EP0320553B1 - Adaptive antenna systems - Google Patents
Adaptive antenna systems Download PDFInfo
- Publication number
- EP0320553B1 EP0320553B1 EP19870311217 EP87311217A EP0320553B1 EP 0320553 B1 EP0320553 B1 EP 0320553B1 EP 19870311217 EP19870311217 EP 19870311217 EP 87311217 A EP87311217 A EP 87311217A EP 0320553 B1 EP0320553 B1 EP 0320553B1
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- EP
- European Patent Office
- Prior art keywords
- adaptive
- processor
- output
- loop
- antenna
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
- H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
- H01Q3/2605—Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays
- H01Q3/2611—Means for null steering; Adaptive interference nulling
- H01Q3/2617—Array of identical elements
Description
- This invention relates to antenna systems and in particular to steered adaptive antenna systems.
- The beam pattern of an antenna array is determined by the type of elements in the array, their orientations and position in space and the amplitude and phase of the currents induced in the elements. An adaptive antenna array modifies the pattern in accordance with some control criteria whereby, for example, to steer the beam. In particular adaptive antenna systems are known comprising a plurality of antenna elements and adaptive processor means for processing signals from the antenna elements whereby to steer an adaptive beam pattern, wherein the adaptive processor means applies adaptive complex weights to the amplitudes and phases of the signals from the antenna elements. British patent application GB 2 178903 A discloses an adaptive beamforming network to which the output signals of an array of antenna elements are applied. The summed output of the network forms an 'ERROR' feedback signal which is correlated with each element signal and applied to a limiter the output of which is added to a steering component. The resultant derived value is used to drive a weight coefficient associated with the output of the antenna array element. Also, US patent 4,635,063 discloses an adaptive antenna including an array of elements. A feedback signal is derived from the weighted summed outputs of the elements, the feedback signal being correlated with the element signals. The outputs of the correlators are transformed by algorithms in individual computing means to generate weighting signals for the associated element outputs.
- In many radio communications systems the optimum reception of desired signals may be adversely affected by the presence of one or more unwanted interference or jamming signals. By employing an adaptive antenna array for the receiver it is however possible to modify the associated radiation pattern of the array to create a null(s) centred on the direction of the incoming jamming signal(s).
- In a number of communications systems the position of the transmitter, or angle of arrival, of a wanted signal is known to a moderate degree of accuracy, such that the signal can be put very nearly at the peak of the beam of a beam steering antenna. However, In the presence of high level jamming, even In the sidelobes of the antenna pattern, the signal to noise plus interference ratio (SNIR) falls and the system fails. If the angle of arrival of the wanted signal is known to a very high degree of accuracy, then a steered beam implementation of the Wiener-Hopf solution:
- (* denotes complex conjugate)
- W opt = Optimal Weight Set;
- R = the total covariance Matrix including the signal, interference and noise;
- S = Space Vector corresponding to the complex envelope of the desired signal received across the array aperture;
- A system which is capable of broad acceptance to main lobe signals, whilst retaining the ability to steer nulls towards jamming signals arriving via the side lobes, is thus desirable for various applications.
- According to one aspect of the present invention there is provided an adaptive antenna system comprising a plurality of antenna elements and adaptive processor means for processing signals from the antenna elements whereby to steer an adaptive beam pattern, wherein the adaptive processor means applies adaptive complex weights to the amplitudes and phases of the signals from the antenna elements, characterised in that the adaptive complex weights have inphase and quadrature components and the adaptive processor means includes means for applying variable, but equal, bounding limits to each individual inphase and quadrature component of each adaptive complex weight.
- Embodiments of the invention will now be described with reference to the accompanying drawings, in which:
- Fig. 1 shows plots of output signal to noise ratio for a single misaligned -10dB source for three processor configurations and various misalignments between processor look direction and signal angle of arrival;
- Fig. 2 shows plots of weight norm of the Wiener-Hopf weight set for two -10dB sources, one fixed and the other swept through the main lobe, for various fixed source positions and artificial noise levels, and various misalignments;
- Fig. 3 shows a conceptual processor loop;
- Fig. 4 illustrates the employed I,Q bounding in the complex plane, and
- Fig. 5 shows a digital processor configuration.
- Referring to Fig. 1, which by way of example, shows the output signal to noise ratio for a single misaligned -10dB source for various processor configurations and misalignments between the processor look direction and the signal angle of arrival, with a thermal noise level at -50dB, the array natural beam width being approximately 21 ° .
- Curve (a) of Fig. 1 corresponds to the known optimum weight solution as defined by the Wiener-Hopf equation (1) with "artifical" noise added at a level of -40dB and clearly shows inadequate output signal to noise ratio for misalignments of 1/8° or more.
- Conversely, the conventional beamformer (curve (b)) maintains gain towards the signal, with adequate signal to noise ratio to beyond 16 misalignment, but with no ability to place nulls against other, unwanted, sources. Curve (c) represents the performance of the weight bounding processor of the present invention which, while 10dB lower than the conventional beam former, retains the important ability to null unwanted signals.
- The process of nulling a slightly misaligned signal by a Wiener-Hopf type processor involves considerable weight norm growth, where weight norm is defined as Nw = W"W 1/2. By way of example, Fig. 2 shows the weight norm growth of the Wiener-Hopf weight set for two -10dB sources, one fixed, the other swept through the mainlobe, for various fixed source positions and artificial noise levels, with thermal noise at -50dB . Curve (a) corresponds to the fixed source located at 35 °, well into the sidelobes, with artificial noise at - 40dB, and shows a rapid increase in weight norm away from perfect alignment. However, as long as the misalignment is less than approximately 5°, no significant reduction in output signal level occurs. Thus, signal to noise degradation for a misaligned signal is achieved by increasing the weight norm and hence noise output level instead of reducing the signal output level.
- Hence, signal to noise ratio improvement may be maintained, even for misaligned signals, by limiting the rise of noise output level, that is, by bounding the weight norm. Bounding the weight norm causes no significant degradation of the sidelobe jammer suppression. Curve (b) of Fig. 2 shows by way of example, the weight norm for a perfectly aligned fixed source with artificial noise added at -40dB. It is apparent that beyond the mainlobe, the weight norm shows no increase over that attained had no swept source been present, confirming that, for a perfectly aligned signal, the processor, even when norm bounded, is able to steer nulls towards sidelobe jammers.
- It may be shown (see "Adaptive Array Principles" J.E. Hudson, IEE 1981, pp 175-176) that applying a weight norm bound is equivalent to adding artificial noise to the processor. Thus, by way of example, in order to simulate norm bounding using Wiener-Hopf direct solution method, artificial noise was added at -15dB as shown in curve (c) of Fig. 2. The fixed source is placed with a misalignment of 0.25*. Again the weight norm with the second source in the sidelobes is not significantly above the norm for no swept source present. Hence, provided a sufficient weight norm bound is applied, it is possible to protect a misaligned signal without jeopardising the null steering capability in the sidelobes.
- The hardware implementation of a norm-bound system is complex. However, we have found that a similar effect to norm bounding may be obtained by applying a variable, but equal, limit on each individual I (Inphase) and Q (Quadrature) component of each complex weight, thus each weight may occupy a square in the complex plane (Fig. 4).
- It is thus proposed to use a weight I, Q bounded processor, which is simple to implement in hardware, to protect misaligned signals whilst also suppressing sidelobe jammers.
- The basic structure of the processor loop employed is indicated schematically in Fig. 3. It is based on a conventional steered adaptive control loop using a time-shared digital correlator and serves to "remove" jammers prior to subsequent processing by means (not shown) following
summer 1. Each loop includes aweighting network 2 and the outputs of thevarious weighting networks 2 are applied tosummer 1 which is common. Signals from thesummer 1 are digitised by ADC (analogue-to-digital converter) 4 and negated bynetwork 7 prior to being passed todigital correlator 12. The signal from antenna element A is digitised byADC 3 and the complex conjugate of this digital signal determined bynetwork 5 and passed to thedigital correlator 12. The correlation result fromcorrelator 12, with the appropriate steering vector added thereto as indicated atadder 10, is passed to a bounding network 11. The network 11 compares the current correlation (weight) with the value contained in a memory and outputs either the weight or the bound, dependent on the result of the comparison. The output is converted back to analogue form and the voltage produced by the digital- to-analogue converter (DAC) controls the weight applied bynetwork 2. - Functionally the
digital correlator 12 comprises amultiplier 6, anamplifier 8 and aleaky integrator 9, in series but not necessarily in that order. - Fig. 5 illustrates a more specific digital processor configuration, like reference numerals being used for equivalent elements, which employs a single processor loop. Associated with each antenna element A1 to An is a
respective weighting network 21 to 2n, the outputs of which are applied to the common summer. Signals from the elements A1 to An are selected in turn by ananalogue multiplexer 13, digitised byADC 3, and the complex conjugate of the output ofADC 3 applied to thecomplex multiplier 6 of the digital correlator which in the processor configuration illustrated in Fig. 5 is combined with the means for adding the steering vector (10-Fig.3) to form a digital correlator andbeam steering network 121. Thenetwork 121 consists of five parts; thecomplex multiplier 6; a multiplier-accumulator 14; aparameter memory 15; a correlation memory 16 and asteering vector memory 17. - The correlation result from
network 121 is passed to the bounding network 11 which consists of three parts; acomparater 18; amultiplexer 19 and a boundmemory 20. The network 11 compares the current correlation (weight) with the value held in the boundmemory 20 and outputs either the weight or the bound, dependent on the result of the comparison. This weight (or bound) is directed to the appropriate DAC, 22, to 22n, by ademultiplexer 21, the voltage produced by the DAC controlling the weight applied by theappropriate weighting network 21 to 2n.
may be employed. Alternatively, if some unique signal trait is know, a reference signal may be generated and the optimal weight set thereby obtained. However, with only moderate signal direction accuracy, slight misalignment between the "look" direction and the signal angle of arrival is inevitable. With such a misalignment the "optimal" weight set as defined by the Wiener-Hopf equation (1) steers an antenna null towards the signal, resulting in severe degradation of the output signal to noise ratio.
Claims (7)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP19870311217 EP0320553B1 (en) | 1987-12-18 | 1987-12-18 | Adaptive antenna systems |
DE19873783771 DE3783771T2 (en) | 1987-12-18 | 1987-12-18 | ADAPTIVE ANTENNA SYSTEM. |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP19870311217 EP0320553B1 (en) | 1987-12-18 | 1987-12-18 | Adaptive antenna systems |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0320553A1 EP0320553A1 (en) | 1989-06-21 |
EP0320553B1 true EP0320553B1 (en) | 1993-01-20 |
Family
ID=8198153
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19870311217 Expired - Lifetime EP0320553B1 (en) | 1987-12-18 | 1987-12-18 | Adaptive antenna systems |
Country Status (2)
Country | Link |
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EP (1) | EP0320553B1 (en) |
DE (1) | DE3783771T2 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
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US6823174B1 (en) * | 1999-10-11 | 2004-11-23 | Ditrans Ip, Inc. | Digital modular adaptive antenna and method |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4635063A (en) * | 1983-05-06 | 1987-01-06 | Hughes Aircraft Company | Adaptive antenna |
GB2178903B (en) * | 1985-08-07 | 1989-09-20 | Stc Plc | Adaptive antenna |
-
1987
- 1987-12-18 EP EP19870311217 patent/EP0320553B1/en not_active Expired - Lifetime
- 1987-12-18 DE DE19873783771 patent/DE3783771T2/en not_active Expired - Fee Related
Also Published As
Publication number | Publication date |
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EP0320553A1 (en) | 1989-06-21 |
DE3783771T2 (en) | 1993-05-06 |
DE3783771D1 (en) | 1993-03-04 |
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