Method for searching signals using phased array antenna and phased array antenna system

Abstract

This application relates to a method and system for searching for signals using a phased array antenna. This system and method are used to quickly find detectable signals within the field of view of a phased array antenna. A tree-based signal detection method is used to generate coarse-to-fine angular beam patterns, modifying the transmit beam pattern over time to improve signal space search performance through typical delay manipulation. A tree-based beam search is employed to select a beam with a narrow beamwidth so that it is transmitted at an angle with respect to the boresight that lies within the angular space of previously detected signals.

Description

Technical Field

[0001] The technology disclosed herein generally relates to phased array antennas. In particular, the technology disclosed herein relates to a method for searching for signals using a phased array antenna. Background Art

[0002] Modern phased array antennas are a technology enabler that supports mobile broadband communications via satellites, aircraft, ships, and land vehicles. Specifically, advanced digital beamforming is needed to provide dynamic, high-throughput robust communications and networking with larger phased array antennas through improved sidelobe performance and grating lobe suppression, faster notching speeds, faster scanning speeds, and faster beam switching to enhance network performance. As a result, beam searching has many different applications, whether it is used to connect to mobile networks, find new radars, provide reliable handoffs when switching satellites or cell towers, etc. As used herein, the term "beam searching" refers to the use of a beam to search for a signal (not searching for a beam).

[0003] At the heart of beam search is the process of beamforming. Beamforming is a signal processing technique used in antenna arrays for directional signal transmission or reception. This is achieved by combining the signal elements in the antenna array so that signals at certain angles interfere constructively, while signals at other angles interfere destructively. These are commonly referred to as phased array antennas. The improvement over omnidirectional reception and / or transmission is known as the array's directivity and is an important measure of antenna performance. Beamforming can be used for radio frequency (RF) or acoustic waves and has many applications in radar, sonar, seismology, wireless communications, radio astronomy, acoustics, and biomedicine. Traditional time-delay beam steering uses a pointing direction (alternatively referred to herein as "boresight angle" or "pointing angle") and creates a setting on the antenna array to maximize signal transmission or reception in the pointing direction and form a narrow beam. The mechanism used to achieve beamforming is to adjust the phase (or time delay) and amplitude (or weight) of each element separately to force constructive or destructive signal summation to generate the desired beam.

[0004] Existing solutions for beam searching using phased arrays all mimic a mechanical dish antenna in their approach to searching for signals. Consequently, these solutions sweep a single narrow beam across the array's field of view, F. This means that the sweep time increases linearly with the size of the array (the total number of elements), since the beam must ultimately be directed at every angular region in the field of view. To see this, consider that the first zero beamwidth of a linear array with N elements, with wavelength λ and d = λ / 2 element spacing, is approximately 4 / N in radians. A similar approximation shows that for a planar array of size N1×N2, the angular area is approximately the product of the linear array's beamwidths, e.g., 16 / (N1N2) in radians. Therefore, the time to fully search F is approximately span(F)*N / 4 for a linear array and area(F)*N1N2 / 16 for a planar array. Here, span() represents the angular range in radians, and area() represents the two-dimensional solid angular range in radians.

[0005] A solution to the problem of how to quickly find all detectable signals within the field of view of a phased array antenna would be beneficial. Summary of the Invention

[0006] The subject matter disclosed in detail below relates to systems and methods for quickly finding detectable signals within the field of view of a phased array antenna. By using a tree-based signal detection method to generate coarse-to-fine angular beam patterns, the transmit beam pattern can be modified over time, thereby improving signal space search performance through typical delay manipulation. The tree-based beam search is employed to select a beam with a narrow beamwidth for transmission at an angle from boresight that lies within the angular space of previously detected signals.

[0007] According to one embodiment, a set of complementary beams is designed with multiple levels. The number of beams in the subsets that make up each level increases as the level increases. The levels of complementary beams are then loaded into a beam steering controller that controls the beams produced by the phased array antenna. Signal detection occurs when the value of a parameter of the detected signal exceeds a threshold. For example, the detected parameter can be the sum of the energy in the signal. Many other detection schemes are also possible. As the level increases, the gain of each beam filter increases and the beam width decreases. Therefore, the signal will pass through more spatial filters, thereby narrowing the possible signal directions while increasing the power of the received signal. This has the dual effect of (1) finding more signals in (2) a narrower angular region.

[0008] As mentioned above, typical phased antenna arrays mimic mechanical antennas in their signal search method. Therefore, a phased array antenna generates a corresponding narrow beam for each commanded angle. In contrast, the beam search method disclosed herein allows the beam pattern to be modified over time to increase signal space search performance through typical delay manipulation. Compared to conventional beam search methods, this method utilizes the power of the phased array. This is clearly demonstrated by the dimensionality argument. If a simple angle search using a single beam is performed across the field of view of a phased array antenna with N elements, the phase and amplitude control only varies within the one (two) dimensions of the linear (planar) array, with azimuth (and elevation) angle control of the beam. Therefore, only N-1 (N-2) dimensions are used to create the narrow beam during the search process. In contrast, due to the increased beam width and pointing angle, the proposed system uses more dimensions for search. Therefore, the proposed system uses up to twice the array size for search. This allows for an efficient trade-off between directivity and search time.

[0009] The beam search method proposed in this paper (hereinafter referred to as "tree beam search") has the following noteworthy features: (1) Using a phased array antenna to perform a tree beam search can find all signals in the field of view (on average) in a time proportional to Dlog2(N) / 2, where D is the time to detect a single signal. This is much faster than traditional methods, in which the time average is proportional to DN / 2. (2) By searching the signal space more quickly, the probability of detecting transient signals is increased. Specifically, the system is able to more reliably detect signals with shorter durations. For example, while the standard search technique detects all signals with duration DN, the proposed method is able to detect most signals with duration Dlog2(N).

[0010] The capabilities described in the previous paragraph benefit phased array antenna systems by improving search performance without increasing antenna size or number, or improving RF receiver performance, which is an expensive and problematic option. The approach employed in this paper employs more robust beamforming and beam steering than typical phased array antennas and can be implemented using commercially available field-programmable gate arrays (FPGAs) and electronics.

[0011] Although various embodiments of systems and methods for rapidly finding detectable signals within the field of view of a phased array antenna are described in detail below, one or more of these embodiments may be characterized by one or more of the following aspects.

[0012] One aspect of the subject matter disclosed in greater detail below is a method for searching for a signal using a phased array antenna, the method comprising: (a) transmitting a first beam having a first beam width and a first angle to a boresight; (b) receiving a first signal after transmitting the first beam; (c) detecting that a parameter value of the first signal exceeds a first threshold; (d) transmitting a second beam having a second beam width that is less than the first beam width and a second angle to the boresight that is disposed within an angular range of the first beam; and (e) transmitting a third beam having a second beam width and a third angle to the boresight that is disposed within an angular range of the first beam, wherein the first angle to the boresight is disposed between the second angle and the third angle to the boresight. According to some embodiments, the second beam width is equal to half the first beam width, and the total angular range of the second and third beams is of the same range as the angular range of the first beam.

[0013] The method described in the immediately preceding paragraph may further include: (f) receiving a second signal after transmitting the second beam; (g) detecting that a parameter value of the second signal exceeds a second threshold; (h) transmitting a fourth beam having a third beam width smaller than the second beam width and a fourth angle to the visual axis set within the angular range of the second beam; and (i) transmitting a fifth beam having the third beam width and a fifth angle to the visual axis set within the angular range of the second beam, wherein the second angle to the visual axis is set between the fourth angle and the fifth angle to the visual axis. The first to fifth beams are selected from a complementary beam set having L levels, the L levels including: a first level having M beams and including the first beam, a second level having 2M beams and including the second and third beams, a third level having 4M beams and including the fourth and fifth beams, and a fourth level having 2 L-1 The Lth level of M beams, where M and L are integers.

[0014] Another aspect of the subject matter disclosed in greater detail below is a method for searching for a signal using a phased array antenna, the method comprising: designing a complementary beam set having L levels; loading the L levels of the complementary beam set into a beam steering controller that controls the beams generated by the phased array antenna; marking a beam (b, l) in the complementary beam set for transmission; setting the phase and amplitude of antenna elements of the phased array antenna to transmit the marked beam having a beam width and a pointing angle; transmitting the marked beam; after transmitting the marked beam, receiving a signal at the phased array antenna; and detecting which , the parameter value of the signal received at the time indicates that the signal is received; determine whether the current level l is less than the total number of levels L; if the current level l is not less than the total number of levels L, declare that the arrival direction of the signal has been detected to correspond to the pointing angle of the current beam; if the current level l is less than the total number of levels L, mark two beams (2b-1) and 2b in the next level (l+1) corresponding to the current beam at level l of the complementary beam set for transmission; set the phase and amplitude of the antenna elements of the phased array antenna to transmit two beams; and transmit the two beams continuously. According to a proposed embodiment, the complementary beam set has L levels, including a first level with M beams, a second level with 2M beams, a third level with 4M beams and a fourth level with 2M beams. L-1 The method may further include: marking a subset of additional beams from the Lth level to fill a search gap in a current search frame; and setting phases and amplitudes of antenna elements of the phased array antenna to transmit the additional beams.

[0015] Another aspect of the subject matter disclosed below is a system comprising: a phased array antenna; a transmitter; a receiver; a transmit module connecting the transmitter to the phased array antenna in a transmit mode and connecting the receiver to the phased array antenna in a receive mode; a beam steering controller configured to control the phased array antenna to transmit a beam having a beam width and an angle to boresight determined by a tree-based beam search; a beam search controller configured to send a command to the transmitter and the beam steering controller, the command causing the beam selected by the tree-based beam search to be transmitted by the phased array antenna; and a complementary beam set data storage medium storing data representing beam specifications of complementary beam sets organized in L levels, wherein the complementary beam set data storage medium is accessible to both the beam search controller and the beam steering controller, the beam search controller further configured to mark the selected beam specified in the complementary beam set data storage medium, and the beam steering controller further configured to steer the beam generated by the phased array antenna based on the beam information read from the complementary beam set data storage medium. The beam search controller includes a module configured to detect a specific parameter of a signal output by the receiver.

[0016] According to some embodiments of the system described in the immediately preceding paragraph, the complementary beam set has L levels, the L levels including a first level having M beams, a second level having 2M beams, a third level having 4M beams, and a third level having 2M beams. L-1 An L-th level of M beams, where M and L are integers. The first level includes beams having a first beamwidth, the second level includes beams having a second beamwidth smaller than the first beamwidth, the third level includes beams having a third beamwidth smaller than the second beamwidth, and the L-th level includes beams having an L-th beamwidth smaller than the third beamwidth and smaller than the beamwidth of any level between the third level and the L-th level.

[0017] According to a proposed implementation, the beam search controller is further configured to perform operations including: marking a beam (b, l) in the complementary beam set (20) for transmission; detecting when a parameter value of a received signal indicates that a signal has been received after the beam transmission; determining whether a current level l to which the transmit beam belongs is less than a total number of levels L; if the current level l is not less than the total number of levels L, declaring that a direction of arrival of a signal has been detected that corresponds to a pointing angle of the transmit beam; and if the current level l is less than the total number of levels L, marking two beams (2b-1) and 2b in a next level (l+1) corresponding to the beam for transmission at level l of the complementary beam set (20) for transmission.

[0018]

[0014] Other aspects of systems and methods for quickly finding detectable signals within the field of view of a phased array antenna are disclosed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The features, functions, and advantages discussed in the preceding sections can be achieved independently in various embodiments, or can be combined in other embodiments. To illustrate the above and other aspects, various embodiments will be described below with reference to the accompanying drawings.

[0020] Figure 1 is a block diagram identifying some of the components of a typical phased array antenna system.

[0021] Figure 2 is a flow chart identifying steps of a method for performing tree beam searching using a phased array antenna, according to one embodiment.

[0022] Figure 3 is a diagram showing how a digital beamformer is connected to multiple elements of a phased array antenna.

[0023] Figure 4A and 4Bare shown for single channel finite impulse response (FIR) filters (see Figure 4A ) and equidistant omnidirectional narrowband line arrays (see Figure 4B ) between the two.

[0024] Figures 5A-5C is a graph of relative beam gain versus pointing angle.

[0025] Figures 6A-6C is a graph of absolute beam gain versus pointing angle.

[0026] Figure 7 is a diagram illustrating a tree for signal detection in a phased array antenna system using a beam searching method.

[0027] Figure 8 is a block diagram identifying some components of a phased array antenna system, according to one embodiment.

[0028] Reference will hereinafter be made to the drawings, in which similar elements in different drawings have the same reference numerals. DETAILED DESCRIPTION

[0029] An illustrative embodiment of a system and method for rapidly finding detectable signals within the field of view of a phased array antenna is described in greater detail below. However, not all features of an actual implementation are described in this specification. Those skilled in the art will appreciate that in the development of any such actual implementation, many implementation-specific decisions must be made to achieve the developer's specific goals, such as complying with system-related and business-related constraints, which will vary from one implementation to another. Furthermore, it will be appreciated that such development work may be complex and time-consuming, but will nevertheless be routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0030] For purposes of illustration, an example embodiment of a method for quickly finding a detectable signal within the field of view of a phased array antenna will now be described. For the avoidance of doubt, reference will now be made to Figure 1 Briefly describe the operating principle of phased array antennas.

[0031] Figure 1FIG2 is a block diagram identifying some components of a typical phased array antenna system 2. Phased array antenna system 2 includes a phased array antenna 4, a transmitter 14, a receiver 16, and a transmit module 12, which connects transmitter 14 to phased array antenna 4 in transmit mode and connects receiver 16 to phased array antenna 4 in receive mode. Phased array antenna 4 includes an array of antenna elements 6 and a corresponding array of phase shifters 8. The feed current for each antenna element 6 flows through a corresponding phase shifter 8 (φ) controlled by a beam steering controller 10. Beam steering controller 10 is a computer configured (e.g., programmed) to control phase shifters 8 so that antenna elements 6 transmit corresponding RF waves, which combine to produce a transmit beam having a pointing angle θ. The individual wavefronts are spherical, but they merge (add together) in front of phased array antenna 4 to produce a plane wave propagating in a specific direction. Phase shifters 8 delay the RF waves, causing each antenna element 6 to transmit its wavefront later than the preceding antenna element. This results in the generated plane wave being directed at an angle θ to the antenna's axis (also called boresight). By varying the phase shift, the beam steering controller 10 can instantly change the angle θ of the transmitted beam. Most phased arrays have a two-dimensional array of antenna elements, rather than a Figure 1 The linear array shown, in this case, can steer the transmit beam in two dimensions. Similarly, the receive beam is formed by controlling the phase shift to combine the wavefronts returning from the pointing angle.

[0032] In telecommunications and radar engineering, the antenna boresight is the axis of maximum gain (maximum radiated power) of a directional antenna. For most antennas, the boresight is the axis of symmetry of the antenna. For example, for an axially fed dish antenna, the antenna boresight is the axis of symmetry of a parabolic dish antenna, and the antenna radiation pattern (main lobe) is symmetrical about the boresight axis. A phased array antenna can electronically steer the transmit beam by changing the relative phases of the RF waves emitted by different antenna elements 6, thereby changing the angle of the boresight (i.e., the pointing angle). As used herein, the term "beamwidth" refers to the angle between the half-power (-3dB) points of the main lobe when referenced to the peak effective radiated power of the main lobe.

[0033] The beam search method disclosed herein allows for modifying the beam pattern produced by the phased array antenna system 2 over time by generating coarse-to-fine angular beam patterns using a tree-based signal detection approach, thereby improving signal space search performance through typical delay manipulation. Figure 2 is a flow chart identifying steps of a method of performing a tree beam search using a phased array antenna 4 according to one embodiment, the method including marking selected beams to be transmitted and then transmitting the marked beams using the phased array antenna 4. Figure 2The steps described in are performed under the control of a beam search controller 1, which is communicatively coupled to a beam steering controller 10. The beam search controller 1 is a computer or processor configured (e.g., programmed) to send commands to the beam steering controller 10. The beam steering controller 10 is, in turn, a computer or processor configured (e.g., programmed) to control the phased array antenna 4 to transmit a marker beam having a beam width and an angle to boresight determined by the tree-based beam search.

[0034] according to Figure 2 In the embodiment depicted in FIG, a complementary beam set 20 having L levels is designed. The beam pattern is pre-designed so that: level 1 has M beams; level 2 has 2M beams, where each pair of beams fits within a corresponding beam in the beam pattern in level 1; level 3 has 4M beams, where each pair of beams fits within a corresponding beam from the beam pattern in level 2; and so on. As used herein, "fits" means that the respective angular ranges of a pair of beams in one level overlap and fit within the respective angular ranges of the respective wider beam in the next lower level, and also means that the angle to the boresight of the wider beam in the next lower level lies between the angles to the boresight of the pair of beams. This can be accomplished using filter design techniques, described in more detail below. Each beam in the beam set is identified by a "tag" denoted by n(l,b), which indicates the bth tagged beam at level l.

[0035] The L levels of complementary beams are then loaded (eg, in the form of a data table) into a non-transitory tangible computer readable storage medium ( Figure 2 Not shown, but see Figure 8 The complementary beam set data storage medium 11 in the complementary beam set data storage medium 11 is accessible to both the beam search controller 1 and the beam steering controller 10. The beam search controller 1 is configured to mark the selected beam specified in the complementary beam set data storage medium 11, while the beam steering controller 10 is configured to control the beam generated by the phased array antenna 4 according to the beam information read from the complementary beam set data storage medium 11. More specifically, the beam steering controller 10 sets a phase delay (as previously described relative to the phase delay) for each antenna element 6 of the phased array antenna. Figure 1 As described above), and also provides a weight for adjusting the amplitude of the wavefront emitted by the antenna element 6.

[0036] In response to the initiation of the beam search for a new search frame, the beam search controller 1 resets the beam index b and the level index l ( Figure 2These indices (identifying the marker beam to be transmitted) are contained in the transmit beam request 22 sent to the beam steering controller 10. The beam steering controller 10 then sets the phase and amplitude of the antenna elements 6 so as to transmit a marker beam having the specified beamwidth and the specified angle to boresight.

[0037] After transmitting the programmed beam, the phased array antenna 4 receives the signal S. The programmed beam B is transmitted at level 1. ln(1,b) The signal received later is expressed as B ln(1,b) (S) indicates that the beam search controller 1 is also configured to detect when the value of the signal parameter indicates that a signal (not noise) is received. In order to detect the received signal B ln(1,b) The parameter value (e.g. energy) of (S), the beam search controller 1 uses the selected detection algorithm d(), which has a threshold T for the level l. l More specifically, it is determined that the detected value of the parameter is greater than a threshold value T1:

[0038] d(B ln(l,b) (S))>T l ?

[0039] Or whether ( Figure 2 If it is determined that the parameter value of the received signal is above the threshold value T1, it is further determined whether the current level l is less than the total number of levels L or not (operation 26). On the one hand, if the current level l is not less than the total number of levels L (for example, l=L), then the detection of a signal above the threshold value will cause the system to declare (operation 27) that the direction of arrival of the detected signal is consistent with the current beam B. ln(1,b) The pointing angle corresponds to .

[0040] On the other hand, if the current level l is less than the total number of levels L, two beams (2b-1) and 2b in the next level (l+1) corresponding to the current beam of level l are marked for use (operation 28). Digital data representing the marks n(l+1, 2b) and n(l+1, 2b-1) are then stored in a first-in, first-out buffer 30. The beam search controller 1 then determines whether to perform a beam search on all marked beams (operation 32). If all marked beams for each level have been transmitted, the beam search controller 1 then determines whether to mark a subset of additional narrow beams to fill the search gap of the current search frame.

[0041] On the one hand, if it is determined (in operation 32) that beam search has not been performed for all marked beams, then beam index b and level index l (which identifies the next marked beam to be transmitted) are included in a transmit beam request 22 sent to the beam steering controller 10. The transmit beam request 22 identifies the next beam B to be transmitted under the control of the beam steering controller 10. ln(1,b)The beam steering controller 10 then sets the phase and amplitude of the antenna elements 6 so that the next marker beam in the complementary beam set 20 will be transmitted.

[0042] On the other hand, if it is determined (in operation 32) that beam search is to be performed on all marked beams of the current search frame, the beam search controller 1 then determines whether the beam search should include additional narrow beams (e.g., beams having a beam width equal to the beam width of the beams in the last level L) (operation 34).

[0043] On the one hand, if it is determined (in operation 34) that no additional narrow beams should be added for the current search frame, the beam search controller 1 resets and initiates a beam search for a new search frame (operations 18 and 22, respectively).

[0044] On the other hand, if it is determined (in operation 34) that additional narrow beams should be added to the current search frame in order to fill the search gap of the current search frame, the beam search controller 1 then marks the additional narrow beams. These additional narrow beams are marked at the end of the beam search frame after all marked beams have been processed. The reason for choosing to mark additional narrow beams to complete the search frame is to handle the situation where the received signal can only be detected using the narrowest beam (with the corresponding highest gain) and therefore may be missed by the effective tree search. For the binary search tree, there are M at the last (narrowest beam) level L. L =2 L-1 M possible beams, where is the N of this level L Mark the set of beams. Under the previous assumption, the remaining t in the search frame is t = 1 / R-(M1+M2+...+M L )D seconds, where R is the search frame rate in frames per second. Therefore, each frame has room for t / D additional beams. The way the additional marking works (this assumes a desired fixed search frame rate of R frames per second with a desired constant beam dwell time D) is as follows:

[0045] Frame F1 will mark the entire set M of unmarked narrow beams at level L for frame F1 L -N L The first set of m=t / D beams acquired consecutively (F1) (labeled as U(F1)={u1, u2, ...}). This set of labels is called A(F1)={u1, ..., u m}.

[0046] Frame F2 will mark the next set of m beams acquired consecutively from the unmarked narrow beams at level L for frame F2, denoted as U(F2), minus those denoted as U(F_2)\U(F_1) in A(F1). This set will be called A(F2).

[0047] This process continues frame by frame until the set of unmarked beams minus the additional marked beams U(F)\(F1)\(F2)... is empty. Then, the additional narrow beam marking process begins again.

[0048] Simple modifications to this scheme are easily designed with non-constant search frame rates and non-constant beam dwell times.The following disclosure describes complementary beam set design and FIR filter design.

[0049] Figure 3 is a diagram showing how a digital beamformer 50 is connected to J antenna elements 6 of a phased array antenna, where J is an integer greater than 1. The digital beamformer 50 includes a plurality of multipliers 40 that apply respective weights to the respective signals output by the plurality of antenna elements 6. The signals output by the multipliers 40 are summed by a summer 42. The output y(k) at time k, given by a linear combination of the data at the J antenna elements 6 at time k, is:

[0050]

[0051] where ()* denotes the complex conjugate. This is the transmit mode as shown. The receive mode is exactly the opposite, where the input signal y(k) generates a set of signals {xj(k)}, one at each of the J antenna elements 6. Although not explicitly stated below, the dependence on time k should be understood in the following text.

[0052] Figure 4A and 4B are respectively shown as single channel finite impulse response (FIR) filter 52 (see Figure 4A ) and an equidistant omnidirectional narrowband linear array beamformer 50 (see Figure 4B ) between the two.

[0053] refer to Figure 4A , FIR filter 52 includes a plurality of element weights applied by multiplier 40 to produce a weighted signal, which is in turn summed by summer 42. Each element is labeled Z -1 The squares represent registers or storage elements that are used to delay the value by one clock cycle. Thus, each multiplier receives its input signal after a delay of a different duration.

[0054] The element weight is The frequency response of a finite impulse response (FIR) filter with an element delay of T seconds is given by

[0055]

[0056] This equation represents the filter's response to a complex sinusoid of frequency ω. Here

[0057] d(ω)=[1 e iωT e iω2T e iωT(J-1) ] H

[0058] is a vector that describes the phase of the complex sinusoid at each tap in the FIR filter relative to the tap with respect to frequency ω.

[0059] refer to Figure 4B , assuming that the input signal is a complex plane wave with direction of arrival θ and frequency ω. Then, the formula for r(w,ω) is given by w H d(ω) becomes here

[0060] d′(ω)=[d1(θ,ω)),d2(θ,ω)),...,dJ(θ,ω)]

[0061] and

[0062]

[0063] where 1≤j≤J and Δj(θ) represents the time delay due to the propagation time from the first element to the jth element at the incident angle θ. is the commonly used Hadamard element-wise product.

[0064] The closest correspondence between FIR filtering and beamforming occurs when the beamformer operates at a single temporal frequency, ω0, and the array geometry is linear and equally spaced, as in the case of a uniform linear array. Let the sensor spacing be d, the propagation speed (the speed of light) be c, and θ be the direction of arrival relative to the boresight (perpendicular to the array). Then, the time delay due to propagation from the first sensor to the jth sensor is given by:

[0065] τ j (θ)=(j-1)(d / c)sin(θ)

[0066] In this case, the relationship between the temporal frequency ω in the term d(ω) (FIR filter) and the direction θ in the term d(θ,ω0) (beamformer) is as follows:

[0067] ω=ω0(d / c)sin(θ)

[0068] Therefore, the temporal frequencies in the FIR filter correspond to the sinusoids of the directions in the narrowband uniform linear array used as a beamformer.

[0069] Figures 5A-5Cis a graph of relative beam gain versus pointing angle, partially illustrating the design of complementary spatial filters for an array with N=256 elements and a beam tree with five levels (with a corresponding number of beams) over the angular space from -60° to +60° for a uniform linear array. Relative gains are shown (forcing a maximum gain of 0 dB for all beams). This helps show how these spatial filters fit together to divide space into equally spaced angular regions that can be traversed in a tree-like fashion.

[0070] Figure 5A Relative beam gain versus pointing angle is shown for a first level consisting of eight beams, each of the eight beams having a beamwidth equal to approximately 15°. Figure 5B Relative beam gain versus pointing angle is shown for a second level consisting of 16 beams, each of which has a beamwidth equal to approximately 7.5°. Figure 5C Relative beam gain versus pointing angle is shown for a third level consisting of 32 beams, each having a beamwidth equal to approximately 3.75°. Similar graphs for the fourth and fifth levels, respectively, having 64 beams (each with a beamwidth equal to approximately 1.875°) and 128 beams (each with a beamwidth equal to approximately 0.9375°), are not shown when depicted in the black line graph. The number of beams makes it difficult to interpret individual beams, and therefore such a graph would not enhance the reader's understanding.

[0071] For example, assume that the beam search controller 1 causes the beam steering controller 10 to Figure 5A ) transmits a beam 70 having an angular range from 0° (corresponding to the boresight) to +15°. Figure 5A Assume further that the detected parameter of the received signal is greater than the first level detection threshold. The system processes the sensor data and determines that the detected signal arrives at an angle that is within the angular range of 0° to +15°.

[0072] The beam search controller 1 then causes the beam steering controller 10 to start from the second level (at Figure 5B ) transmit beams 72 and 74, which have angular ranges from 0° to +7.5° and from 7.5° to +15°, respectively. After beam 72 has been transmitted from the second level (at Figure 5B ), further assuming that the detection parameter of the signal received after transmitting beam 72 is greater than the second level detection threshold. The system processes the sensor data and determines that the detected signal arrives at an angle that is within the angular range of 0° to +7.5°.

[0073] The beam search controller 1 then causes the beam steering controller 10 to select the beam from the third level (at Figure 5C ) transmit beams 76 and 78, which have angular ranges from 0° to +3.75° and from +3.75 to 7.5°, respectively. After beam 76 has been transmitted from the third level (at Figure 5C ), further assuming that the detection parameter of the signal received after transmitting beam 76 is greater than the detection threshold of the third level. The system processes the sensor data and determines that the detected signal arrives at an angle that is within the angular range from 0° to +3.75°.

[0074] The beam search controller 1 then causes the beam steering controller 10 to transmit two beams from the fourth level (not shown). This process continues until at least two beams have been transmitted from the final level. If one of these beams results in a received signal with a detection parameter greater than the detection threshold of the final level, the system processes the sensor data and determines that the detected signal arrived at an angle within the angular range of 0° to +0.9375°. In this way, the direction of arrival of the signal from the target object can be determined.

[0075] Figures 6A-6C is a graph of absolute beam gain versus pointing angle, which partially illustrates the design of a complementary spatial filter for an array with N = 256 elements and a beam tree with five levels (with a corresponding number of beams) over the angular space from -60° to +60° for a uniform linear array. Figure 6A shows the absolute beam gain versus pointing angle for the first level consisting of eight beams; Figure 6B shows absolute beam gain versus pointing angle for a second level consisting of 16 beams; and Figure 6C Absolute beam gain versus pointing angle is shown for the third level consisting of 32 beams. Similar graphs are not shown for the fourth and fifth levels having 64 and 128 beams respectively.

[0076] Although the side lobes can be controlled by the FIR filter design method used (the side lobes are usually 30dB lower than the main beam, or even higher), the maximum gain is sacrificed. In the case of N = 256 elements, the maximum possible gain is 48dB = 20log 10 (N). This is significantly higher than the maximum gain in the 5-level graph (not shown), which is only approximately 23 dB. This is because the constrained design techniques used to keep sidelobe levels under control also reduce the maximum gain. By limiting the sidelobes, maximum gain is achieved. The sidelobes are much higher than for complementary beamsets designed using constrained techniques. Similarly, the gain of each beam shows differences across the field of view. These differences can be easily corrected by adjusting the amplitude of the element weights.

[0077] The design field of FIR filters is vast, with many possible techniques. In addition to describing all the various ways to accomplish filter design (optimization, frequency methods, Remez, etc.), this disclosure will describe one method as a reference. Filter design uses either practical methods or complex methods and is used for FIR or infinite impulse response filters. Since the process of interest is antenna beamforming, complex FIR filter design techniques are used. In particular, complex number approximations are used for the design of filters with nonlinear phase characteristics (e.g., beamforming). The frequency response H(ω) of a FIR digital filter of length N (corresponding to N antenna elements) is typically a complex-valued function of the normalized frequency ω:

[0078]

[0079] Where P = P2-P1+1. Here, the filter coefficient is allowed to be complex and thus represents the amplitude and phase of each antenna element. The complex Chebyshev approximation problem is stated as follows. Let D(ω) be the desired continuous complex function defined on a compact subset B[-π,π). D(ω) will be approximated on B by the frequency response in equation (2). The approximation problem is to find the filter coefficients This will minimize the weighted error for all possible choices of filter coefficients {h(n)}

[0080] E(ω)=W(ω)[D(ω)-H(ω)] (3)

[0081] Chebyshev norm

[0082]

[0083] The weight W(ω) is a design parameter that balances ripple with sidelobe level, etc. There are many algorithms for designing Chebyshev optimal complex FIR filters. We will now describe methods used in MATLAB and other current design software.

[0084] By generalizing Remez exchange, Karam et al. proposed an efficient multiple exchange algorithm for designing complex FIR digital filters in the Chebyshev sense in the following paper: "Complex Chebyshev Approximation for FIR Filter Design." IEEE Transactions on Circuits and Systems, Part II, March 1995. This algorithm is essentially a generalization of the Parks-McClellan algorithm for the complex case. Specifically, for a given set of normalized frequencies, the algorithm converges to the optimal weighted Chebyshev approximation on B, and often to the optimal Chebyshev solution on some compact subset of B, when the optimal error satisfies a given alternating property.

[0085] The method proposed herein consists in sending beams with gradually tapering angular beam patterns according to a tree-based approach. Assume that the tree 60 has Figure 7 L levels are shown. M represents level l L =2 l-1 M beams (or spatial beam patterns) where 1≤l≤L. This number is assumed to be a binary tree. According to the proposed binary tree implementation, Figure 7 As shown, two branches diverge from each node. In this case, the tree 60 has M1=M beams (B 11 , B 12 ,...,B 1M1 ), with M2=2M beams (B 21 , B 22 ,...,B 2M2 ), with M in the last level 66 L =2 l-1 M beams (B L1 , B L2 ,...,B LML More branches may also be considered. For illustrative purposes, a typical application of the tree beam search technique has been described.

[0086] For each level l where 1≤l≤L, the corresponding detection threshold T1 is selected so that the probability of signal detection within each beam is a constant less than 1 (for example, if the constant is 0.5, the number of detected signals remains constant at each level of the binary tree). Symbolically, B(S) represents the signal S filtered by the beam space filter B (i.e., the resulting transmitted signal S received by the antenna with beam pattern B). The detection of such a signal uses a detection algorithm represented by d(), so that signal detection occurs when the value of the parameter of the detected signal exceeds the threshold. In other words, the signal S is declared to be detected when

[0087] d(B(S))>T l

[0088] For level l. Here, a common detection algorithm is the sum of the energy in the signal. In other words, if the signal S consists of complex samples {s1, s2, ..., s n} means, then

[0089]

[0090] Here, when the signal energy exceeds a threshold, detection is declared. Many other detection schemes are also possible.

[0091] As the level increases, the gain of each beam filter increases and the beam width decreases. Therefore, the signal will pass through more spatial filters, narrowing the possible signal directions while increasing the power of the received signal. This has the dual effect of (1) finding more signals in (2) a narrower angular area.

[0092] According to one embodiment, the tree beam search technique includes adaptive learning of the detection threshold. If everything about the signal environment is statistically known, the threshold T1 can be set in advance. However, in practical systems, this is impractical. Therefore, the threshold is adaptively adjusted based on how many signals are detected at each level. The type of adaptive threshold chosen offers considerable freedom. A simple approach is described in the following paragraphs, but many other options are possible.

[0093] If G1 is the gain of each beam at level 1, and G1 <G2<...<G L , then the detection test is

[0094] d(G l S)<or>T l ?

[0095] If the signal S is in a specific beam. Therefore, T1 <T2<...<T L To maintain an efficient search, it is desirable to keep the detection probability statistically constant at each level. Therefore, the optimal detection probability is

[0096] Pr(d(G l S)>T l )=C l .

[0097] For example, for a binary tree, by keeping C l = 1 / 2, a statistically constant number of signal detections can be obtained at each level of the search tree. The adaptation can be simply performed as follows. Let c1 = Pr(d(G l S)>Tl ) and c2=Pr(d(G l S)>T l hi ) By observing the current level and the threshold value T above the current level l Then set the new threshold T′ as follows l .

[0098]

[0099] The above-mentioned type of tree beam search was simulated. The simulation scenario included the following rules and conditions: (1) the number of levels was four, with 32, 64, 128, and 256 beams, respectively; (2) the number of signals present was changed from 16 to 64; (3) the beams were randomly assigned to different wide-angles with different amplitudes; and (4) no marked signal was added at the end of each search frame (as in reference Figure 2 As described in

[15] , the simulation results show that for direct search, the average delay in this case is 128D, where D is the basic detection time. Therefore, the simulation of the tree beam search technique proposed in this paper shows a clear advantage in terms of delay.

[0100] Figure 8 is a block diagram identifying some components of a phased array antenna system 2 according to one embodiment. Phased array antenna system 2 includes a phased array antenna 4, a transmitter 14, a receiver 16, and a transmit module 12, which connects transmitter 14 to phased array antenna 4 in transmit mode and connects receiver 16 to phased array antenna 4 in receive mode. Phased array antenna system 2 also includes a beam steering controller 10 configured (e.g., programmed) to control phased array antenna 4 to transmit a beam having a beam width and an angle from boresight determined by a tree-based beam search. Transmitter 14 and beam steering controller 10 are under the control of a beam search controller 1. Beam search controller 1 is a computer or processor configured (e.g., programmed) to send commands to transmitter 14 and beam steering controller 10, causing the beam selected by the tree-based beam search to be transmitted by phased array antenna 4. Beam search controller 1 also includes a module configured to detect specific parameters (e.g., energy or power) of the signal output by receiver 16.

[0101] The L levels of complementary beams are loaded (e.g., in the form of a data table) into a non-transitory, tangible, computer-readable storage medium 11, which is accessible to both the beam search controller 1 and the beam steering controller 10. The beam search controller 1 is configured to mark the selected beam specified in the complementary beam set data storage medium 11, and the beam steering controller 10 is configured to steer the beam created by the phased array antenna 4 according to the beam information read from the complementary beam set data storage medium 11.

[0102] The embodiments disclosed above use one or more processing or computing devices. Such devices typically include a processor, processing device or controller, such as a general-purpose central processing unit, a microcontroller, a reduced instruction set computer processor, an ASIC, a programmable logic circuit, an FPGA, a digital signal processor and / or any other circuit or processing device capable of performing the functions described herein. The methods described herein may be encoded as executable instructions embodied in a non-transitory tangible computer-readable storage medium, which includes but is not limited to a storage device and / or a storage device. When executed by a processing device, such instructions cause the processing device to perform at least a portion of the method described herein. The above examples are exemplary only and are therefore not intended to limit the definition and / or meaning of the terms "processor" and "computing device" in any way.

[0103] Although the systems and methods for quickly finding detectable signals within the field of view of a phased array antenna have been described with reference to various embodiments, those skilled in the art will appreciate that various changes may be made and equivalents may be substituted without departing from the teachings herein. Furthermore, numerous modifications may be made to adapt the concepts and reductions disclosed herein to the practice to suit a particular situation. Therefore, it is intended that the subject matter covered by the technical solutions is not limited to the disclosed embodiments.

[0104] Furthermore, the present disclosure includes implementations according to the following clauses:

[0105] Clause 1. A method for searching for a signal using a phased array antenna, the method comprising:

[0106] (a) transmitting a first beam having a first beam width and a first angle with a boresight axis;

[0107] (b) receiving a first signal after transmitting the first beam;

[0108] (c) detecting that a parameter value of the first signal exceeds a first threshold;

[0109] (d) transmitting a second beam having a second beam width that is less than the first beam width and a second angle with the boresight that is disposed within the angular range of the first beam; and

[0110] (e) transmitting a third beam having a second beam width and a third angle with respect to the boresight, the third angle being within the angular range of the first beam,

[0111] The first angle to the visual axis is set between the second angle and the third angle to the visual axis.

[0112] Clause 2. The method of clause 1, wherein the second beamwidth is equal to half the first beamwidth.

[0113] Clause 3. The method of clause 1, wherein the total angular extent of the second and third beams is of the same extent as the angular extent of the first beam.

[0114] Clause 4. The method of clause 1, further comprising:

[0115] (f) receiving a second signal after transmitting the second beam;

[0116] (g) detecting that a parameter value of the second signal exceeds a second threshold;

[0117] (h) transmitting a fourth beam having a third beamwidth less than the second beamwidth and a fourth angle with the boresight disposed within the angular range of the second beam; and

[0118] (i) transmitting a fifth beam having the third beam width and a fifth angle with the boresight disposed within the angular range of the second beam,

[0119] The second angle to the visual axis is set between the fourth angle and the fifth angle to the visual axis.

[0120] Clause 5. The method of clause 4, wherein the second beamwidth is equal to half the first beamwidth, and the third beamwidth is equal to half the second beamwidth.

[0121] Clause 6. The method of clause 4, wherein the total angular range of the fourth beam and the fifth beam is equal to the angular range of the second beam.

[0122] Clause 7. A method according to clause 4, wherein the first to fifth beams are selected from a complementary beam set having L levels, the L levels including a first level having M beams and including the first beam, a second level having 2M beams and including the second and third beams, and a third level having 4M beams and including the fourth and fifth beams, wherein M is an integer.

[0123] Clause 8. The method of clause 7, wherein the L levels further comprise a L-1 Lth level of M beams.

[0124] Clause 9. A method for searching for a signal using a phased array antenna, the method comprising:

[0125] Design a set of complementary beams with L levels;

[0126] Loading L levels of complementary beam sets into a beam steering controller that controls the beams generated by the phased array antenna;

[0127] Mark beam (b, l) in the complementary beam set for transmission;

[0128] Setting the phase and amplitude of antenna elements of the phased array antenna to transmit a marker beam having a beam width and a pointing angle;

[0129] transmitting a marked beam;

[0130] After transmitting the marked beam, the signal is received at the phased array antenna;

[0131] detecting when a parameter value of a received signal indicates receipt of a signal;

[0132] Determine whether the current level l is less than the total level L;

[0133] If the current level l is not less than the total number of levels L, it is declared that the direction of arrival of the signal has been detected corresponding to the pointing angle of the current beam;

[0134] If the current level l is less than the total number of levels L, marking two beams (2b-1) and 2b in a next level (l+1) corresponding to the current beam at level l of the complementary beam set for transmission;

[0135] Setting the phase and amplitude of antenna elements of the phased array antenna to transmit two beams; and

[0136] Two beams are transmitted consecutively.

[0137] Clause 10. The method of clause 9, wherein the complementary beam set has L levels, including a first level having M beams, a second level having 2M beams, a third level having 4M beams, and a fourth level having 2M beams. L-1 The Lth level of M beams, where M and L are integers.

[0138] Clause 11. The method of clause 10, wherein the first level comprises at least a first beam having a first beamwidth and a first angle to a boresight, and the second level comprises at least:

[0139] a second beam having a second beamwidth less than the first beamwidth and a second angle with the boresight disposed within the angular range of the first beam; and

[0140] a third beam having a second beam width and a third angle to the boresight, the third angle being disposed within the angular range of the first beam,

[0141] The first angle to the visual axis is set between the second angle and the third angle to the visual axis.

[0142] Clause 12. The method of clause 11, wherein the second beamwidth is equal to half the first beamwidth.

[0143] Clause 13. The method of clause 11, wherein the total angular extent of the second and third beams is of the same extent as the angular extent of the first beam.

[0144] Clause 14. A method according to clause 10, wherein the first level includes beams having a first beamwidth, the second level includes beams having a second beamwidth that is smaller than the first beamwidth, the third level includes beams having a third beamwidth that is smaller than the second beamwidth, and the Lth level includes beams having an Lth beamwidth that is smaller than the third beamwidth and smaller than the beamwidth of any level between the third level and the Lth level.

[0145] Clause 15. The method of clause 14, further comprising:

[0146] Marking a subset of additional beams from the Lth level to fill the search gaps of the current search frame; and

[0147] The phase and amplitude of the antenna elements of the phased array antenna are set to transmit additional beams.

[0148] Clause 16. A phased array antenna system comprising:

[0149] Phased array antennas;

[0150] transmitter;

[0151] Receiver;

[0152] a transmitting module, connecting the transmitter to the phased array antenna in a transmitting mode and connecting the receiver to the phased array antenna in a receiving mode;

[0153] a beam steering controller configured to control the phased array antenna to transmit a beam having a beam width and an angle to boresight determined by a tree-based beam search;

[0154] a beam searching controller configured to send commands to the transmitter and the beam steering controller, the commands causing the beam selected by the tree-based beam searching to be transmitted by the phased array antenna; and

[0155] a complementary beam set data storage medium storing data representing beam specifications of a complementary beam set organized in L levels,

[0156] The beam search controller and the beam steering controller can both access the complementary beam set data storage medium, the beam search controller is further configured to mark the selected beam specified in the complementary beam set data storage medium, and the beam steering controller is further configured to control the beam generated by the phased array antenna according to the beam information read from the complementary beam set data storage medium.

[0157] Clause 17. The phased array antenna system of Clause 16, wherein the beam search controller comprises a module configured to detect a specific parameter of a signal output by the receiver.

[0158] Clause 18. The phased array antenna system of clause 16, wherein the complementary beam set has L levels, the L levels including a first level having M beams, a second level having 2M beams, a third level having 4M beams, and a fourth level having 2M beams. L-1 The Lth level of M beams, where M and L are integers.

[0159] Clause 19. A phased array antenna system according to clause 18, wherein the first level includes beams having a first beamwidth, the second level includes beams having a second beamwidth smaller than the first beamwidth, the third level includes beams having a third beamwidth smaller than the second beamwidth, and the Lth level includes beams having an Lth beamwidth smaller than the third beamwidth and smaller than the beamwidth of any level between the third level and the Lth level.

[0160] Clause 20. The phased array antenna system of clause 16, wherein the beam search controller is further configured to perform operations comprising:

[0161] marking beam (b, l) for transmission in the complementary beam set;

[0162] detecting when a parameter value of a received signal indicates that a signal was received subsequent to said beam transmission;

[0163] Determine whether the current level l to which the transmit beam belongs is less than the total number of levels L;

[0164] If the current level l is not less than the total number of levels L, it is declared that the direction of arrival of the signal has been detected to correspond to the pointing angle of the transmit beam; and

[0165] If the current level l is less than the total number of levels L, two beams (2b-1) and 2b are marked in the next level (l+1), which corresponds to the transmit beam at level l of the complementary beam set (20) for transmission.

[0166] The method solutions set forth below should not be interpreted as requiring that the steps recited therein be performed in alphabetical order (any alphabetical order in the solution is used solely for the purpose of referencing previously recited steps) or in the order in which they are recited, unless the solution language expressly specifies or states a condition indicating a particular order in which some or all of these steps are performed. Process solutions should also not be interpreted as excluding any portion of two or more steps from being performed simultaneously or alternately, unless the solution language expressly states a condition excluding such an interpretation.

Claims

1. A method for searching for a signal using a phased array antenna (4), the method comprising: a transmitting a first beam having a first beam width and a first angle with a boresight; b. receiving a first signal after transmitting the first beam; c. detecting that a parameter value of the first signal exceeds a first threshold; d. transmitting a second beam having a second beam width that is smaller than the first beam width and a second angle with the boresight that is disposed within the angular range of the first beam; and e transmits a third beam, the third beam having a second beam width and a third angle with the boresight, the third angle being within the angular range of the first beam, wherein the first angle to the visual axis is set between the second angle and the third angle to the visual axis, and the method further comprises: f. receiving a second signal after transmitting the second beam; g. detecting that a parameter value of the second signal exceeds a second threshold; h transmitting a fourth beam having a third beamwidth less than the second beamwidth and a fourth angle with the boresight disposed within the angular range of the second beam; and transmitting a fifth beam having the third beam width and a fifth angle with the boresight that is within the angular range of the second beam, Wherein, the second angle with the visual axis is set between the fourth angle and the fifth angle with the visual axis.

2. The method according to claim 1, wherein The second beamwidth is equal to half of the first beamwidth.

3. The method according to claim 1, wherein The total angular range of the second beam and the third beam is equal to the angular range of the first beam.

4. The method according to claim 1, wherein The second beamwidth is equal to half of the first beamwidth, and the third beamwidth is equal to half of the second beamwidth, and wherein a total angular range of the fourth beam and the fifth beam is equal to an angular range of the second beam.

5. A phased array antenna system (2), comprising: Phased array antenna (4); Transmitter (14); receiver (16); a transmitting module (12) connecting the transmitter (14) to the phased array antenna (4) in a transmitting mode and connecting the receiver (16) to the phased array antenna (4) in a receiving mode; a beam steering controller (10) configured to control the phased array antenna (4) to transmit a beam having a beam width and an angle to a boresight determined by a tree-based beam search; a beam search controller (1) configured to send commands to the transmitter (14) and the beam steering controller (10), the commands causing the beam selected by the tree-based beam search to be transmitted by the phased array antenna (4); and A complementary beam set data storage medium (11) stores data representing beam specifications of a complementary beam set (20) organized in L levels, The beam search controller (1) and the beam steering controller (10) are both capable of accessing the complementary beam set data storage medium (11), the beam search controller (1) is further configured to mark a selected beam specified in the complementary beam set data storage medium (11), and the beam steering controller (10) is further configured to control the beam generated by the phased array antenna (4) according to the beam information read from the complementary beam set data storage medium (11).

6. The phased array antenna system (2) according to claim 5, wherein: The beam search controller (1) comprises a module configured to detect specific parameters of a signal output by the receiver (16).

7. The phased array antenna system (2) according to claim 5, wherein: The complementary beam set (20) has L levels, the L levels including a first level having M beams, a second level having 2M beams, a third level having 4M beams and a L‒1 The Lth level of M beams, where M and L are integers.

8. The phased array antenna system (2) according to claim 5, wherein: The first level includes beams having a first beamwidth, the second level includes beams having a second beamwidth smaller than the first beamwidth, the third level includes beams having a third beamwidth smaller than the second beamwidth, and the Lth level includes beams having an Lth beamwidth smaller than the third beamwidth and smaller than the beamwidth of any level between the third level and the Lth level.

9. The phased array antenna system (2) according to claim 5, wherein: The beam search controller (1) is further configured to perform the following operations: marking beam (b, l) in the complementary beam set (20) for transmission; detecting when a parameter value of a received signal indicates that a signal is received after a transmit beam; Determine whether the current level l to which the transmitted beam belongs is less than the total number of levels L; If the current level l is not less than the total number of levels L, it is declared that the direction of arrival of the signal has been detected to correspond to the pointing angle of the transmitted beam; and If the current level l is less than the total number of levels L, two beams 2b-1 and 2b are marked in the next level l+1, the next level corresponding to the beams transmitted at level l of the complementary beam set (20) for transmission.

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