Disclosure of Invention
In order to solve the problems in the prior art, the invention provides an automobile anti-collision millimeter wave radar system, which aims to realize two-dimensional measurement of radial (distance and speed) and transverse (azimuth angle), and gives an alarm to prompt a driver to take corresponding braking measures in time when a dangerous target is detected by a radar, so that traffic accidents are effectively reduced. According to the technical scheme, the radar adopts a Linear Frequency Modulation (LFM) combined Frequency Shift Keying (FSK) composite modulation continuous wave working system, the angle measurement depends on three receiving antennas, the angle measurement is realized by using a phase method, the speed and the distance of a target vehicle are measured, and meanwhile, the operation amount and the processing period during multi-target identification can be reduced, so that the real-time performance is well obtained.
The invention adopts the following technical scheme:
an automotive anti-collision radar system, comprising: the microwave antenna comprises an antenna unit, a microwave front end and a signal processing unit; wherein,
the antenna unit comprises a transmitting antenna and a receiving antenna and is used for transmitting and receiving signals;
the microwave front end is used for generating a transmitting signal and outputting a local oscillation signal through the coupler; outputting six paths of I/Q signals to the received echo signals through orthogonal power division to obtain differential intermediate frequency echo beat signals; the intermediate frequency conditioning circuit performs gain amplification on the mixed intermediate frequency signal through an operational amplifier and outputs the amplified intermediate frequency signal to a signal processing unit;
the signal processing unit is used for generating a frequency sweep control signal and a frequency sweep source control parameter; sampling and spectrum analyzing a beat signal input by a microwave front end; resolving speed, distance, phase and azimuth, identifying dangerous targets according to safety criteria, and communicating through a CAN bus; and converting the input voltage into the voltage required by each functional module in the radar.
Furthermore, the antenna body of the antenna unit adopts a design of separating and sharing a structure of transmitting and receiving antennas, the transmitting and receiving antennas all adopt a microstrip radiating element array form, and one path transmits and three paths receive.
Further, the transmitting antenna is used for receiving a transmitting signal from the microwave front end and radiating electromagnetic waves outwards; the receiving antenna is used for receiving the echo from the tested vehicle in front and transmitting the echo to the microwave front end.
Furthermore, the microwave front-end is used for generating the a sequence and B sequence transmitting signals with the same modulation slope, the same frequency modulation bandwidth and a frequency shift difference.
Further, the wavefront front-end comprises a crystal oscillator, a phase-locked source PLL, a Voltage Controlled Oscillator (VCO), a loop filter, a coupler, a low noise amplifier, a mixer, a low pass filter, and an operational amplifier.
Furthermore, the crystal oscillator is used for generating a reference frequency, the output end is divided into two parts, one part is provided for the phase-locked source PLL as the reference frequency, and the other part is sent to the signal processing unit.
Furthermore, the phase-locked loop circuit is formed by the phase-locked source PLL, the voltage-controlled oscillator VCO and the loop filter, and a sweep frequency signal is generated and output as a transmitting signal;
the coupler couples the sweep frequency signal all the way as a local oscillation signal and sends the local oscillation signal to the front end frequency conversion module.
Further, the low noise amplifier is configured to amplify the echo signal;
a mixer for mixing the amplified signal to obtain an intermediate frequency signal;
the low-pass filter and the operational amplifier condition the intermediate-frequency signal to realize high-gain amplification of the intermediate-frequency signal.
Furthermore, the signal processing unit comprises an analog-to-digital conversion circuit, a DSP device, a CAN bus interface circuit, an alarm circuit, a power conversion circuit and the like;
the analog-to-digital conversion circuit performs analog-to-digital conversion on the echo intermediate frequency signal output by the microwave front end, and the converted digital signal enters a DSP device;
the DSP device performs spectrum analysis on the input digital signal, detects the frequency point and the phase of a target to be detected, and calculates the corresponding distance, speed and azimuth angle;
the CAN bus interface circuit is used for realizing communication with an external bus;
the alarm circuit performs sound-light alarm according to the danger level judgment result output by the DSP device;
and the power supply conversion circuit converts the external input voltage into the voltage required by each functional module in the radar.
According to the technical scheme, the invention has the following beneficial effects:
(1) the functions of distance measurement, speed measurement and multi-target identification can be realized in a single period;
(2) the transmitting signal source of the invention adopts the PLL + VCO technology, and has the characteristics of flexible transmitting waveform design, high frequency modulation linearity and the like.
Detailed Description
The technical solution of the present invention will be explained and explained in further detail with reference to the accompanying drawings and the detailed description.
The invention adopts a Linear Frequency Modulation (LFM) combined with a Frequency Shift Keying (FSK) composite modulation continuous wave working system to realize the two-dimensional measurement function of radial (distance and speed) and transverse (azimuth).
In order to realize the functions of distance measurement and speed measurement in a single modulation period, the invention adopts a Linear Frequency Modulation (LFM) combined Frequency Shift Keying (FSK) composite modulation continuous wave working system, as shown in figure 1, a radar system alternately transmits sub-pulses of an A section and a B section outwards through an antenna, the frequencies of the two signals are changed according to a linear rule, the modulation slope and the modulation bandwidth are the same, and only a small frequency shift f is differentstep. The receiving antenna receives echo signals of the measured reflecting target with the same characteristics as the transmitted signals at the same time, the echo signals and the transmitted signals have a distance-dependent delay tau in time and are shifted in frequency by a speed-dependent fdAs shown in fig. 2.
After mixing, sampling is carried out at the fixed position of each sub-pulse beat signal, after FFT processing, the spectral peak position and the phase difference information of the A sequence and the B sequence are found,
after the frequency and phase difference information of the measured target is obtained, the distance and the speed can be measured.
In the above formula, R: the distance of the measured target;
v: the speed of the detected target relative to the vehicle;
the phase difference of the detected target;
Δ R: radar range resolution;
Δ v: radar speed resolution;
fstep: the frequency difference between two sub-pulse sequences of the transmitting signal;
k: beat signal spectral points;
n: the number of sub-pulses;
in the aspect of realizing the angle measurement function, the automobile anti-collision radar adopts an antenna with one path of emission and three paths of reception, and the angle measurement of the measured target is realized by utilizing a phase method. The schematic diagram of angle measurement by phase method is shown in FIG. 3, where a measured object is arranged in the theta direction, and the distance between the antennas 1 and 2 is d12The distance between the antennas 1, 3 is d13If the signal received by the antenna has a wave path difference Δ R12And Δ R13As can be seen from fig. 3:
in the above formula:
the phase difference between the receiving antenna 1 and the receiving antenna 2;
d12: the distance between the receiving antenna 1 and the receiving antenna 2;
θ: the angle of the measured target;
the phase difference between the receiving antenna 1 and the receiving antenna 3;
d13: the distance between the receiving antenna 1 and the receiving antenna 3;
N：the integer part of the quotient obtained by dividing by 2 pi;
then, it is calculated from the formula (4)And determines theta.
The following describes an automobile anti-collision radar according to an embodiment of the present invention with reference to fig. 4, and fig. 4 shows a block diagram of the automobile anti-collision radar. The anti-collision radar has to have two-dimensional measuring capability of radial (distance and speed) and transverse (azimuth angle), and sends out an alarm under the condition that a dangerous target exists through safety criterion judgment.
This car anticollision radar includes: antenna unit (1), microwave front end (2) and signal processing unit (3), wherein:
the antenna unit (1) adopts a scheme of separating a transmitting antenna from a receiving antenna and sharing a structure body, the transmitting antenna and the receiving antenna all adopt a microstrip radiating element array form, and the design can meet the requirements of miniaturization, low loss and high gain; the transmitting antenna is used for receiving a transmitting signal from the microwave front end (2) and radiating electromagnetic waves outwards, and the receiving antenna is used for receiving an echo from a front vehicle and transmitting the echo to the microwave front end (2);
the microwave front end (2) is used for generating a frequency sweeping signal by a transmitting branch, one branch is directly output as a transmitting signal through the antenna unit (1), and the other branch is coupled to a receiving branch and used as a local oscillation signal; the receiving branch receives the echo signal of the antenna unit (1), and the echo signal is sent to the signal processing unit (3) through frequency conversion processing and an intermediate frequency conditioning circuit;
furthermore, the microwave front-end is used for generating the a sequence and B sequence transmitting signals with the same modulation slope, the same frequency modulation bandwidth and a frequency shift difference. In a multi-target environment, the LFM + FSK composite modulation continuous wave working system is simpler than a simple LFM mode, has good real-time performance and has strong multi-target resolution capability.
And the signal processing unit (3) is used for generating a frequency sweep control signal and frequency sweep source control parameters of the microwave front end (2). The power supply distribution of each extension is realized, and the beat signals input by the microwave front end (2) are sampled and subjected to spectrum analysis; resolving speed, distance, phase and azimuth, identifying dangerous targets according to safety criteria, and realizing communication with the outside through a CAN bus.
Fig. 5 is a schematic block diagram of a microwave front end (2) in the detailed implementation of the present invention, which includes modules such as a crystal oscillator (21), a phase locked source PLL (22), a voltage controlled oscillator (23), a loop filter (24), a coupler (25), a power divider (26), a low noise amplifier (27), a mixer (28), and an operational amplifier (29).
A crystal oscillator (21) in the microwave front end (2) is used for generating a reference frequency source, the output end is divided into two parts, one part is provided for the phase-locked loop PLL (22) to serve as reference frequency, and the other part is sent to a signal processing unit. A phase-locked source PLL (22), a voltage-controlled oscillator (23) and a loop filter (24) form a sweep frequency signal generated by a phase-locked loop circuit and are directly output as a transmitting signal; in addition, the coupler (25) couples one path of the transmitting signal to the frequency conversion module as a local oscillation signal after the transmitting signal is divided into three paths by the power divider (26); the echo signals pass through three receiving branches of the antenna unit (1), and then pass through a low noise amplifier (27) and three local oscillation signals through a mixer (28) to form six paths of I/Q intermediate frequency signals. The six paths of I/Q signals are subjected to gain amplification through an operational amplifier (29) and are sent to signal processing and sampling.
Fig. 6 is a schematic block diagram of the signal processing unit (3) in the detailed implementation of the present invention, which mainly includes an ADC (31), a DSP (32), a CAN (33), an alarm circuit (34), and a power conversion circuit (35).
The analog-to-digital conversion circuit ADC (31) performs analog-to-digital conversion on the echo intermediate frequency signal output by the microwave front end, and the converted digital signal enters a DSP device;
the DSP (32) device performs spectrum analysis on the input digital signal, detects the frequency point and the phase of the target to be detected, and calculates the corresponding distance, speed and azimuth angle;
the CAN (33) bus interface circuit realizes communication with an external bus, receives information such as speed and attitude of the vehicle, and feeds back measurement results of distance, speed and azimuth angle, danger level and the like to the outside.
The alarm circuit (34) performs sound-light alarm according to the danger level judgment result output by the DSP device;
the power supply conversion circuit (35) converts the +12V voltage input from the outside of the radar into +5V, +6V, +3.3V, +1.3V, +1.8V and +1.2V and the like required by each unit in the radar.
An ADC (31) in the signal processing unit (3) samples six intermediate frequency I/Q signals, then the signals are sent to a DSP (32) to be resolved in speed and distance, and then communication with the outside is achieved through a CAN bus (33). The alarm circuit (34) performs sound-light alarm according to the danger level judgment result output by the DSP device (32); and the power supply conversion circuit (35) is used for providing power supply for each extension of the automobile anti-collision radar.
The automobile anti-collision radar system adopts an LFM + FSK composite modulation continuous wave working system. In a multi-target environment, the form of the transmitting signal is simpler than that of a simple LFM mode in algorithm, precious identification time is provided for collision avoidance of vehicles, the real-time performance is good, and meanwhile, the multi-target distinguishing capability is very strong.
The above-described embodiments are merely illustrative and explanatory of the technical aspects of the present invention, and do not constitute limitations of the claims. It should be clear to those skilled in the art that any simple modification or replacement based on the technical solution of the present invention will also result in new technical solutions, which fall within the protection scope of the present invention.