Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q25/00—Antennas or antenna systems providing at least two radiating patterns
  • H01Q25/02—Antennas or antenna systems providing at least two radiating patterns providing sum and difference patterns

Definitions

• the present invention relates to optimization of antenna sum and difference patterns, and in particular, to a sidelobe suppression arrangement for a monopulse antenna using sum and difference patterns to track targets.
• a monopulse antenna may be subdivided into sections, for example, by using horns or quadrants, and the radar then senses the target displace- ment by comparing the amplitude and phase of the echo signal for each horn or.quadrant.
• the RF circuitry for a conventional antenna divided into quadrants subtracts the output of the left pair from the output of the right pair to sense any imbalance in the azimuth direction (azimuth difference pattern) and the output of the top pair from the output of the bottom pair to sense any imbalance in the elevation direction (elevation difference pattern).
• azimuth difference pattern the output of the left pair from the output of the right pair to sense any imbalance in the azimuth direction
• elevation difference pattern elevation difference pattern
• a sum signal usually representative of the energy received over the entire aperture, is generated and used as a reference signal, for video input, and for gain control.
• feed design and radiation patterns Because optimum sum and difference signals, low sidelobe levels, polarization diversity, compactness, and simplicity cannot all be fully satisfied simultaneously, especially when using a single feed.
• a common approach has been to optimize the sum pattern and to tolerate the resulting difference pattern signal.
• optimizing undesirable features of the difference patterns are important in eliminating significant tracking problems. See Corlin, 4,525,716; June 15, 1985. For example, high sidelobes in the difference signals increase radar susceptibility to interference from background clutter or other off axis sources of radiation which results in tracking error and loss of efficiency.
• the invention is a radar system using sum and difference signals to track targets including aperture means having a cross sectional area for transmitting energy toward a target and receiving return energy and circuit means selectively coupled to said aperture means, said circuit means generating a sum signal using return energy from said aperture means and generating difference signals using return energy from said aperture means exclusive of energy from a predetermined cross-sectional area, whereby said sum and difference signals are simultaneously optimized for the system.
• FIG. 1 is a conventional five horn antenna for providing sum and difference patterns
• FIG. 2a is an embodiment of the invention showing an aperture having an array of elements partitioned into quadrants and strips;
• FIG., 2b is a sum and difference network for providing desired sum and difference signals for the embodiment of FIG. 2a;
• FIG. 3a is an alternative embodiment of the invention showing an aperture having an array of elements partitioned into quadrants and a selectively excluded center section;
• FIG. 3b is a sum and difference network for providing desired sum and difference signals for the embodiment of FIG. 3a;
• FIG. 4a is a comparison of the elevation difference pattern signals for the embodiment of FIG. 2a, before and after selectively excluding elements along the elevation axis in generating the signals.
• FIG. 4b is a comparison of the azimuth difference pattern signals for the embodiment of FIG. 2a, before and after selectively excluding elements along the azimuth axis in generating the pattern signals.
• FIG. 1 There is shown a conventional five horn feed antenna for providing sum and difference signals.
• five horn antennas A, B, C, D, E are arranged with antenna A, the left antenna; B, the top antenna; C the right antenna; D, the bottom antenna; and E, the antenna filling the center space around which antennas A, B, C, and D are arranged.
• An elevation difference signal is obtained by subtracting the return energy from antenna D from the return energy of antenna B and an azimuth difference signal is provided by subtracting the return energy of antenna C from the return energy of antenna A.
• a sum signal is provided by the return energy of antenna E alone.
• This form of antenna feed and others have been used in tracking radar systems but have sufferred from the problem of achieving high sum gain while preserving low sidelobes in the difference patterns.
• Similiar problems are encountered where the antenna consists of a single aperture containing an array of radiating elements and the difference patterns are similiarly generated using one half the aperture minus the opposite half of the aperture.
• the antenna 10 is shown as having an aperture 12 circular in shape and as having an array of radiating and receiving elements 20.
• the antenna is a broadband antenna designed to operate, for example, in a missile.
• the aperture is partitioned into substantially equal and symmetrical quadrants 14, 15, 16, 17.
• Quadrants 14 and 15 define the top elevation hemisphere for aperture 12, while quadrants 16 and 17 define the bottom elevation he pisphere for aperture 12. More particularly, quadrant 14 defines the top left quadrant, quadrant 15 the top right quadrant, quadrant 16 the bottom right quadrant, and quadrant 17 the bottom left quadrant.
• Strip 24 includes strip K, which contains elements which may be taken substantially equally from quadrants 14 and 17.
• Strip 24 also includes strip I which contains elements which may be taken substantially equally from quadrants
• Strip 26 includes strip H, which contains elements which may be taken substantially equally from quadrants 14 and 15 and strip J, which contains elements, which may be taken substantially equally from quadrants
• quadrants A, B, C, and D refer to the remainder of quadrants 14, 15, 16, and 17 in FIG. 2a respectively after taking the respective elements for strips 24 and 26.
• strips 24 and 26 are selectively excluded in generating the difference- pattern signals, resulting in a reduction in the sidelobes for the azimuth and elevation difference- patterns as further explained below.
• FIG. 2b there is shown a diagram of the sum and difference network for connecting the return signals from the quadraRts and strips of FIG. 2b for achieving low difference pattern sidelobes.
• the sum pattern to be used for the antenna of FIG. 2a, to be provided by the network of FIG. 2b, is (A + B + C + D) + ( H + I + J + K); the azimuth difference pattern is (A + D + K) - (B + C + I) ; and the elevation difference pattern is (A + B + H) - (C + D + J).
• each quadrant and strip is selectively coupled with that of one other quadrant or strip at parallel hybrids 41, 42, 43, and 44.
• the hybrids are standard commerically available sum and difference hybrids, i.e, sum and difference magic T*s, commonly used in comparator circuits.
• the coupling coefficient for each hybrid would vary depending on aperture design and would be chosen to provide, as close . as possible, an ideal sum distribution pattern.
• the returns from strips K and I are fed into hybrid 41.
• the returns from strips H and J are likewise fed into hybrid 42.
• the returns from quadrants A and D are fed into hybrid 43.
• the returns from quadrants B and C are fed into hybrid 44.
• K and I are combined at hybrid 41 to orovide (K + I) and the difference is taken at hybrid 41 to provide (K - I) .
• the same process is repeated for H and J at hybrid 42 to provide (H+J) and (H-J); at hybrid 43 to provide (A + D) and (A -D) ; and at hybrid 44 to provide (B + C) and (B - C).
• the outputs from hybrids 41, 42, 43, and 44 are selectively added and subtracted to provide further desirable combinations of quadrants A, B, C, D and strips H, I, J, and K.
• the (K + I) output from hybrid 41 and the (H + J) output from hybrid 42 are combined in phase at hybrid 51 for providing at the output of hybrid 51 (H + J + K + I) .
• the (B + C) output at hybrid 44 is substracted from the (A + D) output of hybrid 43 at hybrid 52 for providing at the output of hybrid 52 (A +D)-(B + C) , and is combined in phase with (B + C) to provide (A + D + B + C) .
• the (A-D) output of hybrid 43 is likewise combined with the (B-C) output of hybrid 44 for providing at the output of hybrid 53 (A + B) - (C + D) and is subtracted at hybrid 53 to provide at the output of hybrid 53, (A + C) - (B + D) which is not used and is therefore terminated.
• the output of hybrid 51 (H + J) + (K + I) is combined with the (A + B) + (C + D) output of hybrid 52 at hybrid 61 to provide (A + B + C + D) + (H + I + J + K) .
• FIG. 4a and FIG. 4b are comparisons of measured data for the original difference signals using the whole ("original") aperture return signal of FIG. 2a compared to the difference signals with the horizontal and vertical strips selectively excluded using the return in FIG. 2b.
• the difference signals are for all practical purposes symmetrical on either side of boresight and the discussion below applies to the sidelobe patterns on both the right and left of boresight.
• FIG. 4a Shown is the original configuration elevation sum and difference signals (left side figure) and the elevation difference signal with horizontal strips I and K excluded (right side figure). It is observed from FIG. 4a that the original elevation difference pattern has a near in sidelobe of around -15dB at around 20°. Compare this to the right side figure of 4a, which depicts the elevation difference pattern with the horizontal strip excluded. Here the near in sidelobes rapidly drop to near -25dB at 30° and form deep nulls.
• FIG. 4b Shown are the original azimuth sum and difference signals (left side figure) and the azimuth difference signal with strips H and J excluded (right side figure).
• the original azimuth difference pattern displays near-in sidelobes of -I5dB at around 25°.
• the azimuth difference pattern with the vertical strip excluded is markedly different.
• the near in.sidelobes are -27 dB at 25° and deep nulls are formed.
• FIG. 3a shows an alternative embodiment of the invention wherein a center section of elements are selectively excluded in generating the difference patterns.
• FIG. 3b shows a sum and difference network for providing the desired sum and difference signals.
• the circuit of FIG. 2b has the advantage of using only five hybrids, which is of high utility for applications where space is very important (i.e., missile radar systems, etc.). Data for the embodiment shown in FIG. 3a and 3b is comparable to that for the embodiment shown in FIG. 2a and FIG. 2b.
• one embodiment of the invention by selectively excluding a vertical strip of elements along the azimuth axis can reduce the sidelobes for the azimuth difference pattern and, by selectively excluding a horizontal strip of elements along the elevation axis can reduce the side ⁇ lobes for the elevation difference pattern.
• excluding other pre ⁇ determined cross section patterns of the aperture may permit further optimization of the signals i.e., permit other combinations for reducing the sidelobes in the difference patterns while minimizing circuit complexity and maintaining sum signal quality.

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• Variable-Direction Aerials And Aerial Arrays (AREA)
• Radar Systems Or Details Thereof (AREA)

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• 1987
  • 1987-10-01 JP JP62506862A patent/JPH0682980B2/ja not_active Expired - Lifetime
  • 1987-10-01 DE DE19873786787 patent/DE3786787T2/de not_active Expired - Fee Related
  • 1987-10-01 WO PCT/US1987/002488 patent/WO1988004109A1/en active IP Right Grant
  • 1987-10-01 EP EP87907265A patent/EP0289553B1/de not_active Expired - Lifetime
  • 1987-10-01 EP EP92116842A patent/EP0544081B1/de not_active Expired - Lifetime
  • 1987-10-06 IL IL8411387A patent/IL84113A/xx not_active IP Right Cessation

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