The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.
 Such as figure 1 As shown, the present invention provides an aircraft height control method and system based on radar technology, including an omnidirectional rotating base 1 for fixed installation on the aircraft, and the omnidirectional rotating base 1 is fixed upside down on the lower surface of the aircraft, In addition, a shielding protective cover 2 for reducing external signal interference is installed on the omnidirectional rotating base 1, and a radar ranging unit 3 for height detection and a feedback adjustment unit for height adjustment are installed inside the shielding protective cover 2 4.
 In this embodiment, the omnidirectional rotating base 1 includes an eight-claw base 101 for upside-down installation on the lower surface of the aircraft, and a rotary drive motor 102 is embedded in the center of the eight-claw base 101, and the rotation drive A telescopic shaft 103 is sleeved on the drive shaft of the motor 102, and a rotating base body 104 with a fixed groove excavated on the surface is mounted on the lower surface of the telescopic shaft 103.
 Since the aircraft is flying high in the sky, in order to ensure the accuracy of ranging and extend the service life of the device, the omnidirectional rotating base 1 is used to install the entire measurement system under the aircraft through the eight-jaw base 101, and the telescopic shaft 103 can be driven by the rotating drive motor 102. Rotating clockwise or counterclockwise, the height of the rotating base body 104 can be fine-tuned, the entire base can be stored in the aircraft or the base can be put down, and the angle and direction of the radar ranging unit 3 can be adjusted.
 Such as figure 2 As shown, the radar ranging unit 3 includes an antenna front end 301 for transmitting and receiving signals. The antenna front end 301 includes a transmitting antenna 302 connected to a transmitting channel and a receiving antenna 303 connected to a receiving channel. The input end is connected with a power amplifier 304 for amplifying and driving, the output end of the receiving antenna 303 is connected with a low-noise amplifier 305 for amplifying the received signal; the input channel end of the antenna front end 301 is connected with the transmitting for modulation of the transmitted signal Modulation unit 306, the output channel end of the antenna front end 301 is connected with a phase measurement unit 307 based on high-precision time measurement technology; the output end of the phase measurement unit 307 is also connected with a wireless signal transmitter 308 for communicating with the feedback adjustment unit 4 .
 It is added that radars are divided into pulse radars and continuous wave radars according to the types of transmitted signals. Conventional pulse radars emit periodic high-frequency pulses, and continuous wave radars emit continuous wave signals. The signal transmitted by continuous wave radar can be single frequency continuous wave (CW) or frequency modulated continuous wave (FMCW). There are also many ways of frequency modulation, such as triangle wave, sawtooth wave, code modulation or noise frequency modulation. Among them, the single-frequency continuous wave radar can only be used for speed measurement and cannot measure the distance, while the FMCW radar can measure both distance and speed, and its advantages in short-range measurement are increasingly obvious. The FMCW radar emits a continuous wave with a changing frequency during the sweep period. The echo reflected by the object has a certain frequency difference with the transmitted signal. The distance information between the target and the radar can be obtained by measuring the frequency difference. Low, generally KHz, so the hardware processing is relatively simple, suitable for data acquisition and digital signal processing.
 In this embodiment, the phase measurement unit 307 includes a low-pass filter 309 for introducing a received signal, a reference signal source 310 for providing a reference frequency signal, and a TDC timing chip 313 based on the principle of delay line insertion. The reference signal source 310 has two orthogonal carrier frequency signal outputs, and each output path is connected in series with a signal mixer 311, and the input ends of the two signal mixers 311 respectively introduce a received signal and a transmitted signal. , The output terminal of the signal mixer 310 is connected in series with a filtering and shaping circuit 312, and the outputs of the two filtering and shaping circuits 312 are simultaneously loaded to the TDC timing chip 313.
 The working method for controlling the radar ranging unit 3 includes:
 Step 101: Transmit a continuous frequency modulation radar signal. The transmit modulation unit 306 modulates and generates a signal whose frequency changes according to a certain rule, and is amplified by the power amplifier 304 and then transmitted to the ground via the transmitting antenna 302;
 Step 102: Receive the radar echo signal, the transmitted signal is reflected back after encountering obstacles on the ground, the interference clutter is filtered out by the shielding cover 2, and the receiving antenna 303 is sent to the phase measurement unit 307 for processing;
 Step 103: Time measurement phase difference calculation. The transmitted signal and the received signal are shaped by the filtering and shaping circuit 312, and the time difference between the two is calculated by the TDC time measurement chip 313, converted into the phase difference and combined with the aircraft speed to obtain the current height of the aircraft from the ground.
 When starting the radar ranging unit 3, it is first necessary to generate a continuous frequency modulation transmission wave signal; the transmission modulation unit 306 includes a carrier signal source 314 for providing a carrier signal and an intermediate frequency signal source 315 for providing a transmission number. The output signals of the signal source 314 and the intermediate frequency signal source 315 pass through the mixer and output the modulated signal to the input end of the power amplifier 304.
 The carrier signal generated by the carrier signal 314 and the continuous frequency modulation signal generated by the intermediate frequency signal source 315 are mixed by the mixer to transform the original intermediate frequency transmission signal to a radio frequency level, thereby helping to increase the transmission distance of the transmission signal. The signal is amplified by the power amplifier 304 and sent to the transmitting antenna 302. The transmitting antenna 302 converts the guided waves in the dielectric into electromagnetic waves in free space and transmits them. The transmitted electromagnetic waves return after encountering ground obstacles.
 When the target echo returns to the aircraft, it first passes through the shielding protective cover 2. The shielding protective cover 2 includes a radome base 201 made of polymer space composite materials. The outer surface of the radome base 201 is provided with The frequency selective surface 202 of the gradual cross unit. The frequency selective surface 202 is combined with the radome base 201 to form a hemispherical shell and connected to the outer surface of the radar ranging unit 3; since the returned signal contains a lot of interference clutter, This makes the subsequent processing very difficult. Therefore, a frequency selective surface 202 is designed here. The frequency selective surface 202 is formed by etching a cross slit on a metal plate, and has a bandwidth corresponding to the emission frequency. The internal echo passes, thereby improving the purity of the echo signal and filtering out most of the clutter.
 When the received signal output by the receiving antenna 303 is subjected to secondary de-noise amplification by the low-noise amplifier 305, it enters the phase measurement unit 307; in the phase measurement unit 307, in order to improve the ranging accuracy, combined with the current high-precision time measurement technology, In the phase measurement, the reference signal is introduced through the reference signal source 310, and the reference signal is subjected to difference frequency mixing with the received signal to be measured and the known received signal in the signal mixer 310 to obtain two low-frequency signals, and the phase of the original signal The difference is preserved in the two low-frequency signals. At this time, the calculated frequency is converted from the original carrier frequency to the difference between the carrier frequency and the reference signal frequency. When the frequency decreases, the measurement signal time becomes longer, and the measurement is performed while the phase remains unchanged. The phase accuracy is greatly improved, and the distance measurable range is increased; further, the two low-frequency signals are shaped into square waves by the filtering and shaping circuit 312, and the time difference between the two signals is calculated by the TDC timing chip 313, according to the time and phase The phase difference is obtained by the relationship of, and then the distance difference corresponding to the phase difference is calculated through the differential relationship between the phase and the distance.
 The distance difference calculated by the TDC timing chip 313 is converted into a radio frequency signal by the wireless signal transmitter 308 and transmitted to the feedback adjustment unit 4.
 Such as image 3 As shown, the feedback adjustment unit 4 includes an MCU controller 401 for signal processing and command output, and a signal input end of the MCU controller 401 is connected with a wireless signal receiver 402 for receiving a wireless signal transmitter 308 The control PWM signal output end of the MCU controller 401 is connected with a height control unit 403 for height adjustment and a flight monitoring unit 40404 for obtaining the current flight status of the aircraft, the flight detection unit 404 and the MCU controller 401 and height control Unit 403 forms a PID feedback regulation system.
 The feedback adjustment unit 4 receives the height distance difference from the TDC timing chip 313 through the wireless signal receiver 402, and the MCU controller 401 obtains the vertical height of the current aircraft from this, and then obtains the current aircraft through the flight monitoring unit 40404 Flight parameters.
 In this embodiment, the flight monitoring unit 404 includes a rotation speed sensor 407 for collecting the current working state of the aircraft driving motor, an attitude sensor 408 for collecting the current pitch angle of the aircraft, and a speed sensor 409 for detecting the current horizontal speed of the aircraft. The output signals of the rotational speed sensor 407, the attitude sensor 408, and the speed sensor 409 are transmitted to the analog-to-digital conversion port of the MCU controller 401; the rotational speed sensor 407 measures the current motor speed, and then the MCU controller 401 calls the internal conversion program to obtain the current The vertical movement speed of the aircraft can also obtain the current pitch angle and horizontal speed of the aircraft, thereby establishing the dynamic trajectory equation of the aircraft in the three-dimensional space.
 When height adjustment control is required, the MCU controller 401 obtains the parameters to be adjusted according to the current altitude and the actual parameters of the aircraft, and outputs the corresponding adjustment signal to the height adjustment unit 403 for height adjustment control.
 The height control unit 403 includes a vertical speed controller 405 for adjusting the vertical height and a pitch angle controller 406 for adjusting the pitch angle of the aircraft. The vertical speed controller 405 outputs a speed adjustment signal to the propeller-driven steering gear. , The pitch angle controller 406 is used to output signals to the gyroscope control terminal; the vertical speed controller 405 controls the rotation speed and steering of the elevator driving servo to achieve up or down and acceleration and deceleration, and the pitch angle controller 406 controls the gyroscope to achieve The adjustment of the pitch angle realizes the accurate adjustment of the aircraft height.
 For those skilled in the art, it is obvious that the present invention is not limited to the details of the foregoing exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the foregoing description, and therefore it is intended to fall within the claims. All changes within the meaning and scope of equivalent elements of are included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.