A SURVEY OF RUSSIAN LOW COST PHASED-ARRAY TECHNOLOGY

Dr. Larry E. Corey Georgia Tech Research Institute Georgia Institute of Technology

Atlanta, Georgia 30332

ABSTRACT

During the past five years, GTRI personnel have been working directly with the developers of the modem Russian SAM phased- anay radars exploring the possibilities of jointly developing low-cost phased-array antennas based on the technology used in these systems. This paper surveys the phased-array technologies used in those systems and discusses their potential cost saving features.

INTRODUCTION

Since shortly after the collapse of the Former Soviet Union, re:,earchers from GTRI have been working jointly with the designers of Russian surface-to-air missile ( S A M ) system phased-array radars. These systems include the S300 PMU, S300 V, TOR, URAL, RIF, KLINTOK, and the MIG 31. The S300 PMU, S300V, TOR, KLINKOK, and MIG-3 1 target engagement phased-arrays are shown in Figures 1 though 5 respectively. Senior Russian radar and antenna designers have presented several seminars at Georgia Tech, GTRI personnel have made several visits to Russia, and some demonstration hardware has been evaluated at GTRI. During the seminars at Georgia Tech and through numerous discussions with the Russian designers, it has become obvious that the Russian designers take a very different approach to radar system as well as phased-way antenna design. Phased-array radars developed in the U.S. tend to be multifunction, using the beam agility of the phased- array antenna to perform search, acquisition, track, and missile guidance functions with the same phased-array aperture. The RLISS~UIS develop a SAM system using a suite of simple radars, each only performing a single function. Since they use several phased- mays in one system, each one must be considerably simpler and less expensive than those used in the U.S. For example, in the TOR system a limited field-of-view (LFOV) array is dedicated to tracking and performing missile guidance on only two targets. Phased-arrays that are used in these limited applications must be low cost. As a result, the Russian designers have developed simple cost-effective methods of designing and building phased-arrays.

The joint work has been focused on exploring the possibilities of developing low cost phased-array antennas based on combining the technologies developed by them for their SAM system arrays with U.S. electronic and computer technologies. This paper will present an overview of the low cost phased-array antenna design philosophies and techniques used in the Russian systems and the type of performance that can be expected from them. In Section n, the design philosophy used by the Russian designers will be presented. Section I11 will provide examples of the application of that philosophy to specific systems, and comments concerning the associated performance tradeoffs are presented in Section IV.

Figure 1 . S300 PMU Target Engagement Radar

n-7~03-3232-6/96/$5.00 01996 IEEE

Figure 2. S300V Target Engagement Radar

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Low-Cost Phased-Array Antenna Design Philosophy

Figure 3. TOR Target Engagement Radar

Figure 4. KLINTOK Target Engagement Radar

Figure 5. MIG 31 Radar

The Russian design philosophy can be summarized in five basic points [l]:

1. Minimize the required number of phase shifter modules 2. Simplify the array architecture 3. Design simple and inexpensive components 4. Minimize the size and complexity of the control system 5. Simplify the feed design

These points appear to be obvious and not particularly enlightening. However, they have taken these concepts much further than has been done in Western systems. The implementation of these ideas to the degree that it is done in the Russian designs does have an impact on performance as will be discussed in Section IV. The Russian designers' answer to this is that they make the cost versus performance tradeoffs to achieve the "appropriate" level of performance consistent with the overall system requirements instead of building phased-arrays with the best possible performance.

Specific Design Examples

The minimization of the total number of elements required for a specific field-of-view (FOV) is achieved in full FOV designs by the use a dielectric rod radiator design. The element radiator/phase shifter modules for the space-fed S300 PMU and S300 V arrays are shown in Figures 6 and 7. They have a relatively flat topped element patterns that are well matched as the main beam of the array is scanned across a grating lobe boundary. Therefore, the lattice can be increased to allow grating lobes to form during parts of the FOV. This, in turn, reduces the number of elements required to cover a specific aperture area. A savings of approximately 30% in the number of elements required over a design without grating lobes has been achieved using this method in full FOV designs. Figure 8 [Z] shows the element pattern for the S300 V rddiator. The graling lobe cnters real spacc when the main beam is scanned to approximately 32" and the design scan limit is 42". The figure shows only a slight mismatch at the grating lobe inception point, less than 3 dB scan loss at maximum scan, and a fairly sharp rolloff beyond 42".

The (LFOV) Limited Field-of-View TOR target engagement array has elements in a rectangular lattice with 3A spacing in both directions. It achieves approximately 42 dB gain with only 576 elements and has a design scan limit of 7.5" in any direction. A LFOV design without grating lobes would require approximately 7,000 clcments. Mcasured m a y patterns for this antenna for broadside and maximum scan are presented in Figures 9 and 10 respectively. As Seen from these pattems, the grating lobes are well controlled by the element pattem at broadside scan, but at maximum scan the grating lobe grows to within 3 dB of the main beam.

The simplification of the array architecture is obtained by the use of a fenite phase shifter and driver design in which two coils are placed on each phase shifter (see Figures 11 and 12). One coil is connected in series with a coil on every other phase shifter in the same row, and the other coil is connected in series with the other coil for every other phase shifter in the same column. The phase shift for an element is the sum of the row and column phase shift for its respective row and column. The phase shifter for the S300 V shown in Figurc 7 is of this type.

This row-column phase shifting architecture simplifies the array in several important ways. First, a NxM element array can be controlled by M t N drivers instead of MN drivers. Second, only

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Figure 6 . S300 PMU Phase Shiftermadar Module

Figure 7. S300V Phase Shiftermadiator Module

t

\ I I I I I c

0 10 20 30 40 50 6b On

Angle (degrees)

M+N phase commands need to be computed each time the beam is scanned to a new position. Finally. there are no driver or logic circuits, data busses, or DC power busses required in the aperture. The only electrical interface with the aperture is a single wire that runs in series through the row and column coils of the phase shifter.

The phase shifters are the basic building blocks of the array and therefore must be simple and easy to manufacture. In the S300 V, TOR, and the naval systems, the phase shifter is a non-reciprocal dual-mode type. However, the nc:ed for intemal polarization converters and to reset the phase shifter between transmit and receive is avoided since the radar operates in a single bounce circular (SBC) polarization mode (see Figure 12). It transmits and receives orthogonal circular polarizations taking advantage of the fact that sense of the primary (single bounce) n:turn of a circularly polarized field is reversed upon reflection from the target. The non-reciprocal phase shifters provide the same phase shift for right hand circular (RHC) in one direction as it does lor left hand circular (LHC) polarization in the other. Therefore, there is no requirement to shift the phase shifter between transmit and receive when it operates in the SBC mode. The transmission End reception of orthogonal circular polarizations also provides a natural isolation between the transmit and receive chains in the radar. The result is a space-fed phase shiftedelement module consisting of fewer than ten easily manufactured parts (see Figure 7).

The complexity of the beam steering computer and phase shifter drivers is greatly simplitied by the row-column architecture discussed above. As mentioned above, the computer is only required to calculate M+N phase commands instead of MN. Furthermore, each command for a row or column phase requires only one half the number of calculations as would be required to compute an individual element phase command.

In the Russian systems, the feed designs are also very simple. Those with less than 2,500 elements, such as tke TOR and the MIG-3 1, are linearly polarized and use waveguide series constrained feed with quadrant combining for monopulse. Arrays containing more than 2,500 elements such as the S300 Ph4U, S300 V, and the naval systems, typically are SBC polarized and use space feeds. The S300 PMU multi-hom feed system [3], shown in Figure 13, uses separate transmit and receive homs on opposite sides of a wire grid polarization filter. The field radiated by the horizontally polarized (HL) transmit feed is reflected off the filter and then converted to LHC polarization as it passes througb polarizing lens. The RHC polarized target return is converted to I ertical polarization (VL) by the polarizing lens, passes through the polarization filter, and is received by the VL monopulse feed. 'The multimode S300 V feed is shown in Figure 14. It performs the same functions as the S300 PMU feed system, but uses a single multi-mode feed horn. The transmit port excites HL mode in the throat of the horn which is converted to LHC by the polarizer in the mouth of the horn. The RHC target return is converted to vertical polarization by the polarizer. The throat of the hom has both horizontal and vertical septums through which the target return propagates. This VP energy in each of the four quadrants of the throat is coupled out of sidewall couplers and re-combined through hybrids to form the E, AAz, and AEl monopulse channels.

Figure 8. S300V Element Pattern

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Figure 11. Row-Column Phasing Architecture

RAC Target O0 t RAC - IHC 0 t G.L.

Q.C.

Figure 9. TOR Radiation Pattem Scanned to Broadside

Figure 10. TOR Radiation Pattern Scanned to 7.5" with Grating Lobes

Transmit RHWLHL

Receive LHC/RHC + 720' Differential Phase Shifts

1 Driver per Row & COlUmn

Figure 12. S300V/TOR Phase Shifter Configuration for SBC Operation

DIELECTRIC RADOME

LENS

POLARIZING

HORIZONTAL

.....................

RECEIVE HORN v-POL

Figure 13. S300 PMU Feed System

DIELECTRIC RADOME

LENS ARRAY

POLARIZING

HORIZONTAL

CIRCULAR RECEIVE ELEVATION

RECEIVE HORN v-POL

Figure 13. S300 PMU Feed System

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Figure 14. S300V Feed System

Performance Tradeoffs

The Russian low-cost techniques presented in this paper are very effective in reducing the cost and complexity of phased-array arlteiinas and appear to work well for the purposes for which they wc:re designed. However, when compared to U.S. design practices, there are performance and flexibility penalties associated with these sa.vings. The larger element lattices reduce element count but create grating lobes under certain scan conditions. The row-column phase control architecture is simple and cost effective, but does not allow for errors in individual phase shifters to be corrected using the beam steering computer and can create phase errors that are correlated over entire rows or columns of elements. This lack of individual element control tends increase sidelobe levels, reduce beam pointing accuracy, and slightly defocused the large space-fed arrays. The reduction in phase shifter drivers from MN to M+N means that if a driver fails, an cntire row or column of elements is lost. The multimode feeds in the large space-fed arrays perform well but are not suitable for very low sidelobe or wide bandwidth applications. The simple series constrained feed used in the smaller systems are not capable of simultaneously providing good sidelobe control in the monopulse Z and A modes.

In conclusion, the Russian phased-array designers have developed phased-array antenna components, architectures, and design concepts that are simple, inherently low cost, and very effective. The application of these low-cost techniques allows them to use phased arrays in applications that would not be cost effective if U.S. design practices we^ used. This, in tum, allows them to build large numbers of phased-array radar systems and achieve even further cost savings through the economy of scale. Table 1 provides a summary of the basic features of the modem Russian target engagement phased-arrays and indicated which ones use the cost saving features discussed in this paper.

TABLE 1: Antenna Characteristics

E-E - Elsnrentby6lnnent R-C * Row-column SBC - Smgk Bounce Cimuhr W. * VnficalLtnenr

References

[l] Sophia A. Barsokova, “Russian Low-Cost Phased Array Antennas,” IEEE National Radar Conf. March 28,1994.

[2] IBID

[3] David K. Barton, “The Moscow Airshow,” Microwave Journal, May 1993.

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