Binary options 7 stealth system vertaling
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This invention relates to a means and method for measuring angle of arrival AOA to perform binary options 7 stealth system vertaling direction finding DF. In particular this invention provides a technique for making such measurements using linear interferometer arrays only.
Passive radar emitter direction-finding DF utilizing radio frequency RF interferometers mounted on aircraft requires finding the emitter's azimuth and elevation in the observer's local-level reference frame.
In the description given hereinafter the binary options 7 stealth system vertaling aircraft is meant to encompass any observational platform whose motion involves attitudinal changes, such as roll, pitch and yaw, as well as translational motion. In particular, an interferometer sensor array mounted on the leading edge of an airplane wing measures AOA in relation to the sensor's own system of three dimensional coordinates which are then transformed to the observational body's frame of coordinates and a level frame of coordinates to report azimuth and elevation.
Finally target location is reported in a set binary options 7 stealth system vertaling coordinates for the Earth. Finding emitter elevation and azimuth from aircraft has previously required the use of planar or conformal interferometer arrays. A linear interferometer could not be used, since a single linear array measures angle-of-arrival AOA and not direction-of-arrival DOA. That is, a single linear interferometer produces an AOA cone, and the emitter can be anywhere on the intersection of that cone with the Earth.
A linear interferometer designed to fit on the leading edge of an aircraft wing, is illustrated in FIGS. The phase information from the receiver is supplied to a processor 18 which accomplishes phase ambiguity resolution; the phase-resolved signal 15 is then used for determination of AOA information, as shown at The phase measurement of a plane wave with unit normal DOA vector u across one baseline d is EQU1 Thus the quantity measured is the angle of arrival, or AOA between the interferometer baseline and wavefront.
For a planar earth approximation, this means that any emitter lying on the hyperbola resulting from the intersection of the AOA cone with the earth can generate the same AOA, and hence emitter azimuth is available from this single measurement only in the special circumstance that the emitter lies in the plane containing the linear array baseline.
When this is not true an ad hoc assumption about emitter elevation must be made, typically that the emitter lies on the radar horizon. For emitters not on the horizon the error in using AOA as the true azimuth measurement, typically called the "coning" error, is given by EQU2 This equation is strictly only true for binary options 7 stealth system vertaling sensor coordinates but this caveat is not important here.
Equation 2 indicates the azimuth error becomes quite large when emitters are at steep elevations. It is negligible for emitters on the horizon if the aircraft is flying level, but may become important even for distant emitters when the aircraft has a significant roll or pitch attitude.
Since emitter azimuth is an important parameter in many systems performing passive radar detection, e. Bearings-only ranging utilizing AOA essentially finds the intersection of the multiple AOA-hyperbola generated as the aircraft moves along its track. Thus a positive feature of bearings-only ranging is that the range accuracy can be improved by making the bearing spread larger. DOA dependent bias error is also present on the bearings-only measurement, but has a negligible effect for emitters at bearings essentially normal to the observer's flight path, which is often the case when AOA-only location is used.
This system, as in FIG. The resolved baseline information is then used at 22 to compute AOA information in accordance with the sensor's set of coordinates. After a range estimate is supplied binary options 7 stealth system vertaling 23, the AOA information is calculated in accordance with the platform or body's set of coordinates at 24, and then to level coordinates at The benefits of using a single linear array doing bearings only ranging are the limited number of phase measurements required per dwell compared to multi-dimensional arrays, and compact installation.
The drawbacks are the inability to go from AOA in the sensor frame to azimuth in the level frame without assuming an ad hoc emitter elevation, i. Overcoming these drawbacks and providing accurate azimuth has previously required utilizing an interferometer array extending in at least two dimensions, such as the conventional conformal array.
In the latter array it is necessary to use a vertically disposed sensor array to form an elevation baseline while another sensor array generally disposed horizontally is used to resolve the elevation array ambiguities. The phase measurements in such a multi-baseline system cannot typically be made without receiver switching between the baselines, i.
Besides increasing system complexity, such baseline switching complicates the detection of multipath errors on the phase measurements. There are other problems with switching. In the conformal array discussed above the horizontal array must have its phase measurements completed before making phase measurements on the elevation antennas.
If the emitter is no longer detected after the "horizontal" binary options 7 stealth system vertaling measurements are made, because, for example, of emitter scanning or terrain blockage, binary options 7 stealth system vertaling will not be obtained. Note that the possibility of not getting a full set of phase measurements is increased by the use of elevation arrays on low RCS Radar Cross Section aircraft, since stealth aircraft impose RCS restrictions on the antennas.
Adding an elevation array increases the overall RCS, requiring antenna design trade-offs that reduce system sensitivity and hence may prevent detecting emitter side and backlobes.
Obtaining the space to mount a planar array or three dimensional array is difficult on many smaller aircraft. Also, important delta-wing stealth aircraft designs do not provide extensive vertical area, and hence little space for a planar array no matter what the intrinsic aircraft size. Although by utilizing conformal design techniques elevation arrays can be mounted on the leading edge of delta-wing aircraft, the antenna elements do not have common boresights.
This can introduce significant bias errors, especially when certain popular ESM system antenna elements, such as broadband multi-arm spirals are used. But this very desirable feature is mitigated by the following deficiency:. Thus the estimate is intrinsically inaccurate at lower altitudes and at any altitude for emitters near the binary options 7 stealth system vertaling, with no means binary options 7 stealth system vertaling subsequent refinement, i.
But, as noted above such arrays do not provide true emitter azimuth or monopulse location. It is therefore, an object of this invention to allow such linear arrays to be used to perform the functions associated with more complex multi-dimensional arrays, i.
The foregoing objects, and others, are achieved in accordance with the invention which provides a method for using single linear arrays for making AOA measurements only in sensor coordinates to perform emitter direction finding from an observing aircraft.
The linear arrays used may be mounted on a single or on multiple aircraft. Provide elevation baselines that can be as long as those commonly used for azimuth measurement on aircraft with limited vertical aperture. The measurements from the binary options 7 stealth system vertaling platforms require no time-simultaneity.
In fact, the time at which the measurement is made is not used at all, but instead only the platforms' locations and attitudes. The origin of the phase measurements, i. A significant element of the new invention is the generation of a virtual spatial array from the linear arrays based on aircraft six-degree-of-freedom, or 6DOF, motion.
The generation and intersection of the AOA cones can be done in seconds, as opposed to the conventional multicone AOA approach, bearings-only passive ranging, discussed above. Bearings-only passive ranging requires that the origin of the cones be separated by some intrinsic flight path length in order to form a triangle, and subtend bearing spread at the emitter. In order to aid an understanding of the principles of the invention, FIGS. The labeled blocks sufficiently identify the sequence of functions.
As indicated in FIG. This process is iterative, as is the bearings-only approach of FIG. But the bearings-only iterations extend over minutes to obtain a solution, whereas the virtual array iterations intrinsically require only seconds. The baselines are formed by combining the two separate resolved binary options 7 stealth system vertaling array phase measurements, the arrays being located on the same platform.
This creates a planar array. A virtual array can be created during a single aircraft observer snap roll. This creates a three dimensional array, as does the array created from multiple observers; in the binary options 7 stealth system vertaling case multiple aircraft in close formation can synthesize an array rather than relying on single aircraft attitude changes. During the course of DF'ing an emitter the virtual array embodied by D can be synthesized from any combination of these four methods.
Thus intrinsic system bias errors can tend to random errors in time. Thus sequential averaging can be used to reduce both angle-estimate errors, and location-estimate errors.
The averages shown in FIG. The location averaging is binary options 7 stealth system vertaling term, extending over many dwells. Hence the DOA dependent errors on e become random, and hence the range errors are random from update to update. By contrast, the azimuth and elevation estimate average occurs over binary options 7 stealth system vertaling either close together in time, or observer location.
Hence it is typically an average over a small set. The arrays can be constructed like the interferometer pictured in FIG. The operation is essentially same as that of the conventional system of FIG. In conventional ESM systems the latter process determines which array will be used. In the new approach presented here all measurements available from all arrays will be used at each dwell.
For example the baselines generated during a snap roll could be EQU5 The rows of virbase contain the six parameters required to completely 6DOF characterize the individual baselines. The first three elements in this array are the projections of the baseline unit vector onto the level frame.
This projection is done using platform roll, pitch and yaw angles from the navigation, or NAV, system. The second three elements represent the baseline distance from a common reference. The unit is nautical miles for this second set in the example. Thus, a baseline spatial position and attitude for the binary options 7 stealth system vertaling is established. The first five rows of virbase are for the port array, while the second five rows are for the starboard array. The distance apart on the aircraft of the two arrays is too small to be discernible with the numerical precision used here.
The virtual array is constructed sequentially at 48 by iteratively forming the array matrix D. In forming D only the angular orientation of the baselines are used, that is the d i are all assumed to have a common origin or x,y,z location.
This common origin is taken as the centroid of all the actual translational positions of the baselines currently forming D. Thus the final array matrix in this example is EQU6. However, the solution process begins before the complete array is formed. When two baselines are available an initial D can binary options 7 stealth system vertaling formed and checked for "observability", binary options 7 stealth system vertaling. If a solution is feasible the error variance.
The dominant error is that caused by the difference in phase at the assumed centroid origin compared to the actual position the phase measurement was made.
This error R is a function of the emitter location, and hence is not known. The error can be bounded, though, by initially assuming minimum and maximum emitter ranges 49and using the "dispersion" portion of virbase, which is EQU8 The last column is zero because there was no altitude change in this example.
The phase error actually caused by the different translational positions of the baselines is shown in FIG. The other component of R is the intrinsic system error occurring in conventional interferometers, i. The constrained estimation problem for u, i.
Azimuth and elevation are computed at 54 from the components of EQU10 according to the definition of the DOA unit vector in Equation 6, i. The error variance of this estimate is found next at This is done by noting that the solution to Equation 8 can be written in the form.
This is seen by representing the desired azimuth a and elevation e measurements as a vector EQU12 and finding the error on the estimate of a, which can be approximated by EQU13 Hence the estimate error is strictly a function of D i and R. D i reflects the interaction of the relative orientations of the baselines with R, while R embodies predominantly the error introduced by the baseline relative distances apart.