EP3032638B1

EP3032638B1 - Radiating cable and method of manufacturing a radiating cable

Info

Publication number: EP3032638B1
Application number: EP14197836.1A
Authority: EP
Inventors: Moustafa Raya; Erhard Mahlandt; Axel Schröder
Original assignee: Nokia Shanghai Bell Co Ltd
Current assignee: Nokia Shanghai Bell Co Ltd
Priority date: 2014-12-13
Filing date: 2014-12-13
Publication date: 2020-04-22
Anticipated expiration: 2034-12-13
Also published as: EP3032638A1

Description

Specification

Field of the invention

The invention relates to a radiating cable for radiating electromagnetic energy. The invention further relates to a method of manufacturing such radiating cable.

Background

Conventional radiating cables are generally formed from a coaxial cable comprising a conductive core defining the longitudinal axis of the cable and surrounded by an intermediate insulating medium, particularly sheath, of a dielectric material, an outer conductor provided with usually regularly spaced apertures or slots for the passage of electromagnetic radiation, and a protective outer insulating jacket. By virtue of the apertures formed in the outer conductor, a portion of the power flowing in the cable and transmitted from a transmitting source is coupled to the exterior. The cable thus acts as an antenna and the power coupled to the exterior is called the radiated power. Due to their characteristics, radiating cables may be used under conditions in which signals radiated from a point source are attenuated rapidly, e.g. for forming a distributed antenna system.
Conventional radiating cables functioning as a distributed antenna facilitate e.g. radio communication where the usual free space propagation of electromagnetic waves is hampered, undesired or impossible, for example in tunnels, mines, buildings, alongside tracks or lines and in large complexes like exhibition grounds or airports. Slots in the outer conductor (e.g. formed of copper) allow a controlled portion of the internal RF energy to be radiated into the surrounding environment. Conversely, a signal transmitted near the cable will couple into the slots and will be carried along the cable length. Thus, a radiating cable may be used for both one-way and two-way communication systems.
EP 2169769 A1 discloses a radiating cable wherein an outer conductor has a plurality of apertures each having two sides and enclosing an angle.
US 3 696 433 A discloses a resonant slot antenna structure.
FR 2 096 222 A5 discloses an apparatus for automatically controlling a mobile object.
FR 1 134 384 discloses an antenna system.
EP 0 087 683 a radiant-slot television aerial, especially for indoor use.

Summary

It is an object of the present invention to provide an improved radiating cable which enables to provide a high degree of vertically polarized electromagnetic radiation constituting said radiated power and an improved method of manufacturing such cable.
According to the present invention, regarding the radiating cable, this object is achieved by the feature combination of claim 1. This advantageously ensures that a comparatively high degree of vertically polarized electromagnetic radiation is emitted by said radiating cable. Advantageously, with some embodiments, even a dominant vertical polarization may be achieved, i.e. the amount of radiated energy with vertical polarization may exceed the amount of radiated energy associated with other types of polarization.
According to an embodiment, said first leg and/or said second leg comprise a substantially polygonal shape, which reduces manufacturing costs.
According to a preferred embodiment, at least one of said legs comprises a substantially rectangular shape, which further reduces manufacturing costs due to its comparatively low complexity.
According to the invention, at least one of said legs comprises a substantially trapezoidal shape.
According to further embodiments, combinations of the aforementioned variants are also possible, i.e. in a further variant, the radiating cable may e.g. comprise at least one aperture a first leg of which comprises a substantially trapezoidal or a substantially triangular shape or a substantially rectangular or a substantially polygonal shape, wherein a second leg of said at least one aperture comprises a same or different shape, wherein in case of a different shape, the second leg is not limited to any of the aforementioned variants of the shape of the first leg.
Advantageously, said first leg and/or said second leg comprises in a respective axial end section a tip section with a width changing along the longitudinal axis of said cable, wherein said tip section preferably comprises a basically triangular shape. This ensures a smooth transition of the impedance of the radiating cable in the region of the tip section along the longitudinal axis and thus contributes to reduce reflections within said radiating cable caused by geometric features of the apertures.
According to a further embodiment, said first leg and/or said second leg comprises at least one edge with a serrated and/or meandering shape. According to Applicant's analysis, this leads to an increased phase difference between currents flowing within different edges of said aperture thus contributing to a further increased portion of vertically polarized radiation.
According to a further embodiment, at least two apertures are arranged along said longitudinal axis and/or along a circumference of said cable. Firstly, this ensures that the radiating cable may advantageously serve as a distributed antenna system radiating, preferably mainly vertically polarized, electromagnetic radiation at various spatial positions along the radiating cable. Secondly, the working bandwidth of the radiating cable may advantageously be increased, especially by providing several apertures arranged along a circumference of the cable, i.e. in a dimension at least different from, or particularly orthogonal to, said longitudinal axis.
According to further embodiments, a specific group of apertures may comprise a number of apertures with same shape or with different shape or shapes, respectively.
According to a further embodiment, groups of several, preferably four, apertures each, are arranged along said longitudinal axis, preferably periodically. In other words, such group may comprise a predetermined number of apertures which are arranged within a first longitudinal coordinate range of said cable, said apertures of said group being arranged along said longitudinal coordinate range and/or along the circumference of said cable. According to further embodiments, one or more further groups of apertures of same or different structure may be arranged within further longitudinal coordinate ranges of said cable, said further longitudinal coordinate ranges being different from said first longitudinal coordinate range. The grouping and distribution of several apertures according to some embodiments enables to attain suppression of undesired modes ("mode suppression") thus increasing the usable bandwidth of the radiating cable.
A further solution to the object of the present invention is presented by the enclosed independent method claim.

Brief description of the figures

Further features, aspects and advantages of the present invention are given in the following detailed description with reference to the drawings in which:

Figure 1a: schematically depicts a side view of a portion of a radiating cable according to an embodiment,
Figure 1b: depicts geometric details of said radiating cable of Figure 1a,
Figure 2: schematically depicts a side view of a portion of a radiating cable according to a further embodiment,
Figure 3a: schematically depicts a side view of a portion of a radiating cable according to a further embodiment,
Figure 3b: depicts geometric details of said radiating cable of Figure 3a,
Figure 4: schematically depicts a side view of a portion of a radiating cable according to a further embodiment,
Figure 5: schematically depicts a side view of a portion of a radiating cable according to a further embodiment,
Figure 6a, 6b: schematically depict operational scenarios of radiating cables according to further embodiments,
Figure 7: schematically depicts a side view of a portion of a radiating cable with several groups of apertures,
Figure 8: schematically depicts a side view of a portion of a radiating cable with several groups of apertures,
Figure 9: schematically depicts a coupling loss over a frequency for different polarization types,
Figure 10: schematically depicts an operational scenario of a radiating cable according to a further embodiments,
Figure 11a: schematically depicts a longitudinal loss over a frequency according to an embodiment,
Figure 11b: schematically depicts a reflection chart with a relative reflection over a frequency according to an embodiment,
Figure 11c: schematically depicts a reflection chart with a relative reflection over a frequency according to an embodiment,
Figure 12: schematically depicts a simplified flow-chart of a method according to an embodiment,
Figure 13a to 13c: schematically depict shapes of apertures according to further embodiments,
Figure 14a, 14b: schematically depict various shapes of apertures according to further embodiments, and
Figure 15a to 15d: schematically depict various shapes of apertures according to further embodiments.

Description of the embodiments

Figure 1a schematically depicts a side view of a portion of a radiating cable 10 according to an embodiment. The cable 10 comprises an outer conductor 12 surrounding a longitudinal axis 14 of the cable 10. The cable 10 may comprise one or more inner conductors which are provided radially inwards of said outer conductor 12 and which may be separated from said outer conductor 12 and/or from each other in an electrically isolating fashion by means of insulating means such as dielectric sheaths or other suitable dielectric components. Also, an insulating jacket may be provided on a radial outer surface of said outer conductor 12. Said inner conductor(s) and the insulating jacket are not shown for the sake of clarity.
According to the embodiments, said outer conductor 12 has a plurality of apertures 120 one of which is exemplarily depicted by Fig. 1a, wherein said aperture 120 comprises a first basically slot-shaped leg 122 and a second basically slot-shaped leg 124. Further according to the embodiments, a longitudinal axis 1220 of said first leg 122 is parallel to the longitudinal axis 14 of said cable 10, and a first angle α (also cf. Fig. 1b) between a longitudinal axis 1240 of said second leg 124 and said longitudinal axis 14 of said cable 10 comprises a value larger than 0 degrees and smaller than 180 degrees.
In the context of the present application, the term "slot-shaped" defines a basically oblong geometry with a length dimension and a width dimension, wherein a size of said slot-shaped geometry along said length dimension is larger than a size of said slot-shaped geometry along said width dimension. Generally, according to the embodiments, such slot-shaped geometry may particularly be constituted by either one of the following shapes: a substantially polygonal shape and/or a substantially rectangular shape and/or a substantially trapezoidal shape and/or a substantially triangular shape.
As is well known in the art, the presence of the aperture 120 in the outer conductor 12 of the cable 10 enables a portion of electromagnetic energy transported by said cable 10 to be radiated to the exterior of the cable 10 thus e.g. providing functionality for distributed antenna systems. For example, the cable 10 may be designed as a coaxial cable with one inner conductor (not shown), e.g. arranged along the longitudinal axis 14 radially inward of said outer conductor 12.
Advantageously, the geometry with angle α according to the embodiments enables to attain a particularly high degree of vertically polarized electromagnetic energy radiated from said cable 10 through its aperture(s) 120.
Figure 1b depicts geometric details of the aperture according to Figure 1a. Presently, the angle α is chosen to approximately 30 degrees, and both legs 122, 124 comprise a substantially rectangular shape with an aspect ratio (ratio of length to width) larger than 2.
According to an embodiment, both legs 122, 124 of said aperture 120 may comprise substantially the same length, i.e. 11 = 12. However, according to further embodiments, the length 11 of the first leg 122 may also exceed the length 12 of the second leg 124, i.e. 11 > 12 or vice versa, i.e. 11 < 12. An aggregated length of the aperture 120 measured along the longitudinal axis 14 (Fig. 1a) is denoted with reference sign 112, and an aggregated height of the aperture 120 measured in a direction perpendicular to the longitudinal axis 14 (Fig. 1a) is denoted with reference sign w12.
Figure 2 schematically depicts a side view of a portion of a radiating cable 10a according to a further embodiment, wherein a value of angle α is larger than 90 degrees. Again, both legs 122, 124 comprise a substantially rectangular shape.
Figure 3a schematically depicts a side view of a portion of a radiating cable 10b according to a further embodiment, and Figure 3b depicts geometric details of said radiating cable 10b Figure 3a. In contrast to the embodiments of Figures 1a, 1b, 2, the radiating cable 10b comprises an aperture 120 the two legs 122, 124 of which each comprise basically trapezoidal shape, with an angle α of about 30 degrees between the longitudinal axes 1220, 1240 of the respective legs 122, 124.
According to the present embodiment, said first leg 122 and said second leg 124 comprise in a respective axial end section a tip section or tip 1222, 1242 with a width changing along the longitudinal axis 14 of said cable 10b, wherein said tip section 1222, 1242 preferably comprises a basically triangular shape. The tip, which may be present at both legs' end sections or - according to a further embodiment - only at one of said legs' end sections advantageously effects a comparatively smooth, continuous impedance transformation along said aggregated length 112 (Figure 3b) of the aperture 120 measured along the longitudinal axis 14, which reduces undesired reflections of electromagnetic waves passing said tip sections.
According to a further embodiment, by increasing the intermediate width w1 of the aperture 120, which is measured in the joining region of both legs 122, 124, the degree of vertical polarization radiated from said aperture 120 may further be increased.
According to an embodiment, the geometric parameters of the aperture 120 of the cable 10b of Fig. 3b are chosen as follows: length 11 of first leg 122 (measured along longitudinal axis 14, cf. reference numeral 11 of Fig. 1b) is about 16.2 mm, length 12 of second leg 124 (measured along longitudinal axis 1242) is about 26.2 mm, α is about 13.2°, w12 (also cf. Fig. 1b) is about 6 mm, and w1 is about 3 mm.
Figure 4 schematically depicts a side view of a portion of a radiating cable 10c according to a further embodiment, wherein said first leg 122 comprises at least one edge e1 with a serrated and/or meandering shape. This leads to an increased phase difference between currents flowing within different edges of said aperture 120 thus contributing to a further increased portion of vertically polarized radiation. The serrated or meandering shape is not limited to the depicted edge e1 of the first leg 122, but may also be comprised at another edge of the first leg 122 and/or of the second leg 124.
Figure 5 schematically depicts a side view of a portion of a radiating cable 10d according to a further embodiment, wherein two apertures 120_1, 120_2 are arranged along the longitudinal axis 14 of the cable 10d with a distance therebetween. More precisely, the first aperture 120_1 extends between coordinates x0, x1 of a coordinate axis x which is parallel to the longitudinal axis 14 of the cable 10d, and the second aperture 120_2 extends between coordinates x2, x3 of said coordinate axis x. In other words, an offset between the neighboring apertures 120_1, 120_2 measured between coordinates x1, x3, corresponds to distance P1. According to an embodiment, further apertures may also be arranged at said cable 10d having same or different offsets P1 from the apertures 120_1, 120_2. According to an embodiment, said further apertures may also comprise a same shape as that of the apertures 120_1, 120_2, which basically corresponds to Fig. 3a, 3b. In the alternative, according to a further embodiment, at least one of said further apertures may comprise a different shape.
Figure 6a, 6b schematically depict operational scenarios of radiating cables according to further embodiments, wherein said cables are mounted to a wall 300.
Figure 6a depicts a front view of a radiating cable 10e, i.e. the longitudinal axis 14 or the coordinate axis x extends perpendicular to the drawing plane of Fig. 6a. As can be seen from Fig. 6a, two apertures 120_3, 120_4 are arranged in the outer conductor of cable 10e at a same x coordinate, e.g. in the drawing plane of Fig. 6a. These two apertures 120_3, 120_4 are arranged along a circumference 14' of the cable 10e, wherein γ1 denotes a first angle between a z-axis and the angular position of the first aperture 120_3, wherein γ2 denotes a second angle between a z-axis and the angular position of the second aperture 120_4, and wherein γ denotes a sum angle γ=γ1+γ2. The electromagnetic radiation emanated from aperture 120_3 is designated with reference sign R3, the electromagnetic radiation emanated from aperture 120_4 is designated with reference sign R4, and the superposed radiation of both said apertures 120_3, 120_4 is designated as R34. According to the present embodiment, both angles γ1, γ2 comprise about the same absolute value so that a symmetrical arrangement with reference to the z axis, said z axis representing a horizontal line in Fig. 6a, is given.
Figure 6b depicts a front view of a radiating cable 10g, wherein, similar to the Figure 6a embodiment, two apertures are arranged at a same longitudinal axis position (i.e., x coordinate), i.e. presently in the drawing plane of Fig. 6b. Said apertures are marked by the cross signs in Figure 6b. In difference to the scenario of Fig. 6a, presently the absolute value of the angle γ5 in the y-z-plane of the first of both apertures depicted by Fig. 6b is smaller than the absolute value of the angle γ6 in the γ-z-plane of the second of both apertures depicted by Fig. 6b, so that an asymmetric radiation pattern with respect to the plane y=0 is attained.
Figure 7 schematically depicts a side view of a portion of a radiating cable 10f with several groups G1, G2 of apertures. The first aperture group G1 comprises four apertures 120_4 of similar shape, as does the second aperture group G2. According to further embodiments, a specific group G1, G2 of apertures may comprise a number of apertures with same shape or with different shape or shapes, respectively.
Presently, the groups G1, G2 of four apertures 120_4 each are arranged along said longitudinal axis 14 of the cable 10f, which is parallel to the x axis depicted in Figure 7. According to a preferred embodiment, the cable 10f may comprise more aperture groups than the two depicted groups G1, G2, wherein said further groups are preferably arranged periodically along the x axis.
According to an embodiment, an aperture group G1, G2 may comprise a predetermined number of apertures 120_4 which are arranged within a first longitudinal coordinate range of said cable 10f, said apertures of said group being arranged along said longitudinal coordinate range and/or along the circumference of said cable. Presently, considering group G2 of Figure 7, the first longitudinal coordinate range is denoted by reference signs x51, x52. As can also be seen from Fig. 7, two apertures each are arranged along the circumference of said cable 10f with an angle γ3 defined therebetween.
The apertures 120_4 of the first group G1 extend longitudinally between x coordinates x41, x42, with an offset P2 between the groups G1, G2. A longitudinal spacing between two apertures arranged at the same angular position along the circumference of the cable 10f is designated as P41, defining a longitudinal offset P32 therebetween. A longitudinal offset between the two lower apertures of group G2 of Figure 7 and the two upper apertures is denoted with reference sign P42, and the longitudinal offset between said upper apertures is denoted as P31. Presently, x51, P42 are chosen such that beginning/end sections of the upper left aperture of group G2 in Fig. 7 and the lower right aperture of group G2 in Fig. 7 coincide at x coordinate x6.
According to further embodiments, one or more further groups of apertures of same or different structure may be arranged within further longitudinal coordinate ranges of said cable, said further longitudinal coordinate ranges being different from said first longitudinal coordinate range.
According to a particularly preferred embodiment, the following geometric relations are proposed for an efficient mode suppression which increases the operational bandwidth of the cable 10f. Preferably, according to an embodiment, P31 = P32 = P2 / 4. Preferably, according to an embodiment, P41 = P42 = P2 / 4. According to further embodiments, certain deviations from said geometric relations are tolerable, e.g. in the magnitude of about 20 percent. I.e., it is acceptable if e.g. P31 > 0.8*(P2/4) and P31 < 1.2*(P2/4), and so on.
Figure 8 schematically depicts a side view of a portion of a radiating cable with several groups G3, G4 of apertures according to a further embodiment. The groups G3, G4 are offset along the longitudinal coordinate axis x by an offset P5. Each group G3, G4 comprises two subgroups G41, G42, each of said subgroups G41, G42 having four apertures each and comprising a structure similar to the groups G1, G2 explained above with reference to Fig. 7. Offset value P62 of Fig. 8 corresponds to offset value P32 of Fig. 7, and offset value P63 of Fig. 8 corresponds to offset P42 of Fig. 7. An offset between the subgroups G41, G42 is denoted with reference sign P61.
According to a particularly preferred embodiment, the following geometric relations are proposed for an efficient mode suppression which increases the operational bandwidth of the cable depicted by Fig. 8. Preferably, according to an embodiment, P61 = P5 / 4. Preferably, according to an embodiment, P62 = P5 / 6. Preferably, according to an embodiment, P63 = P5 / 8. According to further embodiments, certain deviations from said geometric relations are tolerable, e.g. in the magnitude of about 20 percent. According to an embodiment, P5 may e.g. be chosen to 244mm (millimeter). Preferably, according to a further embodiment, an angular distance between the upper row of apertures and the lower row of apertures in Fig. 8 (also cf. the sum angle γ of Fig. 6a) ranges between 0° and 45°.
Figure 9 schematically depicts a coupling loss cl over a frequency f within a frequency range from a first frequency f1 (e.g., f1 = 0.5 GHz) to a second frequency f2 (e.g., f2 = 3.0 GHz) for different polarization types of a cable according to the embodiments. Curve c1 denotes vertical polarization, curve c2 denotes radial polarization, and curve c3 denotes parallel polarization. In this context, Figure 10 schematically depicts an operational scenario of a radiating cable 10h together with symbolically depicted dipoles D1, D2, D3, wherein first dipole D1 is a radial dipole with respect to cable 10h, wherein second dipole D2 is arranged vertically with respect to cable 10h, and wherein dipole D3 is arranged parallel with respect to cable 10h. Said dipoles D1, D2, D3 illustrate the different polarization orientations also used for obtaining the curves c1, c2, c3 of Fig. 9.
Figure 11a schematically depicts a longitudinal loss 11 (also denoted as scattering parameter "S12") over a frequency f in a frequency range (f3=0 GHz, f4=3.0 GHz) according to an embodiment. As can be seen, the longitudinal loss 11 is below 10dB in a frequency range f < f31 (f31=2.7 GHz).
Figure 11b schematically depicts a reflection chart with a relative reflection r over a frequency f in the frequency range (f3 = 0 GHz, f4 = 3.0 GHz) according to an embodiment, wherein single apertures are arranged periodically along the longitudinal axis 14 of the cable, cf. e.g. Fig. 5.
Figure 11c schematically depicts a reflection chart with a relative reflection r over a frequency f in the frequency range (f3, f4) according to an embodiment. In contrast to Fig. 11b, the frequency range fr1 ranging from frequency f32 = 1.0 GHz to frequency f33 = 2.5 GHz comprises no significant reflection peaks, which is effected by means of mode suppressing using the grouping methodology according to some embodiments, cf. e.g. Fig. 7, 8.
Figure 12 schematically depicts a simplified flow-chart of a method according to an embodiment. Step 200 represents a method of manufacturing a radiating cable 10 for radiating electromagnetic energy, said method comprising: providing an outer conductor 12 (Fig. 1a) surrounding a longitudinal axis 14 of the cable 10, wherein the outer conductor 12 has a plurality of apertures 120, wherein at least one aperture 120 comprises a first basically slot-shaped leg 122 and a second basically slot-shaped leg 124, wherein a longitudinal axis 1220 of said first leg 122 is parallel to the longitudinal axis 14 of said cable 10, and wherein a first angle α (Fig. 1b) between a longitudinal axis 1240 of said second leg 124 and said longitudinal axis 14 of said cable 10 comprises a value larger than 0 degrees and smaller than 180 degrees.
Figures 13a to 13c schematically depict shapes of apertures according to further embodiments. The aperture 120a of Fig. 13a comprises two legs 122, 124 each of which has a substantially triangular shape, specifically being based on a right triangle, with an angle between the legs' longitudinal axes 1220, 1240 as explained above with respect to Fig. 1a.
The aperture 120b of Fig. 13b comprises two legs each of which has a substantially triangular shape, with an angle between the legs' longitudinal axes 1220, 1240 as explained above with respect to Fig. 1a.
The aperture 120c of Fig. 13c comprises two legs each of which has a substantially triangular shape, with an angle between the legs' longitudinal axes 1220, 1240 as explained above with respect to Fig. 1a.
Figure 14a, 14b schematically depict sections of radiating cables 10i similar to the configuration of Fig. 1a, wherein further advantageous shapes of apertures according to further embodiments are exemplarily depicted.
While the shapes of apertures 120_5, 120_7, 120_11, 120_12, 120_13 basically comprise a geometry with two legs 122, 124 each, wherein each leg comprises triangular shape, shapes 120_6, 120_8 basically comprise a geometry with two triangular legs each, said two legs being connected with each other by means of a basically rectangular center section cs. Aperture shape 120_9 comprises a concatenation of four basically rectangular sections r1, r2, r3, r4, and aperture 120_10 basically comprises an S-shape. Aperture 120_14, cf. Fig. 14b, basically comprises two legs 122, 124, each of which approximately comprises quadrilateral or rhombus form.
Figure 15a to 15d schematically depict various shapes of apertures according to further embodiments.
Figure 15a depicts an aperture 1200 which comprises a polygonal shape having six vertices V1, V2, V3, V4, V5, V6 adjacent to each other. The six vertices V1, V2, V3, V4, V5, V6 are arranged counter-clockwise, i.e. in a mathematical positive sense, and are ordered, which means that in the mentioned counter-clockwise sense, the second vertex V2 follows the first vertex V1, ..., and that finally the first vertex V1 follows the sixth vertex V6 closing the presently hexagonal contour of the aperture. Likewise, the edges E12, E23, E34, E45, E56, E61 connecting subsequent vertices V1, V2, V3, V4, V5, V6 with each other are ordered. This definition is used for all polygonal shapes defined by their vertices herein, i.e. also for the octagonal shape of Fig. 15d. In analogy, the various angles of the polygonal shapes are associated with corresponding vertices of same index value, i.e. an angle α1 is associated with the first vertex V1, and an angle α6 is associated with the sixth vertex V6, and the like.
Returning to the embodiment of Fig. 15a, a second vertex V2 and a fifth vertex V5 define a center region cr of said aperture 1200, wherein a distance d1 between said second vertex V2 and said fifth vertex V5 is smaller than a length of any of said six edges E12, E23, E34, E45, E56, E61, preferably smaller than 20 percent of a length of any of said six edges E12, E23, E34, E45, E56, E61.
According to a further embodiment, the first angle α1 and/or said fourth angle α4 are acute angles, i.e. α1 < 90° and/or α4 < 90°. According to a further embodiment, the second angle α2 and/or said fifth angle α5 are larger than 180°. According to a further embodiment, the third angle α3 and/or the sixth angle α6 are larger than 90°, but smaller than 180°.
According to a further embodiment, the length of the third and/or sixth edge(s) E34, E61 is smaller than the length of either of the first, second, fourth, or fifth edge E12, E23, E45, E56.
Figure 15b depicts an aperture 1200a which comprises a polygonal shape having six vertices V1, V2, V3, V4, V5, V6 adjacent to each other, similar to the embodiment of Fig. 15a. However, presently, a second vertex V2 and a third vertex V3 are connected with each other by a second edge E23, wherein a fifth vertex V5 and a sixth vertex V6 are connected with each other by a fifth edge E56, wherein a distance d2 between said second edge E23 and said fifth edge E56 is smaller than a length of any of said six edges E12, E23, E34, E45, E56, E61, preferably smaller than 20 percent of a length of any of said six edges E12, E23, E34, E45, E56, E61.
According to a further embodiment, the first angle α1 and/or said fourth angle α4 of the aperture 1200a of Fig. 15b are acute angles, i.e. α1 < 90° and/or α4 < 90°, preferably α1 < 30° and/or α4 < 30°. According to a further embodiment, the second angle α2 and/or said fifth angle α5 are larger than 180°, preferably ranging from about 210° to about 250°. According to a further embodiment, the third angle α3 and/or the sixth angle α6 are larger than 90°, but smaller than 150°.
Figure 15c also depicts an aperture 1200b which comprises a polygonal shape having six vertices V1, V2, V3, V4, V5, V6 adjacent to each other. According to an embodiment, a distance d2' between the second edge E23 and the fifth edge E56 is smaller than a length of any of the further edges E12, E34, E45, E56, E67 of said aperture 1200b. According to a further embodiment, the second edge E23 and the fifth edge E56 are substantially parallel (i.e., with a deviation of maximum 10 degrees) to each other. According to a further embodiment, the length of either of the second edge E23, the fourth edge E45 or the sixth edge E67 is smaller than a length of any of the edges E12, E34, E56. According to a further embodiment, the length of the fifth edge E56 is larger than a length of any of the further edges E12, E23, E34, E45, E67.
According to a further embodiment, the first angle α1 and/or said fourth angle α4 and/or said sixth angle α6 of the aperture 1200b of Fig. 15c are acute angles, i.e. α1 < 90° and/or α4 < 90° and/or α6 < 90°. According to a further embodiment, the second angle α2 and/or said third angle α3 are larger than 180°, preferably ranging from about 190° to about 220°. According to a further embodiment, the fifth angle α5 is larger than 90° and/or the sixth angle α6 is smaller than 90°.
Figure 15d depicts an aperture 1200c which comprises a polygonal shape having eight vertices V1, V2, V3, V4, V5, V6, V7, V8 adjacent to each other. Eight edges E12, E23, E34, E45, E56, E67, E78, E81 are provided connecting adjacent vertices V1, V2, V3, V4, V5, V6, V7, V8 with each other.
According to an embodiment, a third vertex V3 and a seventh vertex V7 define a center region cr' of said aperture 1200c, wherein a distance (not shown) between said third vertex V3 and said seventh vertex V7 a) is smaller than a length of any of said eight edges E12, E23, E34, E45, E56, E67, E78, E81, preferably smaller than 20 percent of a length of any of said eight edges, and/or wherein b) said distance between said third vertex V3 and said seventh vertex V7 is smaller than a distance between a second vertex V2 and an eighth vertex V8 and/or smaller than a distance between a fourth vertex V4 and a sixth vertex V6.
According to an embodiment, the second edge E23 is substantially parallel (i.e., with a deviation of maximum 10 degrees) to the fourth edge E45 and/or to the sixth edge E67 and/or to the eight edge E81. According to a further embodiment, the first edge E12 is substantially parallel (i.e., with a deviation of maximum 10 degrees) to the third edge E34 and/or to the fifth edge E56 and/or to the seventh edge E78.
According to a further embodiment, a length of any of the second, third, sixth and seventh edges E23, E34, E67, E78 is in a first range, and at least one of the further edges E12, E45, E56, E81, preferably all further edges E12, E45, E56, E81, comprises a length exceeding said first range.
According to a further embodiment, the first angle α1 and/or said fifth angle α5 of the aperture 1200c of Fig. 15d are acute angles, i.e. α1 < 90° and/or α5 < 90°, preferably α1 < 40° and/or α5 < 40°. According to a further embodiment, the second angle α2 and/or said fourth angle α4 are larger than 90°, preferably ranging from about 120° to about 160°. According to a further embodiment, the sixth angle α6 and/or said eighth angle α8 are larger than 90°, preferably ranging from about 120° to about 160°. According to a further embodiment, the third angle α3 is larger than 180° and/or the seventh angle α7 is larger than 180°.
The apertures 120_5, 120_6, .., 1200a according to the embodiments illustrated with respect to Fig. 14a to Fig. 15d may be combined with any of the further embodiments explained in the present application. Specifically, according to some embodiments, a radiating cable may be provided having one or more apertures of the type shown by Fig. 14a to Fig. 15d. In analogy to the embodiments of Fig. 4, 7, 8, these apertures may also be grouped and/or arranged (either individually or as groups) along the longitudinal axis 14 and/or along a circumference of said cable 10.
The radiating cable according to the embodiments advantageously enables to attain a dominant vertical polarization regarding the electromagnetic radiation emitted through said apertures 120.
For RF signal based communication in confined areas like tunnels, mines etc., leaky coaxial cables (LCX) on the basis of the radiating cable according to the embodiments are a good solution. In case of data transfer between LCX and a fixed antenna on e.g. the top of a train (mostly vertically polarized), the radiation from the LCX, should be also vertically polarized in order to enable efficiency transfer. This is attained by the embodiments. In contrast, non-vertical polarizations are invisible for the antenna of train and these can be considered as losses in this specific field of application. Generally, the higher the decoupling of vertically polarization, the less losses appear in the aforementioned application scenario. Advantageously, by enabling a decoupling between the desired vertical polarization and other, undesired polarizations to an extent greater than 3dB, a better efficiency of data transfer will be achieved. In order to enable communication between LCX and the antenna of train, the coupling loss level should be about 75dB or less. Further, to cover longer distances or larger areas, the longitudinal losses should be less than 10dB, which may also advantageously be attained by employing the principle according to the embodiments. Also, by having better efficiency of transfer, as is enabled by employing the principle according to the embodiments, the amount of required repeaters is decreased, which reduces costs.
According to Applicant's analysis, to have vertically radiated E-Field portions, the current vectors on the outer conductor of the radiating cable 10 (Fig. 1a) around the aperture 120 should distribute in a way that difference of phase appear between upper side and lower side of slot. A TEM (transversal electromagnetic) wave will propagate along the cable 10, and the current will distribute parallel to the cable 10. Further according to Applicant's analysis, advantageously an aperture 120 (Fig. 1b) is proposed which comprises a first basically slot-shaped leg 122 and a second basically slot-shaped leg 124, wherein a longitudinal axis 1220 of said first leg 122 is parallel to the longitudinal axis 14 of said cable 10, and wherein a first angle α between a longitudinal axis 1240 of said second leg 124 and said longitudinal axis 14 of said cable 10 comprises a value larger than 0 degrees and smaller than 180 degrees. In other words, to attain the aperture according to the embodiments, it is proposed to extend a horizontal, basically rectangular, leg 122 with an inclined (cf. angle α) leg 124 in order to achieve a dominant vertical polarization. To some degree, the inclined leg 124 acts as a reflector for transversal waves. Due to reflect waves, the current density is modified which forms a difference of phase from an upper portion of the aperture as compared to a lower portion of said aperture, seen along a circumference of said cable 10. The difference of phases causes the radiation of vertical polarized waves and enables the cable according to the embodiments to yield a higher degree of vertical polarization.
By altering the intermediate width w1 (Fig. 3b) of the aperture 120, especially by increasing it as compared to a nominal vertical width of said leg 122, dominance of vertically polarization may be attained.
According to a further aspect of the embodiments, a plurality (two or more) apertures 120_3, 120_4 may be distributed along a circumferential dimension 14' of the cable 10e (Fig. 6a), i.e. in a direction perpendicular to the longitudinal axis 14 (Fig 1a). According to some embodiments, it is possible to distribute the apertures vertically (along direction 14') on more than two levels, i.e. angular positions.
According to an embodiment, in tunnel installations, LCX are usually installed on walls 300 (Fig. 6a), where slots are aligned outward in order to radiate away from the wall 300 to the destination such as e.g. an antenna of a train (not shown) passing by. Observing the radiation characteristics R34 of Fig. 6a, it shows the radiation of the two apertures 120_3, 120_4. To keep the main radiation perpendicular outward at 0°, i.e. in a positive z direction, the main lobe should stay equal or greater than side lobes. For this purpose, it is beneficial if each of the two apertures 120_3, 120_4 is positioned at an angle γ1, γ1 <= 45°, starting from 0°. In addition, according to a further embodiment, it is preferable if the sum angle γ between the two apertures 120_3, 120_4 does not exceed 90°, in order to keep the bundling of the two apertures' radiations.
The aperture shape according to the embodiments in combination with the aperture grouping (said grouping enabling mode suppression) as e.g. exemplified by Fig. 8 has been simulated, and the results schematically depicted by Fig. 9 and 11b, 11c confirm the dominant vertical polarization (curve c1, Fig. 9). At Fig. 11b, 11c show how it is possible to suppress selected modes by applying the mode suppression methodology according to the embodiments.
According to a further embodiment, to maximize the degree of vertically polarized radiation emanating from the aperture 120 (Fig. 1a), the angle α should vary in range between 0 and 45 degrees, where the radiation level increases with increasing angle α.
By increasing the aggregated height w12 of the aperture 120 measured in a direction perpendicular to the longitudinal axis 14 (Fig. 1b) and keeping angle α constant, so that the ratio l1/12 stays constant for a symmetrical shape, more radiation will emanate through the aperture 120 as long as the size of the aperture 120 is out of self-resonance range.
According to a further embodiment, asymmetrical aperture shapes with different lengths 11, 12 are also possible.
If l1/l2>1, more radiation appear on the 11 part (i.e., the first leg 122) compared to 12 (i.e., the second leg 124). This intensifies the decoupling of vertical polarization.
If l1/l2<1, more radiation appears on the inclined leg 124, where the E-Field radiates diagonally. This reduces the decoupling, but on the other side results to higher radiation due to greater aggregated height w12.
The following descriptions relate to the embodiments of Fig. 6a, 6b. Fig. 6a depicts a first scenario, wherein both apertures 120_3, 120_4 are placed symmetrical to 0° (i.e., the positive z axis), γ1=γ2. If 0°<γ1=γ2<45°: The main lobe at 0°, i.e. in direction of the positive z axis, increases, and the side lobes correspondingly decrease.
If, according to an embodiment, 45°<γ1=γ2<90°: Main lobe at 0° compare to the upper case decrease, side lobes increase. Which make the transfer between LCX and user less efficient, because significant part of radiation get loss due to many reflections before reaching the receiver.
If, according to an embodiment, 90°<γ1=γ2<180°: Main lobe is at 180° in direction of the wall 300. The main part of radiation gets reflected or absorbed, depending on the wall's material and the operation frequency of the radiated RF energy. This case leads to high losses and is not recommendable.
Fig. 6b depicts a second scenario, wherein the apertures (symbolized by crosses "x" in Fig. 6b) are placed asymmetrical to 0°, γ5≠γ6. If, according to an embodiment, 0°<γ5≠γ6<45° and γ5>γ6: The main lobe appears to the upper side between 0 and 45°, the side lobe being near 0 and 90°. In case of γ5<γ6, according to an embodiment, the main lobe turns to the lower side between 0 and -45°. If, according to an embodiment, 45°<γ5≠γ6<90°: The main lobe magnitude approaches the side lobes. If, according to an embodiment, 90°<γ1≠γ2<180°. When, according to an embodiment, γ5>γ6: the main lobe appear at the corner between -90 and 180.
When, according to an embodiment, γ5<γ6: The main lobe appears at the corner between 90 and 180°. Both cases may cause high losses due to reflection and absorbing on walls 300 in tunnel installation according to an embodiment.
The principle according to the embodiments advantageously enables to design broad band vertically polarized radiating cables 10.
The description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its scope.
Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions.
It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

Claims

Radiating cable (10; 10a; 10b; 10c; 10d; 10e; 10g; 10h) for radiating electromagnetic energy, comprising an outer conductor (12) surrounding a longitudinal axis (14) of the cable (10), wherein the outer conductor (12) has a plurality of apertures (120), wherein at least one aperture (120) comprises a first basically slot-shaped leg (122) and a second basically slot-shaped leg (124), wherein a longitudinal axis (1220) of said first leg (122) is parallel to the longitudinal axis (14) of said cable (10), and wherein a first angle (alpha) between a longitudinal axis (1240) of said second leg (124) and said longitudinal axis (14) of said cable (10) comprises a value larger than 0 degrees and smaller than 180 degrees, wherein at least one of said legs (122, 124) comprises a substantially trapezoidal shape, and wherein said first leg (122) and/or said second leg (124) comprises in a respective axial end section a tip section (1222, 1242) with a width changing along the longitudinal axis (14) of said cable (10b), wherein said tip section (1222, 1242) preferably comprises a basically triangular shape.
Cable (10) according to claim 1, wherein said first leg (122) and/or said second leg (124) comprise a substantially polygonal shape.
Cable (10) according to one of the preceding claims, wherein at least one of said legs (122, 124) comprises a substantially rectangular shape.
Cable (10) according to one of the preceding claims, wherein at least one of said legs (122, 124) comprises a substantially triangular shape.
Cable (10) according to one of the preceding claims, wherein said first leg (122) and/or said second leg (124) comprises at least one edge (e1) with a serrated and/or meandering shape.
Cable (10) according to one of the preceding claims, wherein at least two apertures (120_1, 120_2; 120_3, 120_4) are arranged along said longitudinal axis (14) and/or along a circumference (14') of said cable (10).
Cable (10) according to one of the preceding claims, wherein groups (G1, G2) of four apertures (140_4) each are arranged along said longitudinal axis (14), preferably periodically.
Method of manufacturing a radiating cable (10) for radiating electromagnetic energy, said method comprising: providing an outer conductor (12) surrounding a longitudinal axis (14) of the cable (10), wherein the outer conductor (12) has a plurality of apertures (120), wherein at least one aperture (120) comprises a first basically slot-shaped leg (122) and a second basically slot-shaped leg (124), wherein a longitudinal axis (1220) of said first leg (122) is parallel to the longitudinal axis (14) of said cable (10), and wherein a first angle (alpha) between a longitudinal axis (1240) of said second leg (124) and said longitudinal axis (14) of said cable (10) comprises a value larger than 0 degrees and smaller than 180 degrees, wherein at least one of said legs (122, 124) comprises a substantially trapezoidal shape, and wherein said first leg (122) and/or said second leg (124) comprises in a respective axial end section a tip section (1222, 1242) with a width changing along the longitudinal axis (14) of said cable (10b), wherein said tip section (1222, 1242) preferably comprises a basically triangular shape.