Radome wall for communication applications

Abstract

The invention relates to a radome wall for communication, in particular data transmission, in the frequency band from 17 to 31 GHz, in particular for use on commercial aircraft, and also to a radome with a corresponding radome wall. The radome wall is composed of a multilayer structure having an alternating arrangement of force-absorbing solid cover layers and sheer- rigid core layers. In an illustrative embodiment, the radome wall comprises at least four cover layers, of which two form the outer sides of the radome wall, with the cover layers and the core layers being made of dielectric materials.

Description

Radome Wall for Communication Applications The invention relates to a radome wall for communication, in particular data transmission, in the frequency band of from 17 to 31 GHz, in particular for use on commercial aircraft, as well as to a radome having a corresponding radome wall. In order to protect antennas for the emission and / or reception of electromagnetic radiation against external mechanical or chemical influences, for example wind and rain, protective shells referred to as "radomes" for antennas are known. Be- sides the structural strength required for protection of the antennas, for radomes it is essential that they have a suita- ble transmission behavior, i.e. they are to a sufficient ex- tent transparent for electromagnetic radiation in the fre- quency range relevant for the antenna(s) to be protected - for communication applications such as data transmission for exam- ple from 17 to 31 GHz. Particularly for applications in which the shaping of a radome cannot be arbitrarily freely selected, it is furthermore nec- essary for the wall of the radome also to have a good trans- mission behavior in a sufficiently large range of the angle of incidence, starting from orthogonal incidents of the radiation on the wall. One example of such an application is the protec- tion of antennas for satellite communication on commercial aircraft, in the case of which for aerodynamic reasons the ra- domes must be adapted to the shaping of the skin of the air- craft, although because of this electromagnetic radiation gen- erally does not orthogonally strike, and pass through, the ra- domes. In the prior art, as is summarized for example in EP 2 747 202 Al, radomes consisting of three- or five-sheet sandwich structures comprising GFRC sheets and foam sheets are known, which on the one hand have a sufficient transmission behavior and on the other hand offer sufficient structural strength with low weight. To this end sheet arrangements suit- able for the desired frequency ranges may be calculated, par- ticularly with a view to the thickness of the individual sheets, although the dielectric constants of the individual sheet materials must also be taken into account. A disadvantage with the prior art is, however, that the qual- ity of the transmission behavior in the case of an angle of incidence deviating from an orthogonal incidence of the elec- tromagnetic radiation on the radome wall depends strongly on compliance with the previously calculated thicknesses of the individual sheets. Consequently, the manufacturing tolerances in relation to the thicknesses of the individual sheets are very small, which leads to elaborate and expensive production. The object of the present invention is to provide a radome wall with which the disadvantages of the prior art no longer occur, or at least still occur only to a reduced extent. Accordingly, the invention relates to a radome wall for commu- nication, in particular data transmission, in the frequency band of from 17 to 31 GHz for use on commercial aircraft, com- prising a multilayer structure having an alternating arrange- ment of force-absorbing solid cover layers and sheer-rigid core layers, wherein the radome wall comprises at least four cover layers, of which two form the outer sides of the radome wall, the cover layers and the core layers being made of die- lectric materials. • The invention furthermore relates to a radome for use on com- mercial aircraft, the wall of which is configured according to the invention. The radome wall according to the invention is distinguished in that it is formed in sandwich fashion with <com:Math><semantics>n≥4<annotation encoding="application / x-tex">n \geq 4< / annotation>< / semantics>< / com:Math> cover layers and - since the outer sides of the wall are respectively in- tended to be formed by a cover layer <com:Math><semantics>−n−1<annotation encoding="application / x-tex">-n-1< / annotation>< / semantics>< / com:Math> core layers. The cover layers are also force-absorbing solid layers, which are supported and kept at a distance by merely geometrically sta- ble core layers. In this case, the core layers absorb only a small part of the forces acting on the component in comparison with the cover layers, but under load exhibit only a scarcely noticeable and negligible deformation under operating load (often much less than 1%). In general, the density of the cover layer is greater than the density of the core layers. Corresponding sandwich designs are widely known in the prior art and are widespread - not only in relation to radomes. In particular, it is known that a high stiffness with at the same time a low weight can be achieved with the aid of a sandwich design. For use of the sandwich design for radomes, it is furthermore necessary that the radome wall formed in this way has a good transmission behavior. In particular the least possible atten- uation, or a high electromagnetic penetrability should be achieved in the frequency range relevant to the antenna pro- tected by the radome over an angle of incidence range which is as large as possible. While such can in principle also be achieved with three- or five-sheet sandwich structures accord- ing to the prior art, this however requires high-precision manufacturing. Particularly in relation to the thickness of the individual layers, in the prior art it is necessary to comply with very small manufacturing tolerances in order to . . reliably avoid degradation of the transmission properties. The invention is based on the discovery that, in the case of a multilayer structure of the radome wall with at least four cover layers - i.e. an at least seven-sheet sandwich structure - leads to a significantly more tolerant design in relation to minor variations in thickness, without relevant degradation of the relevant transmission properties occurring. Despite the large number of layers, and the associated greater production outlay, the production costs of a radome wall according to the invention can nevertheless be reduced in comparison with a three- or five-sheet design from the prior art, since the man- ufacturing tolerances can be selected to be much more generous compared with the prior art. At the same time, a high overall strength of the radome wall can be achieved, which may corre- spond at least to that of a three- or five-sheet design. Weight savings compared with the prior art are generally also possible. By suitable selection of the thicknesses of the individual cover and core layers - while taking into account the respec- tive dielectric constants - optimal thicknesses for the indi- vidual layers for the desired frequency range, with which good electromagnetic transmission properties can be achieved in the desired frequency range, can be determined by simple parameter studies known per se to the person skilled in the art. In this case, the good transmission properties over a large angle range of from 0° up to about 65°, respectively in terms of the surface normal of the outer side of the radome wall at the po- sition where the electromagnetic radiation is incident. This is advantageous in particular for radomes of antennas for sat- ellite communication on board commercial aircraft, which gen- erally operate in the frequency range of from 17 to 31 GHz. It is thus possible to configure the radome aerodynamically fa- vorably as part of the outer skin of the aircraft, without in- curring a significant bandwidth loss. Thus, fuselage- and em- pennage-mounted antennas for broadband satellite data trans- mission can be produced. It is preferred for the radome wall to be area-symmetrical with respect to the midplane of the radome wall. The symmet- rical structure ensures that there are the same good transmis- sion properties both for transmission and for reception of signals by the antenna protected by the radome wall. It is furthermore preferred for the two core layers closest to the outer sides of the radome wall to be thicker than the core layer(s) closest to the midplane of the radome wall. By a cor- responding configuration of the layers, the good transmittance is in particular ensured over a wide angle of incidence range (for example from <com:Math><semantics>0∘<annotation encoding="application / x-tex">0^{\circ}< / annotation>< / semantics>< / com:Math> to <com:Math><semantics>65∘<annotation encoding="application / x-tex">65^{\circ}< / annotation>< / semantics>< / com:Math>). The tolerance for the thickness of the cover layers for a rated thickness of up to 1 mm may be ±30%, preferably ±20%, and for a rated thickness of more than 1 mm may be <com:Math><semantics>±0.3<annotation encoding="application / x-tex">\pm 0.3< / annotation>< / semantics>< / com:Math> mm, more preferably ±0.2 mm. The tolerance for the core layers is preferably ±0.4 mm, more preferably ±0.3 mm, more preferably ±0.2 mm. Corresponding tolerances can be achieved during the production of a radome wall according to the invention without elaborate and expensive manufacturing methods being required therefor. In one preferred embodiment, four cover layers and three core layers are provided, the material thicknesses of which are, in order, preferably 0.42 mm (cover layer), 2.00 mm (core layer), 0.21 mm (cover layer), 1.00 mm (core layer), 0.21 mm (cover layer), 2.00 mm (core layer), 0.42 mm (cover layer). These ma- terial thicknesses may of course be provided with the toler- ances mentioned above. In an alternative preferred embodiment five cover layers and four core layers are provided, the material thicknesses of which are, in order, preferably 0.63 mm (cover layer), 2.50 mm (core layer), 0.84 mm (cover layer), 2.00 mm (core layer), 1.06 mm (cover layer), 2.00 mm (core layer), 0.84 mm (cover layer), 2.50 mm (core layer), 0.63 mm (cover layer). In this case as well, the aforementioned tolerances may be provided. Both preferred embodiments exhibit very good transmission properties for an angle of incidence range of from 0° to 65°, it being possible to establish the frequency range for the good transmission properties substantially by means of the di- electric constants of the material used for the cover layer and the core layer. Determination of the required dielectric constants for achieving the desired frequency range is readily possible for the person skilled in the art. It is in this case preferred for the dielectric constant of the cover layers to be greater than the dielectric constant of the core layers. For a frequency range of from 17 GHz to 31°Ghz, the dielectric constant of the cover layers is preferably between 2.8 and 4.0, more preferably between 3.0 and 3.6. The dielectric con- stant of the core layers is preferably between 1.0 and 1.4, more preferably between 1.0 and 1.2. The cover layers are preferably respectively formed by one or more sheets of prepreg material, preferably quartz glass fi- ber / epoxy resin prepreg. This may in particular be a quartz fiber fabric preimpregnated with resin, the resin preferably being thermosetting, more preferably an epoxy resin. The use of polyester resin is likewise possible. The thickness of an individual prepreg is in this case preferably 0.21 mm. With a corresponding prepreg, the thicknesses of the individual cover layers of the preferred embodiments can be readily achieved. The core layers are preferably respectively formed by foam ma- terial, preferably from a polyimide hard foam. In this way, a particularly low density of the radome wall is possible. By suitable selection of the foam material, the required geomet- rical stability and the dielectric permeability can be en- sured. Preferably, a homogeneous surface may be produced with the foam material, which allows large-area connection to the cover layer lying above. The radome according to the invention is distinguished from the radomes known in the prior art merely by the configuration of the radome wall. For explanation of the radome according to the invention, reference is therefore made to the comments above. The invention will now be described by way of example with the aid of advantageous embodiments with reference to the appended drawings, in which: Figure 1: shows a schematic section through a first exem- plary embodiment of a radome wall according to the invention; and Figure 2: shows a schematic section through a second exem- plary embodiment of a radome wall according to the invention. Figure 1 represents a first exemplary embodiment of a radome wall 1 according to the invention for communication, in par- ticular data transmission, in the frequency band of from 17 to 31 GHz for use on commercial aircraft in a sectional view. The radome wall 1 comprises four cover layers 11, 12, 12', 11' and three core layers 21, 22, 21'. The cover layers 11 and 11' in this case respectively form an outer side of the radome wall 1, while the core layers 21, 22, 21' are respectively ar- ranged between two cover layers 11, 12, 12', 11'. The cover layers 11, 12, 12', 11' are formed from quartz glass fiber / epoxy resin prepreg, the thickness of an individual pre- preg sheet being 0.21 mm and the thicknesses of the cover lay- ers 11, 12, 12', 11' in each case exclusively being a multiple thereof. The core layers 21, 22, 21' are formed from foam material, namely from a polyimide hard foam. The radome wall 1 is constructed area-symmetrically with re- spect to the midplane 2, the two core layers 21, 21' closest to the outer sides of the radome wall 1 being thicker than the core layer 22 lying in the midplane 2 of the radome wall 1. The thicknesses of the individual cover 11, 12, 12', 11' and core layers 21, 22, 21', as well as their respective dielec- tric constants, may be found in the table below: • [Image disponible dans le document PDF, Image available in the PDF document] • For the aforementioned thicknesses of the cover layers 11, 12, 12', 11', a tolerance of ±20% is provided. For the thicknesses of the core layers 21, 22, 21', the tolerance is <com:Math><semantics>±0.2<annotation encoding="application / x-tex">\pm 0.2< / annotation>< / semantics>< / com:Math> mm. . Despite the relatively large tolerances, the radome wall 1 represented has very good transmission properties for a fre- quency range of from 17 to 31 GHz at an arbitrary angle of in- cidence <com:Math><semantics>α<annotation encoding="application / x-tex">\alpha< / annotation>< / semantics>< / com:Math> of between 0° to 65°. Figure 2 shows a schematic sectional representation of a sec- ond exemplary embodiment of a radome wall 1 according to the . invention, which is likewise configured for communication, or data transmission, in the frequency band of from 17 to 31 GHz for use on commercial aircraft. The radome wall 1 comprises five cover layers 11, 12, 13, 12', 11' and in order four core layers 21, 22, 22', 21'. The cover layers 11 and 11' in this case again respectively form an outer side of the radome wall 1. The arrangement of the other layers 12, 13, 12', 21, 22, 22', 21' may be found in Figure 2. The cover 11, 12, 13, 12', 11' and core layers 21, 22, 22', 21' are constructed in a similar way to the exemplary embodi- ment according to Figure 1. The radome wall 1 according to Figure 2 is also constructed area-symmetrically with respect to the midplane Z, the two core layers 21, 21' closest to the outer sides of the radome wall 1 being thicker than the core layers 22, 22' next to the midplane 2 of the radome wall 1. The thicknesses of the individual cover 11, 12, 13, 12', 11' and core layers 21, 22, 22', 21', as well as the respective dielectric constants, may be found in the table below: [Image disponible dans le document PDF, Image available in the PDF document] [Image disponible dans le document PDF, Image available in the PDF document] For the aforementioned thicknesses of the cover layers 11, 12, 12', 11', a tolerance of ±20% is provided. For the thicknesses of the core layers 21, 22, 22', 21' and for the thickness of the cover layer 13, the tolerance is <com:Math><semantics>±0.2<annotation encoding="application / x-tex">\pm 0.2< / annotation>< / semantics>< / com:Math> mm. The radome wall 1 represented in Figure 2 also has very good transmission properties for a frequency range of from 17 to 31 GHz at an arbitrary angle of incidence <com:Math><semantics>α<annotation encoding="application / x-tex">\alpha< / annotation>< / semantics>< / com:Math> of between 0° to 65°. . .

Claims

1. A radome wall for communication in the frequency band of from 17 to 31 GHz for use on commercial aircraft, comprising a multilayer structure having an alternating arrangement of four force-absorbing solid cover layers and three sheer-rigid core layers, wherein two of the cover layers form outer sides of the radome wall, the material thickness of the alternating arrangement of cover layers and core layers being, respectively, 0.42 mm, 2.00 mm, 0.21 mm, 1.00 mm, 0.21 mm, 2.00 mm, 0.42 mm, whereby two of the three core layers closest to the outer sides of the radome wall are thicker than a remaining of the three core layers closest to a midplane of the radome wall, wherein the four cover layers and the three core layers are made of dielectric materials, wherein the dielectric constant of the cover layers lies between 3.0 and 3.6 and the dielectric constant of the core layers lies between 1.0 and2. The radome wall according to claim 1, wherein the radome wall is area-symmetrical with respect to the midplane of the radome wall.

3. The radome wall according to either one of claims 1 and 2, wherein the cover layers are respectively formed by one or more sheets of prepreg material.

4. The radome wall according to claim 3, wherein the prepreg material is quartz glass fiber / epoxy resin prepreg.

5. The radome wall according to either one of claims 3 3 and 4 4 , wherein the thickness of the prepreg is 0.21 mm.

6. The radome wall according to any one of claims 1 to 5, wherein the core layers are respectively formed by foam material.

7. The radome wall according to claim 6, wherein the foam material is a polyimide hard foam.

8. A radome for use on commercial aircraft, wherein a wall of the radome is configured as per any one of claims 1 to 7.

9. A radome wall for communication in the frequency band of from 17 to 31 GHz for use on commercial aircraft, comprising a multilayer structure having an alternating arrangement of five force-absorbing solid cover layers and four sheer-rigid core layers, wherein two of the cover layers form outer sides of the radome wall, the material thickness of the alternating arrangement of cover layers and core layers being, respectively, 0.63 mm, 2.50 mm, 0.84 mm, 2.00 mm, 1.06 mm, 2.00 mm, 0.84 mm, 2.50 mm, 0.63 mm, whereby two of the four core layers closest to the outer sides of the radome wall are thicker than remaining core layers of the four core layers closest to a midplane of the radome wall, wherein the five cover layers and the four core layers are made of dielectric materials, wherein the dielectric constant of the cover layers lies between 2.8 and 4.0 and the dielectric constant of the core layers lies between 1.0 and 1.2 and the tolerance for the thickness of the cover layers for a nominal thickness up to 1 mm is ±20% and for a nominal thickness above 1 mm is ± 0.2 \pm 0.2 mm and the tolerance for the thickness of the core layers is ± 0.2 \pm 0.2 mm.

10. The radome wall according to claim 9, wherein the radome wall is area-symmetrical with respect to the midplane of the radome wall.

11. The radome wall according to either one of claims 9 and 10, wherein the cover layers are respectively formed by one or more sheets of prepreg material.

12. The radome wall according to claim 11, wherein the prepreg material is quartz glass fiber / epoxy resin prepreg.

13. The radome wall according to either one of claims 11 and 12, wherein the thickness of the prepreg is 0.21 mm.

14. The radome wall according to any one of claims 9 to 13, wherein the core layers are respectively formed by foam material.

15. The radome wall according to claim 14, wherein the foam material is a polyimide hard foam.

16. A radome for use on commercial aircraft, wherein a wall of the radome is configured as per any one of claims 9 to 15.