EP2747202A1 - Radome wall - Google Patents

Abstract

The wall (70) has core layer (72) that is made of dielectric material, and composed of layers (74,76) made of dielectric material. The dielectric constant of dielectric material of core layer is greater than dielectric constant of dielectric material of layers (74,76). Another two layers (78,80) are located towards layer (76) for impedance transformation of dielectric materials whose dielectric constants are selected such that the dielectric constant is progressively decreased starting from core layer towards inside (I) of antenna.

Description

The invention relates to a wall of a radome according to the features of patent claim 1.

From the prior art, various constructions are known, which are suitable to serve as a cover for microwave antennas. A radome (antenna dome) must have a wall, which on the one hand allows the transmission of electromagnetic energy, on the other hand, the wall of the radome must be designed such that the required structural integrity is present and a microwave antenna system is protected.

A radome is essentially an electromagnetic window that can be made in any desired shape. Radomes are commonly used in ground-based systems as well as on board aircraft, unmanned aerial vehicles or other radar or microwave-powered aircraft.

Out US 5,408,244 Radomes are known whose wall has a classic monolithic structure or a construction in A-, B-, C- or D-sandwich construction. The differences between the individual superstructures will be briefly discussed below.

The wall of a radome in a classical construction has a single layer structure in the form of a monolithic structure. This wall is characterized by high stability and high weight. The single layer usually has a homogeneous dielectric constant, which means that the layer and thus the wall of the radome has sufficient transmissive properties only in a certain frequency range. This structure is not suitable for the transmission of a broadband antenna signal.

For the particular case of nose radomes on fighter aircraft, almost exclusively monolithic structures are chosen in the prior art. These are characterized by a sufficiently good transmission behavior in the main band of the primary radar system. In the future, however, more and more sensor functions will be integrated into such a central antenna frontend, which is accompanied by a significant expansion of the frequency band. However, monolithic radomes can not conceptually have consistent transmissivity over the typical 5GHz to 18GHz frequency range, especially when required for all possible angles of incidence and both fundamental polarizations (TE - transverse electric, TM - transverse magnetic).

Superstructures in multilayer construction prove to be more advantageous in the transmission of broadband antenna signals. With these structures, it is possible to achieve electromagnetic transparency of signals having a wide frequency range. Walls in the multilayer structure are characterized essentially by the fact that layers with a high dielectric constant and a low dielectric constant are used. Here, a distinction is made between different arrangements:

A sandwich ( Fig. 1 a) A wall 10 of a radome in A sandwich construction is characterized in that two layers 14,16 of a high dielectric constant dielectric material are separated by a core layer 12 of a low dielectric constant dielectric material. An A sandwich is transparent to electromagnetic energy over a given frequency range. A disadvantage, however, is that with increasing oblique incidence of electromagnetic waves, the electromagnetic transparency decreases sharply. A sandwich structures reduce weight by the use of foams or honeycomb structures made of phenolic paper in the middle layer at the expense of, for example, the bird strike resistance.

B sandwich ( Fig. 1 b) A wall 20 of a radome in B-sandwich construction is characterized in that two layers 24, 26 of a dielectric material with a low dielectric constant are separated by a core layer 22 of a dielectric material with a high dielectric constant. This layer sequence is advantageous in the electromagnetic sense because, starting from the impedance of the free space (377 ohms) through the layers 24, 26, a step-shaped transition to the wave impedance within the core layer 22 takes place. The disadvantage, however, is the fact that the mechanical stability decreases significantly with decreasing size of the dielectric constant. In this sense, the layers 24, 26 are not suitable for carrying large mechanical loads, or significantly more sensitive in terms of bird strike resistance.

C sandwich ( Fig. 1 c) A wall 30 of a C sandwich radome is characterized in that two layers 34, 36 of a low dielectric constant dielectric material are separated by a core layer 32 of a high dielectric constant dielectric material. Each of these two outer layers 34, 36 of a low-dielectric-constant dielectric material has a further layer 38, 40 of a high-dielectric-constant dielectric material applied thereto. A C-sandwich wall has a higher complexity but offers more degrees of freedom in the electromagnetic design than the A or B sandwich structures. However, a disadvantage is a higher mass, but at the same time means a high structural strength.

D sandwich ( Fig. 1d A wall of a C-sandwich radome is characterized in that two layers 54, 56 of a high dielectric constant dielectric material are separated by a core layer 52 of a low dielectric constant dielectric material. Each of these two outer layers 54, 56 of a dielectric material with a high dielectric constant is a further layer 58, 60 of a applied dielectric material with a low dielectric constant. With this arrangement, high electromagnetic transmission is ensured over a wide range of the angle of incidence of the electromagnetic wave on the radome.

The construction of different walls, especially in A- and B-sandwich construction is also from "Ka-band Radome Design"; PHASE REPORT AIRTASK NO. A3533E12021 / RO08-01-01 Work Unit no. 48; Naval Air Development Center; May 20, 1969 known.

Another construction of a wall of a radome in which several layers are used is out EP 0 843 379 A2 known. This structure is characterized in that it is transparent to electromagnetic waves from two widely spaced frequency ranges, in particular 9.3 GHz and 94 GHz. The structure of the wall comprises foam materials whose thickness is selected according to the wavelength. By varying the thickness over the length of the wall, a homogeneous transmission is achieved as a function of the angle of incidence. A disadvantage, however, is the low stability.

For all described walls (A to D sandwich), it can not always be guaranteed that consistent electromagnetic transparency in terms of the two polarizations TE and TM can be guaranteed. Often, transparency increases with increasing angles of incidence θ within the TE polarization, than within the TM polarization.

The object of the invention is to provide a wall of a radome, which ensures a homogeneous and high transmissivity for electromagnetic radiation of both polarizations over a large frequency and incident angle range and at the same time has a high mechanical stability.

This object is achieved by the wall according to the features of the current claim 1. Advantageous embodiments are the subject of dependent claims.

The invention is based on a wall of a type B sandwich antenna dome, namely a wall of an antenna dome having an inside and an outside, the wall comprising a core layer of dielectric material separating two layers of dielectric material, the dielectric constant of the dielectric material of the core layer is larger than the dielectric constant of the dielectric material of the two layers. The invention is characterized in that two further layers for impedance transformation of dielectric material are arranged on the layer facing the inside of the wall. Their dielectric constants are selected such that, layer by layer, a drop in the dielectric constant proceeding from the core layer and progressing towards the inside results.

In a preferred embodiment of the invention, the dielectric constant of the dielectric material of the core layer is between 4.5 and 6.0, wherein the dielectric constant of the dielectric material of the two layers separated by the core layer is between 2.8 and 3.5. Suitably, the dielectric constant of the dielectric material of these two layers is different.

The multilayer structure according to the invention is characterized in that on its outside are three massive layers, which in their sum resemble a quasi-monolithic structure, which relates to the mechanical strength and resilience. In this sense, with the layer structure according to the invention, it is not necessary to impose restrictions with regard to the radome parameters accepted in the past. These three massive layers essentially serve to carry mechanical loads.

In a further preferred embodiment of the invention, the core layer comprises a synthetic resin with E or S2 glass fibers. E-glass fibers are known in the art. For the plastic reinforcement E-glass fibers have gained great importance. E stands for electro-glass, since it was originally mainly in the electrical industry was used. For the production of E-glass, pure quartz glass melts are made with additions of limestone, kaolin and boric acid. In addition to SiO2 (silicon dioxide), they contain different amounts of different metal oxides. The composition determines the properties of the products. S2 glass fibers are characterized by increased rigidity.

In a further preferred embodiment of the invention, the two layers separated by the core layer comprise a synthetic resin with quartz glass fibers, in one expedient embodiment the synthetic resin of the core layer and the synthetic resin of the two layers separated by the core layer being identical.

In a further preferred embodiment of the invention, the dielectric constants of the dielectric materials of the two further layers for impedance transformation are smaller than the dielectric constants of the dielectric materials in the layers separated by the core layer. Expediently, the dielectric constants of these two impedance-transformation layers are selected such that the dielectric constant of the transformation layer closer to the outside of the wall lies between 1.4 and 1.6, and the dielectric constant of the transformation layer closer to the inside of the wall is between 1.05 and 1.05 1,2 is located.

The two last-described dielectric layers in no way bear mechanical loads. They serve exclusively for the impedance matching of incident electromagnetic waves at different angles of incidence. Conveniently, such layers are made from high frequency foam materials which are influenced in their dielectric constant, e.g. by adding fillers. Especially the use of syntactic foams is an advantage here.

In a further preferred embodiment, the impedance transformation layers comprise the use of high-frequency open-cell, closed-cell, or syntactic foam materials Addition of fillers trimmed to a required size of the dielectric constant.

The layer structure of the wall according to the invention for an antenna dome, as already described above, is formally similar to that of a B sandwich. However, the dielectric contrast between the three loaded resin / fiber layers involved in carrying loads is not very high, so that the entire structure with the core layer and the two adjacent layers consists of a single resin grade and two different types of glass fiber (eg quartz glass and E-glass) can be realized. The use of only one resin system simplifies mechanical compatibility with respect to thermal expansion and other shear forces.

As already mentioned, the realization of the wall according to the invention with its layers takes place via different types of glass fibers together with a single suitable resin system. It is up to the expert to choose a suitable resin system. Due to this configuration, the B-sandwich-like construction of the wall can be done in one step e.g. by Harzinfiltrationsverfahren so that a coherent block is formed, which includes in its structure the necessary gradation of the dielectric constant.

It should also be pointed out that the thickness of all the layers together can be made constant over the entire surface of the radome. However, embodiments are also possible in which this thickness is selected differently, at least in sections. Such a change in the total thickness of the layers may be particularly advantageous depending on the longitudinal axis of the radome.

Fig. 1a

eine Wandung im A-Sandwichaufbau gemäß dem Stand der Technik,

Fig. 1b

eine Wandung im B-Sandwichaufbau gemäß dem Stand der Technik,

Fig. 1c

eine Wandung im C-Sandwichaufbau gemäß dem Stand der Technik,

Fig. 1d

eine Wandung im D-Sandwichaufbau gemäß dem Stand der Technik,

Fig. 2a

eine beispielhafte Darstellung der Transmissionsverluste bei einer monolithische Wandung für Transversal-Magnetisch-(TM-) Wellen nach dem Stand der Technik,

Fig. 2b

eine beispielhafte Darstellung der Transmissionsverluste bei einer monolithische Wandung für Transversal-Elektrisch-(TE-) Wellen nach dem Stand der Technik,

Fig. 3

eine Wandung in Mehrschichtaufbau gemäß der Erfindung,

Fig. 4a

eine beispielhafte Darstellung der Transmissionsverluste bei einer erfindungsgemäßen Wandung für Transversal-Magnetisch-(TM-) Wellen,

Fig. 4b

eine beispielhafte Darstellung der Transmissionsverluste bei einer erfindungsgemäßen Wandung für Transversal-Elektrisch-(TE-) Wellen.

The invention and further advantageous embodiments will be explained in more detail with reference to figures. Show it:

Fig. 1a

a wall in the A-sandwich construction according to the prior art,

Fig. 1b

a wall in the B-sandwich construction according to the prior art,

Fig. 1c

a wall in C sandwich construction according to the prior art,

Fig. 1d

a wall in the D-sandwich construction according to the prior art,

Fig. 2a

an exemplary representation of the transmission losses in a monolithic wall for transverse magnetic (TM) waves according to the prior art,

Fig. 2b

an exemplary representation of the transmission losses in a monolithic wall for transversal electrical (TE) waves according to the prior art,

Fig. 3

a wall in multilayer construction according to the invention,

Fig. 4a

an exemplary representation of the transmission losses in a wall according to the invention for transverse magnetic (TM) waves,

Fig. 4b

an exemplary representation of the transmission losses in a wall according to the invention for transverse electric (TE) waves.

Fig. 2a shows an exemplary representation of the transmission losses in a monolithic wall for transverse magnetic (TM) waves according to the prior art. The illustration shows the simplified case of an infinite long wall of a radome at the incidence of plane waves of polarization TM. Fig. 2a shows a typical transmission behavior for a conventional X-band radome with a thickness of 8.5 mm and a dielectric constant er = 3.1 at an incidence of TM waves. Over a frequency range of 5 GHz to 18 GHz, the transmission loss for all angles of incidence between ⊝ = 0 ° and 70 ° is less than 2 dB. The representation in Fig. 2b shows the transmission behavior at an incidence of TE waves. Here it can be seen that with increasing angle of incidence ⊝ the transmission loss in the range below 11 GHz and above 13 GHz increase sharply. The dependence of the transmission behavior on the angle of incidence Eind can be clearly seen.

Figure 3 shows the wall 70 of a radome according to the invention. For easier understanding, the dielectric constants of the individual layers are numbered below.

The wall 70 of the radome has an outer side A and an inner side I. Starting from the outer side A in the direction of the inner side I, the three layers 74, 72, 76 counted from the left correspond to the construction of a B sandwich (FIG. Fig. 1 b) , A core layer 72 comprising a dielectric material of a first dielectric constant is surrounded by two layers 74, 76 with a dielectric material of a second and a third dielectric constant, respectively. The dielectric material of the core layer 72 has, for example, a dielectric constant of ε = 4.8. The dielectric material of the layer A facing the outside A has, for example, a second dielectric constant er = 3.1. The dielectric material of the inner layer I facing layer 76 has, for example, a second dielectric constant e _r = 3.1. However, it is quite possible that the second and third dielectric constants are not identical, it being ensured that, starting from the core layer 72, the dielectric material of the layer 76 directly adjacent to the inner side I, having a dielectric constant which is smaller than the core layer 72 the dielectric constant of the dielectric material of the core layer 72.

The fourth and fifth layers 78, 80 of a dielectric material counted from the outside A are each an impedance transformation layer. These two layers 78, 80 of a dielectric material are only for impedance matching of incident electromagnetic waves at different angles of incidence. These layers 78, 80 of a dielectric material do not have adequate stability to support mechanical loads. These layers 78, 80 consist of HF-compatible foam materials which are open or closed-cell or syntactic. By admixture of fillers familiar to a person skilled in the art, the dielectric constant can be trimmed to the required size, ie the required value. Suitably, the dielectric material of the fourth layer 78 has a dielectric constant e _r = 1.5 and the dielectric material of the fifth layer 80 has a dielectric constant e _r = 1.1. But it is also possible that in a preferred embodiment, the dielectric material of the fourth layer 78 and the fifth Layer 80 is the same and thus the fourth layer 78 and fifth layer 80 can be considered as a single layer.

On the outside A of the wall 70 of the radome, a radome protective layer 82 is applied. This protective layer 82 serves to protect the outer glass fiber / epoxy layer of the multilayer structure of the wall 70 from external influences, e.g. Corrosion etc. It is also expedient to apply a plurality of protective layers 82. These protective layers 82 should expediently be thin, preferably in the μm range, so that there are no negative properties with regard to the transmission of incident electromagnetic waves. On the inner side facing I layer 80 of the multi-layer structure of the wall 70 of the radome is also a thin, preferably in the micron range, protective layer 84 applied.

The two impedance transformation layers 78, 80 are bonded together by means of an adhesive applied in a thin adhesive layer 86. This adhesive layer serves as a boundary layer between the two layers 78, 80 for impedance transformation. The adhesive layer 86 is present at an interface between the two layers for impedance transformation, with the adhesive layer 86 being deposited on opposite surfaces of the two layers 78, 80. This adhesive layer 86 is expediently designed in such a way that it has no or insignificant effects on the transmission behavior of the multilayer construction of the wall. The same applies analogously to the adhesive layer 88 which is present between the third layer 76 counted from the outside A and the first layer 78 for the impedance transformation.

The thickness of the individual layers 72, 74, 76, 78, 80 of the wall according to the invention is constant over the length of the radome. However, it is possible that the thickness of the individual layers 72, 74, 76, 78, 80 or of all layers 72, 74, 76, 78, 80 varies in regions of large angles of incidence of the electromagnetic wave.

The Fig. 4a and 4b show correspond to the Fig. 2a and Fig. 2b Fig. 2a a representation of the transmission losses in a wall according to the invention in the multi-layer structure of a radome for transverse magnetic (TM) waves ( Fig. 4a ) and transversal electric (TE) waves ( Fig. 4b ).

On Fig. 4a It becomes clear that for the entire frequency range from 5 GHz to 18 GHz and for the incident angle range ⊝ = 0 ° to 70 °, the transmission losses for transverse magnetic (TM) waves are less than 2 dB. Likewise with transversal electric (TE) waves the transmission losses transmit less than 2dB in the entire frequency range from 5GHz to 18 GHZ as well as in the incident angle range ⊝ = 0 ° to 70 °.

Claims (14)

A wall (10, 20, 30, 50, 70) of an antenna dome having an inside (I) and an outside (A) comprising a core layer (72) of dielectric material separating two layers (74, 76) of dielectric material, wherein the dielectric constant of the dielectric material of the core layer (72) is greater than the dielectric constant of the dielectric material of the two layers (74, 76), characterized in that on the inside (I) facing layer (76) two further layers (78, 80) are arranged for impedance transformation of dielectric materials whose dielectric constants are selected such that, starting from the core layer (72) in the direction of the inner side (I) progressively, a decrease of the dielectric constant results layer by layer. A wall according to claim 1, characterized in that the dielectric constant of the dielectric material of the core layer (72) is between 4.5 and 6.0. Wall according to one of the preceding claims, characterized in that the dielectric constant of the dielectric materials of the two layers (74, 76) separated by the core layer (72) is between 2.8 and 3.5. A wall according to claim 3, characterized in that the dielectric constants of the dielectric materials of the two layers (74, 76) separated by the core layer (72) are different. Wall according to any one of the preceding claims, characterized in that the dielectric constants of the dielectric materials of the two further layers (78, 80) for impedance transformation are smaller than each of the dielectric constants of the dielectric materials of the two layers (74, 76 separated by the core layer (72) ). Wall according to one of the preceding claims, characterized in that the dielectric constant of the dielectric material of the inside (I) of the wall (70) closer further layer (80) for impedance transformation between 1.05 and 1.2. Wall according to one of the preceding claims, characterized in that the dielectric constant of the dielectric material of the outer layer (A) of the wall (70) closer further layer (78) for impedance transformation is between 1.4 and 1.6. Wall according to one of the preceding claims, characterized in that the core layer (72) consists of a synthetic resin with E or S2 glass fibers. Wall according to one of the preceding claims, characterized in that the two layers (74, 76) separated by the core layer (72) comprise a synthetic resin with quartz glass fibers. A wall according to claim 8 and 9, characterized in that the synthetic resin of the core layers (72) and the two layers (74, 76) separated by the core layer (72) are the same. Wall according to one of the preceding claims, characterized in that the further layers (78, 80) for impedance transformation HF-suitable open cell, closed cell or syntactic foam materials and these are trimmed by addition of fillers to a required size of the dielectric constant. Wall according to one of the preceding claims, characterized in that on the outside (A) at least one radome protective layer (82) and / or on the inside (I) a thin protective layer (84) is deposited over the exposed surface of the impedance transformation layer (80). Wall according to one of the preceding claims, characterized in that at an interface (86) between the two layers (78, 80) for impedance transformation and / or at an interface (88) between a layer (78) for impedance transformation and one of the Core layer (72) separate layers (76), an adhesive layer is present. Wall according to one of the preceding claims, characterized in that deviating only one instead of two layers (78, 80) for impedance transformation in the form of a foam material is present.

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