A non-contact shipborne speed measurement system

Abstract

The invention discloses a non-contact shipborne speed measurement system, which relates to the field of radar technology. The system uses two non-contact shipborne speed meters installed at the edges of cabins on both sides of a ship to achieve non-contact speed measurement based on the radar principle, and uses the Doppler frequency deviation of a moving target. Compared with traditional speed meters that are difficult to achieve accurate speed measurement of new high-speed ships, the system uses a non-contact radar for speed measurement, which can avoid being restricted by factors such as low altitude, swaying, and large wind pressure angles, and can ensure that any high-speed ship can measure its relative motion speed with the water surface in any navigation posture. Multi-beam measurement is used, which can greatly reduce errors caused by beam tilting due to the swaying, longitudinal tilt, and heeling of the carrier ship.

Description

Technical Field

[0001] The invention relates to the field of radar technology, in particular to a non-contact shipborne speed measurement system. Background Art

[0002] Shipboard speedometers can provide information such as speed for ship navigation aids. According to the different measurement reference coordinate systems, they can be divided into two categories: relative shipboard speedometers and absolute shipboard speedometers. Relative shipboard speedometers can only measure the speed of a ship relative to water and accumulate its distance, such as hydraulic and electromagnetic types; absolute shipboard speedometers can measure the speed of a ship relative to the ground and accumulate its distance, such as acoustic Doppler speedometers. Doppler speedometers are products from the early 1970s. With the development of shipping, they were developed to solve the problems of entering and leaving ports, berthing and anchoring of some large and super-large ships. Typical products include the SRD-331 type in the United States, the ATLASDOLOG20 series in Germany, the TD-501 type and MF-100 type in Japan, and the domestic MCDL-1 type.

[0003] At present, the most widely used instrument in the field of shipbuilding is the acoustic Doppler log, which is a high-precision speed measuring instrument designed based on the principle of the Doppler effect. It transmits sound signals to the seabed through a transducer, receives the reflected echo signal, and estimates the difference between the echo signal frequency and the transmitted signal frequency, thereby obtaining the speed of the carrier relative to the seabed. However, due to the complex speed measurement environment, the speed measurement accuracy will be affected by many factors, among which the main factors are the changes in the physical conditions of the seawater medium, the propagation characteristics of ultrasonic waves in seawater, the turbulence and ups and downs of the ship, and the installation accuracy of the Doppler log. Due to the influence of the above many factors, the measurement accuracy is limited when measuring speed.

[0004] At present, with the emergence of new high-speed ships such as hovercraft, hydrofoil, catamaran, small waterplane area ship and ground effect ship, how to accurately measure the speed of these ships has also attracted widespread attention. Because the hull of such ships cannot keep in contact with water from beginning to end, or due to the shape and structure of the hull, the water boundary layer changes irregularly when the ship is sailing, making it difficult for traditional speed meters that must always be in contact with water, such as water pressure logs, electromagnetic logs and acoustic Doppler logs, to accurately measure the sailing speed of their ships. At the same time, such ships are often affected by wind when sailing, so it is necessary to measure not only the velocity vector but also the wind pressure angle. On the other hand, due to the complexity of low-altitude air flow, the traditional speed sensors are not suitable for use on such ships due to the constraints of factors such as low "flying" height, swaying, and large wind pressure angle. Summary of the invention

[0005] In view of the above problems and technical requirements, the inventors have proposed a non-contact shipborne speed measurement system. The technical solution of the present invention is as follows:

[0006] A non-contact shipborne speed measurement system, the system comprises a ship and two non-contact shipborne speedometers respectively installed at the edges of the cabins on both sides of the ship, each non-contact shipborne speedometer respectively comprises a device housing and a processing unit, a transceiver unit and a transceiver antenna arranged inside the device housing, a group of transceiver antennas comprises a transmitting antenna assembly and a receiving antenna assembly, the processing unit is connected to the transceiver unit, and the transceiver unit is connected to the transceiver antenna; the transceiver antennas in the two non-contact shipborne speedometers are at least facing forward in the direction of the ship's navigation, and the transmitting beams in the two non-contact shipborne speedometers are both facing below the horizontal plane to form an angle θ with the horizontal plane, the transceiver antenna in each non-contact shipborne speedometer adopts an inclined beam angle design, and the main beam angle forms an angle φ with the array normal to the outside of the cabin; the processing units in the two non-contact shipborne speedometers are respectively connected to the control center of the ship;

[0007] When the ship is traveling, the processing unit in each non-contact shipborne speed meter transmits microwave signals through the transceiver unit and the transceiver antenna, and receives the corresponding zero-frequency echo signal through the transceiver antenna and the transceiver unit. The zero-frequency echo signal is a signal with Doppler frequency deviation returned by the microwave signal after being reflected by the sea surface. The processing unit extracts the Doppler frequency deviation from the zero-frequency echo signal;

[0008] The two non-contact shipborne speed meters at least send the extracted Doppler frequency deviation to the ship's control center, and the ship's control center calculates the ship's speed based on the Doppler frequency deviation and the angles θ and φ sent by the two non-contact shipborne speed meters.

[0009] The beneficial technical effects of the present invention are:

[0010] The present application discloses a non-contact shipborne speed measurement system, which uses two non-contact shipborne speed meters installed at the edges of the cabins on both sides of the ship to achieve non-contact speed measurement based on the radar principle, and uses the Doppler frequency deviation of the moving target. Compared with the traditional speed meter that is difficult to accurately measure the speed of high-speed new ships, the speed measurement can avoid being restricted by factors such as low "flying" height, swaying, and large wind pressure angles due to the use of non-contact radar, and can ensure that any high-speed ship can measure its relative speed with the water surface in any navigation posture. The non-contact shipborne speed meter uses four-beam large-angle measurement, which can greatly reduce the error caused by beam tilt due to the swaying, pitch, and roll of the carrier ship.

[0011] Since non-contact shipborne speed meters have low power consumption, small size, and are usually installed on the bow or both sides of the ship, they are easy to install and maintain, do not require docking, and are designed with a variety of protection measures to ensure that the equipment can operate normally in harsh environments such as seawater, salt spray, high temperature and high humidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the installation of two non-contact shipborne speed meters on a ship in this application.

[0013] Figure 2 It is the appearance structure diagram of the non-contact shipborne speed meter of the present application.

[0014] Figure 3 It is a schematic diagram of the internal circuit of the non-contact shipborne speed meter of the present application.

[0015] Figure 4 It is a schematic diagram of the bidirectional front beam structure adopted in this application.

[0016] Figure 5 It is a schematic diagram of the four-beam structure of the bidirectional front beam and the bidirectional rear beam adopted in this application.

[0017] Figure 6 It is a schematic diagram of the arrangement of two groups of transmitting and receiving antennas in the non-contact shipborne speed meter of the present application.

[0018] Figure 7 It is a schematic diagram of the internal structure of the non-contact shipborne speed meter of the present application. DETAILED DESCRIPTION

[0019] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0020] The present application discloses a non-contact shipborne speed measurement system, which comprises a ship 1 and two non-contact shipborne speed meters 2 respectively installed at the edges of the cabins on both sides of the ship 1. Figure 2 As shown, each non-contact shipborne speedometer includes a device housing 21 and circuit components disposed inside the device housing 21. The device housing 21 is also provided with various external ports, such as Figure 2 In the figure, the equipment housing 21 is provided with an optical fiber communication port 22, a power supply and bus port 23, an equipment self-inspection port 24 and a signal self-inspection port 25. The optical fiber communication port 22 and the power supply and bus port 23 are used to connect to the ship, and the equipment self-inspection port 24 and the signal self-inspection port 25 are used for self-inspection.

[0021] The circuit components arranged inside the device housing 21 of each non-contact shipborne speedometer include at least a processing unit, a transceiver unit and a transceiver antenna. Figure 3As shown, a group of transceiver antennas includes a transmitting antenna assembly and a receiving antenna assembly, a processing unit is connected to the transceiver unit, and the transceiver unit is connected to the transceiver antenna. The processing units in the two non-contact shipborne speedometers are respectively connected to the control center of the ship.

[0022] The transceiver unit includes a transmitting link and a receiving link. The transmitting link is connected to the transmitting antenna assembly, and the receiving link is connected to the receiving antenna assembly. The transmitting link realizes the functions of filtering and output amplification, and the receiving link is used to realize the functions of receiving amplification, receiving down-conversion, receiving filtering, intermediate frequency AGC, and intermediate frequency coupling output.

[0023] The transmitting and receiving antennas of the two non-contact shipborne speed meters are at least facing the forward direction of the ship's sailing direction, such as Figure 1 As shown, at least beam 1 and beam 3 are included, and the transmitting beams in the two non-contact shipborne speedometers are both directed below the horizontal plane to form an angle θ with the horizontal plane. In order to ensure that the antenna radiation beam can illuminate the water surface but not the hull, the antenna assembly is designed with an inclined beam angle. The inclined beam angle antenna refers to an antenna whose main beam angle is between side-firing (0° angle with the array normal) and end-firing (90° angle with the array normal). The transceiver antenna in each non-contact shipborne speedometer adopts an inclined beam angle design, and the main beam angle forms an angle φ with the array normal toward the outside of the cabin. After calculation, in this application, the normal transmission and reception of the beam can be achieved when the inclined beam angle of the antenna assembly is greater than 35°. A coordinate system is established with the positive X-axis along the horizontal direction of the ship's navigation and the Y-axis along the horizontal direction of the ship's width. Figure 1 The schematic diagram of beam 1 and beam 3 in Figure 4 As shown, the angle θ is the angle between the beam and the horizontal plane, and the angle φ is the angle between the projection of the beam on the horizontal plane and the X-axis.

[0024] In one embodiment, only one set of transceiver antennas is provided in each non-contact shipborne speedometer, and the angle φ formed by the transceiver antennas in the two non-contact shipborne speedometers and the normal line of the array is the same to form a symmetrical structure, such as Figure 4 shown.

[0025] In another embodiment, each non-contact shipborne speedometer includes two transceiver units and two groups of transceiver antennas, both transceiver units are connected to the processing unit, and each transceiver unit is respectively connected to a group of transceiver antennas, such as Figure 3 As shown, the connection structure is the same. One set of transceiver antennas in the non-contact shipborne speedometer faces the forward direction of the ship's navigation direction, and the other set of transceiver antennas faces the backward direction of the ship's navigation direction, and the transmission angle is the same, that is, the four antenna components are all facing below the horizontal plane to form an angle θ with the horizontal plane, and the tilt beam angle is an angle φ, and the beam direction is symmetrical. Figure 1As shown, one non-contact shipborne speedometer is provided with two sets of transceiver antennas to form forward beam 1 and backward beam 2, and another non-contact shipborne speedometer is provided with two sets of transceiver antennas to form forward beam 3 and backward beam 4. Based on this, the schematic diagram of the four beams is as follows Figure 5 shown.

[0026] The non-contact shipborne speed measurement system uses two non-contact shipborne speed meters for non-contact speed measurement in the following process: When the ship is traveling, the processing unit in each non-contact shipborne speed meter transmits microwave signals through the transceiver unit and the transceiver antenna. The waves generated by the propulsion of the ship act as a reflection surface to reflect the signal with Doppler frequency deviation back to the non-contact shipborne speed meter, and the processing unit receives the corresponding zero-frequency echo signal through the transceiver antenna and the transceiver unit. The zero-frequency echo signal is a signal with Doppler frequency deviation returned by the microwave signal after being reflected from the sea surface. The processing unit performs sampling and other operations on the zero-frequency echo signal to extract the Doppler frequency deviation contained therein.

[0027] The two non-contact shipborne speed meters at least send the extracted Doppler frequency deviation to the ship's control center, and the ship's control center calculates the ship's speed based on the Doppler frequency deviation and the angles θ and φ sent by the two non-contact shipborne speed meters.

[0028] When using Figure 4 When the dual forward beam structure is shown, according to the Doppler principle, the Doppler frequency deviation extracted by a non-contact shipborne speed meter is theoretically V x is the longitudinal speed of the ship, f0 is the center frequency, and c is the speed of light. In reality, it will also be affected by the Doppler error caused by the ship's left and right swing, and the Doppler frequency deviation extracted by the two non-contact shipborne speedometers is affected by the Doppler error in the horizontal direction with the same magnitude and opposite direction. Therefore, the ship's control center synthesizes the longitudinal speed of the ship along the length direction based on the Doppler frequency deviation sent by the two non-contact shipborne speedometers and the angles θ and φ, and the longitudinal speed obtained after synthesis is not affected by the Doppler error caused by the ship's left and right swing.

[0029] When using Figure 5 In the four-beam structure shown, the processing unit in each non-contact shipborne speed meter sends two microwave signals of different frequencies through two transceiver units using corresponding transceiver antennas, so that two Doppler frequency deviations can be extracted. When a ship is actually sailing, in addition to being affected by the Doppler error caused by the ship's left and right swing, it will also be affected by the Doppler error caused by the ship's vertical movement. In the above dual forward beam structure, when the ship is bumpy and has a vertical speed, the synthesized speed measurement will produce a large error.

[0030] The four-beam structure can reduce or even eliminate this error. The two Doppler frequency deviations affected by the Doppler error caused by the vertical motion of the ship received by the ship's control center from the same non-contact shipborne speed meter are: as well as Where V x is the longitudinal speed of the ship, U is the speed of the ship in the vertical direction when it moves vertically, f0 is the center frequency, and c is the speed of light. It can be seen that the two beams of the same non-contact shipborne speedometer have the same incident angle, so their horizontal velocity components are the same in magnitude and opposite in direction, while the components of the vertical velocity U received in the beam emission direction are the same. The ship's control center synthesizes the Doppler frequency deviation and the angle θ and the angle φ sent by the two non-contact shipborne speedometers to obtain the longitudinal speed of the ship along the length direction and the lateral speed V along the width direction of the ship. y , and the synthetic speed obtained by vector synthesis of the longitudinal speed and the transverse speed is not affected by the Doppler error caused by the ship's left and right swing and vertical motion. It can be obtained that the longitudinal Doppler frequency deviation on one side is Similarly, the lateral Doppler frequency deviation is

[0031] Regardless of whether a dual-beam structure or a four-beam structure is adopted, in another embodiment, the processing unit in each non-contact shipborne speedometer will not only send the extracted Doppler frequency deviation to the ship's control center, but also calculate the first reference ship speed based on the extracted Doppler frequency deviation and send it to the ship's control center. When the ship's control center receives the Doppler frequency deviation and the first reference ship speed sent by the non-contact shipborne speedometer, it uses the received Doppler frequency deviation to calculate the second reference ship speed in the same way. If the error between the second reference ship speed and the first reference ship speed is within the preset error range, it is determined that the signal transmission of the non-contact shipborne speedometer is normal. Otherwise, it is determined that the signal transmission with the non-contact shipborne speedometer is abnormal, and the data can be discarded without processing. When it is determined that the signal transmission of the two non-contact shipborne speedometers is normal, the ship's speed is calculated based on the Doppler frequency deviation sent by the two non-contact shipborne speedometers and the angle θ and the angle φ, according to the above method. It can be seen from the above formula that the influence of the vertical motion speed U caused by the ship's turbulence has been eliminated. When using four beams (dual forward dual backward four beams), the vertical velocity measurement error introduced by the ship's pitch can be effectively removed, thereby greatly reducing the velocity calculation error caused by beam tilt due to the ship's swaying and pitch and roll.

[0032] Actual Figure 3As shown, the processing unit specifically includes FPGA, ADC circuit, point frequency source, power supply circuit, optical fiber communication interface circuit, CPU circuit, 422 interface circuit. The power supply circuit is connected to the ship through the power supply and bus port 23 to obtain +24V DC power supply, and generates the circuit DC voltage required by each internal circuit. FPGA is connected to the CPU circuit through the EBI bus, the CPU circuit is connected to the 422 interface circuit, and the 422 interface circuit is connected to the ship's control center through the power supply and bus port 23 using the RS422 bus for data communication. FPGA is also connected to the optical fiber communication interface circuit through the high-speed bus, and the optical fiber communication interface circuit is connected to the ship's control center through the optical fiber communication port 22 for data communication. In actual application, the processing unit usually sends Doppler frequency deviation through the optical fiber communication port 22, and sends data such as the first reference ship speed and sampled raw data through the power supply and bus port 23. FPGA is connected to the transmitting link in the transceiver unit through the point frequency source, and is connected to the receiving link in the transceiver unit through the ADC circuit. The processing unit generates a sampling clock from the input reference clock. FPGA completes the control of the point frequency source and the ADC circuit, and completes the automatic gain control of the 4 receiving channels, the sampling of the 4 input zero-frequency signals, filtering extraction, FFT spectrum analysis, CFAR detection, speed calculation and other functions. At the same time, the sampled raw data is packaged and sent back to the control center through optical fiber, and the speed and other information are transmitted to the CPU through the parallel data interface. The CPU completes the exchange of radar working status information with the control center through the RS422 serial port.

[0033] Based on the above principle, in actual application, a dual-forward dual-reverse four-beam architecture is usually used to measure speed. Each non-contact shipborne speedometer contains two sets of transceiver antennas. This application takes this as an example to introduce some specifications and features of the non-contact shipborne speedometer. When there is only one set of transceiver antennas, the structure and features are similar:

[0034] 1. Installation of various circuit components.

[0035] like Figure 6 As shown, one group of transceiver antennas in a non-contact shipborne speedometer includes a transmitting antenna assembly 26 and a receiving antenna assembly 27, and another group of transceiver antennas includes a transmitting antenna assembly 28 and a receiving antenna assembly 29. The four antenna assemblies of the two groups of transceiver antennas are arranged inside the device housing to form two antenna arrays that cross at 90 degrees.

[0036] The radiation front of each antenna component adopts the form of longitudinal slits on the wide side of the waveguide. The directivity of the antenna is enhanced by forming an array antenna with multiple slits. Multiple slits are opened on the same wall of a waveguide according to a certain distribution rule. In order to make full use of the aperture area, as many radiation slits as possible are arranged on the array surface to improve the aperture efficiency. Non-standard waveguides are used to form the radiation array surface. The required aperture amplitude and phase distribution are achieved by controlling the offset or inclination of the slits. The waveguide slit linear array is arranged at a certain spacing on the plane. By controlling the excitation of each waveguide and the inclination or offset of the slits, a controllable two-dimensional aperture distribution is obtained, thereby generating lobes of the desired angle. Figure 1 The present application takes the inclined beam angle of 40° as an example. The transceiver unit is directly mounted on the back of a corresponding group of transceiver antennas, the output waveguide port of the receiving antenna assembly in a group of transceiver antennas is directly connected to the waveguide port of the corresponding transceiver unit, and the transmitting waveguide port of the transmitting antenna assembly is connected to the SMA connector of the corresponding transceiver unit using a radio frequency cable through a waveguide coaxial converter.

[0037] The actual equipment shell 21 includes an outer shell base and an antenna cover. The above-mentioned processing unit, transceiver unit and transceiver antenna are installed in the outer shell base through a mounting bracket. The transceiver antenna is located at the opening of the outer shell base. An antenna cover is installed on the outside to protect the antenna assembly. The antenna cover is installed at the bottom of the ship close to the sea surface.

[0038] 2. Design of transmit and receive isolation.

[0039] Among the various indicators of continuous wave radar, the isolation between the transmitting and receiving antennas is the key indicator. Continuous wave speed measurement radar transmits and receives at the same time. If the problem of transmitter-receiver isolation is not solved, the receiver will not be able to receive the signal normally under the influence of the strong power signal transmitted, and will not be able to continue to track the target. If the transmitter-receiver isolation is not good, the actual sensitivity of the receiver will be reduced and the operating range will be reduced at the least; in severe cases, the receiver will be saturated and the target will not be tracked. If the isolation is not enough, the radar power will be weakened and the radar operating range will be greatly reduced. In severe cases, the receiving channel signal will be saturated and the radar system will not work. Therefore, this application has the following transmitter-receiver isolation design for the non-contact shipborne speed meter. Please combine it with Figure 7 :

[0040] 1. Spatial wave suppression.

[0041] A metal baffle 210 is provided between any two antenna assemblies inside the device housing 21. The metal baffle 210 is provided in close contact with the antenna assemblies, and the upper end surface of the metal baffle 210 is spaced a predetermined distance from the upper surface of the antenna assemblies, such as 22 cm, to achieve spatial wave suppression.

[0042] 2. Surface wave suppression.

[0043] When the antenna is installed in a metal frame, part of the microwave energy received and transmitted by the antenna generates surface wave currents induced by the frame, which deteriorates the isolation of the transmitting and receiving antennas; part of the microwave energy is reflected by the metal surface to form multipath reflections, which deteriorates the antenna radiation pattern. After the metal baffle 210 is installed, the isolation of the transmitting and receiving antennas is improved, but the surface waves will still propagate through the metal isolation plate, affecting the isolation effect. Therefore, further, the inner surface of the equipment housing 21 and the two side walls of each metal baffle 210 are respectively paved with absorbing materials to achieve surface wave suppression. The absorbing material refers to a type of material that can absorb or greatly reduce the electromagnetic wave energy projected onto its surface, thereby reducing electromagnetic wave interference. Installing microwave absorbing materials can effectively reduce the multipath reflections formed by the surface wave currents on the metal surface and the reflections on the metal surface, and improve the isolation and radiation pattern of the antenna. The installation thickness is configured according to actual needs. For example, the present application actually lays 2mm thick absorbing materials. Through the above processing, it is equivalent to laying absorbing material on the surface of the metal material around each antenna component, which can absorb the electromagnetic wave energy on its surface and reduce the direct propagation of surface waves on the metal surface between the transmitting and receiving antennas. The isolation effect is very obvious.

[0044] After adopting the comprehensive treatment methods of adding metal baffles and laying absorbing materials, the isolation of the original continuous wave speed measurement radar transceiver antenna has been significantly improved, from about 40dB to nearly 85dB, basically achieving the purpose of suppressing surface waves and reducing the coupling of transceiver antennas.

[0045] 3. Protection technology for humid, hot and salty fog environments such as seawater.

[0046] Since one side of the non-contact shipborne speedometer antenna cover is installed at the bottom of the boat close to the sea surface, during use, the outside temperature is high, the air in the installation cabin cannot circulate, and seawater mist will penetrate into the installation cabin, which will form a high temperature and high humidity environment, and there are high requirements for equipment protection. In view of the above situation, the following measures are mainly taken:

[0047] (1) For the internal transceiver unit, the high-frequency circuit adopts a baseband board design, the shell and the cover are fully welded, the RF connector adopts a glass sintering structure, and the waveguide port uses a sealing ring to fully seal the contact surface to ensure the full sealing of the entire module.

[0048] (2) For the transceiver antenna, the receiving and transmitting waveguide ports are fully sealed with sealing rings. The outer surface of the antenna array (the side with the gap) is mounted with a high-transmittance protective film that is resistant to high temperature and corrosion, and the back of the antenna is sprayed with anti-corrosion paint.

[0049] (3) For the processing unit, the internal printed circuit boards and component surfaces are coated with conformal coating, the external connectors are watertight connectors, the indicator lights and switches that need to be exposed on the side are designed to be retracted in structure, and a transparent and corrosion-resistant baffle is installed on the outside. The baffle and the upper and lower covers of the shell are fully sealed with sealing rings to ensure the sealing of the entire module.

[0050] (4) The base of the shell is sprayed with a corrosion-resistant and salt-spray-resistant paint coating.

[0051] (5) The radome adopts a sandwich composite material structure, and the skin adopts a high-temperature resistant and high-transmittance composite material, such as fiberglass (a composite material synthesized from resin and glass fiber). The outer surface is sprayed with anti-corrosion paint to achieve UV resistance, crack resistance, corrosion resistance, impact resistance, aging resistance, high and low temperature resistance, strong wave transmission, strong wind resistance, good consistency and not easy to deform. The installation contact surface of the radome and the shell base is equipped with a full sealing gasket, which can provide good protection against harsh environments.

[0052] 4. Demonstration of key indicators.

[0053] (1) Speed ​​measurement accuracy.

[0054] In this system, based on Nyss sampling theorem, the sampling frequency must be greater than twice the highest Doppler frequency deviation. After calculation: V max =51.44m / s(100kn), f0 is the center frequency of 14.9GHz, c is the speed of light, which is 3×10 8 m / s, substitute into the Doppler frequency deviation formula The maximum Doppler frequency deviation f can be obtained from this d_max =5.11kHz, then the sampling frequency should be greater than 10.22kHz to measure a speed of 100kn. Similarly, assuming the minimum speed is 0.5kn (0.25m / s), the minimum Doppler frequency deviation f can be obtained by substituting it into the above formula. d_min =24.8Hz. Taking all factors into consideration, the sampling frequency f s =25kHz, N FFT The expected value is 4096, so the residence time (data block length) is T DWell It is about 4096 / 25000=0.163s. If 0.16s is taken, the dwell interval Δf=1 / T DWell =1 / 0.16=6.25Hz, the speed measurement accuracy can be obtained as ΔV d =Δf*λ / 2=6.25*0.02 / 2=0.0625m / s=0.225km / h.

[0055] (2) Receiver sensitivity.

[0056] Receiver sensitivity is the minimum signal strength that the receiver can capture and the receiver system can be in normal working condition. Its size is the minimum detectable signal power S of the receiver. min To express, improving the receiver's receiving sensitivity helps the receiver system better capture weak signals. The receiving sensitivity formula is as follows: S min (dBm) = -114dB + 10logB (MHz) + F0 (dB), where B is the receiver bandwidth, for example, 20kHz in one example, and F0 is the total noise factor of the receiver. According to the principle block diagram, the receiving channel should be less than 8dB. Here, 7dB is taken and substituted into the above formula to get S min (dBm) = -124dBm.

[0057] (3) Minimum echo power.

[0058] The radar equation is used to estimate the echo power. Among them, P T is the transmitted signal power, set to 100mW. G is the antenna gain, set to 27.5dB. λ is the wavelength, the center frequency is 14.9GHz, then the wavelength λ is 0.02m. R is the distance between the radar antenna and the target. σ T is the back reflection cross-sectional area (RCS) related to the target characteristics. L is the system loss, which can be taken as 9dB. Substituting the above values ​​into the radar receiving power formula, the calculation results are shown in the following table:

[0059] Table 1 Correspondence table of radar echo power at different distance ranges and installation heights

[0060]

[0061] From the above analysis, it can be seen that the approximate range of echo power is about -105dBm to -107dBm (obtained from the table under sea condition level 3, with an average wind speed of 15kn).

[0062] 5. Performance indicators of non-contact shipborne speedometer.

[0063] By adopting the above design scheme, the shipborne speed measurement radar can achieve the following performance indicators:

[0064] (1) Working system: single frequency continuous wave system;

[0065] (2) Operating frequency band: Ku band;

[0066] (3) Speed ​​measurement range: within the range of 0.5m to 30m, the longitudinal speed measurement range is: 0.5kn to 100kn, and the lateral speed measurement range is ±25kn;

[0067] (4) Speed ​​measurement accuracy: 0.0625m / s;

[0068] (5) Operating environment: -10℃~+65℃;

[0069] (6) Protection grade: IP65;

[0070] (7) Dimensions: ≤740 mm × 740 mm × 180 mm;

[0071] (8) External interface: optical fiber and RS422 communication;

[0072] (9)Weight: ≤40kg.

[0073] The above is only a preferred embodiment of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A non-contact shipborne speed measurement system, characterized in that: The system comprises a ship and two non-contact shipborne speedometers respectively installed at the edges of the cabins on both sides of the ship, each of the non-contact shipborne speedometers respectively comprises a device housing and a processing unit, a transceiver unit and a transceiver antenna arranged inside the device housing, a group of transceiver antennas comprises a transmitting antenna assembly and a receiving antenna assembly, the processing unit is connected to the transceiver unit, and the transceiver unit is connected to the transceiver antenna; The transceiver antennas in the two non-contact shipborne speedometers are at least facing forward in the direction of the ship's navigation, and the transmitting beams in the two non-contact shipborne speedometers are both facing below the horizontal plane to form an angle θ with the horizontal plane. The transceiver antenna in each non-contact shipborne speedometer adopts an inclined beam angle design, and the main beam angle forms an angle φ with the array normal to the outside of the cabin; the processing units in the two non-contact shipborne speedometers are respectively connected to the control center of the ship; During the travel of the ship, the processing unit in each non-contact shipborne speed meter transmits a microwave signal through a transceiver unit and a transceiver antenna, and receives a corresponding zero-frequency echo signal through the transceiver antenna and the transceiver unit. The zero-frequency echo signal is a signal with a Doppler frequency deviation returned by the microwave signal after being reflected by the sea surface. The processing unit extracts the Doppler frequency deviation from the zero-frequency echo signal; The two non-contact shipborne speed meters at least send the extracted Doppler frequency deviation to the ship's control center, and the ship's control center calculates the ship's speed based on the Doppler frequency deviation and the angle θ and the angle φ sent by the two non-contact shipborne speed meters; The processing unit in each non-contact shipborne speed meter calculates a first reference ship speed according to the extracted Doppler frequency deviation and sends it to the ship's control center; when the ship's control center receives the Doppler frequency deviation and the first reference ship speed sent by the non-contact shipborne speed meter, the second reference ship speed is calculated using the received Doppler frequency deviation. If the error between the second reference ship speed and the first reference ship speed is within a preset error range, it is determined that the signal transmission of the non-contact shipborne speed meter is normal; When it is determined that the signal transmissions of the two non-contact shipborne speedometers are normal, the ship speed is calculated based on the Doppler frequency deviations and the angles θ and φ sent by the two non-contact shipborne speedometers.

2. The non-contact shipborne speed measurement system according to claim 1, characterized in that: Only one set of transmitting and receiving antennas is arranged in each non-contact shipborne speed meter, and the transmitting and receiving antennas in the two non-contact shipborne speed meters form the same angle φ with the array normal to form a symmetrical structure. Then, the control center of the ship obtains the longitudinal speed of the ship along the direction of the ship length based on the Doppler frequency deviation sent by the two non-contact shipborne speed meters and the angle θ and the angle φ, and the calculated longitudinal speed is not affected by the Doppler error caused by the left and right swaying of the ship.

3. The system according to claim 1, characterized in that Each non-contact shipborne speedometer includes two transceiver units and two groups of transceiver antennas, the two transceiver units are connected to the processing unit, and each transceiver unit is respectively connected to a group of transceiver antennas, one group of transceiver antennas in the non-contact shipborne speedometer faces forward in the direction of the ship's navigation, and the other group of transceiver antennas faces backward in the direction of the ship's navigation, and the transmission angles are the same, and the processing unit in each non-contact shipborne speedometer sends two microwave signals of different frequencies through the two transceiver units using the corresponding transceiver antennas; The ship's control center obtains the longitudinal speed of the ship along the length of the ship and the lateral speed along the width of the ship based on the Doppler frequency deviation and the angles θ and φ sent by the two non-contact shipborne speed meters. The synthetic speed obtained by vector synthesis of the longitudinal speed and the lateral speed is not affected by the Doppler error caused by the ship's left and right swing and vertical movement.

4. The non-contact shipborne speed measurement system according to claim 3, characterized in that: The two Doppler frequency deviations affected by the Doppler error caused by the vertical motion of the ship received by the control center of the ship from the same non-contact shipborne speed meter are: as well as Where V x is the longitudinal speed of the ship, U is the speed of the ship in the vertical direction when it moves vertically, f0 is the center frequency, and c is the speed of light.

5. The non-contact shipborne speed measurement system according to claim 3, characterized in that: The four antenna components of the two groups of transceiver antennas are arranged inside the device shell to form two crossed 90° antenna arrays. The radiation front of each antenna component adopts the form of a longitudinal slit on the wide side of the waveguide. The output waveguide port of the receiving antenna component in one group of transceiver antennas is directly connected to the waveguide port of the corresponding transceiver unit, and the transmitting waveguide port of the transmitting antenna component is connected to the SMA connector of the corresponding transceiver unit using an RF cable through a waveguide coaxial converter.

6. The non-contact shipborne speed measurement system according to claim 1, characterized in that: A metal baffle is arranged between any two antenna assemblies inside the device housing. The metal baffle is arranged in close contact with the antenna assemblies, and a predetermined distance is provided between the upper end surface of the metal baffle and the upper surface of the antenna assemblies to achieve spatial wave suppression.

7. The non-contact shipborne speed measurement system according to claim 6, characterized in that: Wave-absorbing materials are laid on the inner surface of the device shell and the two side walls of each metal baffle to achieve surface wave suppression.

8. The non-contact shipborne speed measurement system according to claim 1, characterized in that: The device shell includes an outer shell base and an antenna cover. The outer shell base is sprayed with a corrosion-resistant and salt-spray-resistant paint coating. The antenna cover is installed at the bottom of the ship close to the sea surface. The antenna cover adopts a sandwich composite material structure, and the skin adopts a high-temperature resistant and high-transmittance composite material. A full sealing gasket is installed on the installation contact surface between the antenna cover and the outer shell base.

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