CN108445483B

CN108445483B - Radar detection system for water-floating plants

Info

Publication number: CN108445483B
Application number: CN201810218324.0A
Authority: CN
Inventors: 陈俊; 贺立新; 雷彬; 董万均; 董波; 凌小佳
Original assignee: Nanjing Institute Of Hydrologic Automation Ministry Of Water Resources; Chengdu Jinjiang Electronic System Engineering Co Ltd
Current assignee: Nanjing Water Conservancy and Hydrology Automatization Institute Ministry of Water Resources
Priority date: 2018-03-16
Filing date: 2018-03-16
Publication date: 2021-08-17
Anticipated expiration: 2038-03-16
Also published as: CN108445483A

Abstract

The invention relates to a radar detection system for aquatic plants, in particular to a radar-based radar detection system for aquatic plants floating on water surface and growing on water surface, which is used for measuring and calculating the area of aquatic plants flowing through monitoring points in real time by utilizing the difference of microwave echo intensities between a floater and the water surface and through high resolution, establishing an aquatic plant growing model according to the area of the aquatic plants flowing through different monitoring points and finally realizing prediction and full-basin supervision.

Description

Radar detection system for water-floating plants

Technical Field

The invention relates to the field of aquatic plant remediation, in particular to a radar detection system for water-floating plants.

Background

The water floating plants are always the key point and the difficulty of river regulation, particularly, the water hyacinth which is a foreign species in recent years is strong in vitality and extremely fast in growth speed, a large number of water hyacinth floats on the water surface, flows down and continues for tens of kilometers, and most of the water surface is covered by the water hyacinth, so that the water environment is polluted, the ship navigation safety is influenced, and even the water hyacinth enters a municipal planning landscape water area, and the wide attention of the society is aroused.

For this reason, the related departments carry out the related remedial work. The method comprises the early warning mainly based on ship patrol, vehicle patrol and video monitoring; the cleaning work mainly including interception centralized fishing and ship cruising fishing and the like, and the remediation achieves certain effect. However, under the influence of environmental factors such as hydrology, climate and geography, the explosion of the water hyacinth has uncertainty, so that the fishing force is blocked to catch one's turn when a large number of water hyacinth in certain areas and time periods are intensively exploded suddenly. Therefore, a set of intelligent management method based on aquatic plant early warning and comprehensive treatment is urgently needed to be established by relevant departments, the detection sensors are used for acquiring the distribution information of the water surface floating plants flowing through the detection points, and through the networking and fusion of information of multiple detection points, other multi-party meteorological and hydrological information is integrated, the growth trend and the overall distribution condition of the watershed of the aquatic plants are judged, an aquatic plant management early warning mechanism is established, the fishing operation force is reasonably arranged, and the purpose of effectively controlling the aquatic plants is achieved.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a radar detection system for aquatic plants, which is a radar-based monitoring system for aquatic plants floating on water surface and growing on water surface.

The purpose of the invention is realized by the following technical scheme:

the radar detection system for the water-floating plants consists of an antenna system, a radio frequency microwave system and a data processing and terminal display system;

the antenna system consists of a transmitting antenna and a receiving antenna, a radar generates a dot frequency continuous wave and a linear frequency modulation continuous wave signal, wherein the dot frequency signal is only used for measuring the speed of the water surface floater, the linear frequency modulation continuous wave signal realizes the area measurement of the water surface floater, the signal is radiated out through the transmitting antenna, and the signal enters the receiving antenna after being reflected by aquatic plants;

the radio frequency microwave system consists of a receiving front end, a data acquisition module and a frequency synthesis assembly, wherein signals reflected by aquatic plants are accessed to the receiving front end, processed by a three-stage mixer and then output by a filter amplifier, a numerical control attenuator and a low-pass filter; the data acquisition module consists of an anti-aliasing filter, an ADC, an FPGA and an Ethernet transmission module and is used for realizing the digitization of intermediate frequency signals, and the frequency synthesis component consists of a clock reference circuit, a waveform generation circuit, a transmitting channel and an interface control circuit and is used for improving local oscillation signals required by a receiving front end, synchronous clock signals required by the data acquisition module and linear frequency modulation excitation signals;

the data processing and terminal display system is composed of a data processing module and a terminal display module, and is used for completing online real-time measurement and display of all information of the water plants.

As a further improvement of the scheme, the antenna system adopts a transmitting-receiving separately-arranged planar array antenna system, and the antenna forms the directional diagram characteristic of a horizontal narrow lobe and a vertical wide lobe.

As a further improvement of the scheme, the planar array antenna system is a waveguide planar array antenna, a sub-array block design structure is adopted, the working frequency is K waveband, f0 +/-150 MHz, and f0 is 24 GHz.

As a further improvement of the scheme, the antenna gain is more than or equal to 30dB, the lobe width is less than or equal to 1 degree horizontally and less than or equal to 5 degrees vertically, and the horizontal and vertical side lobe levels are less than or equal to-20 dB; the VSWR required by the standing wave is less than or equal to 1.6, the polarization mode is vertical polarization, and the isolation of the transmitting and receiving antenna is more than or equal to 80 dB; the beam pointing deviation satisfies the electric axis pointing deviation less than or equal to 0.2 degree in the frequency band.

As a further improvement of the scheme, the three-stage mixer comprises a first-stage mixer, a second-stage mixer and a third-stage mixer;

the radio frequency excitation signal enters a first-stage mixer through an amplitude limiter, a low noise amplifier and a filter to be mixed to obtain a first intermediate frequency signal with the bandwidth of 7.75GHz and the bandwidth of 300 MHz;

the first intermediate frequency signal enters a second-stage mixer through a filter and an amplifier to obtain a second intermediate frequency signal with the bandwidth of 750MHz and 500 KHz;

the second intermediate frequency signal enters a third-stage mixer after passing through a filter, an amplifier and a numerical control attenuator to obtain a third intermediate frequency signal with the bandwidth of 70MHz and 5 MHz;

the third intermediate frequency signal is output through a filter amplifier, a numerical control attenuator and a low-pass filter.

As a further improvement of the scheme, the anti-aliasing filter is mainly used for preventing a noise aliasing phenomenon during ADC band-pass sampling, and the parameters are: center frequency F0 = 70 MHz; BW-1dB = 3-5 MHz; BW-40dB <40 MHz; BW-80dB <70 MHz.

As a further improvement of the scheme, the FPGA enters the ADC sampling data into a three-stage decimation filter after digital down conversion, performs 2-time decimation, 5-time decimation and 5-time decimation in sequence, which is equivalent to a sampling rate of 2MHz, and then packages the data into a fixed format after passing through a high-pass filter, and sends the data to the ethernet transmission module.

As a further improvement of the scheme, the clock reference circuit generates a 100MHz signal by a constant temperature crystal oscillator, outputs one path of the 100MHz signal to a 12G source as a comb spectrum excitation source through an ADP-2-1W power divider, and supplies the other path of the 100MHz signal to a 3.5GHz and CRO phase-locked source through an SCA-4-10 four-path power divider respectively; the LTC6946-2 outputs and receives three local oscillator signals 820 MHz; an emission excitation signal of 750MHz is output through LTC 6946-1; the 13dBm signal is output by the amplifier and is used as a collecting clock by the signal processor.

As a further improvement of this solution, the waveform generation circuit operates as follows:

a CRO phase-locked loop circuit generates a 3.5GHz signal, a comb spectrum generates a 12G signal, a first local oscillation signal is generated after filtering and amplifying and frequency mixing, and the first local oscillation signal is used as a local oscillation for a transmitting channel and a receiving module after filtering, amplifying and power dividing;

the frequency sweeping local oscillator is divided into two paths by 3.5G, and one path is amplified, frequency multiplied and filtered to generate 7GHz as a local oscillator signal; one path of signals is used as a clock for AD9914 to generate 600-900 MHz signals, and the two signals are subjected to frequency mixing by an HMC558 frequency mixer, then are filtered, amplified and power-divided for a transmitting channel and are output to a receiving module to be used as two local oscillators.

As a further improvement of the scheme, the transmitting channel is subjected to frequency mixing with a sweep frequency local oscillation source at 7.6-7.9 GHz by a frequency synthesizer, is subjected to filtering amplification, is subjected to frequency mixing with a local oscillation at 15.5GHz, outputs a signal at 23.85-24.15 GHz, is subjected to filtering frequency mixing, is amplified and is output by an isolator.

As a further improvement of the scheme, various performance indexes of the system are as follows:

1) excitation: 24GHz +/-50 MHz (23.85-24.15 GHz), power: 1-1.3W, phase noise: l (1K) is less than or equal to-103 dBc/Hz, and L (100K) is less than or equal to-113 dBc/Hz;

2) a local oscillator: 15.5GHz, power: 13dBm ± 1dBm, phase noise: l (1K) is less than or equal to-108 dBc/Hz, and L (100K) is less than or equal to-118 dBc/Hz;

3) and II, local oscillation: 7.75GHZ (7.6-7.9), power: 10dBm +/-1 dBm; phase noise: is superior to one local oscillator;

4) three local oscillators: 820MHz, power: 10dBm + -1 dBm, phase noise: the local oscillator is superior to the second local oscillator;

5) clock: 100MHz, power: 13 + -0.5 dBm,

phase noise: l (1K) is less than or equal to-140 dBc/Hz, and L (100K) is less than or equal to-150 dBc/Hz;

6) amplitude consistency in the frequency modulation band width of the sweep frequency signal: less than or equal to 1 dB;

7) outputting clutter: excitation is more than or equal to 60dBc, one local oscillator is more than or equal to 70dBc, two local oscillators are more than or equal to 70dBc, three local oscillators are more than or equal to 70dBc, and clock is more than or equal to 70dBc

8) Harmonic suppression: excitation is more than or equal to 55dBc, a local oscillator is more than or equal to 60dBc, a second local oscillator is more than or equal to 60dBc, a third local oscillator is more than or equal to 60dBc, and a clock is more than or equal to 60dBc

9) Power fluctuation: not more than 0.5dB

10) Power consumption: less than or equal to 30W;

11) the dot frequency and the linear modulation are alternately output for 1 second respectively, the linear frequency modulation time is 1 millisecond, the frequency modulation bandwidth is 300MHz, and the frequency modulation linearity is less than or equal to 2/1000.

As a further improvement of the scheme, the data processing module detects the aquatic plants floating on the water surface by utilizing the difference of the reflecting capacities of the rivers and the aquatic plants. And comprehensively calculating the area of the aquatic plant by measuring the distribution of the aquatic plant flowing through the measuring section and the moving speed under the section.

As a further improvement of the present solution, the data processing module processes the 1 second chirp continuous wave signal as follows:

the area measurement of the water surface floater is realized by linear frequency modulation continuous wave signals, the echo intensity of each distance point of a cross section dimension is measured through broadband signals, the detection is carried out in a frequency domain, and the area of the aquatic plant is determined through the change of the echo intensity of the aquatic plant;

continuously transmitting 1000 linear frequency modulation continuous wave signals of 1 millisecond, and processing data of the 1 millisecond and data of the 1000 millisecond;

s01: under normal conditions, finding a water surface without water-floating plants, and measuring the reflection intensity of water of each resolution unit in the azimuth beam width as a detection reference threshold value;

s02: detecting the echo signal of 1 millisecond, adjusting the echo signal according to the actual condition by taking the value obtained in S01 as a reference threshold, and judging whether the water-floating plants exist in each distinguishing unit;

s03: and storing the intensity value of each distance point, and marking the distance points with the floating plants.

As a further improvement of the scheme, the data processing module processes the 1 second dot frequency continuous wave signal as follows:

s11: calculating power spectral density of the acquired data;

s12: the data of 1kHz is respectively taken at about 500KHz of intermediate frequency for threshold detection, when the data exceeds the threshold, a target is considered to exist, under the normal condition, the water speed is generally less than 0.1m/s,

therefore, the maximum doppler frequency is about 16Hz, and 1KHz is used for each of both sides of the margin in consideration of an abnormality such as wind, and the threshold value is finely adjusted with reference to the detection reference threshold value obtained in S01.

S13: and calculating the target speed according to the detection frequency.

As a further improvement of the solution, the data processing module calculates the target area as follows: the river width is calculated according to 50 meters and divided according to 0.6 meter of a distance resolution unit, the azimuth wave velocity width is 1 degree, and the farthest distance in the azimuth wave beam is about 0.8 meter; the calculation formula is as follows

R = river width;

θ = azimuth beam width;

then at different distances, the azimuth beam covers an azimuth width =2Rtan (θ/2);

s21: the target area is smaller

When the area of the target is less than or equal to the area of one distance resolution unit (<=0.6 × 0.6), the echo intensity measured at this time is a bell curve with a steep change, and the time dimension of the same direction of the water flow measured at this time is the target length

Comprises the following steps:

wherein: 2 represents a measurement time interval of 2 seconds,

representing the water flow velocity found at each measurement interval = water floating plant measurement velocity/sin θ,

representing the number of time intervals in which the target appears continuously,

is a fixed value and refers to the transverse distance in the azimuth beam width corresponding to the unit points with different section dimensions;

the length of the target section dimension can be obtained according to the distance unit of the target

= measuring cross-sectional dimension length, = cos θ;

the area is as follows:

s22: the target area is larger

The target with continuous time and distance units is used as a large target, the change of the measured echo intensity is similar to a band-pass filter, the change of two sides is steeper, the middle is gentler, and the length of the target in the same direction with the water flow is measured by the time dimension

Comprises the following steps:

wherein: 2 represents a measurement time interval of 2 seconds,

representing the water flow rate found for each measurement interval.

The length of the target distance dimension can be obtained according to the distance unit of the target

= measuring cross sectional dimension length cos θ, if the measured target cross sectional dimension is discontinuous from unit

N is the number of distance units with water-floating plants on the cross section dimension;

the area of the water-floating plant measured at each time interval is then:

the target area is then:

the maximum value of the transverse distance in the azimuth beam width corresponding to the unit point with different distances of the target section dimension is indicated,

the last detection speed of the current target is indicated,

refers to the number of time intervals for which the area is repeatedly calculated,

means that the area is repeatedly calculated by the water plants within the beam width, and one total area flowing through the measurement section is given every half hour and the result is saved.

As a further improvement of the present solution, the data processing module further includes a data transmission, processing, storage, and display time calculation module, specifically as follows:

the time for transmitting the A/D data into the data buffer area through the network cable, the input signal is 16-bit floating point number, and 2M sampling points are totally arranged in1 second, so that the data volume required to be transmitted is 32 Mbit;

the data transmission is supposed to adopt a gigabit network, the transmission rate of the gigabit network is 10000Mb/s, the network transmission efficiency is set to be 50%, and the time for transmitting 32Mb of data is 6.4 milliseconds;

writing data into a hard disk, wherein the storage rate of the computer hard disk is 20MB/s, the time for storing 2M point 16bit data is 200 milliseconds, the data is read from the hard disk to an internal memory, the reading rate of the computer hard disk is 30MB/s, the time for reading 2M point 16bit data is 140 milliseconds, the transmission rate of a PCI-E bus from the internal memory to a CPU is 8Gb/s, and the time for reading 32Mb data from the internal memory to the CPU is 4 milliseconds;

the FFT processing and threshold detection of the data by the CPU need 600 milliseconds, 1 second data is adopted for display at the same time, and the required time is 50 milliseconds, so that the 1 second chirp signal processing time is about 1 second.

Then 1 second dot frequency signal, only one small section of data is taken for processing, the speed is calculated, and the time is about 200 milliseconds;

therefore, the 1 second chirp +1 second dot frequency continuous wave processing time is about 1200 milliseconds, so the 2s repetition time interval can complete the processing without losing data.

The invention has the beneficial effects that: the water-floating plant detection radar realizes real-time online monitoring of the areas of floating plants and sundries on the water surface in a river with the width of 100 m. The minimum detectable speed of the floater on the water surface is as low as 0.1m/s, and the distance resolution is less than 1 m; the radar has the following characteristics:

1) real-time measurement of the floating objects on the water surface is realized;

2) the measurement precision is high;

3) the system is unattended and has high reliability;

4) the maximum detection distance is larger than 200 m;

5) the power consumption is low;

6) the method can be suitable for measuring the flow velocity of low-flow river.

Drawings

FIG. 1 is a detection schematic;

FIG. 2 is a schematic view of the cross-sectional dimension measurement principle;

FIG. 3 is a diagram of a theoretical calculated horizontal lobe for a transmit receive antenna;

FIG. 4 is a diagram of a theoretical calculated vertical lobe for a transmit receive antenna;

FIG. 5 is a theoretical three-dimensional lobe pattern for a transmit-receive antenna;

FIG. 6 is a transmit receive antenna simulation model;

figure 7 is a three-dimensional simulated lobe diagram of a transmit-receive antenna;

FIG. 8 is a simulated horizontal lobe pattern of a transmit receive antenna;

figure 9 is a simulated vertical lobe pattern of the transmit and receive antennas;

FIG. 10 is a beam direction diagram of three frequency points of f0-150MHz, f0 and f0+150 MHz;

FIG. 11 is a diagram of actual beam shapes;

FIG. 12 is a clock reference circuit;

FIG. 13 is a waveform generation circuit;

FIG. 14 is a transmit channel circuit;

FIG. 15 is a graph of 3500MHz CRO oscillator phase noise;

FIG. 16 is a receive channel circuit;

FIG. 17 is a graph of an echo input standing wave;

FIG. 18 is a graph of image rejection curves;

FIG. 19 is a block diagram of a data acquisition module;

FIG. 20 is a schematic diagram of noise aliasing;

FIG. 21 is a block diagram of a data acquisition module;

FIG. 22 is a schematic diagram of the calculated area of a water-floating plant.

Detailed Description

The technical solution of the present invention is further described in detail with reference to the following specific examples, but the scope of the present invention is not limited to the following.

The aquatic plant detection radar adopts an azimuth narrow beam to realize a minimum resolution unit for measuring a cross section; the elevation angle adopts a wide wave beam, the energy covers the whole measuring section, and the echo intensity of each distance point of the section dimension is measured through a broadband signal. And determining the area of the aquatic plant by the change of the echo intensity of the aquatic plant.

The radar generates a point frequency continuous wave signal and a linear frequency modulation continuous wave signal, wherein the point frequency signal is only used for measuring the speed of the water surface floater, and the linear frequency modulation continuous wave signal realizes the area measurement of the water surface floater. The signal is radiated by a transmitting antenna after being amplified by power, enters a receiving antenna after being reflected by aquatic plants, is converted into a digital signal after being down-converted and demodulated by a receiver, and is processed and calculated by a signal processor to obtain the echo intensities at different distances, the moving speed and the distribution of the section distance, the flow direction distance and the intensity.

The detection principle is shown in fig. 1.

The radar erection direction and the cross section of the river form an included angle theta,

target cross-sectional length = measured cross-sectional length × cos θ;

target flow direction length = measured cross-sectional target length/sin θ.

Flow direction dimension measuring principle

The target length in the same direction as the river flow = the water flow direction resolution unit × the number of the discrimination units in the detection duration = the measurement time interval × the measurement speed of the water-floating plant × the number of the discrimination units in the duration/sin θ.

(1) The measurement time interval is determined by a detection radar and can be accurately obtained;

(2) the Doppler frequency fd of the target can be measured in a dot-frequency continuous wave signal mode, and the measuring speed = fd multiplied by lambda/2 of the water-floating plant can be calculated according to the working wavelength lambda;

(3) the number of the distinguishing units is distinguished in the duration time, the reflection echo under the pure water surface condition is used as a background, each distinguishing unit establishes a threshold in the distinguishing unit according to the detection background, and establishes a threshold database according to the height characteristics of the water surface, and the existence of the floating plants in the distinguishing unit is judged according to the threshold.

Principle of measuring cross-section dimension

The radar transmits a chirp signal modulated from f0-150MHz to f0+150MHz, and if 1 fixed target appears at R, the echo delay of the target at R is 2R/C. The echo signals are deskewed to form a fixed frequency difference. The relationship is shown in FIG. 2:

when targets are present at different distances, different frequency differences will be formed. Through counting different frequency point echo intensities and comparing the different frequency point echo intensities with the echo intensity of the hydrostatic surface, whether the distance point is an aquatic plant or not is confirmed. And finally, determining the area of the aquatic plant according to the number of the echo points of the aquatic plant flowing through the measuring section.

(1) Scanning forms

The antenna is fixed in azimuth, and the elevation angle can be adjusted downwards, so that the main beam can point to different distances, and the test requirements are met.

(2) Form of measurement of parameters

Frequency domain detection, dot frequency speed measurement and frequency modulation distance measurement.

(3) Antenna feeder form

The upper and lower antennas are divided into two blocks. The concentrated feeding reduces the loss.

(4) Form of emission

Low power, solid state emission and integrated design.

(5) Form of reception

In order to reduce the loss, the integrated design is adopted in the form of firstly amplifying, then frequency converting and then A/D. Reducing the amount of transmitted data

(6) Form of transmission

And the network port is used for transmission, and the low-data-rate AD data is automatically stored.

(7) Terminal form

The notebook bears the weight of, and the C + + language realizes, and the picture is adjustable.

(8) Structural form

Small and exquisite, quick detachable, easy transport, have the every single move instruction, heat dispersion is good.

Antenna system scheme

The continuous wave radar antenna can be in a paraboloid form or a planar array form, and if the transmitting subsystem adopts a T/R component scheme, the antenna is preferably in a planar array form. In addition, if the radar needs to realize multi-polarization, the antenna can realize multi-polarization function by adopting a paraboloid, and the multi-polarization function is difficult to realize by adopting a planar array and has a complex structure.

The parabolic antenna has the advantages of simple feed, no grating lobe, wider frequency band, lower cost and low energy consumption. The focus and difficulty of the parabolic antenna is a reflecting surface and a feed source, while the focus and difficulty of the array antenna is the realization of a feed network and variable polarization, and for a high-gain radar antenna, the array number is more and the requirement is more complex.

In the aspect of antenna isolation, the isolation of the area array antenna is slightly better than that of a parabolic antenna because the area array antenna is multi-unit distributed radiation and has weak edge power; the parabolic antenna is a feed source for concentrated transmission and reception, and the amplitude of a lobe formed by the feed source at a close distance is not very weak at the edge.

After demonstration and analysis, the antenna system adopts a planar array antenna mode of separately transmitting and receiving. The antenna system consists of a transmitting antenna and a receiving antenna. The transmitting antenna and the receiving antenna are arranged up and down, and the transmitting antenna radiates signals generated by the transmitter to the space. The receiving antenna sends the received target echo signal to the receiver.

Main technical indexes of antenna

(1) Working frequency, K wave band, f0 +/-150 MHz; f0 is 24 GHz;

(2) the antenna form is a waveguide planar array antenna (adopting a subarray block design);

(3) an output channel and a signal channel and a coupling signal channel;

(4) the aperture of the antenna is 0.76m multiplied by 0.16m (subject to meeting the index requirement);

(5) the antenna system adopts a transmitting and receiving separate system;

(6) the antenna gain is more than or equal to 30 dB; .

(7) The width of the lobe is less than or equal to 1 degree horizontally and less than or equal to 5 degrees vertically;

(8) the level of the horizontal side lobe and the vertical side lobe is less than or equal to-20 dB;

(9) standing wave requirement VSWR: less than or equal to 1.6;

(10) the polarization mode is vertical polarization;

(11) antenna interface and signal path: a standard BJ260 waveguide interface; coupling channels: an SMA-K interface;

(12) the isolation of the transmitting and receiving antenna is more than or equal to 80 dB;

(13) the beam pointing deviation satisfies the electric axis pointing deviation less than or equal to 0.2 degrees in the frequency band;

(14) the power capacity is 2W.

(15) Environmental suitability

The temperature of the working environment: minus 10 ℃ to plus 50 ℃.

Humidity of working environment: relative humidity: 95% (at 40 ℃).

(16) Reliability of

Passive devices, life-long devices.

Three prevention: water resistance, mildew resistance and salt mist resistance, and no obvious mildew and corrosion;

selecting materials with aging resistance, fatigue resistance and corrosion resistance, and carrying out corresponding anti-aging treatment on a medium part;

(17) structural design

The equipment carries out universalization, serialization and modularization ideas in the design;

the requirements of project requirements such as corrosion resistance, salt spray resistance, electromagnetic environment and the like are met;

the fastener is made of stainless steel materials, so that the fastener is prevented from being corroded;

the structural design of the antenna array takes measures such as sealing, waterproofing and the like into consideration;

the structural reliability is designed, standard series components are adopted as much as possible, and parts, parts and whole parts of the same variety have good interchangeability;

on the basis of fully guaranteeing structural strength and security, reliability, reduce the whole weight of structure through adopting novel material technology.

Antenna assembly

In order to meet the overall detection requirement of observing aquatic plants, the antenna system adopts a transmitting-receiving separately-arranged antenna system, and the antenna forms the directional diagram characteristics of a horizontal narrow lobe and a vertical wide lobe.

The antenna system mainly comprises a transmitting antenna, a receiving antenna, an antenna mounting frame and the like, wherein the transmitting antenna is mounted at the upper end of an antenna pedestal, the antenna aperture is 0.76m wide multiplied by 0.16m high and used for transmitting and receiving signals, the receiving antenna is mounted at the lower end of the antenna pedestal, and the antenna aperture is 0.76m wide multiplied by 0.16m high and used for receiving target echo signals and sending the signals to a receiver.

The antenna system adopts waveguide planar array antennas, and each antenna is composed of an antenna housing, a radiation area array, a coupling waveguide, a feed network, an antenna supporting frame and the like. The radiation area array is formed by combining a plurality of slotted waveguides, a plurality of coupling waveguides which are vertically crossed are arranged on the back surface of each radiation waveguide, and each coupling waveguide is fed through an H-T joint or a feed network. Thus, energy is input into the coupling waveguide through the feed device, coupled into the radiation waveguide through the coupling gap, and finally radiated out through the radiation gap.

Based on the requirement for target detection, the antenna system adopts a continuous wave working system with separate receiving and transmitting. Because the aquatic plants float on the river surface, the aquatic plants continuously flow through the observed area along with the flow of the water flow. In order to ensure the detection accuracy, the radar needs to continuously observe the target, so the antenna also needs to be a continuous wave working system. In order to meet the continuous wave operation requirement, the transmitting antenna and the receiving antenna are separately separated, and operate simultaneously.

In order to enhance the adaptability of the product to the climate environment, the design of environmental protection is emphasized, and the design mainly comprises the following steps: rain-proof, moisture-proof, mildew-proof, salt fog-proof, corrosion-proof, etc. The antenna system is provided with the antenna housing, and the antenna housing is subjected to electrical property design and structural design, so that water or other sundries entering the waveguide array surface are effectively prevented. In addition, in order to avoid rainwater from directly or indirectly splashing to the outer surface of important equipment in design, the direction of the cable is scientifically designed and arranged, and rainwater is prevented from entering the equipment along the cable; when in design, the electronic equipment exposed outdoors fully considers the sealing design, and the damage of the electronic equipment caused by the entering of rainwater is prevented. The antenna structure adopts technologies such as ventilation design and the like, and the antenna area array is ensured to be dry through air flow. The passive feeder equipment connection is designed in a sealing mode, and the protection performance of the assembly is guaranteed to the greatest extent. And a metal material with better corrosion resistance is adopted, so that the contact corrosion of the material is avoided. When metal materials which are not allowed to be contacted are assembled together, corresponding measures are taken for carrying out rust prevention treatment;

the structure for avoiding water accumulation is characterized in that a proper inclined design is made on the outer cover of the equipment, the plane switching part is designed to be smooth downwards, and a drain hole and an exhaust hole are formed at the position where water accumulation and moisture are possible; the design avoids and eliminates a gap structure and an overlap joint structure, and can seal and coat places where gap corrosion can form; the outer edges of all the metal pieces are chamfered into round corners; so as to be beneficial to obtaining a paint layer or a metal coating layer with proper and firm adhesion; for parts of which the surfaces need to be painted, selecting paint species which have strong bonding force with metal parts and stable performance, such as acrylic polyurethane paint; selecting a proper electroplating process or a chemical method for the metal part which is not painted to perform anti-rust treatment; the surface coating is required under the working condition of the structural member, and the fastening member is made of weather-resistant steel material. The exposed structural member avoids welding as much as possible, the welding seam is ensured to be continuous, and the steel structural member needs to be treated by aluminum (zinc) spraying for integral heavy corrosion prevention.

Antenna system correlation calculation

(1) Gain estimation

According to an antenna gain calculation formula:

-antenna effective area

-antenna operating wavelength

Antenna weighted aperture efficiency

-antenna efficiency

By substituting the known parameters into the formula, the gain of the antenna 0.76m × 0.16m can be calculated to be 35 dB.

(2) Antenna array element number selection

The aperture of the receiving and transmitting antenna is 0.76m wide multiplied by 0.16m high, the waveguide is a broadside longitudinal slot array antenna, the waveguide is selected from a non-standard waveguide, and the size of the waveguide is 8.4mm multiplied by 4.2mm multiplied by 0.95 mm. In order to meet the requirements of the standing wave array antenna, the distance between the unit slits is half of the waveguide wavelength. I.e. 18.70 mm. Calculating to obtain the number M of the line source direction array units as follows:

M＝(L-0.5*λ_g)/(0.5*λ_g)＝(760-9.35)/9.35＝80.28

the number of units M is 80 according to the calculation.

Since the waveguide broadside dimension is 8.4mm and the waveguide common wall thickness is 0.95mm during the whole machining, the number of line source rows is 14 by calculation. I.e. the whole array plane antenna unit is 14 x 80.

(3) Antenna theoretical pattern calculation

To obtain the required antenna side lobe level, the amplitude of the excitation current of each antenna element in the array is weighted according to a certain illumination function (such as Chebyshev distribution, Taylor distribution, Hamming distribution, etc.), which is called amplitude weighting method.

Generally, lobes of a Chebyshev distributed antenna array have equal side lobes, and in the aperture distribution corresponding to the lobes, larger current is often formed on units at two ends, which is not easy to achieve in engineering practice. Taylor improves on this by modifying the side lobe structure. Alternatively, the side lobes of the evenly distributed lobe, which are closer to the main lobe, are shifted so that they have approximately equal levels, while the more distant side lobes cause them to change in the shape of the lobe as they are evenly distributed, thus avoiding the formation of large currents in the cells at both ends. Therefore, taylor distributions are often employed in engineering design.

The aperture of the transmitting and receiving antenna: 0.76M wide x 0.16M high, according to the antenna theory, in order to realize horizontal low side lobe level without reducing too much antenna gain, the distribution of the horizontal amplitude is more suitable by selecting Taylor function, according to the antenna theory, for the planar array antenna directional diagram composed of M x N same antenna units, the directional diagram is:

in the formula:

-edge

Axial radiating element spacing;

-edge

Axial radiating element spacing;

—

；

-edge

The number of the radiation units in the axial direction;

-edge

The number of the radiation units in the axial direction;

-a radiation element pattern;

-aperture amplitude distribution function of unit array antennaCounting;

-element array antenna aperture phase distribution function.

When in use

，

When is at time

，

Respectively, a horizontal directional pattern and a vertical directional pattern of the planar array antenna.

To realize the antenna-20 dB side lobe level, the antenna needs to be theoretically designed according to Taylor distribution of at least-25 dB side lobe level according to engineering design experience, and the antenna needs to be realized in a precise amplitude and phase compensation mode. The theoretical antenna pattern obtained by substituting the parameters such as the number of units, the spacing and the like into the Matlab program is shown in fig. 3 and 4, and the three-dimensional lobe pattern of the theoretical transceiver antenna is shown in fig. 5.

Antenna simulation design

A waveguide planar array antenna with 24GHz working frequency is selected through analysis. Wherein the waveguide dimensions are 8.4mm x 4.2mm x 0.95 mm. Wave guide wavelength lambda_gIs 18.70 mm.

Through theoretical analysis calculation, the overall simulation calculation is mainly performed through commercial software CST. The method mainly comprises the steps of extracting conductance parameters of the radiation waveguide and the coupling waveguide, simulating and calculating a radiation area array, simulating and calculating the coupling waveguide, simulating and calculating a feed network and integrally simulating and calculating.

By means of conductance parameter extraction and combination with actual amplitude distribution, the offset of the radiation slot and the inclination angle of the coupling slot are obtained, a receiving and transmitting antenna simulation model is established as shown in fig. 6, the result of calculating a three-dimensional lobe pattern is shown in fig. 7, a receiving and transmitting antenna simulation horizontal plane lobe pattern is shown in fig. 8, and a receiving and transmitting antenna simulation vertical plane lobe pattern is shown in fig. 9.

According to the simulation result, the technical indexes of each antenna system meet the design requirements.

Antenna performance analysis of broadband signals

The radar adopts a 300MHz linear frequency modulation signal, the center frequency f0 is 24GHz, and the signal has transmission group delay in the waveguide slot antenna. Therefore, the beam pointing direction is deviated, and the beam pointing directions of three frequency points of f0-150MHz, f0 and f0+150MHz are calculated by simulation and are shown in FIG. 10.

Since the 300MHz bandwidth is continuous and occurs in one signal period, but cannot be separated in the time domain for frequency domain detection, the deviation of beam pointing causes the broadening of the lobe to be distorted. Finally, the actual beam shape of the antenna system for 300MHz signals is shown in fig. 11. The beam offset can be reduced by the form of sub-matrix blocking. The final beam broadening is expected to be around 0.4 °.

The radio frequency microwave system consists of a receiving front end, a data acquisition module (hereinafter also referred to as an A/D module) and a frequency synthesis assembly, wherein a direct current stabilized voltage power supply of the whole machine is used for supplying power in a centralized manner, and the receiving system and the transmitting system are arranged in an antenna support arm together and work in an outdoor environment.

The frequency synthesis module provides a local oscillator signal required by the receiving front end, a synchronous clock signal required by the ADC module, and a chirp excitation signal.

The frequency synthesis component comprises a clock reference circuit, a waveform generation circuit (hereinafter also referred to as sweep frequency local oscillator), a transmitting channel, an interface control circuit, a power supply processing circuit and the like, and an internal circuit mainly comprises a high-stability low-phase-noise constant-temperature crystal oscillator, a comb spectrum, a microwave digital phase-locked loop, a mixing filtering amplification channel, a digital control and power supply voltage-stabilizing filter circuit and the like.

The clock reference circuit is shown in fig. 12:

the clock reference circuit generates a 100MHz signal by a constant temperature crystal oscillator, and outputs one path of the signal to a 12G source as a comb spectrum excitation source through an ADP-2-1W power divider; one path is respectively supplied to a 3.5GHz and CRO phase-locked source through an SCA-4-10 four-path power divider; the LTC6946-2 outputs and receives three local oscillator signals 820 MHz; an emission excitation signal of 750MHz is output through LTC 6946-1; outputting a 13dBm signal through the amplifier to be used as an acquisition clock by a signal processor;

the waveform generation circuit is shown in fig. 13:

a local oscillation signal is generated by a CRO phase-locked loop circuit, a 3.5GHz signal and a comb spectrum generated 12G signal are filtered, amplified, mixed, generated, filtered, amplified and power-divided, and then supplied to a local oscillation of a transmitting channel and a receiving module.

The frequency sweeping local oscillator is divided into two paths by 3.5G, and one path is amplified, frequency multiplied and filtered to generate 7GHz as a local oscillator signal; one path of signals is used as a clock for AD9914 to generate 600-900 MHz signals, and the two signals are subjected to filtering, amplification and power division after being mixed by an HMC558 frequency mixer and then are output to a receiving module to be used as two local oscillators;

the emission channel is shown in fig. 14:

the transmitting channel is used for generating 750MHz frequency by a frequency synthesizer and mixing with a sweep frequency local oscillation source (7.6-7.9 GHz), and after filtering and amplification, the transmitting channel is mixed with a local oscillation (15.5 GHz) and outputs a 23.85-24.15 GHz signal, and then the transmitting channel is filtered, mixed, amplified and output by an isolator.

The performance indexes are as follows:

5) clock: 100MHz, power: 13 ± 0.5dBm, phase noise: l (1K) is less than or equal to-140 dBc/Hz, and L (100K) is less than or equal to-150 dBc/Hz;

7) outputting clutter: excitation is more than or equal to 60dBc, a local oscillator is more than or equal to 70dBc, a secondary local oscillator is more than or equal to 70dBc, a tertiary local oscillator is more than or equal to 70dBc, and a clock is more than or equal to 70 dBc;

8) harmonic suppression: excitation is more than or equal to 55dBc, a local oscillator is more than or equal to 60dBc, a secondary local oscillator is more than or equal to 60dBc, a tertiary local oscillator is more than or equal to 60dBc, and a clock is more than or equal to 60 dBc;

9) power fluctuation: not more than 0.5dB

10) Power consumption: less than or equal to 30W;

The performance index analysis is calculated as follows:

(1) one local oscillator main index analysis

Factors influencing the phase noise index mainly include the phase noise of a reference source, the low noise of a phase detection chip and the phase noise of a VCO. The phase noise within 10KHz of the final output signal mainly depends on the phase noise of the reference source and the phase detection chip background noise, and the phase noise outside 100KHz mainly depends on the phase noise of the VCO.

1) Key device indicators affecting phase noise:

a. a voltage-controlled oscillator: less than or equal to-130 dBc/Hz @100KHz

b. Constant temperature crystal oscillator: less than or equal to-155 dBc/Hz @1KHz

c, phase discriminator: -153 dBc/Hz @10 kHz offset @100 MHz

2) Analyzing the phase noise of a local oscillator:

a. the calculation formula of the phase noise in the loop bandwidth is as follows: floor +20Log (f0/fpD) +10LogfPD

Wherein Lfloor is the normalized low noise of the PLL chip, f0/fpD is the division of the output frequency by the phase detection frequency, i.e., the frequency multiplication times N, and fpD is the phase detection frequency.

Substituting the above parameters into the formula can calculate:

the phase noise in the loop band is-226 +20Log (3500/100) +10Log (100X 106) ≈ 125 dBc/H.

In addition, the phase noise in the loop band is-123 dBc/Hz due to the deterioration of the actual engineering and the deterioration of other parameters by 2 dB.

b. Calculation of the deterioration of the phase noise of the reference source (3.5 GHz): 20Log (f0/fpD) = 20Log (3500/100) =31dBc/Hz

The degraded phase noise is calculated as-155 dBc/Hz @1KHz with reference phase noise:

-155+31= -124dBc/Hz@1KHz；

because the phase noise after the reference deterioration is higher than the phase noise in the loop band, the phase noise finally output depends on the phase noise in the loop band, namely-123 dBc/Hz @1 KHz; since the 3.5GHz signal is also mixed with the 12GHz signal, the resulting output phase noise depends on the poor one of the signal sources, the 12GHz signal being in frequency doubled form, plus the comb spectrum being degraded:

155+20Log (12000/100) +4 =109 dBc/Hz @1KHz, so the phase noise of the final output local oscillator is: -109dBc/Hz @1 KHz.

c. Loop out-of-band phase noise analysis

The phase noise outside the loop bandwidth mainly depends on the phase noise of the VCO, and the specific index can be estimated according to the phase noise of the 100 KHz-1 MHz phase in the VCO technical index. The estimation of the out-of-loop phase noise of the local oscillator is as follows: 130dBc/Hz @100 KHz.

2) Stray suppression degree analysis of a local oscillator:

the spurious main phase discrimination spurious and mixing spurious 2 kinds of local oscillator, because the phase discrimination frequency of 3.5GHz phase-locked loop is 100MHz, so phase discrimination spurious can distribute respectively in deviating output frequency 100MHz department, and specific calculation is as follows:

for a charge pump type phase-locked loop, the phase discrimination stray mainly comprises two aspects, namely leakage stray and pulse stray, and the stray formula is as follows:

Spur＝10log(10^{LeakageSpur/10}+10^PulseSpur/10)

let the phase detection leakage current be 1nA, and calculate its two spurs below respectively.

The phase-discriminated leakage current is 1nA,

is not determined

But around this value. Because the phase detection frequency is 100MHz and the frequency is higher, the phase detection stray is mainly determined by the pulse stray, and the loop bandwidth is generally less than 500kHz, the stray can be well inhibited in the low-pass property of the loop filter. According to past experience, the scheme selects the loop bandwidth of about 500kHz, and the spurious suppression can be below-85 dBc. Spurs generated by the mixing are shown in the filter spur profile, and the mixing filter output spurs are greater than 75dBc.

(2) Analysis of other indicators

The stray and phase noise indexes of the two local oscillators, the three local oscillators and the transmission excitation signal are all superior to the index of the one local oscillator, and the technical difficulty is avoided. The indexes obtained according to the experimental verification conditions are as follows:

750M phase noise index:

124 dBc/Hz@1KHz，

122 dBc/Hz@100KHz，

820M phase noise index:

123 dBc/Hz@1KHz，

121 dBc/Hz@100KHz，

7G phase noise index (3.5 GHz frequency doubling):

-155+31=6= -116dBc/Hz@1KHz；

-120dBc/Hz@100KHz；

stray index: and more than or equal to 75dBc.

The output power is determined by the output amplifiers of the local oscillators, and the technical indexes of the amplifiers show that large margins are reserved, so that the method is not difficult to realize.

DDS bit noise index and spurs:

noise figure-128 dBc/Hz @1KHz,

-133dBc/Hz@100KHz。

DDS spur broadband spur: 55dBc

The 20KHz step data measured in the 500KHz narrow band was 75dBc.

The main specifications of the 3500MHz CRO oscillator are shown in fig. 15.

The receiving channel circuit is shown in fig. 16:

the method comprises the steps that a receiving channel signal is input into 23.85 GHz-24.15 GHz, a 7.75GHz bandwidth 300MHz intermediate frequency is obtained through amplitude limiter, low noise amplifier, filter and first frequency mixing, the signal is amplified through the filter and enters a second-stage frequency mixer to obtain a second intermediate frequency 750MHz (signal bandwidth 500 KHz), the signal is amplified through the filter and enters a third-stage frequency mixer to output a second intermediate frequency 70MHz, and the signal is amplified through the filter and the numerical control attenuator and is output through a low-pass filter.

The main technical indexes are as follows:

(1) echo frequency: 24GHz +/-150 MHz;

(2) a local oscillation frequency: 15.5 GHz;

(3) second local oscillator frequency: (7.75 MHz. + -. 150 MHz);

(4) three local oscillator frequencies: 820 MHz;

(5) noise coefficient: not more than 4.5dB (low and normal temperature) and not more than 5dB (normal temperature);

(6) the cavity is provided with a 5-bit switch for adjusting the gain of a receiving channel, the step is 1dB, and the attenuation accumulated error is less than or equal to 1 dB;

(7) channel gain: 50 +/-1 dB, when the attenuation is 0;

(8) pin1dB is not less than-20 dBm (when attenuation is 20 dB);

(9) pout1dB ≧ 10dBm (attenuation 0 dB);

(10) bandwidth of the radio frequency filter: BW-1dB is more than or equal to 300MHz (f0 = 24 GHz);

BW-3dB≤500MHz ；

out-of-band suppression: not less than 60dB (f0 +/-2G);

(11) echo channel image frequency suppression system: not less than 70dB (corresponding to the first intermediate frequency and the local oscillator);

(12) receive channel to frequency synthesis component isolation: not less than 80 dB;

(13) intermediate frequency: 70 MHz;

(14) bandwidth of the intermediate frequency band-pass filter: BW-1dB is more than or equal to 5 MHz;

BW-40dB≤40MHz ；

(15) limiter maximum tolerated power (CW): not less than 1.5W;

(16) standing-wave ratio of echo input port: less than or equal to 1.5;

(17) power consumption: less than or equal to 10W.

Technical index analysis and calculation

(1) Receiver bandwidth calculation

According to the principle of a linear frequency modulation radar, the distance of an acting target is obtained by measuring a frequency spectrum deviating from an intermediate frequency, and the calculation formula is as follows:

in the formula f_bThe difference frequency of the bit distance intermediate frequency signal; Δ f is the linear bandwidth of the frequency modulation; r is a target distance; tm is modulation time; and C is the speed of light.

According to the general requirements of radar, the linear frequency modulation bandwidth is 300MHz, the maximum target distance is 200m, the modulation time is 1 millisecond, and the maximum offset frequency fb is calculated to be 400 kHz. According to actual requirements, enough bandwidth is reserved, and the bandwidth of a receiver is designed to be 500 kHz.

(2) Noise coefficient, gain, output P-1dB power

NF=NF1+((NF2-1)/GP1)+((NF3-1)/(GP1*GP2))+((NF4-1)/(GP1*GP2*GP3)；

Receiving a channel: the first stage is waveguide conversion, and the insertion loss is 0.4 dB; the second stage is 0.75dB of limiter, the third stage is 1.8dB of low noise block amplifier, the fourth stage is 1.5dB of insertion loss of echo filter, the later stage is 8dB of mixer, etc.

Noise figure, gain, output P-1dB power calculation

Noise coefficient: 3.73 dB;

gain: 51.3 dB;

output P-1dB compression point: +11.88dBm

(3) Amplitude limiter

The maximum input power of the low noise amplifier is 18dBm, and the limiter index parameters are shown in table 3:

TABLE 3

(4) Echo input standing wave

The received input standing wave is determined by a limiter and a low noise amplifier, and the echo standing wave is less than 1.5, and the curve is shown in figure 17.

(5) The image suppression degree is as shown in fig. 18:

receiving image frequency suppression degree: the low-pass filter is added in the intermediate frequency, the local oscillator and the radio frequency signal are restrained, the band-pass filter is added in the two intermediate frequency local oscillators, the frequency of the local oscillator is 15.5GHz, the down-conversion is carried out, therefore, the image frequency is 7.15 GHz-7.45 GHz, and the restraint is more than 90dBc when viewed from the restraint of the filter.

A/D module

The A/D module, namely the data acquisition module, mainly realizes the digitization of intermediate frequency signals, because the intermediate frequency of output signals of the receiver is 70MHz, and the actual useful bandwidth is only 500kHz, and in order to reduce the data volume processed by the back-end output. Therefore, it is considered to adopt undersampling and extract to a low data rate.

As shown in fig. 19, the data acquisition module mainly includes four parts, namely an anti-aliasing filter, an ADC, an FPGA and an ethernet transmission module. The interfaces are a clock input XS1, a mid-frequency input XS2, a power input interface XS3, a communications interface XS4, and a synchronization interface XS 5.

The ADC requires 12.5 bits of valid bits, and selects LTC2207 of Linear company, and the main performance parameters of the ADC are as follows:

(1) input voltage range (Vpp): 2.25V (11 dBm);

(2) maximum sampling frequency: 105 milliseconds PS;

(3) spurious Free Dynamic Range (SFDR): 82 dB;

(4) noise Floor (Noise Floor): 77.3 dBFS;

(5) valid bit: 12.9 bits.

Anti-aliasing filtering design

The anti-aliasing filter is mainly used for preventing the noise aliasing phenomenon during ADC band-pass sampling. The anti-aliasing bandpass filter parameters are as follows: center frequency F0 = 70 MHz; BW-1dB = 3-5 MHz; BW-40dB <40 MHz; BW-80dB <70MHz

Aliasing of out-of-band noise is illustrated in fig. 20, where the aliasing is to an in-band noise level of less than-77 dB, below the 12.5 bit significance of the ADC.

FPGA implementation

The FPGA adopts XC7K325T-1FFG900I of K7 series of XILINX company, and the signal processing flow is shown in FIG. 21.

ADC sampling data enters an extraction filter after digital down-conversion, a three-level extraction filter (2-time extraction, 5-time extraction and 5-time extraction) is shared, the sampling rate is equivalent to 2MHz, and then the data is packaged into a fixed format after passing through a high-pass filter and is sent to a transmission module.

The Ethernet transmission module transmits the data to the computer through the network port. The computer decodes the data through unpacking software, writes the data into the hard disk according to the data length of 1 second, and marks time and signal format information. Meanwhile, the data can also be put into a designated memory for back-end data processing.

Data processing and terminal display system

The data processing and terminal display system is composed of data processing software and terminal display software. And completing the on-line real-time measurement and display of all information of the floating plants. The terminal system processes, transforms and calculates the data detected by radar to generate needed data and image product, the hardware of the system is selected mainly considering the universality and reliability of hardware platform, and PC is used. The data of the radar echo is transmitted to the PC through the Ethernet.

The software operating platform is selected in consideration of versatility, compatibility, and maintainability. It includes two major aspects of the operating system of the computer and the programming language of the application programs. The selection of the software working platform directly influences the efficiency and the portability of software development and the good running of the whole system. Based on the consideration, Windows is selected as an operating system, and Visual C + + is used as a programming language.

General structure of data processing software system

All software of the system is established under Windows XP/7, developed by adopting Visual C + +, and has a uniform operation interface. All settings are designed in a menu-driven manner, and are performed by a system setup program that provides the user with interactive selection or entry of parameters, while also allowing the user to save the results to disk so that the various radar parameters set can be recalled and modified by the system.

And the real-time parameter setting and the timing parameter setting generate a real-time parameter table and a timing parameter table, and the two tables are called by a radar real-time processing program. The radar real-time processing control radar working state, data acquisition and aquatic plant distribution live display system comprises foreground real-time processing software and background real-time processing software. And the radar real-time processing program stores the acquired original polar coordinate radar data on a magnetic disk.

The product parameter table is generated by the product parameter setting program setting.

The product generation table is generated by the product generation setup program setting.

The raw data is the starting point for the radar output product generation process. All radar output products are generated by corresponding product generation processing programs, calling the original data and under the combined action of a product parameter table and a product generation table.

In the fully automatic product generation mode, the user sets the required product list every time the system processes the product, and the system calls this list by batch job processing mode to generate and archive the corresponding image product file and data product file, so that the system can be distributed to the corresponding user under the control of the product distribution list or called by other users through network or other communication devices.

A unified user interface is employed. The basic picture size is 640X480 (unit is pixel), and if the picture size is changed, the length and the width are adjusted according to the same proportion. The 16 colors are used as the layering of the product, thereby providing convenience for the radar jigsaw puzzle and the radar networking. The product information area in the figure includes: color look-up table, time, date, display distance, antenna azimuth, antenna elevation, display altitude, repetition frequency, radar station name, etc. The additional information display area is mainly used for displaying information which is specially required by a user, such as the intensity and position information of the strong echo, files used for displaying the secondary product, and also can be used for displaying graphs, and the real-time observed speed echo can be synchronously displayed during real-time intensity observation.

The graphic display working area is used for displaying a radar real-time scanning echo diagram and a secondary product diagram. The basic size is 480X480 pixels. The abscissa shows the time axis in seconds. The ordinate shows the river width with a resolution of 1 meter. And drawing data every 1 second, displaying real-time river radar echo distribution and intensity, and scrolling and updating the graph along with the lapse of time to display radar echo distribution and intensity for a period of time. And establishing a corresponding relation between the radar data and the distribution of the water plants at the later stage, namely demonstrating the distribution and the strength of the water plants.

The system setting comprises real-time parameter setting, timing parameter setting, product generation setting, product distribution table setting and the like. All these functions are performed by the system setup program. The program makes full use of the interface function of Windows XP/7 and adopts a pull-down menu driving mode to provide users with the functions of selecting, modifying and checking various radar parameters. The parameters set by the user are correspondingly generated into a real-time parameter table, a timing parameter table, a product generation table and a product distribution table by a system setting program. These parameters are called by different applications that control the system to perform different functions or to generate different radar output products. Therefore, the method not only greatly facilitates the user to add different functions, but also improves the scalability of the system. Document management is to manage all data and product data generated by the system, including automatic and man-machine interaction.

The original file is data collected by the radar real-time processing program from signal processing in each operation process, and is different from a radar output product file, and the original files formed by different working modes are different. File management is a program that provides management of files formed by various radar products on a disk.

To increase the speed of transmission of the output product, the system also provides compression and recovery functions for processing files. When the user sets the transmission mode as the compression mode, the file is automatically compressed before the product is transmitted, and then the file is transmitted. And when the received file is a compressed file, automatically restoring the file to the original format.

The system uses a watchdog software, and the watchdog software is operated in an automatic or man-machine interaction mode through the parameter setting of a user. When operating in the automatic mode, data and image files set by the user to be outdated are automatically deleted. When the man-machine interaction mode is operated, the watchdog software does not automatically delete the outdated file, but gives an alarm prompt when the disk space is lower than a user set value, so that a user can conveniently save the file by using file management and delete the unnecessary file. The file management program provides settings for watchdog software and data compression, specifically setting, data retention time, compression, and remaining space size, and tells the watchdog the setting of the data retention time, and the files before that time can be deleted in an automatic mode. And when the compression setting is carried out in a man-machine interaction mode in a mode of selectable compression and non-compression, if the space of the residual disk is smaller than the set value of the residual space, the watchdog gives alarm information. The working mode of the watchdog is set to be an automatic mode and a man-machine interaction mode.

Data processing module

And detecting the aquatic plants floating on the water surface by utilizing the difference of the reflecting capacities of the river and the aquatic plants. And comprehensively calculating the area of the aquatic plant by measuring the distribution of the aquatic plant flowing through the measuring section and the moving speed under the section.

(2) 1 second linear frequency modulation continuous wave signal processing method

The area measurement of the water surface floater is realized by the linear frequency modulation continuous wave signal. The echo intensity of each distance point of the cross section dimension is measured through a broadband signal, detection is carried out in a frequency domain, and the area of the aquatic plant is determined through the change of the echo intensity of the aquatic plant.

The 1000 chirp continuous wave signals of 1 millisecond are continuously transmitted, and the data of the 1 millisecond and the data of the 1000 millisecond are processed.

Under normal conditions, finding a water surface without water floating plants, and measuring the reflection intensity of water in each distinguishing unit in the azimuth beam width as a detection reference threshold value.

And secondly, detecting 1 millisecond echo signals, adjusting the values obtained in the step one as reference thresholds according to actual conditions, and judging whether water-floating plants exist in each distinguishing unit.

And thirdly, storing the intensity value of each distance point and marking the distance points with the floating plants.

(3) 1 second dot frequency continuous wave signal processing method

The dot frequency signal is only used for the speed measurement of the water surface floating object.

1) Calculating power spectral density of the acquired data;

2) the data of 1kHz is respectively taken at about 500KHz of intermediate frequency for threshold detection, and when the data exceeds the threshold, a target is considered to exist (under the normal condition, the water speed is generally less than 0.1m/s,

therefore, the maximum doppler frequency is about 16Hz, and 1KHz is used for each side that is left with a margin in consideration of abnormal conditions such as wind). The threshold value is finely adjusted by taking the phi in 1.2 as a reference.

3) And calculating the target speed according to the detection frequency.

(4) Calculating the target area

The river width is calculated according to 50 meters and divided according to a distance resolution unit of 0.6 meter, the azimuth wave speed width is 1 degree, and the farthest distance in the azimuth wave beam is about 0.8 meter.

1) The target area is smaller

When the area of the target is less than or equal to the area of one distance resolution unit (<=0.6 × 0.6), as in target 1 in fig. 22, the measured echo intensity is a bell-shaped curve with a relatively steep change, and the measured time dimension of the same direction of water flow is the target length

Comprises the following steps:

wherein: 2 represents a measurement time interval of 2 seconds,

representing the water velocity (= floating plant measurement velocity/sin θ) found at each measurement interval,

is a fixed value, and refers to the lateral distance in the azimuth beam width corresponding to the unit point with different distance in the cross-sectional dimension, as shown in fig. 22.

(= measure cross-sectional dimension length ×) cos θ.

The area is as follows:

2) the target area is larger

Targets that occur continuously in both time and distance units are taken as one large target, such as target 2, target 3, and target 4 shown in fig. 22. The measured echo intensity changes are similar to a band-pass filter, the two sides change steeply, the middle part is gentle, and the time dimension target length in the same direction as the water flow

Comprises the following steps:

wherein: 2 represents a measurement time interval of 2 seconds,

representing the water flow rate found for each measurement interval.

(= measured cross-sectional dimension length cos θ), if the measured target cross-sectional dimension is not continuous from the cell

N is the distance of the water-floating plant on the cross sectionThe number of units.

The area of the water-floating plant measured at each time interval is then:

the target area is then:

the last detection speed of the current target is indicated,

refers to the repeated calculation of area by water-borne plants within the beam width.

One total area flowing through the measurement cross section is given every half hour and the results are saved.

(5) Data storage

1) Raw data storage

The storage data is 16-bit floating point number, the data rate of 2M per second is 1 second 4MB, 1 hour 14GB, and the uninterrupted storage 24 hours a day requires about 340GB of storage space. 1020GB is required for three consecutive days of data. The hard disk of the prototype test computer was 1.2T, so only data for the last three days could be saved. After hardware is subsequently installed, if more data are required to be stored, wireless data transmission can be considered, and the data are transmitted to a data center to be stored, and the specific implementation method needs to be further considered.

2) Detection result storage

The method comprises the steps of detecting time (year, month, day, hour, minute and second), distance and intensity information, storing a detection result every second, storing a half hour as a time interval (tentative, particularly based on a subsequent test result), storing a file every half hour, and giving an area value of the water-floating plant flowing through a measurement section every half hour.

(6) Data transmission, processing, storage and display time calculation

In order to ensure the real-time performance of data processing, the data transmission processing display storage time is required to be adaptive to the data acquisition time. The whole data transmission flow is shown in fig. 21. The computer performance of the principle prototype data processing is temporarily determined to be equivalent to that of the existing server of the signal processing part, and the processor is Intel E5, 2.4G, 8 cores and a memory 64G.

And D, transmitting the data into the data buffer area through the network cable. The input signal is 16-bit floating point number, 2M sampling points are needed in1 second, and therefore the data volume needing to be transmitted is 32 Mbi.

The data transmission is supposed to adopt a gigabit network, the transmission rate of the gigabit network is 10000Mb/s, the network transmission efficiency is set to be 50% (each layer of network protocol analysis occupies the bandwidth), the time for transmitting 32Mb data is 6.4 milliseconds, the data is written into a hard disk, the storage rate of the hard disk of a computer is 20MB/s, and the time for storing 2M 16-bit data is 200 milliseconds. The data is read from the hard disk to the memory, the reading rate of the computer hard disk is 30MB/s, and 140 milliseconds are needed for reading the 2M point 16bit data. The transmission rate of the PCI-E bus from the memory to the CPU is 8Gb/s, the time from the memory to the CPU of 32Mb data is 4 milliseconds, and 600 milliseconds are needed for the CPU to carry out FFT processing and threshold detection on the data. The display is displayed simultaneously with 1 second of data, and the time required is about 50 milliseconds. Thus a 1 second chirp processing time is about 1 second.

Then 1 second dot frequency signal, we only take one of the small data processing segments to find the speed, which is about 200 ms.

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. The radar detection system for the water-floating plants is composed of an antenna system, a radio frequency microwave system, a data processing and terminal display system, and is characterized in that:

the data processing and terminal display system consists of a data processing module and a terminal display module and is used for completing the online real-time measurement and calculation and display of all information of the water plants;

the antenna system adopts a transmitting-receiving separately-arranged planar array antenna system, and the antenna forms the directional diagram characteristics of a horizontal narrow lobe and a vertical wide lobe;

for a planar array antenna pattern composed of M × N identical antenna elements, the following are:

in the formula: dx-the spacing of the radiating elements along the x-axis;

dy-the spacing of the radiating elements along the y-axis;

K—

；

m is the number of radiation units along the x-axis direction;

n is the number of the radiation units along the y-axis direction;

-a radiation element pattern;

-element array antenna aperture amplitude distribution function;

-element array antenna aperture phase distribution function;

when in use

，

When is at time

，

Respectively a horizontal directional diagram and a vertical directional diagram of the planar array antenna;

the data processing module calculates the target area as follows: the river width is calculated according to 50 meters and divided according to 0.6 meter of a distance resolution unit, the azimuth wave velocity width is 1 degree, and the farthest distance in the azimuth wave beam is about 0.8 meter; the calculation formula is as follows:

r = river width;

θ = azimuth beam width;

s21: the target area is smaller

When the area of the target is smaller than or equal to the area of one distance resolution unit, the measured echo intensity is a bell-shaped curve with a steeper change, and the measured time dimension of the same direction of the water flow is the target length

Comprises the following steps:

Figure 415676DEST_PATH_FDA0001599325570000041

wherein: 2 represents a measurement time interval of 2 seconds,

is a fixed value, referred to as the cross-sectional dimensionThe transverse distances in the azimuth beam width corresponding to the different distance unit points;

= measuring cross-sectional dimension length, = cos θ;

the area is as follows:

s22: the target area is larger

Comprises the following steps:

wherein: 2 represents a measurement time interval of 2 seconds,

representing the water flow rate determined for each measurement interval;

Figure 332817DEST_PATH_FDA0001599325570000042

N is the number of distance units with water floating plants on the cross section dimension;

the area of the water-floating plant measured at each time interval is then:

the target area is then:

Figure 112554DEST_PATH_BDA0001599325580000233

the last detection speed of the current target is indicated,

2. The radar detection system for the water-floating plants according to claim 1, wherein the planar array antenna system is a waveguide planar array antenna, a subarray block design structure is adopted, the operating frequency is K band, f0 +/-150 MHz, and f0 is 24 GHz.

3. The radar detection system for the floating plants according to claim 2, wherein the antenna gain is more than or equal to 30dB, the lobe width is less than or equal to 1 degree horizontally and less than or equal to 5 degrees vertically, and the level of horizontal and vertical side lobes is less than or equal to-20 dB; the VSWR required by the standing wave is less than or equal to 1.6, the polarization mode is vertical polarization, and the isolation of the transmitting and receiving antenna is more than or equal to 80 dB; the beam pointing deviation satisfies the electric axis pointing deviation less than or equal to 0.2 degree in the frequency band.

4. The radar detection system for aquatic plants according to claim 1, wherein said three-stage mixer comprises a first-stage mixer, a second-stage mixer, a third-stage mixer;

5. The radar detection system for the aquatic plants according to claim 4, wherein the anti-aliasing filter is mainly used for preventing the noise aliasing phenomenon during ADC band-pass sampling, and the parameters are as follows: center frequency F0 = 70 MHz; BW-1dB = 3-5 MHz; BW-40dB <40 MHz; BW-80dB <70 MHz.

6. The radar detection system for the aquatic plants according to claim 5, wherein the FPGA performs digital down-conversion on ADC sampling data, then enters a three-level extraction filter, performs 2-time extraction, 5-time extraction and 5-time extraction in sequence, and corresponds to a sampling rate of 2MHz, and then packages the data into a fixed format after passing through a high-pass filter, and sends the data to the Ethernet transmission module.

7. The radar detection system for the water-floating plants according to claim 6, wherein the clock reference circuit generates a 100MHz signal by a constant temperature crystal oscillator, outputs one path of the signal to a 12G source as a comb spectrum excitation source through an ADP-2-1W two power divider, and supplies the other path of the signal to a 3.5GHz and CRO phase-locked source through an SCA-4-10 four power divider; the LTC6946-2 outputs and receives three local oscillator signals 820 MHz; an emission excitation signal of 750MHz is output through LTC 6946-1; the 13dBm signal is output by the amplifier and is used as a collecting clock by the signal processor.

8. The radar detection system for aquatic plants according to claim 7, wherein said waveform generation circuit operates as follows:

9. The radar detection system for the water plants according to claim 8, wherein the transmitting channel is generated by a frequency synthesizer, and is mixed with a swept local oscillator source at 7.6-7.9 GHz, after filtering and amplification, the mixed frequency is mixed with a local oscillator at 15.5GHz, and a signal at 23.85-24.15 GHz is output, and then the mixed frequency is filtered, amplified and output through an isolator.

10. The radar detection system for water-floating plants according to any one of claims 1 to 9, wherein the performance indexes of the system are as follows:

1) excitation: 24GHz + -50 MHz, power: 1-1.3W, phase noise: l (1K) is less than or equal to-103 dBc/Hz, and L (100K) is less than or equal to-113 dBc/Hz;

3) and II, local oscillation: 7.75GHZ, Power: 10dBm +/-1 dBm; phase noise: is superior to one local oscillator;

5) clock: 100MHz, power: 13 + -0.5 dBm,

phase noise: l (1K) is less than or equal to-140 dBc/Hz, and L (100K) is less than or equal to-150 dBc/Hz; wherein 1K represents the deviation signal of 1KHz, namely the measured signal of 100MHz, the intensity of phase noise at the position deviating from the frequency point of 1kHz, and 100K represents the same principle as the signal;

9) Power fluctuation: not more than 0.5dB

10) Power consumption: less than or equal to 30W;

11. The radar detection system for aquatic plants according to claim 10, wherein the data processing module detects aquatic plants floating on the water surface by using the difference between the reflection capacities of rivers and the aquatic plants, and calculates the area of the aquatic plants by measuring the distribution of the aquatic plants flowing through the measuring section and the moving speed under the measuring section.

12. The radar detection system for water plants according to claim 11, wherein the data processing module processes the 1 second chirp continuous wave signal as follows:

13. The radar detection system for the water-floating plants according to claim 12, wherein the data processing module processes 1 second dot-frequency continuous wave signals as follows:

s11: calculating power spectral density of the acquired data;

therefore, the maximum doppler frequency is about 16Hz, 1KHz is respectively taken at two sides of the margin left under the abnormal condition of wind, and the threshold value is finely adjusted by taking the detection reference threshold value obtained in S01 as a reference;

s13: and calculating the target speed according to the detection frequency.

14. The radar detection system for water plants according to claim 13, wherein the data processing module further comprises a function of calculating data transmission, processing, storage and display time, specifically as follows:

the FFT processing and the threshold detection of the data by the CPU need 600 milliseconds, 1 second of data is adopted for display at the same time, and the required time is 50 milliseconds, so that the 1 second of linear frequency modulation signal processing time is about 1 second;