The invention relates to techniques for electroni ally varying the partitioning of planar arrays or pha scanned arrays into sub-arrays, and in particular to improved technique for providing electronic roll stab lization of the array difference patterns.

The method generally used to generate sum an difference patterns in gimballed planar arrays or phase scanned arrays is to partition the array into quadrant with a separate output for each. The appropriate quadran outputs are summed or differenced to provide a sum patter and two difference patterns. The two difference pattern provide tracking error signals referenced to the antenna. In many airborne radar modes, in particular th terrain following and terrain avoidance modes, differenc patterns stabilized with respect to the horizon ar required. The current solution to this problem is eithe to provide a third gimbal or to implement rather cumber some and riot entirely satisfactory signal processing t derive roll stabilized tracking outputs. The roll gimba technique is probably not feasible for active arra systems of sufficient size to require liquid cooling. A alternative to the signal processing approach is needed.

It would therefore represent an advance in the ar to provide an electronically roll stabilized active arra without the need for mechanical roll gimbals or cumbersom signal processing.

SUMMARY OF THE INVENTION

An active array system is disclosed for electronic roll stabilization of the array difference patterns. The array comprises a plurality of radiative elements for receiving electromagnetic radiation, and a corresponding plurality of active modules coupled to the respective elements. Each module includes an active amplifier for amplifying the signal received at the element, and a three-way power divider for dividing the received signal n three components. A first component is fed into a first bi-phase phase shifter which shifts the phase of the first component by 0 or 180 degrees. A second component is fed into a second bi-phase phase shifter which shifts the phase of the second component by 0 or 180 degrees. The output of the first phase shifter is coupled to a first array summing network which sums the respective phase-shifted first components from all the modules in the array to provide a first difference signal. The resulting signal is in effect the difference between the sum of those first component signals having a 0 degree phase shift and the sum of those first component signals having a 180 degree phase shift.

The output from the second phase shifter of each module is coupled to a second array summing network which sums these phase-shifted second components to provide a second, difference signal. The -resulting .signal is in effect the- difference between the sum of those second component signals having a 0 degree phase shift and the sum of those second component signals having a Ϊ80 degree phase shift.

The third component from the power divider is fed directly into a third summing network for summation with the corresponding third components from all the array modules to provide an array sum signal.

A phase shifter controller is coupled to the firs and second bi-state phase shifters of each module select the state of each phase shifter, in dependence o attitude position data. By selecting the state of th phase shifters, the partition assignment of each radiativ element may be adjusted to compensate for rolling o rotation of the array boresight in relation to a nomina position.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features and advantages of th present invention will become more apparent from th following detailed description of an exemplary embodimen thereof, as illustrated in the accompanying drawings, i which: FIG. 1 is a perspective diagrammatic view of phased array system with which the present invention ma be implemented.

FIG. 2 is a functional block diagram of a typica module employing the invention. FIG. 3 is diagrammatic depiction of roll sta bilized quac :ants for providing azimuth and elevatio difference patterns.

FIG..4 is a diagrammatic depiction of three secto partitioning of the array to provide three apertures fo low- speed moving target indication (MTI) functions, "cros eye" jammer tracking, and close spaced (in azimuth) targe tracking.

FIG. 5 is a diagrammatic depiction of three secto partitioning of the array to provide multipath reductio capabilities and close spaced (in elevation) targe tracking.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One of the primary advantages of active arra systems is that both the RF source and the receive preamplifiers are associated with each radiating elemen

in the array, thereby negating the effects of RF feed and phase shifter losses. This is illustrated in FIG. 1, a functional depiction of an active array system 50. Th radiating aperture 55 comprises a large number of radia- tive elements indicated generally as elements 60 disposed at the planar aperture 55. The array further comprises a plurality of transmit/receive (T/R) modules 65, one for each of the radiating elements 60. Respective transmit/- receive (T/R) modules 65 are electrically coupled between each radiative element 60 and the RF manifolds 80. Liquid cold plate devices 70 cool the T/R modules 65. For clarity, only some of the radiating elements 60, T/R modules 65 and cold plate devices 70 comprising the system 50 are depicted in FIG. 1. The DC and control signal manifolds 75 distribute DC power and control signals to control the module functions of the T/R active modules. Thus, signals from the beam steering controller 95, power supplies 96 and T/R module controller 174 are coupled to the manifold _^ 75 for dis- tribution to the T/R modules 65. Beam steering controller 95 is directed by system controller 100 to s ^er the beams produced by the array to a desired direction. Module controller 174 controls the operation of the modules 65 as directed by controller 100, as described more fully below. The RF manifolds 80 distribute RF excitation signals to -the T/R modules 65, and collect the received RF signals fro -the modules. Thus, the manifolds 80 comprise a transmit manifold 80 ^* (FIG. 2) for distributing RF excita- tion signals to the modules 65, and three combining manifolds 80B-80D (FIG. 2) for combining respective receive RF signals from the modules 65, as will be de¬ scribed in more detail below. The outputs of the respec¬ tive receive manifolds 80B-80D comprise the sum (Σ) , first difference (Δ.. ) , and second difference (Δ„) channel

outputs, and are coupled to system processor 100 on lin 91-93.

The elements 55, 65, 70, 75 and.80 are depicted FIG. 1 to form an exploded perspective view. As will appreciated by those skilled in the art, these elemen are assembled to form an integrated, compact assembly.

In a phased array system such as system 50 shown FIG. 1, the effect of both phase shifter and corpora feed losses in system performance can be reduced , negligible levels by increasing the gains of the low pow level stages of the transmit and receive modules 65. Th characteristic of active array systems can be exploited provide roll stabilized difference patterns in accordanc with the invention. FIG. 2 is a schematic block diagram of an acti array module 150 that may be used in an active arra system to provide roll stabilized difference patterns i accordance with the invention. The module comprise circulator/duplexer 152 coupled to the correspondin radiative element 60 for separating the respectiv received and transmit signals. The received signals ar coupled from duplexer 152 to low noise amplifier 156 fo amplification. The amplified received signal is passe through the duplexer 158, the beam steering phase shifte 160 and circulator/duplexer 162 to power divider 164. Th divider 164 splits the amplified received signal int three signal components, including one supplied to bi state phase shifter 1 ^' 66, and another component to bi-stat phase shifter 168. The possible states of the bi-stat phase shifters 166, 168 are 0 and 180 degrees, respec tively. The output of phase shifter 166 is the firs component signal for the module,and is coupled to th first RF manifold (Δ-) network 80B. The output of phas shifter 168 is the second component signal for the modul and is coupled to the second RF manifold (Δ ₂ ) 80D. Th

output of the divider 164 on line 165 is the third com¬ ponent signal for the module, and is coupled directly to the third RF manifold (Σ) 80C without any phase correc¬ tion. The purpose of bi-state phase shifters 166, 168 is to provide a received RF signal component with either a positive or negative sign. A difference pattern with any roll orientation is provided by changing the sign of the appropriate module output signals and then summing all the corresponding output signals from each T/R module 65. In effect, the module output signals are first differenced and then summed, rather than being summed first and then differenσed as is done in the conventional corporate feed networks to provide a difference pattern. Thus, each of the first and second networks 80B, 80D provides a summa¬ tion of the respective module difference outputs. The resulting signal at the output of manifold 80B (the first difference channel) is in effect the difference between the sum of those first component signals from all T/R modules having a 0 degree phase shift and the sum of those first component signals having a 180 degree phase shift. Similarly, the resulting signal at the output of manifold 80D (the .second difference channel) is in effect the difference between the sum of those second component signals from all T/R modules having a 0 degree phase shift and the sum of those second component signals having a 180 degree phase shift.

The transmit signal is provided from the transmit RF manifold 85 to duplexer 162, and passes through beam steering phase shifter 160 to duplexer 158, which directs the transmit signals to power amplifier 154. The ampli¬ fied transmit signal is then coupled through duplexer 152 to the radiative element 60.

Beam steering controller 95 provides beam steeri signals to beam steering phase shifter 160 in the conve tional manner.

Module controller 174 is coupled to bi-state pha shifters 166, 168 to control the phase shifts introduc by the elements in dependence on attitude position si nals, provided, in the case of an airborne system, fr the aircraft inertial platform 98. These signals a indicative of the attitude of the array in relation to t horizon.

The power divider 164 does not significantly redu the signal-to-noise ratio of the system because the noi figure has been established by the low noise amplifier 1 that precedes it. Referring now to FIG. 3, a quadrant-partition aperture for providing azimuth and elevation differen patterns is depicted in diagrammatic form. As is we known in the art, many radar systems employ two or mor displaced radiating/receive elements (or groups of ele ments) so that each receives the signal from a poin source at a slightly different phase. The receive signals from each receive element (or group) are summed t form the array sum signal, and the received signal fro one element (or group) is subtracted from the signa received on the other element (or group) to form a differ ence signal. The difference signal is a measure of th relative location of the target from the array boresight since the difference' signal will be nulled if the bore sight is perfectly aligned on the target. Difference signals are typically provided in th azimuth and elevation directions. Thus, the azimut difference signal indicates the angular offset of th boresight from the target along the azimuth axis, with th sign of the signal indicating the direction of the offset Similarly, the magnitude and sign of the elevatio

difference signal indicates the angular offset of the boresight from the target along the orthogonal elevation axis.

The quadrant partitioning of the aperture 55 shown in FIG. 3 may be employed with system 50 to provide the azimuth and elevation difference signals. Thus, the radiative elements 60 of the array are adaptively associ¬ ated with a respective one of the quadrants A, B, C, and D. Assume that axis 200 is aligned with the elevation axis, and that orthogonal axis 210 is aligned with the azimuth axis. To form the azimuth difference signal, the combined contributions from the signals received by the radiating elements in the B and D quadrants are subtracted from the combined signals received by the radiating elements in the A and C quadrants. The elevation differ¬ ence signal is provided by subtracting the combined signals received at the radiating elements in the C and D quadrants from the combined signals received at the elements in the A and B quadrants. The invention provides a means of arbitrarily assigning a particular radiating element to a particular quadrant of the array without requiring changes in hard wired connections or complex signal processing. The array controller is provided with attitude position data, e.g., from the aircraft inertial platform 98 in the case of an aircraft-mounted active array. This data may be used to direct the -module control logic 174 to set the bi-phase phase shifters 166, ^' 168 to the correct state for the particular roll angle, e.g., with the first difference component at the output of phase shifters 166 correspond¬ ing to the azimuth difference module signal, and the second difference signal at the output of phase shifter 168 corresponding to the elevation difference module signal.

This may be appreciated with reference to FIG.

Assume that the aircraft roll axis is initially align with azimuth axis 210. For all modules associated wi radiating elements in the A quadrant, the phase shifte 166 and 168 are set to the 0 degree phase shift stat For all modules associated with radiating elements in t B quadrant, the phase shifter 166 (azimuth difference) a set to the 180 degree phase shift position to associate minus sign with the signal contribution from these el ments, and the phase shifter 168 (elevation difference) set to the 0 degree state.

For all modules associated with radiating elemen in the C quadrant, the phase shifters 166 (azimuth diffe ence) are set to the 0 degree state, and the pha shifters 168 (elevation difference) are set to the 1 degree position. For all modules associated with radia ing elements in the in the D quadrant, the phase shifte 166 and 168 are both set to the 180 degree phase shi state. Now assume that the aircraft rolls to a 30 degre angle with respect to the azimuth axis, such that th aircraft axes are aligned with phantom lines 220 and 23 shown in FIG. 3. To roll stabilize the array with th horizon, the quadrant positions of certain of the radiat ing elements are reassigned. Thus, the radiating element located in the cross-hatched sector 222, nominally in th A quadrant for the case when the aircraft is aligned wit the horizon, are reassigned to the B quadrant. Similarly the radiating elements in sector 224-, nominally ^f in secto D, are reassigned to the B quadrant. The radiatin elements in sector 226, formerly in D quadrant, ar reassigned to the C quadrant. The radiating elements i sector 228, formerly in quadrant C, are reassigned t sector A.

To implement the reassignment of radiating element requires only that the states of the phase shifters 166, 168 of the modules associated with the reassigned element to be adjusted to the states described above for th radiating elements in the respective quadrants. With th array controller, this reassignment may be achieved ver quickly. Thus, the difference pattern of the array may b electronically roll stabilized, without the need fo mechanical roll gimbals or complex signal processing. As an alternative to providing sum and differenc signal patterns, an active array implemented with the rol stabilization modules described in FIG. 2 can be used t provide -three independent receiving ^' apertures. FIGS. and 5 shows circular apertures 55A and 55B partitione into three separate receiving apertures A, B, C require in a number of applications such as low speed movin target tracking, negating cross-eyed jammers, resolvin closely spaced (in azimuth) targets (FIG. 4) , or reducin multipath interference and resolving closely spaced (i elevation) .targets (FIG. 5) . The three summing networ output signals corresponding to the sums of the respectiv sum, first difference and second difference modul components, are

∑ = A + B + C (1)

= A-+ B + (-C) (2)

- A + (-B) + C (3)

where the minus sign in Eq. 2 indicates that all th module component signals in the C segment of the arra feeding the first difference combining manifold 80B have 180 degree phase shift (phase shifters 166) and the minu sign in Eq. 3 indicates that all the module componen

signals in the B segment of the array feeding the seco difference combining manifold 80D have a 180 degree pha shift (phase shifter 168) . The following computations a performed in the signal processor on the three RF manifo signals to separate the signals received from the radia ing elements in the respective A, B and C segments of t array:

A = (Δ _χ + Δ ₂ )/2 = ( (A+B-C)+(A-B+C))/2

B = (Σ- Δ ₂ )/2 = ( (A+B+C)- (A-B+C) ) /2

C = (Σ- Δ^/2 = ( (A+B+C)- (A+B-C)) /2

The shape and orientation of the A, B, C portions o the array can be varied at will with no hardware modifica tions, simply by altering the states of respective ones o the phase shifters 166, 168.

An active array system has been described for pro viding an electronically roll-stabilized and partitione receive aperture.

It is understood that the above-described embodimen is merely illustrative of the possible specific embodi ments which may represent principles of the presen invention. Other arrangements may be devised in accord ance with these principles.. i>y those skilled in the ar without departing from the scope of the invention.