CN110635235B - Millimeter wave MIMO radar antenna and control method thereof - Google Patents

Millimeter wave MIMO radar antenna and control method thereof Download PDF

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CN110635235B
CN110635235B CN201910938332.7A CN201910938332A CN110635235B CN 110635235 B CN110635235 B CN 110635235B CN 201910938332 A CN201910938332 A CN 201910938332A CN 110635235 B CN110635235 B CN 110635235B
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antenna
transmitting
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CN110635235A (en
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王拾玖
程伟
王问
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Nanjing Weitong Electronic Technology Co ltd
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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
    • G01S7/023—Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques
    • 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
    • G01S7/03—Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
    • H01Q1/38—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith formed by a conductive layer on an insulating support
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/50—Structural association of antennas with earthing switches, lead-in devices or lightning protectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00—Antenna arrays or systems
    • H01Q21/0006—Particular feeding systems
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00—Antenna arrays or systems
    • H01Q21/06—Arrays of individually energised antenna units similarly polarised and spaced apart
    • H01Q21/08—Arrays of individually energised antenna units similarly polarised and spaced apart the units being spaced along or adjacent to a rectilinear path
    • H01Q21/12—Parallel arrangements of substantially straight elongated conductive units

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Abstract

A millimeter wave MIMO radar antenna and a control method thereof. The antenna comprises a plurality of groups of transmitting antennas and a plurality of receiving antennas which are sequentially arranged in two rows, wherein each transmitting antenna and each receiving antenna respectively comprise 6 element units connected by a feeder line and an impedance matcher connected to one of the element units by the feeder line. When each transmitting antenna of the antennas transmits the electromagnetic wave signals according to the driving signals, the driving signals can be respectively equivalent to the positions, transmitted by the other transmitting antennas, of the transmitting antennas which transmit the electromagnetic wave signals to transmit the same electromagnetic wave signals, and each equivalent transmitting antenna is respectively corresponding to a plurality of equivalent receiving antennas. Therefore, the invention utilizes the equivalence of the antennas, can multiply the number of the receiving antennas under the smaller size, improves the performance indexes of the system such as angle measurement precision, clutter rejection ratio and the like, and equivalently multiplies the collocation of the signal quality under the condition of not increasing the transmitting power and the area of the antennas.

Description

Millimeter wave MIMO radar antenna and control method thereof
Technical Field
The invention relates to the technical field of microwave communication, in particular to a millimeter wave MIMO radar antenna and a control method thereof.
Background
The MIMO (Multiple-Input Multiple-Output) technology is to use Multiple transmitting antennas and Multiple receiving antennas at a transmitting end and a receiving end, respectively, so that signals are transmitted and received through the Multiple antennas at the transmitting end and the receiving end, thereby improving signal quality. The antenna can make full use of space resources, realize multiple sending and multiple receiving through a plurality of antennas, and improve the signal quality by times under the condition of not increasing the transmitting power of the antennas.
However, since the MIMO antenna is essentially a multi-antenna technology, it inevitably has a problem that an antenna occupation area is large. The excessive antenna area compresses the space available for other circuit elements, and increases the antenna manufacturing cost.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the millimeter wave MIMO radar antenna and the control method thereof, the antenna can have high performance in a smaller size range, and the angle measurement precision and the clutter suppression ratio of the system are improved. The invention specifically adopts the following technical scheme.
First, in order to achieve the above object, a millimeter wave MIMO radar antenna is provided, which is disposed on a surface of a dielectric plate, and includes: the transmitting antennas comprise at least 1 group, each group of transmitting antennas comprises at least 2 transmitting antennas, the transmitting antennas are arranged on the upper surface of the dielectric plate in parallel along a first direction, and the distance D between the transmitting antennas in each group is smaller than the distance D between the transmitting antennas in each group; the receiving antennas comprise at least 2 receiving antennas which are arranged on the upper surface of the dielectric plate in parallel along a first direction, the receiving antennas and the transmitting antennas are arranged in two rows, the distances among the receiving antennas are equal, the distances among the receiving antennas are in the range from D to D, and the distances among the receiving antennas are integral multiples of half-wavelength; wherein each of the transmitting antennas or each of the receiving antennas includes: the number of the vibrator units is 6, the vibrator units are arranged at equal intervals along the second direction, and the sizes of the 6 vibrator units are gradually reduced from the middle to two sides; the feeder line is sequentially connected with the 6 oscillator units and is used for feeding electric signals to the 6 oscillator units in-phase and serial; and the impedance matcher is connected with the outer side of one oscillator unit arranged at the outermost edge of the 6 oscillator units, is of a micro-strip line structure provided with multiple stages of steps with different widths, and matches the impedance of the transmitting antenna or the receiving antenna to 50 ohms.
Optionally, in the millimeter wave MIMO radar antenna, the first direction is parallel to a length direction of a dielectric plate disposed on the millimeter wave MIMO radar antenna; the first direction is parallel to the width direction of a dielectric plate arranged on the millimeter wave MIMO radar antenna; the transmitting antenna and the receiving antenna are symmetrically arranged along a central axis parallel to the width direction of the dielectric plate respectively.
Alternatively, the aboveThe millimeter wave MIMO radar antenna comprises millimeter wave MIMO radar antennas, wherein each transmitting antenna sequentially transmits frequency modulation continuous waves with linearly changing frequencies at fixed time intervals along the first direction; wherein the time interval of transmitting signals between the transmitting antennas is a fixed time
Figure BDA0002222188500000021
Wherein v ismaxRepresenting the maximum measurement speed, fzRepresenting a carrier frequency of the transmit antenna; slope of said frequency linear variation
Figure BDA0002222188500000022
Wherein R ismaxDenotes the maximum measured distance, c denotes the speed of light, fsampleRepresenting the sampling frequency, fsampleIs a set value; when each frequency modulation continuous wave is sampled, sampling is carried out after the frequency modulation continuous wave waits for a sampling waiting time after the frequency modulation continuous wave starts.
Optionally, in the millimeter wave MIMO radar antenna, the outermost 2 oscillator units have the same size and are the smallest of 6 oscillator units, the innermost 2 oscillator units have the same size and are the largest of 6 oscillator units, and the remaining 2 oscillator units have the same size and are between the smallest size and the largest size.
Optionally, in the millimeter wave MIMO radar antenna, a distance d between the transmitting antennas in each group is 1/2 of an operating wavelength of the transmitting antennas; the distance D between the transmitting antennas of each group is 3 times the operating wavelength of the transmitting antennas.
Optionally, in the millimeter wave MIMO radar antenna, a distance between the receiving antennas is equal to an operating wavelength of the receiving antennas, and the operating wavelength of the receiving antennas is equal to an operating wavelength of the transmitting antennas.
Optionally, in the millimeter wave MIMO radar antenna, the dielectric plate is Rogers4350B, the plate thickness is 0.254mm, the dielectric constant is 3.66, each of the transmitting antenna and the receiving antenna is made of a copper foil material attached to the upper surface of the dielectric plate, the thickness of the copper foil material is 1oz, and the lower surface of the dielectric plate is entirely covered with copper and connected to a reference level.
Meanwhile, in order to achieve the above object, the present invention further provides a method for controlling a millimeter wave MIMO radar antenna, which is used for the above millimeter wave MIMO radar antenna, wherein the step of controlling the transmitting antenna includes: the method comprises the following steps that firstly, a driving signal is output to a transmitting antenna arranged on the outermost side edge, and the driving signal is a frequency modulation continuous wave with linearly changing frequency; wherein the time interval for transmitting signals between the transmitting antennas is the slope of the linear change of the frequency
Figure BDA0002222188500000031
Wherein R ismaxDenotes the maximum measured distance, c denotes the speed of light, fsampleRepresenting the sampling frequency, fsampleIs a set value; second, every fixed time
Figure BDA0002222188500000032
Outputting the same driving signal as that of the transmitting antenna in the first step to the next transmitting antenna arranged in the first direction, wherein vmaxRepresenting the maximum measurement speed, fzRepresenting a carrier frequency of the transmit antenna; thirdly, repeating the second step until the driving signals output by the transmitting antennas arranged on the edge of the other side are disconnected, and skipping to the first step at intervals of fixed time T; and fourthly, repeating the first step to the third step until the output of all driving signals in one radar period is finished.
The driving signal drives each transmitting antenna to output an electromagnetic wave signal, the electromagnetic wave signal is radiated to a target object and then reflected to be received by the receiving antenna, and then the received signal is processed according to the following steps: step R1, synchronously receiving all the electromagnetic wave signals reflected by the target object obtained by each of the receiving antennas, and sampling at a sampling frequency fsampleSampling to obtain a sampling signal; step R2, carrying out Fourier operation on the sampling signal, converting the sampling signal from a time domain to a frequency domain, and carrying out constant false alarm processing to obtain a distance serial number R of the target objectnCalculating the distance of the target object
Figure BDA0002222188500000041
Wherein c represents the speed of light, fsampleRepresenting the sampling frequency, K representing the slope of the linear variation of the frequency of the transmission signal of the transmission antenna, NRRepresenting the number of sampling points; and R3, taking out the data of the same sampling position in the continuous multiple emission cycles on the unit corresponding to the distance serial number of the target object, and performing Fourier operation and constant false alarm processing to obtain the speed serial number V of the target objectnCalculating the velocity of the target object
Figure BDA0002222188500000042
Wherein f iszRepresenting the carrier frequency, N, of the transmitting antennavRepresenting the number of transmissions; step R4, according to the velocity v of the target object and the distance R of the target object, extracting data of the position corresponding to each receiving antenna for phase compensation: the phase difference of the k-th echo with respect to the first received echo is
Figure BDA0002222188500000043
Figure BDA0002222188500000044
Wherein V represents a target speed and λ represents a carrier wavelength; the signal data obtained by sampling the signal each time is expressed as e according to the Euler formulajφPerforming phase compensation on the signal data each time, wherein the value of the signal data after the k-th compensation is equal to that of the signal data after the k-th compensation
Figure BDA0002222188500000045
And R5, performing beam forming according to the value of the signal data obtained after compensation to obtain the accurate angle of the target object relative to the millimeter wave MIMO radar antenna.
Optionally, in the above method for controlling a millimeter wave MIMO radar antenna, the receiving antenna and the transmitting antenna operate synchronously during the transmission in the first step to the fourth step and the receiving in the steps R1 to R5.
In the synchronous working process, when each transmitting antenna transmits an electromagnetic wave signal according to the driving signal, each transmitting antenna can be respectively equivalent to the situation that the other transmitting antennas transmit the same electromagnetic wave signal at the position of the transmitting antenna which transmits the electromagnetic wave signal; each equivalent transmitting antenna is respectively corresponding to an equivalent receiving antenna, wherein the position relationship between each equivalent transmitting antenna and the corresponding equivalent receiving antenna is the same as the position relationship between the corresponding transmitting antenna and each receiving antenna in the millimeter wave MIMO radar antenna.
In the step R1, the electromagnetic wave signals reflected by the target object are synchronously received by the receiving antennas and the equivalent receiving antennas corresponding to the equivalent transmitting antennas, and then the processing from the step R2 to the step R5 is performed.
Advantageous effects
The invention utilizes a plurality of groups of transmitting antennas and a plurality of receiving antennas which are sequentially arranged in two rows, so that when each transmitting antenna transmits electromagnetic wave signals according to the driving signals, each transmitting antenna can be respectively equivalent to the situation that the other transmitting antennas transmit the same electromagnetic wave signals at the positions of the transmitting antennas which transmit the electromagnetic wave signals, and each equivalent transmitting antenna is respectively corresponding to a plurality of equivalent receiving antennas. Therefore, the invention utilizes the equivalence of the antenna, can equivalently enlarge the receiving aperture of the antenna under a smaller size, multiply increases the number of receiving antennas, improves the performance indexes of angle measurement precision, clutter rejection ratio and the like of the system, and equivalently multiplies the collocation of signal quality under the condition of not increasing the transmitting power and area of the antenna. The reason for the equivalent improvement in signal quality is: because the number of the receiving antennas of the antenna structure is equivalently increased, the equivalent increase of the number of the receiving antennas can equivalently increase the signal-to-noise ratio of signals and equivalently improve the signal quality by times in the signal processing process.
Furthermore, in order to ensure the signal quality of each antenna, the invention sets each antenna as a structure that the size of the oscillator unit is gradually reduced from the middle to the two sides, and configures a corresponding impedance matcher for each antenna, thereby realizing the improvement of the radiation efficiency of the antenna. Particularly, the 6 oscillator units of each antenna are linearly arranged and connected through a wire to realize in-phase feeding, and the antenna can obtain a high side lobe suppression ratio by matching with the size of each oscillator unit and can obtain good standing wave characteristics by matching with an impedance matcher to the antenna impedance.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
fig. 1 is a schematic view of the overall structure of a millimeter wave MIMO radar antenna of the present invention;
FIG. 2 is a schematic diagram of a structure of a unit within the millimeter wave MIMO radar antenna of FIG. 1;
FIG. 3 is a graph of S11 echo characteristics for a millimeter wave MIMO radar antenna of the present invention;
FIG. 4 is a directional diagram of a millimeter wave MIMO radar antenna of the present invention;
FIG. 5 is a schematic diagram of the transmit signals of 4 transmit antennas of the millimeter wave MIMO radar antenna of the present invention;
fig. 6 is a schematic diagram of an equivalent receiving antenna of the antenna 2 when transmitting;
fig. 7 is a schematic diagram of an equivalent transceiving model in which each time the antennas 2,3,4 transmit, the equivalent transceiving model is equivalent to that in the position of the antenna 1.
Detailed Description
In order to make the purpose and technical solution of the embodiments of the present invention clearer, the technical solution of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Fig. 1 is a millimeter wave MIMO radar antenna according to the present invention, which is disposed on a surface of a dielectric plate, and a main radiation and reception structure of the antenna includes:
the transmitting antenna shown in the upper row of fig. 1 includes at least 1 group, each group of transmitting antennas includes at least 2, the transmitting antennas are arranged on the upper surface of the dielectric plate in parallel along a first direction, wherein the distance D between the transmitting antennas in each group is smaller than the distance D between the transmitting antennas in each group;
the receiving antennas shown in the lower row of fig. 1 include at least 2 receiving antennas, which are arranged on the upper surface of the dielectric plate in parallel along a first direction, the receiving antennas and the transmitting antennas are arranged in two rows, the distances between the receiving antennas are equal, the distance between the receiving antennas is in the range of D-D, and the distance between the receiving antennas is an integral multiple of half-wavelength.
Since the wavelength of the signal is equal to the speed of light/frequency, the spacing between the antennas needs to be designed to be more than half wavelength, and the spatial correlation between the antennas is relatively low. However, considering the design space size, the present invention can select the distance d between the transmitting antennas in each group as half wavelength, commonly called half wavelength, and the distances between the antennas in each group are consistent, so as to simplify the signal processing process. It is further possible to design the distance between each group of transmitting antennas to be 6 half wavelengths, i.e. 3 wavelengths, and the distance between the receiving antennas to be 1 wavelength, i.e. two half wavelengths. The spacing of the equivalent antennas is thus all half-wavelength spacing. That is, since the receiving antenna spacing is 2 half wavelengths, which is equal to twice the spacing of each transmitting antenna in each group, the corresponding virtual receiving antennas can form an array with a half wavelength spacing. Therefore, better performance can be obtained, and the signal processing process can be considered.
Wherein each of the transmitting antennas or each of the receiving antennas includes the antenna shown in fig. 2:
the oscillator units comprise 6 oscillator units, the 6 oscillator units are arranged at equal intervals along the second direction, and the sizes of the 6 oscillator units are gradually reduced from the middle to two sides; the first direction is parallel to the length direction of a dielectric plate arranged on the millimeter wave MIMO radar antenna; the first direction is parallel to the width direction of a dielectric plate arranged on the millimeter wave MIMO radar antenna;
the feeder line is sequentially connected with the 6 oscillator units and is used for feeding electric signals to the 6 oscillator units in-phase and serial;
and the impedance matcher is connected with the outer side of one oscillator unit arranged at the outermost edge of the 6 oscillator units, is of a micro-strip line structure provided with multiple stages of steps with different widths, and matches the impedance of the transmitting antenna or the receiving antenna to 50 ohms.
On the whole, the transmitting antennas and the receiving antennas in the millimeter wave MIMO radar antenna are respectively and symmetrically arranged along a central axis parallel to the width direction of the dielectric plate. The receiving antenna and the transmitting antenna can adopt the same antenna or different antennas. The single antenna adopts a center-fed 6-element unit array series-fed structure. The 6 oscillators of each antenna are linearly arranged and connected through a wire to realize in-phase feeding. The size of the oscillator is gradually reduced from the middle to two sides, so that a high sidelobe suppression ratio is obtained. The antenna dielectric substrate adopts Rogers4350B, the thickness of the plate is 0.254mm, and the dielectric constant is 3.66. The transmitting antenna and the receiving antenna arranged on the upper surface of the dielectric plate are both made of copper foil materials which are arranged on the upper surface of the dielectric plate in a laminating mode, the thickness of each copper foil material is 1oz, and the lower surface of the dielectric plate is integrally coated with copper and connected to a reference level.
The following describes the design of any one of the above millimeter wave MIMO radar antennas at an operating frequency of 24 GHz.
The high frequency signal is output by the chip and then transmitted to the antenna through a 50ohm microstrip line shown in the lower part of fig. 2. The impedance matcher in a microstrip form is provided with a microstrip line structure with 3-level steps with different widths, so that impedance matching with an antenna is realized, and the antenna can obtain good standing wave characteristics.
For 6 element units in the antenna and corresponding feeder lines and impedance matching structures, the current amplitude distribution coefficient of the array is calculated according to-25 dB sidelobe level by utilizing Chebyshev or Taylor polynomials, and then the width and the length of each element are calculated according to the impedance of each element. Due to parasitic influence, finally, the sizes of the vibrator units are determined as the following table (unit: mm) after simulation calculation is carried out by using electromagnetic simulation software such as hfss and cst:
TABLE 1 antenna parts size
L1 L2 L3 L4 L5 L6 L7 L8 L9
0.85 2.75 4.0 4.0 2.75 0.85 0.15 0.2 0.5
W1 W2 W3 W4 W5 W6 W7 W8 W9
3.45 3.25 3.05 3.05 3.25 3.45 3.0 1.6 1.0
That is, in the millimeter wave MIMO radar antenna of the present invention, in each of the transmitting antennas or the receiving antennas, the outermost 2 element units have the same size and are the smallest of 6 element units, the innermost 2 element units have the same size and are the largest of 6 element units, and the remaining 2 element units have the same size and are between the smallest size and the largest size.
The actual test results in the echo ratio characteristic shown in fig. 3 and the pattern 5 shown in fig. 4. The antenna with the structure of fig. 2 has a good standing wave characteristic in the range of 24-24.5GHz, and the center frequency point is about 24.25 GHz.
TABLE 2 characteristics of the echo ratio of the antenna
Bandwidth (GHz) Frequency range (GHz)
-10dB level bandwidth 0.45 24～24.45
And referring to fig. 4, the antenna gain is about 12dbi at the 24.25G frequency point for the antenna-the dashed line is the H-plane pattern and the solid line is the H-plane pattern in fig. 5. It can be seen that the 3dB width of the H-plane is about 80 °, the 3dB width of the E-plane is 17 °, and the first side lobe level is about-26 dB, meeting design requirements.
The antenna described above is driven to emit electromagnetic wave signals in the manner shown in fig. 5. Referring to the numbering of the transmitting antennas in fig. 1, the driving of each transmitting antenna is realized by the following steps:
the method comprises the following steps that firstly, a driving signal is output to a transmitting antenna arranged at the outermost edge, such as the transmitting antenna 1, wherein the driving signal is a frequency modulation continuous wave with linearly changing frequency; wherein each of said transmissionsThe time interval between the antennas for transmitting signals is fixed
Figure BDA0002222188500000101
Wherein v ismaxRepresenting the maximum measurement speed, fzRepresenting a carrier frequency of the transmit antenna; slope of said frequency linear variation
Figure BDA0002222188500000102
Wherein R ismaxDenotes the maximum measured distance, c denotes the speed of light, fsampleRepresenting the sampling frequency, fsampleIs a set value. When each frequency modulation continuous wave is sampled, sampling is carried out after a tiny sampling waiting time is waited after the frequency modulation continuous wave starts, so that ringing or overshoot which is possibly generated at the beginning stage is avoided.
Second, every fixed time
Figure BDA0002222188500000103
I.e. each time a transmission is transmitted to the next transmission with a fixed time T, for the next transmission antenna arranged along said first direction, i.e. according to 2->3->4, sequentially outputting the same driving signals as the transmitting antennas in the first step to the transmitting antennas with the corresponding numbers;
thirdly, repeating the second step until the driving signals output by the transmitting antennas arranged on the edge of the other side are disconnected, and skipping to the first step at intervals of fixed time T;
and fourthly, repeating the first step to the third step until the output of all driving signals in one radar period is finished.
Thus, the 4-way transmitting antenna shown in fig. 1 sequentially transmits continuous waves with the same frequency gradient after every same time interval. The driving signal drives each transmitting antenna to output an electromagnetic wave signal, and the electromagnetic wave signal is radiated to a target object and then reflected to be received by the receiving antenna. In the above process, the switches are turned on in sequence at regular intervals of fixed time T. The frequency modulation continuous wave with linearly changing transmitting frequency transmits 24-24.25G according to the design requirement of an antenna, the transmitting time interval can be configured according to the maximum speed of a target to be measured, and when the maximum speed is required to be measured +/-100 Km/h, the typical period value T is 56.25 us.
T corresponding to the period can be determined according to a formula
Figure BDA0002222188500000111
And calculating and simultaneously obtaining the maximum Doppler frequency. Wherein the content of the first and second substances,
c-speed of light
fzCarrier frequency (24 to 24.25GHz)
T-cycle time
vmaxMaximum measuring speed
fdmaxMaximum Doppler frequency
The slope of the change in the signal frequency determines the ideal maximum measurement range of the system, and the slope is determined by considering the transmission power and whether the gain of the antenna in the beam direction can reach the maximum measurement range. The slope K is typically 6MHz/us when the maximum measurement distance is 500 meters and the sampling frequency is 10 MHz.
According to the formula:
Figure BDA0002222188500000112
the maximum measured distance is inversely proportional to the slope at a given sampling frequency.
Rmax-maximum measured distance
C-speed of light
fsample-sampling frequency
K-slope
The emission time is required to meet the sampling time requirement, ringing and overshoot are possible at the beginning and the end of the emission, and sampling is required to avoid the beginning and the end of the emission.
In the receiving process, all receiving antennas synchronously receive electromagnetic wave signals reflected by the target object and obtained by all the receiving antennas. In this process the transmitting antenna is still actually working synchronously with the receiving antenna. Thus, referring to fig. 6, the transmitting antenna 1 transmits electromagnetic wave signals, and the lower row 8 receiving antennas synchronously receive the reflected electromagnetic wave signals. When the antenna 2 transmits, if the transmitting antenna 2 is translated equivalently to the position of the transmitting antenna 1, as shown in fig. 6, it can be seen that it is equivalent to the antenna 1 to transmit the signal again, and at the same time, the receiving antenna is also translated rightward to the position of the dotted line in fig. 6.
Sequentially and equivalently transmitting the number 2,3 and 4 transmitting antennas at the position of the antenna 1 every time of transmitting according to the equivalent process, and then respectively obtaining the position relationship of the equivalent receiving antennas corresponding to the number 2,3 and 4 transmitting antennas as shown in fig. 7. By removing the overlapped virtual antennas, all the transceiving antennas can be equivalent to 1-transmitting 23-receiving and bilaterally symmetrical transceiving antennas shown at the lower side of fig. 7.
That is to say, in the process of synchronous operation between the antennas, when each transmitting antenna transmits an electromagnetic wave signal according to the driving signal, each transmitting antenna can be respectively equivalent to the position where the other transmitting antennas transmit the same electromagnetic wave signal at the transmitting antenna that transmits the electromagnetic wave signal;
each equivalent transmitting antenna is respectively corresponding to an equivalent receiving antenna, wherein the position relationship between each equivalent transmitting antenna and the corresponding equivalent receiving antenna is the same as the position relationship between the corresponding transmitting antenna and each receiving antenna in the millimeter wave MIMO radar antenna;
that is, in the receiving process, the electromagnetic wave signal reflected by the target object is synchronously received by the receiving antenna and each equivalent receiving antenna corresponding to each equivalent transmitting antenna.
In order to make the antenna obtain better radiation characteristics as a whole and facilitate the realization of equivalence between each transmitting antenna and the corresponding receiving antenna, in the structure, the distance d between each transmitting antenna in each group is 1/2 of the operating wavelength of the transmitting antenna; the distance D between the transmitting antennas in each group is 3 times of the working wavelength of the transmitting antennas; the distance between the receiving antennas is equal to the working wavelength of the receiving antennas, and the working wavelength of the receiving antennas is equal to the working wavelength of the transmitting antennas. The equivalent of the receiving antenna is realized, and the receiving aperture is expanded.
Thereby, the electromagnetic wave signals reflected by the target object and obtained by all the receiving antennas are synchronously received, and the sampling frequency f is adoptedsampleSampling is carried out to obtain a sampling signal. Then, the angle and the moving speed of the target object relative to the millimeter wave MIMO radar antenna are obtained according to the following steps:
step R2, calculating a frequency difference between the electromagnetic wave signal reflected by the target object and the electromagnetic wave signal output by each transmitting antenna driven by the driving signal; calculating the phase deviation of the electromagnetic wave signals reflected by the target object compared with the electromagnetic wave signals output by the driving signal driving each transmitting antenna;
step R2, carrying out Fourier operation on the sampling signal, converting the sampling signal from a time domain to a frequency domain, and carrying out constant false alarm processing to obtain a distance serial number R of the target objectnCalculating the distance of the target object
Figure BDA0002222188500000131
Wherein c represents the speed of light, fsampleRepresenting the sampling frequency, K representing the slope of the linear variation of the frequency of the transmission signal of the transmission antenna, NRRepresenting the number of sampling points;
step R3, on the unit corresponding to the distance serial number of the target object, taking out the data of the same sampling position in the continuous multiple emission period, namely the data of the same position of the multiple frequency change slope curve or the slope (ramp), and performing Fourier operation and constant false alarm processing to obtain the speed serial number V of the target objectnCalculating the velocity of the target object
Figure BDA0002222188500000132
Wherein f iszRepresenting the carrier frequency of said transmitting antenna, T representing the transmission time interval, i.e. fixed time, or periodic time, NvRepresenting the number of transmissions;
step R4, according to the speed v of the target object and the distance R of the target object, extracting the corresponding receiving antennaThe data at this location is phase compensated. Since the transmitting antennas operate in time division, the signal waveforms received by the respective receiving antennas have phase differences in phase due to the movement of the target, and therefore, the phase compensation must be performed in the following manner: the phase difference of the k-th echo with respect to the first received echo is
Figure BDA0002222188500000133
Wherein V represents a target speed and λ represents a carrier wavelength; the signal data obtained by sampling the signal each time is expressed as e according to the Euler formulajφPerforming phase compensation on the signal data each time, wherein the value of the signal data after the k-th compensation is equal to that of the signal data after the k-th compensation
Figure BDA0002222188500000134
Figure BDA0002222188500000141
And R5, carrying out beam synthesis by replacing the original value with the signal data obtained after compensation to obtain the accurate angle of the target object relative to the millimeter wave MIMO radar antenna.
The above process introduces the measurement error of the same distance to the target to be measured while using the equivalent virtual antenna, but the distance to the target is still very small, the distance to the radar target can be neglected in calculating, the velocity of the target is calculated by using the doppler frequency, the maximum doppler frequency is equal to the reciprocal of the transmission interval under the condition of no mirror image velocity, and the velocity is only related to the serial number, the transmission interval and the carrier frequency after the Constant False Alarm Rate (CFAR) processing on the discretization data. Therefore, after the velocity is calculated, the angle of the target can be accurately obtained by performing phase compensation according to the velocity of the target.
The MIMO radar antenna array adopts a 4-transmission 8-reception structure, and is provided with antenna oscillators with 4-path transmission and 8-path reception, wherein the receiving antennas are distributed at equal intervals, and the intervals are equal to millimeter wave wavelengths; the transmitting antenna is divided into 2 paths, the two sides of the medium substrate are symmetrically distributed, the distance between the transmitting antennas is half wavelength, the small distance is half wavelength, and the large distance is 6 half wavelength. Because each unit is close, the visual angle of each antenna unit to the target is approximately the same, therefore, the time division signal can be sent through the antenna, the number of the virtual receiving antennas can reach as much as 23, thereby equivalently expanding the receiving aperture, enabling the antenna to have high performance in a smaller size range, and improving the performance of the system such as angle measurement precision, clutter suppression ratio and the like.
The above are merely embodiments of the present invention, which are described in detail and with particularity, and therefore should not be construed as limiting the scope of the invention. It should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the spirit of the present invention, and these changes and modifications are within the scope of the present invention.

Claims (2)

1. A control method of a millimeter wave MIMO radar antenna is characterized in that the control method is used for the millimeter wave MIMO radar antenna with the following structure:
the transmitting antennas comprise at least 1 group, each group of transmitting antennas comprises at least 2 transmitting antennas, the transmitting antennas are arranged on the upper surface of the dielectric plate in parallel along a first direction, and the distance D between the transmitting antennas in each group is smaller than the distance D between the transmitting antennas in each group;
the receiving antennas comprise at least 2 receiving antennas which are arranged on the upper surface of the dielectric plate in parallel along a first direction, the receiving antennas and the transmitting antennas are arranged in two rows, the distances among the receiving antennas are equal, and the distances among the receiving antennas are in the range of D-D;
wherein each of the transmitting antennas or each of the receiving antennas includes:
the number of the vibrator units is 6, the vibrator units are arranged at equal intervals along the second direction, and the sizes of the 6 vibrator units are gradually reduced from the middle to two sides;
the feeder line is sequentially connected with the 6 oscillator units and is used for feeding electric signals to the 6 oscillator units in-phase and serial; the impedance matcher is connected with the outer side of one oscillator unit arranged at the outermost edge of the 6 oscillator units, is of a micro-strip line structure provided with multiple stages of steps with different widths, and matches the impedance of the transmitting antenna or the receiving antenna to 50 ohms;
the control method controls the transmitting antenna in the millimeter wave MIMO radar antenna according to the following steps:
the method comprises the following steps that firstly, a driving signal is output to a transmitting antenna arranged on the outermost side edge, and the driving signal is a frequency modulation continuous wave with linearly changing frequency; wherein the time interval of transmitting signals between the transmitting antennas is a fixed time
Figure FDA0002718235000000011
Wherein v ismaxRepresenting the maximum measurement speed, fzRepresenting a carrier frequency of the transmit antenna; slope of said frequency linear variation
Figure FDA0002718235000000012
Wherein R ismaxDenotes the maximum measured distance, c denotes the speed of light, fsampleRepresenting the sampling frequency, fsampleIs a set value;
second, every fixed time
Figure FDA0002718235000000013
Outputting the same driving signal as the transmitting antenna in the first step to the next transmitting antenna arranged along the first direction;
thirdly, repeating the second step until the driving signals output by the transmitting antennas arranged on the edge of the other side are disconnected, and skipping to the first step at intervals of fixed time T;
fourthly, repeating the first step to the third step until the output of all driving signals in one radar period is finished;
the driving signal drives each transmitting antenna to output an electromagnetic wave signal, the electromagnetic wave signal is radiated to a target object and then reflected to be received by the receiving antenna, and the electromagnetic wave signal is processed according to the following steps:
step R1, synchronously receiving all the receiving antennasObtaining the electromagnetic wave signal reflected by the target object according to the sampling frequency fsampleSampling to obtain a sampling signal;
step R2, carrying out Fourier operation on the sampling signal, converting the sampling signal from a time domain to a frequency domain, and carrying out constant false alarm processing to obtain a distance serial number R of the target objectnCalculating the distance of the target object
Figure FDA0002718235000000021
Wherein c represents the speed of light, fsampleRepresenting the sampling frequency, K representing the slope of the linear variation of the frequency of the transmission signal of the transmission antenna, NRRepresenting the number of sampling points;
and R3, taking out the data of the same sampling position in the continuous multiple emission cycles on the unit corresponding to the distance serial number of the target object, and performing Fourier operation and constant false alarm processing to obtain the speed serial number V of the target objectnCalculating the velocity of the target object
Figure FDA0002718235000000022
Wherein f iszRepresenting the carrier frequency, N, of the transmitting antennavRepresenting the number of transmissions;
step R4, according to the velocity v of the target object and the distance R of the target object, extracting data of the position corresponding to each receiving antenna for phase compensation: the phase difference of the k-th echo with respect to the first received echo is
Figure FDA0002718235000000023
Wherein V represents a target speed and λ represents a carrier wavelength; the signal data obtained by sampling the signal each time is expressed as e according to the Euler formulajφPerforming phase compensation on the signal data each time, wherein the value of the signal data after the k-th compensation is equal to that of the signal data after the k-th compensation
Figure FDA0002718235000000024
Figure FDA0002718235000000025
And R5, performing beam forming according to the value of the signal data obtained after compensation to obtain the accurate angle of the target object relative to the millimeter wave MIMO radar antenna.
2. The method of claim 1, wherein the receiving antenna and the transmitting antenna operate synchronously during the transmission in the first step to the fourth step and the reception in the steps R1 to R5;
in the synchronous working process, when each transmitting antenna transmits an electromagnetic wave signal according to the driving signal, each transmitting antenna can be respectively equivalent to the situation that the other transmitting antennas transmit the same electromagnetic wave signal at the position of the transmitting antenna which transmits the electromagnetic wave signal;
each equivalent transmitting antenna is respectively corresponding to an equivalent receiving antenna, wherein the position relationship between each equivalent transmitting antenna and the corresponding equivalent receiving antenna is the same as the position relationship between the corresponding transmitting antenna and each receiving antenna in the millimeter wave MIMO radar antenna;
in step R1, the electromagnetic wave signals reflected by the target object are synchronously received by the receiving antennas and equivalent receiving antennas corresponding to equivalent transmitting antennas, and then the processing from step R2 to step R5 is performed.
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