Recent Developments in Russian Radar Systems

David K. Barton ANRO Engineering 450 Bedford Street

Lexington, MA 02173

Abstract - During the past several decades, the Soviet Union investment in air defense systems has exceeded that of the Westem nations. New relationships with the West have provided opportunities for us to see aspects of a new generation of Russian radar engineering not previously evident, with some surprising results. A few of these are described here, in areas of surface-to-air missile control radar systems using new types of phased arrays, unlike those developed in the U.S. and allied countries. The major features of some of these systems, and differences from Westem design practices, are discussed.This paper is an expanded version of a luncheon talk presented at the IEEE National Radar Conference in Atlanta, March 29, 1994.

SURFACE-TO-AIR MISSILE SYSTEM DESIGN

SA-I2 Field Army Defense System

Two major SAM systems provide examples of Russian radar design practice. The SA-12 field army defense system, Russian designation S300V, was designed to defend tactical army forces and their support facilities against tactical ballistic missiles (TBMs), cruise missiles (CMs), aerodynamic missiles, aeroballistic missiles such as the U.S. short-range attack missile (SRAM), and conventional aircraft [l].The system uses two types of interceptor missile, each carried on it transporter-erector-launcher- radar (TELAR), Figs. 1 and 2. The missiles are identical except for a larger booster on the Giant, which gives it a maximum velocity of 2500 m/ s, compared to 1700 m/s for the smaller Gladiator missile (NATO names for the Russian equipment will be used here, rather than the Russian type numbers). The missile is launched vertically from its cannister to about 25 m altitude and then oriented along its initial trajectory by reaction motors prior to firing of the main motor. This gives a 360 field of fire without use of the cumbersome trainable launchers characteristic of U.S. systems. Both types of interceptor are guided by a multitarget tracking phased array, Grill Pan (Fig. 3), which provides target data for prelaunch loading into the missile of approximate midcourse inertial guidance data, for

launch control, and for midcourse corrections resulting from target maneuver. Terminal guidance of the interceptor is provided by a semiactive seeker, homing on reflected CW illumination from the TELAR. An important feature of the missile is its directional warhead, which concentrates most of the 20-g fragments in a 60 60 cone. The missile is rolled within the last second prior to intercept to direct this cone at the target.

Figure carried

2 SA-I2 TELAR for the larger Giant interceptor, two of which are i n cannisters, erected for vertical launch.

Figure 1 SA-12 TELAR for the smaller Gladiator interceptor, four of which are c a n i d i n cannisters, erected for vertical launch.

Figure 3 SA-I2 Grill Pan, an X-band multitarget tracking radar. The Bill Board surveillance radar is behind Grill Pan.

0-7803-2120-0/95/0000-0340 $4.00 0 (1995 IEEE) 340

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Target acquisition data are provided through a command post by two organic surveillance radars, supplemented by an extemal network. The Bill Board 3D radar (Fig. 4) rotates through 360 in azimuth, while electronically scanning a pencil beam in elevation from the horizon to a selected upper limit (up to 65). This radar is designed primarily for aerodynamic targets. The High Screen sector surveillance radar (Fig. 5 ) scans an assigned sector at high elevation, with azimuth coverage up to a 90 sector, covering the TBM threat corridors. Either surveillance radar can be assigned to scan a sector at high or low elevation for special threat conditions.

radio links, with telescopic antenna masts mounted on each vehicle. Each vehicle also has onboard navigation equipment which provides a horizon and North reference and parallax correction. Power is supplied by gas turbines wiih 125 kVA capacity at 400 Hz in the radars, 65 kVA in the TELARs and command post, each having backup from an alternator mounted on the vehicle engine.

SA-IO Air Defense System

The SA-10 system, Russian designation S300PMU, is designed primarily for defense against aerodynamic and aeroballistic targets, with residual capability against TBMs. The equipment was designed for the Air Defense foirces, and has road mobility using wheeled vehicles. The Flap Lid fire control radar (Fig. 6) acquires and tracks up to six designated targets, providing tracking and guidance data for up to twelve interceptor missiles. Tlhe Grumble missile is launched vertically from its cannister and oriented by reaction motors, as with the SA-12 missiles. Command guidance is used for midcourse, and may continue through the terminal phase. Nornnally, semiactive homing takes over for terminal guidance, illumination being supplied by Hap Lid.

Figure 4 Bill Board Wand 3D surveillance radar, used in the SA-12 system primarily for aerodynamic targets.

Figure 6 Flap Lid X-band multitarget tracking and fire control radar, used for guidance of SA-10 missiles.

Figure 5 High Screen X-hand pencil-beam sector-scanning radar, used in the SA-I2 system primarily for ballistic targets.

An SA-12 battery consists of a command unit, with a command post and its two associated surveillance radars, controlling up to four fire units, each having a Grill Pan tracking radar and up to three of each type of TELAR. The command post can handle 200 targets, 70 of them in track simultaneously, and its fire units can engage 24 targets simultaneously with up to 48 missiles. All units of the SA-12 system are mounted on tracked vehicles, designed for off-road mobility with very short setup and redeployment times. Communication between units is entirely through

Figure 7 Big Bird S-hand 3D surveillance radar, used in the SA-IO system for targets at medium and high altitude.

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Target designation and threat ordering are provided by a command post and its associated Big Bird 3D radar (Fig. 7). Data from external radar networks also feeds into the command post, where targets are assigned to one of three to six fire units for Flap Lid acquisition and tracking. To supplement these designations on low-altitude targets, each fire unit has a Clam Shell low-altitude surveillance radar, which scans a 1 beam around the horizon. Pop-up targets are transferred directly to the nearby Flap Lid for tracking, and if they meet the threat profile they are assigned a high priority for intercept. Interceptor launches are normally controlled by the command post, but local reaction at the Flap Lid is possible when the time line is short.

Naval Air Defense System

The SA-N-6 naval air defense system uses the same missile as the SA- 10, but the space-fed lens of Flap Lid is replaced by the space-fed reflectarray radar, Top Dome (Fig. 8). Surveillance and designation data for this system are provided by conventional naval 3D radars.

Figure 8 Top Dome X-band multitarget fire control radar for SA-N-6 naval air defense system, using space-fed reflectarray antenna.

History of Development

Historically, the SA-12 and SA-10 systems were developed in a competitive program for the S300 system, with a decision on which system to produce planned after testing of prototypes. The test results showed the SA-12 to have superior mobility and performance against TBMs, while SA-10 was judged superior against cruise missiles and other targets at low altitude. As a result, both systems were placed in production, with SA-10 leading in time and numbers of units produced. Continued improvements were made in both systems, increasing the overlap of their capabilities. Thus we see an example within Soviet (and now Russian) military system development of competition leading to cost reduction and performance improvement, while the U.S. carried forward a single program without competition (and with predictable results in terms of cost, effectiveness, and obsolescence). Another example of the Russian approach is the use of a common missile for land and naval systems. While the basic radar approach used for the two applications is similar, the Russian naval systems appear to prefer the space-fed reflectarray antenna to the space-fed lens.

LOW-COST, HIGH-PERFORMANCE ARRAY RADARS

The fire control radars of the SA-12 and SA-10 systems (and of SA-N- 6) illustrate a unique Russian approach to modem, high-fire-power SAM systems, achieved at relatively low cost. (While no radar having two- coordinate electronic scan is actually low in cost, there are significant cost differences between the several design options, as will be described below.) The major features of the Russian multitarget fire control radars are :

342 IEEE INTERNATIONAL RADAR CONFERENCE

Use of space-fed arrays with multimode monopulse feeds to provide reduced spillover and low sidelobes in both sum and difference channels;

Use of Faraday rotator phase shifters designed for minimum complexity, loss, and cost, and having reciprocal characteristics for transmission and reception of opposite-sense circular polarizations;

Reliance on polarization duplexing and low-noise electrostatic RF preamplifiers to eliminate TIR devices, circulators, and solid-state limiters and their losses; and

System design to permit the multitarget tracker to use medium- and high-PRF burst waveforms on relatively long dwells, providing rejection of rain, chaff, and birds while retaining the sensitivity needed to detect low-RCS targets.

Each of these features will be discussed in detail below.

Space-Fed Arrays

Westem developers of phased array radars have, since 1960, been preoccupied with constrained-feed designs (for a discussion of altemative feed methods, see [3, 41). Only the Patriot radar has achieved production status with a space-fed array. The Missile Site Radar of the Safeguard AMB system used a space-fed lens at a very high power level, but only two were built and these have been decommissioned. An instrumentation radar, the Multiple Object Tracking Radar, has been built by RCA/GE/ Martin-Marietta to replace or supplement radars of the AN/FPS-16 class at missile test ranges, but only four have been delivered. In spite of its use of a space-fed lens, the cost of this radar has discouraged wider application. The major Westem designers and users of, and writers on, phased arrays tend to ignore or reject the space-fed approach. One major U S . engineering organization, with heavy influence on govemment studies, contributed as recently as 1988 the judgment that space-feed techniques were not sufficiently mature to be considered as an early option for large antennas in space-based radar. A major course in phased array antennas, conducted in 1993-94 by the IEEE, did not even include mention of the space-fed array in its detailed outline of subjects. Such attitudes in Westem radar engineering have left the development of advanced space-fed array technology almost entirely to Russian engineers, and they have moved vigorously into the void.

The primary advantage of space feed is its elimination of multiple couplers and transmission lines as sources of loss, mismatch, weight, and cost in the array. These components are replaced by feed homs in the focal plane of a lens or reflector composed of phase-shifting elements. The elements are coupled through space to the feed, as well as to the target. In a reflectarray (Fig. 9), there is only one set of radiators on the elements, illuminated by the hom, radiating into (and receiving from) the beam in space. A short circuit at the end of each phase shifter retums the wave to space, with twice the one-way phase shift. Obviously, the phase shifter must be reciprocal, and this is accomplished using a circularly polarized wave through a Faraday rotator phase shifting element. A right- hand polarization at the input is converted to left-hand at the short circuit, and vice-versa.

Figure 9 Cross Swords K,-band multitarget naval fire control radar, using space-fed reflectanay antenna.

In a space-fed lens (Figs. 3, 5, 6), there are two radiators on each element, one on the side facing the hom and one facing beam space. A typical group of lens elements is shown in Fig. 10. Matching from space into the circular waveguide is done with elongated dielectric plugs, minimizing reflections from (and losses at) the array faces. In the Russian designs, a thin plastic sheet covers each face, keeping rain, ice, and condensation off the radiators. Some loss will be encountered if a water film forms on this sheet, but its coating discourages the formation of such films.

Figure 10 Phase shifting element group from the SA-10 Flap Lid radar.

The common objections of Western engineers to the space feed are that the illumination cannot be controlled accurately by simple hom structures (e.g., to produce Taylor and Bayliss illuminations), spillover loss and sidelobes may be produced when the hom illuminates the edges of the array structure, and mismatch losses at the face are doubled by the space- feed geometry. However, the design of multimode hom structures has been carried by the Russian designers to the point that low-sidelobe illuminations with negligible spillover are available. They have used the thirty years since appearance of Hannan's classic paper [5] to make advancements in this important area of antenna technology. Careful design of the radiating elements can hold the two-way reflection losses to the order of 0.1 dB over the angles used for feeding and beam scanning.

Advantages of space feed, in addition to its simplicity, lie in the ability to form multiple beams, both for monopulse tracking and for simultaneous search over several beamwidths with long dwells (see below). In future developments, additional beamports in the focal plane may be implemented to support adaptive nulling systems, making use of the high gain of the full aperture and simplifying the control algorithms.

Mechanically, the fact that there are no RF lines coupled to the array face makes it possible to fold the array without using rotary joints and without opening the waveguide ends to extemal contaminants. The elimination of lines and couplers simplifies the array structure and its mechanical supports. Individual array elements are accessible for removal and inspection, and no RF connectors are involved in this process. These considerations are not of great importance in large (e.g., UHF) arrays using active modules, and in such arrays (e.g., Pave Paws) the accessibility of modules is actually better than would have been the case if a space-fed lens had been used. However, for the tactical array radar it must be concluded that a space-fed system has major advantages.

Phase Shifter Design

In 1962, engineers at Raytheon had designed an experimental X-band array, using a space-fed reflector with Faraday rotator phase shifters. This design was the simplest, least expensive option, but it required that circularly polarized waves be used, and is nonreciprocal if the same sense of polarization is to be transmitted and received (as necessary for rain cancellation, for example). This array approach was rejected by military customers in the US., and subsequent developments proceeded along other lines.

The Russian radar establishment embraced the Faraday rotator as the basis for a new class of phased array tracking radars. The use of circular polarization is desirable in missile guidance, as it permits simple, linearly polarized missile antennas to be used without sensitivity to missile attitude. The Faraday rotator phase shifter is reciprocal if opposite senses of circular polarization are used for transmission and reception, capturing the predominant, single-bounce echo from the target. Doppler processing is relied upon for rejection of rain. The availability of reciprocal phase shifters permits multiple-pulse doppler burst waveforms to be transmitted and received without changing the phase shifter magnetization, and switching o~f the magnetic field is needed only when changing beam position. Since the system design is based on relatively long dwells in each beam i(typical1y several ms), a reasonably long time can be allowed for phase shifter switching, and this reduces the cost of the ferrite material and drive circuits [2].

The SA-1% Grill Pan and High Screen radars use space-fed lens arrays of 10,000 and 20,000 elements, respectively. The phase shifters have a control range of 720, using separate row and column control regions in series, each with its control coil. A single driver for each row drives all its element coils in series, and similarly for each column. Thus, a 10,000 element circular array using 112 rows and 112 columns requires only 2 x 112 = 224 drivers, rather than the 10,000 required for individual element control. Array collimation (focusing) is applied as an additive drive command proportional to the square of the row or column displacement from the center of the array. For an fD = 1, the error of this .x? + y2 collimation function, relative to perfect focusing, is less than 0.1 dB, appearing as a 1% broadening of the main lobe. The phase shifter loss for the 720 unit is only 1520% greater than for the conventional 360-deg unit, and is approximately 0.8 dB one way. The control speed with series coils is slower than for individual element control, but times from 30 to 400 s are allowable.

Low -Noise Receiver Protection

Conventional Westem practice in high-power radar design is to use a ferrite circulator or gas-tube T/R device, followed by a solid-state switch or limiter in the receiver path. A loss of 0.4 to 0.6 dB in each of these circuit elements is expected. In arrays using nonreciprocal phase shifters, the circulator can be replaced by phase-shifter switching between transmit and receive. In Patriot, separate feed homs are used, with an additive linear phase function applied to the array on transmit, to focus the array on the transm:it hom (space duplexing). In Aegis, subarray pairs are combined in a hybrid junction, and 180-deg relative phase shift within the pair switches the subarray from the transmit feed port to the receive feed port. The resulting isolation is about 25 dB, depending on array match, and a solid-:state protector is required prior to the receiver.

In the Russian approach, the first 25 dB isolation is obtained by use of opposite (orthogonal) circular polarizations for transmit and receive. On transmit, the linearly polarized wave from the hom passes through a quarter-wave: grating at 45-deg orientation, producing (say) right-hand CP at the array. Single-bounce target reflections arrive at the array with left- hand CP, and are converted to vertical polarization by the 45-deg grating. This polarization is accepted by the multimode monopulse feed, which is isolated frorri the transmitted energy.

In the SA- 10 Flap Lid, the transmit-receive isolation is achieved with a polarized planar reflector (Fig. 1 l), placed between the feed homs and the array at an angle 45-deg from the array axis. In the SA-12 radars, the polarizing grating is integrated with the feedhom assembly, which uses an orthomode born design to separate transmit from receive ports. In each case, transmitter leakage (> 100 W peak) is above the tolerable level for low-noise receivers. A special electrostatic RF amplifier has been designed which can accept such levels without damage, recovering instantly to amplify received signals with a noise factor of 3 - 4 dB. This fast recovery, to an ultrastable gain state, is essential for high clutter cancellation in the high-PRF mode.

The Russian emphasis on overall RF efficiency is in contrast to Westem phased array design practice. Tables 1, 2, and 3 compare the RF losses of Grill Pan with estimates for typical U.S. systems using space feed (Table 2) and constrained feed with subarrays (Table 3). The advantages of 3 and

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Table 3: RF Loss Estimates for U.S Subarray System

Ferrite circulator duplexer

Solid-state receiver protector

0 0

0.4 0.4

Column feed network

Row feed network

Phase shifter

0.8 1.6

0.8 1.6

1.0 2.0

Waveguide, Tx

Waveguide, Rx

1.5 1.5

1 .o 1.0

Transmit loss

Receive loss

7.0

5.0

Ferrite circulator duplexer 0 0

Illumination spillover

Phase shifter

0.8 1.6

0.8 1.6

Ferrite circulator duplexer 0 0

Solid-state receiver protector

Column feed network

0.4 0.4

0 0

Component

Figure 11 Flap Lid antenna feed configuration.

7.6 dB would not apply to active jamming environments in which the sidelobe response of the arrays to jamming exceeds the receiver noise, but even in these cases the transmit power advantages of 1.0 and 4.6 dB would be significant.

1 Face switch I 1.0 I 2.0 1 I O t h e r ~ x loss I 1.9 I 1.9 I

Table 1: RF Loss Estimates for Grill Pan I I I I 1 Total RF loss I I 12.0 I

Component Radar Modes, Waveforms, and Processing

When several targets must be engaged at once, economics dictate the use of an electronically scanned fire control radar. In Westem systems, this fact has become distorted to favor the so-called multifunction array radar (MFAR) approach, in which one radar performs both search and fire control functions. This has been justified on the basis of cost advantages over multiple, more specialized radars, but it has also driven the MFAR costs up and performance down. In fact, the high cost of the MFAR almost guarantees that there will be insufficient program funding to provide supplementary search radars.

The main problems in the WAR approach have been: Need to accept a compromise frequency, too high for good search

Need to budget transmitted power between search and track modes; Need to budget time between search and track modes, with resulting

short dwells and long revisit intervals for both; Need to match waveforms and processing to the available short dwells,

rather than to the requirements of the radar environment; and Need for complex software for dynamic scheduling and control, often

leading to inability to schedule the available radar resources and to conflicts between different modes of operation.

These problems have led to MFAR design compromises which are incompatible with requirements for detection and tracking of low-RCS targets in environments containing extended clouds of rain or chaff, or large numbers of birds in the low-altitude regions. Figure 12 shows the velocity spectra of typical moving clutter sources, the required clutter rejection notch width of 40 m/s, and the response of target doppler filters above this notch. Unless the basic blind speed of the radar waveform can provide adequate target detection while supporting the rejection notch, the radar's sensitivity to low-RCS targets must be compromised in beams covering the lower atmosphere. In chaff and rain, which often extend beyond the unambiguous range of the waveform, even normal targets may be lost.

One practical approach to the clutter problem is to use PRF diversity, with two or more bursts of pulses in each beam position, each burst having a blind speed in excess of about 120 m/s but avoiding overlap with the blind regions of the other. Figure 13 shows the response of an acceptable dual PRF-diversity waveform which covers target velocities from 40 to 480 m/s, requiring an average blind speed of 140 m/s, with 16 pulses per burst (or 32 per search dwell). In tracking, a single 16-pulse burst per dwell would be sufficient, with PRF adapted to the target velocity.

performance and too low for good tracking;

I Solid-state receiver protector I 0 I 0 I I Column feed network I o I o I 1 Row feed network I 0 I o I

I Waveguide, Tx I 0.8 I 0.8 1 I Waveguide, Rx 1 0.4 I 0.4 1 I Transmit loss I 2.4 I I I Receive loss I 2.0 I I 1 Total RF loss I I 4.4 I

Table 2: RF Loss Estimates for U.S. Space-Fed Array

Component

I Row feed network I o I o I I Illumination spillover 1 1.2 I 2.4 I I Phaseshifter I 0.8 I 1.6 I I Waveguide, Tx

I Waveguide, Rx I 1.0 I 1.0 I I Transmit loss I 3.4 I I I Receive loss

I TotalRFloss I I 7.4 I

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Spectral density

Rain (chaff) at target Second-time-around rain (chaff)

Third-timearound chaff Target filter

extended and moving clutter. The use of X-band (h = 0.03 m) results in very narrow beams (< 1 deg). With average powers in the 10 - 20 kW range, and peak powers of 100 - 200 kW, very high effective radiated power @RI’) is brought to bear on the target, and the long dwell gives high energy to overcome jamming. For example, in a typical Westem

-

\ i

Surface wind

Figure 12 Velocity spectra of moving clutter with required doppler filters and extended rejection notch.

- - -~

- \

system, must be derived from careful modulation of the CW carrier, often applied after initial target detection.

Since the: dual-antenna requirement of a CW radar is inconsistent with economy in a multitarget phased array, the Russians elected to use a pulsed waveform at medium or high PRF. The high-PRF system requires only about 100 dB clutter attenuation and dynamic range, giving the CW system designer a margin of 20 dB to cover instabilities due to pulsing the transmitter and range gating the receiver. With medium PRF, somewhat lesser requirements apply. Both systems yield ambiguous range data, with eclipsed range gaps in the coverage, and the medium-PRF system is also ambiguous in velocity, requiring multiple-PRF diversity waveforms for search and larget acquisition dwells. Relatively long dwells are required, typically 5 ms per burst, with two or more bursts per dwell. Such dwells can readily be scheduled when the radar is specialized to the tracking and fire control function on a few targets (e.g., six to twelve). The volume search functions must then be assigned to separate radars.

The fire control radar design resulting from this approach is optimized

single puls~: repetition interval, t, (even if multiple-pulse MTI bursts are used), to the revisit interval, t,, on the target, and to transmit antenna gain

Russian radar with equal average transmitter power has an effective (or the square of the ratio D/h, antenna diameter to wavelength). The

energy per target proportional to the ratio of dwell time, td, to revisit

Voltage response at PRFl

Voltage responsc at PRF2

Average voltage response

-- Symbol

andunits

td (ms)

t , (ms)

Factor ~- ~- PRI, t , 01 dwell

Revisit interval ~-

Western Russian Relative System System dB

1 10 +lo

500 100 4-7

0 100 2 0 0 3 0 0 400 500

Target velocity in m/s

Figure 13 Velocity response for dual PRF-diversity waveform. Wavelength

@/h)’(for D=2.5 m) At S-band (h = 0.1 cm), the resulting PRF is 3200 Hz, giving an unambiguous range of 48 km and a search dwell time of about 10 ms. In practice, this medium-PRF waveform will have to include several “fill

h(m) 0.055 0.03

2067 6944 +5.3

i-22.5

The SA-10 (and SA-N-6) have the option of command guidance all the way. In these systems, illumination is provided by the fire control radar, time-shared with the tracking bursts.

In the SA-12 system, illumination is provided by separate CW transmitters and 1-m reflector antennas on the TELARs (Figs. 1, 2), slaved to the target track data of Grill Pan. Target intercepts are scheduled to permit a TELAR to illuminate each target continuously during homing, a period typically 5 - 8 s prior to intercept. This scheduling and coordination is provided by the command post or from within the fire control radar, and it imposes a minor constraint on firepower which is not present in other Russian systems or in Patriot. The CW nature of the illumination more than compensates for the reduced (D/h)2 of the TELAR antennas. In Westem systems, the MFAR antenna can support homing at C-band, but separate CW illuminators, scheduled as with SA-12, are required when an S-band MFAR is used.

Surveillance Radars

Several types of surveillance radar have been designed to support the fire control radars of the Russian systems. In the SA-10 system, the CW horizon search radar is collocated with the Flap Lid and launchers. The radar uses the dual antennas required for CW operation, and these are of the conventional hom-fed reflector type, elevated on a 25-m tower to maximize low-altitude coverage. The transmitter and receiver are mounted with the antenna to minimize losses. The number of radar vehicles per site is thus doubled, and cost increased by a factor near 1.5. For the entire radar-missile complex, the vehicle count (assuming four launchers) is increased by 6/5 = 1.2 by the presence of the horizon- scanning radar.

At the regimental level, considering one command post and three or four fire control sites, a 3D surveillance radar (Fig. 7) is used, feeding data to the command post. The Big Bird is a space-fed lens array, providing two-coordinate electronic scan along with mechanical rotation through 360 deg. A single pencil beam is scanned in elevation, at an azimuth 30 deg in advance of broadside. Following a target detection, a confirmation beam at broadside is scheduled for the azimuth and elevation of the original detection, and confirmation will occur 30 deg after detection. If the target is c o n f i e d , further track dwells are scheduled every 180 deg of rotation, the first of these occurring 210 deg after initial detection, using the horn on the opposite side of the lens array. Thus, the track-while- scan (TWS) data rate is twice the normal search rate, and TWS energy can be increased by dwelling longer, as may be needed against jamming. The regimental command post also exchanges data with external surveillance networks, feeding these data to the fire control sites along with target assignments and missile launch commands.

The 3D surveillance radar increases the vehicle count per fire control site by 0.33 (assuming three sites), to 6.33 per site, compared to five if an W A R and four launchers were used. This increase, 6.3315 = 1.27, appears entirely reasonable when considering the increased capability of the resulting system over that provided by an MFAR. However, it must be noted that the S-band 3D radar with MTI clutter rejection has no more capability against clutter than the corresponding Westem designs, and this constitutes an important limitation in all the systems.

The SA-12 system has two surveillance radars at the regimental level. The Bill Board (Fig. 4) uses an elevation-scanning pencil beam, with mechanical rotation in azimuth, and is similar to many Westem systems in

its capability and limitations. Its large aperture provides greater search capability than Westem MFARs. If a sector less than 360 deg is assigned for search, the antenna may be sector scanned, with some loss in time for reversal of rotation at each edge of the sector.

The High Screen (Fig. 5) was designed primarily for TBM sector search, using a 20,000-element X-band array with 20 kW average power. The inherent flexibility of the two-coordinate electronically scanned array makes it an excellent candidate for this search assignment, since all a priori information on possible target trajectories can be exploited to concentrate the search resources in the appropriate sector. This radar can also provide specialized search functions near the horizon or in jammed sectors, for airborne targets. These are the advantages normally advertised for MFARs, but when assigned to a separate radar they can be performed without compromising the performance of the fire control tracker. The high-PRF waveforms needed to perform these functions against low-RCS target in a clutter environment also contribute to the effectiveness of the Russian radar.

CONCLUSIONS

1. Russian system designers recognized, twenty years ago, that Ihe prirnaq role of two-coordinate scanning phased arrays was for increased firepower in multitarget tracking and engagement, rather than for "multifunction" operation.

2. High-performance, efficient trackers have been designed, exploiting modem technology in the areas of arrays, stable transmitters and receivers, and digital signal processors.

3. Supplementary search radars have been provided, using rotating phased array (3D) technology, low-frequency rotating systems, and, for TBM search, two-coordinate phased arrays.

4. Clutter problems have been solved with high-PRF waveforms and processing, providing rejection of moving clutter as well as surface clutter, while preserving the ability to detect low-RCS targets.

5. Land-based and naval systems have been developed around common missile designs, reducing cost and development time.

6. Acceptance of disciplined requirements has permitted acceptance of various options for cost reduction, making economically feasible the large- scale production of the Russian surface-to-air missile systems.

REFERENCES

[ I ] V. P. Efremov, "SA-12 System Overview," seminar at IEEE National Radar Conf., 29-31 March, 1994, Atlanta, GA.

[2] S. A. Barsukova, "Low Cost Techniques in Phased Array Antennas," seminar at IEEE National Radar Conf., 29-31 March, 1994, Atlanta, GA.

[3] T. C. Cheston and J. Frank, "Array Antennas," Chap. 7 in Radar Handbook, M. I. Skolnik (ed.), McGraw-Hill, 1990.

[4] D. K. Barton, Modem Radar System Analysis, Artech House, 1988, Chap. 4.

[SI P. W. Hannan, "Optimum Feeds for All Three Modes of a Monopulse Antenna," IEEE Tuans. AP-16, No. 5 , Sept. 1961, pp. 444- 461.

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