Airplane radome assembly and radar
By incorporating a window and isolation partition inside the aircraft radome to transmit millimeter waves, the problem of existing aircraft radars being unable to acquire high-resolution runway images in fog has been solved, enabling high-quality image acquisition under adverse weather conditions while meeting aerodynamic and weight requirements.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- THALES SA
- Filing Date
- 2025-12-24
- Publication Date
- 2026-06-26
AI Technical Summary
Existing aircraft radars cannot acquire high-resolution runway images in fog, and millimeter-wave radars cannot penetrate conventional radomes, affecting the aerodynamic performance and weight of aircraft. In addition, the sharing of transmit and receive antenna areas leads to image distortion.
Design an aircraft radome and radar assembly, including a millimeter-wave band radar within the radome, employing a window and isolation baffle that transmit millimeter waves, ensuring that the transmitted and received lobes pass through the window and reducing reflections, with the isolation baffle maintaining contact with the window and radar, and using a window made of specific materials and with a specific radius of curvature to optimize Brewster angle and reflectivity.
Achieving high-quality runway imagery or video in fog, meeting aircraft material, aerodynamic, and weight constraints, improving pilot approach and landing visibility, and supporting EFVS approach and landing procedures.
Smart Images
Figure CN122276131A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an aircraft radome and radar assembly, and more particularly to an aircraft radome and radar assembly operating in the millimeter-wave band, which is capable of runway imaging in fog. Background Technology
[0002] Currently, due to low visibility, pilots find it difficult to manually perform aircraft approaches and landings in fog. Without visibility, landings must be forced through the use of the Instrument Landing System (ILS) autopilot. In fact, current equipment installed on aircraft to improve pilot visibility during approaches or landings operates in the infrared band, which is incapable of acquiring runway images in fog or lowering decision altitudes in foggy conditions. Weather radars installed in radomes operate in the X-band (8-12 GHz), which does not provide sufficient resolution for pilots during approaches or landings.
[0003] Radar emitting millimeter-wave signals can acquire images or videos in fog. However, in order to obtain usable images, millimeter-wave radar must have good radio frequency (RF) performance and must not degrade the characteristics of the aircraft. For example, its impact on the aerodynamic performance of the aircraft must be negligible, and its impact on the weight of the aircraft must be low.
[0004] Furthermore, in order to obtain an image of sufficient quality for the pilot to clearly see the runway, the radar must be pointed at the runway with a sufficiently directional beam, avoiding the dispersion of transmitted energy in directions unnecessary for image generation. Therefore, this imposes limitations on the radar's angle of view relative to the approach slope in order to correctly align it with the runway.
[0005] The radar's field of view and its associated effective cone must not intersect with the aircraft's metal structure to avoid interfering with the radar's transmitted and received signals. Therefore, this restriction means that the radar must be installed at the front of the aircraft, i.e., inside the aircraft's radome.
[0006] However, millimeter waves cannot penetrate conventional radomes (which are typically made of quartz-epoxy honeycomb structures). Therefore, it is impossible to install radars that transmit millimeter wave frequencies inside existing commercial aircraft radomes.
[0007] Finally, some existing radars share transmit and receive antenna areas. This can create parasitic reflections between these transmit and receive antenna areas, thus distorting the acquired image.
[0008] Therefore, there is a need to develop a solution that can generate real-time images or videos of the approach scene, including the runway, in fog, with sufficient quality to improve the pilot’s visibility during approach or landing, while meeting the limitations of existing commercial aircraft in terms of material strength standards, aerodynamics, and weight. Summary of the Invention
[0009] To overcome the above-mentioned shortcomings, the present invention proposes an aircraft radome and radar assembly, which includes:
[0010] - A radar dome mounted on the nose of the aircraft;
[0011] - A radar housed within a radome, configured to operate in the millimeter-wave band, and comprising a transmitting antenna and a receiving antenna, the transmitting antenna being configured to transmit transverse magnetic (TM) polarized waves;
[0012] The radome includes a window integrated into the radome, which is made of a millimeter-wave-transmitting material and is located in front of the radar.
[0013] The radar is configured such that the angle between the maximum gain direction (MGD) of the transmitting antenna and the normal to the window is within [θ]. B -θ1;θ B Within the angular range of +θ2], where θ B The Brewster angles at the air / window interface, θ1 and θ2, are determined to be below a predetermined threshold for reflectivity at the air / window interface; and
[0014] - An isolation partition is installed between the transmitting and receiving antennas, which maintains minimal contact with the window and radar.
[0015] In one embodiment, the radar is a frequency-modulated continuous wave radar.
[0016] In one embodiment, the radar transmits in a frequency band between 95 GHz and 100 GHz.
[0017] In one embodiment, the window is sized such that both transmitted waves within the transmission angle range and received waves within the radar reception angle range can pass through the window.
[0018] In one embodiment, the window material includes cross-linked polystyrene plastic, polyetherimide resin, or polytetrafluoroethylene.
[0019] In one embodiment, the radius of curvature of the window is greater than 1.2 meters.
[0020] In one embodiment, the dielectric constant of the window material makes the relevant Brewster angle value between 50° and 65°.
[0021] In one embodiment, the dielectric constant of the window material makes the value of the relevant Brewster angle compatible with positioning the radar within the radome and / or with the tilt of the radome.
[0022] In one embodiment, the isolation partition has a metal core covered with a microwave absorbing material.
[0023] In one embodiment, the window is integrated into the radome via connecting material.
[0024] The following describes several embodiments of the aircraft radome and radar assembly of the present invention: these examples do not limit the scope of the invention. These embodiments illustrate both the essential features of the invention and additional features relevant to the embodiments considered. Attached Figure Description
[0025] The invention will be better understood after reading the following description, given as a non-limiting example and with the aid of the accompanying drawings, and other advantages will also become apparent, wherein:
[0026] Figure 1 A schematic diagram of the aircraft radome and radar assembly according to the present invention is shown from the side.
[0027] Figure 2a A top view of the aircraft illustrating the horizontal radiation pattern at the receiving antenna level is shown;
[0028] Figure 2b A side view illustrating the vertical radiation pattern at the receiving antenna level and the vertical radiation pattern at the transmitting antenna level is shown.
[0029] Figure 3 This shows the window is Rexolite TM The change of reflectance of cross-linked polystyrene with incident angle;
[0030] Figure 4 A simplified model of the optical path of a ray from a unit antenna and propagating through a window, based on an example, is shown in the view as an azimuth cross-section; and
[0031] Figure 5 The optical path difference of the wave emitted by the transmitting antenna is shown. Detailed Implementation
[0032] This invention relates to an assembly comprising an aircraft radome and a radar. Figure 1 An aircraft radome and radar assembly EAR according to the present invention are shown.
[0033] The aircraft radome and radar assembly (EAR) includes the radome (Rd) mounted on the nose (NA) of the aircraft. For example, the aircraft could be an airplane or a drone.
[0034] Furthermore, the aircraft radome and radar assembly EAR includes radar Ra. Radar Ra is housed within the radome Rd. Radar Ra is configured to operate in the millimeter-wave band. Advantageously, unlike weather radars commonly used to capture images of weather conditions or to take pictures in clouds or rain, the millimeter-wave band allows for image or video capture in fog while using a small radar. In fact, these weather radars, when capturing images in fog, would require a radar approximately ten times the size of a millimeter-wave radar for the same resolution, making them unsuitable for aircraft. Radar Ra includes a transmitting antenna Tx and a receiving antenna Rx configured to transmit TM-polarized waves. Thus, the millimeter waves emitted by the transmitting antenna Tx propagate toward the runway, which is within radar coverage when the aircraft (e.g., an airplane) is about to land. The waves are then backscattered by the runway, even under adverse weather conditions such as fog. The reflected waves are subsequently captured by the receiving antenna Rx and converted into images or video by radar Ra. Furthermore, millimeter-wave radars can be compact, which is particularly advantageous in situations where space and weight are limited on aircraft.
[0035] The wave transmitted by the transmitting antenna Tx and received by the receiving antenna Rx forms a beam lobe. Figure 2a and Figure 2b The aircraft is shown in top and side views so that... Figure 2b The above describes the vertical radiation pattern of the LRE at the receive antenna level and the vertical radiation pattern of the LTE at the transmit antenna level, as well as... Figure 2a The above describes the horizontal radiation pattern of the LRA at the receiving antenna level.
[0036] Furthermore, the radome Rd includes a window F integrated into it. The window F is made of a millimeter-wave-transmitting material. The window F is located in front of the radar Ra. For example, radomes for commercial aircraft are typically made of a quartz-epoxy honeycomb structure. Millimeter waves of radar Ra cannot penetrate these materials. Therefore, the radome must include a portion that transmits millimeter waves in order to be able to transmit and receive the returning waves. Advantageously, the window F thus allows the use of millimeter-wave band radar located within the radome.
[0037] like Figure 2b As shown, the radar Ra and window F are configured to allow the transmit and receive lobes to pass through window F, thereby enabling the radar to image the runway.
[0038] Furthermore, the radar Ra is set such that the angle θi between the maximum gain direction MGD of the transmitting antenna Tx and the normal N of the window F is within [θ]. B -θ1°;θ B Within the angular range of +θ2], where θ BThe Brewster angle is defined for the air / window interface, and θ1 and θ2 are determined such that the reflectivity obtained at the air / window interface is below a predetermined threshold. The predetermined threshold is, for example, between -25 dB and -10 dB, preferably equal to -15 dB or -20 dB. As described above, the transmitting antenna Tx is configured to transmit TM-polarized waves. The reflection coefficient of TE polarization increases strictly with the incident angle. TM polarization exhibits minimum reflection at Brewster incident, which corresponds to complete wave propagation through window F. In this invention, it is necessary to minimize the reflection coefficient because it corresponds to the loss during transmission (waves reflected into the radome) and the loss during reception (ambient echoes reflected from the radome surface). Furthermore, the energy reflected during transmission often causes antenna mismatch and reduces transmission performance (power, pointing accuracy). Advantageously, when the radar Ra is set such that the angle θi between the maximum gain direction of the transmitting antenna Tx and the normal N of window F is equal to the Brewster angle θi. B At this time, the energy reflected at the air / window interface during launch can be minimized. Around this angle θ B A certain tolerance is acceptable, i.e., -θ1 / +θ2.
[0039] Furthermore, the aircraft radome and radar assembly EAR include an isolation partition CI disposed between the transmitting antenna Tx and the receiving antenna Rx. The isolation partition CI is configured to prevent rays emitted by the transmitting antenna Tx and reflected on the window from being detected by the receiving antenna Rx. Therefore, the partition CI forms a lateral barrier to the transmitted waves. The partition CI is in near-contact with the window F and the radar Ra to prevent the aforementioned reflections. "Near-near-contact" refers to contact with minimal mechanical clearance. In one embodiment, the mechanical clearance is ensured by a deformable absorber (e.g., foam) between the partition and the aircraft radome and / or between the partition and the radar. Thus, the isolation partition CI creates an isolation boundary between the transmitting antenna Tx and the receiving antenna Rx. Therefore, this boundary between the Rx and Tx antennas can preserve the transmitted beam of the transmitting antenna Tx. Advantageously, the isolation partition CI limits parasitic waves by reducing reflections between the transmitting antenna Tx and the receiving antenna Rx, thereby improving the quality of runway images or videos obtained by the radar Ra.
[0040] Therefore, advantageously, this invention helps pilots land in adverse weather conditions, such as fog. The invention allows for the acquisition of images of sufficient quality to improve pilot visibility during approach or landing, while meeting current limitations in materials, aerodynamics, and weight for commercial aircraft. Thus, even in fog, pilots can, for example, perform approach and landing procedures such as “EFVS approach” or “EFVS landing” (EFVS stands for Enhanced Flight Vision System).
[0041] In one embodiment, the isolation bulkhead CI is fixed to the radar Ra, and a baffle is provided in the window F, within which the isolation bulkhead CI is disposed, thereby allowing a mechanical clearance between the isolation bulkhead CI and the window F. In an alternative embodiment, a baffle is provided in the window F, within which the isolation bulkhead CI is disposed, and another baffle is provided on the radar between the transmitting antenna Tx and the receiving antenna Rx, within which the isolation bulkhead CI is also disposed. Advantageously, the baffle can thus resist the mechanical constraints that the radar Ra experiences in harsh flight environments.
[0042] In one embodiment, radar Ra is a frequency-modulated continuous wave radar. Advantageously, frequency-modulated continuous wave radar allows for continuous imaging of the runway during approach or landing.
[0043] In one embodiment, radar Ra is transmitted in the 95 GHz to 100 GHz frequency band. Advantageously, this frequency band allows for image capture through fog, thus enabling the acquisition of runway images, which in turn aids the pilot in landing.
[0044] In one embodiment, the window F is sized such that both the transmitted wave, contained within the transmission angle range, and the received wave, contained within the radar reception angle range, can pass through the window. Advantageously, the window size allows for maximum radar coverage so that the transmitted wave is not blocked by the radome.
[0045] In one embodiment, the dielectric constant of the material of window F makes the associated Brewster angle (air / window interface) compatible with the positioning of the radar within the radome and / or with the tilt of the radome. Specifically, radar Ra must be positioned behind window F to target the runway. Therefore, the positioning angle of radar Ra is limited by the shape of the radome Rd (which is typically defined by the aircraft manufacturer) and also by the angle required for targeting the runway. Thus, given these limitations, it can be quite difficult to ensure that rays emitted from the transmitting antenna Tx (MGD direction) are incident on the window at a Brewster angle. The value of the Brewster angle can be adjusted by changing the dielectric constant of the material of window F. Therefore, the material of window F can be selected whose dielectric constant allows for the desired Brewster angle value.
[0046] Therefore, in one embodiment, the window material includes cross-linked polystyrene plastic, such as Rexolite. TM Type, or polyetherimide resin, such as UItem TM Type, or polytetrafluoroethylene. The dielectric constant of these materials results in Brewster angle values between 50° and 65°. In particular, UItem TM The dielectric constant allows for a Brewster angle of 63°, while polytetrafluoroethylene (PTFE) allows for a Brewster angle of 54°. Rexolite TM A Brewster angle of 58° is allowed. Figure 3 This shows the window is Rexolite TM When cross-linked polystyrene is used, the reflectance of TE and TM polarization varies with the incident angle. Figure 3 Rexolite is clearly shown in the image. TM A Brewster angle of 58° is permissible. However, as mentioned above, a certain range of incident angle values around the Brewster angle is also acceptable for minimizing loss and parasitic reflections, for example, a range of [38°; 73°]. Preferably, an attenuation of at least -15 dB, or even -20 dB, is sought for the reflected wave. Figure 3 As shown, for Rexolite TM With an attenuation of -20 dB, the incident angle value θi is preferably in the range of 46° to 65°.
[0047] Rexolite TM This is particularly advantageous because it allows the thickness of the window (typically about 6 to 7 millimeters) to be reduced to attenuate the signal in an acceptable manner, while maintaining the required rigidity under the harsh environmental conditions of the aircraft.
[0048] In one embodiment, the radius of curvature of window F is greater than 1.2 meters.
[0049] To bring the radar as close to the radome as possible, the window needs to have an acceptable radius of curvature. In practice, a planar shape would complicate its connection with the rest of the radome in the azimuth angle.
[0050] Simulations were performed to evaluate the acceptable radius of curvature for window F. Rexolite was used in the simulations. TM Window. To limit the window size, the antenna beamwidth is considered to be limited by the angle corresponding to a 3dB attenuation relative to the maximum transmission direction. This applies to both the transmit antenna Tx and the receive antenna Rx, and to both azimuth and elevation angles. The angular width of the LTE cone is +10° upwards and -14° downwards around the MGD direction. The angular width of the LTA azimuth transmit cone is 15° to the left and right.
[0051] like Figure 4 As shown, the curvature of the window is modeled as three parts in the azimuth angle, and three rays OM1, OM2, and OM3 are emitted by unit transmitting antennas Tx1, Tx2, and Tx3 respectively, with each ray passing through one part of the window.
[0052] Therefore, the modeled window portion has parallel inner and outer surfaces. Thus (since the dielectric is considered homogeneous), the entry and exit directions of the millimeter waves are parallel. However, as... Figure 4As shown, the locally applied geometry and refraction laws (following the Snell-Descartes law) result in nonlinear propagation from the emitting horn to free space. Therefore, the window introduces an optical path difference compared to free space propagation.
[0053] Figure 5 The optical path difference (expressed as a multiple of the radar transmission wavelength λ) is shown. It is the optical path difference between the central horn and the array's end horns, exceeding the theoretical optical path difference associated with each viewing angle, and expressed as a multiple of λ. Figure 5 The contour lines of the optical path difference, expressed as a fraction of λ, are shown. This additional optical path difference is caused by the shape of the window F and is a function of the emission angle of the millimeter wave through the window F and the angle of inclination of the side segments defining the window F. Depending on the emission angle and the inclination of the side segments, the acceptable region is the area where the additional optical path difference is less than a fixed fraction of the wavelength. It is estimated that for an optical path difference of at most 0.1λ, the resulting image will still be usable. Using this 0.1λ value, the angle reserved with respect to the radome edge can be determined, which, combined with the total antenna width, the dimensions of each section, the angles between sections, and manufacturer constraints, allows for the determination of the minimum acceptable radius of curvature of the window F. As an indication, the minimum acceptable radius of curvature of the window F is 1.2 meters.
[0054] In one embodiment, the isolation septum has a metal core covered with a radar-absorbing material. Advantageously, this allows the isolation septum CI to prevent rays emitted by the transmitting antenna Tx and reflected on the radome Rd from being detected by the receiving antenna Rx. Therefore, by avoiding these reflections, this design improves the quality of images or video acquired using radar, thereby enabling pilots to observe the runway more accurately. In one embodiment, the radar-absorbing material is a dielectric-loaded elastomer, such as silicone. These materials are capable of absorbing millimeter-wave waves.
[0055] In one embodiment, the window F is integrated into the radome Rd via a connecting material. Advantageously, this connecting material can limit mechanical limitations arising from the difference in materials used for the window and the rest of the radome. In one embodiment, the connecting material is a glass fiber composite material.
[0056] Although the invention has been illustrated and described in detail by way of a preferred embodiment, the invention is not limited to the disclosed examples. Other alternatives can be derived by those skilled in the art without departing from the scope of the claimed invention.
Claims
1. An aircraft radome and radar assembly (EAR), comprising: - Radar dome (Rd) mounted on the nose (NA) of the aircraft; - A radar (Ra) disposed within a radome (Rd), the radar (Ra) being configured to operate in the millimeter-wave band and including a transmitting antenna (Tx) and a receiving antenna (Rx), the transmitting antenna (Tx) being configured to transmit TM polarized waves; The radome (Rd) includes a window (F) integrated into the radome, the window (F) being made of a material that transmits millimeter waves, and the window (F) being located in front of the radar (Ra); The radar (Ra) is configured such that the angle (θi) between the maximum gain direction (MGD) of the transmitting antenna (Tx) and the normal (N) of the window (F) is within [θi]. B -θ1;θ B Within the angular range of +θ2], where θ B It is the Brewster angle of the air / window interface, and θ1 and θ2 are determined as the reflectivity obtained at the air / window interface being lower than a predetermined threshold. as well as - An isolation partition (CI) is disposed between the transmitting antenna (Tx) and the receiving antenna (Rx), the isolation partition (CI) maintaining substantially contact with the window (F) and the radar (Ra).
2. The aircraft radome and radar assembly according to claim 1, wherein, The radar is a frequency-modulated continuous wave radar.
3. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The radar transmits in a frequency band between 95 GHz and 100 GHz.
4. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The window's dimensions are designed to allow both transmitted waves within the emission angle range and received waves within the radar reception angle range to pass through it.
5. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The window is made of cross-linked polystyrene plastic.
6. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The window is made of polyetherimide resin.
7. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The window is made of polytetrafluoroethylene.
8. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The radius of curvature of the window is greater than 1.2 meters.
9. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The dielectric constant of the window material makes the relevant Brewster angle value between 50° and 65°.
10. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The dielectric constant of the window material makes the value of the relevant Brewster angle compatible with positioning the radar within the radome and / or with the tilt of the radome.
11. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The isolation partition has a metal core, which is covered with a wave-absorbing material.
12. The aircraft radome and radar assembly according to claim 1 or 2, wherein, The window is integrated into the radar dome via connecting materials.