JPS60120272A - Monopulse detecting system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a detector arrangement for use in active or passive detection systems with monopulse tracking.

A typical monopulse tracking system requires six channels to locate the target within the beam of the detector array. Two signal difference channels are required to provide information about a target that is offset in two mutually orthogonal directions. The sum channel gives amplitude information. Comparing the magnitude and sign of these difference signals with the sum signal then provides the position of the target relative to the center of the beam.

It is an object of the invention to provide an alternative type of monopulse detection system which requires only two channels to determine the position of a target and which is suitable for circular arrays.

The present invention comprises: 0) a flat array of detectors responsive to the energy received; (b) a summation channel that adds together all of the outputs from all of said detectors; and (c) a target object. a monopulse detection system for detecting energy received from a target object, with guidance means for guiding the position, wherein the output of each said detector has a value between 0 and 2π or according to the angular position of each said detector in the plane of said array. Adding a linear constant polar phase delay within an integer multiple thereof and providing only one difference channel for adding together the product signals thus formed to guide the position of said target. There is a means for inducing this in the monopulse detection system using a comparison of the respective outputs from the sum and difference channels.

That is, the present invention requires only two channels, one producing the sum beam and the other producing the difference beam. In this case, the relative amplitude determines the angular offset of the target, and the relative phase determines the direction of this offset projected onto the plane of the array.

The array provides a uniform distribution of detectors, for example by placing each detector in the interstices of a rectangular grid. However, to reduce overall system complexity, the present invention can also be applied to thinned arrays in which selected detectors are removed from uniform arrays.

In a preferred arrangement, the array consists of a waveguide aperture, dipole or similar element for emitting and receiving radio frequency energy. During this reception, each element
It is connected to a receiver that amplifies and/or converts the energy emitted or reflected by the target to a lower frequency. Next, each separate output may be passed through a selectable phase delay used for beam steering.

The separate phase-delayed outputs are directly summed to form a sum beam, and fixed polar-phase-delayed (poiaphase)
dθ:1ay) is applied and then added to form a difference beam.

When the selectable phase delay is set to zero, the sum and difference beams are circularly symmetrical about the normal to the plane of the array, resulting in a central peak and central null, respectively. By adding a phase delay that is linearly dependent on the position of each element in the array, beam steering is achieved by tilting the phase front with respect to the plane of the array.

The system is equipped with a circuit that automatically steers the sum and difference beams to keep the target on the axis of the sum beam.

The side loso of the radiation patterns of both the sum and difference beams is attenuated by performing the summation of each signal on the two channels in a weighting circuit. In this weighting circuit, each detector output is weighted as a function of the detector's distance from the center of the array.

Constant Q added to the receiver output in the difference channel
A 9π Pauday phase delay is introduced by an appropriate length of transmission line connecting the receiver to the difference channel summing circuit.

Embodiments of the monopulse detection system of the present invention will be described in detail below with reference to the accompanying drawings.

The monopulse detection system consists of a rectangular 4
This was caused by using multiple horn antennas. In the typical configuration shown in Figure 1, four rectangular horns AX
B, O, and D are aligned with the axis of the reflector R.

These ho. The signals received from the input terminals are respectively added and subtracted to form a sum signal S and two difference signals ΔX,
yields Δy.

5=A-1-B-1-C-1-D ΔX= (A-1-D )-(B+C) Δy=(A+B
)-(C!+D) By comparing the magnitude and sign of the difference signal ΔX1Δy with the sum signal S, the azimuth and elevation servo motors connected to the antenna system are driven in an appropriate direction and the difference signal is made zero. Keep the target trajectory like this.

This system, with separate ΔX and Δy signal channels, is employed in a conventional antenna array using a centralized transmitter and each receiver with a radio frequency feedline network to separate the sum signal and the two difference signals. do. Since feeder networks are typically arranged horizontally and vertically, it is a logical arrangement to provide separate Cartesian ΔX and Δy difference signal channels. However, this is no longer necessary in electronically scanned active arrays where each element or small group of elements in the array cooperates with each separate receiver. In this case, it is possible to provide the phase shift by mechanical processing or digital processing. With such processing, two or more outputs of any desired phase are obtained from each receiver without loss of signal-to-noise ratio.

FIG. 2 shows a circular or non-circular flat antenna array A filled in whole or in part with antenna elements B. FIG. Each antenna element B is connected to a transmitter 1 or a receiver 2 depending on whether the associated switch S, S2, S3 is in the lower position (the position shown) or in the upper position, respectively.

During transmission, power from the transmitter 1 is sent via a divider 3 to all radiating antenna elements B by a respective phase shifter 4. The output from each phase shifter 4 is sent to antenna element B via a selection amplifier 5. During reception, the frequency divider 3 is used to send power for the local oscillator 6 to the radio frequency mixer in the receiver 2 via each phase shifter 4 and input cuff. The signal received by antenna element B is sent to each receiver 20 input 8. In each receiver 2 each human power 8 is down to the IF frequency signal at the receiver output 9.
down-convert.

The direction of the highest gain for both transmission and reception, that is, the direction of the main beam, is controlled by the setting of the phase shifter 4.

In a normal antenna system, the output signal from each receiver 2 is processed as shown in FIG.
．． yields 12. For the sum signal output 11 (corresponding to S), all the received and sum outputs 9 have mutually equal path lengths to the resistor network F when added together. Signals received by antenna elements 13 toward the edges of antenna array A in many cases have additional resistive attenuation to suppress side lobes of the antenna sensitivity pattern.

The signals from all antenna elements to the left of the centerline 14 of antenna array A with respect to the azimuth signal output 10 (corresponding to ΔXK) are added in antiphase to the signals to the right of network F'2. That is, the signal from each receiver output 9 is transmitted to a network F2 through a phase delay 15, which is set to 0 or π radians depending on whether the associated antenna element B is to the left or to the right of the centerline 14 of the antenna array, respectively. Sent. Similarly, for the elevation signal output 12 (corresponding to Δy), the signals from each antenna element above the centerline 16 of the antenna array are added in opposite phase to the signals below network F3. The signal from each receiver output 9 is sent to network F3 via a phase delay 17 set to ``co or π radians depending on whether the associated antenna element is above or below the middle 6u line 16, respectively. For these difference outputs 10.12, both
Resistor 17' or resistor 1 according to the distance of each individual element in antenna array A with each center line 14.16
A low lateral loso is obtained by attenuating or weighting the individual signal amplitudes by appropriate selection of 8.

Next, the six outputs io, 11.12 signals can be processed in three mutually identical channels. Finally, after isolation in a known manner by distance gates, the phase and amplitude of the signal in each difference channel is compared with the phase and amplitude of the signal in the sum channel, and the phase and amplitude of the signal in the sum channel are compared horizontally and vertically. Determine the angular offset of the mark.

According to the invention, the circuit arrangement shown in FIG. 4 is used in conjunction with the antenna array A and the circus tree shown in FIG. In the present invention, a polar coordinate dependent phase is applied instead of the usual rectangular coordinate system to form a polar coordinate monopulse radar system.

As before, the output 9 of the receiver 2 associated with each antenna element B in the antenna array A is connected to a resistor 19, 2.
0.21 (only three resistors are shown) are summed under a weighting network consisting of 0.21 (only three resistors are shown) to produce a conventional sum signal Σ at the output 22 from the weighting network F. However, the output 9 from each receiver 2 is also connected to a second weighting network F4 consisting of resistors 24, 25, 26 with a constant polar
) is added via a phase delay 23φ to produce a signal-weighted output difference signal 27Δ. The constant polar phase delay 23 introduces a phase shift for each antenna element B equal to the element's angle θ measured clockwise from the centerline 14. This can be done by connecting the receiver 2 to the weighting network F4 using a cable of suitable length. That is, the polar monopulse requires only two channels with two weighting networks Fl+'4 compared to the three networks required in the conventional FIG. 6 configuration. Furthermore, the amplitude weighting of the 24 network of difference channels only depends on the distance of the antenna factor from the center of the antenna array. That is, it is circularly symmetrical with this child to the sum channel. Next, the sum output 22Σ and the difference output 27Δ are combined, the amplitude ratio Δ/Σ is taken, the angular deviation of the target from the aiming direction is given, and the phase difference between the two outputs φΣ−
By taking φΔ and giving the radial direction of the target with respect to the centerline 14, the angular position of the target is uniquely determined.

In a circular array of detectors, the phase mode is such that the phase of each individual element is the total phase 2πn=360, where n is an integer.
These elements can be chosen to vary linearly with the angular position in the case of .degree. By appropriate phased addition of the various modes, beams or nulls can then be generated in specific directions within the plane of the antenna array. This idea can be extended to the circular planar array of the present invention by considering what happens in the plane orthogonal to the antenna array.

Figure 5 makes an angle θ from the center #29 of the antenna array,
An example of antenna elements 28 in a planar array located at a distance r 1 from the center 30 of the antenna array is shown.

The amplitude of the excitation of this array is a function only of the radial distance r and is given by:

If amplitude = f (r ) n = Q, then the phase is constant over the plane of the antenna array and the beam is formed perpendicular to the plane of this array. Therefore, the pattern n is selected to be zero for the sum Σ. The resulting cross-section of the beam is shown by pattern 31 in FIG. 6 as a symmetrical beam about the aiming direction 32 (through the antenna array center 30 and perpendicular to the plane of the antenna array). polar difference (p(,mar different
ce) Beam n is selected to be 1 for Δ.

In this case, the amplitude excitation of the antenna array as shown by pattern 33 is constant in amplitude but with phase around 36
It is symmetrical with respect to a null 34 in the aiming direction 32 surrounded by an annular peak 35 changed by 0°.

That is, if the target is within the sum Σ beam, the ratio of the signal amplitudes is also within the sum 31, and the polar difference 33 indicates the angular distance of the target off the aiming direction 32. Comparison of the phases of the two return paths φΣ:φΔ in this case indicates the radial direction of the target. Also, an integer value of n greater than 1 can be chosen. In this case higher angular resolution is obtained at the expense of ambiguity.

Although not shown in FIG. 6, for the sake of simplification, if the amplitude distribution is made uniform with a difference pattern, the side loso generally increases and the monopulse angle sensitivity decreases. In a typical rectangular monopulse system, the addition of a linear taper of amplitude proportional to the distance from the array center of the antenna elements results in lower siderosers and higher angular sensitivity. This is also true for "polar monopulse"systems; in this latter case, this taper doubles the receiver noise, but for circularly symmetric It can be shown that a difference ray pattern is obtained. The sideroser can be made even lower by reducing the amplitude near the edges of the antenna array. However, in this case the polar monopulse is exactly the same as the ordinary difference ray pattern. does not correspond to

As described above, with uniform phase across the antenna array, the sum beam is aligned with the aiming direction, ie along the array axis orthogonal to the plane of the array. To direct the beam in some other direction, a uniform phase gradient must be applied across the plane of the antenna array. A uniform phase slope is added in a well-known manner by setting a phase lag in the phase shifter 4 that is linearly dependent on the position of each detector in this antenna array. It will be done. polar
In the case of a difference beam, the same phase gradient must be applied to the phase mode.

The annular peak of the difference beam remains undistorted due to sin α, where α is the angle from the aiming direction. However, α makes this annular peak appear somewhat oval-shaped. Therefore, it is preferable to calculate the position of the marker offset from zero using a space of 8 in α, and then convert it to an actual angle. The phase shift applied to the individual antenna elements is quantized (with respect to a normal monopulse). This quantization then introduces angular errors. This angular error also increases by reducing the number of antenna elements, as in the case of conventional thinned arrays. It can be shown that the angular accuracy of a polar monopulse is independent of direction and is equal to the accuracy obtained with an ordinary monopulse at 45 DEG to the centerline 14 of the antenna array.

The polar difference beam according to the invention is more difficult to generate than a common monopulse because it involves radial amplitude variations and circumferential phase variations across the plane of the antenna array. By comparing ordinary monopulses, the difference beam contains a two-dimensional amplitude change but a single phase reversal at the centerline.

However, polar monopulse requires only two channels for tracking instead of five. In this case, a savings of 2 can be achieved in signal processing costs and auxiliary equipment such as pushing the cancellation loop. In contrast to the examples described above, the present invention can be applied to any detection system that can maintain both the phase and amplitude of the individual elements. The combinational network can be applied to rf, if or if. Alternatively, digital signals containing phase information can be combined by a computer. In another variant, the outputs from small groups or subarrays of antenna elements can be combined for the individual antenna elements described above.

Although the present invention has been described above in detail with reference to its embodiments, it goes without saying that the present invention can be modified in various ways without departing from its spirit.

[Brief explanation of drawings]

Fig. 1 is a schematic plan view of a monopulse radar tracking antenna, Fig. 2 is a functional circuit diagram of a monopulse tracking radar, Fig. 6 is a circuit diagram of a signal processing circuit of an ordinary monopulse radar, and Fig. 4 5 is a circuit diagram of a signal processing circuit according to the invention forming a polar monopulse radar; FIG. 5 is a top view of a flat array used to form a polar monopulse radar; FIG. 6 is a polar monopulse radar.
FIG. 2 is a diagram of a radiation pattern (response curve) of two beams. B... Antenna element (detector), 9... Receiver output, 13... Polar coordinate array, 2'2... Sum output, 23.
...Phase delay, 27...Difference output, Fl...Weighting circuit network, F4...Weighting circuit network,

Claims (1)

[Claims] +11 (a) a flat array of detectors responsive to the energy taken; ←) a summation channel that adds together all of the outputs from all of said detectors; In a monopulse detection system for detecting energy received from a target object, the monopulse detection system is equipped with a guiding means for guiding the position of a target object.
The output of each said detector is between 0 and 2π (or an integer multiple thereof) according to the angular position of each said detector in the plane of said array.
adding a linear polar phase delay within the range of , and providing only one difference channel to add together the product signals thus formed to derive the position of said target. A monopulse detection system characterized in that the guiding means is adapted to use a comparison of the respective outputs from the sum channel and the difference channel. (2) During energy reception, each element can be connected to a receiver that amplifies and/or converts the energy emitted or reflected by the target to a lower frequency. Claim No. 1 characterized in (
Monopulse detection system according to item 17. (3) Connect the output from each detector element to a selectable phase delay used for beam steering, and directly add the outputs from these selectable phase delays to form a sum beam. A monopulse detection system according to claim 1 or claim 21, characterized in that the monopulse detection system forms a difference beam by adding a certain polar phase lag and then adding it to form a difference beam. (4) Automatically steer the sum beam and difference beam,
Claim M(3) characterized by comprising a circuitry for keeping the target on the axis of the sum beam.
Monopulse detection system as described in Section. (5) each sidelobe of the radiation pattern of both the sum beam and the difference beam is attenuated by performing summation of each signal in the two channels in a weighting circuit, in which each of the detection Claims (1) to (4) characterized in that the detector output is weighted according to the distance of the detector from the center of the array.
The monopulse detection system according to any of paragraphs. (6) 0°C added to the receiver output in said difference channel.
- A constant polar phase delay of 2π is introduced by connecting a transmission line of an appropriate length between the receiver and the difference channel adder circuit. ) to (5).