CN117572416A - Centimeter-level ultra-wideband ground penetrating radar system based on time expansion framework - Google Patents
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Abstract
The invention provides a centimeter-level ultra-wideband ground penetrating radar system based on a time expansion framework, which comprises: the system comprises a radio frequency subsystem, a main control subsystem and an upper computer subsystem, wherein the main control subsystem is respectively connected with the radio frequency subsystem and the upper computer subsystem; the radio frequency subsystem comprises a signal generating module, a signal transmitting module, a signal receiving module and an antenna module, wherein the signal generating module is respectively connected with the signal transmitting module and the signal receiving module; the signal transmitting module comprises a power distributor, a delay line, a first amplifier, a second amplifier, a first Gaussian pulse shaping circuit, a second Gaussian pulse shaping circuit and a radio frequency transformer; the signal receiving module comprises a third amplifier, a third Gaussian pulse shaping circuit and a mixer. The centimeter-level ultra-wideband ground penetrating radar system provided by the invention can effectively simplify the system structure and reduce the complexity and cost of the system.
Description
Technical Field
The invention relates to a ground penetrating radar system, in particular to a centimeter-level ultra-wideband ground penetrating radar system based on a time expansion framework.
Background
In road pavement detection, flaw detection and detection of various shallow concrete structures, the ground penetrating radar capable of performing nondestructive detection has wide practical requirements and application prospects. The ultra-wideband pulse type ground penetrating radar is widely applied due to the characteristics of large bandwidth and high resolution. Among them, ultra wideband radar based on picosecond-class gaussian pulse has centimeter-level distance resolution, has huge development and application potential, but also puts higher demands on system design.
However, if a conventional radio frequency direct sampling architecture is adopted, under the condition of picosecond Gaussian short pulse, the requirement of an ultra-wideband ground penetrating radar system on an analog-to-digital converter ADC is increased to 1-10G sps level, sps refers to sample per second, namely sampling times per second, and meanwhile, the performance requirement on devices such as an FPGA and the complexity of the system are greatly increased. Another solution adopting an equivalent sampling architecture often relies on complex FPGA control logic and a software and hardware clock synchronization design, and the system is also complex and has high cost.
Disclosure of Invention
The invention aims to solve the technical problem of providing an ultra-wideband ground penetrating radar system which has a simple system structure, picosecond Gaussian pulse and centimeter resolution, so as to reduce the system complexity and cost of the ultra-wideband ground penetrating radar system.
In this regard, the present invention provides a centimeter-level ultra-wideband ground penetrating radar system based on a time expansion architecture, comprising: the system comprises a radio frequency subsystem, a main control subsystem and an upper computer subsystem, wherein the main control subsystem is respectively connected with the radio frequency subsystem and the upper computer subsystem; the radio frequency subsystem comprises a signal generation module, a signal emission module, a signal receiving module and an antenna module, wherein the signal generation module is respectively connected with the signal emission module and the signal receiving module, the antenna module is respectively connected with the signal emission module and the signal receiving module, and the signal receiving module is connected with the main control subsystem; the signal transmitting module comprises a power distributor, a delay line, a first amplifier, a second amplifier, a first Gaussian pulse shaping circuit, a second Gaussian pulse shaping circuit and a radio frequency transformer; the signal receiving module comprises a third amplifier, a third Gaussian pulse shaping circuit and a mixer; the first Gaussian pulse shaping circuit, the second Gaussian pulse shaping circuit and the third Gaussian pulse shaping circuit have the same circuit structure;
the working process of the centimeter-level ultra-wideband ground penetrating radar system comprises the following steps of:
a1, after a system is electrified, the radio frequency subsystem starts to work, and the signal generation module outputs and generates a sine wave PRF1 and a sine wave PRF2;
step A2, the sine wave PRF1 signal is sent to the power distributor, the power distributor equally divides the signal and sends the signal to two branches, wherein one branch sequentially passes through a delay line, a first amplifier and a first Gaussian pulse shaping circuit and then generates a first Gaussian pulse; the other branch sequentially passes through a second amplifier and a second Gaussian pulse shaping circuit to generate a second Gaussian pulse; the first Gaussian pulse and the second Gaussian pulse are input to a radio frequency transformer to be synthesized into first-order Gaussian pulses, and the first Gaussian pulses and the second Gaussian pulses are transmitted through an antenna module;
step A3, the signal receiving module receives the signal of the antenna module as the radio frequency input of the mixer; the sine wave PRF2 sequentially passes through the third amplifier and the third Gaussian pulse shaping circuit to generate a third Gaussian pulse, and the third Gaussian pulse is used as a local oscillation reference input signal of the mixer; the mixer outputs the integrated intermediate frequency signal to the main control subsystem;
step A4, the main control subsystem converts the received intermediate frequency signal into a digital signal, and caches the digital signal after data processing;
step A5, the upper computer subsystem establishes network connection with the main control subsystem, and periodically issues a collection command to the main control subsystem; and the main control subsystem reports data to the upper computer subsystem and displays radar images after the data processing of the upper computer subsystem.
The invention is further improved in that the signal generation module comprises a DDS setting singlechip, a direct digital frequency synthesizer DDS and a crystal oscillator, and the direct digital frequency synthesizer DDS is respectively connected with the DDS setting singlechip and the crystal oscillator.
The invention is further improved in that the direct digital frequency synthesizer DDS outputs sine wave PRF1 and sine wave PRF2 through the generated signals of the crystal oscillator and parameters set by the DDS setting singlechip.
The invention further improves that the main control subsystem comprises a full-programmable system-on-chip, an encoder interface and an analog-to-digital converter ADC, wherein the full-programmable system-on-chip is respectively connected with the encoder interface and the analog-to-digital converter ADC, the full-programmable system-on-chip is connected with the upper computer subsystem, and the analog-to-digital converter ADC is connected with the signal receiving module.
The invention further improves that the fully programmable system on a chip comprises two parts, namely an FPGA and an ARM on the chip; the signal receiving module outputs signals to the analog-to-digital converter ADC, the analog-to-digital converter ADC converts the received signals into digital signals and inputs the digital signals into an FPGA component of the fully programmable system-on-chip, and after data processing in the FPGA component, data processing results are uploaded to the ARM end for caching.
The invention further improves that in the step A2, the calculation formula of the first-order Gaussian pulse generation process is as follows:the method comprises the steps of carrying out a first treatment on the surface of the Wherein (1)>Is a first order Gaussian pulse->For the first Gaussian pulse +.>Is a second gaussian pulse; first Gaussian pulse->Is of the meter(s)The calculation formula is +.>Second Gaussian pulse->The calculation formula of (2) is: />A is amplitude, < >>Is the point in time at which the peak of the gaussian pulse is located, < + >>Is the current time, σ is the standard deviation, ω is the angular frequency of the first gaussian pulse and the second gaussian pulse, and ϕ is the initial phase.
A further development of the invention is that the calculation formula of the first gaussian pulseAnd the calculation formula of said second gaussian pulse +.>The phase difference between them is adjusted by the delay line.
A further improvement of the present invention is that the delay line is a coaxial cable and the phase difference between the first gaussian pulse and the second gaussian pulse is adjusted by adjusting the length of the coaxial cable.
The invention further improves that the calculation formula for generating the third gaussian pulse in the step A3 is as follows:，/>is the angular frequency of the third gaussian pulse.
A further improvement of the present invention is that in the step A3, the mixer outputs a spreading factor EF of the integrated intermediate frequency signalThe calculation formula is as follows:wherein->Outputting the frequency of the generated sine wave PRF1 for the signal generating module, +.>The frequency of the generated sine wave PRF2 is output for the signal generating module.
Compared with the prior art, the invention has the beneficial effects that: the centimeter-level ultra-wideband ground penetrating radar system based on the time expansion framework has the resolution of picosecond Gaussian pulse and centimeter level, can convert the high-frequency signal of the picosecond Gaussian pulse into a low-frequency signal, and can further sample the high-frequency signal by using a low-speed analog-to-digital converter ADC; on the basis, the structure of the system is effectively simplified and the complexity and cost of the system are reduced by further optimizing the system architecture and the working process of the system, and the system can be widely applied to the aspects of road pavement detection, flaw detection, detection of various shallow concrete structures and the like.
Drawings
FIG. 1 is a schematic block diagram of a system architecture of one embodiment of the present invention;
FIG. 2 is a schematic circuit diagram of a signal generation module according to an embodiment of the present invention;
FIG. 3 is a schematic circuit diagram of a signal transmitting module according to an embodiment of the present invention;
fig. 4 is a schematic circuit diagram of a signal receiving module according to an embodiment of the present invention;
FIG. 5 is a schematic circuit diagram of a first Gaussian pulse shaping circuit according to an embodiment of the invention;
FIG. 6 is a schematic diagram of a first order Gaussian pulse test waveform according to an embodiment of the invention.
The attached drawings are identified: a 10-radio frequency subsystem; a 101-signal generation module; 102-a signal transmitting module; 103-a signal receiving module; 104-an antenna module; 20-a master control subsystem; 201-fully programmable system on chip; 30-an upper computer subsystem.
Detailed Description
In the description of the present invention, if an orientation description such as "upper", "lower", "front", "rear", "left", "right", etc. is referred to, it is merely for convenience of description and simplification of the description, and does not indicate or imply that the apparatus or element referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the invention. If a feature is referred to as being "disposed," "secured," "connected," or "mounted" on another feature, it can be directly disposed, secured, or connected to the other feature or be indirectly disposed, secured, connected, or mounted on the other feature.
In the description of the invention, if reference is made to "a number", it means more than one; if "a plurality" is referred to, it means more than two; if "greater than", "less than", "exceeding" are referred to, they are understood to not include the present number; references to "above," "below," "within," and "within" are to be construed as including the present number. If reference is made to "first," "second," etc., it is to be understood that the same or similar technical feature names are used only for distinguishing between them, and it is not to be understood that the relative importance of a technical feature is implied or indicated, or that the number of technical features is implied or indicated, or that the precedence of technical features is implied or indicated.
Preferred embodiments of the present invention will be described in further detail below with reference to the attached drawings:
as shown in fig. 1 to 4, the present embodiment provides a centimeter-level ultra-wideband ground penetrating radar system based on a time expansion architecture, including: the system comprises a radio frequency subsystem 10, a main control subsystem 20 and an upper computer subsystem 30, wherein the main control subsystem 20 is respectively connected with the radio frequency subsystem 10 and the upper computer subsystem 30; the radio frequency subsystem 10 comprises a signal generating module 101, a signal transmitting module 102, a signal receiving module 103 and an antenna module 104, wherein the signal generating module 101 is respectively connected with the signal transmitting module 102 and the signal receiving module 103, the antenna module 104 is respectively connected with the signal transmitting module 102 and the signal receiving module 103, and the signal receiving module 103 is connected with the main control subsystem 20; the signal transmitting module 102 includes a power divider U20, a delay line U30, a first amplifier U40, a second amplifier U41, a first gaussian pulse shaping circuit U50, a second gaussian pulse shaping circuit U51, and a radio frequency transformer U60; the signal receiving module 103 comprises a third amplifier U42, a third gaussian pulse shaping circuit U52 and a mixer U70; the first Gaussian pulse shaping circuit U50, the second Gaussian pulse shaping circuit U51 and the third Gaussian pulse shaping circuit U52 have the same circuit structure;
the working process of the centimeter-level ultra-wideband ground penetrating radar system comprises the following steps of:
step A1, after the system is powered on, the rf subsystem 10 starts to operate, and the signal generating module 101 outputs and generates a sine wave PRF1 and a sine wave PRF2;
step A2, the sinusoidal wave PRF1 signal output by the signal generating module 101 is sent to the power divider U20, the power divider U20 equally divides the signal and sends the signal to two branches, one branch sequentially passes through the delay line U30, the first amplifier U40 and the first gaussian pulse shaping circuit U50 and then generates a first gaussian pulse, the other branch sequentially passes through the second amplifier U41 and the second gaussian pulse shaping circuit U51 and then generates a second gaussian pulse, and the two gaussian pulses are input into the radio frequency transformer U60 and synthesized into a first-order gaussian pulse and then are transmitted through the antenna module 104;
step A3, the signal receiving module 103 receives the signal of the antenna module 104 as a radio frequency input of the mixer U70; the sine wave PRF2 output by the signal generating module 101 sequentially passes through the third amplifier U42 and the third gaussian pulse shaping circuit U52 to generate a third gaussian pulse, where the third gaussian pulse is used as a Local Oscillator (LO) reference input signal of the mixer U70; the mixer U70 outputs the integrated intermediate frequency signal to the main control subsystem 20;
step A4, the main control subsystem 20 converts the received intermediate frequency signal into a digital signal, and after data processing such as peak searching and stack (stack), the processing result is uploaded to a PS end (ARM) through a DMA interface for buffering;
step A5, the upper computer subsystem 30 establishes a network connection with the main control subsystem 20, and issues a collection command to the main control subsystem 20 at fixed time; the main control subsystem 20 reports data to the upper computer subsystem 30, the reported data comprises ranging wheel information, and the upper computer subsystem 30 performs data processing such as filtering and background elimination and then displays radar images.
Signals having a relative bandwidth, which refers to the ratio of the center frequency to the absolute bandwidth, are typically referred to as ultra-wideband signals. The ultra-wideband ground penetrating radar achieves penetration of leaf clusters, soil or walls while obtaining higher distance (or longitudinal) resolution by transmitting ultra-wideband signals, thereby achieving the function of detecting hidden targets.
In this embodiment, the selected mixer U70 is a double balanced mixer with an operating frequency of 5MHz to 3.5GHz, typical conversion loss of 6.9dB, typical LO-RF isolation of 33dB, typical LO-IF isolation of 28dB, typical IP3 of 23dBm, and LO power +13dBm. The Mixer U70 is also called Mixer, and the Mixer U70 outputs the integrated intermediate frequency signal as a time spread signal, and the spread factor is EF, namely the expansion factor. The ground penetrating radar based on the Time expansion architecture is also called Time-Expanded Architecture Ground Penetrating Radar, TEA-GPR for short.
In more detail, as shown in fig. 1, the upper computer subsystem 30 is preferably a portable device of an android operating system, and is provided with acquisition system software, when the upper computer subsystem 30 establishes a network connection with the main control subsystem 20, the upper computer subsystem 30 issues an acquisition command to the main control subsystem 20 at regular time, and the main control subsystem 20 reports data to the upper computer subsystem 30 after receiving the acquisition command. The upper computer subsystem 30 filters the received data, fuses the positioning data, and displays the radar image after the background cancellation operation. Therefore, the design method of the data processing of the upper computer subsystem 30 by adopting the general data acquisition equipment in the embodiment simplifies the system structure and reduces the complexity and cost of the system.
As shown in fig. 2, the signal generating module 101 includes a DDS setting single-chip microcomputer U1, a direct digital frequency synthesizer DDS U2, and a crystal oscillator X3, where the direct digital frequency synthesizer DDS U2 is connected with the DDS setting single-chip microcomputer U1 and the crystal oscillator X3 respectively.
As shown in fig. 2, the direct digital frequency synthesizer DDS U2 outputs a sine wave PRF1 and a sine wave PRF2 through the generated signal of the crystal oscillator X3 and parameters set by the DDS setting singlechip U1.
In more detail, in the present example, as shown in fig. 2, in the signal generating module 101, the model of the DDS setting single-chip microcomputer U1 is preferably STM32F103, the direct digital frequency synthesizer DDS U2 is preferably a 4-channel, 500MSPS (MSPS is millions of samples per second), 10-bit DACs chip, the crystal oscillator X3 frequency is preferably 25MHz, and the crystal oscillator X1 frequency is 8MHz. After the system is powered on, the radio frequency subsystem 10 starts to work, and after the DDS of the signal generating module 101 sets the singlechip U2 to load the configuration program, parameter configuration is performed on the digital frequency synthesizer DDS U2. The digital frequency synthesizer DDS U2 sets configuration parameters sent by the singlechip U2 according to the DDS, and generates two paths of sine waves by utilizing an externally input crystal oscillator X3 signal, wherein the two paths of sine waves are respectively marked as PRF1 and PRF2, the PRF1 is output through a 13 th pin and a 14 th pin of the digital frequency synthesizer DDS U2, and the PRF2 is output through a 29 th pin and a 30 th pin of the digital frequency synthesizer DDS U2. Therefore, the method for configuring the digital frequency synthesizer through the singlechip is adopted in the embodiment, and a complex FPGA transmitting link is not needed for synchronizing clocks and control logic, so that the structure of the system can be effectively simplified, and the complexity and cost of the system are reduced.
In this embodiment, the sine wave PRF 1/sine wave PRF2 output by the signal generating module 101 (DDS) is shaped into a square wave after passing through an amplifier, where the amplifier includes a first amplifier U40, a second amplifier U41, and a third amplifier U42, and a schmitt trigger formed by an operational amplifier can shape the sine wave into a square wave; and then as inputs to a subsequent gaussian pulse shaping circuit comprising a first gaussian pulse shaping circuit U50, a second gaussian pulse shaping circuit U51 and a third gaussian pulse shaping circuit U52.
In more detail, as shown in fig. 3, in this embodiment, the rf transformer U10 preferably uses balun devices, and preferred parameters are: the frequency is 0.3-300 MHz, the amplitude balance is +/-0.15- +/-0.3 dB, the phase balance is 1-2 degrees, the insertion loss is 0.27-2.18 dB, and the current is 30 mA. The preferred parameters of the power divider U20 are: the frequency range is 5MHz to 1GHz. The delay line U30 is a fixed-length delay line. The preferred parameters of the first amplifier U40 and the second amplifier U41 are: -3db bandwidth is 260mhz, gbp gain bandwidth product is 1GHz, output current is 120mA. The first gaussian pulse shaping circuit U50 and the second gaussian pulse shaping circuit U51 in this embodiment use gaussian pulse generating modules based on step recovery diodes SRD. The radio frequency transformer U60 is a balun device, and preferred parameters are: the frequency is 10-4000 MHz, the amplitude balance is +/-0.5 dB, the phase balance is 7 degrees, the insertion loss is 0.27-2.18 dB, and the current is 30 mA.
As shown in fig. 3, the sine wave PRF1 output by the signal generating module 101 is a double-ended signal, the rf transformer U10 converts the double-ended signal into a single-ended signal, the single-ended signal is equally divided after being sent to the power divider U20 and sent to two branches respectively, wherein one branch sequentially passes through the delay line U30, the first amplifier U40 and the first gaussian pulse shaping circuit U50 to generate a first gaussian pulse; the other branch sequentially passes through a second amplifier U41 and a second Gaussian pulse shaping circuit U51 to generate a second Gaussian pulse; the first gaussian pulse and the second gaussian pulse are input into the radio frequency transformer U60 to be synthesized into a first-order gaussian pulse, and then the signal is transmitted through the transmitting antenna of the antenna module 104.
More specifically, as shown in fig. 4, in this embodiment, the rf transformer U11 is also preferably a balun device, and the preferred parameters are consistent with those of the rf transformer U10. The preferred parameters of the mixer U70 are: the frequency range is 5-3500 MHz, the typical conversion loss is 6.9dB, the typical L-R isolation is 33dB, and the typical L-I isolation is 28dB. U80 is a low noise amplifier LNA with an input noise of 1 nV-Output noise 45 nV/->The ac common mode rejection ratio CMRR was 80dB. The third amplifier U42 is a broadband amplifier, and preferred parameters are consistent with the first amplifier U40 and the second amplifier U41. The first gaussian pulse shaping circuit U50, the second gaussian pulse shaping circuit U51 and the third gaussian pulse shaping circuit U52 preferably use gaussian pulse generating modules based on step recovery diodes SRD for outputting gaussian pulse signals.
As shown in fig. 4, the sine wave PRF2 output by the signal generating module 101 is a double-ended signal, the rf transformer U11 converts the double-ended signal into a single-ended signal, the single-ended signal is sent to the third amplifier U42 to amplify the signal, the amplified signal is sent to the third gaussian pulse shaping circuit U52, and the signal is shaped into a third gaussian pulse, and the third gaussian pulse is used as a local oscillation reference input signal of the mixer U70; the receiving antenna of the antenna module 104 takes the received radio frequency signal as the radio frequency input of the mixer U70; the mixer U70 outputs the integrated intermediate frequency signal, and the signal is amplified by the U80 low noise amplifier LNA and then sent to the main control subsystem 20.
As shown in fig. 1, the main control subsystem 20 includes a fully programmable system on chip 201, an encoder interface and an analog-to-digital converter ADC, where the fully programmable system on chip 201 is connected to the encoder interface and the analog-to-digital converter ADC, respectively, and the fully programmable system on chip 201 is connected to the upper computer subsystem 30, and the analog-to-digital converter ADC is connected to the signal receiving module 103. The encoder interface is a rotary photoelectric encoder interface and is used for realizing distance triggering of the ground penetrating radar, and the ABZ three-phase output is respectively connected to the IO ports corresponding to the FPGA on the chip through the bus transceiver and realizes distance triggering through internal logic.
The fully programmable system on chip 201 refers to All Programmable SoC, as shown in fig. 1, the fully programmable system on chip 201 includes two components of an FPGA and an ARM on chip, namely a dual-core ARM Cortex-A9 processor and a conventional Field Programmable Gate Array (FPGA) logic component; the signal receiving module 103 outputs a signal to the analog-to-digital converter ADC, and the analog-to-digital converter ADC converts the received signal into a digital signal and inputs the digital signal to the FPGA component of the fully programmable system-on-chip 201, and after the data processing in the FPGA component, the data processing result is uploaded to the ARM end for buffering.
In this embodiment, the fully programmable system on a chip 201 preferably combines a dual core ARM Cortex-A9 processor with a conventional Field Programmable Gate Array (FPGA) logic component. It should be noted that, the FPGA component of the fully programmable system on chip 201 in this embodiment is mainly used for performing conventional processing in the field of ground penetrating radar for peak searching and superposition of data, and the FPGA does not need to perform complex logic control and software and hardware clock synchronization operation, so that the complexity of the system can be obviously reduced, and the system structure is effectively simplified.
As shown in fig. 1, in the step A2, the calculation formula of the first-order gaussian pulse generation process is as follows:the method comprises the steps of carrying out a first treatment on the surface of the Wherein (1)>Is a first order Gaussian pulse->For the first Gaussian pulse +.>Is a second gaussian pulse; first Gaussian pulse->The calculation formula of (2) is->Second Gaussian pulse->The calculation formula of (2) is: />A is amplitude, < >>Is the point in time at which the peak of the gaussian pulse is located, < + >>Is the current time, σ is the standard deviation, ω is the first Gaussian pulse +.>And a second Gaussian pulse->ϕ is the initial phase.
As shown in fig. 1, the calculation formula for generating the third gaussian pulse in the step A3 is as follows:，/>is the angular frequency of the third gaussian pulse.
The first gaussian pulse shaping circuit U50 adopts a gaussian pulse generating module based on a step recovery diode SRD, as shown in fig. 5, and the circuit includes an inductor L1, an inductor L2, a step recovery diode SRD1, a step recovery diode SRD2, a schottky diode D1, a resistor R2 and a resistor R3, a square wave signal output by a sine wave PRF1 after passing through an amplifier is input from a Vin terminal, and the Vout terminal outputs a first gaussian pulse. The circuit principle is as follows: an inductor L2 and a resistor R1 are used as bias circuits of the step recovery diode SRD1 and the step recovery diode SRD 2; the step recovery diode SRD1 is used as a bias circuit of the step recovery diode SRD2 and the resistor R2; when a positive pulse is input at the Vin end, a reverse bias voltage is provided for the step recovery diode SRD1, and due to the reverse conduction characteristic of the step recovery diode: when the diode in the conducting state suddenly adds reverse voltage, the instant reverse current reaches the maximum value immediately, and maintains for a certain time, and then immediately returns to zero. During this period, the step recovery diode SRD1 generates a sharp positive pulse, and this positive pulse then enters the step recovery diode SRD2, causing the step recovery diode SRD2 to reverse bias, and the reverse bias current generated by the step recovery diode SRD2 passes through the resistor R2, which may generate a gaussian pulse with a picosecond pulse width.
According to the embodiment, the picosecond-level first-order Gaussian pulse is transmitted, the picosecond-level pulse signal is expanded to be millisecond-level by using a time expansion framework, and on the basis, sampling is completed by using a low-speed analog-to-digital converter, and a detection result is displayed on an upper computer after signal processing is completed by the FPGA.
In the embodiment, the calculation formula of the vertical resolution of the ultra-wideband pulse type ground penetrating radar is calculated. Wherein the wave speed of the medium->Press->Calculation of->For the pulse width of the ground penetrating radar, the pulse width output by Vout is 160 picoseconds by adjusting circuit device parameters, and the definition of ultra-wideband signals is met; according to the calculation formula, the resolution of the ground penetrating radar is 8 mm, and the resolution requirement of the centimeter level can be obviously met.
As shown in fig. 1, the first gaussian pulse shaping circuit U50, the second gaussian pulse shaping circuit U51, and the third gaussian pulse shaping circuit U52 according to the present embodiment have the same circuit configuration. Wherein the first Gaussian pulse generated by the first Gaussian pulse shaping circuit U50Second gaussian pulse +.>The phase difference is generated by delayThe line U30 is adjusted, in this embodiment the delay line U30 is a coaxial cable, and the length of the coaxial cable is adjusted to change the first Gaussian pulse +.>And a second Gaussian pulse->Phase difference between them until +.>And->Is a calculation formula of (2). As shown in fig. 6, the two gaussian pulses, i.e., the first gaussian pulse and the second gaussian pulse, are input to the rf transformer U60 to be synthesized into a first-order gaussian pulse, and the first-order gaussian single pulse synthesized and output by the two gaussian pulses has the characteristic of high power.
The synthetic schematic diagram of the first order Gaussian pulse according to this embodiment is shown in FIG. 6, in which the first Gaussian pulse generated by the first Gaussian pulse shaping circuit U50 is controlled by adjusting the coaxial cable length of the delay line U30Delay is generated relative to the second Gaussian pulse generated by the second Gaussian pulse shaping circuit U51>The phase difference is generated, and the length of the delay line U30 is slowly adjusted to change the phase difference between two Gaussian pulses until the generation of an ideal Gaussian single pulse waveform is detected after the balun device is synthesized. Because the circuit synthesizes two Gaussian pulses into one Gaussian single pulse, the Gaussian single pulse synthesized and output by the two Gaussian pulses has the characteristics of high power and narrow pulse width.
It should be noted that balun devices have reciprocity, i.e. both double-ended and single-ended may be input terminals. When a single-ended input mode is adopted, a single end is an input end, a double end is an output end, and two signals with 180 degrees of phases and consistent amplitude are output by the double end of an ideal balun device; when a double-end input mode is adopted, the double end is an input end, the single end is an output end, and an ideal balun device firstly turns one of the phases of the double end 180 degrees and then overlaps with the other signal which is not subjected to phase turning, and then realizes output; the double-ended input mode is actually the inverse of the single-ended input mode. In the present embodiment, the principle of the double-ended input method is used. The model number of the balun device described in this embodiment is preferably TCM2-43x+.
Thus, the present embodiment adjusts the coaxial cable length of the delay line U30 in real time to achieve the first gaussian pulseAnd a second Gaussian pulse->The length of the coaxial cable can be adjusted in real time by controlling the phase difference, the self-defining setting can be carried out according to actual conditions and requirements, and the waveform output by the balun device correspondingly is recorded at the same time until the output waveform meets the preset Gaussian monopulse waveform requirement, namely, until the Gaussian monopulse waveform shown in figure 6 is output by the balun device; the preset requirements of the Gaussian monopulse waveform can also be set and adjusted in a self-defined mode according to actual situations/requirements.
As shown in fig. 1 and 4, in the step A3, the spreading factor EF of the integrated intermediate frequency signal output by the mixer U70 has the following calculation formula:wherein->Outputting the frequency of the generated sine wave PRF1 for the signal generating module 101, +.>The frequency of the generated sine wave PRF2 is output to the signal generating module 101.
It should be noted that, in this embodiment, the first Gaussian pulseAnd a second Gaussian pulse->The angular frequencies of (2) are uniform, 10MHz by default, and the phase difference between the two is used to synthesize a first order gaussian pulse. Third Gaussian pulse->Is 9.9995MHz for use as a reference input signal for a Local Oscillator (LO). />=10MHz、/>= 9.99995MHz, so the spreading factor of the intermediate frequency signal。
Therefore, the architecture of the time expansion technology is utilized in this embodiment, two paths of signals with small frequency differences are input to the mixer U70 at the signal receiving module 103, namely, a radar echo signal with small frequency differences and a reference input signal of a Local Oscillator (LO) are input, the radar echo signal refers to a received radio frequency signal, and a difference frequency signal left after an intermediate frequency signal output by the mixer U70 passes through a low-pass filter is an echo signal after the time expansion, so that the conversion from a high frequency signal to a low frequency signal is realized, the purpose of expanding picosecond gaussian pulses into millisecond gaussian pulses without losing information is achieved, a centimeter-level ultra-wideband ground penetrating radar system based on the time expansion architecture is realized, and the high frequency signal can be sampled by using a lower-speed analog-to-digital converter ADC.
In summary, the embodiment provides a centimeter-level ultra-wideband ground penetrating radar system based on a time expansion architecture, which has picosecond-level gaussian pulse and centimeter-level resolution, and can convert the high-frequency signal of the picosecond-level gaussian pulse into a low-frequency signal, so that a low-speed analog-to-digital converter ADC can be used for sampling the high-frequency signal; on the basis, the structure of the system is effectively simplified and the complexity and cost of the system are reduced by further optimizing the system architecture and the working process of the system, and the system can be widely applied to the aspects of road pavement detection, flaw detection, detection of various shallow concrete structures and the like.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (10)
1. A centimeter-level ultra-wideband ground penetrating radar system based on a time-extended architecture, comprising: the system comprises a radio frequency subsystem, a main control subsystem and an upper computer subsystem, wherein the main control subsystem is respectively connected with the radio frequency subsystem and the upper computer subsystem; the radio frequency subsystem comprises a signal generation module, a signal emission module, a signal receiving module and an antenna module, wherein the signal generation module is respectively connected with the signal emission module and the signal receiving module, the antenna module is respectively connected with the signal emission module and the signal receiving module, and the signal receiving module is connected with the main control subsystem; the signal transmitting module comprises a power distributor, a delay line, a first amplifier, a second amplifier, a first Gaussian pulse shaping circuit, a second Gaussian pulse shaping circuit and a radio frequency transformer; the signal receiving module comprises a third amplifier, a third Gaussian pulse shaping circuit and a mixer; the first Gaussian pulse shaping circuit, the second Gaussian pulse shaping circuit and the third Gaussian pulse shaping circuit have the same circuit structure;
the working process of the centimeter-level ultra-wideband ground penetrating radar system comprises the following steps of:
a1, after a system is electrified, the radio frequency subsystem starts to work, and the signal generation module outputs and generates a sine wave PRF1 and a sine wave PRF2;
step A2, the sine wave PRF1 is sent to the power divider, the power divider equally divides signals and sends the signals to two branches, and one branch sequentially passes through the delay line, the first amplifier and the first Gaussian pulse shaping circuit and then generates first Gaussian pulses; the other branch sequentially passes through a second amplifier and a second Gaussian pulse shaping circuit to generate a second Gaussian pulse; the first Gaussian pulse and the second Gaussian pulse are input to a radio frequency transformer to be synthesized into first-order Gaussian pulses, and the first Gaussian pulses and the second Gaussian pulses are transmitted through an antenna module;
step A3, the signal receiving module receives the signal of the antenna module as the radio frequency input of the mixer; the sine wave PRF2 sequentially passes through the third amplifier and the third Gaussian pulse shaping circuit to generate a third Gaussian pulse, and the third Gaussian pulse is used as a local oscillation reference input signal of the mixer; the mixer outputs the integrated intermediate frequency signal to the main control subsystem;
step A4, the main control subsystem converts the received intermediate frequency signal into a digital signal, and caches the digital signal after data processing;
step A5, the upper computer subsystem establishes network connection with the main control subsystem, and periodically issues a collection command to the main control subsystem; and the main control subsystem reports data to the upper computer subsystem and displays radar images after the data processing of the upper computer subsystem.
2. The centimeter-level ultra-wideband ground penetrating radar system based on the time expansion architecture according to claim 1, wherein the signal generating module comprises a DDS setting single-chip microcomputer, a direct digital frequency synthesizer DDS and a crystal oscillator, and the direct digital frequency synthesizer DDS is respectively connected with the DDS setting single-chip microcomputer and the crystal oscillator.
3. The centimeter-level ultra-wideband ground penetrating radar system based on the time expansion architecture according to claim 2, wherein the direct digital frequency synthesizer DDS outputs sine waves PRF1 and PRF2 through the generated signals of the crystal oscillator and parameters set by a DDS setting singlechip.
4. The cm-level ultra-wideband ground penetrating radar system based on a time expansion architecture according to claim 3, wherein the main control subsystem comprises a fully programmable system-on-chip, an encoder interface and an analog-to-digital converter (ADC), the fully programmable system-on-chip is respectively connected with the encoder interface and the ADC, the fully programmable system-on-chip is connected with the upper computer subsystem, and the ADC is connected with the signal receiving module.
5. The time-extended architecture-based centimeter-level ultra-wideband ground penetrating radar system of claim 4, wherein the fully programmable system-on-a-chip comprises two components, FPGA and ARM; the signal receiving module outputs signals to the analog-to-digital converter ADC, the analog-to-digital converter ADC converts the received signals into digital signals and inputs the digital signals into an FPGA component of the fully programmable system-on-chip, and after data processing in the FPGA component, data processing results are uploaded to the ARM end for caching.
6. The time-extended architecture-based centimeter-level ultra-wideband ground penetrating radar system according to any one of claims 1 to 5, wherein in the step A2, the calculation formula of the first-order gaussian pulse generation process is:the method comprises the steps of carrying out a first treatment on the surface of the Wherein (1)>Is a first order Gaussian pulse->For the first Gaussian pulse +.>Is a second gaussian pulse; first Gaussian pulse->The calculation formula of (2) is->Second Gaussian pulse->The calculation formula of (2) is: />A is amplitude, < >>Is the point in time at which the peak of the gaussian pulse is located, < + >>Is the current time, σ is the standard deviation, ω is the angular frequency of the first gaussian pulse and the second gaussian pulse, and ϕ is the initial phase.
7. The time-extended architecture-based centimeter-level ultra-wideband ground penetrating radar system of claim 6, wherein the first gaussian pulse calculation formulaAnd the calculation formula of said second gaussian pulse +.>The phase difference between them is adjusted by the delay line.
8. The time-extended architecture-based centimeter-level ultra-wideband ground penetrating radar system of claim 7, wherein the delay line is a coaxial cable, and the phase difference between the first gaussian pulse and the second gaussian pulse is adjusted by adjusting a length of the coaxial cable.
9. According to claimThe time-expansion-architecture-based centimeter-level ultra-wideband ground penetrating radar system of claim 6, wherein the calculation formula for generating the third gaussian pulse in the step A3 is as follows:，is the angular frequency of the third gaussian pulse.
10. The time-spread architecture-based centimeter-level ultra-wideband ground penetrating radar system according to claim 6, wherein in the step A3, a spread factor EF calculation formula of the integrated intermediate frequency signal output by the mixer is:wherein->The frequency of the generated sine wave PRF1 is output for the signal generating module,the frequency of the generated sine wave PRF2 is output for the signal generating module.
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