TW201439575A - FMCW radar level meter and signal traceback and phase-locking method thereof - Google Patents

Abstract

The invention is a frequency modulated continuous waves (FMCW) radar level meter and a signal traceback and phase-locking method thereof. It comprises a high-frequency signal module, a low-frequency signal processing module and an operation and display module which are sequentially-connected. A signal generator of the high-frequency signal module generates a first high-frequency signal, which is transmitted to a substance under test from an antenna. The substance under test reflects a second high-frequency signal different from the first high-frequency signal. The Antenna receives the reflected second high-frequency signal. Then the second high-frequency signal is processed by the low-frequency signal processing module. The second high-frequency signal is compared with the first high-frequency signal. The distance is computed and displayed by the operation and display module. Thereby, the second high-frequency signal is processed by the high-frequency signal module and the low-frequency signal processing module for solving the problem of noise of the radar level meter and temperature coefficient drift.

Description

FMCW radar level gauge and its signal traceability and phase locking method

The invention relates to an FMCW radar level gauge, in particular to an FMCW radar level gauge with signal traceability and phase locking.

Recently, industrial development has become more and more technological and precise. In order to monitor the level of materials in storage tanks or measure open space, such as the water level of rivers or reservoirs and the material level of mines, it has been developed and utilized. The antenna transmits a high frequency (GHz level) electromagnetic wave to detect the distance or material level of the FMCW radar level gauge. The FMCW radar level gauge is mainly composed of a microwave transceiver circuit and an antenna, which utilizes FMCW (Frequency Modulated Continuous). Waves) signal modulation method, the FMCW radar level gauge sends a transmission signal, and the received signal is reflected by the test substance, and the FMCW radar level is calculated by detecting the frequency difference between the transmitted signal and the reflected received signal. Calculate the distance from the object to be tested or convert it to the material level.

The microwave transceiver circuit of the FMCW radar level meter generates a first high frequency signal by a high frequency oscillator (Oscillator), and the first high frequency signal is transmitted through a phase locked loop (PLL) to the substance to be tested through the antenna. The substance to be tested reflects the first high frequency signal and is the second high frequency signal, FMCW The radar level gauge receives the second high frequency signal from the antenna and obtains the intermediate frequency signal by obtaining the frequency difference between the first high frequency signal and the first high frequency signal, and the intermediate frequency signal is calculated to obtain the FMCW radar level meter. The distance from the substance to be tested.

Since the oscillator, the phase-locked loop and the mixer in the microwave transceiver circuit are small in size and operate at high frequencies, they are susceptible to external noise interference and temperature changes, and have problems of noise and temperature coefficient drift.

As mentioned above, the existing FMCW radar level gauge oscillator, phase-locked loop and mixer system work at high frequency, which is susceptible to external interference and temperature changes, and has problems of noise and temperature coefficient drift. Therefore, the main purpose of the present invention is to provide an FMCW radar level gauge and a signal tracing and phase locking method thereof, which is characterized in that the signal reflected by the material to be tested is band-pass filtered, and then the intermediate frequency signal is compared with the original transmitted signal to obtain the intermediate frequency signal, and then Low-frequency DC blocking can solve the problem of noise and temperature coefficient drift of existing radar level gauges.

The main technical means adopted to achieve the foregoing objectives is that the FMCW radar level gauge includes: a high frequency signal module including a signal generator, a signal coupler, a low noise amplifier, and a band pass filter. And a mixer, the signal coupler includes a TX signal terminal, an RX signal terminal, an RF signal terminal and an LO signal terminal, and the TX signal terminal is electrically connected to the signal generator The RX signal end is electrically connected to the low noise amplifier, and the RF signal end is connected to an RF connector to be connected to an external antenna. The low noise amplifier is electrically connected to the band pass filter. The mixer is electrically connected. An RX input terminal, an LO input terminal and an IF output terminal are electrically connected to the band pass filter, and the LO input terminal is electrically connected to the LO signal end of the signal coupler; a low frequency signal processing mode The group includes a DC blocker, a band rejection filter and a power amplifier electrically connected to the IF output of the mixer, the band rejection filter being electrically connected to the DC blocker, the power amplifier Electrically coupled to the rejection filter; and an arithmetic and display module including a analog/digital converter, a microcontroller, and a display electrically coupled to the power amplifier, the micro control The devices are electrically connected to the analog digital converter and the display, respectively.

The main technical means adopted to achieve the above objectives is the signal traceability and phase locking method of the FMCW radar level gauge. The FMCW radar level gauge performs the following steps: transmitting a first high frequency signal to a substance to be tested. Receiving a second high frequency signal different from the first high frequency signal by the reflection of the material to be tested; performing signal amplification and band pass filtering on the second high frequency signal, and mixing with the first high frequency signal to obtain the same IF signal with a frequency difference; low-frequency noise blocking the IF signal and after power amplification, The distance of the substance to be tested represented by the intermediate frequency signal.

Using the FMCW radar level gauge composed of the foregoing components, the first high frequency signal is generated by the signal generator of the high frequency signal module, and the first high frequency signal is sent to the TX signal end of the signal coupler, the signal coupler The first high frequency signal is sent to the LO signal end and the RF signal end respectively, and the first high frequency signal of the RF signal end is transmitted to the test object through the antenna through the RF connector, and the first high frequency signal is to be tested. After the material is reflected, it is the second high frequency signal of different frequencies, the antenna receives the second high frequency signal reflected by the antenna, and then the second high frequency signal reflected by the RF signal end is sent from the RX signal end to the low noise amplifier and A bandpass filter filters out the noise and obtains the desired frequency band, which is then sent to the RX input of the mixer. The mixer combines the first high frequency signal at the LO input with the second high frequency signal at the RX input. The difference is converted into an intermediate frequency signal, and then sent from the IF output to the DC blocker to isolate the DC signal. The band rejection filter obtains the frequency band selected by the intermediate frequency signal, and the power amplifier amplifies the signal and sends it to the analog/ Digital converter converts to digital signal, micro control Calculating the distance represented by the signal, and displaying the distance by the display, processing the second high frequency signal by using a band pass filter of the high frequency signal module and a DC blocker and a rejection filter of the low frequency signal processing module With the IF signal, it can solve the problem of noise and temperature coefficient drift of the existing radar level meter.

10‧‧‧High Frequency Signal Module

11‧‧‧Signal Generator

111‧‧‧Oscillator

112‧‧‧ phase-locked loop

12‧‧‧Active Frequency Multiplier

13‧‧‧Signal coupler

14‧‧‧Low noise amplifier

15‧‧‧Bandpass filter

16‧‧‧ Mixer

20‧‧‧Low frequency signal processing module

21‧‧‧DC blocker

22‧‧‧Rejection filter

23‧‧‧Power Amplifier

24‧‧‧Frequency filter

25‧‧‧High frequency filter

30‧‧‧Operation and display module

31‧‧‧ Analog/Digital Converter

32‧‧‧Microcontroller

33‧‧‧ display

40‧‧‧RF connector

50‧‧‧ body

51‧‧‧High frequency circuit board

52‧‧‧Microcontroller Board

53‧‧‧Power circuit board

54‧‧‧Display circuit board

60‧‧‧Integrated circuit board

61‧‧‧First substrate

62‧‧‧second substrate

63‧‧‧ Third substrate

64‧‧‧High frequency circuit metal layer

65‧‧‧High frequency circuit ground plane

66‧‧‧Intermediate frequency circuit ground plane

67‧‧‧Medium frequency circuit metal layer

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a circuit in accordance with a first preferred embodiment of the present invention.

Figure 2 is a cross-sectional view showing a radar level gauge according to a first preferred embodiment of the present invention.

Figure 3 is a partially exploded view of a radar level gauge in accordance with a first preferred embodiment of the present invention.

Figure 4 is a cross-sectional view showing an integrated circuit board in accordance with a first preferred embodiment of the present invention.

Figure 5 is a block diagram of a circuit in accordance with a second preferred embodiment of the present invention.

Referring to FIG. 1 , a high frequency signal module 10 , a low frequency signal processing module 20 and an operation and display module 30 , the high frequency signal module 10. The low frequency signal processing module 20 and the computing and display module 30 are serially connected in sequence.

The high frequency signal module 10 includes a signal generator (OSC & PLL) 11, an active frequency multiplier 12, a signal coupler 13, and a low noise amplifier (LNA: Low Noise Amplifier). 14. A Band Pass Filter 15 and a Mixer 16, the signal generator 11 is electrically connected to the active frequency multiplier 12, and the signal coupler 13 includes a TX signal terminal. An RX signal terminal, an RF signal terminal and an LO signal terminal, the TX signal terminal is electrically connected to the active frequency multiplier 12, and the RX signal terminal is electrically connected to the low noise amplifier 14, and the RF signal terminal is connected. The RF connector 40 is connected to an external antenna (not shown), and the low noise amplifier 14 is electrically connected to the band pass filter 15, and the mixer 16 includes An RX input terminal, an LO input terminal and an IF output terminal are electrically connected to the band pass filter 15, and the LO input terminal is electrically connected to the LO signal end of the signal coupler 13; the signal generator 11 includes an oscillator (OSC) 111 and a phase locked loop (PLL) 112, which is a voltage controlled quartz oscillator (VCXO: Voltage-Controlled Oscillator) or a temperature controlled quartz oscillator (TCXO: Temperature- Controlled Oscillator, the oscillator generator 11 outputs a first high frequency signal by a oscillator (OSC) 111 and a phase locked loop (PLL) 112. The first high frequency signal is a linearly varying sawtooth waveform (Triangularly) or string. Wave (Sine/Cosin); the active frequency multiplier 12 multiplies the frequency of the first high frequency signal outputted by the signal generator 11 by two times, and the signal coupler 13 sends the first high frequency signal to the RF connection. The device 40 and the mixer 16 or the RF connector 40 receives a second high frequency signal to the low noise amplifier 14, the low noise amplifier 14 amplifies the second high frequency signal and is filtered by the band pass. The filter 15 is configured to process the first high frequency signal and the second high frequency signal The frequency difference.

The low frequency signal processing module 20 includes a DC block 21, a Twin-T Notch Filter 22 and a Power Amplifier 23, and the DC blocker 21 is connected to the mixer. The IF output terminal of 16 is electrically connected, and the band rejection filter 22 is electrically connected to the DC blocker 21, and the power amplifier 23 is electrically connected to the band rejection filter 22.

The operation and display module 30 includes an analog/digital converter (A/D converter) 31, a microcontroller (MCU) 32 and a display (D/P: Display) 33. The analog/digital converter 31 is The power amplifier 23 is electrically connected, and the microcontroller 32 is electrically connected to the analog/digital converter 31 and the display 33, respectively.

The FMCW radar level meter generates a first high frequency signal from the signal generator 11 of the high frequency signal module 10, and the frequency is doubled by the active frequency multiplier 12, and then the first high frequency signal is sent. The signal coupler 13 sends the first high frequency signal to the LO signal end and the RF signal end, and the first high frequency signal of the RF signal end passes through the RF connector 40 and is connected to the TX signal end of the signal coupler 13 The antenna is emitted to the substance to be tested, and the first high frequency signal reflects the second high frequency signal of different frequencies after hitting the substance to be tested, and the second high frequency signal is received by the antenna, and the second high frequency is received by the RF signal end. The frequency signal is sent to the low noise amplifier 14 and the band pass filter 15 via the RX signal terminal to filter out the noise and obtain the required frequency band, and then sent to the RX input terminal of the mixer 16, and the mixer 16 inputs the LO input terminal. The frequency difference between the first high frequency signal and the second high frequency signal at the RX input is converted into an intermediate frequency signal, which is then sent from the IF output to the DC blocker 21 to isolate the DC signal. The band rejection filter 22 is Obtaining the frequency band selected by the intermediate frequency signal, and amplifying the signal by the power amplifier 23 and sending it to the analogy The digital converter 31 converts the digital signal into a digital signal, and the microcontroller 32 calculates the distance represented by the digital signal and displays the distance by the display 33; the band pass filter 15 of the high frequency signal module 10 And the DC blocker 21 and the rejection filter 22 of the low frequency signal processing module 20 filter out the noise of the second high frequency signal and the intermediate frequency signal and compensate the temperature coefficient drift, thereby solving the noise of the existing radar level meter and The problem of temperature coefficient drift.

Referring to FIGS. 2 and 3, the FMCW radar level gauge of the present invention comprises a body 50 for sequentially stacking a high frequency circuit board (RF PCB) 51 and a microcontroller circuit board (MCU). A high-voltage circuit module 51 and a low-frequency signal processing module 20 are provided for the high-frequency circuit board 51 and a display circuit board 54. An RF connector 40 is provided for the analog/digital converter 31 and the microcontroller 32 of the computing and display module 30. The power circuit board 53 is provided with a power supply circuit. The display circuit The board 54 is provided with the display 33 of the computing and display module 30; the microcontroller circuit board 52 is interposed between the high frequency circuit board 51 and the power circuit board 53, and can be used as a barrier shield to reduce the power circuit board 53. The power source radiates interference with the frequency signal in the high frequency circuit board 51, and can reduce the distance that the control signal of the microcontroller circuit board 52 is transmitted to the high frequency circuit board 51, so that the transmission is shortest and the loss is the lowest.

Referring to FIG. 4, the present invention further provides an integrated circuit board 60 which integrates the aforementioned high frequency circuit board (RF PCB) 51, a microcontroller circuit board (MCU PCB) 52, and a power circuit board (POWER PCB). 53 in the same circuit board, the integrated circuit board 60 includes a sequentially stacked one a first substrate (Core Layer) 62, a second substrate (Core Layer 2) 62 and a third substrate (Core Layer 3) 63. The surface of the first substrate 61 is provided with a high frequency circuit metal layer (RF) 64 for connection. The components of the high-frequency signal module 10 are as shown in the mixer 16; a high-frequency circuit ground layer (RF GND) 65 is interposed between the first substrate 61 and the second substrate 62 to provide a high-frequency signal. Grounding of each component of the module 10; an intermediate frequency circuit ground layer (IF GND) 66 is interposed between the second substrate 62 and the third substrate 63 to provide grounding of each component of the low frequency signal processing module 20; The bottom surface of the three substrate 63 is provided with an intermediate frequency circuit metal layer (IF Power) 67 for connecting the power supply circuit and the components of the low frequency signal processing module 20, such as the DC blocker 21 shown in the figure; the high frequency circuit metal layer 64 A plurality of micro strips are disposed in the metal layer 67 of the intermediate frequency circuit; the components of the surface of the first substrate 61 and the bottom surface of the third substrate 63, the microstrip lines, and the metal layers are connected through the filling holes or the blind holes. .

Referring to FIG. 5, the low frequency signal processing module 20 further includes a low frequency filter 24 and a high frequency filter 25 connected in series, the low frequency filter. The 24 series is electrically connected to the rejection filter 22, and the high frequency filter 25 is electrically connected to the power amplifier 23. The intermediate frequency signal outputted by the rejection filter 22 is further filtered through the low frequency filter 24 and the high frequency filter 25. In addition to noise and temperature coefficient compensation, the problem of the second high frequency signal and the intermediate frequency signal being affected by external noise and temperature can be reduced.

10‧‧‧High Frequency Signal Module

11‧‧‧Signal Generator

111‧‧‧Oscillator

112‧‧‧ phase-locked loop

12‧‧‧Active Frequency Multiplier

13‧‧‧Signal coupler

14‧‧‧Low noise amplifier

15‧‧‧Bandpass filter

16‧‧‧ Mixer

20‧‧‧Low frequency signal processing module

21‧‧‧DC blocker

22‧‧‧Rejection filter

23‧‧‧Power Amplifier

30‧‧‧Operation and display module

31‧‧‧ Analog/Digital Converter

32‧‧‧Microcontroller

33‧‧‧ display

40‧‧‧RF connector

Claims (9)

An FMCW radar level gauge includes: a high frequency signal module including a signal generator, a signal coupler, a low noise amplifier, a band pass filter and a mixer, the signal coupler comprising There is a TX signal end, an RX signal end, an RF signal end and an LO signal end. The TX signal end is electrically connected to the signal generator, and the RX signal end is electrically connected to the low noise amplifier, and the RF signal end is connected. Connected to an RF connector for connection to an external antenna, the low noise amplifier is electrically connected to a band pass filter, the mixer includes an RX input, an LO input and an IF output, the RX input The end system is electrically connected to the band pass filter, and the LO input end is electrically connected to the LO signal end of the signal coupler; and the low frequency signal processing module comprises a DC blocker, a band rejection filter and a power amplifier, The DC blocker is electrically connected to the IF output of the mixer, the band rejection filter is electrically connected to the DC blocker, the power amplifier is electrically connected to the band rejection filter; and an operation and display module includes There is a kind of ratio/number Converter, a microcontroller and a display, such ratio / digital converter system and the power amplifier electrically connected to the microcontroller are connected to the analog to digital converter and a display electrically. The FMCW radar level gauge according to claim 1, wherein the low frequency signal processing module further comprises a low frequency filter serially connected between the band rejection filter and the power amplifier. The FMCW radar level gauge according to claim 2, wherein the low frequency signal processing module further comprises a high frequency filter, the high frequency filter string Connected between the low frequency filter and the power amplifier. The FMCW radar level gauge according to claim 3, wherein the signal generator comprises an oscillator and a phase locked loop, the oscillator being a voltage controlled quartz oscillator (VCXO) or a temperature controlled quartz oscillator (TCXO). . The FMCW radar level gauge according to claim 4, wherein the signal generator outputs a linearly varying sawtooth waveform or a sine wave (Sine/Cosin). The FMCW radar level gauge according to any one of claims 1 to 5, comprising a body for sequentially stacking a high frequency circuit board (RF PCB) and a microcontroller circuit board (MCU) PCB), a power circuit board (POWER PCB) and a display (Display PCB), the high frequency circuit board is provided with a high frequency signal module and a low frequency signal processing module and an RF connector, the microcontroller circuit board setting An analog/digital converter of an arithmetic and display module, and a microcontroller, wherein the power circuit board is provided with a power supply circuit, the display circuit board is a display for setting an operation and display module, and the high frequency circuit board and the power circuit board The microcontroller circuit board is interposed. The FMCW radar level gauge according to any one of claims 1 to 5, comprising a body, the system for accommodating an integrated circuit board, the integrated circuit board comprising a first layer a substrate, a second substrate and a third substrate, the first substrate surface is provided with a high frequency circuit metal layer (RF components) for connecting the high frequency signal module, and the first substrate and the second substrate are interposed There is a high frequency circuit ground plane (RF GND), an intermediate frequency circuit ground layer (IF GND) is interposed between the second substrate and the third substrate, and an intermediate frequency circuit metal layer (IF Power) is disposed on the bottom surface of the third substrate. , the power circuit and the low frequency signal processing module for connecting the first substrate surface and the first Each element or a plurality of microstrip lines or metal layers of the bottom surface of the three substrates are connected through a filling hole or a blind hole. The FMCW radar level gauge according to claim 6, comprising a body, the system for accommodating an integrated circuit board, the integrated circuit board comprising a first substrate and a second stacked in sequence a substrate and a third substrate, wherein a surface of the first substrate is provided with a high frequency circuit metal layer (RF) for connecting the high frequency signal module, and a high frequency circuit ground layer is sandwiched between the first substrate and the second substrate (RF GND), an intermediate frequency circuit ground layer (IF GND) is interposed between the second substrate and the third substrate, and an IF Power metal layer (IF Power) is disposed on the bottom surface of the third substrate for connecting The power circuit and the low-frequency signal processing module, the components of the first substrate surface and the bottom surface of the third substrate or the plurality of microstrip lines or the metal layers are connected through the filling holes or the blind holes. A signal tracking and phase locking method for a FMCW radar level gauge is performed by an FMCW radar level gauge performing the following steps: transmitting a first high frequency signal to a substance to be tested, and receiving one of the reflections of the substance to be tested a second high frequency signal having a different high frequency signal; after performing signal amplification and band pass filtering on the second high frequency signal, mixing with the first high frequency signal to obtain an intermediate frequency signal having a frequency difference; blocking the intermediate frequency signal After the low frequency noise is amplified by power, the distance of the substance to be tested represented by the intermediate frequency signal is calculated.