A multi-function altimeter for terrain matching navigation

Abstract

This invention discloses a multi-functional altimeter for terrain-matching navigation, compatible with both high-resolution altimetry and high-mobility altimetry functions. Differentiated designs are required in antenna beamforming and signal processing to meet these requirements. To ensure hardware compatibility, altimetry mode switching is achieved through software switching, employing compatibility design measures. Specifically, the receiving antenna integrates a wide-beam antenna and a narrow-beam antenna on the same substrate. The signal processing group and hardware are designed for compatibility, using different signal processing flows for the signal characteristics of high-resolution altimetry and high-mobility altimetry, ensuring that both altimetry functions and performance meet the requirements.

Description

Technical Field

[0001] This invention relates to the field of urban rail transit technology, and more specifically to a multifunctional altimeter for terrain-matching navigation. Background Technology

[0002] Radio altimeters are used to measure the relative altitude between an aircraft platform and the ground / sea surface. They offer the advantages of all-weather, all-day operation and are widely used in navigation. In recent years, with the development of terrain-aided navigation technology, higher requirements have been placed on the performance of radio altimeters.

[0003] To adapt to the high mobility of the platform, altimeter antennas are generally designed with a wide beam to cover the platform's attitude range. Traditional altimeter methods operate with a solid aperture. Under wide beam conditions, the corresponding ground footprint (or illumination area) is relatively large, and the beam coverage area increases rapidly with altitude, resulting in a decrease in ground resolution and measurement accuracy. This makes it difficult to achieve terrain matching tasks under conditions of large terrain undulations.

[0004] To improve ground resolution, the Doppler effect within the antenna beam is used to subdivide ground bands. The core technology is synthetic aperture radar (SAR) altimeter technology. Doppler beam sharpening (DBS) technology effectively improves the resolution of ground cells, enabling altimeters to achieve high-resolution, high-precision altimeter measurement. However, this technology has certain requirements regarding the speed and attitude of the platform. If the altimeter antenna beam is wide, the Doppler frequency generated within the detection beam is high and the echo varies greatly during high-speed, large-attitude movement of the mobile platform. To avoid Doppler blurring during high-resolution measurements using DBS technology, a high detection pulse frequency is required under high-speed conditions, posing significant challenges to high-resolution measurements. Therefore, high-resolution measurements are generally applied under conditions of small-attitude platform movement. A relatively narrow antenna beamwidth can constrain the Doppler frequency within a certain range, facilitating hardware design and system implementation, and offering good cost-effectiveness. Because the hardware of these two altimeter products is incompatible, high-resolution altimeter and high-mobility altimeter products are currently used independently on their respective mobile platforms. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-functional altimeter for terrain-matching navigation, which combines high-resolution altimetry and high-maneuverability altimetry. The two altimetry modes can be switched via software, which can meet the requirements of aircraft for terrain-matching navigation and conventional altimetry.

[0006] A multi-functional altimeter for terrain-matching navigation, comprising:

[0007] A microwave transceiver assembly is used to generate a detection signal, receive and process the echo signal;

[0008] The signal processing unit is used to communicate with the control system in real time, generate control timing according to the height measurement mode, control the microwave transceiver unit to generate the detection signal, perform sampling, spectrum analysis and angle calculation on the echo signal, and send the measurement results and other telemetry data to the control system.

[0009] An antenna for transmitting the detection signal and receiving the echo signal;

[0010] The altimeter modes include a high-resolution altimeter mode and a high-mobility altimeter mode.

[0011] Optionally, it also includes: a secondary power supply for converting the primary power supply into multiple secondary power supplies for use by the signal processing assembly and the microwave transceiver assembly.

[0012] Optionally, the antenna includes a transmitting antenna and a receiving antenna; the transmitting antenna is used to transmit the detection signal, and the receiving antenna is used to receive the echo signal.

[0013] Optionally, the transmitting antenna is a wide-beam antenna with a beamwidth adaptable to a wide range of maneuvering attitudes; the receiving antenna integrates a wide-beam antenna and a narrow-beam antenna with a beamwidth adaptable to a wide range of maneuvering attitudes and a high-resolution altimeter attitude range; the wide-beam antenna or the narrow-beam antenna can be selected by a selection switch.

[0014] Optionally, the transmitting antenna and the receiving antenna are respectively provided with a radome, and the radome achieves the stealth function of the transmitting antenna and the receiving antenna through frequency selective design.

[0015] Optionally, the receiving antenna, the selection switch, and the low-noise amplifier are integrated into a single design; wherein the wide-beam antenna and the narrow-beam antenna are designed on the same substrate, the feed port adopts a waveguide form, and microwave devices such as the channel selection switch, isolator, limiter, and low-noise amplifier are arranged inside the LNB and the signal is transmitted through the waveguide feed port.

[0016] Optionally, the pulse repetition frequency (PRF) in high-resolution mode is calculated using the following formula:

[0017]

[0018] Among them, v s θ is the horizontal velocity, θ is the main beamwidth of the antenna, and λ is the wavelength of the detection signal;

[0019] The transmitted signal of each pulse is a linear frequency modulated broadband signal, the pulse width is no greater than the pulse repetition period, and each cluster generates N pulses of detection signal. The number of pulses N is related to the strip resolution.

[0020] According to the control command, the narrow beam receiving antenna is selected to enter the high-resolution altimeter mode. The pulse repetition period is calculated according to formula (1), and a cluster of detection signals with a pulse quantity of N is generated. After sampling the echo, range FFT processing and azimuth FFT processing are performed in sequence. Combined with the aircraft's sky velocity realization point strip extraction, the strip extraction is calculated according to the following formula:

[0021]

[0022] Among them, v h Where λ is the upward velocity, N is the number of pulses, λ is the wavelength of the detection signal, and PRF is the pulse repetition frequency.

[0023] The high-resolution altitude measurement mode specifically includes: after entering the high-resolution altitude measurement mode, a narrow beam receiving antenna is selected, the pulse repetition frequency is calculated in real time according to the platform's horizontal flight speed, and a detection signal is generated. Each detection cycle contains a certain number of pulse trains, and the transmission signal of each pulse is a linear frequency modulated signal. The echo signal is first processed by range FFT, and then processed by azimuth FFT. The lower point strip of the aircraft is selected according to formula (3), and the height of the strip is extracted to realize the altitude calculation.

[0024] Optionally, the high-mobility altimeter mode includes: using a wide-beam receiving antenna to generate a wide-pulse frequency-modulated detection signal, wherein the Doppler information formed by the platform's celestial velocity is coupled into the range echo, and the coupled Doppler solution and range compensation are realized through the velocity information.

[0025] Optionally, the multi-functional altimeter has different requirements for altitude measurement accuracy under different airspace conditions. Under low airspace conditions, the altimeter parameter design adopts a large bandwidth detection method to ensure that the distance resolution is high enough to achieve high-precision detection. Under high airspace conditions, the altimeter parameter design adopts a large pulse width detection method to ensure that the echo capability within the resolution unit is high enough to ensure that the altimeter can stably track ground echoes without losing lock.

[0026] Optionally, the altitude acquisition and tracking process includes: after the altimeter is powered on, it enters a full-space search. After acquiring a valid ground / sea surface echo, it adjusts the altitude parameters according to the current altitude range to ensure the altimeter operates in the optimal detection state. During tracking, if the ground / sea surface echo is lost, it searches for the nearest echo within the current altitude range. Once a valid altitude is reacquired, it enters the tracking state. If a ground echo cannot be acquired, it enters a full-space search until a valid ground / sea surface echo is acquired. After acquiring a valid ground / sea surface echo, the altimeter detection parameters are adaptively adjusted according to the relative altitude, controlling parameters such as detection power, receiver gain, frequency modulation bandwidth, and frequency modulation pulse width to achieve optimal detection.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. This invention provides a multi-functional altimeter for terrain matching navigation, which combines high-resolution altimetry and high-maneuver altimetry on the same hardware platform. The two altimetry modes can be switched through software to achieve high-resolution altimetry and high-maneuver altimetry, thus meeting the needs of the carrier platform for terrain matching navigation and normal altimetry during high-maneuver.

[0029] 2. This invention combines the functions of high-resolution altimetry and high-maneuver altimetry. The two altimetry modes can be switched via software, which can meet the requirements of aircraft for terrain matching navigation and conventional altimetry. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the multi-functional altimeter in an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram showing the connections of the various parts of the altimeter in an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of the layout of the receiving antenna and LNB in ​​an embodiment of the present invention;

[0033] Figure 4 This is a block diagram of the signal processing assembly in an embodiment of the present invention;

[0034] Figure 5 This is a flowchart illustrating the workflow of the altimeter in an embodiment of the present invention.

[0035] Figure 6 This is a flowchart of the high-resolution altimeter processing in an embodiment of the present invention;

[0036] Figure 7 This is a flowchart of the high-speed mobile altimeter measurement process in an embodiment of the present invention;

[0037] Figure 8 This is a flowchart of height capture and tracking processing in an embodiment of the present invention. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. These embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0039] This invention provides a multi-functional altimeter for terrain-matching navigation. To accommodate both high-resolution altimetry and high-mobility altimetry functions, the hardware design of the multi-functional altimeter requires differentiated designs in antenna beamforming and signal processing to meet requirements. To ensure hardware commonality, altimetry mode switching is achieved through software switching, employing compatibility design measures. Specifically, the receiving antenna integrates a wide-beam antenna and a narrow-beam antenna on the same substrate. The signal processing group and hardware are designed for compatibility, employing different signal processing flows for the signal characteristics of high-resolution altimetry and high-mobility altimetry, ensuring that both altimetry functions and performance meet requirements.

[0040] 1) Antenna compatibility design

[0041] Wide-beam and narrow-beam antennas are suitable for high-maneuver altimetry and high-resolution altimetry, respectively. To reduce system overhead while ensuring measurement performance, a wide-beam antenna is selected for the transmitting antenna, with a beamwidth suitable for the high-maneuverability attitude range. The receiving antenna integrates both wide-beam and narrow-beam antennas, with beamwidths suitable for both the high-maneuverability attitude range and the high-resolution altimetry attitude range. Antenna selection is achieved through a selector switch. The radome is frequency-selectively designed to ensure the antenna has stealth characteristics, as shown in the figure below.

[0042] To improve receiver performance and reduce signal transmission attenuation, the receiving antenna, selection switch, and low-noise amplifier are integrated into a single design. The wide-beam antenna and narrow-beam antenna are designed on the same substrate, and the feed port adopts a waveguide form. Microwave devices such as the channel selection switch, isolator, limiter, and low-noise amplifier are arranged in a low-noise block downconverter and the signal is transmitted through the waveguide feed port.

[0043] 2) Signal processing hardware compatibility design

[0044] The signal processing combination principle block diagram is shown in the figure below. It needs to complete information interaction with the control system, control the microwave transceiver combination to generate detection signals according to the detection timing, process the echo signals such as sampling, spectrum analysis, and altitude calculation, and transmit the final measurement results and other telemetry data to the control system through the communication interface.

[0045] The signal processing unit's filter amplifier circuit has a passband range, ADC maximum sampling rate, signal processor processing speed, and data capacity that take into account the maximum envelope of the signals to be processed for both large-scale mobile altimetry and high-resolution altimetry. It can also control the microwave transceiver unit to generate frequency modulation signals according to the corresponding timing sequence in real time.

[0046] 3) Differentiated design of signal processing flow

[0047] The altimeter's workflow is shown in the figure. After the altimeter is powered on, it begins loading the program. After basic configuration and initialization, it ensures that the communication module is ready and automatically completes self-test to enter standby mode. Upon receiving the RF power-on command, it enters the corresponding altimeter mode according to the control command.

[0048] In high-mobility altimetry mode, a wide-beam receiving antenna is selected to cover the platform's attitude range. A continuous-wave frequency modulation (FM) system is used for altitude acquisition and tracking, and the FM bandwidth and detection timing are adjusted according to the detected altitude to ensure optimal operation. In high-resolution altimetry mode, the altimeter receives platform speed and attitude information in real time. Based on the horizontal speed and narrow antenna beamwidth, the pulse repetition frequency is calculated in real time to determine the altimetry timing. Combined with speed information, this enables the selection of the lower-point strip and altitude calculation.

[0049] a. High-resolution altimetry processing flow

[0050] In high-resolution mode, the PRF pulse repetition frequency can be calculated according to the following formula to ensure that Doppler is not blurred.

[0051]

[0052] Among them, v s Let θ be the horizontal velocity, θ be the main beamwidth of the antenna, and λ be the wavelength of the detection signal. Each pulse transmits a linear frequency modulated broadband signal with a pulse width no greater than the pulse repetition period. Each cluster generates N pulses of detection signal. The number of pulses N is related to the strip resolution; for ease of calculating the radix-2 Fourier transform, N is generally taken as a power of 2. The high-resolution altimeter processing flowchart is shown below. Figure 5 As shown, the narrow-beam receiving antenna is selected to enter the high-resolution altimeter mode according to the control command. The pulse repetition period is calculated according to formula (1), and a cluster of detection signals with a pulse quantity of N is generated. After sampling the echo, range FFT processing and azimuth FFT processing are performed in sequence. Combined with the aircraft's sky velocity realization point strip extraction, the strip extraction is calculated as follows:

[0053]

[0054] Among them, v h λ represents the upward velocity, N represents the number of pulses, λ represents the wavelength of the detection signal, and PRF represents the pulse repetition frequency.

[0055] The high-resolution altitude measurement process is as follows: after entering the high-resolution altitude measurement mode, a narrow beam receiving antenna is selected. The pulse repetition frequency is calculated in real time according to the platform's horizontal flight speed to generate a detection signal. Each detection cycle contains a certain number of pulse trains. The transmission signal of each pulse is a linear frequency modulated signal. The echo signal is first processed by range FFT (Fast Fourier Transform) and then by azimuth FFT. The aircraft's lower point strip is selected according to formula (3), and the height of the strip is extracted to realize the altitude calculation.

[0056] b. Large-scale mobile altimetry processing flow

[0057] After entering the high-mobility altimeter mode, a wide-beam receiving antenna is selected to generate a wide-pulse frequency-modulated detection signal. The Doppler information formed by the platform's celestial velocity is coupled into the range echo, and the coupled Doppler solution and range compensation are realized through the velocity information.

[0058] c. Acquisition and tracking strategy and adaptive parameter adjustment

[0059] In wide-airspace conditions, the platform's altitude measurement accuracy requirements vary depending on the airspace. For example, in low-altitude conditions, higher measurement accuracy is required, so the altimeter's parameter design employs a wide-bandwidth detection method to ensure sufficient distance resolution and achieve high-precision detection. In high-altitude conditions, higher altitude measurement reliability is required, so the altimeter's parameter design employs a wide-pulse-width detection method to ensure sufficient echo capability within the resolution unit, ensuring the altimeter can stably track ground echoes without losing lock. The altitude acquisition and tracking process is shown in the figure below. After the altimeter's RF is powered on, it enters a full-airspace search (altimeter altitude measurement range). After acquiring a valid ground / sea surface echo, the altitude parameters are adjusted according to the current altitude range to ensure the altimeter operates in the optimal detection state. During tracking, if the ground / sea surface echo is lost, the platform first searches for the nearest point within the current altitude range. Once a valid altitude is reacquired, it enters tracking mode. If a ground echo cannot be acquired, the platform enters a full-airspace search until a valid ground / sea surface echo is acquired.

[0060] After capturing valid echoes from the ground / sea surface, the altimeter detection parameters are adaptively adjusted according to the relative altitude, controlling parameters such as detection power, receiver gain, frequency modulation bandwidth, and frequency modulation pulse width to achieve optimal detection.

[0061] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A multi-functional altimeter for terrain-matching navigation, characterized in that, include: A microwave transceiver unit is used to generate probe signals, receive and process echo signals; The signal processing unit is used to communicate with the control system, generate control timing according to the height measurement mode, control the microwave transceiver unit to generate the detection signal, sample the echo signal, perform spectrum analysis and angle calculation, and send the measurement results to the control system. An antenna is used to transmit the detection signal and receive the echo signal. The antenna includes a transmitting antenna and a receiving antenna; the transmitting antenna is used to transmit the detection signal, and the receiving antenna is used to receive the echo signal. The altimeter modes include a high-resolution altimeter mode and a high-maneuver altimeter mode; the transmitting antenna is a wide-beam antenna with a beamwidth adaptable to a wide-maneuver attitude range; the receiving antenna integrates a wide-beam antenna and a narrow-beam antenna with a beamwidth adaptable to both a wide-maneuver attitude range and a high-resolution altimeter attitude range; the wide-beam antenna or the narrow-beam antenna can be selected via a selection switch. The pulse repetition frequency (PRF) in high-resolution mode is calculated using the following formula: Among them, v s θ is the horizontal velocity, θ is the main beamwidth of the antenna, and λ is the wavelength of the detection signal; The transmitted signal of each pulse is a linear frequency modulated broadband signal, the pulse width is no greater than the pulse repetition period, and each cluster generates N pulses of detection signal. The number of pulses N is related to the strip resolution. According to the control command, the narrow beam receiving antenna is selected to enter the high-resolution altimeter mode. The pulse repetition period is calculated according to formula (1), and a cluster of detection signals with a pulse quantity of N is generated. After sampling the echo, range FFT processing and azimuth FFT processing are performed in sequence. Combined with the aircraft's sky velocity realization point strip extraction, the strip extraction is calculated according to the following formula: Among them, v h Where λ is the upward velocity, N is the number of pulses, λ is the wavelength of the detection signal, and PRF is the pulse repetition frequency. The high-resolution altitude measurement mode specifically includes: after entering the high-resolution altitude measurement mode, a narrow beam receiving antenna is selected, the pulse repetition frequency is calculated in real time according to the platform's horizontal flight speed, and a detection signal is generated. Each detection cycle contains a certain number of pulse trains, and the transmission signal of each pulse is a linear frequency modulated signal. The echo signal is first processed by range FFT, and then processed by azimuth FFT. The lower point strip of the aircraft is selected according to formula (3), and the height of the strip is extracted to realize the altitude calculation.

2. The multi-functional altimeter for terrain-matching navigation as described in claim 1, characterized in that, Also includes: A secondary power supply is used to convert the primary power supply into multiple secondary power supplies for use by the signal processing assembly and the microwave transceiver assembly.

3. The multi-functional altimeter for terrain-matching navigation as described in claim 1, characterized in that, The transmitting antenna and the receiving antenna are each equipped with a radome, and the radome is frequency-selective to enable the transmitting antenna and the receiving antenna to have stealth function.

4. The multi-functional altimeter for terrain-matching navigation as described in claim 1, characterized in that, The receiving antenna, the selection switch, and the low-noise amplifier are integrated into a single design. The wide-beam antenna and the narrow-beam antenna are designed on the same substrate, and the feed port adopts a waveguide form. The selection switch, isolator, limiter, and low-noise amplifier are arranged inside the LNB and the signal is transmitted through the waveguide feed port.

5. The multi-functional altimeter for terrain-matching navigation as described in claim 1, characterized in that, The high-mobility altimeter measurement mode includes: using a wide-beam receiving antenna to generate a wide-pulse frequency-modulated detection signal, wherein the Doppler information formed by the platform's celestial velocity is coupled into the range echo, and the coupled Doppler solution and range compensation are realized through the velocity information.

6. The multi-functional altimeter for terrain-matching navigation as described in claim 1, characterized in that, The multi-functional altimeter has different requirements for altitude measurement accuracy under different airspace conditions. Under low airspace conditions, the altimeter parameter design adopts a large bandwidth detection method to ensure that the distance resolution is high enough to achieve high-precision detection. Under high airspace conditions, the altimeter parameter design adopts a large pulse width detection method to ensure that the echo capability within the resolution unit is high enough to ensure that the altimeter can stably track ground echoes without losing lock.

7. The multi-functional altimeter for terrain-matching navigation as described in claim 1, characterized in that, Altitude acquisition and tracking processing includes: after the altimeter's radio frequency is powered on, it enters a full-space search. After acquiring a valid ground / sea surface echo, it adjusts the altitude parameters according to the current altitude range to ensure the altimeter operates in the optimal detection state. During tracking, if the ground / sea surface echo is lost, it searches for the nearest echo within the current altitude range. Once a valid altitude is reacquired, it switches to tracking mode. If a ground echo cannot be acquired, it enters a full-space search until a valid ground / sea surface echo is acquired. After acquiring a valid ground / sea surface echo, the altimeter's detection parameters are adaptively adjusted according to the relative altitude, controlling its detection power, receiver gain, frequency modulation bandwidth, and frequency modulation pulse width to achieve optimal detection.

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