CN110632583B - Digital radio altimeter - Google Patents
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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
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/08—Systems for measuring distance only
- G01S13/32—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
- G01S13/36—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated with phase comparison between the received signal and the contemporaneously transmitted signal
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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
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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
- G01S7/35—Details of non-pulse systems
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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
- G01S7/35—Details of non-pulse systems
- G01S7/352—Receivers
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Abstract
The invention discloses a digital radio altimeter, and relates to the technical field of electronics. The altimeter is used for solving the problems that two altimeters are installed on each existing airplane, the altimeters are mutually influenced, the wrong height measurement result can be caused, and the flight safety is influenced. The digital radio altimeter comprises: control and signal processing components, radio frequency components and antenna components; the radio frequency component forms a local oscillation signal with switchable working frequency according to the frequency control signal; sequentially carrying out phase modulation on the TTL pseudo codes, carrying out frequency mixing with a local oscillator signal to obtain a first transmitting signal, carrying out power adjustment on the first transmitting signal according to a power control signal to obtain a second transmitting signal, and transmitting through an antenna assembly; receiving a digital intermediate frequency signal corresponding to the second transmitting signal through the antenna assembly, and sequentially carrying out digital orthogonal down-conversion processing and a code loop acquisition and tracking algorithm on the digital intermediate frequency signal to obtain a code NCO2(ii) a Code NCO2And generating a local code by a second pseudo code generator, and comparing the phase difference of the local code and the TTL pseudo code to obtain a height value.
Description
Technical Field
The invention relates to the technical field of electronics, in particular to a digital radio altimeter.
Background
The currently used radio altimeters can be classified according to the signal characteristics of the transmitted signal: frequency Modulated Continuous Wave (FMCW) regime, PULSE regime (PULSE) and pseudo code phase modulated continuous wave regime.
The frequency modulation continuous wave height meter is characterized by that it uses the modulation signal in the form of triangular wave, saw-tooth wave or sine wave, etc. and adds it on the voltage-controlled oscillator to produce high-frequency transmission signal whose frequency range is changed greatly and its frequency range is identical to that of modulation signal, said signal is radiated towards ground surface by means of transmitting antenna, the echo signal reflected from ground surface is fed into receiver by means of receiving antenna, and mixed with partial energy of transmission signal, and the difference frequency signal containing height information is outputted. The current relatively perfect frequency modulation continuous wave height meter is a constant beat system frequency modulation continuous wave height meter. The altimeter is mainly used for measuring the low altitude below 1500m, has the advantages of high altitude measurement resolution, small error and high tracking speed, is suitable for the use of an airplane during approach and landing, and has smaller required transmitting power than a pulse system altimeter in a certain altitude measurement range; the method has the defects that the inherent anti-interference capability is poor, the height measurement range is limited by the isolation degree of the antenna, the height is easily influenced by high-power emission leakage, and the height measurement precision is influenced by the linearity and the maximum frequency deviation of the voltage-controlled oscillator.
The pulse system altimeter uses a nanosecond high-voltage pulse to modulate a high-frequency oscillator to generate a high-power radio-frequency pulse, the high-power radio-frequency pulse is radiated to the ground through a transmitting antenna, an echo signal reflected from the ground enters a receiver through a receiving antenna, and after frequency mixing, amplification and detection, the delay of the transmitting pulse and the receiving pulse is compared, so that the height value is calculated. The altimeter is mainly used for measuring the middle and high heights of more than 1500m, and has the advantages of strong anti-interference capability, large height measurement range, easy increase of the measurement range, high height measurement precision and the like compared with a continuous wave system altimeter; the disadvantage is that the low height is susceptible to transmit leakage, and the processing speed is not fast enough, resulting in poor real-time performance.
The two altimeters generally adopt an analog working mode, wherein the number of discrete devices such as resistors, capacitors, operational amplifiers and the like is large, so that the equipment is large in size, high in power consumption, low in measurement precision and low in reliability, and the application capability of an avionic integrated system is supported.
In recent years, with the appearance of a pseudorandom coding technology, a pseudo code ranging technology is developed very rapidly, and a radio altimeter using the pseudo code ranging technology appears at home and abroad, and the pseudo code radio altimeter is a radio altimeter adopting a direct sequence spread spectrum technology, and has high ranging precision by utilizing a sharp correlation peak in pseudo random code correlation. Compared with the PULSE and FMCW radio altimeters, the pseudo-code radio altimeter has the advantages of strong anti-interference capability, large height measurement range, high distance measurement precision and the like, and is mainly applied to height measurement in high-dynamic and low-signal-to-noise-ratio environments. The method has the defects that each airplane is generally provided with two altimeters, when the altitude measurement is carried out by adopting a pseudo code distance measurement system, if each altimeter adopts the same working frequency and the same pseudo code pattern, one altimeter can track the echo signal of the other altimeter during flying, and the altimeter of one airplane can track the echo signals of other altimeters during team flying, so that the wrong tracking can cause wrong altitude measurement results and influence the flying safety.
In summary, in the prior art, two altimeters are installed on each airplane, and the same working frequency and the same pseudo code pattern are adopted, so that the height measurement result is wrong, and the flight safety is affected.
Disclosure of Invention
The embodiment of the invention provides a digital radio altimeter, which is used for solving the problem that in the prior art, when two altimeters are installed on each airplane or the airplanes form a team to fly, the altimeters adopt the same working frequency and the same pseudo code pattern, and mutual interference among the altimeters can cause wrong height measurement results and influence the flight safety.
The embodiment of the invention provides a digital radio altimeter, which comprises: control and signal processing components, radio frequency components and antenna components;
the control and signal processing assembly is electrically connected with the radio frequency assembly and is used for sending TTL pseudo codes, power control signals and frequency control signals to the radio frequency assembly; so that the radio frequency component forms a local oscillation signal with switchable working frequency according to the frequency control signal; the radio frequency assembly sequentially performs phase modulation on the TTL pseudo codes, performs frequency mixing with the local oscillator signals to obtain first transmitting signals, performs power adjustment on the first transmitting signals according to the power control signals to obtain second transmitting signals, and transmits the second transmitting signals through an antenna assembly;
receiving a digital intermediate frequency signal corresponding to the second transmitting signal through the antenna assembly, and sequentially carrying out digital orthogonal down-conversion processing and a code loop acquisition and tracking algorithm on the digital intermediate frequency signal to obtain a code NCO2(ii) a The code NCO2Generating a local code by a second pseudo code generator, and comparing the local code with the local codeAnd comparing the phase differences of the TTL pseudo codes to obtain a height value.
Preferably, the transmitting unit of the radio frequency assembly comprises a DDS chip, a frequency mixer, a first local oscillation module, a numerical control attenuator, a power amplification module and a singlechip;
the radio frequency component forms a local oscillation signal with switchable working frequency according to the frequency control signal; the radio frequency assembly sequentially performs phase modulation on the TTL pseudo codes, performs frequency mixing with the local oscillator signal to obtain a first transmitting signal, performs power adjustment on the first transmitting signal according to the power control signal to obtain a second transmitting signal, and transmits the second transmitting signal through an antenna assembly, and specifically includes:
the single chip microcomputer is used for receiving the power control signal and the frequency control signal sent by the control and signal processing assembly;
the DDS chip is used for carrying out 0/pi phase modulation on the TTL pseudo code;
the first local oscillation module is configured to form local oscillation signals with switchable working frequencies according to the frequency control signal sent by the single chip microcomputer, where the local oscillation signals include 11 working frequencies with a frequency interval of 20MHz between 4200MHz and 4400 MHz;
the frequency mixer is used for mixing the local oscillator signal with the TTL pseudo code of the phase modulation to obtain the first transmitting signal;
the numerical control attenuator is used for adjusting the power of the first transmitting signal according to the power control signal transmitted by the singlechip to obtain a second transmitting signal;
and the power amplification module is used for carrying out power amplification on the second transmitting signal and transmitting the second transmitting signal through an antenna component.
Preferably, the receiving, by the antenna assembly, the digital intermediate frequency signal corresponding to the second transmission signal specifically includes:
the receiving unit of the radio frequency component is used for mixing the ground reflected signals received by the antenna, forming intermediate frequency signals after sequentially passing through an AGC circuit, a filter and an amplifier and sending the intermediate frequency signals to the control and signal processing component;
the control and signal processing assembly includes an a/D converter that samples the intermediate frequency signal to form the digital intermediate frequency signal.
Preferably, the control and signal processing assembly comprises a programmable logic device FPGA and a DSP chip; the FPGA is provided with a power registering module and a frequency registering module; a power conversion unit and a random frequency generation unit are arranged in the DSP chip;
the random frequency generation unit is used for generating a frequency serial number to be replaced and replacement time and sending the frequency serial number to be replaced to the frequency registering module; the frequency registering module is used for storing preset N frequencies, and when the frequency serial number to be replaced is received, the frequency registering module generates the frequency control signal according to the frequency serial number to be replaced;
the power conversion unit is used for generating a power control instruction according to the power frequency band to which the height value belongs and sending the control instruction through the power register module.
Preferably, after obtaining the height value, the method further includes:
and transmitting the height value to an avionics system through an RS422 or ARINC429 data interface chip. Preferably, the power supply assembly is electrically connected with the radio frequency assembly and the control and signal processing assembly respectively;
the power supply assembly supports two power supply voltages of DC28V or AC115V @400 Hz.
Preferably, the radio frequency assembly further comprises a constant temperature crystal oscillator; the constant temperature crystal oscillator is used for generating a plurality of paths of clock signals.
Preferably, the digital intermediate frequency signal is sequentially subjected to digital quadrature down-conversion processing and a code loop acquisition and tracking algorithm to obtain a code NCO2The method also comprises the following steps:
carrier NCO obtained through carrier capturing and tracking algorithm1。
The embodiment of the invention provides a digital radio altimeter, which comprises: control and signal processing components, radio frequency components and antenna components; the control sum signalThe physical component is electrically connected with the radio frequency component and is used for sending the TTL pseudo code, the power control signal and the frequency control signal to the radio frequency component; so that the radio frequency component forms a local oscillation signal with switchable working frequency according to the frequency control signal; the radio frequency assembly sequentially performs phase modulation on the TTL pseudo codes, performs frequency mixing with the local oscillator signals to obtain first transmitting signals, performs power adjustment on the first transmitting signals according to the power control signals to obtain second transmitting signals, and transmits the second transmitting signals through an antenna assembly; receiving a digital intermediate frequency signal corresponding to the second transmitting signal through the antenna assembly, and sequentially carrying out digital orthogonal down-conversion processing and a code loop acquisition and tracking algorithm on the digital intermediate frequency signal to obtain a code NCO2(ii) a The code NCO2And generating a local code by a second pseudo code generator, and comparing the phase difference between the local code and the TTL pseudo code to obtain a height value. In the digital radio altimeter provided by the embodiment of the invention, a plurality of frequencies are stored in a video component of the altimeter in advance, when the altimeter runs, a control and signal processing component adjusts and controls a local oscillator signal in a radio frequency component along with a generated frequency control instruction so as to realize the random change of the frequency of the altimeter, moreover, the radio frequency component performs phase modulation on a received TTL pseudo code and performs frequency mixing with the local oscillator signal of which the frequency is adjusted to obtain a first transmitting signal, and adjusts the first transmitting signal according to a received power control signal to obtain a second transmitting signal, so that the function of automatically adjusting the transmitting power along with the altitude is realized; further, the control and signal processing module NCO is adapted to receive a code corresponding to the second transmitted signal2And comparing the phase difference with the phase difference of the TTL pseudo code to obtain a height value, and further generating a frequency control instruction and a power control instruction according to the height value, thereby solving the problem that a plurality of pieces of equipment with the same fixed frequency and pseudo code type are installed and used at the same time or the pieces of aircraft formation flying equipment are mutually interfered.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a digital radio altimeter according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a transmitting unit according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a receiving unit according to an embodiment of the present invention;
FIG. 4 is a schematic structural diagram of a control and signal processing module according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of a power supply module according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 exemplarily shows a schematic structural diagram of a digital radio altimeter provided by an embodiment of the present invention, as shown in fig. 1, the digital radio altimeter mainly includes: control and signal processing components, radio frequency components, and antenna components.
Specifically, the antenna assembly comprises a receiving end and a transmitting end; the radio frequency assembly comprises a receiving unit and a transmitting unit; the control and processing component comprises an FPGA, a DSP and the like; in practical application, a receiving end of the antenna assembly is connected with an input port of the receiving unit through a feeder line, and an output port of the receiving unit is connected with the control and signal processing assembly; the transmitting end of the antenna component is connected with the output port of the transmitting unit through a feeder line, and the input port of the transmitting unit is connected with the pseudo code output port of the control and signal processing component; the clock output port of the radio frequency assembly is connected with the clock input port of the control and signal processing assembly; the control port of the radio frequency assembly is connected with the control port of the control and signal processing assembly; each component unit is powered by a power supply component.
In the embodiment of the invention, the control and signal processing assembly is used for sending the TTL pseudo code, the power control signal and the frequency control signal to the radio frequency assembly; further, after receiving the information, the radio frequency component first forms a local oscillation signal with switchable working frequency according to the frequency control signal; and then, sequentially carrying out phase modulation on the received TTL pseudo codes, then carrying out frequency mixing on the TTL pseudo codes after the phase modulation and the local oscillator signals to obtain first transmitting signals, further carrying out power adjustment on the first transmitting signals according to the power control signals to obtain second transmitting signals, and then transmitting the second transmitting signals through a transmitting end of the antenna assembly.
Fig. 2 is a schematic structural diagram of a transmitting unit according to an embodiment of the present invention, and as shown in fig. 2, the transmitting unit of the radio frequency assembly according to the embodiment of the present invention mainly includes: the digital synthesizer comprises a DDS chip, a low-phase-noise constant-temperature crystal oscillator, a frequency mixer, a first local oscillator module, a numerical control attenuator, a power amplifier module, a single chip microcomputer and the like. In the embodiment of the invention, the control instruction mainly comprises a power control signal and a frequency control signal, when the singlechip receives the power control signal and the frequency control signal, the frequency control signal is respectively sent to the first local oscillator module and the power control signal is sent to the numerical control attenuator, and the random switching of working frequency and the automatic adjustment of transmitting power according to elevation are realized by controlling the frequency control circuit and the power control circuit. In application, 11 operating frequencies with 20MHz intervals between 4200MHz and 4400MHz are included, that is, through regulation and control of the frequency control signal, 11 operating frequencies with 20MHz intervals between 4200MHz and 4400MHz can be switched randomly.
As shown in fig. 2, the DDS chip performs 0/pi phase modulation on the received TTL pseudo code; the constant temperature crystal oscillator generates clock signals to provide reference clock signals for each component unit; the first local oscillation module forms a local oscillation signal with switchable working frequency according to a frequency control signal sent by the singlechip, and further, the local oscillation signal and the TTL pseudo code of phase modulation are subjected to up-conversion in the frequency mixer to form a first transmitting signal; the first transmitting signal enters the numerical control attenuator through the filter, and the numerical control attenuator adjusts the power of the received first transmitting signal according to the power control signal transmitted by the single chip microcomputer to obtain a second transmitting signal; and after the second transmitting signal is sent to the power amplifier module, the power amplifier module amplifies the power of the received second transmitting signal, and then sends the second transmitting signal to the antenna assembly to be transmitted through the transmitting end of the antenna assembly.
Fig. 3 is a schematic structural diagram of a receiving unit according to an embodiment of the present invention, and as shown in fig. 3, the receiving unit of the radio frequency component according to the embodiment of the present invention mainly includes a limiter, a low noise amplifier, a first-stage mixer, a second-stage mixer, a first-stage AGC circuit, a second-stage AGC circuit, a final-stage amplifier, a detector, a single chip, and the like. The receiving unit is used for receiving the ground reflected signal received by the antenna assembly, wherein the ground reflected signal received by the antenna is opposite to the second transmitting signal sent by the transmitting end of the antenna assembly. The receiving unit receives the reflected signal and then carries out frequency mixing, and outputs an intermediate frequency signal to the control and signal processing component for processing after passing through the second-stage AGC circuit, the filter and the final-stage amplifier. In practical application, when the received signal strength is greater than a set value, the gain control loop starts to work, so that the constant output of the intermediate frequency signal amplitude can be ensured, namely when the first-stage AGC circuit and the second-stage AGC circuit are started, the constant 1Vp-p intermediate frequency signal can be output.
Further, after the control and signal processing module receives the intermediate frequency signal corresponding to the second transmission signal, the control and signal processing module needs to process the intermediate frequency signal, that is, the control and signal processing module samples the received intermediate frequency signal through the a/D converter included in the control and signal processing module to form a digital intermediate frequency signal.
Further, the digital intermediate frequency signal is sequentially subjected to digital quadrature down-conversion processing, a carrier capture tracking algorithm and codesCarrier NCO obtained by loop capture tracking algorithm1Sum code NCO2(ii) a The obtained code NCO2And generating a local code by a second pseudo code generator, and comparing the phase difference between the local code and the TTL pseudo code to obtain a height value.
Fig. 4 is a schematic structural diagram of a control and signal processing component according to an embodiment of the present invention, and as shown in fig. 4, the control and signal processing component according to the embodiment of the present invention mainly includes an a/D converter, a programmable logic device FPGA, a DSP chip, an RS422, an ARINC429 data interface chip, and the like.
Specifically, the FPGA is provided with a power registering module and a frequency registering module, and a power conversion unit and a random frequency generation unit are arranged in the DSP chip; in practical application, the random frequency generation unit is used for generating a frequency serial number to be replaced and replacement time, and sending the frequency serial number to be replaced to the frequency registration module; furthermore, the frequency registering module is used for storing preset N frequencies, and when the frequency registering module receives the frequency serial number to be replaced, the frequency registering module generates a frequency control signal according to the frequency serial number to be replaced and the pre-stored N middle frequencies, and sends the generated frequency control signal to the transmitting unit of the radio frequency component. And then, the power conversion unit acquires a height value obtained by calculation according to the local code and the TTL pseudo code, generates a power control instruction according to the power frequency band to which the height value belongs, and sends the power control instruction to the transmitting unit of the radio frequency component through the power register module of the FPGA.
It should be noted that the single chip microcomputer included in the sending unit is configured to receive the generated power control signal and the frequency control signal. Furthermore, the power control signal and the frequency control signal are respectively used for controlling the frequency control circuit and the power control circuit, so that the random switching of the working frequency and the automatic adjustment of the transmitting power according to the elevation are realized. In practical application, the frequency control circuit mainly comprises a singlechip, a first local oscillation module, a frequency mixer and the like; the power control circuit mainly comprises a singlechip, a numerical control attenuator and the like.
Further, after the DSP chip determines the height value through the local code and the TTL pseudo code, the determined height value needs to be transmitted to the avionics system through the RS422 or ARINC429 data interface chip.
As shown in fig. 4, a local pseudo-code generator, an emission pseudo-code generator, a frequency register module, a power register module, a digital quadrature down converter, etc. are arranged in the FPGA; specifically, the pseudo code generator is used for generating a TTL pseudo code and inputting the TTL pseudo code to the transmitting unit, and the pseudo code generated by the local pseudo code generator is used as a tracked local code; the first path of digital voltage-controlled oscillator NCO1 included by the digital orthogonal down converter is used as a local oscillator of the digital orthogonal down converter and is called carrier NCO1, the second path of digital voltage-controlled oscillator NCO2 included by the digital orthogonal down converter is used as a clock for capturing and tracking chips in a loop by using a modulation code and is called code NCO2, and the frequency of the two paths of digital voltage-controlled oscillators is set by a DSP.
A power conversion unit and a random frequency generation unit are arranged in the DSP; the random frequency generation unit is used for generating a frequency serial number to be replaced and replacement time, sending the selected frequency serial number to a frequency register module in the FPGA through a data bus, generating a frequency control instruction, and sending the frequency control instruction to the radio frequency assembly through an RS422 interface to complete frequency control; the power conversion unit judges the power section to which the sent height value belongs, selects a corresponding power control word, sends the selected power control word to a power control module in the FPGA through a data bus, generates a power control instruction, and sends the power control instruction to the radio frequency assembly through an RS422 interface to finish the automatic control of the transmitting power along with the elevation; the DSP is internally solidified with signal processing software, and the calculated height information is output by an RS422 or ARINC429 data interface chip. The whole control and signal processing assembly is used for generating pseudo-random codes, power control signals and frequency setting signals, finishing the relevant time delay processing of receiving signals and sending signals and outputting height information through RS422 and ARINC429 data interface chips.
In practical applications, the digital intermediate frequency signal is represented by formula (1):
S(i)＝A·C(iTs-τ)cos[(wI+wd)i+φ]+n(i) (1)
where A is the received signal amplitude,
for a sampling period, C (iT)s- τ) ± 1 is the delayed pseudo-random code signal, wIIs a carrier intermediate frequency digital angular frequency, wdIs the doppler digital angular frequency shift of the carrier, phi is the phase shift of the carrier, and n (i) is the received signal noise.
The digital intermediate frequency signal is subjected to digital quadrature down-conversion to obtain I, Q two-path signals, which are shown in the following equations (2) and (3):
wherein,
Δwd＝wd-w'd。
I. the Q two paths of signals are respectively related to the early, real-time and late pseudo codes generated by the local pseudo code generator to obtain (I)PS，Qps)、(IES，QES)、(ILS，QLS) Three groups of signals, and calculating the three groups of signals to obtain three modes EP、EE、EL。
Wherein E isP、EE、ELRespectively expressed by the following formulas:
further, according to EP、EE、ELThe moving direction of local code is regulated by the magnitude of three-way modulus value to make the instantaneous pseudo-random code correlation modulus maximum, and then the carrier NCO is regulated1Finally, the carrier frequency difference and the carrier phase difference are zero, and the capturing and tracking of the carrier and the modulation code are completed. Then the FPGA and the DSP chip compare the phase of the received pseudo-random code with the local code and finish the two steps of rough measurement and fine measurement, wherein the rough measurement is to plan the time delay of the received pseudo-random code into a single code element width to obtain a rough time delay t0τ × n, where τ is the symbol width and n is the number of symbol delays; the precise measurement is to divide the single crystal into M parts, and step by step through a digital voltage controlled oscillator
The phase shift obtains a time delay delta t within one code element width, and the propagation time delay of the transmitting code is t ═ t0+ Δ t, and then
And calculating a height value.
It should be noted that, the FPGA and the DSP chip cooperate to complete carrier capture and tracking, the two branches I and Q output by the digital quadrature down conversion pass through the correlator and the integral cleaner to obtain two signals of the instant branch, and after the identification of the carrier frequency difference and the carrier phase difference is completed by the software algorithm in the DSP chip, the two signals are sent to the carrier NCO1And then adjusting the frequency and the phase of the local oscillation signal to make the finally achieved carrier frequency difference and carrier phase difference zero.
The FPGA and the DSP chip are matched to complete the capture of modulation codes, and three groups of signals (I) are obtained after an I branch and a Q branch which are output by the digital quadrature down-conversion pass through a correlator and an integral cleanerPS，Qps)、(IES，QES)、(ILS，QLS) Calculating to obtain three-way modulus value EP、EE、ELRespectively with digital signal processingComparing self-adaptive thresholds in the device, judging whether the modulation code and the local pseudo-random code are synchronous or not, and performing coarse adjustment asynchronously; after the modulation code and the local pseudo-random code are roughly synchronized, the phase difference between the local pseudo-random code and the received modulation code in one chip is identified by adopting a normalized lead-lag envelope, and the calculated phase difference is fed back to the code NCO2And adjusting the code phase to enable the phase difference to meet the precision requirement.
Fig. 5 is a schematic structural diagram of a power supply module according to an embodiment of the present invention, and as shown in fig. 5, the power supply module mainly includes an AC-DC power supply module, a filter, a surge suppressor, a DC-DC power supply module, an isolation filter, and the like, and in an embodiment of the present invention, the power supply module supports two power supply voltages of DC28V or AC115V @400 Hz.
The embodiment of the invention provides a digital radio altimeter, which comprises: control and signal processing components, radio frequency components and antenna components; the control and signal processing assembly is electrically connected with the radio frequency assembly and is used for sending TTL pseudo codes, power control signals and frequency control signals to the radio frequency assembly; so that the radio frequency component forms a local oscillation signal with switchable working frequency according to the frequency control signal; the radio frequency assembly sequentially performs phase modulation on the TTL pseudo codes, performs frequency mixing with the local oscillator signals to obtain first transmitting signals, performs power adjustment on the first transmitting signals according to the power control signals to obtain second transmitting signals, and transmits the second transmitting signals through an antenna assembly; receiving a digital intermediate frequency signal corresponding to the second transmitting signal through the antenna assembly, and sequentially carrying out digital orthogonal down-conversion processing and a code loop acquisition and tracking algorithm on the digital intermediate frequency signal to obtain a code NCO2(ii) a The code NCO2And generating a local code through a second pseudo code generator, and comparing the phase difference between the local code and the TTL pseudo code to obtain a height value. The digital radio altimeter provided by the embodiment of the invention adopts a digital signal processing technology, so that a large number of analog discrete devices are avoided, the volume of equipment is reduced, and the weight of the equipment is reduced; the pseudo code ranging technology is adopted, the processing gain is higher, the transmitting power can be reduced, and therefore the coupling between the transmitting antenna and the receiving antenna is reducedThe interference of the signal improves the height measurement range of the radio altimeter. The 11 working frequencies with the interval of 20MHz between 4200MHz and 4400MHz are randomly switched, and when the aircraft is provided with more than two altimeters or is flying in a team, the situation of mutual tracking is avoided, so that mutual interference is avoided. The transmitting power can be automatically adjusted along with the elevation, the influence of low-height and high-power transmitting leakage is reduced, and the measuring precision of low height is ensured. In the process of obtaining the related time delay of a received signal and a sent signal, the phase difference of a received pseudo-random code and a local code is compared, the process of rough measurement and precise measurement is completed, the delay time of the transmission modulation code propagation is obtained, the measurement precision is improved, namely, the NCO of a code is adjusted2The accuracy can be made 0.01 chip width, and the measurement distance accuracy can be 0.15M for a pseudo-random code rate of 10M. The video assembly of the altimeter stores various frequencies in advance, when the altimeter runs, the control and signal processing assembly adjusts and controls a local oscillator signal in the radio frequency assembly along with a generated frequency control instruction, so that the frequency of the altimeter changes randomly, moreover, the radio frequency assembly performs phase modulation on a received TTL pseudo code, performs frequency mixing with the local oscillator signal of which the frequency is adjusted to obtain a first transmitting signal, adjusts the first transmitting signal according to a received power control signal to obtain a second transmitting signal, and accordingly, the function of automatically adjusting the transmitting power along with the altitude is realized; further, the control and signal processing module NCO is adapted to receive a code corresponding to the second transmitted signal2And comparing the phase difference with the phase difference of the TTL pseudo code to obtain a height value, and further generating a frequency control instruction and a power control instruction according to the height value, thereby solving the problem that a plurality of pieces of equipment with the same fixed frequency and pseudo code type are installed and used at the same time or the pieces of aircraft formation flying equipment are mutually interfered.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (7)
1. A digital radio altimeter, comprising: control and signal processing components, radio frequency components and antenna components;
the control and signal processing assembly is electrically connected with the radio frequency assembly and is used for sending TTL pseudo codes, power control signals and frequency control signals to the radio frequency assembly; so that the radio frequency component forms a local oscillation signal with switchable working frequency according to the frequency control signal; the radio frequency assembly sequentially performs phase modulation on the TTL pseudo codes, performs frequency mixing with the local oscillator signals to obtain first transmitting signals, performs power adjustment on the first transmitting signals according to the power control signals to obtain second transmitting signals, and transmits the second transmitting signals through an antenna assembly;
receiving a digital intermediate frequency signal corresponding to the second transmitting signal through the antenna assembly, and sequentially carrying out digital orthogonal down-conversion processing and a code loop acquisition and tracking algorithm on the digital intermediate frequency signal to obtain a code NCO2(ii) a The code NCO2Generating a local code through a second pseudo code generator, and comparing the phase difference between the local code and the TTL pseudo code to obtain a height value;
the transmitting unit of the radio frequency assembly comprises a DDS chip, a frequency mixer, a first local oscillation module, a numerical control attenuator, a power amplification module and a single chip microcomputer;
the radio frequency component forms a local oscillation signal with switchable working frequency according to the frequency control signal; the radio frequency assembly sequentially performs phase modulation on the TTL pseudo codes, performs frequency mixing with the local oscillator signal to obtain a first transmitting signal, performs power adjustment on the first transmitting signal according to the power control signal to obtain a second transmitting signal, and transmits the second transmitting signal through an antenna assembly, and specifically includes:
the single chip microcomputer is used for receiving the power control signal and the frequency control signal sent by the control and signal processing assembly;
the DDS chip is used for carrying out 0/pi phase modulation on the TTL pseudo code;
the first local oscillator module is used for forming a local oscillator signal with switchable working frequency according to the frequency control signal sent by the single chip microcomputer;
the frequency mixer is used for mixing the local oscillator signal with the TTL pseudo code modulated by the phase to obtain the first transmitting signal, and the first transmitting signal comprises 11 working frequencies with the frequency of 4200 MHz-4400 MHz and the interval of 20 MHz;
the numerical control attenuator is used for adjusting the power of the first transmitting signal according to the power control signal transmitted by the singlechip to obtain a second transmitting signal;
and the power amplification module is used for carrying out power amplification on the second transmitting signal and transmitting the second transmitting signal through an antenna component.
2. The digital radio altimeter of claim 1, wherein the receiving of the digital intermediate frequency signal corresponding to the second transmitted signal by the antenna assembly comprises:
the receiving unit of the radio frequency component is used for mixing the ground reflected signals received by the antenna, forming intermediate frequency signals after sequentially passing through an AGC circuit, a filter and an amplifier and sending the intermediate frequency signals to the control and signal processing component;
the control and signal processing assembly includes an a/D converter that samples the intermediate frequency signal to form the digital intermediate frequency signal.
3. The digital radio altimeter of claim 1, wherein the control and signal processing components comprise programmable logic devices (FPGAs) and DSP chips; the FPGA is provided with a power registering module and a frequency registering module; a power conversion unit and a random frequency generation unit are arranged in the DSP chip;
the random frequency generation unit is used for generating a frequency serial number to be replaced and replacement time and sending the frequency serial number to be replaced to the frequency registering module; the frequency registering module is used for storing preset N frequencies, and when the frequency serial number to be replaced is received, the frequency registering module generates the frequency control signal according to the frequency serial number to be replaced;
the power conversion unit is used for generating a power control instruction according to the power frequency band to which the height value belongs and sending the control instruction through the power register module.
4. The digital radio altimeter of claim 1, wherein after obtaining the altitude value, further comprising:
and transmitting the height value to an avionics system through an RS422 or ARINC429 data interface chip.
5. The digital radio altimeter of claim 1, further comprising a power supply component electrically coupled with the radio frequency component and the control and signal processing component, respectively;
the power supply assembly supports two power supply voltages of DC28V or AC115V @400 Hz.
6. The digital radio altimeter of claim 1, wherein the radio frequency component further comprises a crystal oven; the constant temperature crystal oscillator is used for generating a plurality of paths of clock signals.
7. The digital radio altimeter of claim 1, wherein the digital intermediate frequency signal is sequentially subjected to digital quadrature down-conversion processing and code loop acquisition and tracking algorithm to obtain code NCO2The method also comprises the following steps:
carrier NCO obtained through carrier capturing and tracking algorithm1。
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| CN112558019B (en) * | 2020-12-14 | 2023-08-15 | 北京遥感设备研究所 | A Transceiver Isolation System Based on Pseudo-code Modulation for Landing Measurement Radar of Extraterrestrial Objects |
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