A Doppler radar for speed measurement using overlapping synthetic beams

Abstract

The present invention relates to a Doppler radar that uses overlapping composite beams for speed measurement. The radar comprises an antenna unit, a beam transceiver control unit, and a beam transceiver control unit. During transmission, the antenna unit radiates four-channel signals F1 and F2 into space, overlapping each other to form four groups of overlapping composite beams. During reception, the radar receives four groups of overlapping composite beam echo signals and outputs four-channel signal F1 echo signals and four-channel signal F2 echo signals. The beam transceiver control unit is used to control the timing of the antenna unit's input signals to form four groups of overlapping composite beams and to control the timing of the antenna unit's output signals to receive the echo signals of the four groups of overlapping composite beams. The speed measurement processing unit is used to extract the Doppler frequency shift in the overlapping region of the four groups of overlapping composite beams to measure the speed of an aircraft. The Doppler spectrum width of the present invention is 20%-25% narrower than that of a conventional four-beam radar, thereby improving the spectrum purity and greatly enhancing the speed measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the field of radar technology, and in particular to a Doppler radar that uses overlapping synthetic beams to measure speed. Background Art

[0002] Doppler radar can automatically, continuously, and accurately measure the velocity vector information of drones and other flying vehicles. Its operation is unrestricted by geographical and meteorological conditions, and its speed measurement accuracy remains constant throughout the entire flight range. Conventional Doppler radars only provide speed measurement accuracy sufficient for civilian aircraft and struggle to meet the very high speed measurement accuracy requirements of flying vehicles. Two main factors affect the accuracy of Doppler speed radars: 1) non-uniform ground scattering coefficients; and 2) insufficiently narrow antenna beamwidth, which reflects as a wideband spectrum in the Doppler frequency shift.

[0003] Given a fixed radar antenna size and beam angle, existing technology generally applies a correction factor based on the scattering characteristics of the current flight area to improve Doppler radar velocity measurement accuracy in real time. However, this method requires a large amount of flight data from various terrains to build a library of target clutter models. Existing Doppler radars use the pointing angles of four tilted beams to calculate velocity, which requires extremely high accuracy in the echo's pointing angle. However, due to the limited antenna aperture, the beam illuminates a single area on the ground, and the radar receives a spectrum with a limited bandwidth. Relying on algorithms to correct the center of gravity leads to significant errors. Summary of the Invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide a Doppler radar that uses overlapping synthetic beams to measure speed, so as to solve the problem of poor accuracy of existing Doppler speed measurement radars.

[0005] The technical solution provided by the present invention is:

[0006] The present invention discloses a Doppler radar for speed measurement using overlapping synthetic beams, comprising an antenna unit, a beam transceiver control unit and a beam transceiver control unit;

[0007] The antenna unit is a common antenna for both transmission and reception. During transmission, the 4-channel signal F1 fed into the antenna radiates into space as 4 centrally symmetrical X-shaped radar beams; the 4-channel signal F2 fed into the antenna radiates into space as 4 centrally symmetrical X-shaped radar beams; the 4 radar beams of the signal F1 and the 4 radar beams of the signal F2 overlap in pairs to form 4 groups of overlapping synthetic beams; during reception, the echo signals of the 4 groups of overlapping synthetic beams are received respectively, and the 4-channel signal F1 echo signal and the 4-channel signal F2 echo signal are fed out;

[0008] The beam transceiver control unit is used to control the timing of the antenna unit's feed signals to form four sets of overlapping synthetic beams; control the timing of the antenna unit's feed signals to receive the echo signals of the four sets of overlapping synthetic beams;

[0009] The speed measurement processing unit is used to extract the Doppler frequency shift of the overlapping area of ​​the four groups of overlapping synthetic beams to measure the speed of the aircraft.

[0010] Furthermore, the antenna unit includes a radiation array subunit and a feeding subunit;

[0011] The radiation array subunit includes N parallel and evenly arranged radiation waveguides;

[0012] The feeding subunit includes first, second, third and fourth feeding waveguides having the same structure;

[0013] The radiating waveguides and feeding waveguides are both rectangular waveguides; wherein the first and third feeding waveguides are arranged in a row on the left side of the radiating array subunit, feeding power to the left input end of each radiating waveguide; the second and fourth feeding waveguides are arranged in a row on the right side of the radiating array subunit, feeding power to the right input end of each radiating waveguide;

[0014] Both ends of each feeding waveguide are feeding ports. Both ends of the first feeding waveguide and the second feeding waveguide in the upper layer of the four feeding waveguides placed in pairs are fed with signal F1 or feed out the echo signal of signal F1; both ends of the third feeding waveguide and the fourth feeding waveguide in the lower layer of the four feeding waveguides placed in pairs are fed with signal F2 or feed out the echo signal of signal F2.

[0015] Furthermore, each of the radiating waveguides includes horn sections located at the left and right ends and a radiating section in the middle; wherein the wide ends of the horn sections at the left and right ends accommodate the first and third feeding waveguides located at the left end and the second and fourth feeding waveguides located at the right end of the radiating waveguide respectively; the narrow end of the horn section is connected to the radiating section; the horn section is used to realize the transition of the signal from the feeding waveguide to the radiating section; and the radiating section is used to radiate the signal.

[0016] Furthermore, the radiation section of the radiation waveguide is a traveling wave slot radiation waveguide with narrow side slots; a plurality of narrow side slots of the same length and width with staggered inclination angles are provided on the narrow side of the waveguide, the intervals between every two adjacent narrow side slots are the same, and the narrow side slots are symmetrically distributed with respect to the center line of the radiation waveguide;

[0017] N narrow side cracks are formed on the short side walls of the first, second, third and fourth feeding waveguides facing the radiation section, and electromagnetic signals are transmitted to the emitting and radiating waveguide array through the narrow side cracks.

[0018] Furthermore, the deflection angle of a group of overlapping synthetic beams radiated outward by the antenna unit in the X direction of the pattern is Deflection angle in the Y direction of the pattern Where i = 1 or 2, λ1 and λ2 are the wavelengths of signals F1 and F2 in free space, and λ 1g ,λ 2g is the wavelength of signals F1 and F2 in the waveguide; d1 is the distance between the centers of two adjacent narrow-side cracks on the radiating waveguide; d2 is the distance between the centers of two adjacent narrow-side cracks on the feeding waveguide; by controlling the frequencies of signals F1 and F2, the deflection angles of signals F1 and F2 in the X and Y directions of the radiation pattern are controlled, thereby controlling the degree of overlap of the overlapping synthetic beams.

[0019] Furthermore, the amplitude distribution function of the narrow side crack on the radiation waveguide to the waveguide coupling function is: Where E(x) is the amplitude distribution function, P(x) is the power passing through the waveguide, and x is the value normalized relative to half the length of the antenna; P(0) = P0; φ(+1)=[P(+1)-P0] / [P(+1)+P0].

[0020] Further, each port of the first, second, third and fourth feeding waveguides includes a waveguide isolator;

[0021] When one of the four ports in the first and second feeding waveguides is incident, the isolators at the other three ports function as reverse load absorbers.

[0022] When one of the four ports of the third and fourth feeding waveguides is incident, the isolators at the other three ports function as reverse load absorbers.

[0023] Furthermore, the beam transceiver control unit adopts a time-sharing control method. At a certain transmission control timing, it controls the ports on the same side of the first and third feeding waveguides or the second and fourth feeding waveguides placed in parallel, and simultaneously feeds signals F1 and F2, which are radiated into space through the radiation array sub-unit to form a group of overlapping synthetic beams; at a reception control timing after the transmission control timing, it receives the echo signals of the overlapping synthetic beams, and feeds the signal F1 echo signal and the signal F2 echo signal from the port on this side.

[0024] Furthermore, the beam transceiver control unit controls the illumination order of the four groups of overlapping synthetic beams to be random illumination, so as to overcome co-channel interference.

[0025] Furthermore, the speed measurement processing unit calculates the speed measurement information in the navigation information of the aircraft according to the Doppler frequency shift of the overlapping area as follows:

[0026]

[0027] Where, f is the velocity component of the carrier coordinate system X, Y, and Z axes measured by the Doppler radar; d1 、f d2 、f d3 、f d4 are the Doppler shifts of the relative signal F1 of the four beams; γ0 is the angle between the center line of each beam and the X-axis of the aircraft carrier coordinate system; δ0 is the angle between the projection of the beam line on the corresponding plane and the Y-axis of the carrier coordinate system; λ is the wavelength of the radar transmission signal F1.

[0028] The Doppler radar of the present invention that uses overlapping synthetic beams to measure speed receives overlapping beams of four echoes. The Doppler spectrum width is narrower by 20%-25% compared with that of an ordinary four-beam radar, thereby improving spectrum purity and greatly improving speed measurement accuracy.

[0029] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0031] Figure 1 FIG1 is a block diagram of a Doppler radar according to an embodiment of the present invention;

[0032] Figure 2 A top view of a Doppler radar four-beam antenna according to an embodiment of the present invention;

[0033] Figure 3 A side view of a Doppler radar four-beam antenna according to an embodiment of the present invention;

[0034] Figure 4 Schematic diagram of the relationship between four beams overlapping in pairs generated by the antenna in an embodiment of the present invention;

[0035] Figure 5 Schematic diagram of the projection of the antenna pattern on the emitting surface in an embodiment of the present invention;

[0036] Figure 6 Schematic diagram of the feeding structure of the overlapping beam antenna in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0038] A specific embodiment of the present invention discloses a Doppler radar that uses overlapping synthetic beams to measure velocity, such as Figure 1 As shown, it includes an antenna unit, a beam transceiver control unit and a beam transceiver control unit;

[0039] The antenna unit is a common antenna for both transmission and reception. During transmission, the 4-channel signal F1 fed into the antenna radiates into space as 4 centrally symmetrical X-shaped radar beams; the 4-channel signal F2 fed into the antenna radiates into space as 4 centrally symmetrical X-shaped radar beams; the 4 radar beams of the signal F1 and the 4 radar beams of the signal F2 overlap in pairs to form 4 groups of overlapping synthetic beams; during reception, the echo signals of the 4 groups of overlapping synthetic beams are received respectively, and the 4-channel signal F1 echo signal and the 4-channel signal F2 echo signal are fed out;

[0040] The beam transceiver control unit is used to control the timing of the antenna unit feeding signals to form four sets of overlapping synthetic beams; control the timing of the antenna unit feeding echo signals and receive the echo signals of the four sets of overlapping synthetic beams;

[0041] The speed measurement processing unit is used to extract the Doppler frequency shift of the overlapping area of ​​the four groups of overlapping synthetic beams to measure the speed of the aircraft.

[0042] By extracting the Doppler frequency shift in the overlapping area of ​​four sets of overlapping synthetic beams, the Doppler spectrum width is 20%-25% narrower than that of ordinary four-beam radar, thereby improving the spectrum purity. It can effectively eliminate the influence of Doppler radar on ground scattering, improve the speed measurement accuracy by at least 5 times, and greatly improve the speed measurement accuracy.

[0043] Specifically, such as Figure 2 and Figure 3 As shown, the antenna unit includes a radiation array subunit and a feeding subunit;

[0044] The radiation array subunit includes N parallel and evenly arranged radiation waveguides;

[0045] The feeding subunit includes first, second, third and fourth feeding waveguides having the same structure;

[0046] The radiating waveguide and feeding waveguide are both rectangular waveguides; wherein the first and third feeding waveguides are arranged in a row on the left side of the radiating array subunit to feed power to the left input end of each radiating waveguide; the second and fourth feeding waveguides are arranged in a row on the right side of the radiating array subunit to feed power to the right input end of each radiating waveguide;

[0047] Both ends of each of the feeding waveguides are feeding ports, and both ends of the first feeding waveguide and both ends of the second feeding waveguide in the upper layer of the four feeding waveguides placed in pairs are fed with signal F1 or feed out the echo signal of signal F1; both ends of the third feeding waveguide and both ends of the fourth feeding waveguide in the lower layer of the four feeding waveguides placed in pairs are fed with signal F2 or feed out the echo signal of signal F2.

[0048] The frequencies of the signal F1 and the signal F2 are set to have a certain frequency difference between each other. When radiating outward through the N radiation waveguides, two directional patterns of different frequencies will appear in the antenna radiation field because the antenna responds differently to signals of different frequencies. By controlling the range of the frequency difference, the two beams generated by the signal F1 and the signal F2 can be controlled to have a certain overlap. Therefore, when the antenna of this embodiment transmits signals of frequency F1 and frequency F2, it will produce the following: Figure 4 The projections of the four overlapping beams on the ground are as follows: Figure 5 As shown in Figure 2, the close proximity of the two beams does not change the ground reflection characteristics. With the drift angle corrected, the frequency corresponding to the intersection of the Doppler spectrum envelopes of the two signals is found to be independent of the type of reflecting surface.

[0049] More specifically, in order to realize the interaction of the feed waveguide and the radiation waveguide signals placed in pairs, such as Figure 6 As shown, each radiating waveguide includes horn sections located at the left and right ends and a radiating section in the middle; wherein the wide ends of the horn sections at the left and right ends accommodate the first and third feeding waveguides located at the left end of the radiating waveguide and the second and fourth feeding waveguides located at the right end thereof; the narrow end of the horn section is connected to the radiating section; the horn section is used to realize the transition of the signal from the feeding waveguide to the radiating section; and the radiating section is used to radiate the signal.

[0050] Preferably, the radiation section of the radiation waveguide is a traveling wave slot radiation waveguide with a narrow side slit; a plurality of narrow side slits of the same length and width with staggered inclination angles are arranged on the narrow side of the waveguide, the intervals between every two adjacent narrow side slits are the same, and the narrow side slits are symmetrically distributed on both sides relative to the center line of the radiation waveguide; the spacing between the narrow side slits of the radiation waveguide determines the X-direction beam pointing angle of the radiation pattern.

[0051] The first, second, third, and fourth feed waveguides have N narrow side slits on their short sides facing the radiating section. These N narrow side slits have staggered inclinations, and electromagnetic signals are transmitted through these narrow side slits to the radiating waveguide array. The spacing between the narrow side slits in the feed waveguides is the same as the spacing between the radiating waveguides in the radiating waveguide array. Therefore, the spacing between the narrow side slits in the radiating waveguides determines the Y-axis beam pointing angle of the radiation pattern.

[0052] More specifically, the deflection angle of a set of overlapping composite beams radiated outward by the antenna unit in the X direction of the pattern is Deflection angle in the Y direction of the pattern Where i = 1 or 2, 1 represents signal F1, 2 represents signal F2; λ1 and λ2 are the signal wavelengths of signals F1 and F2 in free space, λ 1g ,λ 2g is the wavelength of the signals F1 and F2 in the waveguide; d1 is the distance between the centers of two adjacent narrow cracks on the radiating waveguide; d2 is the distance between the centers of two adjacent narrow cracks on the feeding waveguide; by controlling the frequencies of the signals F1 and F2, the deflection angles θ of the signals F1 and F2 in the X and Y directions of the radiation pattern are controlled. i 、φ i , thereby controlling the degree of overlap of the overlapping synthetic beams.

[0053] The four groups of overlapping synthetic beams in this embodiment are in a centrally symmetrical X-shape, and their beam pointing angles are strictly symmetrical, ensuring that the precise flight speed of the flying vehicle in three directions can be subsequently calculated through the relationship between the Doppler frequency shift and the beam pointing angle.

[0054] Furthermore, unlike conventional traveling wave array designs, to ensure symmetrical patterns for incoming waves in both directions of a single radiating waveguide and an even slot coupling function, the radiating waveguide of this embodiment has symmetrical slots at both ends. This means that the slot-to-waveguide coupling function is an even function relative to the middle of the radiating aperture. In this case, the amplitude distribution function is no longer symmetrical (as is the case with conventional traveling wave antennas).

[0055] Therefore, the amplitude distribution function of the coupling function of the narrow side crack of the radiating waveguide of this embodiment to the waveguide is:

[0056] Where E(x) is the amplitude distribution function, P(x) is the power passing through the waveguide, and x is the value normalized relative to half the length of the antenna; P(0) = P0;

[0057]

[0058]

[0059] φ(+1)=[P(+1)-P0] / [P(+1)+P0].

[0060] After obtaining the degree distribution function (amplitude characteristics), the directional pattern characteristics can be obtained, thus fully solving the directional Figure 4 Beam symmetry problem.

[0061] Furthermore, the inclination angle and penetration depth of each slot in a narrow-side slotted single waveguide can be determined through the amplitude distribution function and the coupling function of the waveguide.

[0062] More specifically, each port of the first, second, third and fourth feeding waveguides includes a waveguide isolator;

[0063] in,

[0064] When one of the four ports in the first and second feeding waveguides is in the input or output mode, the isolators at the three ports function as reverse load absorbers.

[0065] When one of the four ports of the third and fourth feeding waveguides is used for input or output, the isolators at the other three ports function as reverse load absorption.

[0066] Isolation ensures that transmission and reception of each beam do not affect each other, and each beam can utilize the radiation waveguide of the entire radiation array sub-unit of the antenna unit for transmission or reception.

[0067] In a specific embodiment of the present invention, the total structural size of the antenna unit is no more than 400 mm×200 mm×30 mm.

[0068] Among them, the radiation array subunit is composed of 22 radiation waveguides, each of which has 36 narrow-edge slots with staggered inclination angles, which are used to radiate electromagnetic energy into space. The spacing between the radiation slots is 11 mm, and the inner cavity size of the radiation waveguide is 17 mm × 4 mm; the amplitude distribution function of the radiation waveguide is weighted by -20 dB Chebyshev, the inclination angle of each slot is determined according to the weighted result, and the penetration depth is determined according to the simulated resonant size of each slot.

[0069] The feed subunit contains four feed waveguides, two of which are arranged in a row on the left, and the other two are stacked and placed on the right. The feed waveguide dimensions are 18.75mm × 4mm. Each feed waveguide has 22 narrow slots with staggered angles on the narrow side facing the radiating waveguide. The spacing between the feed waveguide slots is 9mm.

[0070] Preferably, the frequencies of the feed signal F1 and the feed signal F2 are 13.325 GHz and 13.5 GHz respectively.

[0071] In this embodiment, the beam transceiver control unit adopts a time-sharing control method. At a certain transmission control timing, it controls the ports on the same side of the first and third feeding waveguides or the second and fourth feeding waveguides arranged in a row, and simultaneously feeds signals F1 and F2, which are radiated into space through the radiation array sub-unit to form a group of overlapping synthetic beams; at a reception control timing after the transmission control timing, the echo signals of the overlapping synthetic beams are received, and the echo signals of signal F1 and signal F2 are fed out from the ports on that side.

[0072] A time-sharing control method of this embodiment includes:

[0073] 1) At time T1, the beam transceiver control unit controls the antenna unit to transmit. Signal F1 is fed into feed port 1 on one side of the first feed waveguide, while signal F2 is fed into feed port 5 on the same side of the third feed waveguide. This generates two beams within the geodetic quadrant I of the beam projection: one beam generated by signal F1, with an azimuth angle of 1 and an elevation angle of 1; the other beam generated by signal F2, with an azimuth angle of 5 and an elevation angle of 5. Because the frequencies of signals F1 and F2 are very close, the angular difference between azimuth angles 1 and 5, and between elevation angles 1 and 5, is very small, between 0.5 and 3 degrees, and can be controlled by the frequency difference between signals F1 and F2. This results in overlapping beams with mutually incoherent frequencies, resulting in overlapping projections on the ground.

[0074] 2) After the radiation array subunit radiates the signal, the beam transceiver control unit controls the antenna unit to receive the signal; the echo signal of the two beams generated in the geodetic quadrant I is received by the antenna unit, fed from the feed port 1 of the first feed waveguide and the feed port 5 of the third feed waveguide to the velocity measurement processing unit, and the Doppler spectrum information of the area where the two frequencies form the beam overlap is extracted. The velocity is calculated by knowing the azimuth and pitch angles after the beam overlap of ports 1 and 5;

[0075] 3) At time T2, the beam transceiver control unit controls the antenna unit to transmit; feed port 2 on one side of the first feed waveguide is fed with signal F1, while feed port 6 on the same side of the third feed waveguide, which is arranged together, is fed with signal F2. Two beams are generated within the geodetic quadrant II of the beam projection: one beam generated by signal F1, with an azimuth angle of 2 and an elevation angle of 2; the other beam generated by signal F2, with an azimuth angle of 6 and an elevation angle of 6. Because the frequencies of signals F1 and F2 are very close, the angular difference between azimuth angles 2 and 6, and between elevation angles 2 and 6, is very small, between 0.5 and 3 degrees, and can be controlled by the frequency difference between signals F1 and F2. This results in overlapping beams with mutually incoherent frequencies, resulting in an overlapping area projection on the ground.

[0076] 4) After the radiating array subunit radiates the signal, the beam transceiver control unit controls the antenna unit to receive it; the echo signals of the two beams generated in the geodetic quadrant II are received by the antenna unit and fed from the feed port 2 of the first feed waveguide and the feed port 6 of the third feed waveguide to the velocity measurement processing unit. The spectrum information of the area where the two frequencies form the beam overlap is extracted, and the velocity is calculated by knowing the azimuth and pitch angles after the beam overlap of ports 1 and 5.

[0077] 5) The working principles of the other four feeding ports are the same as above. The projections of the four beams generated on the earth are also X-shaped and symmetrical about the orthocenter of the antenna. The overlapping beams generated by ports 1 and 5 are in quadrant 1, the overlapping beams generated by ports 2 and 6 are in quadrant 2, the overlapping beams generated by ports 3 and 7 are in quadrant 3, and the overlapping beams generated by ports 4 and 8 are in quadrant 4.

[0078] Therefore, by receiving the overlapping beams of four echoes, the radar's high-frequency receiving system can extract the spectrum of the beam overlapping area, and the spectrum width is narrower by 20%-25%, thereby improving the spectrum purity and greatly improving the accuracy of speed measurement.

[0079] Furthermore, if four sets of overlapping beams are used in a fixed order for illumination in each illumination cycle, if co-frequency interference occurs, it will occur in each illumination process, which will have a great impact on the Doppler radar speed measurement performance and may even cause the speed measurement data to be unavailable.

[0080] Therefore, the beam transceiver control unit controls the illumination order of the four groups of overlapping synthetic beams to be random illumination to overcome co-channel interference.

[0081] Specifically, methods to overcome co-channel interference include:

[0082] 1) numbering the four groups of overlapping synthetic beams of the Doppler radar; arranging the numbers to form a one-dimensional array as an illumination sequence set of the four groups of overlapping synthetic beams of the Doppler radar;

[0083] More specifically, the four groups of overlapping composite beams are numbered 1, 2, 3, and 4;

[0084] Arrange the 4 numbers to form 24 combinations, forming a one-dimensional array with a length of 24, which is:

[0085] {3142,4312,3421,4321,2413,4213,2431,4231,2314,3214,2341,3241,1423,4123,1432,4132,1324,3124,1342,3142,1234,1243,2134,2143}.

[0086] The one-dimensional array is used as the illumination sequence set of each beam of the Doppler radar,

[0087] 2) Generate a corresponding random number in each data collection cycle;

[0088] The random number may be generated by a software random number generator or a hardware random number generator.

[0089] 3) Performing a modulo operation on the random number of the current data acquisition cycle and the length of the array; using the modulo value to index the value at the corresponding position in the array, and using the order of the numbers in the values as the beam irradiation order of the current cycle.

[0090] Specifically, the random number generated by the random number generator is modulo 24, and the remainder range is [0, 23]. Then, the remainder value is used to index the corresponding subscript of the sequence array to determine the beam irradiation order of the current cycle.

[0091] For example, if the generated random number is 0, the remainder is 0, and the first value in the array is 3142. The beam illumination order is 3-1-4-2. If the generated random number is 47, the remainder is 23, and the 24th value in the array is 2143. The beam illumination order is 2-1-4-3, and so on. This achieves random control of beam illumination. This overcomes the problem of co-channel interference caused by the fixed beam illumination order in each data acquisition cycle.

[0092] Furthermore, the speed measurement processing unit calculates the speed measurement information in the navigation information of the aircraft according to the Doppler frequency shift of the overlapping area as follows:

[0093]

[0094] Where, are the velocity components of the carrier coordinate system X, Y, and Z axes measured by the Doppler radar; γ0 is the angle between the center line of the overlapping beam and the X axis of the aircraft carrier coordinate system; δ0 is the angle between the projection of the overlapping beam line on the corresponding plane and the Y axis of the carrier coordinate system; when λ is the wavelength of the radar transmission signal F1, f d1 、f d2 、f d3 、f d4 are the Doppler frequency shifts of the relative signal F1 of the four beams; when λ is the wavelength of the radar transmission signal F2, f d1 、f d2 、f d3 、f d4 These are the Doppler shifts of the relative signal F2 of the four beams.

[0095] Therefore, as long as the Doppler instantaneous frequency values of the four overlapping beams are measured in real time, the components of the radar carrier velocity vector (i.e., the longitudinal velocity along the heading, the lateral velocity perpendicular to the heading, and the vertical velocity) can be calculated in real time according to the above formula for navigation.

[0096] In summary, this embodiment utilizes overlapping synthetic beams to effectively eliminate the effects of Doppler radar on ground scattering. This transforms the beam projection area used by the Doppler radar antenna from a single beam to an overlapping beam area, reducing the beam projection area and, to a certain extent, sharpening the available beam. This improves the Doppler spectrum purity and increases velocity measurement accuracy by at least five times. For Doppler radar, the velocity measurement accuracy of the Doppler navigation radar is directly related to the effectiveness of the remaining inertial navigation system. Therefore, overlapping beam antenna technology is of great significance for high-precision Doppler velocity radar.

[0097] The test results show that the speed measurement accuracy is forward vertical Lateral Speed measurement range: 25m / s≤v x ≤250m / s,|v y |≤40m / s,|v z |≤40m / s. Triaxial random error: ≤1.5m / s.

[0098] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A Doppler radar for speed measurement using overlapping synthetic beams, characterized in that: It includes an antenna unit, a beam receiving and transmitting control unit, and a beam receiving and transmitting control unit; The antenna unit is a common antenna for both transmission and reception. During transmission, the 4-channel signal F1 fed into the antenna radiates into space as 4 centrally symmetrical X-shaped radar beams; the 4-channel signal F2 fed into the antenna radiates into space as 4 centrally symmetrical X-shaped radar beams; the 4 radar beams of the signal F1 and the 4 radar beams of the signal F2 overlap in pairs to form 4 groups of overlapping synthetic beams; during reception, the echo signals of the 4 groups of overlapping synthetic beams are received respectively, and the 4-channel signal F1 echo signal and the 4-channel signal F2 echo signal are fed out; The frequencies of the signal F1 and the signal F2 are set to have a certain frequency difference between each other; by controlling the range of the frequency difference, the two beams generated by the signal F1 and the signal F2 are controlled to have a certain overlap with each other; The antenna unit includes a radiation array subunit; the radiation array subunit includes N parallel and evenly arranged radiation waveguides; each radiation waveguide includes horn sections at the left and right ends and a radiation section in the middle; the radiation section is a traveling wave slot radiation waveguide with a narrow side slit; multiple narrow side slits of the same length and width with staggered inclination angles are provided on the narrow side of the waveguide, the interval between each two adjacent narrow side slits is the same, and the narrow side slits are symmetrically distributed with respect to the center line of the radiation waveguide; The beam transceiver control unit is used to control the timing of the antenna unit's feed signals to form four sets of overlapping synthetic beams; control the timing of the antenna unit's feed signals to receive the echo signals of the four sets of overlapping synthetic beams; The speed measurement processing unit is used to extract the Doppler frequency shift in the overlapping area of the four sets of overlapping synthetic beams to measure the speed of the aircraft; The beam transceiver control unit controls the illumination order of the four groups of overlapping synthetic beams to be random, which is used to overcome co-frequency interference; Methods to overcome co-channel interference include: 1) numbering the four groups of overlapping synthetic beams of the Doppler radar; arranging the numbers to form a one-dimensional array as an illumination sequence set of the four groups of overlapping synthetic beams of the Doppler radar; Number the four groups of overlapping composite beams as 1, 2, 3, and 4; Arrange the 4 numbers to form 24 combinations, forming a one-dimensional array with a length of 24, which is: {3142,4312,3421,4321,2413,4213,2431,4231,2314,3214,2341,3241,1423,4123,1432,4132,1324,3124,1342,3142,1234,1243,2134,2143}； Using the one-dimensional array as an illumination sequence set of each beam of the Doppler radar; 2) Generate a corresponding random number in each data collection cycle; 3) performing a modulo operation on the random number of the current data collection period and the length of the array; The remainder value is used to index the value at the corresponding position in the array, and the order of the numbers in the values is used as the beam irradiation order of the current cycle; The random number generated by the random number generator is modulo 24, and the remainder range is [0, 23]. Then, the remainder value is used to index the corresponding subscript of the sequence array to determine the beam irradiation order of the current cycle. The speed measurement processing unit calculates the speed measurement information in the aircraft's navigation information based on the Doppler frequency shift in the overlapping area: Where, f is the velocity component of the carrier coordinate system X, Y, and Z axes measured by the Doppler radar; d1 、f d2 、f d3 、f d4 are the Doppler frequency shifts of the relative signal F1 of the four beams; γ0 is the angle between the center line of each beam and the X-axis of the aircraft carrier coordinate system; δ0 is the angle between the projection of the beam line on the corresponding plane and the Y-axis of the carrier coordinate system; λ is the wavelength of the radar transmission signal F1.

2. The Doppler radar according to claim 1, characterized in that The antenna unit includes a feeding unit; The feeding subunit includes first, second, third and fourth feeding waveguides having the same structure; The radiating waveguides and feeding waveguides are both rectangular waveguides; wherein the first and third feeding waveguides are arranged in a row on the left side of the radiating array subunit, feeding power to the left input end of each radiating waveguide; the second and fourth feeding waveguides are arranged in a row on the right side of the radiating array subunit, feeding power to the right input end of each radiating waveguide; Both ends of each feeding waveguide are feeding ports. Both ends of the first feeding waveguide and the second feeding waveguide in the upper layer of the four feeding waveguides placed in pairs are fed with signal F1 or feed out the echo signal of signal F1; both ends of the third feeding waveguide and the fourth feeding waveguide in the lower layer of the four feeding waveguides placed in pairs are fed with signal F2 or feed out the echo signal of signal F2.

3. The Doppler radar according to claim 1, characterized in that The wide ends of the horn sections at the left and right ends of each radiation waveguide accommodate the first and third feeding waveguides located at the left end of the radiation waveguide and the second and fourth feeding waveguides located at the right end thereof; The narrow end of the horn section is connected to the radiation section; the horn section is used to realize the transition of the signal from the feed waveguide to the radiation section; the radiation section is used to radiate the signal.

4. The Doppler radar according to claim 3, characterized in that N narrow side cracks are formed on the short side walls of the first, second, third and fourth feeding waveguides facing the radiation section, and electromagnetic signals are transmitted to the emitting and radiating waveguide array through the narrow side cracks.

5. The Doppler radar according to claim 3, characterized in that: The deflection angle of a set of overlapping synthetic beams radiated outward by the antenna unit in the X direction of the pattern Deflection angle in the Y direction of the pattern Where i = 1 or 2, λ1 and λ2 are the wavelengths of signals F1 and F2 in free space, and λ 1g ,λ 2g is the wavelength of signals F1 and F2 in the waveguide; d1 is the distance between the centers of two adjacent narrow-side cracks on the radiating waveguide; d2 is the distance between the centers of two adjacent narrow-side cracks on the feeding waveguide; by controlling the frequencies of signals F1 and F2, the deflection angles of signals F1 and F2 in the X and Y directions of the radiation pattern are controlled, thereby controlling the degree of overlap of the overlapping synthetic beams.

6. The Doppler radar according to claim 3, characterized in that: The amplitude distribution function of the coupling function of the narrow side crack on the radiation waveguide to the waveguide is: Where E(x) is the amplitude distribution function, P(x) is the power passing through the waveguide, and x is the value normalized relative to half the length of the antenna; P(0) = P0; φ(+1) = [P(+1)-P0] / [P(+1)+P0].

7. The Doppler radar according to claim 5, characterized in that: Each port of the first, second, third and fourth feed waveguides includes a waveguide isolator; When one of the four ports in the first and second feeding waveguides is incident, the isolators at the other three ports function as reverse load absorbers. When one of the four ports of the third and fourth feeding waveguides is incident, the isolators at the other three ports function as reverse load absorbers.

8. The Doppler radar according to claim 3, characterized in that: The beam transceiver control unit adopts a time-sharing control method. At a certain transmission control timing, it controls the ports on the same side of the first and third feeding waveguides or the second and fourth feeding waveguides placed in parallel, and simultaneously feeds signals F1 and F2, which are radiated into space through the radiation array sub-units to form a group of overlapping synthetic beams; at a reception control timing after the transmission control timing, it receives the echo signals of the overlapping synthetic beams and feeds the echo signals of signal F1 and signal F2 from the ports on that side.

Images