Radio positioning system applied to Mars unmanned aerial vehicle

Abstract

The invention discloses a radio positioning system applied to a Mars unmanned aerial vehicle, and belongs to the field of radio positioning in the radio technology. The invention aims to solve the problem that the Mars unmanned aerial vehicle cannot be effectively positioned through an external means. Comprising the following steps: arranging an antenna at each of four corners of the front surface of a square PCB to form a planar pseudo-Doppler antenna circular array; four microwave switches, a baseband circuit and a single chip microcomputer are also arranged on the front surface of the PCB; four microstrip radio frequency transmission lines, four sets of TOF ranging chips and a peripheral circuit are arranged on the back surface of the PCB; each antenna is correspondingly connected with a microwave switch, each microwave switch is correspondingly connected with the head end of one microstrip radio frequency transmission line, and terminals of the four microstrip radio frequency transmission lines are converged to the central point of the square PCB and then are connected with a baseband circuit; each set of TOF ranging chip and peripheral circuit is arranged close to one antenna correspondingly and is connected with one antenna through a microwave switch; the microwave switch is controlled through the single-chip microcomputer, and unmanned aerial vehicle positioning based on signals is carried out. The method is used for radio positioning.

Description

Technical Field

[0001] The invention relates to a radio positioning system applied to a Mars unmanned aerial vehicle, and belongs to the field of radio positioning in radio technology. Background Art

[0002] With the development of aerospace technology, the forms of extraterrestrial probes have gradually become richer, from satellite in-orbit observations to landing in-situ probes, and mobile rovers and aircraft have appeared. Taking Mars as an example, drones have been successfully launched on Mars. Due to the thin air on Mars, the lift that can be generated by Mars drones is very limited, so the weight of each subsystem is strictly limited. The distance between Mars and the Earth is too large, and the communication delay is too high. The probe cannot be remotely controlled from the ground in real time. Therefore, all actions such as navigation, guidance and control rely on the onboard computer to perform autonomously, which also places high demands on the performance of the onboard computer. On the other hand, in order to ensure reliability, the probe usually uses a combined navigation method to correct the accumulated error of inertial navigation. However, for Mars drones, since the global satellite navigation system cannot be used on Mars, the onboard navigation system lacks a reliable positioning information, resulting in its range of activities being limited. Therefore, an external positioning reference that can be used to correct the accumulated error of inertial navigation is needed.

[0003] Radio direction finding technology uses an antenna array to receive radio signals and calculates the relative direction between the receiver and the source (the direction of the incoming wave) based on the difference in the signals received by the antenna units. It is suitable for relatively open scenes and is currently used in civil aviation passenger aircraft, ship positioning, etc. Through radio direction finding, combined with the distance between the receiver and the source, positioning can be performed, and each measurement result of this positioning method is independent and there is no error accumulation. Radio direction finding can usually achieve passive direction finding, which only requires passive reception of incoming wave signals, which is beneficial to saving energy. However, existing radio direction finding equipment usually requires a larger antenna array and more complex receiving equipment to achieve high-precision and real-time estimation of the direction of the incoming wave.

[0004] In summary, there is currently no complete external positioning method for Mars drones. Summary of the invention

[0005] In order to solve the problem that the Mars UAV cannot be effectively positioned by external means, the present invention provides a radio positioning system applied to the Mars UAV.

[0006] A radio positioning system for a Mars drone of the present invention comprises: an antenna is arranged at each of the four corners of the front side of a square PCB board to form a circular array of planar pseudo-Doppler antennas; four microwave switches, a baseband circuit and a single-chip microcomputer are also arranged on the front side of the square PCB board; four microstrip radio frequency transmission lines, four sets of TOF ranging chips and peripheral circuits are arranged on the back side of the square PCB board;

[0007] Each antenna is connected to a microwave switch, and each microwave switch is connected to the head end of a microstrip RF transmission line. The terminals of the four microstrip RF transmission lines converge at the center point of the square PCB board and are connected to the baseband circuit. The microwave switch is controlled by a single-chip microcomputer. Each set of TOF ranging chip and peripheral circuit is set close to an antenna and connected to an antenna through the corresponding microwave switch.

[0008] Use a single-chip microcomputer to control the on and off of the microwave switch to achieve direction or distance measurement:

[0009] When used for direction finding, the four antennas in the circular array of planar pseudo-Doppler antennas are switched on in turn at a frequency of 4kHz through the control of the single-chip microcomputer, simulating the state of a single antenna rotating at a frequency of 1kHz; each antenna receives a plane wave signal generated by a source at the slave end, and the microwave switch, under the control of the single-chip microcomputer control signal, transmits the plane wave signal received by the corresponding antenna to the baseband circuit through a microstrip RF transmission line for down-conversion and filtering, and obtains a pre-processed plane wave signal and transmits it to the single-chip microcomputer; the single-chip microcomputer performs FM demodulation on the received signal, and then uses FFT transformation to obtain the frequency component corresponding to the Doppler frequency shift, performs phase extraction on the pre-processed plane wave signal under the frequency component, and obtains the incoming direction of the plane wave;

[0010] When used for ranging, the single-chip microcomputer controls the corresponding microwave switch to connect a selected set of TOF ranging chips and peripheral circuits to the antenna; the selected set of TOF ranging chips and peripheral circuits send ranging signals to the source of the slave end through the antenna, and the single-chip microcomputer is used to calculate the distance between the positioning system and the slave end according to the ranging response signal of the slave end;

[0011] The slave end is a slave end with known settings;

[0012] The Mars UAV positioning is achieved based on the direction-finding results of the plane wave and the distance measurement results of the positioning system and the slave end.

[0013] According to the radio positioning system applied to the Mars UAV of the present invention, the antenna is an omnidirectional antenna, and a coaxial line interface is used to connect the microwave switch through a microstrip line; the microwave switch is close to the coaxial line interface.

[0014] According to the radio positioning system applied to the Mars UAV of the present invention, each antenna and the corresponding microwave switch and microstrip radio frequency transmission line form a group of signal units, and the four groups of signal units are centrally symmetrically distributed with the center point of the PCB board as the center.

[0015] According to the radio positioning system applied to the Mars UAV of the present invention, the microwave switch is a reflective switch that uses a surface mount package and works in the 2.4G frequency band, and has a radio frequency signal input port, a control signal port, a signal output port A, and a signal output port B;

[0016] When used for direction finding, the RF signal input port is used to receive the plane wave signal, and the control signal port is used to receive the control signal of the single-chip microcomputer; the control signal is a high-level signal and a low-level signal; the control signal port turns on the signal output port A according to the received control signal to transmit the signal, and at the same time turns off the other signal output port;

[0017] When used for ranging, the direction finding function is turned off; the RF signal input port is used to receive the ranging signal sent by a selected set of TOF ranging chips and peripheral circuits; the control signal port turns on the output port B according to the control signal of the received microcontroller, so that the ranging signal is sent to the antenna through the output port B, and the antenna then sends the ranging signal to the signal source at the slave end.

[0018] According to the radio positioning system applied to the Mars UAV of the present invention, the geometric size of the square PCB board does not exceed 10*10cm.

[0019] According to the radio positioning system applied to the Mars UAV of the present invention, the impedance of each microstrip RF transmission line is 50 ohms; the length of each microstrip RF transmission line is an integer multiple of 1 / 4λ, where λ is the wavelength of the 2.4G frequency band signal when propagating in the microstrip RF transmission line; when one microstrip RF transmission line transmits a signal, the input impedances of the other three microstrip RF transmission lines are all in an open circuit state.

[0020] According to the radio positioning system applied to the Mars UAV of the present invention, the terminals of the four microstrip RF transmission lines are connected at the center point of the square PCB board to form a cross layout, and each microstrip RF transmission line extends in a zigzag manner from the head end to the terminal, and the zigzag corners are realized by arcs.

[0021] According to the radio positioning system applied to the Mars UAV of the present invention, the baseband circuit includes a down-conversion module composed of a radio frequency front-end I / Q modulation and demodulation chip and its peripheral circuits, and a differential-to-single-ended and low-pass filtering module composed of a dual-channel integrated operational amplifier and its peripheral circuits;

[0022] The plane wave signal transmitted by the microstrip RF transmission line is converted into a differential signal through the balun in the baseband circuit, and then enters the down-conversion module to obtain the I\Q differential signals. Then, the differential to single-ended and low-pass filtering module outputs the low-frequency I\Q single-ended signals, which are transmitted to the microcontroller as pre-processed signals.

[0023] According to the radio positioning system applied to the Mars UAV of the present invention, the method for the single chip microcomputer to perform FM demodulation on the received signal includes:

[0024] Assume that the plane wave signal generated by the source is f(t):

[0025]

[0026] Where f c is the carrier frequency, ω c is the carrier angular frequency, is the initial phase of the carrier signal, t is the time;

[0027] The four antennas are turned on in turn, integrating the four plane wave signals into one signal in time sequence. The signal entering the baseband circuit is S n (t):

[0028]

[0029] Where n is the number of the antenna, B n is the amplitude of the plane wave signal received by the nth antenna, is the phase of the carrier signal, D is the diameter of the pseudo-Doppler antenna circular array, ε is the elevation angle of the plane wave signal, N is the number of antennas, and θ is the angle between the plane wave signal and the antenna when t = 0;

[0030] Signal S n (t) After being processed by the baseband circuit, the pre-processed plane wave signal obtained is a low-frequency I\Q two-way single-ended signal;

[0031] The microcontroller performs an inverse tangent operation on the low-frequency I\Q two-way single-ended signal to obtain the instantaneous phase φ(t) of the plane wave signal:

[0032]

[0033] in The Doppler frequency shift is generated by the four antennas switching on in turn. When the ratio of the height difference between the signal source and the antenna to the distance from the signal source to the center of the pseudo-Doppler antenna circular array is less than 1 / 10, the elevation angle ε of the plane wave signal is considered to be 0 and coSε is considered to be 1.

[0034] Taking the derivative of the instantaneous phase φ(t), we can obtain the instantaneous frequency ω(t) of the plane wave signal:

[0035]

[0036] This enables the microcontroller to perform FM demodulation of the received signal.

[0037] According to the radio positioning system applied to the Mars UAV of the present invention, the method for obtaining the incoming direction of the plane wave is:

[0038] Perform FFT transformation on the instantaneous frequency w(t) to obtain a plane wave signal spectrum diagram; the frequency component corresponding to the antenna rotation contained in the spectrum diagram is the frequency component corresponding to the Doppler frequency shift; the frequency component is expressed in complex form, and the phase of the complex form frequency component is calculated to obtain the incoming wave angle with a constant offset

[0039]

[0040] Where θ0 represents the constant offset, and θ is calculated to determine the incoming direction of the plane wave.

[0041] Beneficial effects of the present invention: The system of the present invention has the characteristics of high integration, small size and low power consumption, and is a narrow-band radio positioning system.

[0042] The system of the present invention adopts PCB technology, and the signal frequency band selects the 2.4G frequency band with a shorter wavelength, which realizes the miniaturization of the antenna array and the integration of the signal processing system, greatly reducing the volume and weight of the system. In the case of long distance, the present invention regards the source signal as a plane wave. The rapid switching between the four antenna units is used to simulate the rotation of a single antenna to receive the radio frequency signal, and the baseband circuit is used to down-convert, filter, amplify and other processes the radio frequency signal, and finally send it to the single-chip microcomputer for AD sampling, and perform signal processing in the single-chip microcomputer. The phase change value of the switching frequency signal is obtained by processing the received signal, and the wave arrival direction of the signal is calculated using this result. At the same time, the TOF ranging chip is used to measure the distance based on the set slave end, thereby realizing the radio positioning of the Mars UAV.

[0043] The system of the present invention is integrated into a small-volume PCB, utilizes fewer components and materials, occupies a smaller volume and weight to achieve radio positioning, and can be applied to the radio positioning and autonomous navigation of Mars UAVs or other space probes with strict weight and volume constraints.

[0044] The system of the present invention only connects one antenna at a time and can be completed using only a single receiver, thereby saving equipment weight and complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the structure of the radio positioning system applied to the Mars UAV according to the present invention;

[0046] Figure 2 This is a schematic diagram of the layout of four microstrip RF transmission lines on the back of a square PCB board;

[0047] Figure 3 It is a schematic diagram of the signal transmission process of the radio positioning system applied to the Mars UAV according to the present invention;

[0048] Figure 4 It is a flow chart of signal processing in baseband circuit;

[0049] Figure 5 It is the signal processing flow chart of the single chip microcomputer;

[0050] Figure 6 It is a schematic diagram of the principle of the system of the present invention in the ranging state. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0053] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0054] Specific implementation method 1. Combination Figures 1 to 3 and Figure 6 As shown, the present invention provides a radio positioning system applied to a Mars UAV, comprising:

[0055] The entire system is distributed on a square PCB board. An antenna 1 is arranged at each of the four corners of the front of the square PCB board to form a circular array of planar pseudo-Doppler antennas. Four microwave switches 3, a baseband circuit 4 and a single-chip microcomputer 5 are also arranged on the front of the square PCB board. Four microstrip radio frequency transmission lines 2, four sets of TOF ranging chips and peripheral circuits are arranged on the back of the square PCB board.

[0056] Each antenna is connected to a microwave switch, and each microwave switch is connected to the head end of a microstrip RF transmission line. The terminals of the four microstrip RF transmission lines converge at the center point of the square PCB board and are connected to the baseband circuit. The microwave switch is controlled by a single-chip microcomputer. Each set of TOF ranging chip and peripheral circuit is set close to an antenna and connected to an antenna through the corresponding microwave switch.

[0057] Use a single-chip microcomputer to control the on and off of the microwave switch to achieve direction or distance measurement:

[0058] When used for direction finding, the four antennas in the circular array of planar pseudo-Doppler antennas are switched on in turn at a frequency of 4kHz through the control of the single-chip microcomputer, simulating the state of a single antenna rotating at a frequency of 1kHz; each antenna receives a plane wave signal generated by a source at the slave end, and the microwave switch, under the control of the single-chip microcomputer control signal, transmits the plane wave signal received by the corresponding antenna to the baseband circuit through a microstrip RF transmission line for down-conversion and filtering, and obtains a pre-processed plane wave signal and transmits it to the single-chip microcomputer; the single-chip microcomputer performs FM demodulation on the received signal, and then uses FFT transformation to obtain the frequency component corresponding to the Doppler frequency shift, performs phase extraction on the pre-processed plane wave signal under the frequency component, and obtains the incoming direction of the plane wave;

[0059] When used for ranging, the single-chip microcomputer controls the corresponding microwave switch to connect a selected set of TOF ranging chips and peripheral circuits to the antenna; the selected set of TOF ranging chips and peripheral circuits send ranging signals to the source of the slave end through the antenna, and the single-chip microcomputer is used to calculate the distance between the positioning system and the slave end according to the ranging response signal of the slave end;

[0060] The slave end is a slave end with known settings;

[0061] The Mars UAV positioning is achieved based on the direction finding results of the plane wave incoming wave and the distance measurement results of the positioning system and the slave end.

[0062] The square PCB board also integrates a power supply part 6 to supply power to the baseband circuit 4 and the single-chip microcomputer 5. The square PCB board also carries a 422 serial port output interface for outputting the direction finding result to the host computer through the serial port.

[0063] The positioning system acts as the host, and the single chip microcomputer can calculate the distance between the host and the slave according to the time difference between the host sending the ranging signal and the slave receiving the response signal. In this embodiment, the slave can send a 2.4GHz radio frequency signal to the outside, which can be used as a direction finding signal source, and can also be used as a TOF ranging chip ranging slave.

[0064] The working principle of the system of the present invention:

[0065] Assume that there is a fixed-position positioning beacon sending a direction-finding signal. In the case of a long distance, this signal can be considered as a plane wave. For a plane wave arriving at the pseudo-Doppler antenna array at a certain angle, each antenna unit will receive a slightly delayed or advanced signal relative to other antenna units. The switching between antenna units causes the received signal to have a phase step discontinuity, and such a signal will generate pulses after passing through the FM demodulator. These pulses are essentially sampling points on a continuous sinusoidal signal, and the period is equal to the time it takes to simulate a single antenna rotating one circle, that is, the time required for all antenna units to switch one circle in turn. By using strict time synchronization control in the program and then performing FM demodulation, the wave direction can be extracted.

[0066] In this embodiment, the antenna is an omnidirectional antenna, and is connected to a microwave switch through a microstrip line using a coaxial line interface; the microwave switch is close to the coaxial line interface. The four antennas in the pseudo-Doppler antenna circular array are located in the same plane and have the same model.

[0067] Each antenna and the corresponding microwave switch and microstrip RF transmission line form a group of signal units, and the four groups of signal units are centrally symmetrically distributed around the center point of the PCB board. In this embodiment, the antenna position, the position of the microwave switch and the components of the peripheral circuit, and the geometric structure of the RF transmission line are strictly centrally symmetrical around the center of the antenna array.

[0068] Further, the microwave switch is a reflective switch that uses a surface mount package and operates in the 2.4G frequency band, and has a radio frequency signal input port, a control signal port, a signal output port A, and a signal output port B;

[0069] When used for direction finding, the RF signal input port is used to receive the plane wave signal, and the control signal port is used to receive the control signal of the single-chip microcomputer; the control signal is a high-level signal and a low-level signal; the control signal port turns on the signal output port A according to the high and low levels of the received control signal to transmit the signal, and at the same time turns off the other signal output port; the single-chip microcomputer sends the control signal through GPIO.

[0070] When used for ranging, the direction finding function is turned off; the RF signal input port is used to receive the ranging signal sent by a selected set of TOF ranging chips and peripheral circuits; the control signal port turns on the output port B according to the control signal of the received single-chip microcomputer, so that the ranging signal is sent to the antenna through the output port B, and the antenna then sends the ranging signal to the source of the slave end. The single-chip microcomputer can control whether the TOF ranging chip is connected to the antenna by controlling the on and off of the microwave switch, that is, whether the system enters the ranging state. When entering the ranging state, the direction finding function is turned off, the single-chip microcomputer selects a TOF ranging chip, connects the antenna to this chip, and the single-chip microcomputer communicates data with the TOF ranging chip through the SPI bus. The TOF ranging chip sends a direction finding signal, sends the direction finding signal to the slave end, and calculates the master-slave distance according to the slave's response signal. According to the ranging results and direction finding results, the single-chip microcomputer calculates the position of the slave relative to the host, and realizes the positioning of the host relative to the slave.

[0071] As an example, the geometric size of the square PCB board does not exceed 10*10cm, and a 6-layer stacking scheme is adopted. The stacking structure is non-RF circuit layer L1, power layer L2, signal layer L3, ground layer L4, ground layer L5 and signal layer L6 from top to bottom. The microstrip RF transmission line is located in the L6 layer.

[0072] In this embodiment, the microstrip RF transmission line is composed of 4 microstrip lines on the PCB board. Each line starts from a microwave switch near each antenna port and converges at the center of the circle. Then, it changes from 4 lines to 1 line and enters the baseband circuit. The impedance of each microstrip RF transmission line is 50 ohms. In order to prevent mutual interference between the four antennas, since the microwave switch is reflective, combined with the 1 / 4 wavelength impedance transformation property of the transmission line, the length of each microstrip RF transmission line is controlled to be an integer multiple of 1 / 4λ, where λ is the wavelength of the 2.4G frequency band signal when propagating in the microstrip RF transmission line. When one microstrip RF transmission line transmits a signal, the input impedance of the other three microstrip RF transmission lines is in an open circuit state when the convergence point is used as the input port.

[0073] As an example, considering component layout, system weight, etc., the length of the microstrip RF transmission line is selected to be 5 / 4λ.

[0074] Combination Figure 2 As shown, the terminals of the four microstrip RF transmission lines are connected at the center point of the square PCB board to form a cross layout. Each microstrip RF transmission line extends in a zigzag manner from the head end to the terminal. In order to reduce signal reflection, arcs are used at the zigzag corners.

[0075] The microstrip RF transmission line transmits the signal of the antenna array to the baseband circuit, and at the same time avoids interference between the four microstrip lines of the microstrip RF transmission line by controlling the length.

[0076] Going a step further, combined Figure 4 As shown, the baseband circuit includes a down-conversion module consisting of a zero-IF architecture RF front-end I / Q modulation and demodulation chip and its peripheral circuits operating in the 2.4G frequency band, and a differential-to-single-ended and low-pass filtering module consisting of a dual-channel integrated operational amplifier and its peripheral circuits;

[0077] The plane wave signal (single-ended signal) transmitted by the microstrip RF transmission line is converted into a differential signal in the baseband circuit through the balun, and then enters the down-conversion module to obtain the zero intermediate frequency I\Q two-way differential signal, and then outputs the low-frequency band (about 10kHz) I\Q two-way single-ended signal through the differential to single-ended and low-pass filter module, which is transmitted to the AD sampling port of the microcontroller as a pre-processed signal. The baseband circuit is only responsible for the analog signal processing from the RF signal to the baseband signal.

[0078] The LO oscillation frequency inside the I / Q modulation and demodulation chip can be changed by modifying the internal registers, which can be modified through SPI. In this system, an SPI communication interface is reserved for the microcontroller 5 and the I / Q modulation and demodulation chip, and the registers of the I / Q modulation and demodulation chip can be modified through the microcontroller 5. By default, the LO frequency f LO The I / Q modulation and demodulation chip converts the carrier frequency to f c The RF signal is down-converted to baseband, and the frequency of the baseband signal is f IF =f LO- f c For example, when you need to receive a carrier frequency f c When the signal is 2436.99MHz, the signal is first down-converted to f in the I / Q modulation and demodulation chip. IF =2436.999512-2436.99=0.009512MHz=9.512kHz, and then the high-frequency components such as the image frequency are filtered out by a low-pass filter, and finally the I / Q orthogonal two-way baseband signal with an intermediate frequency of 9.512kHz can be output and enter the next processing stage.

[0079] In order to avoid high-frequency signal interference and increase the signal amplitude for easy sampling, the signal is sent to a low-pass filter composed of an operational amplifier after passing through the I / Q modulation and demodulation chip, and its cut-off frequency is about 24kHz. Since the signal output by the I / Q modulation and demodulation chip is a differential signal, it also needs to be converted into a single-ended signal at the filter. The low-pass filter outputs two I / Q signals, which are sent to the microcontroller for sampling.

[0080] The power supply part 6 includes multiple low-dropout linear regulators LDO and DC-DC circuits, which are distributed at different locations on the PCB. The total power input of the system is 5V, which is then sent to each LDO. The LDO output voltage includes 3.3V and 2.85V, which are supplied to the microcontroller and I / Q modulation and demodulation chip. The DC-DC outputs ±5V power supply, which is used to power the operational amplifier.

[0081] In this embodiment, the single-chip microcomputer is mainly responsible for the switching control of microwave switches, the acquisition and processing of direction finding signals, the output of direction finding results, and the system status indication functions, and reserves a serial port and a program debugging port for the outside.

[0082] In this embodiment, the pseudo-Doppler antenna circular array receives the 2.4G source direction finding signal. The signal of each antenna is synthesized into a serial signal according to the antenna conduction timing. The signal received by the antenna is down-converted and filtered in the baseband circuit and then enters the single-chip microcomputer. The single-chip microcomputer receives two I\Q signals. According to the antenna switching time, the corresponding received signal of each antenna is stored in the memory respectively. The direction finding result can be obtained by using the single-chip microcomputer to extract the phase, compare the phase, and take the average value of the signal of each antenna.

[0083] Example:

[0084] Assuming that the signal source is a signal with a frequency of 2436.99 MHz generated by a radio signal source, the system of the present invention is applicable to all signals in the 2.4 GHz frequency band under the ISM frequency band.

[0085] Combination Figure 3 As shown, a control signal is sent to the microwave switch group through the single chip microcomputer 5 to control the antenna units in the planar four-antenna circular array to take turns to receive the direction finding signal. After that, the signal first enters the baseband circuit 4 for down-conversion and filtering, and then is sent to the single chip microcomputer 5.

[0086] Combination Figure 5 As shown, after the single-chip microcomputer 5 receives the signal from the baseband circuit 4, it first passes through a digital low-pass filter to further remove most of the noise other than the target received signal; then FM demodulation is performed, and then the FFT transformation is used to find the frequency component corresponding to the antenna rotation, and the signal phase under this component is extracted to finally obtain the incoming wave direction.

[0087] Combination Figure 5 As shown, the method for the single chip microcomputer to perform FM demodulation on the received signal includes:

[0088] When the signal source is far enough from the antenna array, the incoming wave can be regarded as a plane wave. The radius of the antenna array is r, and the angle between the incoming wave and the antenna is θ when t=0. Consider the case where the antenna rotates once, that is, the four antennas are turned on in turn:

[0089] Assume that the plane wave signal generated by the source is f(t):

[0090]

[0091] Where f c is the carrier frequency, ω c is the carrier angular frequency, is the initial phase of the carrier signal, t is the time;

[0092] The four antennas are turned on in turn, integrating the four plane wave signals into one signal in time sequence. The signal entering the baseband circuit is S n (t):

[0093]

[0094] Where n is the number of the antenna, B n is the amplitude of the plane wave signal received by the nth antenna, is the phase of the carrier signal, D is the diameter of the pseudo-Doppler antenna circular array, ε is the elevation angle of the plane wave signal, N is the number of antennas, and θ is the angle between the plane wave signal and the antenna when t = 0;

[0095] Signal S n (t) After being processed by the baseband circuit, down-conversion and orthogonal decomposition are performed in the I / Q modulation and demodulation chip, and the pre-processed plane wave signal obtained is a low-frequency I\Q two-way single-ended signal; it is output to the single-chip microcomputer 5, sampled by the ADC of the single-chip microcomputer 5, and the signal is stored in the on-chip storage. Subsequent signal processing is performed in the single-chip microcomputer 5.

[0096] The microcontroller performs an inverse tangent operation on the low-frequency I\Q two-way single-ended signal to obtain the instantaneous phase φ(t) of the plane wave signal:

[0097]

[0098] in The Doppler frequency shift caused by the four antennas switching on in turn, that is, the rotation of the antenna, is a sinusoidal signal with a single frequency. The carrier frequency is the rotation frequency of a single antenna. It is the phase change caused by carrier modulation. For this embodiment, the carrier is not modulated, so this item can be ignored. When the ratio of the height difference between the signal source and the antenna to the distance from the signal source to the center of the pseudo-Doppler antenna circular array is less than 1 / 10, that is, when the height difference between the signal source and the antenna is much smaller than the distance from the signal source to the center of the pseudo-Doppler antenna circular array, the elevation angle ε of the plane wave signal is regarded as 0. coSε Considered as 1;

[0099] The instantaneous phase φ(t) is derived, and a differential operation is performed on the discrete signal collected by the microcontroller to obtain the instantaneous frequency ω(t) of the plane wave signal:

[0100]

[0101] This enables the microcontroller to perform FM demodulation of the received signal.

[0102] The method to obtain the incoming direction of a plane wave is:

[0103] Perform FFT transformation on the instantaneous frequency ω(t) to obtain the plane wave signal spectrum diagram; the frequency component corresponding to the antenna rotation contained in the spectrum diagram is the frequency component corresponding to the Doppler frequency shift; due to the presence of noise in the actual system and the influence of higher harmonics, there will be noise components and higher harmonic components in the spectrum diagram, but the signal corresponding to the above formula is the fundamental wave, which has the largest amplitude in the spectrum diagram, so it is only necessary to find the component with the largest amplitude in the spectrum diagram, which is the component corresponding to the instantaneous frequency ω(t). The frequency component is expressed as a complex number and stored in the single-chip microcomputer, and the phase of the complex number frequency component is calculated to obtain the angle of the incoming wave with a constant offset.

[0104]

[0105] Where θ0 represents the constant offset, and θ is calculated to determine the incoming direction of the plane wave.

[0106] In the above formula It represents the angle of the incoming wave output before calibration. After experimental calibration, the constant offset θ0 can be determined.

[0107] In the ranging state, the microcontroller controls the four TOF ranging chips and peripheral circuits carried by the system through the SPI bus. The microcontroller selects one of the four TOF ranging chips and peripheral circuits to activate and enter the ranging working mode. The host sends a ranging request signal to the slave and starts timing. After receiving the signal, the slave records the time used for signal processing and then sends a response signal. The response signal contains the time used for signal processing t r The host receives the response signal and stops timing to obtain the time difference t0; the slave processing signal time t is read from the response signal r , the actual signal flight time is t = t0-t r According to the time t and the speed of radio wave propagation and the speed of light c, we can get the master-slave distance d = t / t / c, thus completing the distance measurement.

[0108] By obtaining the angle information between the master and slave machines through direction finding and the distance information between the master and slave machines through distance measurement, the position of the master machine relative to the slave machine can be obtained to achieve the positioning effect.

[0109] Combination Figure 6 As shown, the system of the present invention has two working states: direction finding state and communication state. Since the antenna adopts a multiplexing design, the two states will not occur at the same time. The communication and direction finding states adopt a time-division multiplexing strategy. Since no mechanical structure changes are involved, a higher switching speed can be achieved.

[0110] When the system is working in the direction finding state, the single chip microcomputer controls the microwave switch to select the antenna in turn, and the direction finding signal received by the antenna is transmitted to the RF front end in turn. The down conversion is completed in the RF front end, and then after low-pass filtering, the ADC of the single chip microcomputer samples and processes it to obtain the direction of the incoming wave.

[0111] When the system is working in the communication state, the single chip microcomputer controls the microwave switch to connect one of the antennas to a group of TOF ranging chip communication channels for TOF ranging chip communication and ranging.

[0112] In summary, the present invention utilizes high-speed switching between four antenna units to receive direction-finding signals, and utilizes the single-chip microcomputer 5 to extract the pseudo-Doppler characteristics of the incoming wave signal, and obtains the three-dimensional spatial wave arrival direction of the direction-finding signal. By optimizing the direction-finding algorithm, only one receiving channel is used for measurement, and radio direction-finding is realized under the premise of low weight and low power consumption. Combined with the technical means of ranging, it has application prospects in the navigation technology direction of light and small probes such as Mars drones.

[0113] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A radio positioning system for a Mars drone, characterized in that: include, An antenna is set at each of the four corners of the front of the square PCB board to form a circular array of planar pseudo-Doppler antennas; four microwave switches, baseband circuits and single-chip microcomputers are also set on the front of the square PCB board; four microstrip RF transmission lines, four sets of TOF ranging chips and peripheral circuits are set on the back of the square PCB board; Each antenna is connected to a microwave switch, and each microwave switch is connected to the head end of a microstrip RF transmission line. The terminals of the four microstrip RF transmission lines converge at the center point of the square PCB board and are connected to the baseband circuit. The microwave switch is controlled by a single-chip microcomputer. Each set of TOF ranging chip and peripheral circuit is set close to an antenna and connected to an antenna through the corresponding microwave switch. Use a single-chip microcomputer to control the on and off of the microwave switch to achieve direction or distance measurement: When used for direction finding, the four antennas in the circular array of planar pseudo-Doppler antennas are switched on in turn at a frequency of 4kHz through the control of the single-chip microcomputer, simulating the state of a single antenna rotating at a frequency of 1kHz; each antenna receives a plane wave signal generated by a source at the slave end, and the microwave switch, under the control of the single-chip microcomputer control signal, transmits the plane wave signal received by the corresponding antenna to the baseband circuit through the microstrip RF transmission line for down-conversion and filtering, and then obtains the pre-processed plane wave signal and transmits it to the single-chip microcomputer; After the single chip microcomputer performs FM demodulation on the received signal, it uses FFT transformation to obtain the frequency component corresponding to the Doppler frequency shift, extracts the phase of the pre-processed plane wave signal under the frequency component, and obtains the incoming direction of the plane wave; When used for ranging, the single-chip microcomputer controls the corresponding microwave switch to connect a selected set of TOF ranging chips and peripheral circuits to the antenna; the selected set of TOF ranging chips and peripheral circuits send ranging signals to the source of the slave end through the antenna, and the single-chip microcomputer is used to calculate the distance between the positioning system and the slave end according to the ranging response signal of the slave end; The slave end is a slave end with known settings; The Mars UAV positioning is achieved based on the direction finding results of the plane wave incoming wave and the distance measurement results of the positioning system and the slave end.

2. The radio positioning system for Mars UAV according to claim 1, characterized in that: The antenna is an omnidirectional antenna, and is connected to a microwave switch through a microstrip line using a coaxial line interface; the microwave switch is close to the coaxial line interface.

3. The radio positioning system for Mars UAV according to claim 2, characterized in that: Each antenna and the corresponding microwave switch and microstrip radio frequency transmission line form a group of signal units, and the four groups of signal units are centrally symmetrically distributed around the center point of the PCB board.

4. The radio positioning system for Mars UAV according to claim 3, characterized in that: The microwave switch is a reflective switch that uses a surface mount package and works in the 2.4G frequency band, and has a radio frequency signal input port, a control signal port, a signal output port A and a signal output port B; When used for direction finding, the RF signal input port is used to receive the plane wave signal, and the control signal port is used to receive the control signal of the single-chip microcomputer; the control signal is a high-level signal and a low-level signal; the control signal port turns on the signal output port A according to the received control signal to transmit the signal, and at the same time turns off the other signal output port; When used for ranging, the direction finding function is turned off; the RF signal input port is used to receive the ranging signal sent by a selected set of TOF ranging chips and peripheral circuits; the control signal port turns on the output port B according to the control signal of the received microcontroller, so that the ranging signal is sent to the antenna through the output port B, and the antenna then sends the ranging signal to the signal source at the slave end.

5. The radio positioning system for Mars UAV according to claim 4, characterized in that: The geometric dimensions of the square PCB board do not exceed 10*10cm.

6. The radio positioning system for Mars UAV according to claim 5, characterized in that: The impedance of each microstrip RF transmission line is 50 ohms; the length of each microstrip RF transmission line is an integer multiple of 1 / 4λ, where λ is the wavelength of the 2.4G frequency band signal when propagating in the microstrip RF transmission line; when one microstrip RF transmission line transmits a signal, the input impedances of the other three microstrip RF transmission lines are all in an open circuit state.

7. The radio positioning system for Mars UAV according to claim 6, characterized in that: The terminals of the four microstrip RF transmission lines are connected at the center point of the square PCB board to form a cross layout. Each microstrip RF transmission line extends in a zigzag manner from the head end to the terminal, and arcs are used at the zigzag corners.

8. The radio positioning system for Mars UAV according to claim 7, characterized in that: The baseband circuit includes a down-conversion module composed of a radio frequency front-end I / Q modulation and demodulation chip and its peripheral circuits, and a differential-to-single-ended and low-pass filtering module composed of a dual-channel integrated operational amplifier and its peripheral circuits; The plane wave signal transmitted by the microstrip RF transmission line is converted into a differential signal through the balun in the baseband circuit, and then enters the down-conversion module to obtain the I\Q differential signals. Then, the differential to single-ended and low-pass filtering module outputs the low-frequency I\Q single-ended signals, which are transmitted to the microcontroller as pre-processed signals.

9. The radio positioning system for Mars UAV according to claim 8, characterized in that: The method of FM demodulation of the received signal by the single chip microcomputer includes: Assume that the plane wave signal generated by the source is f(t): Where f c is the carrier frequency, ω c is the carrier angular frequency, is the initial phase of the carrier signal, t is the time; The four antennas are turned on in turn, integrating the four plane wave signals into one signal in time sequence. The signal entering the baseband circuit is S n (t): Where n is the number of the antenna, B n is the amplitude of the plane wave signal received by the nth antenna, is the phase of the carrier signal, D is the diameter of the pseudo-Doppler antenna circular array, ε is the elevation angle of the plane wave signal, N is the number of antennas, and θ is the angle between the plane wave signal and the antenna when t = 0; Signal S n (t) After being processed by the baseband circuit, the pre-processed plane wave signal obtained is a low-frequency I\Q two-way single-ended signal; The microcontroller performs an inverse tangent operation on the low-frequency I\Q two-way single-ended signal to obtain the instantaneous phase φ(t) of the plane wave signal: in The Doppler frequency shift is generated by the four antennas switching on in turn. When the ratio of the height difference between the signal source and the antenna to the distance from the signal source to the center of the pseudo-Doppler antenna circular array is less than 1 / 10, the elevation angle ε of the plane wave signal is considered to be 0, and cosε is considered to be 1. Taking the derivative of the instantaneous phase φ(t), we can obtain the instantaneous frequency ω(t) of the plane wave signal: This enables the microcontroller to perform FM demodulation of the received signal.

10. The radio positioning system for Mars UAV according to claim 9, characterized in that: The method to obtain the incoming direction of a plane wave is: Perform FFT transformation on the instantaneous frequency ω(t) to obtain a plane wave signal spectrum diagram; the frequency component corresponding to the antenna rotation contained in the spectrum diagram is the frequency component corresponding to the Doppler frequency shift; the frequency component is expressed in complex form, and the phase of the complex form frequency component is calculated to obtain the incoming wave angle with a constant offset Where θ0 represents the constant offset, and θ is calculated to determine the incoming direction of the plane wave.

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