CN111722218A - Double-frequency composite waveform high-frequency radar system - Google Patents
Double-frequency composite waveform high-frequency radar system Download PDFInfo
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- CN111722218A CN111722218A CN202010495403.3A CN202010495403A CN111722218A CN 111722218 A CN111722218 A CN 111722218A CN 202010495403 A CN202010495403 A CN 202010495403A CN 111722218 A CN111722218 A CN 111722218A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/50—Systems of measurement based on relative movement of target
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
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Abstract
The invention discloses a dual-frequency composite waveform high-frequency radar system, which is based on a composite waveform combining a frequency modulation interrupted continuous wave system and a linear frequency modulation pulse system, adopts the linear frequency modulation pulse system working at a lower frequency band and a narrower frequency sweep period and the frequency modulation interrupted continuous wave system working at a higher frequency band and a longer frequency sweep period to simultaneously work, ensures that two waveforms simultaneously work not only without mutual interference but also have complementary advantages through reasonable parameter design, simultaneously completes the demodulation of two waveform echo signals at a receiving end echo signal demodulation unit through a matched filtering method and a slope removal method, ensures that the radar has the advantages of sea state parameter real-time monitoring while having the detection capability of moving targets at different distances and different speeds and in low altitude, and greatly improves the detection performance of the radar.
Description
Technical Field
The invention relates to the field of high-frequency beyond visual range radars, in particular to a dual-frequency composite waveform high-frequency radar system.
Background
The high-frequency ground wave radar is a new ocean remote sensing device, has the advantages of large detection area, all-weather working, low operation cost and the like, can realize the monitoring of the dynamic state of the ocean surface for tens of thousands of square kilometers, can also realize the detection and tracking of the moving target on the sea surface and low altitude, and can play a positive role in the aspects of ocean supervision, maritime search and rescue, traffic management and the like. The real-time monitoring information of the ocean surface dynamics state can be used as the basis for sea clutter suppression in the real-time detection of targets, and the sea target detection is used for important links such as channel calibration, clutter suppression and the like in the ocean state monitoring.
However, the traditional high-frequency ground wave radar mostly adopts a single waveform system, is difficult to realize the simultaneous detection of the far and near distance ocean state and the fast and slow speed targets, and cannot give full play to the advantages of the high-frequency ground wave radar. Most high-frequency ground Wave radars adopt a receiving and transmitting common station, in order to avoid the influence of strong direct waves on a receiver, Frequency Modulated Interrupted Continuous Waves (FMICW) are adopted, the high-frequency ground Wave radar has the advantages of linear sweep Continuous waves and a pulse system, the harsh requirements of large difference of echo intensities of far and near sea surfaces on the dynamic range of the receiver can be better overcome, sea condition information of a plurality of distance points can be obtained through one-time measurement, however, the sweep period needs to be reduced when a high-speed moving target is detected, the limitation of receiving and transmitting pulses is realized, and the maximum distance capable of being detected is very limited. A Chirp Pulse (Chirp Pulse) waveform is often used in the detection of a long-distance high-speed moving target of a radar to ensure a longer detection distance and a wider doppler spectrum width, but due to the influence of different times of transceiving required by a transceiving common station, the bandwidth of an echo at a short distance is reduced, so that a short distance is blurred, and when the detection distance needs to be considered far and near, the waveform system has a very high requirement on the dynamic range of a receiver. Therefore, the method for designing the waveform of the high-frequency ground wave radar and realizing the system is researched, a complementary waveform system which does not interfere with each other is constructed and applied to the system, the complementary waveform system is applied to an actual system, and a dual-frequency composite waveform radar high-frequency receiver system is designed, so that the high-frequency radar can realize the simultaneous detection of the near-far distance ocean state and the fast-slow speed target, and has important research significance and application value.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a dual-frequency composite waveform high-frequency radar system which has the capability of simultaneously detecting a far-near distance ocean state and fast and slow targets.
In order to achieve the purpose, the invention provides the following technical scheme: a dual-frequency composite waveform high-frequency radar system is characterized in that a composite waveform system is adopted, a Frequency Modulation Interrupt Continuous Wave (FMICW) system and a Chirp Pulse (Chirp Pulse) system are combined, and waveform parameters are reasonably set to enable the radar to work together, so that the radar has the capability of simultaneously detecting a far-near marine state and a fast-slow target.
The composite waveform system adopts a Chirp Pulse (Chirp Pulse) system working at a lower frequency band and with a narrower Pulse period to realize remote detection; meanwhile, a Frequency Modulation Interrupted Continuous Wave (FMICW) system working at a higher frequency band and a longer frequency sweep period is adopted to realize short-distance detection.
The design of the composite waveform system comprises a working frequency f of a Chirp Pulse (Chirp Pulse) system0LEmission pulse period TLEmission pulse width TpLReceiving a pulse width TBLSelecting; operating frequency f of frequency-modulated interrupted continuous wave (FMICW) system0MSweep period TsGate control pulse period TMGate control pulse width TpMReceiving a pulse width TBHSelecting; and determining the working time sequence of the two waveform systems. Specific process packet for designing composite waveform systemComprises the following steps:
step 1: selecting a working carrier frequency of a linear frequency modulation pulse system according to the farthest detection distance required by the radar, determining a transmission pulse period of the linear frequency modulation pulse system according to the maximum speed of a target to be detected, determining a transmission pulse width of the linear frequency modulation pulse system and a receiving pulse width of the linear frequency modulation pulse system to obtain a distance detection range of the linear frequency modulation pulse system, and further constructing a transmission signal model of the linear frequency modulation pulse system;
preferably, the operating carrier frequency of the chirp system in step 1 is f0L；
Step 1, determining the transmission pulse period of a linear frequency modulation pulse system according to the maximum speed of the target to be detected as follows:
the transmission pulse period T of the linear frequency modulation pulse systemLWith the maximum velocity v of the object to be detectedmaxSatisfy the relationship
Wherein, TLThe transmission pulse period being a chirp system, c being the speed of light, fdmaxDoppler shift, f, corresponding to the maximum velocity of the object to be measured0LSelecting T for the working carrier frequency of the linear frequency modulation pulse system on the premise of satisfying the formulaL；
Step 1 determining the transmission pulse width T of the chirp systempLIt should satisfy:
wherein, TpLTransmission pulse width, B, of a chirp systemLSwept bandwidth, Δ R, for signals transmitted over the systemLFor the range resolution of the regime, c is the speed of light, and in combination with this relationship, T is determined according to the detection requirements of the range resolutionpLSelecting T on the premise of satisfying the formulapL；
Step 1 receiving pulse width T of said linear frequency modulation pulse systemBLIt should satisfy:
wherein, TBLSelecting T for the pulse width of the linear frequency modulation pulse system on the premise of satisfying the formulaBL；
Step 1, the distance detection range of the linear frequency modulation pulse system is RminL～Rmax；
Wherein R isminLLower limit of range detection, R, for a chirp systemmaxThe maximum detection range required for the radar;
step 1, the emission signal model of the chirp system is as follows:
wherein k isL＝BL/TpLFor slope of frequency sweep, TpLTransmission pulse width, B, of a chirp systemLThe sweep bandwidth of the transmitted signal for this system, T being the time, TLTransmission pulse period, f, of a chirp system0LWorking carrier frequency of linear frequency modulation pulse system;
step 2: determining the working carrier frequency, the frequency sweep period, the frequency sweep bandwidth, the gate control pulse period, the gate control pulse width and the receiving pulse width of a frequency modulation interrupt continuous wave system according to the lower limit of the distance detection range of the linear frequency modulation pulse system, and constructing a transmitting signal model of the frequency modulation interrupt continuous wave system;
preferably, the operating carrier frequency of the fm interrupted continuous wave system determined in step 2 is f0HMaximum detection of the frequency-modulated interrupted continuous wave regimeThe distance is greater than the lower limit of the distance detection range of the linear frequency modulation pulse system, namely RminL.。
Preferably, the determining of the modulation-interrupted continuous wave system gating pulse period T as described in step 2LPulse period T of gate control pulse corresponding to frequency modulation interrupt continuous wave systemHEqual and the two pulse edges are aligned to realize simultaneous triggering.
Preferably, the determining of the pulse width T of the gating pulse of the modulated-frequency interrupted continuous wave system as described in step 2pHPulse width T of transmission pulse corresponding to linear frequency modulation pulse systemPLAre equal.
Preferably, the sweep period T of the frequency-modulated discontinuous continuous wave system in step 2sIt should satisfy:
Ts＝Ns*TH＝Ns*TL
wherein, TH、TpH、BHThe gate control pulse period of the frequency modulation interruption continuous wave system, the gate control pulse width of the frequency modulation interruption continuous wave system and the sweep frequency bandwidth of the frequency modulation interruption continuous wave system are sequentially arranged, c is the light speed, N is the light speedsThe number of gate control pulses in the sweep frequency period of the frequency modulation interrupted continuous wave system can be selected according to actual requirementsminLThe lower limit of the range detection range of the linear frequency modulation pulse system;
preferably, the receiving pulse width T of the fm interrupted continuous wave system described in step 2BHIt should satisfy:
wherein, TH、TpHThe gate control pulse period and gate control pulse width of the frequency modulation interrupted continuous wave system, c is the speed of light, RminLThe lower limit of the range detection range of the linear frequency modulation pulse system;
preferably, frequency modulationPulse width T of received pulse of interrupted continuous wave systemBHPulse width T of received pulse of linear frequency modulation pulse systemBLEqual;
step 2, the emission signal model of the frequency modulation interruption continuous wave system is as follows:
wherein f is0HThe working carrier frequency of the frequency modulation interrupted continuous wave system; t isH、TpH、Ts、TBHAnd BHRespectively a gate control pulse period, a gate control pulse width, a sweep frequency period, a receiving pulse width and a sweep frequency bandwidth of a frequency modulation interrupt continuous wave system; k is a radical ofH＝BH/TpHSlope of sweep frequency, T is time, rect (T/T)pH) Indicates a width of TpHAnd a rectangular window centered at the origin;
and step 3: transmitting signal carrier frequency f according to chirp system0LBandwidth BLPulse period T of the emission pulseLPulse width TPLGenerating a transmission signal of a chirp system, according to a carrier frequency f of the transmission signal of a FM discontinuous continuous wave system0HBandwidth BHGate control pulse period THGate control pulse width TpHSweep period TsSweep bandwidth BHGenerating a transmitting signal of a frequency modulation interrupted continuous wave system;
and 4, step 4: receiving pulse width T according to chirp systemBLControlling the receiving and transmitting switch to receive the echo signal of the system according to the receiving pulse width T of the frequency modulation interrupted continuous wave systemBHAnd controlling the receiving and transmitting switch to receive the echo signals of the system.
In order to realize a composite waveform system, the dual-frequency high-frequency radar receiver system comprises: the device comprises a synchronous control unit, a transmitting signal synthesis unit, a receiving analog front end, an echo signal demodulation unit, a data transmission unit and an upper computer;
the synchronous control unit is connected with the transmitting signal synthesis unit in a wired mode; the synchronous control unit is connected with the receiving analog front end in a wired mode; the synchronous control unit is connected with the echo signal demodulation unit in a wired mode; the synchronous control unit is connected with the data transmission unit in a wired mode; the receiving analog front end, the echo signal demodulation unit, the data transmission unit and the upper computer are connected in sequence in a wired mode;
the transmitting signal synthesis unit completes the generation of the transmitting signal, and the generated signal is transmitted to the external power amplification unit; the power amplification unit is composed of a first power amplifier and a second power amplifier;
preferably, the transmitting signal synthesizing unit comprises a first transmitting path and a second transmitting path which are parallel, the first transmitting path generates a transmitting signal of a linear frequency modulation pulse system, the second transmitting path generates a transmitting signal of a frequency modulation interrupted continuous wave system, and the first transmitting path and the second transmitting path respectively comprise a signal generating circuit, a filter circuit, a transceiving switch and an amplifying circuit which are sequentially connected; a transmission signal of a chirp system generated by the first transmission channel is accessed to a first transmission antenna through an external first power amplifier and is radiated; the transmission signal of the frequency modulation interrupted continuous wave system generated by the second transmission channel is accessed to a second transmission antenna through an external second power amplifier to be radiated;
the signal generating circuit of the first transmitting channel transmits signal carrier frequency f according to a linear frequency modulation pulse system0LBandwidth BLPulse period T of the emission pulseLPulse width TPLTo set parameters to generate a transmit signal in a chirp regime.
The signal generating circuit of the second transmitting channel transmits signal carrier frequency f according to frequency modulation interrupt continuous wave system0HBandwidth BHGate control pulse period THGate control pulse width TpHSweep period TsSweep bandwidth BHTo set parameters to generate transmission of a frequency modulated interrupted continuous wave regimeA signal.
The receiving and transmitting switches of the first transmitting path and the second transmitting path are subjected to the pulse period T output by the synchronous control unitLA pulse width of TPLThe on-off of the signal is realized by controlling the emission pulse, the switch is closed in the high level of the pulse, the signal is emitted, and the switch is opened in the low level, and the signal is not emitted;
the central frequency of the filter of the first transmission path is matched with the transmission signal carrier frequency f of the chirp system0LThe consistency is achieved;
the central frequency of the filter of the second transmission path follows the transmission signal f of the frequency modulation interrupted continuous wave system0HThe consistency is achieved;
preferably, the receiving analog front end completes the amplification filtering and the digital-to-analog conversion of the echo signal.
Further, the receiving analog front end includes a transceiving switch, a power divider, a first receiving path, and a second receiving path; the receiving and transmitting switch is connected with the power divider in a wired mode; the power divider is respectively connected with the first receiving channel and the second receiving channel in parallel in sequence in a wired mode;
the pulse period of the receiving and transmitting switch output by the synchronous control unit is TLA pulse width of TBLThe on-off of the signal is realized by the control of the received pulse, the switch is closed in the high level of the pulse, the signal is received, and the switch is opened in the low level and is not received;
the power divider divides the echo signal into two paths of signals with equal power and respectively transmits the two paths of signals to the first receiving path and the second receiving path;
the first receiving path and the second receiving path respectively comprise a filter, an amplifier and an analog-to-digital conversion circuit which are connected in sequence;
the filter of the first receive path is the same as the filter in the first transmit path. After the echo signal passes through the filter, the echo signal of the linear frequency modulation pulse system is reserved, and the echo signal of the frequency modulation interrupt continuous wave system is filtered;
the filter of the second receive path is the same as the filter in the second transmit path. After the echo signal passes through the filter, the frequency modulation interrupt continuous wave system echo signal is reserved, and the linear frequency modulation pulse system echo signal is filtered;
the first receiving channel outputs a chirp system echo digital signal;
the second receiving channel outputs a frequency modulation interrupted continuous wave system echo digital signal;
preferably, the echo signal demodulation unit comprises a first demodulation path and a second demodulation path;
the first demodulation channel demodulates the frequency modulation pulse system echo digital signal to obtain a linear frequency modulation pulse baseband signal; and the second demodulation channel demodulates the frequency modulation interrupt continuous wave body modulation echo digital signal to obtain a frequency modulation interrupt continuous wave baseband signal.
The first demodulation path adopts a matched filtering method for demodulation and comprises a quadrature frequency mixing module, an extraction filtering module and a matched filtering module which are connected in sequence; the matched filtering module comprises an FFT module, a complex multiplier module and an IFFT module which are connected in sequence;
the second demodulation channel adopts a slope removal method for demodulation and comprises an orthogonal frequency mixing module and a decimation filtering module which are connected in sequence;
the data transmission unit completes data transmission of the demodulated baseband signal and transmission of control parameters, and the data transmission interface is connected with the upper computer.
Preferably, said control parameter comprises the operating frequency f of a previously defined chirp system0LSweep bandwidth BLEmission pulse period TLEmission pulse width TpLReceiving a pulse width TBL(ii) a Working frequency f of frequency-modulated interrupted continuous wave system0MSweep bandwidth BHSweep period TsGate control pulse period TMGate control pulse width TpMReceiving a pulse width TBHAnd the like. The data transmission unit can be controlled by FPGA, and the data transmission can be completed by Ethernet port, USB and other modes.
The synchronous control unit generates a transmitting pulse control signal and a receiving pulse control signal according to the control parameters transmitted by the data transmission unit.
Preferably, the transmission pulse is a transmission pulse of a determined chirp system, and the relevant parameter is a transmission pulse period TLEmission pulse width TpL. Preferably, the received pulse is a received pulse of a determined chirp system, and the related parameter is a received pulse width TBL. Preferably, the synchronous control unit may be implemented by an FPGA.
Compared with the prior art, the invention has the advantages that:
the dual-frequency composite waveform high-frequency radar system breaks through the limitation of a traditional single waveform system of the series of radars, and combines a Chirp Pulse (Chirp Pulse) system and a Frequency Modulation Interrupt Continuous Wave (FMICW) system through reasonable parameter design to realize the complementary advantages of the two waveforms without mutual influence;
the double-frequency composite waveform high-frequency radar system enables the radar receiver to have the advantages of detecting a long-distance high-speed moving target in real time, considering short-distance low-speed target detection and ocean state monitoring, and greatly improving the radar detection performance;
the transmitting signal synthesis and signal demodulation processing mechanisms in the two waveform systems of the dual-frequency composite waveform high-frequency radar system are easy to configure, high in flexibility, capable of being changed according to actual requirements, and easy to maintain and upgrade.
Drawings
FIG. 1 is a flow chart of the design of the composite waveform system in the method of the present invention;
FIG. 2 is a timing diagram of the Chirp Pulse and FMICW transmit-receive in the composite waveform system designed by the present invention;
FIG. 3 is a block diagram of a dual-frequency complex waveform high-frequency radar system designed by the present invention;
FIG. 4 is a block diagram of a Chirp Pulse echo signal demodulation module and a block diagram of a digital down-conversion module in the invention;
FIG. 5 is a block diagram of a FMICW echo signal demodulation module and a digital down-conversion module according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A dual-frequency composite waveform high-frequency radar system is characterized in that the system adopts a composite waveform system, so that the radar has the capability of simultaneously detecting a far-near distance ocean state and fast and slow targets. The composite waveform design is to adopt a Chirp Pulse (Chirp Pulse) system working at a lower frequency band and a narrower sweep frequency period to realize the real-time detection of a high-speed target at a long distance; meanwhile, a Frequency Modulation Interrupted Continuous Wave (FMICW) system working at a higher frequency band and a longer frequency sweep period is adopted to realize the fine detection of the ocean state parameters and the low-speed target at a close distance.
The following describes the embodiments of the present invention with reference to fig. 1 to 5:
according to the design process of the composite waveform system in the method of the present invention as shown in FIG. 1, the farthest detection distance R of the radar is usedmaxFor example, 300km and 5km distance resolution are required, and a waveform system is designed.
According to the radar equation, the target echo intensity P of the ground wave over-the-horizon radar propagating along the ocean surfacerGenerally expressed as:
wherein, PavRepresents the average transmitted power of the radar; gtRepresenting the directional gain of the transmit antenna; grRepresents the directional gain of the receiving antenna; r represents the distance between the target and the radar base station; σ represents a scattering cross-sectional area of the target; l issCharacterizing radar system loss; f (R) represents a Norton attenuation term at a distance R; λ ═ c/f denotes the operating wavelength. To achieve detection, the target echo intensity PrMust be greater than the sensitivity of the radar receiver. By combining the two relations and combining the available frequency range of the ground wave radar, the working frequency f of a proper Chirp Pulse (Chirp Pulse) waveform system can be selected0L. The working carrier frequency of the linear frequency modulation pulse system is f by combining the available distribution frequency of the ground wave radar0LTake 4.4 MHz.
Assuming a maximum velocity v of the object to be detectedmax300m/s, the transmission pulse period T of the linear frequency modulation pulse systemLShould satisfy the relationship
T is selected on the premise of satisfying the formulaLTake 4 ms.
According to the requirement of distance resolution, the sweep frequency bandwidth B of the transmitted signal of the linear frequency modulation pulse system is takenLAt 30kHz, the transmission pulse width T of the linear frequency modulation pulse systempLIt should satisfy:
TpLtake 0.8 ms. RminLLower limit of range detection range of chirp system
Receiving pulse width T of linear frequency modulation pulse systemBLIt should satisfy:
TBLtake 3.18 ms.
The transmitted signal model of the chirp system is:
wherein k isL＝BL/TpLFor sweeping the frequencyRate, TpLIs 0.8ms, BLAt 30kHz, T is time, TLIs 4ms, f0LIs 4.4 MHz;
lower limit R of range detection according to linear frequency modulation pulse systemminLSelecting the working carrier frequency f for determining the frequency modulation interrupted continuous wave system0HThe farthest detection distance of the frequency modulation interrupted continuous wave system is required to be greater than RminL.Combined with the allocated frequency, f, available for ground-wave radar0HTaken to be 9.3 MHz.
Next, the gating pulse period T of the frequency modulation interrupted continuous wave system is determinedHGate control pulse width TpHSweep period TsReceiving a pulse width TBHSweep bandwidth BHThe number of gated pulses N within the sweep frequency periodsRespectively 4ms, 0.8ms, 500ms, 3.18ms, 30kHz and 125, and further determining that the emission signal model of the frequency modulation interruption continuous wave system in the step 2 is as follows:
wherein k isH＝BH/TpHSlope of sweep frequency, T is time, rect (T/T)pH) Indicates a width of TpHAnd a rectangular window centered at the origin;
and combining the parameters to generate a transmitting signal of a composite waveform system, and utilizing the designed receiving pulse control system to receive the echo signal.
The timing diagram of the transmitting and receiving of the designed radar with the composite waveform system is shown in fig. 2, fig. 2(a) is the timing diagram of the transmitting and receiving of the chirp system, and fig. 2(b) is the timing diagram of the transmitting and receiving of the fm interrupt continuous wave system. The pulse periods of the transmission pulse of the chirp system in fig. 2(a) and the gate pulse of the fm-interrupted continuous wave system in fig. 2(b) are equal (both are 4ms), the pulse widths of the transmission pulse of fig. 2(a) and the gate pulse of fig. 2(b) are equal (both are 0.8ms), and the pulse edges of the transmission pulse of fig. 2(a) and the gate pulse of fig. 2(b) are aligned and are at TpThe two waveform systems transmit signals simultaneously. The pulse widths of the received pulses of fig. 2(a) and 2(b) are equal (both of them3.18ms), equal pulse period and edge alignment, at TBAnd simultaneously receiving echo signals of two waveform systems. By the mode, the purpose that the two waveform systems work simultaneously and do not interfere with each other can be achieved.
In order to realize a composite waveform system, the dual-frequency high-frequency radar receiver system comprises: the device comprises a synchronous control unit, a transmitting signal synthesis unit, a receiving analog front end, an echo signal demodulation unit, a data transmission unit and an upper computer; the structure of the dual-frequency composite waveform high-frequency radar system is shown in figure 3.
In order to realize the dual-frequency composite waveform operation of the system, the transmitting signal synthesis unit comprises a first transmitting path THLAnd a second transmission path THH. First transmission path THLThe carrier wave of the linear frequency modulation pulse system is generated to be 4.4MHz transmitting signal (S)TL) Second transmission path THHGenerating a transmission signal (S) of 9.3MHz carrier wave of a frequency-modulated discontinuous continuous wave systemTH) The two transmission paths comprise a signal generating circuit, a filter circuit, a transceiving switch, an amplifying circuit and the like which are connected in sequence. The signal generating circuit can be realized by an FPGA and a DAC circuit, and can also be realized by an FPGA and a DDS chip. When the signal generating circuit is realized by adopting an FPGA and a DAC circuit, two paths of parallel NCO are needed to set parameters respectively according to the frequency, the bandwidth, the sweep frequency period and the like of two types of transmitting waveforms designed in the prior art by utilizing an NCO IP core in the FPGA and two paths of transmitting signals, two types of digital transmitting signals meeting the requirements are generated, and then the digital-to-analog conversion is realized through a two-channel DAC chip such as an AD 9747. When the FPGA and the DDS chip are adopted for realizing, two DDS chips such as AD9910 or a double-circuit DDS chip such as AD9958 are needed, the FPGA configures the DDS chips according to the frequency, the sweep frequency bandwidth, the sweep frequency period and the like of the two emission waveforms designed in the front, the DDS chips directly synthesize two emission signals, STLThe sweep frequency period is 4ms, STHThe sweep period is 500 ms.
The filters of the first and second transmission paths often adopt band-pass filters, and the transmission path THLThe center frequency of the medium filter is 4.4MHz, and the transmission path THHMedium filterThe center frequency was 9.3 MHz.
The transceiving switches of the first transmitting path and the second transmitting path can adopt SA630, the transceiving switches are controlled by the transmitting pulse output by the synchronous control unit to realize the on-off of signals, the switches are closed in a pulse high level to transmit signals, the switches are opened in a low level to not transmit signals;
the receiving analog front end completes the amplification filtering and the digital-to-analog conversion of the echo signal.
The receiving analog front end comprises a receiving and transmitting switch, a power divider, a first receiving path and a second receiving path; the power generation switch is connected with the power divider in a wired mode; the power divider is respectively connected with the first receiving channel and the second receiving channel in parallel in sequence in a wired mode;
the receiving and transmitting switches can adopt SA630, and are controlled by the receiving pulse output by the synchronous control unit to realize the on-off of signals, the switches are closed in the high level of the pulse, the signals are received, and the switches are opened in the low level and are not received;
the power divider divides the echo signal into two paths of signals with equal power and respectively transmits the two paths of signals to the first receiving path and the second receiving path;
the first receiving path and the second receiving path respectively comprise a filter, an amplifier and an analog-to-digital conversion circuit which are connected in sequence;
the filter of the first receive path is the same as the filter in the first transmit path. After the echo signal passes through the filter, the echo signal of the linear frequency modulation pulse system is reserved, and the echo signal of the frequency modulation interrupt continuous wave system is filtered;
the filter of the second receive path is the same as the filter in the second transmit path. After the echo signal passes through the filter, the frequency modulation interrupt continuous wave system echo signal is reserved, and the linear frequency modulation pulse system echo signal is filtered;
the first receiving channel outputs a chirp system echo digital signal;
the second receiving channel outputs a frequency modulation interrupted continuous wave system echo digital signal;
the echo signal demodulation unit comprises a first demodulation channel and a second demodulation channel;
the first demodulation channel demodulates the frequency modulation pulse system echo digital signal to obtain a linear frequency modulation pulse baseband signal; and the second demodulation channel demodulates the frequency modulation interrupt continuous wave body modulation echo digital signal to obtain a frequency modulation interrupt continuous wave baseband signal.
The first demodulation path adopts a matched filtering method for demodulation and comprises a quadrature frequency mixing module, an extraction filtering module and a matched filtering module which are connected in sequence; the matched filtering module comprises an FFT module, a complex multiplier module and an IFFT module which are connected in sequence;
the demodulation of the Chirp Pulse echo signal is explained below with reference to fig. 4. The Chirp Pulse echo signal demodulation path adopts a matched filtering method for demodulation and comprises an orthogonal frequency mixing module, an extraction filtering module and a matched filtering module which are sequentially connected, wherein the orthogonal frequency mixing module also comprises two paths of orthogonal local oscillator signal synthesis and a digital mixer, but the local oscillator signals are single-frequency signals, so that carrier waves are removed after frequency mixing, the obtained linear frequency sweeping signals are still linear frequency sweeping signals, the linear frequency sweeping signals with lower data rate are obtained by filtering wave extraction, and the corresponding I/Q signals are sequentially input to the matched filtering module as the real part and the imaginary part of a complex analytic signal. The matched filtering module comprises an FFT module, a complex multiplier module and an IFFT module which are connected in sequence, and the baseband signal with lower data rate can be obtained through matched filtering. The whole processing process is completed in the FPGA, and the parameter setting can be modified according to the change of the actual transmitting waveform parameters.
The second demodulation channel adopts a slope removal method for demodulation and comprises an orthogonal frequency mixing module and a decimation filtering module which are connected in sequence;
the following describes the demodulation of the FMICW echo signal with reference to fig. 5, the FMICW echo signal demodulation path adopts a slope removal method for demodulation, and includes a quadrature frequency mixing module and an extraction filtering module which are connected in sequence, the quadrature frequency mixing module includes two paths of orthogonal local oscillator signal synthesis and digital mixers, the local oscillator is an FMICW signal, and is also realized by using an NCO IP core of an FPGA, the frequency and the frequency sweep slope of the NCO IP core are the same as those of a transmitting signal, and the quadrature frequency mixing completes the slope removal and the carrier removal of the echo signal to become a single-frequency signal. The decimation filtering module comprises a CIC decimation filter and a low-pass FIR filter which are connected in sequence, and the mixed signal can be subjected to decimation filtering to obtain a baseband signal with a lower data rate. The whole processing process is completed in the FPGA, and the parameter setting can be modified according to the change of the actual transmitting waveform parameters.
The data transmission unit completes data transmission of the demodulated baseband signal and transmission of control parameters, and the data transmission interface is connected with the upper computer. The data transmission unit can be realized by FPGA, and the data transmission can be completed by Ethernet port, USB and other modes.
The control parameters include the operating frequency f of the previously determined chirp system0LSweep bandwidth BLEmission pulse period TLEmission pulse width TpLReceiving a pulse width TBL(ii) a Working frequency f of frequency-modulated interrupted continuous wave system0MSweep bandwidth BHSweep period TsGate control pulse period TMGate control pulse width TpMReceiving a pulse width TBHAnd the like. The data transmission unit can be controlled by FPGA, and the data transmission can be completed by Ethernet port, USB and other modes.
The synchronous control unit generates control signals such as a transmitting pulse and a receiving pulse according to the control parameters transmitted by the data transmission unit, such as the transmitting pulse and the receiving pulse in two waveform systems in fig. 2. Preferably, the synchronous control unit may be implemented by an FPGA.
And after the data are uploaded to an upper computer, respectively processing according to a conventional high-frequency ground wave radar target/sea state detection flow to obtain the required target/sea state information.
It should be understood that the above description of the preferred embodiments is given for clarity and not for any purpose of limitation, and that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (8)
1. A method for generating a dual-frequency composite waveform, comprising the steps of:
step 1: selecting a working carrier frequency of a linear frequency modulation pulse system according to the farthest detection distance required by the radar, determining a transmission pulse period of the linear frequency modulation pulse system according to the maximum speed of a target to be detected, determining a transmission pulse width of the linear frequency modulation pulse system and a receiving pulse width of the linear frequency modulation pulse system to obtain a distance detection range of the linear frequency modulation pulse system, and further constructing a transmission signal model of the linear frequency modulation pulse system;
step 2: determining the working carrier frequency, the frequency sweep period, the frequency sweep bandwidth, the gate control pulse period, the gate control pulse width and the receiving pulse width of a frequency modulation interrupt continuous wave system according to the lower limit of the distance detection range of the linear frequency modulation pulse system, and constructing a transmitting signal model of the frequency modulation interrupt continuous wave system;
and step 3: generating a transmitting signal of a linear frequency modulation pulse system according to the carrier frequency and the bandwidth of a transmitting signal of the linear frequency modulation pulse system, the pulse period of the transmitting pulse and the pulse width, and generating the transmitting signal of the frequency modulation interrupt continuous wave system according to the carrier frequency and the bandwidth of the transmitting signal of the frequency modulation interrupt continuous wave system, the gate control pulse period, the gate control pulse width, the frequency sweep period and the frequency sweep bandwidth;
and 4, step 4: and controlling a receiving and transmitting switch according to the receiving pulse width of a linear frequency modulation pulse system to realize the receiving of the echo signals of the system, and controlling the receiving and transmitting switch according to the receiving pulse width of a frequency modulation interrupt continuous wave system to realize the receiving of the echo signals of the system.
2. The dual-frequency composite waveform generation method of claim 1, wherein: step 1 the working carrier frequency of the linear frequency modulation pulse system is f0L；
Step 1, determining the transmission pulse period of a linear frequency modulation pulse system according to the maximum speed of the target to be detected as follows:
the transmission pulse period T of the linear frequency modulation pulse systemLWith the maximum velocity v of the object to be detectedmaxSatisfy the relationship
Wherein, TLThe transmission pulse period being a chirp system, c being the speed of light, fdmaxDoppler shift, f, corresponding to the maximum velocity of the object to be measured0LSelecting T for the working carrier frequency of the linear frequency modulation pulse system on the premise of satisfying the formulaL；
Step 1 determining the transmission pulse width T of the chirp systempLIt should satisfy:
wherein, TpLTransmission pulse width, B, of a chirp systemLSwept bandwidth, Δ R, for signals transmitted over the systemLFor the range resolution of the regime, c is the speed of light, and in combination with this relationship, T is determined according to the detection requirements of the range resolutionpLSelecting T on the premise of satisfying the formulapL；
Step 1 receiving pulse width T of said linear frequency modulation pulse systemBLIt should satisfy:
wherein, TBLSelecting T for the pulse width of the linear frequency modulation pulse system on the premise of satisfying the formulaBL；
Step 1, the distance detection range of the linear frequency modulation pulse system is RminL～Rmax；
Wherein R isminLLower limit of range detection, R, for a chirp systemmaxThe maximum detection range required for the radar;
step 1, the emission signal model of the chirp system is as follows:
wherein k isL＝BL/TpLFor slope of frequency sweep, TpLTransmission pulse width, B, of a chirp systemLThe sweep bandwidth of the transmitted signal for this system, T being the time, TLTransmission pulse period, f, of a chirp system0LIs the working carrier frequency of the linear frequency modulation pulse system.
3. The dual-frequency composite waveform generation method of claim 1, wherein:
step 2, determining the working carrier frequency of the frequency modulation interrupted continuous wave system as f0HThe farthest detection distance of the frequency modulation interrupted continuous wave system is required to be larger than the lower limit of the distance detection range of the linear frequency modulation pulse system, namely RminL.；
Step 2, determining the gating pulse period T of the frequency modulation interrupt continuous wave systemLPulse period T of gate control pulse corresponding to frequency modulation interrupt continuous wave systemHThe two pulse edges are aligned to realize simultaneous triggering;
step 2, determining the pulse width T of the gating pulse of the frequency modulation interrupt continuous wave systempHPulse width T of transmission pulse corresponding to linear frequency modulation pulse systemPLEqual;
step 2, the sweep frequency period T of the frequency modulation interrupt continuous wave systemsIt should satisfy:
Ts＝Ns*TH＝Ns*TL
wherein, TH、TpH、BHThe gate control pulse period of the frequency modulation interruption continuous wave system, the gate control pulse width of the frequency modulation interruption continuous wave system and the sweep frequency bandwidth of the frequency modulation interruption continuous wave system are sequentially arranged, c is the light speed, N is the light speedsThe number of gate control pulses in the sweep frequency period of the frequency modulation interrupted continuous wave system can be selected according to actual requirementsminLThe lower limit of the range detection range of the linear frequency modulation pulse system;
step 2 receiving pulse width T of frequency modulation interrupt continuous wave systemBHIt should satisfy:
wherein, TH、TpHThe gate control pulse period and gate control pulse width of the frequency modulation interrupted continuous wave system, c is the speed of light, RminLThe lower limit of the range detection range of the linear frequency modulation pulse system;
pulse width T of received pulse of frequency modulation interrupted continuous wave systemBHPulse width T of received pulse of linear frequency modulation pulse systemBLEqual;
step 2, the emission signal model of the frequency modulation interruption continuous wave system is as follows:
wherein f is0HThe working carrier frequency of the frequency modulation interrupted continuous wave system; t isH、TpH、Ts、TBHAnd BHRespectively a gate control pulse period, a gate control pulse width, a sweep frequency period, a receiving pulse width and a sweep frequency bandwidth of a frequency modulation interrupt continuous wave system; k is a radical ofH＝BH/TpHSlope of sweep frequency, T is time, rect (T/T)pH) Indicating widthIs TpHAnd a rectangular window centered at the origin.
4. A dual-frequency composite waveform high-frequency radar system applied to a dual-frequency composite waveform generation method is characterized in that:
the device comprises a synchronous control unit, a transmitting signal synthesis unit, a receiving analog front end, an echo signal demodulation unit, a data transmission unit and an upper computer;
the synchronous control unit is connected with the transmitting signal synthesis unit in a wired mode; the synchronous control unit is connected with the receiving analog front end in a wired mode; the synchronous control unit is connected with the echo signal demodulation unit in a wired mode; the synchronous control unit is connected with the data transmission unit in a wired mode; the receiving analog front end, the echo signal demodulation unit, the data transmission unit and the upper computer are connected in sequence in a wired mode;
the transmitting signal synthesis unit completes the generation of the transmitting signal, and the generated signal is transmitted to the external power amplification unit; the power amplification unit is composed of a first power amplifier and a second power amplifier;
the transmitting signal synthesizing unit comprises a first transmitting channel and a second transmitting channel which are parallel, wherein the first transmitting channel generates a transmitting signal of a linear frequency modulation pulse system, and the second transmitting channel generates a transmitting signal of a frequency modulation interrupt continuous wave system;
the signal generating circuit of the first transmitting channel transmits signal carrier frequency f according to a linear frequency modulation pulse system0LBandwidth BLPulse period T of the emission pulseLPulse width TPLSetting parameters to generate a transmitting signal of a linear frequency modulation pulse system;
the signal generating circuit of the second transmitting channel transmits signal carrier frequency f according to frequency modulation interrupt continuous wave system0HBandwidth BHGate control pulse period THGate control pulse width TpHSweep period TsSweep bandwidth BHTo set parameters to generate frequency modulation interrupt connectionsAnd transmitting signals in a continuous wave system.
The receiving and transmitting switches of the first transmitting path and the second transmitting path are subjected to the pulse period T output by the synchronous control unitLA pulse width of TPLThe on-off of the signal is realized by controlling the emission pulse, the switch is closed in the high level of the pulse, the signal is emitted, and the switch is opened in the low level, and the signal is not emitted;
the central frequency of the filter of the first transmission path is matched with the transmission signal carrier frequency f of the chirp system0LThe consistency is achieved;
the central frequency of the filter of the second transmission path follows the transmission signal f of the frequency modulation interrupted continuous wave system0HAnd (5) the consistency is achieved.
5. The dual-frequency complex waveform high frequency radar system according to claim 4, wherein:
the first transmitting path and the second transmitting path respectively comprise a signal generating circuit, a filter circuit, a receiving and transmitting switch and an amplifying circuit which are connected in sequence; a transmission signal of a chirp system generated by the first transmission channel is accessed to a first transmission antenna through an external first power amplifier and is radiated; and the transmission signal of the frequency modulation interrupt continuous wave system generated by the second transmission channel is accessed to a second transmission antenna through an external second power amplifier to be radiated.
6. The dual-frequency complex waveform high frequency radar system according to claim 4, wherein:
the receiving analog front end completes the amplification filtering and digital-to-analog conversion of the echo signal;
the receiving analog front end comprises a receiving and transmitting switch, a power divider, a first receiving path and a second receiving path; the receiving and transmitting switch is connected with the power divider in a wired mode; the power divider is respectively connected with the first receiving channel and the second receiving channel in parallel in sequence in a wired mode;
the pulse period of the receiving and transmitting switch output by the synchronous control unit is TLA pulse width of TBLThe on-off of the signal is realized by the control of the received pulse, the switch is closed in the high level of the pulse, the signal is received, and the switch is opened in the low level and is not received;
the power divider divides the echo signal into two paths of signals with equal power and respectively transmits the two paths of signals to the first receiving path and the second receiving path;
the first receiving path and the second receiving path respectively comprise a filter, an amplifier and an analog-to-digital conversion circuit which are connected in sequence;
the filter of the first receive path is the same as the filter in the first transmit path. After the echo signal passes through the filter, the echo signal of the linear frequency modulation pulse system is reserved, and the echo signal of the frequency modulation interrupt continuous wave system is filtered;
the filter of the second receive path is the same as the filter in the second transmit path. After the echo signal passes through the filter, the frequency modulation interrupt continuous wave system echo signal is reserved, and the linear frequency modulation pulse system echo signal is filtered;
the first receiving channel outputs a chirp system echo digital signal;
and the second receiving channel outputs a frequency modulation interrupted continuous wave system echo digital signal.
7. The dual-frequency complex waveform high frequency radar system according to claim 4, wherein:
the echo signal demodulation unit comprises a first demodulation channel and a second demodulation channel;
the first demodulation channel demodulates the frequency modulation pulse system echo digital signal to obtain a linear frequency modulation pulse baseband signal; and the second demodulation channel demodulates the frequency modulation interrupt continuous wave body modulation echo digital signal to obtain a frequency modulation interrupt continuous wave baseband signal.
The first demodulation path adopts a matched filtering method for demodulation and comprises a quadrature frequency mixing module, an extraction filtering module and a matched filtering module which are connected in sequence; the matched filtering module comprises an FFT module, a complex multiplier module and an IFFT module which are connected in sequence;
the second demodulation path adopts a slope removal method for demodulation and comprises an orthogonal frequency mixing module and a decimation filtering module which are connected in sequence.
8. The dual-frequency complex waveform high frequency radar system according to claim 4, wherein:
the data transmission unit completes data transmission of the demodulated baseband signal and transmission of control parameters, and is connected with the upper computer;
the control parameters comprise: working frequency f of linear frequency-modulated pulse system0LSweep bandwidth BLEmission pulse period TLEmission pulse width TpLReceiving a pulse width TBL(ii) a Working frequency f of frequency-modulated interrupted continuous wave system0MSweep bandwidth BHSweep period TsGate control pulse period TMGate control pulse width TpMReceiving a pulse width TBH；
The data transmission unit can be controlled by an FPGA;
the synchronous control unit generates a transmitting pulse control signal and a receiving pulse control signal according to the control parameters transmitted by the data transmission unit, and is realized by an FPGA.
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