High-speed spatial searching using phased array antennas

Abstract

To provide systems (2) and methods for rapidly finding detectable signals within the field of view of a phased array antenna (4).SOLUTION: A transmit beam pattern is modified over time to increase signal spatial search performance over typical time-delay steering by producing a coarse-to-fine angular beam pattern with a tree-based signal detection method. A tree-based beam search is employed to select a beam having a narrower beamwidth for transmission at an angle from boresight that lies in an angular space where a signal has been previously detected.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The techniques of this disclosure relate generally to phased array antennas, and more particularly to methods for searching for signals using phased array antennas. [Background technology]

[0002] Modern phased array antennas are enabling technologies supporting broadband mobile communications via satellites, aircraft, ships, and land vehicles. In particular, advanced digital beamforming is needed with large phased array antennas to improve sidelobe performance and suppress grating lobes to provide dynamic, high throughput, robust communications and network formation, as well as to provide fast nulling for jamming, fast scanning, and fast beam switching to improve network performance. Thus, beam searching has a wide variety of applications, such as connecting mobile networks, discovering new radars, and providing robust handoffs when switching between satellites and cell phone base stations. In this application, the term "beam searching" refers to searching for signals using beams (not searching for beams).

[0003] Key to beam finding is the process of beamforming. Beamforming is a signal processing method used in antenna arrays for directional signal transmission and reception. This is achieved by combining signal elements in the antenna array so that signals at certain angles experience constructive interference and other signals experience destructive interference. Such antenna arrays are typically referred to as phased array antennas. The improvement over omnidirectional (non-directional) transmission and reception is known as the directivity of the array and is an important measure of the antenna's 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 takes a pointing direction (also referred to herein as the "pointing angle" or "pointing angle") and configures the antenna array to maximize signal transmission and reception in the pointing direction to form a narrow beam. The mechanism that enables beamforming is the adjustment of the phase (or time delay) and amplitude (or weight) separately at each element, resulting in a constructive or destructive superposition of signals to produce the desired beam.

[0004] Existing phased array beamfinding solutions mimic mechanical dishes in the way they search for signals. Thus, these solutions sweep the field of view F of the array with a single narrow beam. This means that the sweep time increases linearly with the size of the array (total number of elements) since the beam must eventually be pointed to all angular regions in the field of view. To understand this, note that the first null beam width (FNBW) of a linear array with N elements at wavelength λ and element spacing of d=λ / 2 is approximately 4 / N in radians. A similar approximation is N 1 ×N 2 For a planar array of size N, the angular area is approximately the product of the beamwidths of the linear array, e.g., 16 / (N 1 N 2) Thus, the time for a complete search of a field of view F is approximately span(F) × N / 4 for a linear array and approximately area(F) × N for a planar array. 1 N 2 / 16, where span() represents the angular extent in radians, and area() represents the two-dimensional solid angle extent in steradians. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Karam et al., “Complex Chebyshev Approximation for FIR Filter Design”, IEEE Trans. on Circuits and Systems, Part II, March 1995 Summary of the Invention [Problem to be solved by the invention]

[0006] A solution to the problem of how to quickly find all detectable signals within the field of view of a phased array antenna is desired. [Means for solving the problem]

[0007] The subject matter detailed below is directed to a system and method for quickly locating detectable signals within the field of view of a phased array antenna. A tree-based signal detection approach generates coarse and fine angular beam patterns, which modify the transmit beam pattern over time to improve signal space search performance over typical time-delay steering. More specifically, a tree-based beam search is employed to select a beam with a narrow beamwidth for transmission at an angle from the boresight in the angular space where a signal was previously detected.

[0008] In one embodiment, a set of complementary beams with multiple levels is designed. The number of beams in the subsets that make up each level increases with increasing levels. The multiple levels of complementary beams are then loaded into a beam steering controller that controls the beams generated by the phased array antenna. Signal detection occurs when the value of a parameter of the detected signal exceeds a threshold. For example, the parameter detected can be the sum of the energy of the signal. Many other detection schemes are possible. As the levels increase, the gain of each beam filter increases and the beam width decreases. Thus, the signal is injected into more spatial filters, narrowing the possible signal directions while at the same time increasing the power of the received signal. This has the dual effect of (1) finding more signals and (2) in a narrower angular region.

[0009] As mentioned above, a typical phased antenna array mimics a mechanical dish in its signal search methodology. Thus, with a phased array antenna, a narrow beam is generated for each commanded angle. In contrast, the beam search methodology of the present disclosure can change the beam pattern over time to improve signal space search performance over typical time delay steering. This approach uses more of the phased array's capabilities than is typically used for beam search. This becomes evident by considering the dimensions. For a simple angle search with a single beam swept across the field of view of a phased array antenna with N elements, for a linear array (planar array) with azimuth control (azimuth and elevation control) for the beam, the phase and amplitude control will only differ in one spatial dimension (two spatial dimensions). Thus, only N-1 dimensions (N-2 dimensions) will be used during the search to generate the narrow beam. In contrast, the proposed system uses more dimensions for the search because the width and pointing angle of the beam increase. Thus, the proposed system uses up to twice the array size for the search. This allows for an efficient tradeoff between directivity and search time.

[0010] The proposed beam search methodology (hereafter referred to as "tree-type beam search") has the following notable features: (1) By performing a tree-type beam search using a phased array antenna, Dlog 2 It is possible to find all signals in the field of view (on average) in a time proportional to (N) / 2, where D is the time to detect a single signal. This is much faster than conventional methods, whose time is proportional to DN / 2 on average. (2) By rapidly searching the signal space, the probability of detecting transient signals is increased. In particular, the system can more reliably detect signals with shorter durations. For example, while standard search methods find all signals with duration DN, the proposed method finds signals with duration Dlog 2 Most signals with (N) can be detected.

[0011] The above features provide advantages to phased array antenna systems by improving search performance without the need to increase antenna size and number and improve RF receiver performance, which are costly and problematic options. The techniques employed herein employ more robust beamforming and beamsteering than those employed by typical phased array antennas and can be implemented using commercially available field programmable gate arrays (FPGAs) and electronics.

[0012] Various embodiments of systems and methods for quickly locating detectable signals within the field of view of a phased array antenna are described in detail below, one or more of which may be characterized by one or more of the following aspects.

[0013] One aspect of the subject matter detailed 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 beamwidth and a first angle from a boresight, (b) receiving a first signal after transmitting the first beam, (c) detecting a value of a parameter of the first signal exceeding a first threshold, (d) transmitting a second beam having a second beamwidth smaller than the first beamwidth and a second angle from a boresight that is within an angular range of the first beam, and (e) transmitting a third beam having the second beamwidth and a third angle from a boresight that is within an angular range of the first beam, the first angle from a boresight being between the second angle and the third angle from a boresight. According to some embodiments, the second beamwidth is equal to half the first beamwidth, and the sum of the angular range of the second beam and the angular range of the third beam is coextensive with the angular range of the first beam.

[0014] The method may further comprise: (f) detecting a second signal after transmitting the second beam; (g) detecting that a value of the parameter of the second signal exceeds a second threshold; (h) transmitting a fourth beam having a third beamwidth smaller than the second beamwidth and a fourth angle from the boresight that is within an angular range of the second beam; and (i) transmitting a fifth beam having the third beamwidth and a fifth angle from the boresight that is within an angular range of the second beam, the second angle from the boresight being between the fourth angle and the fifth angle from the boresight. The first to fifth beams may be divided into 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 2M beams and including the fourth and fifth beams. L-1 A complementary beam set having L levels is selected from a set of complementary beams having L levels, comprising an L-th level having M beams, where L and M are integers.

[0015] Another aspect of the subject matter detailed below is a method for searching for a signal using a phased array antenna, the method including: designing a complementary beam set having L levels; loading the complementary beam set with the L levels into a beam steering controller that controls a beam generated by the phased array antenna; marking a beam (b, l) in the complementary beam set for transmission; setting phases and amplitudes of antenna elements of the phased array antenna to transmit the marked beam having a beam width and a directivity angle; receiving the signal at the phased array antenna after transmitting the marked beam; The method comprises: detecting a value of a parameter of the received signal indicating that a signal has been received; determining 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, declaring that a signal has been detected in a direction of arrival corresponding to a pointing angle of the current beam; if the current level l is less than the total number of levels L, marking for transmission two beams (2b-1) and 2b of the next level (l+1) corresponding to the current beam of level l of the complementary beam set; setting the phases and amplitudes of antenna elements of the phased array antenna to transmit the two beams; and transmitting the two beams consecutively. According to a proposed embodiment, the complementary beam set comprises 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 Lth level has L levels, with an Lth level having M beams, where M and L are integers. The method may further comprise marking a subset of additional beams from the Lth level to fill search gaps in the current search frame, and setting phases and amplitudes of antenna elements of the phased array antenna to transmit the additional beams.

[0016] A further aspect of the subject matter disclosed below is a system comprising a phased array antenna, a transmitter, a receiver, a transmission 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 an angle from the bore of sight and a beam width determined by a tree-type beam search, a beam search controller configured to transmit an instruction to the transmitter and the beam steering controller to transmit a beam selected by the tree-type beam search to the phased array antenna, and a complementary beam set data storage medium storing data representing characteristics of beams of a complementary beam set configured with L levels, the complementary beam set data storage medium being accessible by both the beam search controller and the beam steering controller, the beam search controller being further configured to mark the identified and selected beams in the complementary beam set data storage medium, and the beam steering controller being further configured to control the beams generated by the phased array antenna in response to the beam information read from the complementary beam set data storage medium. The beam search controller comprises a module configured to detect a particular parameter of a signal output by the receiver.

[0017] In some embodiments of the system, the complementary beam sets include 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 The system has L levels, including an Lth level having M beams, where M and L are integers. The first level includes a beam having a first beam width, the second level includes a beam having a second beam width smaller than the first beam width, the third level includes a beam having a third beam width smaller than the second beam width, and the Lth level includes a beam having an Lth beam width smaller than the third beam width and smaller than the beam width of any level between the third level and the Lth level.

[0018] According to one proposed embodiment, the beam search controller is further configured to mark a beam (b, l) in the complementary beam set for transmission, detect that the value of a parameter of the received signal after transmission of the beam indicates that a signal has been received, determine whether the current level l to which the transmission beam belongs is less than the total number of levels L, declare that a signal has been detected in the direction of arrival corresponding to the directivity angle of the transmission beam if the current level l is not less than the total number of levels L, and mark two beams (2b-1) and 2b of the next level (l+1) corresponding to the transmission beams of level l of the complementary beam set for transmission if the current level l is less than the total number of levels L.

[0019] Other aspects of systems and methods for quickly locating detectable signals within the field of view of a phased array antenna are disclosed below.

[0020] The above-mentioned features, functions and advantages may be achieved independently in various embodiments and may also be combined in yet other embodiments. For purposes of illustrating the above-mentioned and other aspects, various embodiments are described below with reference to the drawings. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a block diagram illustrating some components of a typical phased array antenna system. [Diagram 2] 5 is a flow chart illustrating method steps for performing tree-based beam searching using a phased array antenna according to one embodiment. [Diagram 3] FIG. 2 illustrates how a digital beamformer is connected to the various elements of a phased array antenna. [Figure 4A] FIG. 4 illustrates the similarity between a single channel finite impulse response (FIR) filter (see FIG. 4A) and a uniformly spaced omnidirectional narrowband linear array (see FIG. 4B). [Figure 4B]FIG. 4 illustrates the similarity between a single channel finite impulse response (FIR) filter (see FIG. 4A) and a uniformly spaced omnidirectional narrowband linear array (see FIG. 4B). [Figure 5A] Graph of relative beam gain versus pointing angle. [Figure 5B] Graph of relative beam gain versus pointing angle. [Figure 5C] Graph of relative beam gain versus pointing angle. [Figure 6A] 1 is a graph of absolute beam gain versus pointing angle. [Figure 6B] 1 is a graph of absolute beam gain versus pointing angle. [Figure 6C] 1 is a graph of absolute beam gain versus pointing angle. [Figure 7] FIG. 1 illustrates a tree for signal detection in a phased array antenna system using beam searching. [Figure 8] FIG. 1 is a block diagram illustrating some components of a phased array antenna system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Reference will now be made to the drawings in which like elements have the same reference numerals throughout.

[0023] Exemplary embodiments of systems and methods for quickly locating detectable signals within the field of view of a phased array antenna are described in detail below. However, not all features of an actual embodiment are described herein. Those skilled in the art will appreciate that the development of an actual embodiment will involve numerous implementation-specific decisions to be made to meet the specific goals of the developer, including system and business constraints that vary from implementation to implementation. It will be further appreciated that such development efforts, while complex and time-consuming, will be routine for those skilled in the art having the benefit of this disclosure.

[0024] For illustrative purposes, an exemplary embodiment of a method for quickly locating detectable signals within the field of view of a phased array antenna will now be described. To avoid any misunderstanding, a brief explanation of the working principle of a phased array antenna will first be given with reference to FIG.

[0025] FIG. 1 is a block diagram illustrating some components of a typical phased array antenna system 2. The phased array antenna system 2 includes a phased array antenna 4, a transmitter 14, a receiver 16, and a transmission module 12 that connects the transmitter 14 to the phased array antenna 4 in a transmit mode and connects the receiver 16 to the phased array antenna 4 in a receive mode. The 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 passes through each phase shifter 8 (φ) that is controlled by a beam steering controller 10. The beam steering controller 10 is configured (e.g., programmed) to control the phase shifters 8 such that each antenna element 6 emits RF waves that combine to generate a transmit beam having a pointing angle θ. The individual wavefronts are spherical, but combine (overlap) in front of the phased array antenna 4 to generate a plane wave that propagates in a particular direction. The phase shifter 8 delays the RF wave so that each antenna element 6 emits its wavefront later than the previous antenna element. This results in a plane wave oriented at an angle θ relative to the antenna axis (also known as boresight). By changing the phase shift, the beam steering controller 10 can instantaneously change the angle θ of the transmit beam. Most phased arrays have a two-dimensional array of antenna elements instead of the linear array shown in FIG. 1, in which case the transmit beam is steerable in two dimensions. The receive beam is similarly formed by controlling the phase shift to combine the wavefronts returning from the pointing angles.

[0026] In telecommunications and radar engineering, the antenna borehole is the axis of maximum gain (maximum radiated power) of a directional antenna. In most antennas, the borehole is the axis of symmetry of the antenna. For example, in an axially fed dish antenna, the antenna borehole is the axis of symmetry of the parabolic dish and the antenna radiation pattern (main lobe) is symmetric about the borehole axis. Phased array antennas can electronically steer the transmit beam, changing the angle of the borehole (also known as the pointing angle) by shifting the relative phases of the RF waves emitted by the different antenna elements 6. In this application, the term "beamwidth" refers to the angle between the half power (approximately 3 dB) points of the main lobe when referenced to the peak effective radiated power of the main lobe.

[0027] The beam searching method of the present disclosure allows the beam pattern generated by the phased array antenna system 2 to change over time, and improves signal space searching performance over typical time delay steering by generating a coarse-fine angular beam pattern with a tree-based signal detection approach. FIG. 2 is a flow chart illustrating steps of a method for performing tree-based beam searching using a phased array antenna 4 according to an embodiment, including marking a beam selected for transmission and transmitting the marked beam using the phased array antenna 4. The steps illustrated in FIG. 2 are performed under the control of a beam searching controller 1 communicatively coupled to a beam steering controller 10. The beam searching controller 1 is a computer or processor configured (e.g., programmed) to send instructions to the beam steering controller 10. And the beam steering controller 10 is a computer or processor configured (e.g., programmed) to control the phased array antenna 4 to transmit a marked beam having an angle from boresight and a beam width determined by the tree-based beam searching.

[0028] According to the embodiment shown in FIG. 2, a complementary beam set 20 with L levels is designed. The beam pattern is pre-designed to be as follows: Level 1 has M beams; Level 2 has 2M beams, each beam pair fits within the corresponding beam of the beam pattern from Level 1; Level 3 has 4M beams, each beam pair fits within the corresponding beam of the beam pattern from Level 2. In this application, "fit" means that the angular range of a beam pair at a level overlaps and fits within each part of the angular range of the corresponding wider beam at the next lower level, and furthermore, the angle from the boresight of the wider beam at the next lower level is between the respective angles from the boresight of the beam pair. This can be achieved using a filter design method, which will be described in more detail below. Each beam of the beam set is identified by a "marking" denoted as n(l,b), which represents the bth marked beam at level l.

[0029] The L levels of complementary beams are then loaded into a non-transitory tangible computer-readable storage medium (not shown in FIG. 2, but see the complementary beam set data storage medium 11 in FIG. 8). The non-transitory tangible computer-readable storage medium is accessible by both the beam search controller 1 and the beam steering controller 10. The beam search controller 1 is configured to mark the identified and selected beams in the complementary beam set data storage medium 11, while the beam steering controller 10 is configured to control the beams 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 the phase delay for each antenna element 6 of the phased array antenna (as previously described with reference to FIG. 1) and also sets the weighting used to adjust the amplitude of the wavefront emitted by the antenna array 6.

[0030] In response to initializing the beam search for a new search frame, the beam search controller 1 resets the beam index b and the level index l (step 34 in FIG. 2). A transmit beam request 22 containing these indices (which identify the marked beam to be transmitted) is sent to the beam steering controller 10. The beam steering controller 10 then sets the phase and amplitude of the antenna elements 6 to transmit the marked beam having a particular angle from the borehole and a particular beam width.

[0031] Following the transmission of the programmed beam, the signal S is received by the phased array antenna 4. In this application, the programmed beam B at level l is ln(l,b) The signal received following transmission of B ln(l,b) The beam search controller 1 is further configured to detect that the value of the signal parameter indicates that a signal (and not noise) has been received. ln(l,b) To detect the value of a parameter (e.g., energy) of (S), the beam search controller 1 uses a selected detection algorithm d() and sets a threshold T l More specifically, the detected value of the parameter is set to have a threshold T l Determine whether (step 24 in FIG. 2 ): d(B ln(l,b) (S))>T l ? The parameter value of the received signal is the threshold T l If it is determined that the current level l exceeds the total number of levels L, then it is further determined whether the current level l is less than the total number of levels L (step 26). And if the current level l is not less than the total number of levels L (e.g., l=L), then the signal detection exceeding the threshold is determined to be a current beam B ln(l,b) This leads to the system declaring (step 27) that a signal has been detected in the direction of arrival corresponding to the pointing angle of

[0032] On the other hand, if the current level l is less than the total number of levels L, then the two beams (2b-1) and (2b) of the next level (l+1) corresponding to the current beam of level l are marked for use (step 28). Digital data representing the markings n(l+1,2b) and n(l+1,2b-1) are then stored in a first-in first-out (FIFO) buffer 30. The beam search controller 1 then determines whether beam searching has been performed on all marked beams (step 32). If all marked beams of all levels have been released, then the beam search controller 1 determines whether to mark an additional subset of narrow beams to fill the search gaps of the current search frame.

[0033] On the other hand, if it is determined (at step 32) that the beam search has not been performed on all marked beams, a transmit beam request 22 including a beam index b and a level index l (identifying the next marked beam to transmit) is 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(l,b) The beam steering controller 10 then sets the phase and amplitude of the antenna elements 6 for the next marked beam in the set of complementary beams 20 to be transmitted.

[0034] On the other hand, if it is determined that beam search has been performed on all marked beams for the current search frame (in step 32), then the beam search controller 1 determines whether the beam search should include an additional narrow beam (e.g., a beam having a beam width equal to the beam width of the last level L beam) (step 34).

[0035] On the other hand, if it is determined (at step 34) that no additional narrow beams should be added for the current search frame, then the beam search controller 1 resets (step 18) and initializes (step 22) the beam search for the new search frame.

[0036] On the other hand, if it is determined (at step 34) that additional narrow beams should be added to the current search frame to fill the search gaps of the current search frame, then the beam search controller 1 marks a subset of additional narrow beams. These additional narrow beams are marked at the end of the beam search frame where all marked beams have already been processed. The reason for choosing to mark additional narrow beams to complete the search frame is to handle the case where the received signal is detectable only in the narrowest beam (correspondingly with the highest gain) and would be missed by an efficient tree-based search. For a binary search tree, M L =2 L-1 There may be M beams, and

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[0037] Frame F 1 Frame F 1 Unmarked narrow beam (U(F) 1 )={u 1 ,u 2 ,…}) of M L -N L (F 1 ) and mark the first set of m=t / D beams taken in succession from the complete set of F 1 )={u 1 ,…,um} is called.

[0038] Frame F 2 This frame F 2 Unmarked narrow beam (U(F) 2 ) to A(F 1 ) beam (U(F 2 )\U(F 1 Mark the next set of m beams taken consecutively from A(F 2 )

[0039] This process is called the unmarked beam minus the additionally marked beam, U(F)\(F 1 )\(F 2 This continues frame by frame until the set of . . . is exhausted. Then the process of marking additional narrow beams begins again.

[0040] A simple modification to this scheme is easily designed with a non-constant search frame rate and a non-constant beam dwell time. The following disclosure describes the complementary beamset design and FIR filter design.

[0041] 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 number of multipliers 40, each of which weights a respective signal output by the multiple antenna elements 6. The signals output by the multipliers 40 are summed by a summer 42. The output y(k) at time instant k is given as a linear combination of the data at the J antenna elements 6 at time instant k as follows:

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[0042] 4A and 4B illustrate the similarity between a single channel finite impulse response (FIR) filter 52 (see FIG. 4A) and a beamformer 50 (see FIG. 4B) in the form of a uniformly spaced omnidirectional narrowband linear array.

[0043] 4A, the FIR filter 52 includes a number of element weights that are applied by a multiplier 40 to generate a weighted signal, which is summed by a summer 42. Z -1 Each square labeled represents a register or memory element that functions to delay a value by one clock period. Thus, each multiplier receives the incoming signal after a delay of a different duration.

[0044] Element weight w j * The frequency response of a finite impulse response (FIR) filter with (1≦j≦J) and element delay of T seconds is given by:

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[0045] Referring to FIG. 4B, we assume that the incident signal is a complex plane wave with arrival direction θ and frequency ω. Then, the equation for r(w,ω) isH From d(ω)

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[0046] The correspondence between FIR filtering and beamforming is that the beamformer filters a single time frequency ω 0 and is closest when 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 (speed of light) be c, and θ represent the direction of arrival relative to the boresight (which is normal to the array). Then the time delay due to propagation from the 1st sensor to the jth sensor is given by: τ j (θ)=(j-1)(d / c)sin(θ) In this case, the time frequency ω of the term d(ω) (FR filter) and the term d(θ,ω 0 ) (beamformer) direction θ is as follows: ω=ω 0 (d / c)sin(θ) The time frequency of the FIR filter therefore corresponds to the sine of the orientation of the narrowband uniform linear array used as the beamformer.

[0047] Figures 5A-C are graphs of relative beam gain vs. pointing angle that partially show 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) spanning the angular space from -60° to +60° for a uniform linear array. The relative gains are shown (with all beams having a maximum gain of 0 dB). This helps to show how these spatial filters combine with each other to divide the space into equally spaced angular regions that can be traversed like a tree.

[0048] FIG. 5A shows the relative beam gain vs. pointing angle for a first level consisting of 8 beams, each of which has a beam width approximately equal to 15°. FIG. 5B shows the relative beam gain vs. pointing angle for a second level consisting of 16 beams, each of which has a beam width approximately equal to 7.5°. FIG. 5C shows the relative beam gain vs. pointing angle for a third level consisting of 32 beams, each of which has a beam width approximately equal to 3.75°. The graphs for the fourth level consisting of 64 beams (each of which has a beam width approximately equal to 1.875°) and the fifth level consisting of 128 beams (each of which has a beam width approximately equal to 0.9375°) are similar, but are not shown in the black line diagram because the large number of beams makes it difficult to distinguish the individual beams and such graphs do not enhance the reader's understanding.

[0049] For example, assume that the beam search controller 1 causes the beam steering controller 10 to transmit a beam 70 (see FIG. 5A) from a first level, which has an angle range from 0° (corresponding to boresight) to +15°. Assume further that after the beam 70 (see FIG. 5A) from the first level is transmitted, the detection parameter of the received signal is greater than the detection threshold of the first level. The system processes the sensor data and determines that the detection signal arrives at an angle that is within the angle range from 0° to +15°.

[0050] The beam search controller 1 then causes the beam steering controller 10 to transmit beams 72 and 74 (see FIG. 5B) from the second level, where beam 72 has an angular range of 0° to +7.5° and beam 74 has an angular range of 7.5° to +15°. Assume further that after beam 72 (see FIG. 5B) from the second level is transmitted, the detection parameter of the signal received after transmitting beam 72 is greater than the detection threshold of the second level. The system processes the sensor data to determine that the detection signal arrived at an angle that is within the angular range of 0° to +7.5°.

[0051] The beam search controller 1 then causes the beam steering controller 10 to transmit beams 76 and 78 (see FIG. 5C) from the third level, where beam 76 has an angular range of 0° to +3.75° and beam 78 has an angular range of +3.75° to 7.5°. Assume further that after beam 76 (see FIG. 5C) from the third level is transmitted, 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 to determine that the detection signal arrived at an angle that is within the angular range of 0° to +3.75°.

[0052] The beam search controller 1 then causes the beam steering controller 10 to transmit two beams (not shown) from the fourth level. This process continues at least until the two beams from the last level are transmitted. If one of these beams results in a received signal having a detection parameter greater than the detection threshold for the last level, then the system processes the sensor data to determine that the detected signal arrived at an angle, for example, within an angle range from 0° to +0.9375°. In this way, the direction of arrival of the signal from the target object can be determined.

[0053] 6A-6C are graphs of absolute beam gain vs. pointing angle partially illustrating 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) spanning the angle space from -60° to +60° for a uniform linear array. FIG. 6A shows absolute beam gain vs. pointing angle for a first level of 8 beams. FIG. 6B shows absolute beam gain vs. pointing angle for a second level of 16 beams. FIG. 6C shows absolute beam gain vs. pointing angle for a third level of 32 beams. The graphs for the fourth level with 64 beams and the fifth level with 128 beams are similar but not shown.

[0054] Using FIR filter design methods, side lobes are kept under control (side lobes are typically 30 dB below the main lobe or less), but at the expense of maximum gain. The maximum achievable gain with N=256 elements is 48 dB=20 log 10 (N), which is well above the maximum gain in the level 5 graph (not shown), which is only about 23 dB. The reason for this is that the constrained design method to keep the sidelobe levels under control also reduces the maximum gain. By not constraining the sidelobes, the maximum gain can be achieved, which is much higher than that of the complementary beam set designed using the constrained approach. Also, the gain of each beam shows differences across the field of view. These differences can be easily corrected by amplitude adjustment of the element weights.

[0055] FIR filter designs are quite varied and can be achieved in many ways. Rather than describing all the many ways to achieve filter design (optimization, frequency methods, Remez's algorithm, etc.), this disclosure describes one approach for reference. Filter design can be either real or complex methods, for FIR filters or infinite impulse response filters. Since the process of interest is antenna beamforming, complex FIR filter design methods are used. In particular, complex approximations are used for designing filters with nonlinear phase characteristics such as beamforming. The frequency response H(ω) of an FIR digital filter of length N (corresponding to N antenna elements) is typically a complex-valued function of normalized frequency ω:

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[0056] An efficient multiple exchange algorithm for the design of complex FIR digital filters in Chebyshev space is proposed in [1] by generalizing the Remez exchange algorithm. This algorithm is essentially a generalization of the Parks-McClellan algorithm to the complex case. Specifically, given a set of normalized frequencies, this algorithm converges to the best weighted Chebyshev approximation for B if the optimal error satisfies a given alternation property, and typically converges to the optimal Chebyshev solution for some compact subset of B.

[0057] The methodology proposed in this application involves transmitting beams with increasingly finer angular beam patterns according to a tree-based approach. Assuming a tree 60 has L levels, as shown in FIG. 7, M for level l (1≦l≦L) L =2 l-1 M beams (or spatial beam patterns)

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[0058] For each level l of 1≦l≦L, each detection threshold T l is chosen such that the probability of signal detection in each beam is a constant less than 1 (e.g., if the constant is 0.5, the number of detected signals remains constant at each level of the binary tree). The notation B(S) denotes a signal S filtered by a beam spatial 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, denoted d(), such that signal detection occurs when the value of a parameter of the detected signal exceeds a threshold. In other words, for level l, d(B(S))>T l A detection of a signal S is declared if: 1 ,s 2 ,…,s n}, it becomes:

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[0059] As the level increases, the gain of each beam filter increases and the beamwidth decreases. Thus, the signal is injected into more spatial filters, narrowing the possible signal directions while increasing the received signal power. This has the dual effect of (1) finding more signals and (2) finding them in a narrower angular region.

[0060] In one embodiment, the tree beam search method includes adaptive learning of the detection threshold. When all is well known about the signal environment, the threshold T 1 can be preset. However, in a real system, this is not practical. Therefore, the thresholds are adaptively adjusted depending on how much signal is being detected at each level. There are many types of adaptive thresholding to choose from. Below, a simple approach is described, but many other options are possible.

[0061] G l is the gain of each beam at level l, and G 1 <G 2 <… <G L and if the signal S is in a particular beam, the detection test is as follows: d(G l S) <T l ? or d(G l S)>T l ? Therefore, T 1 <T 2 <… <T L To maintain an efficient search, it is desirable to maintain a statistically constant probability of detection across levels. Thus, the optimal probability of detection is: Pr(d(G l S)>T l )=C l

[0062] For example, in a binary tree, C l By keeping c = 1 / 2, we can obtain a statistically constant number of signal detections at each level of the search tree. The adaptation is simple: 1 =Pr(d(G l S)>T l ), c 2 =Pr(d(G l S)>T l hi ) at the current level and the threshold T lA new threshold Tl' is then set as follows:

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[0063] A simulation of the above type of tree beam search was carried out. The simulation plan included the following rules and conditions: (1) the number of levels was 4, and the four levels had 32 beams, 64 beams, 128 beams, and 256 beams, respectively; (2) the number of signals was varied from 16 to 64; (3) the beams were randomly assigned a wide range of angles and various amplitudes; (4) no marked signals were added at the end of each search frame (as described above with reference to FIG. 2). The simulation result showed that for direct search, the average latency in this situation was 128D, where D is the basic detection time. Thus, the simulation of the tree beam search technique proposed in this application shows a clear advantage in latency.

[0064] FIG. 8 is a block diagram illustrating some components of a phased array antenna system 2 according to an embodiment. The phased array antenna system 2 includes a phased array antenna 4, a transmitter 14, a receiver 16, and a transmission module 12 that connects the transmitter 14 to the phased array antenna 4 in a transmit mode and connects the receiver 16 to the phased array antenna 4 in a receive mode. The phased array antenna system 2 further includes a beam steering controller 10 configured (e.g., programmed) to control the phased array antenna 4 to transmit a beam having an angle from the boresight and a beam width determined by the tree-type beam search. The transmitter 14 and the beam steering controller 10 are under the control of a beam search controller 1. The beam search controller 1 is a computer or processor configured (e.g., programmed) to send instructions to the transmitter 14 and the beam steering controller 10, which cause the phased array antenna 4 to transmit the beam selected by the tree-type beam search. The beam search controller 1 also includes a module configured to detect certain parameters (e.g., energy and power) of the signal output by the receiver 16.

[0065] 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 accessible by both the beam searching controller 1 and the beam steering controller 10. The beam searching controller 1 is configured to mark identified and selected beams in the complementary beam set data storage medium 11, while the beam steering controller 10 is configured to control beams generated by the phased array antenna 4 according to the beam information read from the complementary beam set data storage medium 11.

[0066] The above embodiments use one or more processing or computing devices. Such devices typically include processors, processing devices, controllers, such as general purpose central processing units (general purpose CPUs), microcontrollers, reduced instruction set computer processors, ASICs (application specific integrated circuits), programmable logic circuits, FPGAs (field programmable gate arrays), digital signal processors, and / or other circuits or processing devices capable of performing the functions disclosed herein. The methods of the present disclosure may be encoded as executable instructions in a non-transitory tangible computer readable storage medium, such as, but not limited to, a storage device and / or a memory device. Such instructions, when executed by a processing device, cause the processing device to perform at least a portion of the methods of the present disclosure. The above examples are merely illustrative and are not intended to limit the definition and / or meaning of the terms "processor" and "computing device."

[0067] Although a system and method for quickly locating detectable signals within the field of view of a phased array antenna has been described with reference to various embodiments, those skilled in the art will recognize that various modifications may be made and equivalents substituted without departing from the teachings of the present disclosure. Furthermore, numerous variations may be made to adapt the concepts of the present disclosure to implement a particular situation. Accordingly, the subject matter covered by the claims is not limited to the embodiments of the present disclosure.

[0068] Furthermore, the present disclosure includes embodiments according to the following clauses:

[0069] Item 1 1. A method for searching for a signal using a phased array antenna, comprising: (a) transmitting a first beam having a first beamwidth and a first angle from a boresight; (b) receiving a first signal after transmitting the first beam; and (c) detecting that a value of the parameter of the first signal exceeds a first threshold; (d) transmitting a second beam having a second beamwidth smaller than the first beamwidth and a second angle from the boresight that is within the angular range of the first beam; (e) transmitting a third beam having a second beamwidth and a third angle from the boresight that is within the angular range of the first beam; The method, wherein the first angle from the sight is between the second angle and the third angle from the sight.

[0070] Section 2 Item 1. The method of claim 1, wherein the second beam width is equal to half the first beam width.

[0071] Section 3 Item 2. The method of item 1, wherein the sum of the angular range of the second beam and the angular range of the third beam is coextensive with the angular range of the first beam.

[0072] Section 4 (f) receiving a second signal after transmitting the second beam; and (g) detecting that a value of the parameter of the second signal exceeds a second threshold; and (h) transmitting a fourth beam having a third beamwidth less than the second beamwidth and a fourth angle from the boresight that is within the angular range of the second beam; (i) transmitting a fifth beam having a third beamwidth and a fifth angle from the boresight that is within the angular range of the second beam; Item 2. The method of item 1, wherein the second angle from the aim is between the fourth angle and the fifth angle from the aim.

[0073] Section 5 Item 5. The method of item 4, wherein the second beam width is equal to half the first beam width and the third beam width is equal to half the second beam width.

[0074] Section 6 5. The method of claim 4, wherein the sum of the angular range of the fourth beam and the angular range of the fifth beam is coextensive with the angular range of the second beam.

[0075] Section 7 Item 5. The method of item 4, wherein the first beam to the fourth beam are selected from a complementary beam set having L levels, including a first level having M beams and including the first beam, a second level having 2M beams and including the second beam and the third beam, and a third level having 4M beams and including the fourth beam and the fifth beam, where M is an integer.

[0076] Section 8 L levels, 2 L-1 Item 8. The method of item 7, further comprising an Lth level having M beams.

[0077] Section 9 1. A method for searching for a signal using a phased array antenna, comprising: Designing a set of complementary beams having L levels; loading the L-level complementary beam sets into a beam steering controller that controls a beam generated by the phased array antenna; marking a beam (b, l) of a set of complementary beams for transmission; setting phases and amplitudes of antenna elements of a phased array antenna to transmit a marked beam having a beamwidth and a directivity angle; Transmitting a marked beam; receiving a signal with a phased array antenna after transmitting the marked beam; detecting when a value of a parameter of the received signal indicates that a signal has been received; determining whether a current level l is less than a total number of levels L; Declaring that a signal has been detected in a direction of arrival corresponding to the directivity angle of the current beam if the current level l is not less than the total number of levels L; marking for transmission two beams (2b-1) and 2b of the next level (l+1) corresponding to the current beam of the level l of the complementary beam set when the current level l is less than the total number of levels L; setting phases and amplitudes of antenna elements of a phased array antenna to transmit two beams; transmitting two beams in succession.

[0078] Item 10 The complementary beam sets include 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 10. The method of claim 9, having L levels, with an Lth level having M beams, where M and L are integers.

[0079] Section 11 the first level includes at least a first beam having a first beam width and a first angle from the boresight; The second level is a second beam having a second beam width less than the first beam width and a second angle from the boresight that is within the angular range of the first beam; a third beam having a second beam width and a third angle from the boresight that is within the angular range of the first beam; 11. The method of claim 10, wherein the first angle from the boresight is between the second angle and the third angle from the boresight.

[0080] Item 12 Item 12. The method of item 11, wherein the second beam width is equal to half the first beam width.

[0081] Item 13 12. The method of claim 11, wherein the sum of the angular range of the second beam and the angular range of the third beam is coextensive with the angular range of the first beam.

[0082] Section 14 Item 11. The method of item 10, wherein the first level includes a beam having a first beam width, the second level includes a beam having a second beam width smaller than the first beam width, the third level includes a beam having a third beam width smaller than the second beam width, and the L level includes a beam having an L beam width smaller than the third beam width and smaller than the beam width of any level between the third level and the L level.

[0083] Section 15 marking a subset of additional beams from the Lth level to fill search gaps in the current search frame; and 15. The method of claim 14, further comprising: setting phases and amplitudes of antenna elements of the phased array antenna to transmit additional beams.

[0084] Section 16 Phased array antenna and A transmitter; A receiver; a transmission module for connecting the transmitter to the phased array antenna in a transmit mode and for 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 an angle from the boresight and a beamwidth determined by the tree beam search; a beam search controller configured to send instructions to the transmitter and the beam steering controller to cause the beam selected by the tree-type beam search to be transmitted to the phased array antenna; a complementary beam set data storage medium storing data representative of beam characteristics of a complementary beam set consisting of L levels; A phased array antenna system, wherein the complementary beam set data storage medium is accessible by both the beam search controller and the beam steering controller, the beam search controller being further configured to mark identified and selected beams in the complementary beam set data storage medium, and the beam steering controller being further configured to control beams generated by the phased array antenna in response to beam information read from the complementary beam set data storage medium.

[0085] Section 17 Item 17. The phased array antenna system of item 16, wherein the beam searching controller comprises a module configured to detect certain parameters of the signal output by the receiver.

[0086] Section 18 The complementary beam sets include 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 Item 17. The phased array antenna system of item 16, having L levels with an Lth level having M beams, where M and L are integers.

[0087] Section 19 Item 19. The phased array antenna system of item 18, wherein the first level includes a beam having a first beamwidth, the second level includes a beam having a second beamwidth smaller than the first beamwidth, the third level includes a beam having a third beamwidth smaller than the second beamwidth, and the Lth level includes a beam 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.

[0088] Section 20 A beam search controller marking a beam (b, l) of a set of complementary beams for transmission; detecting when a value of a parameter of the received signal indicates that a signal has been received; determining whether a current level l to which a transmitted beam belongs is less than a total number of levels L; Declaring that a signal has been detected in a direction of arrival corresponding to the directivity angle of the transmit beam if the current level l is not less than the total number of levels L; Item 17. The phased array antenna system of item 16, further configured to: mark for transmission two beams (2b-1) and 2b of the next level (l+1) corresponding to the transmission beams of level l of the complementary beam set when the current level l is less than the total number of levels L.

[0089] The method claims in the appended claims should not be construed as requiring the recited steps to be performed in alphabetical order (the alphabetical order in the claims is used only to refer to previously recited steps) or in the order recited, unless a condition indicating a particular order in which some or all of the steps are performed is specifically stated. The method claims should not be construed as excluding the simultaneous or alternating performance of portions of two or more steps, unless a condition expressly states otherwise excluding such an interpretation. [Explanation of symbols]

[0090] 1 Beam Search Controller 2 Phased Array Antenna System 4 Phased Array Antenna 6 Antenna elements 8 Phase Shifter 10 Beam steering controller 12 Transmission module (transmitting and receiving module) 14 Transmitter 16 Receiver 20 Complementary Beam Sets 40 Multiplier 42 Adder 50 Digital Beamformer 52 Finite Impulse Response (FIR) Filters

Claims

1. A method for searching for a signal using a phased array antenna (4), comprising the steps of: (a) transmitting a first beam having a first beamwidth and a first angle from a boresight; (b) receiving a first signal after transmitting the first beam; and (c) detecting that a value of a parameter of the first signal exceeds a first threshold; and (d) transmitting a second beam having a second beamwidth smaller than the first beamwidth and a second angle from the boresight that is within an angular range of the first beam; (e) transmitting a third beam having the second beam width and a third angle from boresight that is within an angular range of the first beam; a first angle from the sight is between a second angle from the sight and a third angle from the sight; The method further comprises determining whether to add additional narrow beams to fill a search gap.

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

3. 3. The method of claim 1 or 2, wherein the sum of the angular range of the second beam and the angular range of the third beam is coextensive with the angular range of the first beam.

4. (f) receiving a second signal after transmitting the second beam; and (g) detecting a value of the parameter of the second signal exceeding a second threshold; and (h) transmitting a fourth beam having a third beamwidth less than the second beamwidth and a fourth angle from boresight that is within the angular range of the second beam; (i) transmitting a fifth beam having the third beamwidth and a fifth angle from boresight that is within an angular range of the second beam; 4. The method of claim 1, wherein the second angle from the sight is between a fourth angle from the sight and a fifth angle from the sight.

5. 5. The method of claim 4, wherein the second beam width is equal to half the width of the first beam, the third beam width is equal to half the width of the second beam, and the sum of the angular extent of the fourth beam and the angular extent of the fifth beam is coextensive with the angular extent of the second beam.

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