Three-dimensional and four-dimensional mapping of space using microwave and millimeter wave parallax

Description

FIELD OF THE INVENTION

[0001] The present invention relates to location determination using radio frequency signals.BACKGROUND OF THE INVENTION

[0002] Determining the location and rate of movement of an object within a limited area can benefit a broad range of applications, such as gaming, human machine interface, security, environment awareness, health systems, wireless power transfer, hospitality, and the like. Three dimensional (3D) maps of various entities within an area (for example a room) can be done by determining the distance from an object to a source at different directions.

[0003] Document US2005270229A1 discloses a system and method for determining the position of an object in relation to a positioning system using a sparse antenna array.

[0004] In a four-dimensional (4D) imaging system, in addition to location information, additional information about the various targets, such as their speed and direction of movement is also obtained. In standard lidar and radar solutions, the distance from the signal source to a remote target is measured by evaluating the time of flight, i.e., the time it takes for the signal to reach the target and travel back to the source of the signal. Therefore, a timing marker on the probing signal is required to enable such measurement. This can be performed as a pulse radar (i.e. amplitude modulation of the radar signal) where a short pulse of radio-frequency signal is transmitted toward the target and its time of flight is measured.

[0005] Frequency-modulated continuous-wave (FM-CW) radars and phase-modulated continuous-wave (PM-CW) radars may also be used to determine the distance (range) by evaluating the difference between the frequency of reflected and transmitted signals, when a chirp frequency that linearly increases with time is used as the transmit signal.

[0006] However, in such conventional methods, because the range resolution is mainly determined by the bandwidth of the transmitted signal, the modulated signal occupies a significant bandwidth. The bandwidth limitation affects the range resolution.BRIEF SUMMARY OF THE INVENTION

[0007] A method of determining an object's distance, in accordance with one embodiment of the present invention, includes, in part, delivering a first RF signal from a first transmitter to the object while a second transmitter is deactivated, changing the direction of the first transmitter along both azimuth and elevation until the first transmitter reaches a first direction defined by first and second angles at which the power of the first RF signal as reflected off the object and received by a receiver reaches a maximum value, delivering a second RF signal from the second transmitter to the object while the first transmitter is deactivated, changing the direction of the second transmitter along both azimuth and elevation until the second transmitter reaches a second direction defined by third and fourth angles at which the power of the second RF signal as reflected off the object and received by the receiver reaches a maximum value, and determining the distance between the object and the first transmitter using the distance between the two transmitters, and the first, second, third and fourth angles.

[0008] In one embodiment, the method further includes, in part, determining the distance between the object and the second transmitter using the distance between the two transmitters, and the first, second, third and fourth angles. In one embodiment, the method further includes, in part, determining the distance between the object and the receiver using the distance between the two transmitters, the distance between the first transmitter and the receiver, and the first, second, third and fourth angles.

[0009] In one embodiment, the first transmitter, the second transmitter and the receiver are positioned along a substantially straight line. In one embodiment, the receiver is a Doppler receiver.

[0010] A mapping system, in accordance with the present invention, includes, in part, a first transmitter adapted to deliver a first RF signal to an object, a second transmitter adapted to deliver a second RF signal to the object, wherein the second transmitter is deactivated when the first transmitter delivers the first RF signal, and wherein the first transmitter is deactivated when the second transmitter delivers the second RF signal, a receiver, and a controller configured to change the direction of the first transmitter along both azimuth and elevation until the first transmitter reaches a first direction defined by first and second angles at which the power of the first RF signal as reflected off the object and received by the receiver reaches a maximum value. The controller is further configured to change the direction of the second transmitter along both azimuth and elevation until the second transmitter reaches a second direction defined by third and fourth angles at which the power of the reflected RF signal as reflected off the object and received by the receiver reaches a maximum value. The controller is further configured to determine the distance between the object and the first transmitter using the distance between the two transmitters, and the first, second, third and fourth angles.

[0011] In one embodiment, the controller is further configured to determine the distance between the object and the second transmitter using the distance between the two transmitters, and the first, second, third and fourth angles. In one embodiment, the controller is further configured to determine the distance between the object and the receiver using the distance between the two transmitters, the distance between the first transmitter and the receiver, and the first, second, third and fourth angles.

[0012] In one embodiment, the first transmitter, the second transmitter and the receiver are positioned along a substantially straight line. In one embodiment, the receiver is a Doppler receiver.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1A shows mapping system, in accordance with an example useful to understand the present invention. Figure 1B shows a mapping system, in accordance with an example useful to understand the present invention. Figure 2 shows a mapping system, in accordance with an example useful to understand the present invention. Figure 3A shows a mapping system, in accordance with one embodiment of the present invention. Figure 3B shows a mapping system, in accordance with an example useful to understand the present invention. Figure 4 shows a mapping system, in accordance with an example useful to understand the present invention. Figure 5 shows a mapping system, in accordance with an example useful to understand the present invention. Figure 6 shows a mapping system, in accordance with an example useful to understand the present invention. Figure 7 shows a mapping system, in accordance with an example useful to understand the present invention. Figure 8 shows a Doppler mapping system, in accordance with an example useful to understand the present invention. Figure 9 shows a Doppler mapping system, in accordance with one embodiment of the present invention. Figure 10A shows a pair of transmitters transmitting signals to a target to determine the target's range, in accordance with one embodiment of the present invention. Figure 10B shows a pair of phased arrays transmitting signals to a target to determine the target's range, in accordance with one embodiment of the present invention. Figure 10C shows a phased array transmitting signals to a target to determine the target's range, in accordance with one embodiment of the present invention DETAILED DESCRIPTION OF THE INVENTION

[0014] In accordance with one embodiment of the present invention, the range of stationary and moving objects are determined using continuous-wave radio frequency to form 3D and / or 4D maps while consuming minimal signal bandwidth. To achieve this, embodiments of the present invention use parallax, defined herein as the angular difference resulting from viewing an object from different lines of sight. In a 3D / 4D mapping context and in its simplest case, the angular difference may be attained via a displacement either between at least two receivers (RX) that capture a reflected signal at two slightly different angles, or between at least two transmitters (TX) whose radiated signals arrive at the target at two slightly different angles.

[0015] Figure 1A shows a pair of transmitters 10 and 12 transmitting signals to target 15 at respective angels of θ 1 and θ 2 so as to determine the target 15's range, in accordance with an example useful to understand the present invention and as described further below. Figure 1B shows a pair of receivers 20 and 22 receiving signals from target 15 at respective angels of θ 1 and θ 2 in order to determine the target 15's range, in accordance with another embodiment of the present invention and as described further below. In both Figures 1A and 1B parallax is obtained by way of the separation between the transmitters and / or receivers causing the angular difference.

[0016] Figure 2 shows a 3D / 4D mapping system 100, in accordance with one example useful to undertand the present invention. Mapping system 100 is shown as including, in part, transmitters 10, 12, receiver 20 and controller / computer 90. Transmitters 10 and 12 may be components of a dual-beam transmitter / scanner that are spaced apart by a distance D. In the exemplary mapping system 100, receiver 20 is assumed to be positioned along a line connecting transmitters 10, 12 and positioned away from transmitters 10, 12 by respective distances of D 1 and D 2 . Therefore, in Figure 2, D = D 1 + D 2 . It is understood that embodiments of the present invention are not so limited and that in other embodiments, transmitters 10, 12 and receiver 50 may not be positioned on a straight line. Controller / computer 90 is configured, in part, to control the operation of the transmitters and receiver, and further to perform the computations described below to determine the range of target 15.

[0017] To determine the range of target 15 and generate a 3D / 4D map, while one of the transmitters is activated to scan the environment, the other transmitter is deactivated. For example, when transmitter 10 is activated to scan the environment, transmitter 12 remains deactivated. Conversely, when transmitter 12 is activated to scan the environment, transmitter 10 is deactivated.

[0018] During an active scan by either of the two transmitters, the strength of the signal reflected by target 15 and captured (or received) by receiver 20 is at a maximum value when the active transmitter's beam is pointed toward the target. For example, assume transmitter 10 is activated to be in a scan mode so as to scan the environment, while transmitter 12 is off. The signal received by receiver 20 as a result of the reflection from target 15 reaches a maximum value when the beam radiated from transmitter 10 is pointed directly toward target 15. Therefore, in accordance with one aspect of the present invention, the beam direction θ 1 of transmitter 10 giving rise to the maximum received signal by receiver 20 is used as one of the parameter in determining the range of target 15.

[0019] Similarly, the signal received by receiver 20-as a result of the reflection by target 15 of the signal transmitted by transmitter 12 when transmitter 10 is off-reaches a maximum value when the beam radiated from transmitter 12 is pointed directly toward target 15. The beam direction θ 2 of transmitter 12 giving rise to the maximum received signal by receiver 20 is also used as a parameter in determining the range of target 15.

[0020] The two angles θ 1 and θ 2 , obtained as described above, define the parallax angle Δθ = θ 1 - θ 2 . Using the geometry of the arrangement, these two angles are then used to calculate the range of target 15 from transmitters 10, 12 and receiver 20, as described further below. Applying the law of sines to the triangle formed by transmitters 10, 12, and the target 15 yields the following: R 1 sin π 2 + θ 2 = R 2 sin π 2 − θ 1 = D sin Δθ

[0021] Distances R 1 and R 2 , i.e. the range from transmitters 10, 12 to the target, respectively, are obtained as: R 1 = D cos θ 2 sin Δθ R 2 = D cos θ 1 sin Δθ

[0022] Knowing R 1 and R 2 , distance R 0 between receiver 20 and target 15 is calculated by applying the law of cosines to either the triangle formed by receiver 20, transmitter 10 and target 15, or the triangle formed by receiver 20, transmitter 12 and target 15: R 0 2 = D 1 2 + R 1 2 − 2 D 1 R 1 cos π 2 − θ 1 = D 2 2 + R 2 2 − 2 D 2 R 2 cos π 2 + θ 2

[0023] Distance R 0 is thus determined as shown below: R 0 = D 1 2 + D 2 cos 2 θ 2 sin 2 Δθ − 2 D 1 D cosθ 2 sinθ 1 sin Δθ = D 2 2 + D 2 cos 2 θ 1 sin 2 Δθ + 2 D 2 D cosθ 1 sinθ 2 sin Δθ

[0024] In one embodiment, target 15 is an active target that includes circuitry for receiving the RF signals transmitted by the transmitters 10, 12, and modulating and / or encoding the signal that target 15 subsequently transmits to receiver 20 to help determine the distances computed by the computer.

[0025] Referring to Figure 1A, transmitters 10, 12 and controller / computer 90 form a mapping system 75, in accordance with another embodiment of the present invention. In such embodiments, target 15, which may be a smart phone or another mobile device, includes, among other components, power sensing circuitry adapted to sense the power level target 15 receives form the transmitters, and communication circuitry adapted to transmit to controller / computer 90 the power level sensed by target 15. Controller / computer 90 is configured, in part, to control the operation of the transmitters, perform the computations described below to determine the range of target 15, and receive information from target 15.

[0026] To determine the range of target 15 so as to generate a 3D / 4D map, while one of the transmitters is activated to scan the environment, the other transmitter is deactivated. For example, when transmitter 10 is activated to scan the environment, transmitter 12 remains deactivated. Conversely, when transmitter 12 is activated to scan the environment, transmitter 10 is deactivated.

[0027] During an active scan by either of the two transmitters, the strength of the signal received by target (or mobile device) 15 is at a maximum value when the active transmitter's beam is pointed toward the target. For example, assume transmitter 10 is activated to be in a scan mode so as to scan the environment, while transmitter 12 is off. The signal received by target 15 reaches a maximum value when the beam radiated from transmitter 10 is pointed directly toward target 15. Target 15 is adapted to transmit the maximum power it receives from transmitter 10 when transmitter 10 is in a scan mode. Therefore, in accordance with one aspect of the present invention, the beam direction θ 1 of transmitter 10 giving rise to the maximum received signal by target 15 is used as one of the parameter in determining the range of target 15.

[0028] Similarly, the signal received by target 15-as a result of the transmission by transmitter 12 when transmitter 10 is off-reaches a maximum value when the beam radiated from transmitter 12 is pointed directly toward target 15. Target 15 is adapted to transmit the maximum power it receives from transmitter 12 when transmitter 12 is in a scan mode. The beam direction θ 2 of transmitter 12 giving rise to the maximum received signal by target 20 is also used as a parameter in determining the range of target 15.

[0029] The two angles θ 1 and θ 2 , obtained as described above, define the parallax angle Δθ = θ 1 - θ 2 . Using the geometry of the arrangement, these two angles are then used to calculate the range of target 15 from transmitters 10, 12, as described further below. Applying the law of sines to the triangle formed by transmitters 10, 12, and the target 15 yields the following: R 1 sin π 2 + θ 2 = R 2 sin π 2 − θ 1 = D sin Δθ

[0030] Distances R 1 and R 2 , i.e. the range from transmitters 10, 12 to the target, respectively, are obtained as: R 1 = D cosθ 2 sin Δθ R 2 = D cosθ 1 sin Δθ

[0031] Figure 3A shows a 3D / 4D mapping system 150, in accordance with the present invention. Mapping system 150 is shown as including, in part, a pair of two-dimensional transmitters 30, 32, a receiver 20, and a controller / computer 90. In the exemplary mapping system 150, receiver 20 is assumed to be positioned along a line connecting transmitters 30, 32 and positioned away from transmitters 30, 32 by respective distances of D 1 and D 2 . Therefore, in Figure 3, D = D 1 + D 2 . It is understood that embodiments of the present invention are not so limited and that in other embodiments, transmitters 30, 32 and receiver 20 may not be positioned along a straight line. Controller / computer 90 is configured, in part, to control the operation of the transmitters and receiver, and further to perform the computations described below to determine the range of target 15.

[0032] To determine the range of target 15 and generate a 3D / 4D map, while one of the transmitters is activated to scan the environment, the other transmitter is deactivated. The 12 scanning of the environment by the transmitters is carried out in both elevation and azimuth directions. For example, when two-dimensional transmitter 30 is activated to scan the environment, transmitter 32 remains deactivated. Conversely, when transmitter 12 is activated to scan the environment, transmitter 10 is deactivated.

[0033] During an active scan by either of the transmitters, the strength of the signal reflected by target 15 and captured by receiver 20 is at a maximum value when the active transmitter's beam is pointed toward the target. For example, assume transmitter 30 is in a scan mode to scan the environment while transmitter 32 is off. The signal received by receiver 20 as a result of the reflection from target 15 reaches a maximum value when the beam radiated from transmitter 30 is directed at {θ = θ 1 , φ = φ 1 }, as shown. Similarly, the signal received by receiver 20 as a result of the reflection by target 15 of the signal transmitted by transmitter 32 when transmitter 30 is off, reaches a maximum value when the beam radiated from transmitter 32 is directed at {θ = θ 2 , φ = φ 2 }, as shown. Using these measured values and by taking advantage of the placement of the transmitters and receiver, values of sin α 1 , cos α 1 , sin α 2 , cos α 2 , and sin(α 1 - α 2 ) may be calculated as shown below: sin α 1 = sin θ 1 cos φ 1 , cos α 1 = 1 − sin 2 α 1 = cos 2 θ 1 + sin 2 θ 1 sin 2 φ 1 , − π 2 ≤ α 1 ≤ π 2 sin α 2 = sin θ 2 cos φ 2 , cos α 2 = 1 − sin 2 α 2 = cos 2 θ 2 + sin 2 θ 2 sin 2 φ 2 , − π 2 ≤ α 2 ≤ π 2 sin α 1 − α 2 = sinθ 1 cosφ 1 cos 2 θ 2 + sin 2 θ 2 sin 2 φ 2 − sinθ 2 cosφ 2 cos 2 θ 1 + sin 2 θ 1 sin 2 φ 1

[0034] Therefore, distances R 1 , R 2 and R 0 may be determined using the following expressions: R 1 = D cos α 2 sin α 1 − α 2 R 2 = D cos α 1 sin α 1 − α 2 R 0 = D 1 2 + D 2 cos 2 α 2 sin 2 α 1 − α 2 − 2 D 1 D cosα 2 sinα 1 sin α 1 − α 2

[0035] In one embodiment, target 15 is an active target that includes circuitry for receiving the RF signals transmitted by the transmitters 30, 32, and modulating and / or encoding the signal that target 15 subsequently transmits to receiver 20 to help determine the distances computed by the computer.

[0036] Figure 3B shows a 3D / 4D mapping system 95, in accordance with an example useful to understand the present invention. Mapping system 95 is shown as including, in part, a pair of two-dimensional transmitters 30, 32, and a controller / computer 90. In such embodiments, target 15, which may be a smart phone or another mobile device, includes, among other components, power sensing circuitry adapted to sense the power level target 15 receives form the transmitters, and communication circuitry adapted to transmit to controller / computer 90 the power level sensed by target 15. Controller / computer 90 is configured, in part, to control the operation of the transmitters, perform the computations described below to determine the range of target 15, and receive information from target 15.

[0037] To determine the range of target 15 and generate a 3D / 4D map, while one of the transmitters is activated to scan the environment, the other transmitter is deactivated. The scanning of the environment by the transmitters is carried out in both elevation and azimuth directions. For example, when two-dimensional transmitter 30 is activated to scan the environment, transmitter 32 remains deactivated. Conversely, when transmitter 12 is activated to scan the environment, transmitter 10 is deactivated.

[0038] During an active scan by either of the transmitters, the strength of the signal reflected by target 15 is at a maximum value when the active transmitter's beam is pointed toward the target. For example, assume transmitter 30 is in a scan mode to scan the environment while transmitter 32 is off. The signal received by target 15 reaches a maximum value when the beam radiated from transmitter 30 is directed at {θ = θ 1 , φ = φ 1 }, as shown. Target 15 is adapted to transmit the maximum power it receives from transmitter 30 while transmitter 30 is in a scan mode. Similarly, the signal received by target 15 reaches a maximum value when the beam radiated from transmitter 32 is directed at {θ = θ 2 , φ = φ 2 }, as shown. Target 15 is adapted to transmit the maximum power it receives from transmitter 32 while transmitter 32 is in a scan mode. Therefore the direction of the beam radiated by transmitter 30 and defined by angles {θ = θ 1 , φ = φ 1 }, and which corresponds to the maximum power received by target 15 and communicated back to transmitter 30 is determined. Similarly, the direction of the beam radiated by transmitter 32 and defined by angles {θ = θ 2 , φ = φ 2 }, and which corresponds to the maximum power received by target 15 and communicated back to transmitter 32 is determined. Using these measured values and by taking advantage of the placement of the transmitters, values of sin α 1 , cos α 1 , sin α 2 , cos α 2 , and sin(α 1 - α 2 ) may be calculated as shown below: sinα 1 = sinθ 1 cosφ 1 , cosα 1 = 1 − sin 2 α 1 = cos 2 θ 1 + sin 2 θ 1 sin 2 φ 1 , − π 2 ≤ α 1 ≤ π 2 sinα 2 = sinθ 2 cosφ 2 , cosα 2 = 1 − sin 2 α 2 = cos 2 θ 2 + sin 2 θ 2 sin 2 φ 2 , − π 2 ≤ α 2 ≤ π 2 sin α 1 − α 2 = sinθ 1 cosφ 1 cos 2 θ 2 + sin 2 θ 2 sin 2 φ 2 − sinθ 2 cosφ 2 cos 2 θ 1 + sin 2 θ 1 sin 2 φ 1

[0039] Therefore, distances R 1 , R 2 and may be determined using the following expressions: R 1 = D cos α 2 sin α 1 − α 2 R 2 = D cos α 1 sin α 1 − α 2

[0040] Figure 4 shows a 3D / 4D mapping system 200, in accordance with an example useful to understand the present invention. Mapping system 200 is shown as including, in part, a transmitter 10, receivers 20, 22, and controller / computer 90. In the exemplary mapping system 200, transmitter 10 is assumed to be positioned along a line connecting receivers 20, 22 and positioned away from receivers 20, 22 by respective distances of D 1 and D 2 . Therefore, in Figure 4, D = D 1 + D 2 . It is understood that embodiments of the present invention are not so limited and that in other embodiments, transmitter 10 and receivers 20, 22 may not be positioned on a straight line. Controller / computer 90 is configured, in part, to control the operation of the transmitter and receivers, and further to perform the computations described below to determine the range of target 15.

[0041] To determine the range of target 15, as transmitter 10 scans the area by sweeping the angle θ, the signals received by receivers 20 and 22 both reach maximum values when angle θ reaches a specific value shown in Figure 4 as θ 0 . The scan determines the angular direction of the target, however, the signal reflections from target 15 arrive at slightly different angles at the two receivers, namely angle θ 1 associated with receiver 20, and angle θ 2 associated with receiver 22. Assuming both receivers 20 and 22 have similar gain patterns, G RX (θ), the difference in the angle and range may be calculated by the difference in the signal strength received by the two receivers. Using the well-known radar equations, the measured signal power at receiver unit 20, namely P RX1 , and the measured signal power at receiver unit 22, namely P RX2 , may be defined as shown below: P RX 1 = P TX G TX θ 0 G RX θ 1 λ 2 σ θ 1 4 π 3 R 0 2 R 1 2 P RX 2 = P TX G TX θ 0 G RX θ 2 λ 2 σ θ 2 4 π 3 R 0 2 R 2 2 where P TX represents the power of the signal transmitted by transmitter 10, G TX (θ) represents the gain pattern of the transmitter 10 antenna, and σ(θ) represents the radar cross-section of target 15.

[0042] Assuming, R 0 » D, then both θ 1 and θ 2 may be approximated by θ 0 , and σ(θ 1 ) = σ(θ 2 ) = σ(θ 0 ). Due to the arrangement of the receivers, transmitter and the target shown in Figure 4, it is seen that R 0 cos θ 0 = R 1 cos θ 1 = R 2 cos θ 2 . Hence, parameters P RX1 and P RX2 may be defined as: P RX 1 = P TX λ 2 4 π 3 ⋅ σ θ 0 G TX θ 0 R 0 4 cos 2 θ 0 ⋅ G RX θ 1 cos 2 θ 1 P RX 2 = P TX λ 2 4 π 3 ⋅ σ θ 0 G TX θ 0 R 0 4 cos 2 θ 0 ⋅ G RX θ 2 cos 2 θ 2

[0043] By using Taylor expansion of G RX (θ) cos 2< θ around θ = θ 0 , the following is achieved: P RX 1 ≈ P TX λ 2 4 π 3 ⋅ σ θ 0 G TX θ 0 R 0 4 cos 2 θ 0 ⋅ G RX θ 0 cos 2 θ 0 + dG RX dθ θ 0 cos 2 θ 0 − G RX θ 0 sin 2 θ 0 θ 1 − θ 0 P RX 2 ≈ P TX λ 2 4 π 3 ⋅ σ θ 0 G TX θ 0 R 0 4 cos 2 θ 0 ⋅ G RX θ 0 cos 2 θ 0 + dG RX dθ θ 0 cos 2 θ 0 − G RX θ 0 sin 2 θ 0 θ 2 − θ 0

[0044] Therefore, the difference between the two received signals P RX1 and P RX2 may be defined as: P RX 1 − P RX 2 = P TX λ 2 4 π 3 ⋅ σ θ 0 G TX θ 0 R 0 4 cos 2 θ 0 ⋅ dG RX dθ θ 0 cos 2 θ 0 − G RX θ 0 sin 2 θ 0 θ 1 − θ 2

[0045] The average of the two received signals P RX1 and P RX1 is defined as: P RX 1 + P RX 2 2 = P 0 + P TX λ 2 4 π 3 ⋅ σ θ 0 G TX θ 0 R 0 4 cos 2 θ 0 ⋅ dG RX dθ θ 0 cos 2 θ 0 − G RX θ 0 sin 2 θ 0 θ 1 + θ 2 2 − θ 0

[0046] In the immediately above equation, P 0 = P TX λ 2 4 π 3 ⋅ σ θ 0 G TX θ 0 R 0 4 ⋅ G RX θ 0 represents the signal strength received by a hypothetical receiver positioned at the same location as transmitter 10.

[0047] Assuming that target 15 is positioned sufficient far from the mapping system such that condition (R 0 » D) is satisfied if |D 1 - D 2 | « D then (θ 1 - θ 0 ) ≈ (θ 0 - θ 2 ), as a consequence of which the following expression is obtained: P RX 1 + P RX 2 / 2 ≈ P 0

[0048] Therefore, by dividing the difference (P RX1 - P RX2 ) of the two measured signals by the average (P RX1 + P RX2 ) / 2 of these two signals, it is seen that: P RX 1 − P RX 2 P RX 1 + P RX 2 / 2 ≈ P RX 1 − P RX 2 P 0 = dG RX dθ θ 0 cos 2 θ 0 − G RX θ 0 sin 2 θ 0 θ 1 − θ 2 G RX θ 0 cos 2 θ 0 where the only unknown is the parallax angle difference Δθ = θ 1 - θ 2 . Therefore, the above equation directly relates the measured power of the reflected signal received by the two receivers to the parallax angle. Accordingly, by determining Δθ, the range R 0 of the target from transmitter 10 may be readily determined using the following: R 0 = 1 2 D 2 − D 1 sin θ 0 + D cos θ 0 tan Δθ + D 2 − D 1 sin θ 0 + D cos θ 0 tan Δθ 2 + 4 D 1 D 2

[0049] If D 1 = D 2 = D / 2, the above equation may be simplified to: R 0 = D 2 cosθ 0 tan Δθ + 1 + cos 2 θ 0 tan 2 Δθ

[0050] In one embodiment, target 15 is an active target that includes circuitry for receiving the RF signals transmitted by transmitter 10, and modulating and / or encoding the signal that target 15 subsequently transmits to receivers 20, 22 to help determine the distances computed by the computer.

[0051] Figure 5 shows a 3D / 4D mapping system 250, in accordance with an example useful to understand the present invention. Mapping system 250 is similar to mapping system 200 except that in mapping system 250 transmitter 10 and receiver 20 are placed substantially near the same point such that D 1 = 0 and D 2 = D. As a result, in system 250 θ 1 = θ 0 is known, while θ 2 and the target range from transmitter 10 or receiver 20 (R 1 = R 0 ) are the unknown parameters determined, by controller / computer 90, as shown below.

[0052] Parameter P 0 , defined above, may be calculated as: P 0 = P RX 1 = P TX λ 2 4 π 3 ⋅ σ θ 1 G TX θ 1 R 1 4 ⋅ G RX θ 1 .

[0053] Therefore θ 2 , and consequently Δθ = θ 1 - θ 2 , may be calculated as shown below: P RX 1 − P RX 2 P RX 1 = dG RX dθ θ 1 cos 2 θ 1 − G RX θ 1 sin 2 θ 1 θ 1 − θ 2 G RX θ 1 cos 2 θ 1

[0054] Accordingly, the range, R 1 = R 0 , may be obtained as shown below: R 0 = R 1 = D sinθ 0 + cosθ 0 tan Δθ .

[0055] Figure 6 shows a 3D / 4D mapping system 300, in accordance with an example useful to understand the present invention. Mapping system 300 is shown as including, in part, a pair of receivers 40, 42, a transmitter 10 adapted to change both azimuth and elevation (to enable scan in both θ and φ directions), and a controller / computer 90. In the exemplary mapping system 300, transmitter 10 is assumed to be positioned along a line connecting receivers 40, 42 and positioned away from the receivers by respective distances of D 1 and D 2 . Therefore, in Figure 6, D = D 1 + D 2 . It is understood that embodiments of the present invention are not so limited and that in other embodiments, receivers 40, 42 and transmitter 10 may not be positioned along a straight line. Controller / computer 90 is configured, in part, to control the operation of the transmitter and receivers, and further to perform the computations described below to determine the range of target 15.

[0056] The signals received at receivers 40, 42, namely signals P RX1 and P RX2 , are at maximum values when the beam radiated from transmitter 10 is pointed toward the target. Hence, as the transmitter is scanned in both θ and φ directions, the received power levels at the receiver is recorded. The angles θ and φ at which the power levels received at both receivers 40 and 42 attain their highest values correspond to angles θ 0 and φ 0 .

[0057] By transforming variables θ and φ to new variables α and β, as shown in Figure 6, the same procedure described above, may be used to achieve the parallax angle and, consequently, detect the range based on the received power levels of the reflected signals at the two receivers.

[0058] As is seen from Figure 6: sinα 0 = sinθ 0 cos φ 0 , − π 2 ≤ α 0 ≤ π 2 tanβ 0 = tanθ 0 sin φ 0 , − π 2 ≤ β 0 ≤ π 2

[0059] These equations may be used to transform the known gain pattern of the receiver units G RX (θ, φ)-defined in terms of angles θ, φ-to a gain pattern Ĝ RX (α, β)-defined in terms of angles α and β. Using this transformation, the following is obtained: P RX 1 − P RX 2 P RX 1 + P RX 2 / 2 ≈ P RX 1 − P RX 2 P 0 = d G ^ RX dα α 0 β 0 cos 2 α 0 − G ^ RX α 0 β 0 sin 2 α 0 α 1 − α 2 G ^ RX α 0 β 0 cos 2 α 0

[0060] This equation provides the parallax angle, Δα = α 1 - α 2 , which in turn, provides the range, as shown below: R 0 = 1 2 D 2 − D 1 sinα 0 + D cos α 0 tan Δα + D 2 − D 1 sinα 0 + D cos α 0 tan Δα 2 + 4 D 1 D 2

[0061] If transmitter 10 is placed at exactly the midpoint between receivers 40, 42, i.e., D 1 = D 2 = D / 2, the above equations simplifies to: R 0 = D 2 cosα 0 tan Δα + 1 + cos 2 α 0 tan 2 Δα .

[0062] In one embodiment, target 15 is an active target that includes circuitry for receiving the RF signals transmitted by transmitter 10, and modulating and / or encoding the signal that target 15 subsequently transmits to receivers 40, 42 to help determine the distances computed by the computer.

[0063] Figure 7 shows a 3D / 4D mapping system 350, in accordance with an example useful to understand the present invention. Mapping system 350 is similar to mapping system 300 except that in mapping system 350, transmitter 10 and receiver 40 are positioned substantially near the same point, thus dispensing the need to approximate P 0 . In mapping system 350, parameters Δα and R 0 may be calculated as shown below: P RX 1 − P RX 2 P RX 1 = d G ^ RX dα α 1 β 0 cos 2 α 1 − G ^ RX α 1 β 0 sin 2 α 1 α 1 − α 2 G ^ RX α 1 β 0 cos 2 α 1 R 0 = R 1 = D sinα 1 + cosα 1 tan Δα

[0064] Conventional CW radars often use the Doppler shift to detect a moving target's radial velocity. Embodiments of the present invention, described above, may also be used to determine the range of moving objects by measuring the reflected signal while also detecting the velocity using the Doppler shift.

[0065] Figure 8 shows a 3D / 4D Doppler mapping system 400 adapted to detect the range of a moving target, in accordance with an example useful to understand the present invention. Doppler mapping system 400 is shown as including, in part, Doppler receivers 20, 22, transmitter 10, and a controller / computer 90. For simplicity, the following description is provided with reference to the transmitter as being a one-dimensional transmitter / scanner. It is understood, however, that transmitter 10 may be a two-dimensional scanner, as described above. In the exemplary mapping system 400, transmitter 10 is assumed to be positioned along a line connecting receivers 20, 22 and positioned away from the receivers by respective distances of D 1 and D 2 . Therefore, in Figure 8, D = D 1 + D 2 . It is understood that embodiments of the present invention are not so limited and that in other embodiments, receivers 20, 22 and transmitter 10 may not be positioned along a straight line. Controller / computer 90 is configured, in part, to control the operation of the transmitter and receivers, and further to perform the computations described below to determine the range of target 15.

[0066] In a manner similar to embodiment 300 described above with reference to Figure 6, the range of target 15 from the transmitter may be determined by first calculating the parallax angle through measuring the strength of the signals received by the Doppler receivers (referred to herein alternatively as Doppler signals) at the two receiving units using the following expression in which signals P RX1 and P RX2 respectively represent the power levels of the Doppler signals received by receivers 20, 22: P RX 1 − P RX 2 P RX 1 + P RX 2 / 2 ≈ P RX 1 − P RX 2 P 0 = dG RX dθ θ 0 cos 2 θ 0 − G RX θ 0 sin 2 θ 0 θ 1 − θ 2 G RX θ 0 cos 2 θ 0

[0067] The range of the target from transmitter 10 may then be obtained using the following expression: R 0 = 1 2 D 2 − D 1 sinθ 0 + D cos θ 0 tan Δθ + D 2 − D 1 sinθ 0 + D cos θ 0 tan Δθ 2 + 4 D 1 D 2

[0068] In one embodiment, target 15 is an active target that includes circuitry for receiving the RF signals transmitted by transmitter 10, and modulating and / or encoding the signal that target 15 subsequently transmits to receivers 20, 22 to help determine the distances computed by the computer.

[0069] Figure 9 shows a 3D / 4D Doppler mapping system 450 adapted to detect the range of a moving target, in accordance with another exemplary embodiment of the present invention. Doppler mapping system 450 is shown as including, in part, transmitters 10, 12, Doppler receiver 20, and a controller / computer 90. For simplicity, the following description is provided with reference to transmitters 10, 12 each being a one dimensional transmitter / scanner and adapted to scan along one dimension. It is understood, however, that transmitters 10, 12 may be two-dimensional scanners, as described above. Furthermore, in the exemplary mapping system 450, receiver 20 is assumed to be positioned along a line connecting transmitters 10, 12 and positioned away from the receivers by respective distances of D 1 and D 2 . Therefore, in Figure 9, D = D 1 + D 2 . It is understood that embodiments of the present invention are not so limited and that in other embodiments, transmitters 10, 12 and receiver 20 may not be positioned along a straight line. Controller / computer 90 is configured, in part, to control the operation of the transmitter and receivers, and further to perform the computations described below to determine the range of target 15.

[0070] Each transmitter scans the area when the other transmitter is off and finds the direction at which the maximum Doppler signal is captured by the receiver, thereby to determine angles θ 1 and θ 2 , as shown. The range may then be determined as shown below: R 1 = D cos θ 2 sin Δθ R 2 = D cos θ 1 sin Δθ R 0 = D 1 2 + D 2 cos 2 θ 2 sin 2 Δθ − 2 D 1 D cosθ 2 sinθ 1 sin Δθ

[0071] In one embodiment, target 15 is an active target that includes circuitry for receiving the RF signals transmitted by transmitters 10, 12, and modulating and / or encoding the signal that target 15 subsequently transmits to receivers 20 to help determine the distances computed by the computer.

[0072] Any number of techniques may be used to form a transmitter / scanner and implement the required displacement between two transmitter units. In one embodiment, shown in Figure 10A, each transmitter / scanner may be a unit transmitter antenna which uses angle encoders to mechanically rotate and radiate its beam toward a specific direction and thus scan the desired area to determine the range of target 15. Two such transmitters / scanners 10, 12, may be placed physically apart by distance D to create a parallax, as shown in Figure 10A.

[0073] In another embodiment, each transmitter / scanner may be a phased array having multiple transmit elements / antennas which electronically controls the direction of the radiated beam by varying the relative phases of each antenna element to scan the entire desired area. Figure 10B shows two phased arrays 10 and 12 each having a two-dimensional array of 3x3 transmit elements / antennas. The two phased arrays are physically spaced apart by a distance of D from their respective centers to create a parallax.

[0074] In accordance with yet another embodiment, each transmitter / scanner may be a sub-array of a phased array having multiple transmit elements / antennas. Each sub-array steers its beam electronically and independent of the other sub-array. The effective displacement required for parallax is equal to the distance between the centers of the sub-arrays. Figure 10C shows an exemplary phased arrays 60 having a two-dimensional arrays of 3x14 transmit elements / antennas. Phased array 60 is shown as being divided into 2 subarrays, 62 and 64, each having a two-dimensional array of 3x7 transmit elements / antennas. The distance between the centers of the two subarrays is shown as being equal to D.

Claims

1. A method of determining an object's distance, the method comprising: delivering a first RF signal from a first transmitter (10) to the object while a second transmitter (12) is deactivated; changing a direction of the first transmitter (10) along both azimuth and elevation until the first transmitter (10) reaches a first direction defined by first and second angles at which a power of a first reflected RF signal reflected off the object and received by a receiver (20, 22) reaches a maximum value; delivering a second RF signal from the second transmitter (12) to the object while the first transmitter (10) is deactivated; changing a direction of the second transmitter (12) along both azimuth and elevation until the second transmitter (12) reaches a second direction defined by third and fourth angles at which a power of a second reflected RF signal reflected off the object and received by the receiver (20, 22) reaches a maximum value; and determining a distance between the object and the first transmitter (10) in accordance with a distance between the two transmitters (10, 12), and the first, second, third and fourth angles.

2. The method of claim 1 further comprising: determining a distance between the object and the second transmitter (12) in accordance with the distance between the two transmitters (10, 12), and the first, second, third and fourth angles.

3. The method of claim 2 further comprising: determining a distance between the object and the receiver (20, 22) in accordance with the distance between the two transmitters (10, 12), the distance between the first transmitter (10) and the receiver (20, 22), and the first, second, third and fourth angles.

4. The method of claim 3 wherein said first transmitter (10), said second transmitter (12) and said receiver (20, 22) are positioned along a substantially straight line.

5. The method of claim 1 wherein said receiver (20, 22) is a Doppler receiver.

6. A mapping system comprising: a first transmitter (10) adapted to deliver a first RF signal to an object; a second transmitter (12) adapted to deliver a second RF signal to an object, wherein the second transmitter (12) is deactivated when the first transmitter (10) delivers the first RF signal, and wherein the first transmitter (10) is deactivated when the second transmitter (12) delivers the second RF signal; a receiver (20, 22); and a controller (90) configured to: change a direction of the first transmitter (10) along both azimuth and elevation until the first transmitter (10) reaches a first direction defined by first and second angles at which a power of a first reflected RF signal reflected off the object and received by the receiver (20, 22) reaches a maximum value; change a direction of the second transmitter (12) along both azimuth and elevation until the second transmitter (12) reaches a second direction defined by third and fourth angles at which a power of a second reflected RF signal reflected off the object and received by the receiver (20, 22) reaches a maximum value; and determine a distance between the object and the first transmitter (10) in accordance with a distance between the two transmitters (10, 12) and the first, second, third and fourth angles.

7. The mapping system of claim 6 wherein said controller (90) is further configured to: determine a distance between the object and the second transmitter (12) in accordance with a distance between the two transmitters (10, 12) and the first, second, third and fourth angles.

8. The mapping system of claim 7 wherein said controller (90) is further configured to: determine a distance between the object and the receiver (20, 22) in accordance with a distance between the two transmitters (10, 12), the distance between the first transmitter (10) and said receiver (20,22) and the first, second, third and fourth angles.

9. The mapping system of claim 8 wherein said first transmitter (10), said second transmitter (12) and said receiver (20, 22) are positioned along a substantially straight line.

10. The mapping system of claim 6 wherein said controller (90) is configured to: change the direction of the first transmitter (10) by mechanically rotating the transmitter.

11. The mapping system of claim 6 wherein said first transmitter (10) is a phased array transmitter.

12. The mapping system of claim 6 wherein said first transmitter (10) is a first subarray of a phased array transmitter, and said second transmitter (12) is a second subarray of the phased array transmitter.

13. The mapping system of claim 6 wherein said receiver (20, 22) is a Doppler receiver adapted to detect a difference between a frequency of the first RF signal and a frequency of the first reflected RF signal to determine a speed of the object.