Antenna array system with different beamforming networks and nonlinear filtering to mitigate interference

Abstract

The present invention discloses an antenna array system, which includes an antenna array of N≥2 antenna elements that outputs N antenna signals; an interference source return-to-null beam forming network (IN‑BFN) coupled to the antenna array, N nonlinear filters coupled to the IN‑BFN, and a desired signal BFN. The IN‑BFN may include N "null BFNs" to generate N null signals, each null BFN applying a corresponding return-to-null beam weight set to the N antenna signals to generate a corresponding one of the N null signals. Each corresponding return-to-null beam weight set corresponds to a different set of corresponding (N‑1) independent nulls. Each of the N nonlinear filters may filter a corresponding one of the N null signals to provide a corresponding one of the N filtered signals. The desired signal BFN may apply a desired signal beam weight set to the N filtered signals to generate an output signal.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 62 / 714,547, filed in the U.S. Patent and Trademark Office on August 3, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to antenna arrays, and more particularly to techniques for mitigating interfering signals received by an antenna array and thereby improving the signal quality of received desired signals.

[0004] Discussions in related fields

[0005] Antenna systems employing antenna arrays of N antenna elements (N = two or more) may occasionally face operational challenges of accurately recovering information carried by a weak desired signal received in a noisy environment with N stronger interfering signals (interchangeably referred to as "interfering signals"). In addition, the desired signal and / or the N interfering signals may arrive at the antenna array from unknown directions. That is, the interfering signals may have different unknown spatial eigenvectors. In addition, the interfering signals and the desired signal may partially or completely overlap in the time domain and the frequency domain.

[0006] Conventional signal processing methods for attenuating interfering signals, such as those employing linear spatial filtering or conventional excision algorithms, are generally unable to recover the desired signal in such environments without unsatisfactorily degrading its signal quality and signal-to-noise ratio. Summary of the invention

[0007] In one aspect of the technology disclosed in the present invention, an antenna array system includes an antenna array of N≥2 antenna elements that outputs N antenna signals; an interference source return-to-null beamforming network (IN-BFN) coupled to the antenna array; N nonlinear filters coupled to the IN-BFN; and a desired signal BFN. The IN-BFN may include N "null beamforming networks" (null BFNs) to generate N null signals, each null BFN applying a corresponding return-to-null beam weight set to the N antenna signals to generate a corresponding one of the N null signals. Each corresponding return-to-null beam weight set corresponds to a different set of corresponding (N-1) nulls. Each of the N nonlinear filters may filter a corresponding one of the N null signals to provide a corresponding one of the N filtered signals. The desired signal BFN may apply a desired signal beam weight set to the N filtered signals to generate an output signal.

[0008] The antenna array system can improve the signal quality of a desired weak signal in an environment with N stronger interfering signals by significantly attenuating the interfering signals relative to the desired signal. The N interfering signals may each arrive at the antenna array from a different direction.

[0009] On the other hand, a method for suppressing multiple interference signals received by an antenna array that simultaneously receives a desired signal involves: receiving N antenna signals from an antenna array including N antenna elements, where N is greater than one. Obtaining a corresponding direction of arrival of the interference signal on the antenna array. Applying each of a plurality of return-to-null beam weight sets to a corresponding one of the N null BFNs of an interference source return-to-null beam forming network coupled to the antenna array to generate N null signals. Each return-to-null beam weight set corresponds to a different corresponding set of (N-1) independent nulls corresponding to (N-1) directions of arrival, so that within each null signal, (N-1) interference signals in the interference signal are suppressed relative to each of the remaining one interference signal in the interference signal and the desired signal. Using a corresponding one of the N nonlinear filters, each of the N null signals is filtered to suppress the corresponding remaining one interference signal in the interference signal relative to the desired signal, thereby generating N filtered signals. The N filtered signals are combined to generate an output signal corresponding to the desired signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and other aspects and features of the disclosed technology will become more apparent from the following detailed description in conjunction with the accompanying drawings, in which the same reference numerals indicate the same elements or features. Various elements of the same or similar type can be distinguished by attaching the reference numeral directly to a second label or to a dash and a second label (e.g., -1, -2) that distinguish the same / similar elements. However, if a given description uses only the first reference label, it applies to any of the same / similar elements with the same first reference label, regardless of the second reference label.

[0011] Figure 1 is a functional block diagram of an antenna array system according to an embodiment.

[0012] Figure 2 yes Figure 1 A schematic block diagram of an implementation scheme of an antenna array system.

[0013] Figure 3A , Figure 3B and Figure 3C is a block diagram of a corresponding exemplary antenna array system in which a processor / controller is configured to detect interfering signals and calculate their angles of arrival at the antenna array.

[0014] Figure 4A graph is shown illustrating exemplary components of various signals in an antenna array system according to an embodiment.

[0015] Figure 5 is a flow chart of an exemplary method performed by an antenna array system for mitigating interfering signals.

[0016] Figure 6 is a schematic diagram illustrating exemplary signals arriving at an antenna array of an exemplary antenna array system.

[0017] Fig. 7A , Figure 7B and Figure 7C Each shows a respective graph of an exemplary radiation pattern for a corresponding scan angle condition established by an exemplary antenna system.

[0018] Figure 8 is a schematic diagram showing an example of standard deviation of antenna received signal power at different scanning angle settings in an exemplary antenna array system to illustrate an exemplary method of determining the arrival direction of an interference signal.

[0019] Fig. 9 is an exemplary graph of antenna received signal power versus standard deviation of the spatial signal vector θ, illustrating an exemplary technique for determining the direction of arrival of an interfering signal.

[0020] Fig.10 is a flow chart of an exemplary method performed by an antenna array system for mitigating interfering signals. DETAILED DESCRIPTION

[0021] For illustrative purposes, the following description is provided with reference to the accompanying drawings to assist in a comprehensive understanding of certain exemplary embodiments of the technology disclosed herein. The description includes various specific details to assist one of ordinary skill in the art in understanding the technology, but these details should be considered as merely exemplary. When including a description of known functions and structures may obscure a skilled person's understanding of the technology, the description of known functions and structures may be omitted for clarity and brevity.

[0022] In this article, a signal that "substantially" only contains components of one or more specific signals means that the signal may also contain components of one or more other signals in a minimum amount, which does not exclude the use of the signal to achieve the purpose it is intended to provide. For example, in some embodiments, the components of one or more other signals may be at least 10 dB lower than the components of one or more specific signals. As another example, in some embodiments, the components of one or more other signals may be at least 20 dB lower than the components of one or more specific signals. As yet another example, in some embodiments, the components of one or more other signals may be at least 30 dB lower than the components of one or more specific signals.

[0023] In this article, the term "nonlinear filter" refers to a filter whose output signal is not a linear function of its input signal. A nonlinear filter as described herein filters the magnitude of an input signal to remove a constant envelope component of the input signal. The input signal may be a superposition of a constant envelope interference signal and a desired signal. The nonlinear filter removes the interference signal component of the input signal, thereby generating an output signal containing the desired signal component of the input signal. In such a case, the nonlinear filter can recover the desired signal within the input signal even if the amplitude of the interference signal is high and overlaps with the desired signal in the time domain and frequency domain.

[0024] Embodiments described herein provide an antenna array system having N antenna elements (where N is greater than or equal to 2) that can mitigate (e.g., suppress or remove) interference caused by up to N interfering signals relative to a desired signal. As described in more detail below, N antenna signals from the N antenna elements can be provided to each of N different "null beamforming networks" (null BFNs) of an "interference source return-to-null beamforming network" (IN-BFN). Each null BFN applies a corresponding return-to-null beam weight set to the N antenna signals to generate a corresponding null signal. The corresponding return-to-null beam weight set corresponds to N-1 independent null sets of corresponding antenna patterns of the N antenna signals. In this article, the term "independent null" refers to the null of the corresponding antenna pattern, which can be independently formed in a specific direction independent of the direction of other independent nulls by applying the corresponding return-to-null beam weight set to the N antenna signals. The weighting of the N antenna signals of the N antenna elements can define a corresponding antenna pattern with N-1 independent nulls. Depending on the individual element patterns of the antenna elements and the arrangement of the antenna elements in the array, the corresponding antenna pattern may also include additional zeros that are not independent zeros. The corresponding zeroing beam weight set of each zero position BFN of the interference source zeroing BFN may correspond to a different set of independent zeros that vacate all interference signals except one of the interference signals. Each zero position BFN outputs a "zero position signal", which is a composite signal having a desired signal component and an interference signal component, and then the zero position signal is nonlinearly filtered to suppress / remove the interference signal component and restore the desired signal. Nonlinear filtering can remove the interference signal component, even if its spectrum bandwidth may overlap with the spectrum bandwidth of the desired signal. Therefore, using the technology described in this article, an antenna array with as few as N antenna elements can be used to restore a desired signal with a spectrum overlapping with the spectrum of up to N interference signals. On the other hand, a conventional N-element beamforming system makes N-1 interference signals zero. Conventional methods using linear beamforming technology cannot separate spatially overlapping co-channel and co-polarization signals. Therefore, the technology disclosed in the present invention suppresses more interference signals than these conventional methods.

[0025] Figure 1 1 is a functional block diagram of an antenna array system 100 according to an implementation of the technology disclosed in the present invention. The antenna array system 100 may include N antenna elements 30-1 to 30-N forming an antenna array, an "interference source nulling (IN-) beamforming network (BFN)" 10 that generates N "null signals"; N nonlinear filters 40-1 to 40-N, which output N filtered signals; and a "desired signal BFN" 20. To facilitate understanding of the technology described herein, the following description will mainly discuss an example of N=2. The following will discuss an implementation using N=three or more. Therefore, the exemplary dual-element array antenna system 100 includes a first antenna element 30-1 and a second antenna element 30-2 and two nonlinear filters 40-1, 40-2. The antenna array system 100 can be designed to operate on any desired radio frequency (RF) band.

[0026] The following discussion of the N=2 embodiment will generally be described as receiving a weaker desired signal "b" in an environment where a first stronger interference signal a1 and a second stronger interference signal a2 may also be received. The desired signal b and each of the interference signals a1, a2 may arrive at the antenna array from different directions. In the later discussed N=three or more embodiments, the antenna array system 100 may include the capability to mitigate each of the three or more interference signals.

[0027] Interference source nulling BFN ("IN-BFN") 10 receives first antenna signal AS1 and second antenna signal AS2 from antenna elements 30-1 and 30-2, respectively, each antenna signal including signals b, a1 and a2 (plus noise "w", discussed later). Figure 1As shown, the first null BFN of the IN-BFN 10 generates a first null signal originating from the antenna signals AS1 and AS2, i.e., null signal #1. Null signal #1 is a signal in which the interference signal #1 is removed due to "nulling", while the desired signal b and the interference signal #2 (if also received) remain. Such nulling can be achieved by applying the first nulling beam weight (NBW) set bw1 of the multiple NBW sets bw1 to bwN to the antenna signals AS1 and AS2 by the first null BFN within the IN-BFN 10. The first NBW set bw1 indicates the amplitude and / or phase values ​​to be applied to the antenna signals AS1 and AS2 to define a first antenna pattern having an independent null aligned with the arrival direction of the interference signal #1. In the example shown with N=2, the corresponding antenna pattern has one independent null. Therefore, no independent null is aligned with the arrival direction of the desired signal b or the interference signal #2. Therefore, null signal #1 may contain the desired signal b and the interference signal #2. Similarly, the second null BFN of IN-BFN 10 can apply a second return-to-null beam weight set bw2 (from the set bw1 to the set bwN) to the antenna signals AS1 and AS2 to generate a second null signal, namely, null signal #2. The second return-to-null beam weight set bw2 corresponds to a second antenna pattern whose independent nulls are aligned with the arrival direction of the interference signal #2. In doing so, the interference signal #2 is removed, but the desired signal b and the interference signal #1 can be retained in the null signal #2.

[0028] The null signals #1 and #2 are then applied to corresponding nonlinear filters 40-1 and 40-2, which filter out interference signals a2 and a1, respectively. As previously described, a nonlinear filter refers to a filter configured to receive a signal containing an undesired signal (e.g., an interference signal) and a desired signal and output a filtered signal, wherein the signal energy of the undesired signal is completely removed or suppressed relative to the desired signal even if the undesired signal overlaps with the desired signal in the frequency domain and the time domain. The resulting pair of filtered signals, i.e., filtered signals #1 and #2, are applied to the desired signal BFN 20, which applies a "desired signal beam weight set" bw3 (where bw(N+1)=bw3 for the case where N=2), and the weighted filtered signals are combined to generate an output signal OS consisting essentially only of the desired signal b component. As explained later, the desired signal beam weight set can be applied to two or more weighted paths within the desired signal BFN 20 to maximize the output signal OS. The desired signal beam weight set indicates amplitude and / or phase values ​​to be applied to filtered signals #1 and #2 to define a third antenna pattern having a beam peak aligned with the direction of arrival of the desired signal b.

[0029] In the following discussion, narrowband channelization of an array of N = 2 antenna elements (also referred to as a "dual element array") may be considered by using the following phase shift. More generally, time delays may be used for wider bandwidth channelization mathematical considerations. The received uniform plane wave spatial signature may be represented by equation (1). The transpose operator is given by [.] T Therefore, the spatial eigenvector in equation (1) is a complex-valued C 2x1 Vector space.

[0030]

[0031] The time series of the first interference signal a1 received by the dual-element array can be expressed by equation (2), which is the complex value C when there are M time domain samples from each of the two antenna elements. 2xM A vector in a vector space.

[0032]

[0033] Following the same form, the time series of the second interference signal a2 received by the dual-element array can be expressed by equation (3):

[0034]

[0035] The time series of the desired signal b received by the dual-element array can be expressed by equation (4):

[0036]

[0037] The final component can be a complex-valued additive white Gaussian noise (AWGN) w (expressed in equation (5)) with zero mean and covariance σ 2 I, where I represents the identity matrix.

[0038] w[n]=[w1[n]w2[n]] T Equation (5).

[0039] The dual element array consisting of antenna elements 30-1 and 30-2 delivers antenna signals AS1, AS2, which can be represented as complex valued 2xM matrix vector signals:

[0040] AS[n]=a1[n]+a2[n]+b[n]+w[n] Equation (6)

[0041] Where AS is any one of the antenna signals AS1 to AS2. For example, for two element arrays and M time domain samples, there will be 2xM samples.

[0042] Embodiments of this paper can estimate b[n] and recover data from b[n] of given AS[n]. Any phase modulation can be independent between interference signal and expectation. In addition, interference signals a1, a2 can each have completely random phase modulation. Each of interference signals a1 and a2 can completely overlap with desired signal b in time and frequency. Therefore, interference signals a1, a2 may not be fully separated from desired signal b using linear filters or linear spatial filters. Embodiments described herein use nonlinear signal processing to perform signal separation.

[0043] Figure 2 is a schematic block diagram of an antenna array system 100-a, which may be Figure 1 The antenna array system 100-a includes an antenna array with N≥2 antenna elements, where N=2. Figure 2 The antenna array system 100-a may also include: an interference source nulling BFN (IN-BFN) 10-a; nonlinear filters 40-1, 40-2; a controller 70 coupled to a memory 80; and a desired signal BFN 20-a.

[0044] IN-BFN 10-a is coupled to each of antenna elements 30-1 and 30-2 and includes a first null BFN 18-1 and a second null BFN 18-2. Antenna elements 30-1 and 30-2 provide antenna signals AS1 and AS2 to each of the first null BFN 18-1 and the second null BFN 18-2, which output first null signals NS1 and second null signals NS2 derived from antenna signals AS1 and AS2, respectively. As described in more detail below, each null BFN 18 applies weights to antenna signals AS1 and AS2 to define different antenna patterns with independent nulls aligned in the directions of arrival of different interference signals.

[0045] Antenna signal AS1 routed from antenna A1 on transmission line 62 is divided between transmission lines 61 and 60 and provided to first null BFN 18-1 via transmission line 61 and to second null BFN 18-2 via transmission line 60. Antenna signal AS2 from antenna 30-2 on transmission line 64 is divided between transmission lines 65 and 66 and provided to first null BFN 18-1 via transmission line 66 and to second null BFN 18-2 via transmission line 65.

[0046] The first null BFN 18-1 includes a first signal weighting path P1 having a variable phase shifter 12-1 coupled in series with a variable amplitude adjuster 14-1 to apply phase and amplitude adjustments to the antenna signal AS1 in response to a first return-to-null beam weight (NBW) set bw1 provided by the controller 70. The amplitude adjuster 14 may include a variable attenuator and / or a variable gain amplifier. It is noted that in some applications, the amplitude adjuster 14 may be omitted in the antenna array system 100-a. The first null BFN 18-1 also includes a second signal weighting path P2 having a variable phase shifter 12-2 coupled in series with the variable amplitude adjuster 14-2 to apply phase and amplitude adjustments to the antenna signal AS2 in response to the first NBW set bw1 provided by the controller 70. The outputs of the signal weighting paths P1 and P2 are combined to output a first null signal NS1. The second null BFN 18-2 includes a third signal weighting path P3 having a variable phase shifter 12-3 coupled in series with a variable amplitude adjuster 14-3 to apply phase and amplitude adjustments to the antenna signal AS1 in response to a second NBW set bw2 provided by the controller 70. The second null BFN 18-2 also includes a fourth signal weighting path P4 having a variable phase shifter 12-4 coupled in series with a variable amplitude adjuster 14-4 to apply phase and amplitude adjustments to the antenna signal AS2 in response to a second NBW set bw2 provided by the controller. The outputs of the signal weighting paths P3 and P4 are combined to output a second null signal NS2. The controller 70 also applies the desired signal beam weight set bw3 to the desired signal BFN 20-a to achieve a peak output signal OS (substantially containing only the desired signal b component).

[0047] The controller 70 includes control circuitry to generate a first NBW set bw1 to a first null BFN 18-1 corresponding to a first antenna pattern having independent nulls aligned in the direction of arrival of the interference signal #1. The NBW set bw1 may be composed of control signals that control the phase shifts of the phase shifters 12-1, 12-2 and the amount of amplitude adjustment performed by the amplitude adjusters 14-1, 14-2. Similarly, the controller 70 may provide a second null BFN 18-2 of beam weights corresponding to a second antenna pattern having independent nulls aligned in the direction of arrival of the interference signal #2 to the second NBW set bw2. The controller 70 may be embodied with processing circuitry that may be in the form of a general or special purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof to perform its operations as described herein. For example, the controller 70 may read and execute instructions read from the memory 80 to perform its operations. The memory 80 may be any suitable non-transitory computer-readable storage medium.

[0048] In one embodiment, the controller 70 receives an arrival direction signal AoA indicating the angle of arrival of any interfering signals from an external system (not shown). In this case, the controller 70 can retrieve the NBW set bw1, bw2 and the desired signal beam weight set bw3 from a lookup table stored in the memory 80, or can calculate the NBW set bw1, bw2 and the desired signal beam weight set bw3 using an algorithm based on equations (1) to (6) herein. In other embodiments, the controller 70 includes processing circuitry that detects any interfering signals and generates an A / D conversion signal based on the input from the coupler, sample / hold, and A / D conversion circuitry (in the example of FIG. 1 ) within the antenna array system 100-a. Figure 2 The sampling signals SS coupled to the receiver (not shown) are used to calculate their arrival angles.

[0049] In doing so, the null signal NS1 is substantially composed of only the interference signal a2 component and the desired signal b component. Similarly, the null signal NS2 is substantially composed of only the interference signal a1 component and the desired signal b component.

[0050] The antenna array system 100 - a also includes N nonlinear filters 40 - 1 to 40 -N, each of which is coupled to the output of the null BFN 18 . Figure 2 1 and 2 for two antenna elements. The filters 40-1 and 40-2 convert the filtered signals FS1 and FS2 (similar to Figure 1The desired signal BFN 20-a may include a fifth signal weighting path P5, in which the variable phase shifter 12-5 is coupled in series with the amplitude adjuster 14-5; and a sixth signal weighting path P6, in which the variable phase shifter 12-6 is coupled in series with the amplitude adjuster 14-6. The desired signal BFN 20-a may receive a desired signal beam weight set bw3 from the controller 70 for weighting the signals FS1 and FS2 to define a third antenna pattern having a beam peak aligned with the arrival direction of the desired signal b, thereby forming an output signal that substantially only contains the desired signal b component. The NBW sets bw1 and bw2 and the desired signal beam weight set bw3 may vary from implementation to implementation and depend on the individual element patterns of the antenna elements 30-1, 30-2 and the arrangement of the antenna elements 30-1, 30-2 in the array (e.g., spacing, orientation, etc.).

[0051] The interference source nulling BFN 10-a and the desired signal BFN 20-a can perform analog or digital beamforming. In an analog beamforming embodiment, the phase shifter 12 and the amplitude adjuster 14 (if any) use analog circuits. For a digital beamforming embodiment, each of the antenna signals AS1, AS2 can pass through an analog-to-digital (A / D) converter to form a corresponding digital data stream. In such a case, the phase shifter 12 and the amplitude adjuster 14 can be implemented by a processing circuit (e.g., within the controller 70) that executes instructions to implement digital beamforming. Similarly, the nonlinear filters 40-1, 40-2 and the desired signal BFN 20-a can be implemented with dedicated circuit elements (analog circuits and / or digital circuits) or by a processing circuit of a processor that executes instructions for digital signal processing in a virtual case.

[0052] As described above, in some embodiments, the controller 70 may be configured to calculate the angular direction of arrival of any interfering signal. In this case, in order to determine whether there are any interfering signals and their direction of arrival, the controller 70 may (as part of a test routine) provide sequentially different weighted values ​​for the NBW set bw1 and / or the NBW set bw2 to form individual antenna patterns that effectively steer the beam (and steer the zero position of the beam) within the desired spatial region. The direction of arrival of any interfering signal may then be determined by the controller 70 using any suitable algorithm. An example is a method based on standard deviation (SD) described in further detail later. In such an SD-based method, the controller 70 may store the temporary scanning beam SD results in the memory 80 to find the SD minimum among all SD results. As described later, in order to identify the direction of arrival, the controller 70 may obtain signal samples through a coupler, a sample-and-hold circuit, and an A / D converter.

[0053] In some embodiments, the controller 70 may be configured to change the mode operation of the antenna array 100-a over time based on the number of interfering signals present. In some embodiments, when the number of interfering signals is N (in this example, N=2), the controller 70 may control the antenna system 100-a (and more generally, the antenna array 100-a) by forming N null signals, etc. Figure 1 In contrast, when the number of interference sources is less than N, the controller 70 may control the antenna system 100-a (and more generally, the antenna system 100-b) to operate in the first mode as described above. Figure 1 The antenna system 100) operates in a second mode. In the second mode, the controller provides a collective beam weight set to a specific one of the null positions BFN of the interference nulling BFN. When the number of interference sources is less than N, the N antenna elements provide sufficient degrees of freedom so that when applied to N antenna signals, the collective beam weight set defines an antenna pattern having independent null positions aligned with the arrival direction of each of the (less than N) interference sources, while also having a beam peak aligned with the arrival direction of the desired signal. The collective beam weight set can be calculated or otherwise obtained by the controller 70, such as by using the above-mentioned techniques. In the second mode, the output signal NS1 ("beam signal") of the specific null position BFN of the interference nulling BFN is a beam signal corresponding to the desired signal b. In some embodiments, in the second mode, the controller 70 controls a bypass circuit (not shown) of the antenna array (e.g., a switch) to selectively bypass the nonlinear filter and the desired signal BFN, and provides the beam signal to an additional processing circuit (not shown), which demodulates and processes the beam signal in a manner similar to processing the output signal OS output by the desired signal BFN in the first mode. In other embodiments, in the second mode, the beam signal passes through the corresponding nonlinear filter, and the controller 70 provides a through beam weight set to the desired signal BFN, which allows the beam signal to reach the output of the desired signal BFN through the corresponding signal path and attenuates (e.g., by applying a zero weight) other signal paths within the desired signal BFN.

[0054] Figure 3A , Figure 3B and Figure 3C 1 is a block diagram of a respective embodiment of an antenna array system in which a controller is configured to detect interference signals and calculate their angles of arrival at the antenna array. Each embodiment includes a circuit for providing a sequence of signal samples to the controller so that the controller can detect any interference signals and their angles of arrival. Other aspects of these embodiments may be the same as those already described for antenna array systems 100 and 100-a.

[0055] like Figure 3AAs shown, the antenna array system 100-b includes a first directional coupler ("coupler") C1 coupled between the antenna 30-1 and the IN-BFN 10-a and a second directional coupler C2 coupled between the antenna 30-2 and the IN-BFN-10-a. Couplers C1 and C2 couple signal energy from antenna signals AS1 and AS2 to provide coupled signals AS1-c and AS2-c to sample / hold circuits 32-1 and 32-2, respectively. The sampling levels output from the sample / hold circuits 32-1 and 32-2 are applied to corresponding analog-to-digital (A / D) converters 34-1 and 34-2, which output sampling sequences SS-1 and SS-2 to the controller 70, respectively. Each instance of the sampling sequence SS-1 or SS-2 may consist of M equally spaced samples. (In Figure 2 and Figure 3A-3C In the antenna array system of each of the above, another directional coupler (not shown) may be provided at the output of the desired signal BFN 20-a to couple the signal energy from the output signal OS back to the controller 70 through another path having a series connection of the sample and hold circuit 32 and the A / D converter 34 in a similar manner. This feedback may facilitate the controller 70 to set the desired signal beam weight set bw3 to peak the output signal OS. )

[0056] like Figure 3B As shown, the antenna array system 100-c differs from the embodiment 100-b in that it includes couplers C1 and C2 placed between the interference source nulling BFN 10 and the nonlinear filters 40-1 and 40-2, respectively. In this case, the couplers C1 and C2 couple the signal energy from the null signals NS1 and NS2 to provide the coupled signals NS1-c and NS2-c to the sample / hold circuits 32-1 and 32-2, respectively. Figure 3C Another embodiment of an antenna array system 100-d is shown, in which couplers C1 and C2 are placed between nonlinear filters 40-1 and 40-2, respectively. Here, couplers C1, C2 couple the signal energy of signals FS1, FS2 to provide coupled signals FS1-c, FS2-c to sample / hold circuits 32-1, 32-2, respectively. Other aspects of antenna array systems 100-c and 100-d may be the same as described for antenna array system 100-a. Note that two antenna element examples are depicted in each case, but these concepts are equally applicable to systems having N≥3 antenna elements 30-1 to 30-N and N≥3 null BFNs 18 by using N couplers C together with N sample / hold circuits 32 and N A / D converters 34 in the corresponding signal paths.

[0057] Figure 4A graph is shown illustrating exemplary components of various signals in antenna array system 100 after a set of nulling beam weights has been fixed to achieve the desired nulling of the interference signal described above. (Here, and in the subsequent description, reference to antenna array system 100 applies to any of antenna array systems 100, 100-a, 100-b, 100-c, or 100-d unless the context indicates otherwise.) As can be seen, null signal #1 may be primarily composed of a first interference signal a2 and a signal b-1 representing a first portion of the signal energy of the desired signal b received by antenna elements 30-1 and 30-2. (Signals b-1 and b-2 are understood to be part of the incoming desired signal b due to their power distribution between null BFNs 18-1 and 18-2.) Noise w may also be present in the null signal, but is removed from the null signal for clarity of explanation. Figure 4 . The zero signal #2 may be mainly composed of the second interference signal a1 and the signal b-2 representing the second part of the received desired signal b. The levels of the signals a1 and a2 may be respectively at least one order of magnitude greater than the levels of the signals b-1 and b-2. Each of the interference signals a1 and a2 may have a spectrum content that partially or completely overlaps with the spectrum content of the desired signal b. Each of the interference signals a1 and a2 is also shown in this example as occupying a frequency range that is approximately the same as the frequency range of the desired signal b. In other cases, the bandwidth of the desired signal b only partially overlaps with the bandwidth of the interference signal, and / or has a bandwidth that is narrower or wider than the bandwidth of the interference signal.

[0058] The zero signal #1 is filtered by a nonlinear filter 40-1, which removes the interference signal a2 and outputs a filtered signal #1 consisting mainly of the desired signal portion b-1, as shown. Similarly, the zero signal #2 is filtered by a nonlinear filter 40-2 to produce a filtered signal #2 consisting mainly of the desired signal portion b-2. Such nonlinear filtering for removing a single interference signal from a composite signal and recovering the desired signal from the composite signal can be implemented in any suitable manner. One example uses a "polarity excision" method, such as described in the inventor P. Wyckoff's U.S. Patent Publication 2015 / 0311999A1 on October 29, 2015, "Systems and methods for reducing a relatively high power, approximately constant envelope interference signal that spectrally overlaps a relatively low power desired signal (systems and methods for reducing relatively high power approximately constant envelope interference signals that spectrally overlap with relatively low power desired signal spectrum)". Such a polarity excision method can derive the in-phase (I) and quadrature-phase (Q) components of the received signal and convert the I and Q components into polar signals. The estimated amplitude of the interference signal can be obtained from the amplitude and phase samples of the polar signal obtained in the time domain. The desired signal can be obtained by analyzing the difference amplitude of each time domain sample in polar coordinates based on the amplitude of the sample and the estimated amplitude of the interference signal. Another exemplary polarity excision method is described in Henttu's "A New Interference Suppression Algorithm Against Broadband Constant Envelope Interference," IEEE Miclom 2:742-746 (2000). The method requires converting the composite received signal into polar coordinates, calculating the fast Fourier transform (FFT) of the amplitude sample sequence, and then excising the spectrum of the amplitude sample. The excised spectrum is then transformed into the time domain using the inverse FFT (iFFT). It should be noted here that if the antenna array system 100 utilizes a polarization removal method, orthogonal demodulation is performed to convert the RF signal to baseband and derive I and Q signal components before converting the RF signal to a polarity signal; therefore, the blocks of nonlinear filters 40-1 and 40-2 can be considered to include suitable demodulation circuits for this purpose.

[0059] In addition to the two polarity excision techniques just outlined, other nonlinear filtering techniques may be used to recover the desired signal portions b-1 and b-2 from the null signals #1 and #2. The desired signal portions b-1 and b-2 may be combined by the desired signal BFN 20 to obtain an output signal OS (consisting essentially of the signal energy of only the desired signal b) having a signal level higher than the signal levels of the individual signal portions b-1 and b-2.

[0060] Figure 5 Flowchart of an exemplary method 500 for mitigating interference signals performed by the antenna array system 100. Antenna signals received by the antenna array system are routed (S502) from antenna elements 30-A1 to 30-N to each of the N null BFNs 18. Estimated directions of arrival of the N interference signals (if any) are obtained (S504). As described above, the directions of arrival may be determined by an external system and provided to the controller 70 as signal AoA. Alternatively, the controller 70 may determine whether there are interference signals, and if there are interference signals, calculate their directions of arrival based on a sampling sequence obtained from the signal path using a directional coupler, a sample / hold circuit, and an A / D converter as previously described.

[0061] N return-to-zero beam weight sets bw1-bwN may then be generated (S506), each return-to-zero beam weight set being used to form different beams having different sets of (N-1) nulls at (N-1) of the arrival directions, respectively. Each return-to-zero beam weight set bw may then be applied (S508) to a different null BFN 18, such that each null BFN 18 outputs a null signal having only one interference signal. In the example of a 2-element antenna array having two null BFNs 18-1 and 18-2, each having two signal paths (e.g., P1, P2), an antenna pattern having a first null and a second null may be formed at a typical spacing, depending on the spacing of the array elements 30-1 and 30-2. In this case, if the values ​​of the return-to-zero beam weight set bw are sorted to "steer" the first null over a spatial region, the second null is also manipulated, but not independently of the first null. In other words, in any given null BFN 18, there is one degree of freedom for manipulating the null. Considering another example of N=3, each null BFN 18 may then have three signal paths, each having an independently settable phase shifter 12. In this case, two of the nulls may be independently manipulated by adjusting the nulling beam weight set bw applied to the null BFN 18. The two independently manipulable nulls may be manipulated to coincide with two interfering signals that have arrived from two different directions of arrival. Thus, in the general case where N null BFNs each receive N antenna signals AS1-ASN, there are (N-1) degrees of freedom in each null BFN for digitally manipulating the nulls thus formed. Thus, each null BFN effectively eliminates all but one interfering signal.

[0062] In the case where each null BFN 18 outputs a null signal containing a portion of the desired signal b and substantially only one different interference signal, the method 500 uses nonlinear filters 40-1 to 40-N to nonlinearly filter the null signal (S510) to provide N filtered signals FS1-FSN composed of desired energy (e.g., the above-mentioned signals b-1, b-2). The filtered signals are then combined (S512) to peak the output desired signal.

[0063] Figure 6is a schematic diagram showing an exemplary signal arriving at the antenna array of the antenna array system 100. To simplify the description, antenna elements 30-1 and 30-2 are depicted as isotropic elements separated by a distance d. The type (e.g., dipole, microstrip patch, etc.) and distance d (e.g., λ / 4, λ / 2, etc.) of antenna elements 30-1 and 30-2 can be selected to achieve any suitable design goal. Antenna elements A1 and A2 are aligned along axis x so that the normal axis y can be drawn to the center of the antenna array at the origin "o". An angle θ in the yx plane can be drawn relative to the y-axis and a line intersecting the origin o.

[0064] An example is given below to facilitate understanding of the systems and methods described herein. In this example, the first interference signal a1 arrives at the origin o from an angle θa1=10°; the second interference signal a2 arrives at an angle θa2=80°; and the desired signal b arrives at an angle θb. In this example, the interference signals a1 and a2 are constant envelope signals with approximately equal signal strengths, and each arrives with a signal strength that is at least one order of magnitude higher (i.e., at least 10 times higher) than the desired signal b. In this example, the antenna elements 30-1, 30-2 are positioned in free space, resulting in a field strength pattern spanning + / -180°. Alternatively, they may be placed above a ground plane, in which case a pattern spanning + / -90° may be spanned.

[0065] Fig. 7A An exemplary antenna pattern that can be established using the interferer nulling BFN 10 of the antenna array system 100 is shown. This pattern corresponds to "Scan Case 1" where Figure 2 The antenna signals of antenna elements A1 and A2 are weighted with equal insertion phase and loss. This produces an ideal broadside pencil beam pattern with a beam peak θsc=0°, a first null at θw1=90°, and a second null at θu1=-90°. Before applying the corresponding set of return-to-null beam weights applied to the corresponding null BFN 18-1 or 18-2 to null out one of the interfering signals, the antenna pattern for the scanning case can be assumed to be given by Figure 1 The zero position signal #1 or zero position signal #2 indicates that. Therefore, Fig. 7A May correspond to a scanning beam formed during an initial step before obtaining the direction of arrival of one or more interfering signals to be nulled. Since signal a1 arrives at an angle close to the beam peak, and signal a2 arrives close to the beam null, the resulting null signal #1 or null signal #2 will have a higher signal a1 component than signal a2. However, if the optimal beam weight setting is applied, null signal #1 will have the minimum signal power of interfering signal a1, and null signal #2 will have the minimum signal power of signal a2.

[0066] Therefore, a test scanning beam sequence can be generated by the IN-BFN 10 (for example, as controlled by the controller 70 in any of the antenna array systems 100-b to 100-d) to obtain a first set of return-to-null beam weights and a second set of return-to-null beam weights having null positions coinciding with θa1 and θa2, respectively, thereby generating a null signal. Figure 7B The antenna pattern for scan case 2 is shown, where the first (independent) null θw2 has been moved to 80°, coinciding with the angle of arrival θa2 (or direction of arrival) of the interfering signal a2. Therefore, in the null signal representing scan case 2, the signal energy of the interfering signal a2 is zero. Therefore, the set of return-to-null beam weights used to generate this condition can then be applied by the second null BFN 18-2 to generate the null signal #2.

[0067] Similarly, if Figure 7C As shown, scan case 3 can use a scan angle of -80° to achieve a first (independent) null θw3 at 10° and a second null θu3 at -170°. Since the first null θw3 coincides with the arrival angle θa1 (or arrival direction) of the interference signal #1, this case results in the interference signal #1 being nulled. Therefore, the nulling beam weight set used to generate scan case 3 can then be applied by the first null BFN 18-1 to generate the null signal #1.

[0068] Figure 8 An exemplary method of determining the direction of arrival of an interfering signal incident on the antenna array system 100 is shown. The method utilizes a standard deviation (SD) based technique in which the SD of "n" consecutive samples of each test scanning beam signal in a plurality of test scanning beam signals is measured. For example, when the SD of the scanning beam test signal is one of the N minimum values ​​of the SD of the full set of test scanning beam signals, it can be assumed that the scanning beam has a null at the angle of arrival of one of the interfering signals. This condition can be understood using the following example:

[0069] The scanning beam signal can be understood as one of the null signals #1 or #2 in the initial step / test phase before setting fixed beamforming weights for zeroing. In the case of N=2 (and when there are two interference signals a1 and a2), the scanning beam signal is a composite signal consisting of: i) the desired signal b; ii) the first interference signal a1; iii) the second interference signal a2; and iv) noise w. When the null does not coincide with either of the interference signals a1 or a2, since the interference signals can be large constant envelope information signals with random phases, they can randomly combine over time. Therefore, if a sufficient number of n sequential samples are acquired, the SD of the scanning beam signal of the n samples will be relatively large. This is in the case corresponding to scanning case 1. Figure 8This is shown in the upper graph of , where the resulting standard deviation SD1 is much higher than the expected value for the zero condition.

[0070] Note that in this example, the levels of the interference signals a1 and a2 are each significantly higher than the desired signal plus noise (b+w). Therefore, the (b+w) component has no significant effect on the SD of the scanning beam signal. Figure 8 As further shown in the center curve diagram, in scanning case 2 corresponding to the interference signal a2 being zeroed, the standard deviation SD2 coincides with the first minimum value (minimum value #1) in the SD of all test scanning beams. Similarly, for scanning case 3 in which the interference signal a1 is zeroed, the standard deviation SD3 is found to be the second minimum value (minimum value #2) in the SD of all test scanning beams. Therefore, the method can conclude that one of the two zero positions formed in scanning case 2 coincides with the arrival angle of the first interference signal, and one of the two zero positions formed in scanning case 3 coincides with the other interference signal. The beam weight sets used to generate scanning cases 2 and 3 can then be allocated as the first and second zeroed beam weight sets bw1 and bw2, respectively, to be subsequently used to generate zero position signals #1 and #2 for continuous recovery of the desired signal.

[0071] Fig. 9 is an exemplary simulated graph of the antenna received signal power versus the standard deviation of the space signal vector (SSV) θ. The parameter SSVθ can be understood as the angle of arrival of the signal at the antenna aperture. Fig. 9 The example corresponds to the case illustrated above, where two interfering signals are incident on the dual element antenna array at respective angles of 10° and 80°. Using the standard deviation minimum detection method just outlined above, it can be seen that the simulation correctly finds the presence of interfering signals at 10° and 80°.

[0072] Fig.108 is a flow chart of an exemplary method 800 for mitigating interference signals performed by the antenna array system 100. For example, the method 800 may be controlled by the controller 70 and corresponds to the analog circuit case of the IN-BFN10 described above. The method 800 applied to the dual antenna element case of the antenna array system will be discussed below for the purpose of explanation; the method can be extended to antenna systems with a greater number of antenna elements. The method 800 may include the following operations: determining the direction of arrival of any identified interference signal, and establishing a set of nulling beam weights bw1, bw2 to selectively null the interference signal, thereby improving the recovery of the subsequently received desired signal. The method 800 may be periodically performed by the antenna system 100 during normal receive operation. To this end, the initial operation S802 may involve the controller 70 setting the total number "m" of test scanning beams, where the peaks are pointed at different test angles over the desired spatial region, for example, at angles equally spaced over a span of 180° or 360° in each desired plane. As previously described, the signal energy received by each scanning beam can be represented by null signal #1 (NS1) or null signal #2 (NS2), and then the beam weight set bw1 / bw2 is finally set to null out the interference signal. Regardless of whether the antenna array composed of antenna elements 30-1 to 30-N is a linear array, a planar array, or a 3D array, the m scanning beams can be formed with nulls that can be steered to a desired arrival angle relative to a reference axis, where the arrival angle can be a direction anywhere in three-dimensional space.

[0073] The controller 70 may then assign (S804) beam weights "bw" (each a subset of beam weights within a beam weight set bw1 or bw2) to the corresponding paths of nulls BFN #1 and / or #2 to form each test scanning beam based on the known path lengths between nulls BFN #1 and / or #2 and each antenna element A1, A2. For example, in Figure 2 , the combined insertion phase of transmission lines 60 and 62 (the path length from antenna element A1 to phase shifter 12-3) may be equal to or different from the combined insertion phase of transmission lines 64 and 65 (the path length from antenna element A2 to phase shifter 12-4). The controller 70 may consider the path length relationship when setting the beam weights that control the phase shift in phase shifter 12 to generate the test scanning beam. For each test scanning beam, the controller 70 may determine the null angles θu, θw, for example, by calculation or by reading the corresponding null angle data for each test scanning beam from a lookup table in memory 80.

[0074] For each scanning beam, a sampling sequence of n samples can be obtained (S806) from the magnitude of each of the null signal #1 and the null signal #2 by sampling the signal energy obtained by the directional couplers C1 and C2 using the sample / hold circuit 32 and the A / D converter 34. Then the first standard deviation SD#1 of the n samples of the null signal #1 can be calculated. The second standard deviation SD#2 of the n samples of the null signal #2 can also be calculated. In the total number m of each of the SD#1 and SD#2 results corresponding to the m scanning beams, the controller 70 can determine (S808) a local minimum on the spatial test area. Here, the controller 70 can determine whether at least one of the local minima indicates an interference signal. The determination can be based on a statistically based model that considers at least the following factors: the expected range of standard deviations on the spatial test area; the expected level of the desired signal relative to any interference signal; the expected amount of multipath interference; and AWGN. The statistical model can be based on the type of signal expected for any interference signal and the type of the desired signal. For example, in one example, the desired signal is a spread spectrum signal, and the desired interfering signal is a constant envelope signal, such as FM, GMSK, PSK, or a frequency hopping signal, such as an OFDM signal. In other examples, the desired signal is a constant envelope signal.

[0075] For example, the model may expect that if at least two strong interfering signals are received, there will be a wide range of SDs on the test space, resulting in the SD at the minimum being significantly smaller than the SD at the local maximum. If exactly two strong interfering signals are received, the model may expect each of the minima to be below a threshold "H" and the maximum within a certain range of the test space to be above another threshold "Q". On the other hand, if there are no interfering signals or only a single strong interfering signal, the model may expect a small range of SDs on the test space, whereby the average difference between the minimum and maximum values ​​will be small.

[0076] If the test scanning beam is generated by null BFN #1 and null BFN #2, the results can be correlated between null BFN #1 and null BFN #2 to identify the angle of arrival of any interfering signal at a higher confidence level. If no local minimum indicates an interfering signal based on the model, the controller 70 can assign (S810) a default beam weight to the null BFN #1 and null BFN #2 signal paths for subsequent signal reception. If only one of the local minima indicates an interfering signal, the beam weight associated with the scanning beam can be assigned (S812) to the null BFN #1 signal path and / or the null BFN #2 signal path to suppress the interfering signal.

[0077] If at least two of the local minima each indicate an interference signal, a corresponding beam weight may be assigned to each of the null BFN#1 signal path and the null BFN#2 signal path. For example, when the first test scanning beam generated by the null BFN#1 is identified as a scanning beam that generates SD minimum #1, and based on the statistical model, it is estimated that two strong interference sources are received, it can be assumed that the first null θw or the second null θu of the scanning beam is aligned with one of the two interference signals. When the second test scanning beam generated by the null BFN#1 is identified as a scanning beam that generates SD minimum #2, it can be assumed that the first null θw or the second null θu of the second scanning beam is aligned with the other of the two interference signals. Thus, the weight bw1 used to generate the minimum value #1 may then be assigned (S814) to the null BFN #1 signal path for the subsequent fixed null beam weight set, and the weight bw2 used to generate the minimum value #2 may then be assigned (S810) to the null BFN #2 signal path. The samples of the subsequent null signal #1 / #2 obtained using the final null beam weight set may then be applied (S816) to the corresponding nonlinear filter 40-1 or 40-2.

[0078] Method 800 has been described in the context of one or more null BFNs that generate test beams to steer nulls into directions aligned with one or more interfering signals. In other embodiments, a dithering technique may be employed to dither a beam formed by a set of nulling beam weights currently used to receive (and subsequently demodulate) data within a desired signal b obtained from the output signal OS. Using this technique, a sequence of samples may be acquired in real time while demodulating the output signal OS from the desired signal BFN 20 and decoding its data. In yet other embodiments, another statistical parameter (e.g., variance) may be substituted for the standard deviation.

[0079] In other embodiments of the method for determining the angle of the direction of arrival and setting the set of null-return beam weights accordingly, the sample sequences are obtained from other points in the antenna system 100. For example, if the IN-BFN 10 is actually implemented by processing circuits within a processor, then the sample sequences may be used. Figure 3A The antenna array system 100-b is configured to obtain a sampling sequence by coupling energy from signals AS1 and AS2. Figure 3C A sample sequence of the filtered signals FS1, FS2 is obtained as in the antenna array system 100-d of FIG. 1 and used by the controller 70 to calculate the angle of arrival. In yet another embodiment, a sample sequence of the output signal OS is obtained and used to calculate the angle of arrival. Other operations of these embodiments may be similar to those for FIG. Fig.10 The operations are the same or similar to those described.

[0080] The above embodiments have been described in the context of N interfering signals and one desired signal received by an antenna array having N antenna elements. Although the antenna array system 100 is capable of recovering the desired signal in such an environment, as previously mentioned, they are also configured to recover the desired signal when there are fewer than N interfering signals. For example, when it is determined that there are no interfering signals, the phase shifter 12 and the amplitude adjuster 14 in the antenna array system 100-(ad) can be set to a default setting, in which equal phase shifts and / or amplitude adjustments are made in each signal weighting path P1-P4. If it is determined that there are only (N-1) interfering signals, a set of zeroing beam weights for zeroing at least one interfering signal can be applied in only (N-1) of the N null BFNs 18.

[0081] In addition, the above-described embodiments have been primarily described in the context of an antenna array system configuration having "N=2". The concepts described herein are equally applicable to embodiments where N=3 or more. In these cases, the antenna array system 100 may include N≥3 antenna elements 30-1 to N30-N; N≥3 null BFNs 18-1 to 18-N, which output N≥3 null signals #1 to #N; N≥3 nonlinear filters 401 to 40-N; and N≥3 signal paths within the desired signal BFN 20-a (similar to paths P5, P6). In addition, each null BFN 18 will include N≥3 signal paths similar to signal paths P1 and P2, wherein each of the N≥3 signal paths may include a phase shifter 12 and an amplitude adjuster 14. In these cases, each null signal #1 to #N can be a composite signal consisting essentially of a first component and a second component, wherein the first component contains the signal energy of a different one of the interfering signals #1 to #N, and the second component contains the signal energy of a corresponding divided portion of the received desired signal b (plus noise w). Thus, each null BFN 18 effectively nulls a different set of (N-1) interfering signals among the N interfering signals #1 to #N.

[0082] Furthermore, while the above-described embodiments may have optimal performance in environments where interfering signals are constant envelope signals each having a signal strength at least one order of magnitude greater than the desired signal, the embodiments may still achieve beneficial results when interfering signals not having such characteristics are received.

[0083] As mentioned, the controller 70 may include a processor that reads instructions from the memory 80 to perform its operations as described herein. As used herein, the term "processor" is intended to include any processing device, such as a processing device that includes a central processing unit (CPU) and / or other processing circuits (e.g., a digital signal processor (DSP), a microprocessor, etc.). In addition, a "processor" includes computing hardware and may refer to a multi-core processor that includes multiple processing cores in a computing device. Various elements associated with a processing device may be shared by other processing devices.

[0084] While the technology described herein has been particularly shown and described with reference to exemplary embodiments of the technology described herein, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the claimed subject matter as defined by the following claims and their equivalents.

Claims

1. An antenna array system, comprising: an antenna array comprising N antenna elements that output N antenna signals, wherein N is greater than one; an interferer return-to-null beamforming network coupled to the antenna array and comprising N null beamforming networks (BFNs) to generate N null signals, each of the N null BFNs applying a corresponding set of return-to-null beam weights to the N antenna signals to generate a corresponding one of the N null signals, wherein each corresponding set of return-to-null beam weights corresponds to a different corresponding set of N-1 independent nulls; N nonlinear filters coupled to the interferer nulling beamforming network, each nonlinear filter filtering a corresponding one of the N null signals to provide a corresponding one of N filtered signals; and A desired signal beamforming network applies a desired signal beam weight set to the N filtered signals to generate an output signal.

2. The antenna array system according to claim 1, wherein: Each of the N null signals includes (i) an interference signal component; and (ii) a desired signal portion of the desired signal received by the antenna array system; and Each of the N nonlinear filters attenuates the interference signal component of the corresponding one of the N null signals relative to the desired signal portion.

3. The antenna array system according to claim 2, wherein the corresponding one of the N filtered signals from each of the N nonlinear filters is not a linear function of the corresponding one of the N null signals.

4. The antenna array system according to claim 1, further comprising a controller, the controller being configured to generate the corresponding return-to-null beam weight set for each of the null BFNs, and also to generate the desired signal beam weight set for the desired signal BFN.

5. The antenna array system of claim 4, wherein the corresponding set of nulling beam weights for each of the nulling BFNs is based on a direction of arrival of an interfering signal within the N antenna signals. 6 . The antenna array system according to claim 5 , wherein the controller is further configured to detect the interference signal and determine the arrival direction of the interference signal on the antenna array.

7. The antenna array system according to claim 6, wherein the controller detects the interference signal and the arrival direction thereof based on an analysis of instances of statistical parameters of samples of the at least one null signal obtained by respectively corresponding to a test scanning beam formed in at least one null BFN in the null BFN.

8. The antenna array system of claim 7, wherein the statistical parameter is a standard deviation, and the controller detects the arrival direction of the interference signal by identifying a local minimum of the standard deviation of the samples over a spatial test area, the local minimum being determined to correspond to a test scanning beam among a plurality of consecutive test scanning beams having a null at the arrival angle of the interference signal, wherein a beam weight set corresponding to the test scanning beam is set to receive a subsequent signal in at least one of the null BFNs.

9. The antenna array system of claim 1, wherein each of the interferer nulling beamforming network, the nonlinear filter, and the desired signal beamforming network comprises analog circuits.

10. The antenna array system of claim 1, wherein each of the interferer nulling beamforming network, the nonlinear filter, and the desired signal beamforming network is a virtual element having a corresponding function implemented by a digital circuit.

11. The antenna array system according to claim 1 further includes a controller, which is used to operate the antenna array system in a first mode when the number of interference signals is equal to N, and to operate the antenna array system in a second mode when the number of interference signals is less than N.

12. The antenna array system according to claim 11, wherein: In the first mode, the controller provides the corresponding return-to-zero beam weight set to each of the null BFNs and provides the desired signal beam weight set to the desired signal beamforming network; and In the second mode, the controller provides an aggregate beam weight set to a specific null BFN among the null BFNs, wherein the aggregate beam weight set corresponds to an independent null aligned with an arrival direction of the interfering signal and a beam peak aligned with an arrival direction of a desired signal.

13. A method for suppressing multiple interfering signals received by an antenna array simultaneously receiving a desired signal, the method comprising: receiving N antenna signals from an antenna array including N antenna elements, where N is greater than one; Obtaining a corresponding arrival direction of the interference signal on the antenna array; applying each of a plurality of return-to-null beam weight sets to a corresponding one of N null beam forming networks nulls BFN of an interferer return-to-null beam forming network coupled to the antenna array to generate N null signals, wherein each return-to-null beam weight set corresponds to a different corresponding set of N-1 independent nulls corresponding to N-1 of the directions of arrival, such that within each null signal, N-1 of the interfering signals are suppressed relative to each of a remaining one of the interfering signals and the desired signal; filtering each of the N null signals using a corresponding one of the N nonlinear filters to suppress a corresponding remaining one of the interfering signals relative to the desired signal, thereby generating N filtered signals; as well as The N filtered signals are combined to generate an output signal corresponding to the desired signal. The method of claim 13 , wherein the obtaining the estimated respective directions of arrival comprises receiving the estimated respective directions of arrival from an external system.

15. The method of claim 13, wherein obtaining the estimated respective directions of arrival comprises: coupling signal energy from at least one signal path between the antenna array and a signal path containing the output signal to provide at least one coupled signal; sampling the coupled signal to provide a sample sequence; as well as The direction of arrival is calculated using the sequence of samples.

16. The method of claim 15, wherein the calculating the arrival direction using the sample sequence comprises analyzing instances of statistical parameters of the sample sequence respectively obtained corresponding to a test scanning beam formed in a corresponding at least one of the null BFNs.

17. The method of claim 16, wherein the statistical parameter is a standard deviation, and the calculating the direction of arrival further comprises identifying a local minimum of the standard deviation of the samples over a spatial test area, wherein the local minimum is determined to correspond to a test scanning beam of a plurality of consecutive test scanning beams having a null at the angle of arrival of the interference signal, and The method also includes setting a set of beam weights corresponding to the test scanning beam for receiving a subsequent signal in at least one of the null BFNs.

18. The method of claim 13, wherein each of the N interfering signals received by the antenna array system has a greater magnitude than the desired signal.

19. The method of claim 13, wherein a magnitude of each of the N interfering signals received by the antenna array system is at least ten times a magnitude of the desired signal.

20. The method of claim 13, wherein each of the N interfering signals is a substantially constant envelope signal that overlaps the desired signal in spectrum and time.

21. The method of claim 13, wherein performing the non-linear filtering on each of the null signals comprises polarity-chopping each of the null signals.

22. The method of claim 13, wherein the corresponding one of the N filtered signals from each of the N nonlinear filters is not a linear function of the corresponding one of the N null signals.

23. The method of claim 13, further comprising generating the corresponding set of return-to-null beam weights for each of the N null BFNs, and generating a set of desired signal beam weights for combining the N filtered signals.

24. The method of claim 13, wherein each of the interferer nulling beamforming network and the nonlinear filter comprises analog circuitry.

25. The method of claim 13, wherein each of the interferer nulling beamforming network and the nonlinear filter is a virtual element having a corresponding function implemented by a digital circuit.

26. The method of claim 13, further comprising operating in a first mode using the plurality of beam weight sets when the number of interfering signals is equal to N, and operating in a second mode when the number of interfering signals is less than N.

27. The method according to claim 26, further comprising: in the first mode, providing the respective set of return-to-null beam weights to each of the null BFNs and providing the desired signal beam weight set to a desired signal beamforming network to combine the filtered signals to generate the output signal; and In the second mode, a set of aggregate beam weights is provided to specific ones of the null BFNs, wherein the set of aggregate beam weights corresponds to an independent null aligned with an arrival direction of the interfering signal and a beam peak aligned with an arrival direction of the desired signal.

28. A non-transitory computer-readable recording medium storing instructions that, when executed by a processor, implement a method for suppressing a plurality of interfering signals received by an antenna array that simultaneously receives a desired signal, and comprising: receiving N antenna signals from an antenna array including N antenna elements, where N is greater than one; Obtaining a corresponding arrival direction of the interference signal on the antenna array; applying each of a plurality of return-to-null beam weight sets to a corresponding one of N null beam forming networks nulls BFN of an interferer return-to-null beam forming network coupled to the antenna array to generate N null signals, wherein each return-to-null beam weight set corresponds to a different corresponding set of N-1 independent nulls corresponding to N-1 of the directions of arrival, such that within each null signal, N-1 of the interfering signals are suppressed relative to each of a remaining one of the interfering signals and the desired signal; filtering each of the N null signals using a corresponding one of the N nonlinear filters to suppress a corresponding remaining one of the interfering signals relative to the desired signal, thereby generating N filtered signals; as well as The N filtered signals are combined to generate an output signal corresponding to the desired signal. 29 . The non-transitory computer-readable recording medium of claim 28 , wherein the obtaining the estimated respective directions of arrival comprises receiving the estimated respective directions of arrival from an external system.

30. The non-transitory computer-readable recording medium of claim 28, wherein the obtaining the estimated respective directions of arrival comprises: coupling signal energy from at least one signal path between the antenna array and a signal path containing the output signal to provide at least one coupled signal; sampling the coupled signal to provide a sample sequence; as well as The direction of arrival is calculated using the sequence of samples.

31. The non-transitory computer-readable recording medium of claim 30, wherein the calculating the arrival direction using the sample sequence comprises analyzing instances of statistical parameters of the sample sequence obtained corresponding to test scanning beams formed in corresponding at least one of the null BFNs, respectively.

32. The non-transitory computer readable recording medium of claim 31 , wherein the statistical parameter is a standard deviation, and the calculating the direction of arrival further comprises identifying a local minimum of the standard deviation of the samples over a spatial test area, wherein the local minimum is determined to correspond to a test scanning beam of a plurality of consecutive test scanning beams having a null at an angle of arrival of an interference signal, and The method also includes setting a set of beam weights corresponding to the test scanning beam for receiving a subsequent signal in at least one of the null BFNs.

33. The non-transitory computer-readable recording medium of claim 28, wherein each of the N interference signals received by the antenna array system has a greater magnitude than the desired signal.

34. The non-transitory computer-readable recording medium of claim 28, wherein a magnitude of each of the N interference signals received by the antenna array system is at least ten times a magnitude of the desired signal.

35. The non-transitory computer readable recording medium of claim 28, wherein each of the N interference signals is a substantially constant envelope signal that overlaps the desired signal in spectrum and time. 36 . The non-transitory computer readable recording medium of claim 28 , wherein performing the nonlinear filtering on each of the zero-bit signals comprises polarity-cutting each of the zero-bit signals.

37. The non-transitory computer-readable recording medium of claim 28, wherein the corresponding one of the N filtered signals from each of the N nonlinear filters is not a linear function of the corresponding one of the N zero-bit signals.

38. The non-transitory computer readable recording medium of claim 28, wherein the method further comprises generating the corresponding return-to-zero beam weight set for each of the N null BFNs, and generating a desired signal beam weight set for combining the N filtered signals.

39. The non-transitory computer readable recording medium of claim 28, wherein each of the interferer nulling beamforming network and the nonlinear filter comprises an analog circuit.

40. The non-transitory computer readable recording medium of claim 28, wherein each of the interferer nulling beamforming network and the nonlinear filter is a virtual element having a corresponding function implemented by a digital circuit.

41. The non-transitory computer-readable recording medium of claim 28, wherein the method further comprises operating in a first mode using the plurality of beam weight sets when the number of interfering signals is equal to N, and operating in a second mode when the number of interfering signals is less than N.

42. The non-transitory computer readable recording medium of claim 41, wherein the method further comprises: In the first mode, the corresponding return-to-zero beam weight set is provided to each null BFN in the null BFN, and the desired signal beam weight set is provided to the desired signal beamforming network to combine the filtered signals to generate the output signal; and in the second mode, a set of aggregate beam weights is provided to specific null BFNs in the null BFNs, wherein the set of aggregate beam weights corresponds to an independent null aligned with the arrival direction of the interference signal and a beam peak aligned with the arrival direction of the desired signal.

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