and reliability of modern solid state microwave components and modern high speed control computers. Table II COMPARISON OF RADAR TRANSMITTERS Radiated Power PAVE PAWS PAR FPS-85 Peak 580kW lOMW 26MW Average l45kW SOOkW l30kW Duty Cycle 0.25 0.05 0.005 Number of Active Transmitting Elements l,792 6,l44 4,660 Transmitting Beamwidth 2° l.2° l.4°