AN/FPS-17 - Operation

Operation

The system has eight separate radar sets or channels, each with its own exciter, transmitter, duplexer, receiver, and data display unit. These eight channels feed electromagnetic energy into sixteen fixed beams formed by the two antennas, each channel, or transmitter-receiver combination, being time-shared between two beams. Pneumatically driven switches operate on a three-second cycle to power each beam alternately for 1.5 seconds. There are antenna feeds for two additional beams which could be made to function with some patchwork in the wiring.

The antenna feeds are positioned to produce in space the beam pattern depicted in the figure. Beams 1 and 18 are those not ordinarily energized. Beams 1 through 7 use the older of the two antennas; 8 through 18 are formed by the newer, "cinerama" antenna, whose 300-foot (90 m) width gives them their narrow horizontal dimension.

Beams 2 through 9 are projected in horizontal array; 10 through 17 (although 10 actually lies in the horizontal row) are grouped as the vertical component. All beams of each group are powered simultaneously. Except for being controlled by a master timing signal, each of the eight channels operates independently of the others. Each transmitter is on a slightly different frequency to prevent interaction with the others. The transmitted pulse, 2000 microseconds long, is coded, or tagged, by being passed through a tapped delay line which may reverse the phase at 20-microsecond intervals. Upon reception the returned signal is passed through the same tapped delay line and compressed 100:1, to 20 microseconds in order to increase the accuracy and resolution of the range measurement, which is of course a function of the interval between transmission and return.

A delay line is an artificial transmission detour that serves to retard the signal, made up with series inductances and parallel capacitances that yield a constant delay. Pick-off points at 20-microsecond intervals permit these sub-pulses to be extracted in such sequence that they all arrive together, to achieve the compression effect.

The total azimuthal coverage is from 18° to 49.7°. The system normally detects missiles or satellites launched from Kapustin Yar at a nominal range of 800 nautical miles (1,500 km); it tracks one type of missile out as far as 1,625 nautical miles (3,010 km). The missiles and satellites are not sensed at their maximum detectable range because the coverage of the fixed beam configuration does not conform with the test range layout.

The electrical characteristics of each of the channels are:

Frequency ............................... 175-215 megahertz Peak power per beam ..................... 1.2 megawatts Pulse length ............................ 2000 microseconds Pulse repetition rate ................... 30 cycles per second Duty cycle (portion of time transmitting) 0.06 Beam width (horizontally elongated) ..... 2.5° x 1.8° Beam width (vertically elongated) ....... 1° x 2° Pulse compression ratio ................. 100:1 Range accuracy .......................... within 5 nmi (9 km)

To illustrate how the capability of the system is calculated, we can take typical logs which show channel 4, for example, operating with the following parameters:

Peak power output .............. 1.0 megawatt Minimum discernible signal ..... 130 decibels below one milliwatt Frequency ...................... 192 megahertz

Channel 4's maximum range of intercept capability for a target one square meter in cross section is then determined by using these parameters in the radar range equation

where:

• is the range in meters
• is the peak power transmitted in watts
• is the antenna gain over isotropic (omnidirectional) radiator
• is the wavelength in meters
• is the minimum discernible signal in watts
• is the target size in square meters

Substituting,

where:

• is the speed of light in meters per second
• is the frequency in hertz (1/s)

converting.

and

Range = 4,184 kilometres (2,260 nmi).

Sightings made by the fixed-beam system include vertical firings (for upper-atmosphere research vehicles or booster checkout ), ballistic missiles fired to the nominal 650-nautical-mile (1,200 km), 1,050-nautical-mile (1,940 km), and 2,000-nautical-mile (3,700 km) impact areas, launches of Cosmos satellites, orbiting satellites, and natural abnormalities such as ionospheric disturbances or aurora.