Transmitter system and ground penetrating radar large-amplitude first-order differential Gaussian pulse forming method

Abstract

The invention discloses a transmitter system which comprises a shielding shell, a trigger signal interface, a power interface, a time delay control interface and an output interface are arranged on the shielding shell, a pulse source circuit board is arranged in the shielding shell, and the power interface supplies power to a circuit on the pulse source circuit board. A trigger shaping circuit, an adjustable delay circuit, two Gaussian pulse generation circuits, a transformer balun circuit and a clipping shaping circuit are arranged on the pulse source circuit board. According to the transmitter system disclosed by the invention, the circuit adopts a module-level design, and subsequent upgrading is convenient. The transformer balun circuit is adopted to carry out positive and negative pulse superposition synthesis, the circuit is simple, and implementation is convenient.

Description

Technical Field

[0001] The invention belongs to the field of underground target detection, and in particular relates to a transmitter system and a method for forming a large-amplitude first-order differential Gaussian pulse of a ground-penetrating radar in the field. Background Art

[0002] A radar transmitter is a device that provides a transmission signal for a radar system. The transmitter generates a radio frequency signal, feeds the antenna, and radiates it into space or underground.

[0003] Unlike continuous wave radar, impulse pulse ground penetrating radar uses carrier-free pulse signals to obtain information, so the design of the transmitted pulse waveform is very important. In applied research, the selection of pulses depends on many factors, including ensuring effective radiation of energy and considering the characteristics of the antenna.

[0004] The classification of ground-penetrating radar antennas is different from that of air-to-air radars. Following international practice, ground-penetrating radar antennas are classified according to the coupling method (i.e., working mode), generally divided into ground-coupled antennas (Ground-Coupled Antenna) and air-coupled antennas (Air-Launched Horn Antenna). Ground-coupled antennas are generally used close to the ground, and the adapted pulse source is generally a Gaussian pulse, the pulse spectrum of which is as follows Figure 1 As shown in the figure, there are many low-frequency components, and most of the low-frequency energy is difficult to be radiated by the antenna; air-coupled antennas can be used without contacting the ground, and are widely used in rapid non-destructive testing applications such as roads, railways, and air-raid shelters in vegetation-covered areas. The pulse source adapted to the air-coupled antenna generally uses a first-order differential Gaussian pulse, which is the first-order derivative of the Gaussian pulse, and its spectrum is as follows Figure 2 As shown, compared with the Gaussian pulse, the pulse has less low-frequency components and concentrated energy, which avoids the generation of oscillation when the low-frequency energy is fed to the antenna and can improve the accuracy of underground target detection.

[0005] The first-order differential Gaussian pulse is usually realized by differentiating the Gaussian pulse, but the differential circuit has a large energy loss and it is difficult to obtain a large-amplitude pulse. When the ground penetrating radar is used in deep-depth detection scenarios, the transmitter power should be increased accordingly, and a large-amplitude first-order differential Gaussian pulse needs to be designed.

[0006] For ground penetrating radar, the first-order differential Gaussian pulse should meet the following requirements: (1) The pulse width meets the system detection resolution requirements; (2) From the pulse time domain waveform, the signal tail amplitude should not be greater than 5% of the main signal; (3) To fully utilize the bandwidth, the signal spectrum should be flat and smooth; (4) To ensure the detection depth, the pulse signal amplitude should be as large as possible. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a transmitter system and a method for forming a large-amplitude first-order differential Gaussian pulse of a ground-penetrating radar, so as to ensure good matching between the transmitter and the antenna within an ultra-wideband range, reduce time-domain tail oscillation, and improve the detection performance of the ground-penetrating radar.

[0008] The present invention adopts the following technical solution: A transmitter system, the improvement of which is as follows: it comprises a shielding shell, a trigger signal interface, a power interface, a delay control interface and an output interface are arranged on the shielding shell, a pulse source circuit board is arranged inside the shielding shell, the power interface supplies power to the circuit on the pulse source circuit board, a trigger shaping circuit, an adjustable delay circuit, two Gaussian pulse generating circuits, a transformer balun circuit and a clipping shaping circuit are arranged on the pulse source circuit board, the trigger shaping circuit is electrically connected to the trigger signal interface, the output of the trigger shaping circuit is divided into two paths, one path is electrically connected to a Gaussian pulse generating circuit, and the other path is electrically connected to another Gaussian pulse generating circuit through the adjustable delay circuit, the adjustable delay circuit is electrically connected to the delay control interface, the output ends of the two Gaussian pulse generating circuits are respectively electrically connected to the positive and negative input ends of the transformer balun circuit, the output end of the transformer balun circuit is electrically connected to the clipping shaping circuit, and the output end of the clipping shaping circuit is electrically connected to the output interface.

[0009] Furthermore, the shielding shell is used as the system ground, the shielding shell and the pulse source circuit board are grounded, and the delay control interface is also grounded.

[0010] Furthermore, the trigger signal interface is in SMA form.

[0011] Furthermore, both Gaussian pulse generating circuits are avalanche circuits, and the charging and discharging circuits of the avalanche circuits are emitter followers.

[0012] Furthermore, the output ends of the two Gaussian pulse generating circuits are electrically connected to the positive and negative input ends of the transformer balun circuit through microstrip lines, respectively, and the impedance of the microstrip lines is 50Ω.

[0013] Furthermore, the balun of the transformer balun circuit is an isolated transformer balun.

[0014] A method for forming a large-amplitude first-order differential Gaussian pulse of a ground penetrating radar uses the above-mentioned transmitter system, and its improvement lies in that: a trigger shaping circuit shapes the received trigger signal, and the shaped signal is divided into two paths, one path is directly sent to a Gaussian pulse generating circuit, and the other path is delayed by an adjustable delay circuit and then sent to another Gaussian pulse generating circuit, and the two Gaussian pulses generated by the two Gaussian pulse generating circuits are respectively sent to the positive and negative input terminals of a transformer balun circuit, and the balun inverts the delayed Gaussian pulse and then superimposes it with the other Gaussian pulse, and outputs a differential Gaussian pulse to a clipping shaping circuit, and the clipping shaping circuit clips and shapes the differential Gaussian pulse and then outputs it.

[0015] Furthermore, the clipping shaping circuit uses a short-circuited clipping line to reduce the pulse tail amplitude, and smoothes the pulse shape through a first-order passive differential circuit.

[0016] Furthermore, the short-circuit clipping line adopts a coaxial line or a microstrip short-circuit line.

[0017] The beneficial effects of the present invention are: The transmitter system disclosed in the present invention adopts a module-level circuit design, which is convenient for subsequent upgrades. A transformer balun circuit is used to perform positive and negative pulse superposition synthesis. The circuit is simple and easy to implement. By changing the Gaussian pulse generation circuit, the amplitude of the differential Gaussian pulse will be increased accordingly. At the same time, when the Gaussian pulse is converted into a first-order differential Gaussian pulse, the energy loss is very small. Most importantly, due to the use of the balun, the broadband matching effect is better, and the amplitude can reach several hundred volts, which basically solves the problem of deep detection of ground penetrating radar. Since the balun can achieve ultra-wideband matching, it is easy to achieve ultra-wideband matching between the transmitter and the antenna, ensuring the time domain characteristics of the transmitted signal.

[0018] The formation method disclosed by the present invention selects a broadband balun for pulse synthesis, which can make full use of the Gaussian pulse power, with small energy loss and high efficiency; the formed first-order differential Gaussian pulse signal has good positive and negative symmetry, a flat and smooth spectrum, and a high utilization rate; by adjusting the Gaussian pulse amplitude, differential Gaussian pulses of different amplitudes can be obtained to adapt to different detection depth requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a Gaussian pulse waveform and spectrum diagram; Figure 2 It is the first-order differential Gaussian pulse waveform and spectrum diagram; Figure 3 It is a schematic diagram of the design of the transmitter system disclosed in the present invention; Figure 4 This is the circuit diagram of the pulse source circuit board; Figure 5 It is the design schematic diagram of the avalanche circuit; Figure 6 This is a graph of the first-order differential Gaussian pulse test results formed by the formation method disclosed in the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] Embodiment 1: This embodiment discloses a transmitter system for ground penetrating radar detection. Figure 3 As shown, it includes a shielding shell, a trigger signal interface, a power interface, a delay control interface and an output interface are arranged on the shielding shell, a pulse source circuit board is arranged in the shielding shell, and the power interface supplies power to the main circuit in series on the pulse source circuit board, such as Figure 4 As shown, a trigger shaping circuit, an adjustable delay circuit, two Gaussian pulse generating circuits, a transformer balun circuit and a clipping shaping circuit are arranged on a pulse source circuit board. The trigger shaping circuit is electrically connected to a trigger signal interface. The output of the trigger shaping circuit is divided into two paths, one path is electrically connected to a Gaussian pulse generating circuit, and the other path is electrically connected to another Gaussian pulse generating circuit through an adjustable delay circuit. The adjustable delay circuit is electrically connected to a delay control interface. The output ends of the two Gaussian pulse generating circuits are electrically connected to the positive and negative input ends of the transformer balun circuit, respectively. The output end of the transformer balun circuit is electrically connected to the clipping shaping circuit, and the output end of the clipping shaping circuit is electrically connected to the output interface.

[0022] The shielding shell is used as the system ground, the shielding shell and the pulse source circuit board are well grounded, and the delay control interface is also well grounded. The trigger signal interface is in SMA form.

[0023] Both Gaussian pulse generating circuits are as follows Figure 5 In the avalanche circuit shown, the transistor has four working areas, namely, the amplification area, the saturation area, the cut-off area, and the avalanche area. The avalanche effect can generate ns-level Gaussian pulses. The avalanche circuit of the present invention has two key points: First, the pulse repetition frequency is an important indicator of pulse-based ground penetrating radar. The higher the repetition frequency, the higher the number of sampling points, and the higher the system operation speed. At the same time, the higher the repetition frequency, the higher the average transmission power. In order to increase the repetition frequency of Gaussian pulses, the charging and discharging circuit of the avalanche circuit is changed to an emitter follower form. According to the transmitter index requirements, the avalanche circuit can choose a multi-stage series connection to increase the amplitude.

[0024] Secondly, the two avalanche circuits are strictly screened to ensure that the amplitude, rising edge and waveform shape of the two Gaussian pulses are basically the same.

[0025] The output ends of the two Gaussian pulse generating circuits are electrically connected to the positive and negative input ends of the transformer balun circuit through microstrip lines, respectively. The impedance of the microstrip lines is 50Ω, which can be realized by designing on a circuit board.

[0026] The balun of the transformer balun circuit is an isolated transformer balun (input and output isolation form), and a transmission line balun cannot be selected.

[0027] This part of the design makes full use of the coupling function of the transformer. The single-ended output result is the difference between the double-ended input signals. Due to the time delay between the two Gaussian pulses, a differential Gaussian pulse is obtained.

[0028] This embodiment also discloses a method for forming a large-amplitude first-order differential Gaussian pulse of a ground-penetrating radar. The above-mentioned transmitter system is used to trigger a shaping circuit to shape the trigger signal sent by the main control subsystem (main control circuit). The shaped signal is divided into two paths, one of which is directly sent to a Gaussian pulse generating circuit, and the other is delayed by an adjustable delay circuit and then sent to another Gaussian pulse generating circuit. The delay control signal sent by the main control subsystem is used to adjust the delay time. The delay time is determined according to the pulse width index to ensure that the positive and negative polarities of the differential Gaussian pulse are smoothly connected, and can also be properly fine-tuned according to actual test results. The two positive Gaussian pulses generated by the two Gaussian pulse generating circuits are respectively sent to the positive and negative input terminals of the transformer balun circuit. The balun inverts the delayed Gaussian pulse and then superimposes it with the other Gaussian pulse to output the differential Gaussian pulse to the clipping shaping circuit. The clipping shaping circuit clips and shapes the differential Gaussian pulse and then outputs it.

[0029] The differential Gaussian pulse generated by the combination will have an uneven waveform and a pulse tail. To solve this problem, the clipping shaping circuit uses a short-circuited clipping line to reduce the pulse tail amplitude and smoothes the pulse shape through a first-order passive differential circuit (series capacitor). The short-circuited clipping line uses a coaxial line or a microstrip short-circuit line designed on the circuit board. The reflection coefficient of the microstrip short-circuit line is -1, and the line length is adjusted according to the pulse width.

[0030] Pulse amplitude adjustment design: By adjusting the avalanche Gaussian pulse amplitude, the differential Gaussian pulse amplitude change can be easily achieved. The Gaussian pulse amplitude adjustment methods mainly include: adjusting the power supply voltage, replacing the avalanche device, adjusting the emitter follower circuit, increasing the number of series stages, etc.

[0031] Pulse width adjustment design: The differential Gaussian pulse width can be adjusted by adjusting the Gaussian pulse width. The Gaussian pulse width adjustment methods mainly include: replacing the avalanche transistor, adjusting the charge and discharge time, etc. At the same time, you can also choose baluns with different bandwidths, or adjust the differential circuit parameters to reduce the output differential Gaussian pulse width.

[0032] The test results of the first-order differential Gaussian pulse formed by the formation method disclosed in the present invention are as follows: Figure 6 shown.

Claims

1. A transmitter system, characterized in that: It comprises a shielding shell, on which a trigger signal interface, a power interface, a delay control interface and an output interface are arranged, a pulse source circuit board is arranged inside the shielding shell, the power interface supplies power to the circuit on the pulse source circuit board, a trigger shaping circuit, an adjustable delay circuit, two Gaussian pulse generating circuits, a transformer balun circuit and a clipping shaping circuit are arranged on the pulse source circuit board, the trigger shaping circuit is electrically connected to the trigger signal interface, the output of the trigger shaping circuit is divided into two paths, one path is electrically connected to a Gaussian pulse generating circuit, and the other path is electrically connected to another Gaussian pulse generating circuit through the adjustable delay circuit, the adjustable delay circuit is electrically connected to the delay control interface, the output ends of the two Gaussian pulse generating circuits are respectively electrically connected to the positive and negative input ends of the transformer balun circuit, the output end of the transformer balun circuit is electrically connected to the clipping shaping circuit, and the output end of the clipping shaping circuit is electrically connected to the output interface.

2. The transmitter system according to claim 1, characterized in that: The shielding shell is used as the system ground, the shielding shell and the pulse source circuit board are grounded, and the delay control interface is also grounded.

3. The transmitter system according to claim 1, characterized in that: The trigger signal interface is in SMA form.

4. The transmitter system according to claim 1, characterized in that: The two Gaussian pulse generating circuits are both avalanche circuits, and the charging and discharging circuits of the avalanche circuits are emitter followers.

5. The transmitter system according to claim 1, characterized in that: The output ends of the two Gaussian pulse generating circuits are electrically connected to the positive and negative input ends of the transformer balun circuit through microstrip lines, respectively, and the impedance of the microstrip lines is 50Ω.

6. The transmitter system according to claim 1, characterized in that: The balun of the transformer balun circuit is an isolated transformer balun.

7. A method for forming a large-amplitude first-order differential Gaussian pulse of a ground penetrating radar, using the transmitter system of claim 1, characterized in that: The trigger shaping circuit shapes the received trigger signal, and the shaped signal is divided into two paths. One path is directly sent to a Gaussian pulse generating circuit, and the other path is delayed by an adjustable delay circuit and then sent to another Gaussian pulse generating circuit. The two Gaussian pulses generated by the two Gaussian pulse generating circuits are respectively sent to the positive and negative input terminals of the transformer balun circuit. The balun inverts the delayed Gaussian pulse and then superimposes it with the other Gaussian pulse to output a differential Gaussian pulse to the clipping shaping circuit, which clips and shapes the differential Gaussian pulse and then outputs it.

8. The method for forming a large-amplitude first-order differential Gaussian pulse of a ground penetrating radar according to claim 7, characterized in that: The clipping shaping circuit uses a short-circuited clipping line to reduce the pulse tail amplitude and smoothes the pulse shape through a first-order passive differential circuit.

9. The method for forming a large-amplitude first-order differential Gaussian pulse of a ground penetrating radar according to claim 8, characterized in that: The short-circuit clipped line uses a coaxial line or a microstrip short-circuit line.

Images