Method and system for vertical stabilizer mismatch loss reduction

Abstract

An antenna arrangement, or a method of making the antenna arrangement, comprises: a flat panel phased array antenna 150 located in a cavity of a vertical stabilizer 100 of an aircraft, where an impeda

Description

FIELD OF THE INVENTION

[0001] The present invention relates generally to the reduction of mismatch losses in antenna systems, particularly to antennas internal to an aircraft vertical stabilizer. BACKGROUND OF THE INVENTION

[0002] Prior to setting forth a detailed description of the invention, the following term definitions are provided:

[0003] The terms ‘antenna’, ‘antennas’ and ‘antennae’ refer generally to at least one antenna that is capable of operating in a receiving “RX” mode and / or in a transmitting “TX” mode.

[0004] The terms “aircraft” and “craft” refer generally to piloted vehicles, either unmanned and controlled remotely or manually piloted by a person or persons. Examples of such craft may include, but are not limited to: aero planes, planes, jet planes, helicopters, hovercraft, unmanned aerial vehicles (UAVs), drones, space craft, or any other craft where an internal antenna is preferable.

[0005] The term “vertical stabilizer” refers generally to structures located in the tail section of aero planes intended to reduce aerodynamic side slip and provide direction stability. Vertical stabilizers may have a honeycomb core material sandwiched between two sheets of glass fibre reinforced plastic (also referred to as fiberglass or GFRP).

[0006] In aviation there is a need for antennae onboard aircraft for a multitude of reasons, for example two-way communication with ground-based air-traffic control systems and communication with navigation satellites. Providing these antennae internal to the aircraft avoids the introduction of radome structures non-conformal with that of the aircraft body resulting in increased drag and lessened aero-dynamic performance of the craft. Despite this however, the signal acquisition / transmission of an antenna inside the aircraft may be reduced due to material losses arising from propagation by the signal through the aircraft structure and / or impedance mismatch losses.

[0007] US Patent Application Publication No. US 2007 / 0001909 discloses a method for guiding waves over objects, a method for improving a performance of an antenna, and a method for improving a performance of a radar. The methods disclosed teach how an impedance structure can be used to guide waves over objects. SUMMARY OF THE PRESENT INVENTION

[0008] The present invention provides an antenna arrangement comprising: a flat panel phased array antenna configured to simultaneously steer a plurality of beams, each beam capable of being directed up to an angle of 70° perpendicular to the plane of the antenna, the antenna located within a cavity formed by a vertical stabilizer of an aircraft; and an impedance matching structure coupling the antenna to an inner side of the vertical stabilizer, wherein the impedance matching structure reduces mismatch losses of the beams, caused by the vertical stabilizer, by up to at least 2dB and up to the angle of 70°.

[0009] The present invention further provides a method for inserting an antenna arrangement within a cavity formed by a vertical stabilizer of an aircraft, the method comprising the steps of: determining a cross-section of substantially uniform thickness of the vertical stabilizer, the cross-section having a cross-sectional area at least equal to that of the antenna arrangement to be inserted; orientating the antenna arrangement substantially parallel to the determined cross section; and coupling the antenna arrangement having said orientation to an inner surface of the vertical stabilizer via an impedance matching structure, the inner surface inclusive of the determined cross-section, wherein the antenna arrangement comprises a flat panel phased array antenna configured to simultaneously steer a plurality of beams, each beam capable of being directed up to an angle of 70° perpendicular to the plane of the antenna, and wherein upon execution the method reduces mismatch losses of the beams, caused by insertion into the cavity of the vertical stabilizer, by up to at least 2dB and up to the angle of 70°.

[0010] These and other advantages of the present invention are set forth in detail in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a better understanding of the invention and in order to show how it may be implemented, references are made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections. In the accompanying drawings:

[0012] Figure 1A is a block diagram showing the structure of a vertical stabilizer known in the art;

[0013] Figure IB is a high-level diagram showing an antenna array located in a cavity formed by a vertical stabilizer of an aircraft;

[0014] Figures 2A- 2D are a series of plots comparing experimental and simulated data;

[0015] Figure 3A is a block diagram according to an embodiment of the invention;

[0016] Figures 3B-3K are plots of mismatch reductions due to embodiments of the invention;

[0017] Figure 4A is a block diagram according to another embodiment of the invention;

[0018] Figures 4B and 4C are plots of mismatch reductions due to an embodiment of the invention;

[0019] Figures 5A and 5B are equivalent circuit diagrams illustrating the matching in accordance with some embodiments of the invention; and

[0020] Figure 6 is a flowchart outlining a method of inserting an antenna array into a vertical stabilizer of an aircraft, according to some embodiments of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] With specific reference now to the drawings in detail, it is stressed that the particulars shown are for the purpose of example and solely for discussing the preferred embodiments of the present invention, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The description taken with the drawings makes apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

[0022] Before explaining the embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following descriptions or illustrated in the drawings. The invention is applicable to other embodiments and may be practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

[0023] Figure lisa block diagram of a (rotated) cross section of an exemplary prior art vertical stabilizer 100 having an outer layer of paint 110 disposed on an outer GFRP layer 120. Paint layer 110 may be transparent to radio waves. A honeycomb core material 130 may be sandwiched between the outer painted GFRP layer and another, unpainted GFRP layer 120.

[0024] The present invention provides an antenna arrangement wherein an antenna such as a flat panel phased array multi steerable beams antenna may be inserted into such a vertical stabilizer of an aircraft. Figure IB shows a vertical stabilizer 100 with a flat panel phased array multi steerable beams antenna 150 located within a cavity 102 formed by vertical stabilizer 100. An impedance matching structure 160 may be used to couple antenna 150 to an inner surface 104 of the vertical stabilizer 100 (i.e. vertical stabilizer inner surface 104 is an outer surface of cavity 102). A coupling location on inner surface 104 may be chosen that has a substantially uniform thickness through to an outer side of vertical stabilizer 100. Antenna 150 and impedance matching structure 160 may be orientated substantially parallel to such a chosen coupling location on inner surface 104, as shown in the inset portion of figure 2. A substantially parallel orientation to such a chosen coupling location may ensure that a rate of change of impedance between antenna 150 and vertical stabilizer 100 is substantially uniform for any steerable beam 152 received / transmitted by / from any part of antenna 150. A directionality of steerable beams 152 in figure IB or in subsequent figures is not intended to be limiting as to whether steerable beams 152 are entering cavity 102 or exiting cavity 102, i.e. a directionality of beams 152 does not limit a TX or RX operating mode of antenna 150.

[0025] Insertion losses are to be expected for such internal placement of an antenna into a vertical stabilizer, for example due to the aircraft materials used and mismatch (discontinuity) of impedances between vertical stabilizer 100 and antenna 150. Such losses may be characterised as material losses and mismatch losses, respectively. Material losses are due to power dissipation within the material due to the loss tangent (DF). Material losses are intrinsic to the materials used and cannot be resolved. A mismatch loss is the ratio of incident power to the difference between incident and reflected power. Unlike material losses, mismatch losses may be mitigated, for example by using an impedance matching structure 160.

[0026] Figures 2A and 2B are plots of signal frequency against insertion loss comparing vertical stabilizer measurements 224 and optimized EM model simulation 222 (HFSS, or high frequency structure simulation) for different angles. The measurements were performed on the real A330 Airbus vertical stabilizer in Toulouse and the scan performance angles in the IT-plane (the plane containing the magnetic field vector and direction of maximum radiation) considered in order to validate the model were 0 = 0 degrees (i.e. broadside) and 0 = 30 degrees elevation (polar). Figures 2C and 2D show that the larger part of the insertion loss is due to mismatch losses by showing magnitude considering lossy materials 226 and magnitude considering lossless materials 228.

[0027] Figure 3 A shows a cross section of an antenna arrangement 300. Antenna arrangement 300 may be located within a cavity formed by a vertical stabilizer 100 of an aircraft. Vertical stabilizer 100 may be separated from an antenna 350 by a distance 340 (Distance D) It can be shown that the optimal distance D which optimises mismatch losses varies between different types of antenna. In the case of an RX narrow band SDA antenna (structure defined antenna) where the objective is to keep mismatch losses under 2dB for up to 60 degrees scan, the optimal distance is D = 1.5mm. For a TX narrow band SDA antenna at 14.14 GHz where the same objective is to keep mismatch losses under 2dB for up to 60 degree scan the optimal distance is D = 2.5mm. Figures 3B-3E show these mismatch loss data for different distances D and different operating modes of a narrow band SDA antenna, in which: line 312 shows the theoretical model at 11GHz; line 314 shows the theoretical model at 11 5GHz; line 316 shows the theoretical model at 12GHz; line 322 shows the EM simulation at 11GHz; line 324 shows the EM simulation at 11.5GHz; line 324 shows the EM simulation at 11.5GHz; and line 326 shows the EM simulation for 12GHz. In Figure 3E: line 331 corresponds to the theoretical model in which D = 1,5mm; line 341 corresponds to the EM simulation in which D = 1,5mm; line 332 corresponds to the theoretical model in which D = 2mm; line 333 corresponds to the theoretical model in which D = 2.5mm; line 334 corresponds to the theoretical model in which D = 3mm; line 335 corresponds to the theoretical model in which D = 3.5mm; line 336 corresponds to the theoretical model in which D = 4mm; and line 337 corresponds to the theoretical model in which D = 4.5mm. Figure 3C highlights the achieved objective of the model in the oval region. It may be preferable to have an antenna arrangement where performance is independent of the distance 340 between stabilizer and antenna however, so as to be applicable for different types of antenna.

[0028] Figure 3 A also shows that at least one layer of matching material 360 may be placed adjacent to antenna 350. Such a layer of matching material may alter an impedance discontinuity between antenna 350 and vertical stabilizer 100 and may improve mismatch losses independently of the separation distance 340. This extra layer 360 may be formed of a composite material and may possess defined thickness and known spacings from pre-existing components. In some embodiments, two layers of matching material 360 may be used, placed on either side of the vertical stabilizer. In some embodiments the matching material used may be FR4.

[0029] Figures 3F M show mismatch loses when considering different antenna arrangements, for example with no insertion into a vertical stabilizer (i.e. no radome), with insertion into a vertical stabilizer (i.e. with the vertical stabilizer acting as a radome), and with matching. In Figure 3F: line 352 corresponds to simulation (HFSS) without radome; line 354 corresponds to simulation with radome; line 356 corresponds to measurement without radome; and line 358 corresponds to measurement with radome. In Figure 3G: line 362 corresponds to values without radome; line 364 corresponds to values with radome; line 364 corresponds to values with slightly tilted radome; and line 368 corresponds to values with radome and matching. In Figures 3H-3K: line 371 corresponds to D = 1cm; line 372 corresponds to D = 1.5cm; line 373 corresponds to D = 2cm; line 374 corresponds to D = 2.5cm; and line 375 corresponds to D = 3cm. Mismatch losses were observed to be reduced for RX operation at 11.1 GHz and TX operation at 14.14GHz for separation distance D ranging between l-3cm, at elevation angles that scan across from 0 to 70 degrees when using a matching material.

[0030] Figure 4A shows another embodiment of the invention. Vertical stabilizer 100 may have a frequency selective structure (FSS) 470 located on at least an inner side of the vertical stabilizer. FSS 470 may be made from metal and may be very thin. FSS 470 acts to alter the RF (radio frequency) properties of the vertical stabilizer, an embodiment which is far less dependent on the properties of the antenna itself than any previous embodiment. FSS 470 is a repetitive surface that acts as a metal-mesh microwave filter by virtue of a regular periodic metallic pattern imprinted upon it. When properly designed and placed onto the fibreglass layers of the vertical stabilizer, FSS 470 acts to reduce impedance mismatches and signal reflections by greatly reducing the resonant behaviour of the vertical stabilizer 100 over different frequencies and scanning angles. Thus, the insertion loss may be reduced to under 2dB for a tuned frequency and scanning angles between 0 and 70 degrees.

[0031] In some embodiments FSS 470 may be placed on an outer side of vertical stabilizer 100. Such an externally located FSS 470 may be conformal with the exterior curvature of the aircraft. Paint layer 110 of the vertical stabilizer may reapplied over the top of FSS 470. In some embodiments two layers of FSS 470 may be used, with one disposed on an outer surface of vertical stabilizer 100 and the other disposed on an inner surface of vertical stabilizer 100.

[0032] Figure 4B and 4C show insertion losses before and after use of an FSS, in which: line 412 corresponds to EM simulation at 10.75GHz; line 414 corresponds to EM simulation at 11GHz; line 416 corresponds to EM simulation at 11.5GHz; and line 418 corresponds to EM simulation at 12GHz. The total insertion losses at 11GHz are less than 2 dB up to 70 degrees.

[0033] Figures 5A and 5B are equivalent circuit diagrams illustrating the matching in accordance with some embodiments of the invention. Figure 5A is an equivalent circuit diagram illustrating an implementation of the mismatch reduction using matching layers. Figure 5B is an equivalent circuit diagram illustrating an implementation of the mismatch reduction using the FSS. Both equivalent circuit diagrams illustrate how a concrete mismatch reduction arrangement can be designed, given a specified antenna and a specified vertical stabilizer. The circuit diagram can be used in simulation tools to select the dimensions and the materials for designing the mismatch reduction arrangement.

[0034] Figure 6 is a flow chart outlining a method of inserting an antenna arrangement within a cavity formed by a vertical stabilizer of an aircraft. In step 610 a cross-section of substantially uniform thickness of the vertical stabilizer may be determined. The cross-section may have a cross-sectional area at least equal to that of the antenna arrangement to be inserted. In step 620 the antenna arrangement may be orientated substantially parallel to the determined cross section. In step 630 the orientated antenna arrangement may be coupled to an inner surface of the vertical stabilizer via an impedance matching structure. The inner surface involved may be inclusive of the determined cross-section.

[0035] The antenna arrangement may include a flat panel phased array antenna configured to simultaneously steer a plurality of beams, where each beam may be capable of being directed up to an angle of 70° perpendicular to the plane of the antenna, as described above.

[0036] At least one layer of matching material may be used as the impedance matching structure (step 640). The layer of matching material may be located between the antenna and the inner surface of the vertical stabilizer. The layer of matching material may alter a discontinuity between the antenna and inner surface of the vertical stabilizer. The matching material may be a composite material and more than one layer may be used. The matching material may possess defined thickness and known spacings from pre-existing components. The matching material used may be FR4. Different matching materials may be used across different layers.

[0037] In an alternative embodiment to locating the impedance matching structure (step 640), at least one layer of frequency selective structure “FSS” may be located on at least an inner surface of the vertical stabilizer (step 650). The FSS may reduce a resonant behaviour of the vertical stabilizer. The FSS may have an imprinted periodic metallic pattern and the FSS may be a thin layer. A layer of FSS may be located on an outer surface of the vertical stabilizer and may be conformal with the exterior curvature of the aircraft. Two layers of FSS may be used, with one disposed on an outer surface of vertical stabilizer 100 and the other disposed on an inner surface of vertical stabilizer 100.

[0038] The aforementioned flowchart and diagrams illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each portion in the flowchart or portion diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the portion may occur out of the order noted in the figures. For example, two portions shown in succession may, in fact, be executed substantially concurrently, or the portions may sometimes be executed in the reverse order, depending upon the functionality involved, It will also be noted that each portion of the portion diagrams and / or flowchart illustration, and combinations of portions in the portion diagrams and / or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

[0039] As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system or an apparatus. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.”

[0040] The aforementioned figures illustrate the architecture, functionality, and operation of possible implementations of systems and apparatus according to various embodiments of the present invention. Where referred to in the above description, an embodiment is an example or implementation of the invention. The various appearances of “one embodiment,” “an embodiment” or “some embodiments” do not necessarily all refer to the same embodiments.

[0041] Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment.

[0042] Reference in the specification to “some embodiments”, “an embodiment”, “one embodiment” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the inventions. It will further be recognized that the aspects of the invention described hereinabove may be combined or otherwise coexist in embodiments of the invention.

[0043] It is to be understood that the phraseology and terminology employed herein is not to be construed as limiting and are for descriptive purpose only.

[0044] The principles and uses of the teachings of the present invention may be better understood with reference to the accompanying description, figures and examples.

[0045] It is to be understood that the details set forth herein do not construe a limitation to an application of the invention.

[0046] Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in embodiments other than the ones outlined in the description above.

[0047] It is to be understood that the terms “including”, “comprising”, “consisting” and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps or integers.

[0048] If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element.

[0049] It is to be understood that where the claims or specification refer to “a” or “an” element, such reference is not be construed that there is only one of that element.

[0050] It is to be understood that where the specification states that a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included.

[0051] Where applicable, although state diagrams, flow diagrams or both may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described.

[0052] Methods of the present invention may be implemented by performing or completing manually, automatically, or a combination thereof, selected steps or tasks.

[0053] The term “method” may refer to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the art to which the invention belongs.

[0054] The descriptions, examples and materials presented in the claims and the specification are not to be construed as limiting but rather as illustrative only.

[0055] Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined.

[0056] The present invention may be implemented in the testing or practice with materials equivalent or similar to those described herein.

[0057] While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other or equivalent variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents.

Claims

1. An antenna arrangement comprising:a flat panel phased array antenna (150) configured to simultaneously steer a plurality of beams (152), each beam (152) capable of being directed up to an angle of 60° relative to a direction which is perpendicular to the plane of the antenna, said antenna located within a cavity (102) formed by a vertical stabilizer (100) of an aircraft; andan impedance matching structure (160) located between said antenna (150) and an inner side (104) of said vertical stabilizer (100),wherein a separation distance (340) between the vertical stabilizer and the antenna are optimized for a predetermined tuned frequency of the antenna (150) such that said impedance matching structure (160) keeps mismatch losses of said beams (152), caused by said vertical stabilizer (100), below 2dB for up to said angle of 60°.

2. The antenna arrangement according to claim 1, wherein said impedance matching structure (160) comprises at least one layer of matching material (360), said at least one layer located between said antenna (150) and an inner surface (104) of said vertical stabilizer (100).

3. The antenna arrangement according to claim 2, wherein said at least one layer of matching material (360) comprises FR4.

4. The antenna arrangement according to claim 1, wherein at least one layer of FSS (470) is located on an external surface of said vertical stabilizer (100).

5. A method of inserting an antenna arrangement within a cavity (102) formed by a vertical stabilizer (100) of an aircraft, the method comprising:step 1 (510): determining a cross-section of substantially uniform thickness of said vertical stabilizer (100), said cross-section having a cross-sectional area at least equal to that of the antenna arrangement to be inserted;step 2 (520): orientating said antenna arrangement substantially parallel to said determined cross section; andstep 3 (530): placing an impedance matching structure (160) between said antenna arrangement having said orientation and an inner surface (104) of said vertical stabilizer (100), said inner surface (104) inclusive of said determined crosssection,wherein placing the impedance matching structure (160) includes optimizing a separation distance (340) between the vertical stabilizer (100) and the antenna arrangement for a predetermined tuned frequency of the antenna arrangement,wherein the antenna arrangement comprises a flat panel phased array antenna (150) configured to simultaneously steer a plurality of beams (152), each beam (152) capable of being directed up to an angle of 60° relative to a direction which is perpendicular to the plane of the antenna, andwherein upon execution the method keeps mismatch losses of said beams (152), caused by insertion into said cavity (102) of said vertical stabilizer (100), below 2dB for up to said angle of 60°.

6. The method according to claim 5 wherein said impedance matching structure (160) comprises at least one layer of matching material (360), said at least one layer located between said antenna (150) and said inner surface (104) of said vertical stabilizer (100).

7. The method according to claim 6, wherein said at least one layer of matching material (360) comprises FR4.

8. The method according to claim 7, wherein at least one layer of FSS (470) is located on an external surface of said vertical stabilizer (100).

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