Aircraft radio altimeter having an adjustable aperture angle and method for measuring ground height using this radio altimeter

Abstract

The present invention relates to a method for measuring the ground height (Hs) of an aircraft (30) using a radio altimeter (1) comprising a transmitting antenna (10) emitting a primary electromagnetic signal (51, 52), a receiving antenna (20) receiving a reflected electromagnetic signal (55, 56) resulting from a reflection of said primary electromagnetic signal (51), and a computer (2). Said radio altimeter (1) comprises an adjustable antenna, among said transmitting antenna (10) and receiving antenna (20), equipped with a processing unit (80) and several radiating elements (11-19) separated respectively by a non-zero gap (L).The method comprises adjusting (100) the opening angle of the adjustable antenna by electrically connecting one or more of the radiating elements (11-19) to the processing unit (80), and after adjusting (100), determining (300) a ground height (Hs) as a function of a minimum elapsed time between the emission (310) of the primary electromagnetic signal (51) and the reception (320) of the reflected electromagnetic signal (55). Abbreviated figure: Figure 1.

Description

Title of the invention: Radio altimeter for aircraft having an adjustable aperture angle and method for measuring ground height using this radio altimeter

[0001] The present invention is in the technical field of instruments equipping aircraft, and more particularly instruments for measuring the ground height of an aircraft, namely the shortest distance between this aircraft and the surface overflown.

[0002] The present invention relates to a method for measuring the ground height of an aircraft using a radio altimeter having an adjustable opening angle, as well as a radio altimeter for an aircraft implementing such a method and an aircraft equipped with such a radio altimeter.

[0003] A radio altimeter employs a pair of antennas, including a transmitting antenna that emits a primary electromagnetic signal and a receiving antenna that captures a reflected electromagnetic signal resulting from the reflection of this primary electromagnetic signal off the surface being overflown. The term "surface being overflown" refers to any surface, such as the ground, a body of water, the surface of a ship or building, etc. Optionally, the transmitting and receiving antennas may be combined to form a single antenna.

[0004] The aircraft's ground height is determined by a radio altimeter's computer by dividing the time elapsed between the emission of the primary electromagnetic signal and the reception of the reflected electromagnetic signal by twice the propagation speed of the electromagnetic signal in air. For aircraft safety, the radio altimeter takes into account the shortest measured travel time, which in most cases corresponds to the minimum height below the aircraft, defined along a vertical direction, i.e., parallel to the direction of Earth's gravity.

[0005] The radio altimeter antennas are positioned to avoid reflection of the electromagnetic signal off aircraft components. Therefore, the antennas are typically mounted on the underside of the aircraft. Furthermore, the radio altimeter antennas are commonly protected from the external environment, particularly inclement weather, by a radome, typically arranged as a dome transparent to electromagnetic waves.

[0006] However, aircraft may occasionally be operated for specific flight missions requiring the carriage of additional equipment or a load carried by a sling system. In this context, the problem may arise of a possible reflection of the primary electromagnetic signal by one of these pieces of equipment. Additional equipment or the load carried by slings, which is also swaying beneath the aircraft, can distort the ground height measurement provided by the radio altimeter. In particular, the reflection of electromagnetic signals off additional equipment can cause the radio altimeter to emit a very low, or even zero, ground height reading.

[0007] Furthermore, the risk of reflection of the primary electromagnetic signal of the radio altimeter on one of the additional equipment or on a load transported by sling is increased for an aircraft of moderate size, due in particular to the small surface area available under the aircraft to install on the one hand the transmitting and receiving antennas of the radio altimeter and, on the other hand, additional equipment for example.

[0008] The risk of reflection of the primary electromagnetic signal on a load transported by sling has been known for a long time. A commonly used solution to avoid this risk consists of installing on board the aircraft so-called "horn" antennas which emit a primary electromagnetic signal in a cone with a narrow opening angle.

[0009] The beamwidth, also called the "beam angle," relative to the emission of a signal by an antenna is defined as the angular region covered by this signal on either side of a central axis of the antenna. It is customary to characterize this beamwidth by the directions for which the radiated power of this signal is equal to half, corresponding to -3 decibels (-3 dB), of the radiated power of the same signal in the most favorable direction, which is the axis of the main lobe of this signal and generally corresponds to the central axis of the transmitting antenna. As a first approximation, when comparing the performance of several radio altimeters, a signal whose radiated power is less than half the radiated power of the same signal in the most favorable direction cannot be measured and is therefore unusable.

[0010] In addition, the measurement field corresponds to the projection of this opening angle onto the surface being flown over.

[0011] Although effective, such a solution has the disadvantage of significantly reducing the radio altimeter's ground height measurement capacity when the aircraft is making steep turns, particularly in roll.

[0012] Another solution for using a sling-carried load is described in document EP 3002604 and consists of a radio altimeter equipped with planar antennas and a lens that modifies the aperture angle relative to the signal emitted by these antennas in order to exclude the sling-carried load. Such a solution can also be used to avoid reflection of the primary electromagnetic signal on additional equipment attached under the aircraft.

[0013] Another solution is to select the radio altimeter antennas from a set of interchangeable antennas to adapt the radio altimeter's measurement field to the missions. However, such antenna replacement operations are costly and difficult to perform, and are ultimately little used in practice.

[0014] Consequently, given the occasional nature of aircraft missions involving the transport of cargo by sling, it is standard practice to equip aircraft with planar antennas providing maximum radio altimeter measurement range. Such arrangements allow the pilot to obtain reliable information regarding the aircraft's ground height for most missions, excluding cargo transport by sling. However, the radio altimeter is sometimes deactivated by the aircraft crew when cargo is being transported by sling, or when additional equipment is attached under the aircraft that could interfere with the ground height measurement.

[0015] The present invention aims to provide an alternative solution for measuring the ground height of an aircraft in flight, overcoming the limitations mentioned above in order to provide a reliable measurement of this ground height, regardless of the configuration of the additional equipment attached under the aircraft. The present invention thus relates to a method for measuring the ground height of an aircraft using a radio altimeter having an adjustable aperture angle, as well as to such a radio altimeter implementing this method. The present invention also relates to an aircraft equipped with such a radio altimeter.

[0016] The present invention relates firstly to a method for measuring the ground height H s of an aircraft by means of a radio altimeter comprising a transmitting antenna equipped with a source generating a primary electromagnetic signal, a receiving antenna equipped with a receiver capable of receiving a reflected electromagnetic signal resulting from a reflection of the primary electromagnetic signal, and a computer.

[0017] This method is remarkable in that the radio altimeter includes an adjustable antenna among the transmitting antenna and the receiving antenna, the adjustable antenna being provided with at least two radiating elements and a processing element, two adjacent radiating elements being separated by a non-zero gap, the processing element comprising the source when the adjustable antenna is the transmitting antenna or the receiver when the adjustable antenna is the receiving antenna.

[0018] The process then comprises the following main steps: - an adjustment of the opening angle of this adjustable antenna between the transmitting antenna and the receiving antenna by electrically connecting one or more radiating elements from among said radiating elements to this processing unit, and - after adjustment, a determination of a ground height Hs as a function of a minimum elapsed time between an emission of the primary electromagnetic signal and a reception of the reflected electromagnetic signal.

[0019] Thus, the method according to the invention initially allows for the adjustment of the adjustable antenna's beamwidth to adapt this beamwidth to the aircraft's flight conditions, and in particular to the presence of equipment located beneath the aircraft. This adjustment enables a correct and reliable measurement of the aircraft's ground height Hs, notably by preventing the reflection of the primary electromagnetic signal off any of this equipment. This beamwidth adjustment is achieved by electrically connecting a suitable number of radiating elements to the processing unit.

[0020] The radiating elements comprise an electrically conductive material, for example a metallic material. The radiating elements can take the form of all known types of antennas, for example planar, wire, or others.

[0021] When the adjustable antenna is the transmitting antenna, the adjustment of the beamwidth is relative to the emission of the primary electromagnetic signal and is achieved by electrically connecting a suitable number of radiating elements to the source of the transmitting antenna to adapt the shape of the emitted primary electromagnetic signal. The primary electromagnetic signal is generated by the source and then transmitted to one or more radiating elements electrically connected to the source. These radiating elements then emit the primary electromagnetic signal towards the environment external to the transmitting antenna, and in particular towards the surface overflown by the aircraft. The use of one or more radiating elements separated by a non-zero gap advantageously allows the transmitting antenna to modify its beamwidth, and consequently, the area overflown swept by the primary electromagnetic signal.This opening angle decreases particularly as the number of radiating elements electrically connected to the source increases. This opening angle is thus maximal when only one radiating element is electrically connected to the source.

[0022] When at least two radiating elements are electrically connected to the source, the source preferably transmits a primary electromagnetic signal having the same phase and amplitude to each radiating element electrically connected to the source, or even the same primary electromagnetic signal. Alternatively, an adjustment of the phase and amplitude can also be applied to the primary electromagnetic signal for each radiating element electrically connected to the source, for example, according to the relative positions of these radiating elements.

[0023] When the adjustable antenna is the receiving antenna, the adjustment of the beamwidth is related to the reception of the reflected electromagnetic signal resulting from a reflection of the primary electromagnetic signal and is achieved by electrically connecting a suitable number of radiating elements to the receiver of the receiving antenna to adjust the beamwidth at which the reflected electromagnetic signal can be received. The reflected electromagnetic signal is thus received by the radiating element(s) electrically connected to the receiver of the receiving antenna, and then transmitted to that receiver. The use of one or more radiating elements separated by a non-zero gap advantageously allows the receiving antenna to modify its beamwidth, and consequently, the surface area over which it passes is capable of reflecting and returning the primary electromagnetic signal to the receiving antenna.This opening angle decreases particularly as the number of radiating elements electrically connected to the receiver increases. This opening angle is thus maximal when only one radiating element is electrically connected to the receiver.

[0024] The electrical connection of one or more radiating elements to the processing unit of the adjustable antenna can be achieved via connectors that electrically link the processing unit to the radiating elements. Each connector can be controlled independently of the other connectors by the computer to open or close the electrical connection linking a radiating element to the processing unit.

[0025] The equipment located on the underside of the aircraft, and in particular on the underside of an aircraft fuselage, includes, for example, landing gear, radar, a camera, a spotlight, or any other equipment that may be used by an aircraft. The transmitting antenna and the receiving antenna may also be positioned on the underside of the aircraft fuselage.

[0026] Next, the determination of a ground height Hs is reliably and conventionally carried out using the radiating element(s) electrically connected to the processing unit during the adjustment of the beamwidth, for example, to transmit the primary electromagnetic signal outside the transmitting antenna. For example, the following steps are carried out: - emission of the primary electromagnetic signal by the transmitting antenna, - reception by the receiving antenna of the reflected electromagnetic signal resulting from a reflection of the primary electromagnetic signal, and - calculation by the calculator of the ground height as a function of a minimum elapsed time between the emission of the primary electromagnetic signal and the reception of the reflected electromagnetic signal.

[0027] The method according to the invention may include one or more of the following features, taken alone or in combination.

[0028] According to one possibility, the radiating elements that can be electrically connected to the processing unit can be arranged in a single row. The radiating elements are therefore aligned in this single row, which is, for example, oriented in a longitudinal or transverse direction of the aircraft.

[0029] Consequently, the beamwidth of the adjustable antenna can be adjusted during the tuning step solely according to the direction of this row of radiating elements. For example, the primary electromagnetic signal emitted by the transmitting antenna, which is the adjustable antenna, can then form a cone with a circular base when a single radiating element is electrically connected to the processing unit, in this case the source. This primary electromagnetic signal can also take the form of a cone with a substantially oval or oblong base when several radiating elements are electrically connected to the processing unit.

[0030] A reduction in the opening angle obtained by electrically connecting several radiating elements to the processing unit can thus allow the primary electromagnetic signal to avoid equipment located for example in the extension of this row of radiating elements.

[0031] Alternatively, the radiating elements may be arranged in at least two rows. Each row may contain a number of radiating elements equal to the number of rows, the radiating elements possibly forming a square. Each row may also contain a number of radiating elements different from the number of rows, the radiating elements possibly forming a rectangle.

[0032] In this way, the beamwidth of the adjustable antenna can be adjusted during the tuning step in several distinct directions. For example, the primary electromagnetic signal emitted by the transmitting antenna, which is the adjustable antenna, can optionally form a circular cone when the number of rows in which radiating elements are electrically connected to the processing unit is equal to the number of radiating elements in those rows electrically connected to the processing unit. This primary electromagnetic signal can also take the form of a cone with different bases, for example, oval or oblong, when the number of rows in which radiating elements are electrically connected to the processing unit is different from the number of radiating elements in those rows electrically connected to the processing unit.

[0033] A reduction in the opening angle obtained by electrically connecting several radiating elements to the processing unit can thus allow the primary electromagnetic signal to avoid equipment located around the transmitting antenna, and in particular several pieces of equipment located in different directions.

[0034] For example, a square arrangement of the radiating elements makes it possible to optimize the angular opening in several directions, in particular along the longitudinal and transverse axes of the aircraft, in order to avoid, for example, the presence of a fixed landing gear, located transversely on either side of the transmitting antenna, and the placement of a light, a camera and / or a radar located longitudinally in front of or behind the transmitting antenna.

[0035] According to a possibility compatible with the preceding ones, the setting of an opening angle may include a control of at least one connector among connectors electrically linking the processing unit respectively to the radiating elements, such a control being carried out by an operator using a human-machine interface.

[0036] Indeed, the radiating element(s) to be electrically connected to the processing unit can be predetermined based on the equipment mounted under the aircraft. This radiating element(s) to be electrically connected to the processing unit may have been determined through testing or simulations, or even following a previous flight of the aircraft.

[0037] An operator can then use the human-machine interface to directly select the radiating element(s) to be electrically connected to the processing unit as needed. The computer then controls the corresponding connector(s) to electrically close them. This operator can be a pilot or co-pilot of the aircraft. This operator can be located inside the aircraft. Alternatively, the operator can be located outside the aircraft and thus pilot it remotely. In this latter case, the aircraft can be a drone.

[0038] The human-machine interface can also allow the selection of a carrier configuration for the equipment installed on or carried by the aircraft, with the computer consequently controlling the connector(s) associated with that configuration. The computer then includes a memory in which information is stored allowing one or more electrically closed connectors to be associated with each of the known configurations.

[0039] The human-machine interface can further allow the selection of one or more pieces of equipment installed on or carried by the aircraft, as well as their respective positions. The computer then controls the corresponding connector(s) associated with the selected equipment and positions. The computer includes a memory in which information is stored to associate one or more electrically closed connectors with different equipment and position configurations. A message can be sent to the operator if the selected equipment and position configuration is unknown.

[0040] Regardless of the embodiment mentioned above, the human-machine interface can be selected on the ground, before the aircraft takes off, or in flight.

[0041] Alternatively, the setting of an opening angle can be carried out automatically using the computer in order to automatically adjust and adapt the opening angle of the adjustable antenna according to the equipment installed on or carried by the aircraft, and in particular under the aircraft cell.

[0042] Several variations of this automatic adjustment of the adjustable antenna's beamwidth are possible. In all these variations, the adjustment of this beamwidth first involves an initial electrical connection to the processing unit of a single radiating element. During this initial connection, the computer controls, on the one hand, the closure of a single connector, and on the other hand, the opening or holding open of the other connectors. Thus, when the adjustable antenna is the transmitting antenna, the primary electromagnetic signal generated by the source is emitted outside the transmitting antenna by this single radiating element connected to the source. Alternatively, when the adjustable antenna is the receiving antenna, the reflected electromagnetic signal is captured by this single radiating element connected to the receiver, and then transmitted to the receiver.

[0043] Next, the adjustment includes a test phase comprising the emission of at least one electromagnetic signal, the reception of at least one reflected electromagnetic signal, and an analysis of said at least one reflected electromagnetic signal to determine whether an additional radiating element should be connected to the processing unit. If so, an additional radiating element is connected to the processing unit and a further test phase is undertaken until the test is deemed satisfactory.

[0044] According to a first embodiment of the invention, at least one tuning iteration is performed, and each iteration may include the following steps: - initial emission by the transmitting antenna of a calibrated primary electromagnetic signal of known power towards at least one panel made of electromagnetic wave-absorbing material located on the ground, at a predetermined distance from the transmitting antenna, - initial reception by the receiving antenna of a reflected calibrated electromagnetic signal, - initial measurement of the power received from the reflected calibrated electromagnetic signal, - initial comparison of the received power with an initial threshold, and - if the received power is greater than or equal to the initial threshold, new connection to the processing unit of an additional radiating element among the radiating elements.

[0045] Following this new connection, a new adjustment iteration is carried out and repeated until the received power is less than the initial threshold.

[0046] Thus, this first variant can be carried out on the ground, for example following the installation of equipment under the aircraft, or even just before the aircraft takes off.

[0047] The reflected calibrated electromagnetic signal may originate from a reflection of the calibrated primary electromagnetic signal on the panel, placed on the ground beneath the aircraft, or on equipment installed on or carried by the aircraft. The distance between the panel and the transmitting antenna is known.

[0048] Since the electromagnetic wave absorption characteristics of this panel are known, the power of the reflected calibrated electromagnetic signal resulting from a reflection only on the panel can be estimated, for example as a function of the power of the calibrated primary electromagnetic signal, the distance between the panel and the transmitting and receiving antennas, as well as these electromagnetic wave absorption characteristics of this panel.

[0049] The initial threshold can then be equal to this estimated reflected calibrated electromagnetic signal power, possibly taking into account a first safety margin.

[0050] The initial threshold may alternatively be equal to a percentage of the known power of the calibrated primary electromagnetic signal emitted by the transmitting antenna. This percentage is less than one hundred and can be determined based on at least one characteristic of the absorbing material panel, such as its electromagnetic wave absorption rate, and the distance between the transmitting antenna and the panel, or even possibly the first safety margin at this power.

[0051] Thus, if the received power is below this initial threshold, it can be deduced that the calibrated primary electromagnetic signal was indeed reflected only by the panel. The beamwidth of the adjustable antenna is then compatible with the equipment installed on or carried by the aircraft. The determination of the ground height Hs by the radio altimeter can then be considered reliable under these conditions. No further adjustment iterations are therefore necessary. A confirmation message for this beamwidth can be sent, for example via an aircraft display, to an operator.

[0052] Conversely, if the received power is greater than or equal to this initial threshold, it can be deduced that the calibrated primary electromagnetic signal has been reflected at least partially by equipment installed on or carried by the aircraft. The beamwidth is therefore incompatible with the equipment installed on or carried by the aircraft.

[0053] A new connection to the processing unit of an additional radiating element is thus made, for example, in a predetermined order. The additional radiating element connected to the processing unit is generally a radiating element adjacent to a radiating element that is already connected to the processing unit. Alternatively, when the tunable antenna has several rows of radiating elements, if the aircraft equipment deemed responsible for the unwanted reflection faces the radiating elements of a row, that is, is located vertically above these radiating elements, which are located substantially horizontally, a radiating element from another row is added. If, on the other hand, this unwanted equipment is aligned with the radiating elements of a row, that is, is located in line with this row but does not face it, a radiating element from that same row is added.

[0054] Next, a new adjustment iteration is performed. The adjustment iteration is repeated as long as the received power is greater than or equal to the initial threshold.

[0055] According to a second variant of the invention, following the initial connection, a first measurement of a first power received from the reflected electromagnetic signal is carried out before takeoff of the aircraft.

[0056] Next, at least one tuning iteration is performed and may include the following steps: - second measurement of a second power received from the reflected electromagnetic signal after the aircraft took off, - comparison of the first power received and the second power received, - if a difference between the first power received and the second power received is less than or equal to a predetermined value, a new connection to the processing unit of an additional radiating element among the radiating elements.

[0057] Following this new connection, a new adjustment iteration is carried out and repeated until the difference between the first power received and the second power received is greater than the predetermined value.

[0058] Thus, this second variant is carried out partly on the ground and partly in flight, with at least one adjustment iteration being performed after the aircraft has taken off. Only the initial connection and the first measurement are performed on the ground.

[0059] Whether before or after takeoff, the reflected electromagnetic signal may originate from a reflection of the primary electromagnetic signal off the surface overflown by the aircraft or off equipment installed on or carried by the aircraft. The power of the primary electromagnetic signal emitted by the transmitting antenna is substantially constant when the ground height Hs is low.

[0060] Therefore, after takeoff, the power of the reflected electromagnetic signal resulting from a reflection of the primary electromagnetic signal on the surface overflown by the aircraft decreases as the ground height Hs of the aircraft increases.

[0061] Consequently, if the first received power and the second received power are substantially identical or close, it can be deduced that the primary electromagnetic signal was reflected at least partially by equipment installed on or carried by the aircraft. The beamwidth of the adjustable antenna is therefore incompatible with the equipment installed on or carried by the aircraft. The determination of the ground height Hs by the radio altimeter cannot therefore be considered reliable under these conditions.

[0062] Conversely, if this first received power and this second received power are significantly different, it can be deduced that the primary electromagnetic signal was reflected only by the surface overflown. The beamwidth of the adjustable antenna is then compatible with the equipment installed on or carried by the aircraft. The determination of the ground height Hs by the radio altimeter can then be considered reliable under these conditions. No further adjustment iterations are therefore necessary. A confirmation message for this beamwidth can be transmitted, for example using an aircraft display, to an operator.

[0063] Consequently, in order to take into account a second safety margin within the framework of the invention, it can be considered that the primary electromagnetic signal has been reflected at least partially by equipment installed on or carried by the aircraft when the difference between the first power received and the second power received is less than or equal to a non-zero predetermined value, the predetermined value being for example substantially equal to the second safety margin.

[0064] A new connection to the processing unit of an additional radiating element is then made, for example according to a predetermined order. The additional radiating element connected to the processing unit may be, for example, a radiating element adjacent to a radiating element that is already connected to the processing unit, or a radiating element in a row aligned with the equipment in question, as in the first variant.

[0065] Then, a new adjustment iteration is carried out, and so on until the difference between the first power received and the second power received is greater than the predetermined value.

[0066] The second measurement of the second power received from the electromagnetic signal reflected on the receiving antenna after takeoff of the aircraft can be performed at the command of an operator using a human-machine interface or automatically as soon as the aircraft has risen from a normal height greater than or equal to a predetermined height. The current height can be determined using an aircraft altimeter.

[0067] According to a third embodiment of the invention, following the initial connection, at least one adjustment iteration is performed and may include the following steps: - Measurement of the power received from the electromagnetic signal reflected on the receiving antenna after the aircraft has taken off, - comparison of the received power with a power threshold, - if the received power is greater than or equal to the power threshold, new connection to the processing unit of an additional radiating element among the radiating elements.

[0068] Following this new connection, a new adjustment iteration is carried out and repeated until the received power is below the power threshold.

[0069] Thus, this third variant is carried out partly on the ground and partly in flight, with at least one adjustment iteration being performed after the aircraft has taken off. Only the initial connection is made on the ground, before the aircraft takes off.

[0070] This third variant is similar to the second variant. However, the power received from the electromagnetic signal reflected by the receiving antenna after takeoff of the aircraft is not compared to an initial power received from the electromagnetic signal reflected by the receiving antenna before takeoff, but to a predetermined power threshold. Advantageously, no operation other than the initial electrical connection to the processing unit of a single radiating element is required before takeoff of the aircraft.

[0071] The power threshold can be determined by calculations, tests, or simulation. The power threshold is, for example, equal to the power of the reflected electromagnetic signal resulting from a reflection off the ground when the aircraft is on the ground, possibly less a third safety margin. The power threshold can be determined in this case by ensuring that the primary electromagnetic signal is indeed reflected only by the ground, and that no reflection of this primary electromagnetic signal occurs on any equipment fixed under the aircraft.

[0072] Consequently, if the received power is below this power threshold, it can be deduced that the primary electromagnetic signal was indeed reflected only by the surface overflown. The adjustable antenna beamwidth is compatible with the equipment installed on or carried by the aircraft. The determination of the ground height Hs by the radio altimeter can then be considered reliable under these conditions. No further adjustments are therefore necessary. A confirmation message for this beamwidth can be sent, for example, via an aircraft display, to an operator.

[0073] Conversely, if the received power is greater than or equal to this power threshold, it can be deduced that the primary electromagnetic signal has been reflected at least partially by equipment installed on or carried by the aircraft. The adjustable antenna's beamwidth is therefore incompatible with the equipment installed on or carried by the aircraft. Consequently, the determination of the ground height Hs by the radio altimeter cannot be considered reliable under these conditions.

[0074] A new connection to the processing unit of an additional radiating element from among the radiating elements is thus made, for example according to a predetermined order. The additional radiating element connected to the processing unit can be defined as for the previous variants.

[0075] Then, a new adjustment iteration is carried out, and so on until the power received is less than the power threshold.

[0076] The power received adjustment measurement can be performed on command by an operator using a human-machine interface or automatically as soon as the aircraft has climbed to a current altitude greater than or equal to a predetermined altitude. The current altitude can be determined using an aircraft altimeter.

[0077] According to a fourth embodiment of the invention, following the initial connection, a first determination of a first value of the ground height Hs before takeoff of the aircraft is performed. This first determination of a first value of the ground height Hs is carried out in the usual way by calculating, using the computer, the ground height Hs as a function of a minimum elapsed time between the emission of the primary electromagnetic signal and the reception of the reflected electromagnetic signal. The reflected electromagnetic signal may result from a reflection of the primary electromagnetic signal on the surface overflown by the aircraft or on equipment installed on or carried by the aircraft, depending on the angle of incidence.

[0078] Next, at least one tuning iteration is performed and may include the following steps: - second determination of a second value for the ground height after the aircraft has taken off, - comparison of the first and second values ​​of the ground height, - if a difference between the second value and the first value is less than or equal to a predetermined gap, a new connection to the processing unit of an additional radiating element among the radiating elements.

[0079] Following this new connection, a new adjustment iteration is carried out and repeated until the difference between the second value and the first value is greater than the predetermined gap.

[0080] Thus, this fourth variant is carried out partly on the ground and partly in flight, said at least one adjustment iteration being carried out after the aircraft has taken off.

[0081] After takeoff, the ground height Hs increases progressively as the aircraft climbs. The second value of the ground height after takeoff obtained during the second determination confirms this when the reflected electromagnetic signal originates from a reflection solely on the surface overflown by the aircraft.

[0082] However, if the reflected electromagnetic signal originates from a reflection on equipment installed on or carried by the aircraft, the second value of the aircraft's ground height Hs is substantially identical or close to the first value of the ground height Hs. A small difference may be due, in particular, to measurement accuracy.

[0083] Consequently, if the first and second ground height (Hs) values ​​determined using the reflected electromagnetic signals actually received by the receiving antenna before and after takeoff of the aircraft are substantially identical or close, it can be deduced that the primary electromagnetic signal was at least partially reflected by equipment installed on or carried by the aircraft. The adjustable antenna beamwidth is therefore incompatible with the equipment installed on or carried by the aircraft. The determination of the ground height (Hs) by the radio altimeter cannot therefore be considered reliable under these conditions.

[0084] Conversely, if this first and second values ​​of the ground height Hs are significantly different, it can be deduced that the primary electromagnetic signal was reflected only by the surface overflown. The beamwidth is then compatible with the equipment installed on or carried by the aircraft. The determination of the ground height Hs by the radio altimeter can then be considered reliable under these conditions. No further adjustment iterations are therefore necessary. A validation message for this beamwidth can be transmitted, for example, via an aircraft display, to an operator.

[0085] Consequently, in order to take into account a fourth safety margin within the scope of the invention, the primary electromagnetic signal can be considered to have been reflected at least partially by equipment installed on or carried by the aircraft when the difference between the first and second values ​​of the ground height Hs is less than or equal to a predetermined deviation, the predetermined deviation being, for example, substantially equal to the fourth safety margin. Such a predetermined deviation is, for example, equal to one or two feet (2 ft), or 3.048 to 6.096 meters.

[0086] A new connection to the processing unit of an additional radiating element is then made, for example in a predetermined order. The radiating element additional connected to the processing organ can be defined as for the previous variants.

[0087] Next, a new adjustment iteration is carried out, and so on until the difference between the first value and the second value of the ground height H s is greater than the predetermined gap.

[0088] The second determination of the second ground height value Hs after takeoff of the aircraft can be performed at the command of an operator, using a human-machine interface, or automatically as soon as the aircraft has climbed to a current height greater than or equal to a predetermined height. The current height can be determined using an aircraft altimeter.

[0089] According to another aspect and a possibility compatible with the previous ones, the length of the gap separating two adjacent radiating elements can be proportional to a wavelength of the primary electromagnetic signal emitted by the source of the transmitting antenna.

[0090] The length of the gap separating two adjacent radiating elements can be identical for all radiating elements, and in at least two distinct directions when the transmitting antenna has at least two rows of radiating elements.

[0091] According to another aspect, the radiating elements can be of planar configuration, and / or are preferably implanted at the level of an underside of the aircraft, and for example under an aircraft cell.

[0092] According to another aspect, the transmitting antenna and the receiving antenna can form a single antenna. In this case, the radiating elements are connected respectively to the source of the transmitting antenna and to the receiver of the receiving antenna.

[0093] According to a possibility compatible with the preceding ones, the method may include a determination of a maximum angle of inclination of the aircraft for which the determination of the ground height Hs is considered correct, the maximum angle of inclination being a function of a number of radiating elements electrically connected to the processing unit, and a display of the maximum angle of inclination on a display of the aircraft.

[0094] Indeed, following the adjustment of the adjustable antenna's beamwidth, this beamwidth may have been reduced to prevent the primary electromagnetic signal from interfering with aircraft equipment, and thus to allow for the determination of a correct ground height Hs. Consequently, a significant bank angle of the aircraft, for example in roll or even pitch during a turn, may result in the primary electromagnetic signal not being directed towards the ground in a vertical direction, i.e., parallel to the direction of Earth's gravity.

[0095] Consequently, the shortest time between the emission of the primary electromagnetic signal and the reception of the reflected electromagnetic signal used to determine the ground height Hs corresponds to a path of this electromagnetic signal that is not in a vertical direction. The ground height Hs thus determined is therefore incorrect and is either higher or lower than the actual ground height Hs.

[0096] It is therefore important, even essential, to inform the operator of this risk.

[0097] To this end, the method according to the invention may include determining a maximum aircraft tilt angle for which the determination of the ground height Hs is considered correct. This maximum tilt angle can be calculated by the computer according to a stored formula and as a function of the adjustable antenna's beamwidth, and therefore as a function of the number of radiating elements electrically connected to the processing unit. This maximum tilt angle is, for example, equal to half the adjustable antenna's beamwidth or to half the adjustable antenna's beamwidth minus a safety margin. Furthermore, this safety margin can vary depending on the aircraft's flight altitude.This angular safety margin can, for example, be equal to 30% of the adjustable antenna's opening angle for flight altitudes less than or equal to 100 feet (100 ft), or 30.48 meters, and 20% for higher flight altitudes.

[0098] The adjustable antenna's beamwidth is solely a function of the radiating elements electrically connected to the processing unit. Therefore, a memory within the computer or a memory connected to the computer may contain a lookup table or a database, for example, allowing different maximum tilt angles to be associated with different configurations of radiating elements electrically connected to the processing unit. The computer can thus determine the maximum tilt angle associated with the current configuration of radiating elements electrically connected to the processing unit.

[0099] Next, this maximum bank angle is displayed on an aircraft display to inform the operator of this maximum bank angle. This maximum bank angle may also be a limit taken into account by certain modes of an aircraft autopilot.

[0100] Alternatively or in addition, an alert device connected to the computer can issue a visual, audible, or haptic alert when the aircraft approaches, reaches, or even exceeds this maximum bank angle. This alert can also serve as input for certain modes of the aircraft's autopilot. For this purpose, a current bank angle of the aircraft, determined, for example, by a standard aircraft bank angle measuring device, is compared to this maximum bank angle.

[0101] The present invention also relates to a radio altimeter for an aircraft, the radio altimeter comprising a transmitting antenna equipped with a source generating a primary electromagnetic signal, a receiving antenna equipped with a receiver capable of receiving a reflected electromagnetic signal resulting from a reflection of said primary electromagnetic signal, and a computer, the computer determining the ground height Hs of the aircraft from data provided by the transmitting antenna and the receiving antenna. Furthermore, the radio altimeter comprises an adjustable antenna among the transmitting and receiving antennas, the adjustable antenna being equipped with a processing unit, at least two radiating elements, and a plurality of connectors for electrically connecting the radiating elements to the processing unit, two adjacent radiating elements being separated by a non-zero gap.Finally, the radio altimeter is configured to implement the previously described procedure.

[0102] The present invention also relates to an aircraft equipped with the aforementioned radio altimeter.

[0103] The invention and its advantages will become apparent in more detail in the following description, with illustrative examples given by reference to the accompanying figures, which represent: - [Fig. 1], a view of a radio altimeter according to the invention, - [Fig. 2], a view of a radio altimeter according to the invention, - [Fig. 3], a graph relating to the primary electromagnetic signal emitted by a transmitting antenna, - [Fig. 4], a view of an aircraft equipped with a radio altimeter according to the invention, - [Fig. 5], a synoptic view of a process according to the invention, - [Fig. 6], a representation of the realization of a variant of the step of adjustable antenna opening angle, and - Figures 7 and 8 are views of the aircraft.

[0104] Elements present in several separate figures are assigned one and the same reference.

[0105] Figures 1 and 2 show radio altimeters 1 according to the invention intended to equip an aircraft. Regardless of the embodiment, such a radio altimeter 1 commonly comprises a transmitting antenna 10, a receiving antenna 20, and a computer 2. The computer 2 is connected to the transmitting antenna 10 and the receiving antenna 20 by a wired or wireless connection.

[0106] The transmitting antenna 10 comprises a source 5 generating a primary electromagnetic signal 51, 52 and may comprise one or more radiating elements 11-19 capable of being electrically connected to the source 5. The receiving antenna 20 comprises a receiver 25 capable of receiving a reflected electromagnetic signal 55, 56 resulting for example from a reflection of the primary electromagnetic signal 51 and may include one or more radiating elements 21 capable of being connected to the receiver 25.

[0107] The radio altimeters 1 according to the invention also include an adjustable antenna equipped with a processing unit 80 and several radiating elements capable of being electrically connected to the processing unit 80 respectively by electrical links each comprising a connector 41-49. Each connector 41-49 may include a relay, a contactor or a switch for example.

[0108] Each connector 41-49 is also connected by a wired or wireless link to the computer 2. The computer 2 thus independently controls the switching of each connector 41-49 from an open position to a closed position, and vice versa, in order to electrically connect a radiating element to the processing unit 80 or to break the electrical connection between a radiating element and the processing unit 80.

[0109] The adjustable antenna can be the transmitting antenna 10, the processing element 80 then being the source 5 of the transmitting antenna 10. The adjustable antenna can be the receiving antenna 20, the processing element 80 then being the receiver 25 of the receiving antenna 20. According to the examples of radio altimeters 1 shown in Figures 1 and 2, the adjustable antenna is the transmitting antenna 10.

[0110] According to [Fig. 1], the adjustable antenna, namely the transmitting antenna 10, may comprise a row 31 of several radiating elements, for example five radiating elements 11-15 as shown in the example. The radiating elements 11-15 may, for example, be square and planar.

[0111] According to [Fig.2], the adjustable antenna, namely the transmitting antenna 10, can comprise at least two rows 32-34 of several radiating elements, for example three rows 32,33,34 of three radiating elements 11-19 each according to the example shown.

[0112] Regardless of the embodiment and irrespective of the number of rows 31-34 of radiating elements 11-19, two adjacent radiating elements 11-19 are separated by a gap of non-zero length D. In this way, two adjacent radiating elements 11-19 are never in contact with each other in any direction.

[0113] These gaps may be identical between all the radiating elements 11-19 of a row 31-34, and may also be identical with the gap separating two adjacent rows 31-34. Alternatively, gaps may be different between some radiating elements 11-19 of the adjustable antenna.

[0114] The length D of this gap separating two adjacent radiating elements 11-19 can be proportional to a wavelength of the primary electromagnetic signal 51 emitted by the source 5 of the transmitting antenna 10. For example, the length D of this The gap between two adjacent radiating elements 11-19 can be equal to one-quarter or one-half of the wavelength of the primary electromagnetic signal 51. Thus, for a primary electromagnetic signal 51 emitted by the radio altimeter 1 with a frequency between 4.2 and 4.4 gigahertz, i.e., a wavelength on the order of 7 centimeters, the length D of this gap can be equal to 17.5 millimeters. Furthermore, the length and width of a radiating element 11-19 can be between 20 and 50 millimeters.

[0115] The receiving antenna 20 may comprise a single receiving element 21, as shown in Figures 1 and 2. Alternatively, the receiving antenna 20 may comprise several receiving elements 21. Furthermore, the transmitting antenna 10 and the receiving antenna 20 may be separate, as shown in Figures 1 and 2. Alternatively, the transmitting antenna 10 and the receiving antenna 20 may be combined into a single antenna, as shown in [Fig. 3]. In this case, the radiating elements 11-19 of the transmitting antenna 10 may be used for the radiating elements 21 of the receiving antenna 20 or may be separate.

[0116] The source 5 is capable of generating a primary electromagnetic signal 51,52 which is transmitted, via the electrical link(s) whose respective connectors 41-49 are electrically closed, to one or more radiating elements 11-19. This or these radiating elements 11-19 can then jointly emit this primary electromagnetic signal 51,52 outside the transmitting antenna 10.

[0117] Remarkably, when the adjustable antenna is the transmitting antenna 10, this primary electromagnetic signal 51,52 is emitted at an opening angle varying according to the number of radiating elements 11-19 electrically connected to the source 5, although the electromagnetic signal generated by the source 5 and transmitted to these radiating elements 11-19 is unchanged.

[0118] Figure 3 shows a graph indicating the evolution of the power of the primary electromagnetic signal 51, 52 emitted by the transmitting antenna 10, used as a tunable antenna, as a function of the beamwidth covered by a beam formed by this primary electromagnetic signal 51, 52 for three different numbers of radiating elements 11-19 electrically connected to the source 5, which is the processing unit 80 of the tunable antenna. Curve A corresponds to four radiating elements 11-19 electrically connected to the source 5, curve B corresponds to six radiating elements 11-19 electrically connected to the source 5, and curve C corresponds to eight radiating elements 11-19 electrically connected to the source 5.

[0119] It is customary to consider that a primary electromagnetic signal 51,52 emitted by the transmitting antenna 10 is usable when its radiated power is greater than or equal to half (-3 dB) of the radiated power of the same signal in the direction the most favorable, generally corresponding to the central axis of the transmitting antenna 10.

[0120] It can be seen from the graph in [Fig.3] that the relative opening angle of the emission of the primary electromagnetic signal by the transmitting antenna 10 corresponding to a power of the primary electromagnetic signal 51 greater than or equal to -3 dB decreases with the increase in the number of radiating elements 11-19 electrically connected to the source 5.

[0121] Indeed, with four radiating elements 11-19 electrically connected to the source 5, the opening angle at -3 dB is 61 degrees (61°), with six radiating elements 11-19 electrically connected to the source 5, this opening angle is reduced to 34°, and for eight radiating elements 11-19 electrically connected to the source 5, this opening angle decreases to 23°.

[0122] In the case where the transmitting antenna 10 comprises a single row 31 of radiating elements 11-15 oriented along a direction X, as shown in [Fig.1], the variation of the opening angle as a function of the number of radiating elements 11-15 electrically connected to the source 5 occurs only along this direction X.

[0123] In the case where the transmitting antenna 10 has three rows 32-34 of radiating elements 11-19 oriented along two orthogonal directions X,Y, as shown in [Fig.2], the variation of the opening angle as a function of the number of radiating elements 11-19 electrically connected to the source 5 can occur along these two directions X,Y as well as along intermediate directions U,T, depending on the number of radiating elements 11-19 electrically connected to the source 5 and their respective positions.

[0124] The radio altimeter 1 according to the invention is intended to equip an aircraft 30, shown in [Fig. 4], in order to provide a measurement of the ground height Hs of the aircraft 30, namely the distance between the aircraft 30 and the surface overflown 70. This ground height Hs is generally measured along a direction DV referred to as "vertical" in a terrestrial frame of reference, and parallel to the direction of Earth's gravity. The altimeter 1 can be mounted on the underside of the aircraft 30, with the transmitting antenna 10 and the receiving antenna 20 directed towards the surface overflown 70 by the aircraft 30. The transmitting antenna 10 and the receiving antenna 20 are, for example, mounted under a cell 35 of the aircraft 30, and oriented towards the ground when the aircraft 30 is considered to be on the ground.

[0125] The illustrated airframe 35 supports a skid landing gear 33, rotors 31, 32, and stabilization devices 34, 36. Optional equipment 60 can be installed under the airframe 35 depending on the intended missions. For example, a searchlight 61 can be installed under the nose of the aircraft 30, i.e., at the front of the airframe 35. A radar 62 can also be installed under the airframe 35, behind the landing gear. landing gear 33 for example. Other equipment 60, such as a camera, can also be installed under the cell 35.

[0126] According to the example of [Fig.4], the transmitting antenna 10 and the receiving antenna 20 are combined and installed under the cell 35, between the landing gear skids 33.

[0127] In addition, instructions or a computer program can be stored in a memory 3 of the computer 2 or in a memory linked to this computer 2. The computer 2 can then execute these instructions or this program to implement a method of measuring the ground height Hs of the aircraft 30 by means of the radio altimeter 1.

[0128] Figure 5 shows a block diagram of this method for measuring the ground height Hs. This method can include two main steps, namely a step of adjusting 100 an opening angle of the adjustable antenna by electrically connecting one or more of the radiating elements 11-19 to the processing unit 80 via the connectors 41-49, and a step of determining 300 a ground height Hs of the aircraft 30.

[0129] The step 300 for determining a ground height Hs may ordinarily include the following sub-steps: - emission 310 of the primary electromagnetic signal 51 by the transmitting antenna 10, - a reception 320 by the receiving antenna 20 of the reflected electromagnetic signal 55 resulting from a reflection of the primary electromagnetic signal 51, and - calculation 330 by calculator 2 of the ground height Hs as a function of a minimum elapsed time between the emission 310 of the primary electromagnetic signal 51 and the reception 320 of the reflected electromagnetic signal 55.

[0130] During calculation 300, the computer 2 measures the minimum elapsed time between transmission 310 and reception 320, for example, using a chronograph that the computer 2 includes. This determination step 300 may further include the transmission of the ground height Hs by the computer 2 to an avionics system of the aircraft 30, and for example to a display 9 configured to show the calculated ground height Hs value. In this way, the ground height Hs can be displayed, for example, on an instrument panel 8 of the aircraft 30, using a dedicated display 9 or a multifunction display.

[0131] This determination 300 of a ground height Hs is, for example, carried out continuously, from the takeoff of the aircraft 30, or even from the start of the engine(s) of the aircraft 30. Thus, the primary electromagnetic signal 51 can in particular be emitted by the transmitting antenna 10 from the takeoff of the aircraft 30.

[0132] The adjustment step 100 allows the opening angle of the adjustment antenna to be defined or modified and adapted by electrically connecting an appropriate number of radiating elements 11-19 electrically connected to the processing unit 80 via the connectors 41-49.

[0133] Indeed, an excessively large beamwidth of the transmitting antenna 10 can induce reflection of the primary electromagnetic signal 51 off equipment 60 of the aircraft 30, or even its landing gear 33, thus distorting the ground height measurement HS. Similarly, an excessively large beamwidth of the receiving antenna 20 can cause it to pick up a reflected electromagnetic signal 55 off equipment 60 of the aircraft 30, or even its landing gear 33, also distorting the ground height measurement HS.

[0134] In both cases, the realization of such an adjustment 100 of the adjustable antenna, which can be the transmitting antenna 10 or the receiving antenna 20, makes it possible to define the number of radiating elements 11-19 to be electrically connected to the processing unit 80 and to connect them in order to define or adapt the opening angle of the adjustable antenna to the presence or absence of equipment 60.

[0135] Consequently, the adjustable antenna is considered to be the transmitting antenna 10, the processing element 80 then being the source 5 of the transmitting antenna 10. The radiating elements of the adjustable antenna are therefore the radiating elements 11-19 of the transmitting antenna 10. A similar operation when the adjustable antenna is the receiving antenna 20 can be deduced from the examples described.

[0136] The adjustment step 100 can be implemented in various ways.

[0137] First, the adjustment step 100 may include control 110 of at least one of the connectors 41-49 by an operator using a human-machine interface 7. The human-machine interface 7 may be located, for example, on the instrument panel 8 of the aircraft 30 or on the instrument panel of a remote cockpit of the aircraft 30. Indeed, the operator may be a pilot or co-pilot present in the aircraft 30, or piloting the aircraft 30 remotely. The human-machine interface 7 may include, for example, a screen equipped with a touch panel, a screen associated with a selection device such as a mouse or equivalent, one or more buttons, etc.

[0138] Indeed, depending on the configuration of the equipment 60 fixed under the aircraft 30, tests or simulations may have made it possible to determine beforehand the radiating element(s) 11-19 to be electrically connected to the source 5 in order to have an opening angle relative to the emission of the primary electromagnetic signal compatible with this equipment 60 and their positions under the aircraft 30.

[0139] For example, the operator can directly select the radiating element(s) 60 to be electrically connected to the source 5 using the human-machine interface 7, the computer 2 consequently controlling the closure of the connector(s) 41-49 corresponding to connect electrically to source 5 the selected radiating element(s) 11-19.

[0140] According to another example, the operator can select a configuration of one or more pieces of equipment 60 installed under the aircraft 30 using the human-machine interface 7. The computer 2 then controls the necessary connector(s) 41-49 to electrically connect the corresponding radiating elements 11-19 to the source 5. For this purpose, the computer 2 uses information stored in memory 3. This information may be in the form of a model comprising a rule, a table, or a database that associates each of the known configurations with the radiating element(s) 11-19 to be electrically connected to the source 5.

[0141] In both cases, the computer 2 controls the connector(s) 41-49 by transmitting a control signal to them, electrical or optical, analog or digital.

[0142] Alternatively, the adjustment step 100 can be carried out automatically using the calculator 2 in order to automatically adjust and adapt the opening angle according to the equipment 60 installed.

[0143] Several variants of an automatic implementation of this setting 100 are conceivable. An operator can select, for example using the human-machine interface 7, the variant of this setting 100 to be implemented automatically, prior to the takeoff of the aircraft 30. A variant can also be automatically pre-selected to be executed at the start-up of the aircraft 30.

[0144] According to a first embodiment, the setting 100 of an opening angle relative to the emission of the primary electromagnetic signal initially comprises an initial connection 120 for electrically connecting a single radiating element 11-19 from among the radiating elements 11-19 to the source 5. This initial connection 120 makes it possible to obtain a maximum opening angle. In this case, the computer 2 controls the closing of only one connector 41-49, the other connectors 41-49 being open.

[0145] Next, at least one adjustment iteration 130 is carried out, firstly to check if this maximum opening angle allows a reliable and correct measurement of the ground height Hs, then, if not, to modify and adapt it until a reliable and correct measurement of the ground height Hs is obtained.

[0146] Each tuning iteration 130 comprises several substeps performed before the takeoff of the aircraft 30, and before the execution of the ground height determination step 300 Hs. First, the method comprises an initial emission 131, by the transmitting antenna 10, of a calibrated primary electromagnetic signal 52 towards at least one panel 65 made of electromagnetic wave-absorbing material located on the ground 68 as shown in [Fig. 6]. During this initial emission 131, the source 5 generates the calibrated primary electromagnetic signal 52 which is transmitted to a or to several radiating elements 11-19 via the electrical connection(s) whose respective connectors 41-49 are electrically closed, to one or more radiating elements 11-19, this or these radiating element(s) 11-19 then emitting the calibrated primary electromagnetic signal 52 towards the environment outside the transmitting antenna 10. The panel(s) 65 have been previously placed on the ground 68 vertically above the transmitting antenna 10 and receiving antenna 20 and at a known distance from these antennas 10,20. Such a panel 65 has known and significant electromagnetic wave absorption characteristics to allow identification of the waves reflected by such a panel 65. The calibrated primary electromagnetic signal 52 has a known power.

[0147] Next, and again with reference to [Fig. 5], the method includes an initial reception 132 of a reflected calibrated electromagnetic signal 56 by the receiving antenna 20. This reflected calibrated electromagnetic signal 56 may result from a reflection of the calibrated primary electromagnetic signal 52 on the panel 65 or on a piece of equipment 60, for example. An initial measurement 134 of a power, referred to as the "received power," of the reflected calibrated electromagnetic signal 56 is then performed using a dedicated sensor 26 of the receiving antenna 20. This initial measurement 134 of the received power may be carried out by measuring an electrical voltage across a predetermined load on this sensor 26.

[0148] When the reflected calibrated electromagnetic signal 56 results solely from a reflection of the calibrated primary electromagnetic signal 52 on the panel 65, the received power is a function of the power of the calibrated primary electromagnetic signal 52, which is known, of the distance between the panel 65 and the transmitting antenna 10 and receiving antenna 20 as well as the known absorption characteristics of the electromagnetic waves of this panel 65. Such a theoretical received power is therefore known and can be estimated.

[0149] When the reflected calibrated electromagnetic signal 56 results from a reflection of the calibrated primary electromagnetic signal 52 on the panel 65 and on at least one piece of equipment 60, the received power is different from and greater than the estimated received power. This is because the equipment 60 is located closer to the antennas 10, 20 than the panel 65, and is also made of a material that absorbs electromagnetic waves less than the panel 65, or even reflects them entirely.

[0150] Therefore, an initial comparison 138 of this received power with an initial threshold is then performed by the computer 2, the initial threshold being, for example, a function of this estimated received power, possibly taking into account a first safety margin. The initial threshold can also be equal to a percentage of the known power of the electromagnetic signal 52 emitted by the transmitting antenna 10. The initial threshold has been determined beforehand and is stored, for example, in memory 3.

[0151] Following this initial comparison 138, if the received power is greater than or equal to the initial threshold, the calibrated primary electromagnetic signal 52 has been reflected at least partially by equipment 60. The radio altimeter 1 cannot therefore be considered reliable.

[0152] A new connection 138 to the source 5 of an additional radiating element 11-19 from among the radiating elements 11-19 is therefore required and is made by the computer 2, via one of the connectors 41-49. The additional radiating element 11-19 electrically connected to the source 5 is a radiating element 11-19 adjacent to a radiating element 11-19 already connected to the source 5.

[0153] A new adjustment iteration 130 is then carried out and repeated if necessary until the power received from the reflected calibrated electromagnetic signal 56 actually captured by the receiving antenna 20 is less than this initial threshold.

[0154] Indeed, as soon as the received power of the reflected calibrated electromagnetic signal 56 is below the initial threshold, it can be deduced that the calibrated primary electromagnetic signal 52 has been reflected only by the panel 65. The beamwidth is then compatible with the equipment 60 of the aircraft 30. The determination of the ground height Hs by the radio altimeter 1 can then be considered reliable and correct. No further adjustment iteration 130 is necessary. A validation message for this beamwidth can be sent, for example, via a display 9 of the aircraft 30 controlled by the computer 2, to the operator.

[0155] According to a second variant of the invention, the adjustment 100 of an opening angle relative to the emission of the primary electromagnetic signal initially comprises the initial electrical connection 120 to the source 5 of a single radiating element 11-19 in the same way as in the first variant.

[0156] Next, a first measurement 122 of a first received power of the reflected electromagnetic signal 55 captured by the receiving antenna 20 is carried out before takeoff of the aircraft 30. This reflected electromagnetic signal 55 can result from a reflection on the ground or on equipment 60 of the primary electromagnetic signal 51 emitted by the transmitting antenna 10. This first measurement 122 is carried out using the sensor 26.

[0157] Next, at least one adjustment iteration 140 is performed after takeoff of the aircraft 30 and comprises several sub-steps. As with the first variant, this adjustment iteration 140 verifies whether the maximum opening angle allows for a reliable and correct measurement of the ground height Hs, and then, if not, modifies and adjusts it until a reliable and correct measurement of the ground height Hs is obtained.

[0158] During each iteration 140, a second measurement 142 of a second received power of the reflected electromagnetic signal 55 captured by the receiving antenna 20 is performed using the sensor 26. This reflected electromagnetic signal 55 can The first measurement results from a reflection of the primary electromagnetic signal 51 emitted by the transmitting antenna 10 onto the surface being flown over 70 or onto equipment 60, for example. The second measurement 142 can be performed at the operator's command using the human-machine interface 7 or automatically as soon as the aircraft 30 has climbed to a current altitude greater than or equal to a predetermined altitude, for example, 100 ft. The current altitude is determined, for example, using an altimeter 6 on the aircraft 30.

[0159] A comparison 145 of the first received power and the second received power is then performed by the computer 2. Following the takeoff of the aircraft 30, if the reflected electromagnetic signal 55 captured by the receiving antenna 20 results solely from a reflection of the primary electromagnetic signal 51 on the surface overflown 70, the second received power decreases with the aircraft 30's altitude gain and is therefore different from the first received power. Conversely, if the reflected electromagnetic signal 55 captured by the receiving antenna 20 after takeoff results at least partially from a reflection of the primary electromagnetic signal 51 on equipment 60, the second received power does not vary or varies very little and is substantially constant with the aircraft 30's altitude gain. This second received power is therefore substantially equal to the first received power.

[0160] Consequently, if a difference determined by the computer 2 between the first received power and the second received power is less than or equal to a predetermined value, a new connection 148 to the source 5 of an additional radiating element 11-19 is required and is made, similarly to the new connection 138 of the first variant, by the computer 2, via one of the connectors 41-49. The predetermined value is, for example, non-zero and allows for variations in the measurements of the first and second received power, due, for example, to vibrations of the aircraft 30 or the variability of these measurements. The predetermined value is, for example, equal to a second safety margin.

[0161] A new adjustment iteration 140 is then carried out and repeated if necessary until the difference between the first power received and the second power received is greater than the predetermined value.

[0162] According to a third variant of the invention, the adjustment 100 of an opening angle relative to the emission of the primary electromagnetic signal initially comprises the initial electrical connection 120 to the source 5 of a single radiating element 11-19 in the same way as the previous variants.

[0163] Next, at least one adjustment iteration 150 is performed after takeoff of the aircraft 30 and comprises several sub-steps. As with the previous variants, this adjustment iteration 150 verifies whether the maximum opening angle allows a reliable and correct measurement of the ground height Hs, and then, if not, modify and adapt it until a reliable and correct measurement of the ground height Hs is obtained.

[0164] Thus, during each iteration 150, a measurement adjustment 152 of a received power of the reflected electromagnetic signal 55 captured by the receiving antenna 20 is carried out via the sensor 26. This reflected electromagnetic signal 55 can result from a reflection, for example, on the surface overflown 70 or on a piece of equipment 60 of the primary electromagnetic signal 51 emitted by the transmitting antenna 10.

[0165] This adjustment measurement 152 can be performed at the operator's command using the human-machine interface 7 or automatically as soon as the aircraft 30 has climbed to a current height greater than or equal to a predetermined height. The current height is, for example, determined using an altimeter 6 on the aircraft 30.

[0166] A comparison 155 of this received power with a power threshold is then carried out by the computer 2. Following the takeoff of the aircraft 30, if the reflected electromagnetic signal 55 captured by the receiving antenna 20 actually results solely from a reflection of the primary electromagnetic signal 51 on the surface overflown 70, this received power decreases with the altitude gain of the aircraft 30 and is, or becomes, below the predetermined power threshold, at least from the predetermined height.

[0167] The power threshold may have been previously determined by calculations, tests or simulations and stored for example in memory 3. The power threshold is, for example, equal to a power of the reflected electromagnetic signal 55 captured by the receiving antenna 20 and resulting from a reflection of the primary electromagnetic signal 51 on the ground when the aircraft 30 is on the ground, preferably taking into account a third non-zero safety margin.

[0168] On the contrary, if the reflected electromagnetic signal 55 captured by the receiving antenna 20 after takeoff results at least partially from a reflection of the primary electromagnetic signal 51 on equipment 60, this received power does not vary or varies little after takeoff, and is substantially constant with the altitude gain of the aircraft 30. The received power is therefore substantially equal to a received power measured before takeoff.

[0169] Consequently, if the power received is greater than or equal to the power threshold, a new connection 158 to the source 5 of an additional radiating element 11-19 is required and made in a similar way to the new connections 138, 148 of the previous variants.

[0170] A new adjustment iteration 150 is then carried out and repeated if necessary until the power received is less than the power threshold.

[0171] According to a fourth variant of the invention, the adjustment 100 of an opening angle relative to the emission of the primary electromagnetic signal initially comprises the initial electrical connection 120 to the source 5 of a single radiating element 11-19 in the same way as in the previous variants.

[0172] Then, setting 100 includes a first determination 124 of a first ground height value Hs, performed before takeoff of the aircraft 30, using the reflected electromagnetic signal 55 received on the receiving antenna 20. This first determination 124 of the first ground height value Hs is carried out by applying the ground height determination step 300. This reflected electromagnetic signal 55 can result from a reflection on the ground or on equipment 60 of the primary electromagnetic signal 51 emitted by the transmitting antenna 10.

[0173] Next, setting 100 includes at least one setting iteration 160 performed after takeoff of aircraft 30 and comprising several sub-steps. As with the previous variants, this setting iteration 160 verifies whether the maximum opening angle allows for a reliable and correct measurement of ground height Hs, and if not, modifies and adjusts it until a reliable and correct measurement of ground height Hs is obtained.

[0174] During each iteration 160, a second determination 162 of a second ground height value Hs is performed, using the reflected electromagnetic signal 55 captured by the receiving antenna 20 by again applying the step 300 of determining a ground height Hs. This reflected electromagnetic signal 55 can again result from a reflection of the primary electromagnetic signal 51 on the surface overflown 70 or on a piece of equipment 60.

[0175] The second determination 162 can be performed at the operator's command using the human-machine interface 7 or automatically as soon as the aircraft 30 has climbed to a current height greater than or equal to a predetermined height. The current height is, for example, determined using an altimeter 6 on the aircraft 30.

[0176] A comparison 165 between the first and second values ​​of the ground height Hs is then performed by the computer 2. Following the takeoff of the aircraft 30, if the reflected electromagnetic signal 55 received by the receiving antenna 20 is indeed solely a reflection of the primary electromagnetic signal 51 on the surface overflown 70, the second value of the ground height Hs increases with the altitude gain of the aircraft 30 and is therefore different from the first value of the ground height Hs. Conversely, if the reflected electromagnetic signal 55 received by the receiving antenna 20 after takeoff results at least partially from a reflection of the primary electromagnetic signal 51 on equipment 60, the second value of the ground height Hs does not vary or varies very little and is substantially constant with the altitude gain. of aircraft 30. This second value of the ground height Hs is therefore approximately equal to the first value of the ground height Hs.

[0177] Consequently, if the difference between the second value and the first value is less than or equal to a predetermined deviation, a new connection 168 to the source 5 of an additional radiating element 11-19 is required and made in a manner similar to the new connections 138, 148, 158 of the previous variants. The predetermined deviation is, for example, non-zero and allows for variations in the determinations of the first and second values, due, for example, to vibrations of the aircraft 30. The predetermined deviation is, for example, equal to one-fourth of a safety margin.

[0178] A new adjustment iteration 160 is then carried out and repeated if necessary until the difference between the first and second value is greater than the predetermined gap.

[0179] Furthermore, the method may include a determination 180 of a maximum tilt angle of the aircraft 30 for which the determination 300 of the ground height Hs is considered correct and a display 185 of this maximum tilt angle on a display 9 of the aircraft 30. This maximum tilt angle is for example a function of a number of the radiating elements 11-19 electrically connected to the source 5.

[0180] Indeed, depending on the number of radiating elements 11-19 connected to the source 5, the beamwidth relative to the emission of the primary electromagnetic signal by the transmitting antenna 10 can be more or less reduced. Thus, for a first beamwidth ai and when the aircraft 30 has an inclination angle θ with respect to the vertical direction DV less than half of this first beamwidth ai as shown in [Fig. 7], the primary electromagnetic signal 51 can be emitted from the transmitting antenna 10 in the vertical direction DV to the surface overflown 70 by the aircraft 30, then the reflected electromagnetic signal 55 can also be directed in the vertical direction DV towards the receiving antenna 20. In this case, the determination 300 of the ground height Hs can be carried out reliably and correctly.

[0181] Conversely, for a second aperture angle a2 and with the same inclination angle [3] of the aircraft 30, which is then greater than half of this second aperture angle a2 as shown in [Fig. 8], neither the primary electromagnetic signal 51 emitted from the transmitting antenna 10 towards the surface overflown 70 by the aircraft 30, nor the reflected electromagnetic signal 55 can follow the vertical direction DV to the receiving antenna 20. In this case, the determination 300 of the ground height Hs cannot be reliably and correctly performed. The determination 300 of the ground height Hs provides, according to the example shown, an inflated value of the ground height Hs. In a mountainous environment, the determination of the ground height Hs may provide a lower value of the ground height Hs.

[0182] The maximum tilt angle is, for example, equal to half the opening angle relative to the emission of the primary electromagnetic signal, possibly less a safety margin for tilt. Displaying this maximum tilt angle on the display 9 indicates to the operator the maximum tilt angle up to which the ground height Hs is reliably and correctly determined. The maximum tilt angle can be displayed digitally on a dedicated screen or indicated on an artificial horizon instrument.

[0183] This maximum tilt angle is determined by the computer 2 based on the number of radiating elements 11-19 electrically connected to the source 5. A memory 3 of the computer 2 may include a lookup table, a law or a database, for example, allowing the computer 2 to associate different maximum tilt angles of the aircraft 30 with the different configurations of radiating elements 11-19 electrically connected to the source 5. The computer 2 can thus determine the maximum tilt angle associated with the current configuration of radiating elements electrically connected to the source 5 and transmit a signal carrying information relating to this maximum tilt angle to this dedicated screen or to the artificial horizon instrument.

[0184] Alternatively or in addition, an alert device connected to the computer 2 may issue a visual, audible, or haptic alert when a current bank angle of the aircraft 30 approaches, reaches, or even exceeds this maximum bank angle. For this purpose, the aircraft 30 may include a conventional measuring device for measuring this current bank angle of the aircraft 30.

[0185] Naturally, the present invention is subject to numerous variations in its implementation. Although several embodiments have been described, it is understood that it is not conceivable to exhaustively identify all possible embodiments. It is, of course, conceivable to replace a described means with an equivalent means without departing from the scope of the present invention and the claims.

Claims

1. Demands A method for measuring the ground height (Hs) of an aircraft (30) using a radio altimeter (1) comprising a transmitting antenna (10) equipped with a source (5) generating a primary electromagnetic signal (51, 52), a receiving antenna (20) equipped with a receiver (25) capable of receiving a reflected electromagnetic signal (55, 56) resulting from a reflection of said primary electromagnetic signal (51), and a computer (2), said radio altimeter (1) comprising an adjustable antenna selected from said transmitting antenna (10) and said receiving antenna (20), said adjustable antenna being equipped with at least two radiating elements (11-19) and a processing unit (80), two adjacent radiating elements (11-19) being separated by a non-zero gap (L), said processing unit (80) comprising said source (5) when said adjustable antenna is said antenna transmitting antenna (10) or said receiver (25) when said adjustable antenna is said receiving antenna (20),said process comprising: - an adjustment (100) of an opening angle of said adjustable antenna by electrically connecting said processing unit (80) one or more radiating elements (11-19) from among said radiating elements (11-19), and - after said adjustment (100), a determination (300) of a ground height (Hs) as a function of a minimum elapsed time between an emission (310) of said primary electromagnetic signal (51) and a reception (320) of said reflected electromagnetic signal (55), characterized in that said adjustment (100) of said opening angle comprises: - an initial electrical connection (120) to said processing unit (80) of a single radiating element (11-19) from among said radiating elements (11-19), then - at least one tuning iteration (130) comprising the following steps: • initial emission (131) by said transmitting antenna (10) of a calibrated primary electromagnetic signal (52) of known power towards at least a panel (65) of electromagnetic wave-absorbing material located on the ground at a predetermined distance from said transmitting antenna (10), • initial reception (132) of a calibrated reflected electromagnetic signal (56) by said receiving antenna (20), • initial measurement (134) of a received power of said calibrated reflected electromagnetic signal (56), • initial comparison (138) of said received power with an initial threshold, and • if said received power is greater than or equal to said initial threshold, new connection (138) to said processing unit (80) of an additional radiating element (11-19) from among said radiating elements (11-19), then - carrying out a new tuning iteration (130).

2. Method according to claim 1, wherein said initial threshold is equal to a percentage of said known power of said electromagnetic signal (52) emitted by said transmitting antenna (10).

3. A method for measuring the ground height (Hs) of an aircraft (30) by means of a radio altimeter (1) comprising a transmitting antenna (10) equipped with a source (5) generating a primary electromagnetic signal (51, 52), a receiving antenna (20) equipped with a receiver (25) capable of receiving a reflected electromagnetic signal (55, 56) resulting from a reflection of said primary electromagnetic signal (51), and a computer (2), said radio altimeter (1) comprising an adjustable antenna selected from said transmitting antenna (10) and said receiving antenna (20), said adjustable antenna being equipped with at least two radiating elements (11-19) and a processing unit (80), two adjacent radiating elements (11-19) being separated by a non-zero gap (L), said processing unit (80) comprising said source (5) when said adjustable antenna is said transmitting antenna (10) or said receiver (25) when said adjustable antenna is said receiving antenna (20),said process comprising: an adjustment (100) of an opening angle of said adjustable antenna by electrically connecting said processing unit (80) one or more radiating elements (11-19) from among said radiating elements (11-19), and after said adjustment (100), a determination (300) of a ground height (Hs) as a function of a minimum elapsed time between an emission (310) of said primary electromagnetic signal (51) and a reception (320) of said reflected electromagnetic signal (55), characterized in that said adjustment (100) of said opening angle comprises:

4. - an initial electrical connection (120) to said processing unit (80) of a single radiating element (11-19) from among said radiating elements (11-19), then - a first measurement (122) of a first power received from said reflected electromagnetic signal (55) on said receiving antenna (20) before takeoff of said aircraft (30), and - at least one tuning iteration (140) comprising the following steps: • second measurement (142) of a second power received from said reflected electromagnetic signal (55) on said receiving antenna (20) after takeoff of said aircraft (30), • comparison (145) of said first power received and said second power received, • if a difference between said first power received and said second power received is less than or equal to a predetermined value, a new connection (148) to said processing unit (80) of an additional radiating element (11-19) from among said radiating elements (11-19), then - implementation of a new adjustment iteration (140). Method according to claim 3, in which said second measurement (142) is performed on command using a human-machine interface (7) or

5. automatically as soon as said aircraft (30) has risen to a current height greater than or equal to a predetermined height, said current height being determined using an altimeter (6) of said aircraft (30). A method for measuring the ground height (Hs) of an aircraft (30) using a radio altimeter (1) comprising a transmitting antenna (10) equipped with a source (5) generating a primary electromagnetic signal (51, 52), a receiving antenna (20) equipped with a receiver (25) capable of receiving a reflected electromagnetic signal (55, 56) resulting from a reflection of said primary electromagnetic signal (51), and a computer (2), said radio altimeter (1) comprising an adjustable antenna selected from said transmitting antenna (10) and said receiving antenna (20), said adjustable antenna being equipped with at least two radiating elements (11-19) and a processing unit (80), two adjacent radiating elements (11-19) being separated by a non-zero gap (L), said processing unit (80) comprising said source (5) when said adjustable antenna is said antenna transmitting antenna (10) or said receiver (25) when said adjustable antenna is said receiving antenna (20),said process comprising: - an adjustment (100) of an opening angle of said adjustable antenna by electrically connecting said processing unit (80) one or more radiating elements (11-19) from among said radiating elements (11-19), and - after said adjustment (100), a determination (300) of a ground height (Hs) as a function of a minimum elapsed time between an emission (310) of said primary electromagnetic signal (51) and a reception (320) of said reflected electromagnetic signal (55), characterized in that said adjustment (100) of said opening angle comprises: - an initial electrical connection (120) to said processing unit (80) of a single radiating element (11-19) from among said radiating elements (11-19), and - at least one tuning iteration (150) comprising the following steps: • adjustment measurement (152) of a received power of said reflected electromagnetic signal (55) on said receiving antenna (20) after takeoff of said aircraft (30), • comparison (155) of said received power with a power threshold, • if said received power is greater than or equal to said power threshold, new connection (158) to said processing unit (80) of an additional radiating element (11-19) from among said radiating elements (11-19), then - carrying out a new adjustment iteration (150).

6. A method according to claim 5, wherein said adjustment measurement (151) of said received power of said reflected electromagnetic signal (55) on said receiving antenna (20) after takeoff of said aircraft (30) is carried out on command using a human-machine interface (7) or automatically as soon as said aircraft (30) has risen to a current height greater than or equal to a predetermined height, said current height being determined using an altimeter (6) of said aircraft (30).

7. A method for measuring the ground height (Hs) of an aircraft (30) by means of a radio altimeter (1) comprising a transmitting antenna (10) equipped with a source (5) generating a primary electromagnetic signal (51, 52), a receiving antenna (20) equipped with a receiver (25) capable of receiving a reflected electromagnetic signal (55, 56) resulting from a reflection of said primary electromagnetic signal (51), and a computer (2), said radio altimeter (1) comprising an adjustable antenna selected from said transmitting antenna (10) and said receiving antenna (20), said adjustable antenna being equipped with at least two radiating elements (11-19) and a processing unit (80), two adjacent radiating elements (11-19) being separated by a non-zero gap (L), said processing unit (80) comprising said source (5) when said adjustable antenna is said transmitting antenna (10) or said receiver (25) when said adjustable antenna is said receiving antenna (20),said process comprising:

8. - an adjustment (100) of an opening angle of said adjustable antenna by electrically connecting said processing unit (80) one or more radiating elements (11-19) from among said radiating elements (11-19), and - after said adjustment (100), a determination (300) of a ground height (Hs) as a function of a minimum elapsed time between an emission (310) of said primary electromagnetic signal (51) and a reception (320) of said reflected electromagnetic signal (55), characterized in that said adjustment (100) of said opening angle comprises: - an initial electrical connection (120) to said processing unit (80) of a single radiating element (11-19) from among said radiating elements (11-19), then - a first determination (124) of a first value of said ground height (Hs) before takeoff of said aircraft (30), and - at least one tuning iteration (160) comprising the following steps: • second determination (162) of a second value of said ground height (Hs) after takeoff of said aircraft (30), • comparison (165) of said first value and said second value of said ground height (Hs), • if a difference between said second value and said first value is less than or equal to a predetermined gap, new connection (168) to said processing unit (80) of an additional radiating element (11-19) from among said radiating elements (11-19), then - implementation of a new adjustment iteration (160). Method according to claim 7, in which said second determination (162) of said second value of said ground height (Hs) is carried out on command using a human-machine interface (7) or automatically as soon as said aircraft (30) has risen from a current height greater or equal to a predetermined height, said current height being determined using an altimeter (6) of said aircraft (30).

9. A method according to any one of claims 1 to 8, wherein said method comprises a determination (180) of a maximum tilt angle of said aircraft (30) for which said determination (300) of said ground height (Hs) is considered correct, said maximum tilt angle being a function of a number of said radiating elements (11-19) electrically connected to said processing unit (80), and a display (185) of said maximum tilt angle on a display (9) of said aircraft (30).

10. A method according to any one of claims 1 to 9, wherein said adjustment (100) of said opening angle comprises a control (110) of at least one connector (41-49) among connectors (41-49) electrically linking said processing unit (80) respectively to said radiating elements (11-19) using a human-machine interface (7).

11. A method according to any one of claims 1 to 10, wherein said radiating elements (11-19) are arranged in a single row (31).

12. A method according to any one of claims 1 to 10, wherein said radiating elements (11-19) are arranged respectively in at least two rows (32-34).

13. A method according to any one of claims 1 to 12, wherein a length (D) of said gap separating two adjacent radiating elements (11-19) is proportional to a wavelength of said primary electromagnetic signal (51) emitted by said source (5).

14. Radio altimeter (1) for aircraft (1), said radio altimeter (1) comprising a transmitting antenna (10) having a source (5) generating a primary electromagnetic signal (51,52), a receiving antenna (20) having a receiver (25) capable of receiving a reflected electromagnetic signal (55,56) resulting from a reflection of said primary electromagnetic signal (51), and a computer (2), said computer (2) determining said ground height (Hs) of said aircraft (30) from data (18) provided by said transmitting antenna (10) and said receiving antenna (20),

15. characterized in that said radio altimeter (1) comprises an adjustable antenna among said transmitting antenna (10) and said receiving antenna (20), said adjustable antenna being provided with at least two radiating elements (11-19), a processing member (80) and a plurality of connectors (41-45) for connecting said radiating elements (11-19) electrically to said processing member (80), two adjacent radiating elements (11-19) being separated by a non-zero gap (D), said processing member (80) comprising said source (5) when said adjustable antenna is said transmitting antenna (10) or said receiver (25) when said adjustable antenna is said receiving antenna (20), said radio altimeter (1) being configured for implementation of the method according to any one of claims 1 to 13. Aircraft (1) equipped with a radio altimeter (1) according to claim 14.