JPH0682980B2 - Monopulse antenna with improved sidelobe suppression - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to the efficient use of antenna sum and difference patterns, and more particularly to side rope suppression arrangements for monopulse antennas that use sum and difference patterns for tracking targets. .

As is generally known, a monopulse antenna is subdivided into parts, for example by using horns or four quadrants, and the radar is then targeted by comparing the amplitude and phase of the echo signal for each horn or four quadrant. Detect movement.

The RF circuit for a normal antenna divided into four quadrants has an arbitrary imbalance in the azimuth direction (patterns with different directions)
Subtracts the output of the left pair from the output of the right pair for sensing, and subtracts the output of the top pair from the output of the bottom pair for sensing any imbalance (altitude difference pattern) in the altitude direction. Radar Handbook (Merrill Skolnick, Mc G
Raw Hill, published 1970). Subtractor output,
That is, the difference pattern is zero when the target is on-axis and increases in amplitude with increasing displacement of the target from the antenna axis.

The sum signal, which typically represents the energy received on all devices, is
It is generated and used as a reference signal for video input and for gain control.

The optimal sum and difference signals, low sidelobe levels, polarization diversity, compactness of the device and simple construction cannot be satisfied at the same time when using a single feeding means. First, many compromises were required regarding the design of the power supply means and the radiation pattern.

Therefore, the sum pattern is usually optimized and the resulting difference pattern signal is allowed to be in an insufficient state. However, it is important to improve the undesired properties of the difference pattern in order to solve tracking problems, as also described in US Pat. No. 4,525,716. For example, the side ropes in the difference pattern receive interference signals from a range off the axial direction of the background clutter and radar radiation beam, thus reducing efficiency,
There is a drawback that causes tracking errors.

An object of the present invention is to obtain an antenna device having a relatively simple structure that simultaneously optimizes the sum signal and the difference signal side lobes.

This object is achieved by an antenna device for use in a target tracking radar system according to the invention, comprising a monopulse antenna and a single feed network forming sum and difference signals. It

The antenna device of the first invention of the present invention comprises an array of antenna elements in which a monopulse antenna is arranged symmetrically with respect to the azimuth and elevation axes, the array transmitting energy towards a target and then being reflected from it. Defining an opening having a cross-sectional area for receiving
The openings are the first, second, third, and third antenna element groups that extend from the center to the periphery of the array of antenna elements.
And a fourth swath and four substantially equal quadrants separated thereby, the feed network is coupled to the array and one input is coupled to the first swath. A first hybrid having a second input coupled to a second swath to form a sum and difference output of outputs from the swaths, and an antenna element having a first input in the third swath A second hybrid having two inputs coupled to each antenna element of the fourth swath to form a sum and difference output of outputs from those swaths, and a first input having a first hybrid. A third hybrid coupled to each antenna element in the quadrant region and having a second input coupled to each antenna element in the second quadrant region to form a sum and difference output of outputs from those quadrant regions; Input 1 is the third quadrant A fourth hybrid coupled to each antenna element, the second input coupled to each antenna element in the fourth quadrant to form a sum and difference output of the outputs from those swaths, and a first input Is coupled to the sum output of the first hybrid, the second input is coupled to the sum output of the second hybrid, and the fifth hybrid forming and outputting those sum outputs and the first input to the A sixth hybrid coupled to the sum output of the three hybrids and having a second input coupled to the sum output of the fourth hybrid to form and output their sum and difference outputs; A seventh hybrid coupled to the difference output of the third hybrid, the second input coupled to the difference output of the fourth hybrid, forming a sum output thereof and outputting the first hybrid;
The input of is coupled to the sum output of the fifth hybrid,
Input is coupled to the sum output of the sixth hybrid to form and output those sum outputs, and the first input is coupled to the difference output of the first hybrid and the second input is A ninth hybrid coupled to the differential output of the sixth hybrid to form and output their sum output, and a first input coupled to the differential output of the second hybrid and a second input to the seventh hybrid. And a tenth hybrid which is coupled to the sum output of the hybrids and forms and outputs the sum output.

Also, the antenna device of the second invention of the present invention comprises an array of antenna elements in which a monopulse antenna is symmetrically arranged with respect to an azimuth axis and an altitude axis, the array transmitting energy toward a target, and then An aperture is defined having a cross-sectional area for receiving the reflected energy, the aperture defining a central area of the antenna element array surrounding the intersection of the azimuth axis and the elevation axis and four substantially equal quadrant areas around the antenna element array. Segmented and the feed network is coupled to the array, the feed network having a first input coupled to each antenna element in the first quadrant and a second input coupled to the second quadrant. A first hybrid that is coupled to each antenna element of the quadrant to form a sum and difference output of the outputs from those quadrants, and each antenna element of which the first input is the third quadrant A second hybrid that is coupled and has a second input coupled to each antenna element in the fourth quadrant to form a sum and difference output of the outputs from those swaths; And a second input coupled to the sum output of the second hybrid and a second hybrid coupled to form a sum output and a difference output of the second hybrid and the first input. A fourth hybrid coupled to the differential output of the first hybrid and a second input coupled to the differential output of the second hybrid to form and output the differential outputs of the first hybrid and the first input to the central region. A fifth hybrid coupled to each of the antenna elements, the second input coupled to the sum output of the third hybrid, and forming and outputting the sum output thereof.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 shows a conventional 5 for supplying sum and difference patterns.
One horn antenna.

Figure 2a is an embodiment of the invention showing an aperture having an array of elements divided into four quadrants and strips.

Figure 2b is a sum and difference network for providing the desired sum and difference signals for the embodiment of Figure 2a.

FIG. 3a is another embodiment of the invention showing an array with an array of elements divided into four quadrants and a selectively excluded central portion.

FIG. 3b is a sum and difference network for providing the desired sum and difference signals for FIG. 3a.

FIG. 4a shows a comparison of the altitude difference pattern signals of the embodiment of FIG. 2a before and after selectively excluding elements along the altitude axis in signal generation.

FIG. 4b shows a comparison of the misorientation pattern signals of the embodiment of FIG. 2a before and after selectively excluding elements along the azimuth axis in the generation of the pattern signal.

Detailed Description of the Drawings Referring again to FIG. Shown here are five conventional horn-fed antennas for providing sum and difference signals. As shown in FIG. 1, five horn antennas
A, B, C, D, E are left antenna A, top antenna B, right antenna C, bottom antenna D, and antenna E that fills the central space in which antennas A, B, C, and D are arranged. It is arranged. The altitude difference signal is obtained by subtracting the reflected energy from antenna D from the reflected energy of antenna B, and the azimuth difference signal is obtained by subtracting the reflected energy of antenna C from the reflected energy of antenna A. The sum signal is provided by the reflected energy of antenna E. This form of antenna feed and other forms used in tracking radar systems are required to achieve high sum gain while retaining low sidelobes in the difference pattern. A similar problem is found when the antenna consists of a single aperture containing an array of radiating elements and the difference pattern is similarly generated using half of the aperture minus the other half of the aperture.

Referring to FIG. 2, although an embodiment of the invention is shown herein, it is understood that other embodiments may be derived from the disclosed invention. In FIG. 2a, the antenna 10 is shown as having a circular aperture 12 and having an array of radiating and receiving elements 20. This antenna is, for example, a broadband antenna designed to operate in missiles. The aperture is divided into four quadrants 14,15,16,17 which are substantially equal and symmetrical. Quadrants 14 and 15 have openings 12
Quadrants 16 and 17 define the lower hemisphere for the aperture 12. In particular, quadrant 14 defines the upper left quadrant, quadrant 15 defines the upper right quadrant, quadrant 16 defines the lower right quadrant, and quadrant 17 defines the lower left quadrant.

A horizontal strip 24 of elements along the elevation axis and a vertical strip 26 of elements along the azimuth axis are also shown in FIG. 2a. Strip 24 includes strip K, which is a quadrant
Includes elements taken from 14 and 17 in substantially equal numbers. Strip 24 also includes strip I containing elements taken from quadrants 15 and 16 in substantially equal numbers. Strip 26 includes strip H containing elements taken in substantially equal numbers from quadrants 14 and 15, and strip J containing elements taken in substantially equal numbers from quadrants 16 and 17.
Including and Further in FIG. 2a, strips 24 and 26
After taking each element for quadrant 14,15,1 of Figure 2a respectively
Quadrants A, B, C, and D referencing the rest of 6, and 17 are shown.

In operation in this embodiment, strip 24 and
26 is selectively excluded in the generation of the difference pattern signal, resulting in a reduction in side lobes for the azimuth and altitude difference patterns, as further described below.

Referring to FIG. 2b, there is shown a diagram of the sum and difference network for connecting the reflected signals from the four quadrants and strips of FIG. 2a to achieve low difference pattern side lobes.

The sum pattern used for the antenna of FIG. 2a provided by the network of FIG. 2b is (A + B + C + D) + (H
+ I + J + K), and the misorientation pattern is (A + D +
K)-(B + C + I), and the altitude difference pattern is (A +
B + H)-(C + D + J).

To achieve the required combination of reflected signals to provide the desired sum and difference patterns described above, first the reflected signals of each quadrant and strip are parallel hybrids 41, 42, 4
3, and 44 are selectively combined with that of the other quadrant or strip. The hybrid is a standard sum and difference hybrid commercially available, that is, the sum and difference magic T normally used in comparison circuits. The coupling coefficient for each hybrid varies depending on the design of the aperture and is chosen to be as close as possible to the ideal sum distribution pattern. The reflected signals from strips K and I are fed to hybrid 41, as shown in FIG. 2b. Reflected signals from strips H and J are similarly fed to hybrid 42. Reflected signals from quadrants A and D are provided to hybrid 43. Reflected signals from quadrants B and C are provided to hybrid 44. K and I are (K + I)
Are combined with a hybrid 41 to supply (K-I)
The difference is also taken out by the hybrid 41 in order to supply. The same process applies to H and J as (H + J) and (H-
J) in the hybrid 42, (A + D) and (A-D) in the hybrid 43, and (B + C) and (BC) in the hybrid 44.

With further reference to FIG. 2b, the outputs from hybrids 41, 42, 43, and 44 are further quadrants A, B, C, D and strips H, I,
It is selectively added and subtracted to give the desired combination with J, and K. Hybrid 41 from (K + I)
The output and the (H + J) output from the hybrid 42 are combined in phase at the hybrid 51 to output (H + J + K + I) at the output of the hybrid 51. The (B + C) output at the hybrid 44 is subtracted from the (A + D) output of the hybrid 43 at the hybrid 52 to provide (A + D)-(B + C) at the output of the hybrid 52 and also (A + D + B +
Combined in phase with (B + C) to provide C). The (AD) output of the hybrid 43 is the hybrid 44
Are combined in the same manner as the (B-C) output of the above, and supply (A + B)-(C + D) at the output of the hybrid 53. The output (A + C)-(B + D) subtracted by hybrid 53 is not used and therefore this output is terminated.

In order to obtain the sum signal (A + D + B + C) + (H + I + J + K), the direction difference signal (A + D + K)-(B + C + I), and the altitude difference signal (A + B + H)-(C + D + J), the outputs from the hybrids 51, 52, and 53 are further output. Selectively combined.

Output of hybrid 51 (H + J) + to obtain sum signal
(K + I) is the output of hybrid 52 (A + B) + (C +
D) and hybrid 61 to form (A + B + C
+ D) + (H + I + J + K) is output.

The hybrid 41 (K-I) output is the hybrid 62 output and the hybrid 52 output (A + D) to obtain the azimuth difference signal.
Combined with-(B + C), (A + D + K)-(B + C +
I) is output.

In order to obtain the altitude difference signal, the (H-J) output of the hybrid 42 is the hybrid 63 (A, B)-
Combined with (C + D) output, (A, B, H)-(C + D +
J) is output.

In Figures 4a and 4b, using the full ("original") aperture reflection signal of Figure 2a, the difference signal was compared by horizontal and vertical strips selectively removed using the reflection signal in Figure 2b. A comparison of the data measured on the original difference signal is shown. The difference signal is symmetrical on both sides of the boresight for all practical purposes, and the discussion below gives the sidelobe pattern on both sides of the right and left boresights.

Please refer to FIG. 4a. The original altitude sum and difference signal (left figure) and the altitude difference signal with horizontal strips I and K omitted (right figure) are shown. It can be seen from Figure 4a that the original altitude difference pattern has a side lobe of about -15 dB at about 20 °. Compare this to the diagram on the right side of FIG. 4a showing the excluded height difference pattern of the horizontal strip. There is 30 near the side lobe
It suddenly drops to near -25 dB at ゜ and forms a deep valley.

A more striking result is shown in Figure 4b. The figure shows the original heading sum and difference signal (left figure) and the excluded heading signals of strips H and J (right figure). The original misorientation pattern shows a side lobe pattern of about -15 dB at about 25 °. The excluded misorientation patterns of the vertical strips are significantly different. Near the side lobes is -27 dB at 25 °, forming a deep valley.

In both cases, this side lobe was suppressed by more than 10 dB.
This is most noticeable near the side lobes, which are critical for clutter and jamming.

FIG. 3a shows another embodiment of the invention in which the central portion of the device is selectively excluded in the difference pattern generation. 3b
The figure shows a sum and difference network for providing the desired sum and difference signals. The circuit of Figure 2b has the advantage of also using five hybrids, which is very useful for applications where space is very important (ie missile radar systems, etc.). The data for the embodiment shown in Figures 3a and 3b is comparable to that for the embodiment shown in Figures 2a and 2b.

Accordingly, one embodiment of the present invention can reduce side lobes to misorientation patterns by selectively excluding vertical strips of elements along the azimuth axis, and reducing horizontal strips of elements along the elevation axis. It can be seen that the sidelobe for the altitude difference pattern can be reduced by selectively excluding it.

Eliminating other pre-determined cross-sectional patterns of apertures further optimizes the signal while minimizing circuit complexity and maintaining the quality of the sum signal, that is, the side lobes in the difference pattern. It is also found to allow other combinations for reduction.

It should be further understood that the described embodiments are set forth for clarity and should not be construed as limiting the scope of the claims below.

Claims (2)

[Claims] 1. An antenna device for use in a radar system for tracking a target, comprising a monopulse antenna and a single feed network for forming sum and difference signals, wherein the monopulse antenna (10) has an azimuth direction. It consists of an array of antenna elements (20) symmetrically arranged about the axis and the altitude axis, the array having an aperture (with an area of cross section for transmitting energy towards a target and receiving energy reflected from it ( 12) define this opening (1
2) is the first, second, third, and fourth strip regions (H, I, J, K) of the antenna element (20) group extending from the center of the array of antenna elements (20) to the periphery. ) And four substantially equal quadrants (A, B, C, D) separated by the feed network coupled to the array, the first input being the first To each antenna element of the strip region (K), the second input coupled to each antenna element of the second strip region (I), and from each antenna element of those strip regions (K, I). A first hybrid (41) forming a sum output and a difference output of outputs, a first input coupled to each antenna element of a third strip (H), and a second input connected to a fourth strip. (J) is coupled to each antenna element to form a sum output and a difference output of the outputs from the strip regions (H, J) A hybrid of two (42) and a first input coupled to each antenna element in the first quadrant (A) and a second input coupled to each antenna element in the second quadrant (D), Third hybrid (43) forming sum and difference outputs of those quadrants
And a first input is coupled to each antenna element in the third quadrant (B) and a second input is coupled to each antenna element in the fourth quadrant (C), Fourth hybrid (44) forming sum and difference outputs
And the first input is coupled to the sum output of the first hybrid (41) and the second input is coupled to the sum output of the second hybrid (42) to form and output their sum output. The fifth hybrid (51) and the first input are coupled to the sum output of the third hybrid (43), the second input is coupled to the sum output of the fourth hybrid (44), and their sum is calculated. A sixth hybrid (52) forming and outputting an output and a differential output, the first input is coupled to the differential output of the third hybrid (43), and the second input is the fourth hybrid (44). Of the seven hybrids (53) that are coupled to the difference output of to form and output their sum output, and the first input is coupled to the sum output of the fifth hybrid (51) and the second input is coupled to the Combined to the sum output of the 6 hybrids (52) to form and output those sum outputs An eighth hybrid (61) with a first input coupled to the differential output of the first hybrid (41) and a second input coupled to the differential output of the sixth hybrid (52), A ninth hybrid (62) that forms and outputs a sum output, the first input is coupled to the differential output of the second hybrid (42), and the second input is the sum of the seventh hybrid (53). An antenna device, comprising: a tenth hybrid (63), which is coupled to an output and forms a sum output thereof and outputs the sum. 2. An antenna device for use in a radar system for tracking a target, comprising a monopulse antenna and a single feed network for forming sum and difference signals, wherein the monopulse antenna (10) Consisting of an array of antenna elements symmetrically arranged about an axis and an altitude axis, the array defining an aperture having a cross-sectional area for transmitting energy towards a target and receiving energy reflected therefrom, The aperture is the central area (E) of the antenna element array that surrounds the intersection of the azimuth axis and the altitude axis.
And four surrounding quadrants (A, B, C, D) that are substantially the same
And the feed network is coupled to the array, the first input is coupled to each antenna element in the first quadrant (A) and the second input is coupled to the second quadrant ( A first hybrid (81) coupled to each antenna element of B) to form a sum and difference output of the outputs from those quadrants (A, B), and a first input of which is a third quadrant (C) is coupled to each antenna element, the second input is coupled to each antenna element in the fourth quadrant region (D), and the sum output and difference output of outputs from those quadrant regions (C, D) are provided. Forming a second hybrid (82) and a first input coupled to the sum output of the first hybrid (81) and a second input coupled to the sum output of the second hybrid (82), A third hybrid (91) for forming and outputting a sum output and a difference output thereof, and a first hybrid An input is coupled to the differential output of the first hybrid (81) and a second input is coupled to the differential output of the second hybrid (82) to form and output the differential output of a fourth hybrid ( 92) and a first input is coupled to each antenna element in the central region (E) and a second input is coupled to the sum output of the third hybrid (91) to form their sum output. 5th to output
An antenna device comprising: a hybrid (101).