Dual band radar altimeter system and method

An altimeter apparatus for an aircraft includes an altimeter circuit and can use a method of determining altitude. The method includes receiving a first signal in a first band via a first receive antenna, and receiving a second signal in a second band via a second receive antenna. The first band is a C-Band and the second band is at least one of a W-Band, Ku-Band, Ka-Band, V-band, or K-Band. The method also includes providing an altitude in response to the first signal or the second signal.

BACKGROUND

Embodiments of the inventive concepts disclosed herein relate generally to the field of altimetry. Embodiments of the inventive concepts disclosed herein relate to low range altimeters (LRA) for aircraft and methods of determining altitude.

Altimetry is the technique by which altitude is measured. An altimeter is an instrument that measures altitude. Altimeters are frequently used in avionics where the altitude of an aircraft such as a commercial jet, a helicopter, and/or any other vehicle must be known. In many cases, altimeters can be used in aircraft to notify a pilot of the altitude of an aircraft or to provide altitude data to a warning system or other aircraft equipment. Altimeters may be sonic altimeters, pressure altimeters, or radar altimeters. A conventional radar altimeter, such as a low range altimeter (LRA), uses C-Band radio frequency (RF) waves to determine an altitude above terrain for an aircraft.

SUMMARY

In one aspect, the inventive concepts disclosed herein are directed to a dual range altimeter apparatus. The dual range altimeter apparatus includes an altimeter circuit, a first band transmit antenna for a first band, a second band transmit antenna for a second band, a first band receive antenna physically separate from the first band transmit antenna, and a second band receive antenna. The second band is a higher frequency band than the first band. The altimeter circuit is coupled to the first band receive antenna, the first band transmit antenna, the second band receive antenna, the second band transmit antenna system. The altimeter circuit is configured to provide a first signal in the first band, transmit the first signal via the first band transmit antenna, and receive a second signal via the first band receive antenna. The second signal is a reflected version of the first signal. The altimeter circuit is also configured to provide a third signal in the second band, transmit the third signal via the second band transmit antenna, and receive a fourth signal via the second band receive antenna. The fourth signal is a reflected version of the third signal. The altimeter circuit is also configured to determine an altitude value based on the first signal and the second signal or the third signal and the fourth signal.

In a further aspect, the inventive concepts disclosed herein are directed a method of determining altitude. The method includes receiving a first signal in a first band via a first receive antenna, and receiving a second signal in a second band via a second receive antenna. The first band is a C-Band and the second band is at least one of a W-Band, Ku-Band, Ka-Band, V-band, or K-Band. The method also includes providing an altitude value in response to the first signal or the second signal.

In a further aspect, the inventive concepts disclosed herein are directed a low range altimeter (LRA) apparatus. The LRA apparatus includes a first band RF circuit, a second band RF circuit, and a processor. The processor is configured to receive baseband data from the first band RF circuit and the second band RF circuit and calculate an altitude value in response to the baseband data. The first band is a C-Band and the second band is a higher frequency band than the first band.

DETAILED DESCRIPTION

Before describing in detail the inventive concepts disclosed herein, it should be observed that the inventive concepts disclosed herein include, but are not limited to, a novel structural combination of data/signal processing components, sensors, and/or communications circuits, and not in the particular detailed configurations thereof. Accordingly, the structure, methods, functions, control and arrangement of components, software, and circuits have, for the most part, been illustrated in the drawings by readily understandable block representations and schematic diagrams, in order not to obscure the disclosure with structural details which will be readily apparent to those skilled in the art, having the benefit of the description herein. Further, the inventive concepts disclosed herein are not limited to the particular embodiments depicted in the exemplary diagrams, but should be construed in accordance with the language in the claims. The term dual band as used herein should be interpreted to mean two or more bands.

Referring generally to the figures, systems and methods for a low range altimeter (LRA) apparatus are described with respect to various aspects of the inventive concepts. The low range altimeter (LRA), otherwise referred to as a low range radar altimeter (LRRA), can be used in an aircraft to determine the altitude (e.g., height above terrain) of the aircraft, more particularly, the distance between the ground and the LRA in some embodiments. The LRA discussed herein can be used in commercial aircraft, military aircraft, spacecraft, and/or any other vehicle, system, or apparatus where the distance between a surface (e.g., the ground) and the LRA needs to be determined. The LRA transmits a pair of transmit signals via a pair transmit antennas in some embodiments. The transmit signals are reflected by terrain or a surface and are received by a pair of receive antennas. The reflected signals are delayed versions of the transmitted signals. For this reason, the frequency of the received signals trails the frequency of the respective transmitted signals. Circuity of the LRA (e.g., mixers) can be configured to determine the difference (e.g., in frequency in a frequency modulated system) between the transmitted signals and the received signals. Based on the difference, the altitude of the aircraft can be determined.

Conventional LRAs operate in a 4.2 to 4.4 gigahertz (GHz) frequency range and have a 75 decibel (dB) isolation requirement between a single transmit antenna and a single receive antenna at the specified minimal operational performance standards (MOPS). This level of transmit to receive antenna isolation can be very challenging to achieve, especially when the aircraft is landing. In some embodiments, the LRA is a dual band LRA that has improved resolution so that a reduced isolation requirement between the transmit and receive antennas can be used. The reduced isolation requirement (the isolation between a first band (e.g., C-Band) transmit antenna and a first band receive antenna is equal to or less than 30 dB in some embodiments) advantageously enables improved packaging concepts such as a dual combined antenna or a single antenna radar altimeter. In some embodiments, a dual band LRA utilizes C-Band for higher altitudes and a higher frequency band (e.g., X-band, Ku-Band, or W-Band) to provide improved altitude resolution at lower altitudes. In some embodiments, a dual band LRA provides improved altitude resolution/accuracy at low altitudes, improved integrity and availability at low altitudes by providing true dual independent measurements, and/or three dimensional radar imaging using a combination of range, Doppler and angle of arrival processing. In some embodiments, three dimensional radar imaging is achieved using signals from one or more of the higher frequency bands (e.g., the W-Band).

Referring toFIG. 1, an aircraft100includes a radar altimeter102according to some embodiments. The radar altimeter102is an apparatus that includes circuits and circuit components in addition to antennas together in a single enclosure or multiple enclosures in some embodiments. The radar altimeter102is a dual band radar altimeter, e.g., a dual band LRA that is configured to determine the altitude of aircraft100in some embodiments. The radar altimeter102is used in avionics or in other fields where the distance between two objects needs to be determined in some embodiments. The radar altimeter102provides a transmit signal104, and a transmit signal105and receives a respective receive signal106and receive signal107. The radar altimeter102is configured to use both transmit signals104and105and receive signals106and107to determine the altitude of the aircraft100in some embodiments.

The transmit signal104and the receive signal106are provided in the C-Band frequency range (e.g., 4-8 GHz), and the transmit signal105and the receive signal107are provided in a higher frequency range (e.g., Ku-Band (e.g., 12-18 GHz), Ka-Band (e.g., 26-40 GHz), V-band (e.g., 40-75 GHz), or W-Band (e.g., 75-111 GHz)) in some embodiments. Additional transmit and receive signals can be used. For example, one or more of the listed bands above can be used in addition to the C-Band and the W-Band or other band. The particular bands and the number of bands used are discussed as examples. Other RF frequency ranges and numbers of bands (e.g., a three band radar altimeter) can be utilized.

The aircraft100ofFIG. 1is shown to be an airliner. However, the aircraft100can be any kind of commercial aircraft, military aircraft, helicopter, unmanned aerial vehicle (UAV), spacecraft, and/or any other kind of vehicle, manned or unmanned. In some embodiments, the aircraft100includes a number of altimeters (e.g., dual band radar altimeters102). For example, aircraft100includes three separate radar altimeters102in some embodiments. The number of the radar altimeters102provides altitude data to a central system that can cross-check the altitude data.

The transmit signal104and the received signal106can be the same signal, i.e., a signal transmitted by radar altimeter102and reflected off of terrain108. The transmit signal105and the received signal107can also be the same signal, i.e., a signal transmitted by radar altimeter102and reflected off of the terrain108. The received signal106can be a delayed version of transmit signal104, and the received signal107can be a delayed version of transmit signal105. The received signals106and107may be a combination of signals with different delays and amplitudes. The signals104,105,106and107are frequency-modulated continuous-wave (FMCW) signals with frequencies in the super high frequency (SHF) band (e.g., frequencies between 3 GHz and 30 GHz). The signals104and106have frequencies between 4225 MHz and 4375 some embodiments.

With reference toFIG. 2, a graph200of the frequencies of transmit signal104and received signal106is shown according to some embodiments. In graph200, the vertical axis210, the y-axis, indicates frequency (e.g., frequencies between 4225 MHz and 4375 MHz) while horizontal axis212, the x-axis, indicates time. A line202indicates the frequency of the transmit signal, e.g., the transmit signal104. A dashed line204indicates the frequency of the received signal, e.g., the received signal106. A difference in frequency between line202and dashed line204, a difference206, is indicative of the altitude of aircraft100in some embodiments. The radar altimeter102is configured to determine the difference206in frequency between the two signals, e.g., the transmit signal104and received signal106, to determine the altitude of aircraft100in some embodiments. The frequencies of the transmit signal105and received signal107can be distributed similarly to the signals104and106as shown inFIG. 2in their respective band or bands and the difference in frequency between the two signals, the transmit signal105and received signal107, is used to determine the altitude of aircraft100in some embodiments. For example, the altitude is related to one half of the delay multiplied by the velocity of the RF signals (e.g., signal104,105,106, and/or107).

The particular frequency pattern of graph200is illustrative only. Other frequency patterns can be utilized without departing from the scope of the inventive concepts disclosed herein. Various modulation schemes can be used to determine the time of travel from the emission of the transmit signals104and105and the receipt of the received signals106and107.

The two altitude values or signals calculated from the signals104and106and105and107can be compared, combined or selected to provide a final altitude signal or value. Various criteria can be used to calculate the final altitude, including but not limited to averaging, weighted averaging, historical averaging, or selection of one calculation in response to phase of flight or altitude. In some embodiments, the altitude value calculated using the signals105and107is selected at lower altitudes or during approach and take-off while the altitude calculated using the signals104and106is selected at higher altitudes or during cruise.

In some embodiments, the altitude vale is calculated according to a weighted average calculation. In some embodiments, the weighted average calculation is weighted according to one or previously calculated final altitudes. In some embodiments, the following equation or similar equations are used to calculate the altitude value: FAt=((1−30,000 ft/FAt-1)*A1+(30,000 ft/FAt-1)*A2)/2 where FAtequals the final altitude at time tin feet, FAt-1equals the final altitude at time t−1 in feet, A1 equals the altitude calculated using the signals105and107, and A2 equals the altitude calculated using the signals104and106.

The value FA is low pass filtered, Kalman filtered or averaged over time in some embodiments. In some embodiments, the values for A1 and A2 are qualified in accordance with changes over time or other thresholds. If an error is detected in a current value of A1 or A2, the value is discarded and the other value is utilized as FA or a previous value (e.g., very recent) of A1 or A2 is utilized in the weighted average calculation in some embodiments. In some embodiments, if the values of A1 and A2 differ from each other significantly, an error is detected and the A1 or A2 value consistent with other sensor values or historical values is chosen.

With reference toFIG. 3, a dual band LAR300can be used as the radar altimeter102ofFIG. 1. The LRA300includes an altimeter circuit301, transmit antennas314and315and receive antennas316and317. The transmit antennas314and315can be part of an integrated patch antenna system, and the receive antennas316and317can be part of an integrated patch antenna system in some embodiments. The antennas316and317are configured for W-Band operation in some embodiments. The antennas314and315are configured for C-Band operation in some embodiments.

The altimeter circuit301and the transmit antennas314and315generate and transmit a pair of FMCW signals and the altimeter circuit301and the receive antennas316and317receive respective reflections of the transmit signals. In some embodiments, the altimeter circuit301includes a processor302, a C-Band RF circuit306, and a W-Band RF circuit304. The altimeter circuit301can include various processing circuits, filters, circulators, RF coupler circuits, RF mixer circuits, RF amplifier circuits, RF antennas, voltage controlled oscillators (VCOs), frequency tripler circuits, direct digital synthesizers (DDSs), and/or any other circuit (e.g., application specific integrated circuit (ASCI)), logic circuit, processor, microprocessor, and/or memory component (e.g., random access memory (RAM), read only memory (ROM), hard drive, or other non-transitory or transitory storage mediums).

The processor302include a one or more processing circuits (e.g., a signal processors, general purpose processors and memory) that can be configured (e.g., via software) to calculate altitude in response to baseband signals or data received from the W-Band RF circuit304and the C-Band RF circuit306as well as perform some and/or all of the functions of the LRA300described herein. The processor302calculates an altitude value in response to the baseband data from the W-Band RF circuit304and the C-Band RF circuit306. In some embodiments, the processor302calculates an altitude value in response to the baseband data from the W-Band RF circuit304and the C-Band RF circuit306and phase of flight information from a flight management computer (FMC) or other aviation equipment. In some embodiments, the processor302calculates an altitude value in response to the baseband data from the W-Band RF circuit304and the C-Band RF circuit306and other data from other altitude sensors.

In some embodiments, the W-Band RF circuit304uses hardware and software associated with automotive distance sensing solutions. Advantageously, the W-Band RF circuit304leverages the W-Band radar solutions provided in small low power packages. The W-Band RF circuit304includes mixers, filters, power amplifiers, and low noise amplifiers configured for W-Band operations. In some embodiments, the W-Band RF circuit304is an S-band, K-Band, Ka-Band, or Ku-Band circuit. The W-Band RF circuit304can includes a circulator for coupling to the transmit antenna315and the receive antenna317.

In some embodiments, the C-Band RF circuit306uses hardware and software to provide baseband signals or data to the processor302. The C-Band RF circuit306includes mixers, filters, power amplifiers, and low noise amplifiers configured for C-Band operations. The C-Band RF circuit306includes a circulator for coupling to the transmit antenna314and the receive antenna316in some embodiments.

In some embodiments, an analog to digital converter (ADC) in the C-Band RF circuit306is configured to the sample a down converted difference signal filtered by a low pass filter in the C-Band RF circuit306and provide the sampled signal to the processor302. The down converted difference signal filtered by the low pass filter is derived from the difference between the transmit signal provided to the transmit antenna314and the received signal receive by the receive antenna316. The down converted difference signal in the C-Band RF circuit306is a based band signal or data representative of an altitude value provided to the processor302in some embodiments.

In some embodiments, an analog to digital converter (ADC) in the W-Band RF circuit304is configured to the sample a down converted difference signal filtered by a low pass filter in the W-Band RF circuit304and provide the sampled signal to the processor302. The down converted difference signal filtered by a low pass filter is derived from the difference between the transmit signal provided to the transmit antenna315and the received signal received by the receive antenna317. The down converted difference signal in the W-Band RF circuit304is a based band signal or data representative of an altitude value provided to the processor302in some embodiments.

In some embodiments, ADCs sample the filtered signals at 625 kHz. Based on the sampled signals, processor302determines the altitude based on the difference in frequencies between the transmit signal on the transmit antenna314and the received signal on the receive antenna316and between the transmit signal on the transmit antenna315and the received signal on the receive antenna317as indicated by the frequencies of the filtered signals. In some embodiments, the processor302selects or combines altitude values or and presents a representation of the altitude of aircraft100on a display (e.g., a flight display).

With reference toFIG. 4, a dual band LAR400can be used as the radar altimeter102ofFIG. 1. The dual band LRA400is similar to the dual band LRA300(FIG. 3) and includes an altimeter circuit401, transmit antennas408and409and receive antennas410and411. The altimeter circuit401includes transmit side including a C-Band fractional-N synthesizer402, a W-Band fractional synthesizer403, a C-Band voltage controlled oscillator (VC)404, a W-Band VCO405, a C-Band power amplifier406, and a W-Band power amplifier407. The altimeter circuit401includes are receive side including a C-Band low noise amplifier (LNA)412, W-Band LNA413, a C-Band mixer414, W-Band mixer415, a C-Band low pass filter amplifier416, a W-Band low pass filter amplifier417, an analog-to-digital converter (ADC)418, and an ADC419. The altimeter circuit401also includes an altitude circuit420, a communications circuit422, a power supply circuit424, a C-Band filter426, and a W-Band filter427.

The antennas408,409,410and411are similar to the antennas314,315,316, and317(FIG. 3) and can be part of an antenna system. The antenna system can include one or more antennas that are configured to transmit signals generated by altimeter circuit401.

The fractional-N synthesizer402and/or VCO404can be configured to directly generate a FMCW signal in the C-Band which can be amplified by amplifier406and transmitted via the transmit antenna408as the transmit signal104. The fractional-N synthesizer403and/or VCO405can be configured to directly generate a FMCW signal in the W-Band which can be amplified by amplifier407and transmitted via the transmit antenna409as the transmit signal105. In some embodiments, the fractional-N synthesizers402and403are integer-N synthesizers or other indirect digital synthesizer.

The altimeter circuit401can include various processing circuits, RF coupler circuits, RF mixer circuits, RF amplifier circuits, RF antennas, voltage controlled oscillators (VCOs), and/or any other circuit (e.g., wired logic circuit, microprocessor, application specific integrated circuit (ASCI)), logic circuit, low power system on a chip (SoC), processor, microprocessor, and/or memory component (e.g., random access memory (RAM), read only memory (ROM), hard drive, or other non-transitory or transitory storage mediums.). The altimeter circuit401can include one or more processing circuits (e.g., a processor and memory) that can be configured to perform some and/or all of the functions of LRA400.

The fractional-N synthesizers402and403can operate with and/or otherwise drive respective VCOs404and405. For example, VCOs404and405may generate respective signals at a particular frequency based on voltages received from respective fractional-N synthesizers402and403. In some embodiments, the fractional-N synthesizers402and403drives the VCOs404and405causing VCOs404and405to generate signals that ramp up and down in frequency (e.g., ramps between 4225-4375 MHz in the C-Band and ramps within the W-Band).

The fractional-N synthesizers402and403each can include VCOs404and405and/or may be combined with VCOs404and405as a single integrated circuit. The signal generated by fractional-N synthesizer402and/or VCO404may be applied as an input to the mixer414. The signal generated by fractional-N synthesizer403and/or VCO405can be applied as an input to the mixer415. In some embodiments, the signals are provided to the mixers414and415via a coupler. The signals may further be amplified by the respective amplifiers406and407for transmission on the transmit antennas408and409.

The receive antenna410can be configured to receive the reflected signal (e.g. the signal106), and the receive antenna411can be configured to receive the reflected signal (e.g. the signal107). The LNAs412and413can be configured to amplify respective received signals106and107. The mixer414is configured to mix the signal generated by fractional-N synthesizers402and/or VCO404and the signal received by antenna410and amplified by amplifier412. The mixer415is configured to mix the signal generated by fractional-N synthesizers403and/or VCO405and the signal received by antenna411and amplified by amplifier413. The result of the multiplication of these signals in the mixers414and415are a signals that include both the sum and the difference of the frequencies of the respective transmit and receive signals104,105,106, and107. The low pass filter amplifiers416and417can be configured to filter the mixed signals and amplify the mixed signals, removing the sum of the frequencies and leaving the difference of the frequencies. The ADCs418and419can be configured to sample the respective filtered signals (e.g., sampled at 625 kHz) and provide the sampled signals to the altitude circuit420.

In some embodiments, the altitude circuit420is configured to determine the altitude of aircraft100based on the sampled signals. The samples provides by the ADCs418and419are indicative of the difference in frequency between the transmit signal104and the received signal106and the transmit signal105and the receive signal107in some embodiments. Based on the differences in frequency, the altitude circuit420can be configured to determine the altitude of aircraft100. In some embodiments, the altitude circuit420determines the absolute differences between the frequencies and uses the absolute difference to determine the altitude of aircraft100. The differences in frequency are indicative of the altitude of aircraft100(e.g., the altitude of aircraft100is a function of the difference in frequency) in some embodiments. The altitude value can be calculated by a processor within the altitude circuit420according to the discussions above in some embodiments.

The altitude determined by the altitude circuit420can be transmitted to other systems of aircraft100. Communications circuit422can be configured to act as an interface between the altimeter circuit401and other systems of aircraft100. For example, communications circuit422can be configured to communicate the altitude determined by the altitude circuit420via a bus such as aeronautical radio Inc. (ARINC)429. Communications circuit422can be configured, in some embodiments, to communicate the determined altitude via a controller area network (CAN) bus, ARINC429, UART, Ethernet, and/or any other type of communication protocol. The communications circuit422is coupled to a display429(e.g., a primary flight display computer coupled to a primary flight display) for displaying the altitude value.

The power supply circuit424can be configured to receive power from an external power source. In some embodiments, the power supply circuit424can be configured to receive AC power and/or DC power from an external power source and power the altimeter circuit401. In some embodiments, the power supply circuit424can include one or more filters, power regulators, rectifiers, or other circuits necessary for powering the LRA400.

With reference toFIG. 3andFIG. 4, the antennas314,315,216, and317can be located separately from a circuit board that includes LRA300, and the antennas408,409,410, and antenna411can be located separately from a circuit board that includes LRA400. The LRA400, however, can be located on a single circuit board along with the antennas408,409,410and411in some embodiments. Since LRA400and antennas408,409,410and411can be located on a signal circuit board, the signal circuit board itself can be located outside an aircraft, i.e., connected to the outside of a fuselage of the aircraft.

With reference toFIG. 5, an antenna system450is configured as an integrated antenna with W-Band and C-Band elements. The antenna system450is a patch antenna system including a four by four array452of C-Band elements and a four by four array454of W-Band elements. The antenna system450can serve as transmit antennas314and315, transmit antennas408and409, receive antennas316and317(FIG. 3) or receive antennas410and411(FIG. 4) in some embodiments. The antenna system450is provided on a single circuit board in some embodiments.

With reference toFIG. 6, a simulated field magnitude470for the four by four array452of C-Band elements of the antenna system450is shown. With reference toFIG. 7, a simulated field magnitude472for the four by four array454of the W-Band elements of the antenna system450is shown.

With reference toFIG. 8, a graph600illustrates a simulated response (e.g., a line606) of a C-Band radar altimeter having 75 dB of isolation between the receive antenna and the transmit antenna at an altitude of 20 ft. An X-axis604represents altitude and a Y-axis602axis represents magnitude of the received signal in Db.

With reference toFIG. 9, graph700shows first graph702first y-axis706, second graph712, and second y-axis716, and x-axis718. First y-axis706and second y-axis represents the magnitude of a C-band response in decibels (dB). Graph a graph700illustrates a simulated C-Band response (e.g., a line710) of a dual band radar altimeter (LRAs300or400) having 30 dB of isolation between the receive antenna and the transmit antenna at an altitude of 20 ft. An X-axis708represents altitude and a Y-axis706represents magnitude of the received signal in Db. The graph700also illustrates a simulated W-Band response (e.g., a line720) of a dual band radar altimeter having 30 dB of isolation between the receive antenna and the transmit antenna at an altitude of 20 ft. (e.g., using a 1.8 GHz sweep).

The scope of this disclosure should be determined by the claims, their legal equivalents and the fact that it fully encompasses other embodiments which may become apparent to those skilled in the art. All structural, electrical and functional equivalents to the elements of the above-described disclosure that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. A reference to an element in the singular is not intended to mean one and only one, unless explicitly so stated, but rather it should be construed to mean at least one. No claim element herein is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.” Furthermore, no element, component or method step in the present disclosure is intended to be dedicated to the public, regardless of whether the element, component or method step is explicitly recited in the claims.

Embodiments of the inventive concepts disclosed herein have been described with reference to drawings. The drawings illustrate certain details of specific embodiments that implement the systems and methods and programs of the present disclosure. However, describing the embodiments with drawings should not be construed as imposing any limitations that may be present in the drawings. The present disclosure contemplates methods, systems and program products on any machine-readable media for accomplishing its operations. Embodiments of the inventive concepts disclosed herein may be implemented using an existing computer processor, or by a special purpose computer processor incorporated for this or another purpose or by a hardwired system.

The foregoing description of embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the subject matter to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the subject matter disclosed herein. The embodiments were chosen and described in order to explain the principals of the disclosed subject matter and its practical application to enable one skilled in the art to utilize the disclosed subject matter in various embodiments and with various modifications as are suited to the particular use contemplated. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the embodiments without departing from the scope of the presently disclosed subject matter.