EP1524720B1 - Antenna system for multiple frequency bands - Google Patents

Abstract

The antenna system has at least 2 quadrifilary helix antennae (3,4) offset from one another by 90 degrees and provided with double coils (R0,R90; T0,T90) having a 90 degree phase shift, both antennae wound about a cooom longitudinal axis and rotated through an angle of 45 degrees to one another, such that the double coils have the same spacing from the longitudinal axis in a given perpendicular plane.

Description

I. Field of application

The invention relates to an antenna system for simultaneous operation in at least two different frequency ranges, in particular for transmitting and receiving in full-duplex operation, in particular for use in submarines.

II. Technical background

Satellite communications between fixed and moving aeronautical and aeronautical users, including but not limited to submarine satellite communication, typically uses antenna structures that exhibit a quasi-hemispherical radiation pattern in circular polarization, in which case the need for a Tracking the antenna system can be avoided to the possibly geostationary satellite systems.

As far as we know today, the only antenna structure with these required properties is a resonant quadrifilar helix antenna. This usually consists of two double helices that wind around a common longitudinal axis, are mounted orthogonally to each other and are excited by 90 ° phase shift.

Since such an antenna system is a resonant-working system, the usable bandwidth is limited and it is difficult to achieve

Adaptation to broadband usage or use for two different frequencies. Consequently, in cases where operation in different frequency ranges is required, usually two separate spatially separated quadrifilar helix antennas must be used. This is especially true if operation is to be possible simultaneously in both frequency ranges.

An example of such a case is the UHF Satcom satellite communication system, where the transmission and reception of data occurs in different frequency ranges: UHF Satcom reception 240-270 MHz UHF Satcom broadcast 290-320 MHz

It is to be regarded as advantageous if it is possible to send and receive at the same time and independently of each other (so-called full-duplex operation). In this case, a low coupling, ie a low crosstalk between the transmitting / receiving antennas is required. For this purpose, as already mentioned above, it is usually necessary for the transmitting and receiving antennas to be designed as separate elements.

However, if the dimensions of the antenna system are limited by the available space, then a spatial separation of transmitting and receiving antennas can be done only with considerable effort.

An example of this is an antenna system of a submarine. In addition to the above-mentioned frequency ranges for satellite communication in the UHF Satcom system, even more frequency ranges are usually required beyond this, for example: Shortwave reception 1 - 30 MHz VHF reception (marine radio) 155-160 MHz Line of sight function 225 - 400 MHz GPS 1575.41 / 1227.6 MHz

In addition to the limited space available, there is a further requirement in particular for an antenna system used by submarines that the entire structure of the antenna due to the positioning on the outer skin of the submarine hull and the associated burden of the circulating water as possible must be compact. At the same time, the greatest possible stability of the antenna system with respect to mechanical loads is to be ensured since short-term horizontal loads of up to 400 G and vertical loads of up to 150 G can occur due to shock waves in the water.

In the EP 0 715 369 a multi-band antenna system is described in which an L-band antenna element and an S-band antenna element, each in the form of a quadrifilar helix, spaced from each other on the surface of a hollow cylindrical insulator are arranged. In addition, a UHF band antenna element in the form of a cage dipole is arranged inside the insulator. The two quadrifilar helix antenna elements are powered by feed network cards while the UHF antenna is connected to a corresponding feed port via a split-sheath balun.

The EP 0 856 906 discloses an antenna for radiotelephones for use in satellite communications. In this case, a flexible printed circuit board is formed into a shortened cylindrical bearing on which elements and matching networks are provided to form a helical multi-element antenna.

In the US 6,545,649 describes a quadrifilar helical antenna system in which the pitch of the helices changes towards the top of the antenna. The upper ends of the bifilar helices are each connected to terminals powered by a 90 1/4 directional coupler. The antenna is preferably used in mobile communication between a vehicle and a satellite.

III. Presentation of the invention a) Technical task

It is therefore the object of the invention to provide a possible compact antenna system, which allows a preferably simultaneous operation in at least two different frequency bands, in particular in the field of satellite communication using circularly polarized waves with a quasi-hemispheric radiation characteristic.

In this case, such an antenna system is preferably used on a submarine. However, a user can benefit from the inventive advantages when operating on conventional ships over water or on land.

b) Solution of the task

This object is solved by the characterizing features of claim 1. Advantageous embodiments result from the subclaims.

Accordingly, an antenna system for simultaneous operation, in particular for transmitting and receiving in full duplex operation, proposed in at least two different frequency ranges, which in addition to possibly other existing antennas comprises at least two quadrifilar helix antennas, each of which two orthogonal to each other and excited with 90 ° phase shift Double helix has. Here, orthogonal is to be understood that the two double helices of a helical antenna each run with an offset of 90 ° in the direction of rotation about the longitudinal axis of the helical antenna into each other, so that viewed in a radial sectional plane the imaginary connecting lines between the intersections of the respective helices of a double helix the plane orthogonal to each other, such as in FIG. 3 is indicated by the dashed lines. According to the invention, the two helical antennas wind around a common longitudinal axis, wherein they are rotated with respect to this longitudinal axis by an angle of 45 ° to each other. The double helixes of both helix antennas each have the same distance to the longitudinal axis in an arbitrary sectional plane transverse to the longitudinal axis.

This special arrangement of the two helical antennas is characterized by a particularly high symmetry, so that according to the invention, the mutual influence of the two antennas is minimized.

In a preferred embodiment, the respective double helices of the two helical antennas also have the same pitch, whereby the symmetry of the system can be improved even further.

Preferably, in this case the double helices of the two helical antennas are arranged on the lateral surface of a body rotationally symmetrical to the longitudinal axis. As a rotationally symmetrical body is in particular a cylinder in question, but other geometric body such as a cone are conceivable.

The feeding of the respective helical antenna takes place in a plane extending transversely to the longitudinal axis, which lies at one end of the respective helix.

In this feed-in level, the feed of the respective helical antenna is carried out in the usual way, i. H. that the respective double helices are operated with a phase shift of 90 degrees, wherein the feeding of each single coiled coil via a balancing transformer takes place in the form of a short-circuit line with λ / 4-length.

The out of phase feed to generate the circular polarization is preferably done using hybrid couplings or the like.

In a preferred embodiment, the two feed planes of the two helical antennas coincide. In this case, the common feed-in level of both helical antennas may preferably lie at the end of the helix antennas facing the emission direction. In this case, the preferably used balancing transformers can be easily accommodated in a symmetrical arrangement inside the helix antennas.

Preferably, the double helices of at least one helix antenna are open at the unexcited end. In this way, over the length of the double helices, the respective resonance of the helical antenna can be influenced. In this embodiment, the double helices of the two nested helix antennas have a different length, so that the two helix antennas have different resonance frequencies.

The two frequency ranges on which the two helix antennas of the antenna system according to the invention can be operated may preferably be the ranges of 210-300 MHz, in particular 240-270 MHz and of 260-350 MHz, in particular 290-320 MHz. to enable sending and receiving in the UHF Satcom system.

Although the two helical antennas of the antenna system according to the invention can preferably be operated simultaneously, d. H. In so-called full-duplex operation, they can also be used in so-called half-duplex mode, in which only one of the two antennas is always in operation.

Which of the two modes of operation will ultimately be used depends on the requirements of the user and the electronic equipment of the antenna system.

Preferably, the two helical antennas are of their geometric dimensions, so for example number of turns or pitch of the turns, but in particular from their ratio of diameter to length designed so that the one helical antenna their resonance in the range of 210-300 MHz, in particular 240-270 MHz and the second helical antenna has its resonance in the range of 260-350 MHz, in particular 290-320 MHz, and at the same time for circular (preferably right-polarized) polarized waves an omni-hemispherical radiation characteristic is achieved.

According to a further aspect of the present invention, the antenna system according to the invention comprises at least one further antenna, which is arranged coaxially to the two helix antennas, preferably in the interior defined by the two helices.

This at least one further antenna may, for example, be a monopole radiator, in particular a rod antenna. However, in this case also other types of antennas are conceivable as long as a coaxial arrangement, preferably in the interior, of the helix antennas is possible.

In order to achieve the lowest possible coupling between the helical antennas on the one hand and the additional antenna on the other hand, the most accurate coaxial alignment of the additional antenna in the center of the helix is desirable. The emitters of the additional antenna therefore preferably have a rotationally symmetrical shape.

In a preferred embodiment of the antenna system according to the invention is in the other antenna to a rod antenna with a roof capacity in the form of a plate, due to their geometric dimensions for receiving in the frequency ranges of 0.5 - 60 MHz and 125 - 190 MHz, in particular can be used in the frequency ranges of 1 - 30 MHz and 155 - 160 MHz.

As already indicated above, the most symmetrical possible arrangement of the antenna system for a decoupling of the individual antennas from each other is extremely important. In order to ensure such a symmetrical arrangement in the environmental conditions to which the antenna is subjected in use, according to a further aspect of the present invention, a special mechanical structure is provided.

Accordingly, the antenna system according to the invention preferably comprises a stable base body, on whose outer surface the double turns of the two helical antennas are fixedly arranged along a longitudinal axis of the base body. The double helices may in this case, for example, have the form of wires which are fastened on the outer surface. Preferably, however, are bands of an electrically conductive material, such as copper bands, which are arranged flat on the outer surface of the base body.

The main body is made of any electrically non-conductive material having the desired mechanical properties in terms of stability and / or rigidity. Conceivable here are polymers or other plastics, for example Kapton, Mylar or the like.

According to a preferred embodiment, the main body of the antenna system in the form of a hollow cylinder. The feeding of the helical antennas takes place on an end face of the main body, preferably seen from the attachment side of the antenna system at the distal end and thus at the end facing the direction of irradiation.

On the front side of the main body, the feeding of the double helices takes place from a central point, which essentially coincides with the longitudinal axis of the helical antennas and thus the base body, via radially outwardly extending segments of conductive material, which are applied on the front side and respectively to the lead together associated double helices.

In order to prevent that running in the interior of the body feeder lines and the respective associated baluns in the form of λ / 4 short-circuit lines under mechanical stress of the antenna system change their position and thus lose their necessary for decoupling the two helical antennas, symmetrical arrangement, are These lines according to the invention held by a sufficiently rigid foam material stationary at their positions. As a foam material, for example, polyurethane foam, polystyrene, polyvinyl chloride, but also other foams can be used here, as long as the stiffness necessary for holding the lines is ensured.

In addition to the necessary stiffness of the foam used should also have special electrical properties, in particular to influence the radiation characteristics of the helical antennas as little as possible. Accordingly, according to the invention, the foam used preferably has a dielectric constant and a loss factor comparable to those of air.

According to the invention, the holder of the corresponding lines in grooves on the lateral surface of separate foam bodies.

According to the invention, the lines are held by the foam used over the majority of the length in the interior of the body at a constant distance. However, this distance is reduced near the feed point on the end face of the base body in order to obtain the best possible symmetrization by the lowest possible transition between the respective feed line and the associated balancing transformer.

In a preferred embodiment, of course, can be provided in the interior of the foam body holes for further lines for the supply of additional antennas.

In order to protect the antenna system against water and the usual prevailing water pressure when used with a submarine, the entire construction according to the invention is provided with a hood e.g. surrounded by plastic. This plastic hood has a substantially cylindrical shape, which is provided at its distal with respect to the attachment of the antenna system to the submarine hull end with a hemispherical cover and is connected at its proximal end with the hull to be fastened plate. The outer diameter of this plastic hood is determined by the space available during installation. As materials come here, for example, glass fiber reinforced plastic, epoxy resin or the like in question.

When used on a normal ship or on land, this plastic hood essentially serves to protect against external environmental influences. Since the requirement of withstand pressure in this case does not exist, For example, the thickness of the hood may be smaller and / or lower requirements may be placed on the material used.

c) embodiments

Fig. 1:

eine Schnittansicht durch eine Ausführungsform eines erfindungs- gemäßen Antennensystems mit zwei quadrifilaren Helixantennen;

Fig. 2:

eine Aufsicht auf die Deckplatte an der Stirnseite des in der in Fig. 1 gezeigten Ausführungsform verwendeten Grundkörpers, auf der die gemeinsame Einspeiseebene der Helixantennen liegt;

Fig. 3:

eine Aufsicht auf die Anschlussplatte der Einspeiseleitungen der in Fig. 1 gezeigten Ausführungsform;

Fig. 4:

eine Schnittansicht der in Fig.2 dargestellten Deckplatte und

Fig. 5:

eine Detailldarstellung eines Teilbereichs von Fig.1.

An embodiment according to the invention is described in more detail below by way of example with reference to the figures. Show it:

Fig. 1:

a sectional view through an embodiment of an inventive antenna system with two quadrifilar helical antennas;

Fig. 2:

a plan view of the cover plate on the front side of the in Fig. 1 shown embodiment, on which lies the common feed plane of the helix antennas;

3:

a plan view of the connection plate of the feed lines of in Fig. 1 embodiment shown;

4:

a sectional view of in Fig.2 shown cover plate and

Fig. 5:

a detailed representation of a portion of Fig.1 ,

FIG. 1 shows a sectional view through an embodiment of an antenna system according to the invention. This comprises two quadrifilar helix antennas 3, 4, which are arranged on the lateral surface of a basic body 1 in the form of a hollow cylinder.

In the cylindrical base body 1, a semi-open mounting cylinder 6 is introduced at its proximal relative to the attachment of the antenna system end, the closed end points in the direction of radiation of the antenna system. In the middle of this end face 61 of the mounting cylinder 6 is a circular recess for receiving a mounting plate 5 is provided, which is fastened by means of screws 56 to the mounting cylinder 6.

Fig. 2 shows a bottom plan view of the mounting plate 5. In addition to the screw holes 55 for fixing the plate 5 to the mounting cylinder 6, the plate 5, four first terminals 51,52,53,54 for the feed lines of the double helices T0, R0, T90, R90 of both helix antennas 3, 4, to which the respective ones of the hybrid couplings 62 (see Figure 5 ) of the base module of the antenna system coming supply lines can be connected. These cables are conventional coaxial cables.

For each of these four terminals 51,52,53,54 diametrically to the longitudinal axis of the base body 1, a terminal 51 a, 52 a, 53 a, 54 a is provided, each of which the end of belonging to the corresponding double helix T0, R0, T90, R90 λ / 4 short-circuit line 8 represents. These total of eight terminals 51,52,53,54,51a, 52a, 53a, 54a are arranged symmetrically at the same angular intervals of 45 degrees on a circular line with a constant distance to the longitudinal axis of the base body 1.

Of the four terminals 51,52,53,54 1 coaxial cable 7 extend in the interior of the cylindrical base body in the direction of the distal end of the base body 1 to there first the cover plate 2, with the distal end of the base body 1 is closed in one pierced central area. As in Fig. 3 is shown, in this case the respective outer conductor of the coaxial cable 7 on the front side of the cover plate 2 with sectors 21,22, 23,24 are connected. These consist of conductive material and lead from the central region in each case radially outward, to feed from there the first coil of the respective double helix T0, R0, T90, R90. In the present case, the sectors 21,22, 23,24 made of a copper foil, which are applied to the cover plate 2 made of non-conductive material.

Respectively diametrically to the sectors 21,22,23,24, which are respectively connected to the outer conductors of the corresponding feed lines 7, there are sectors 21a, 22a, 23a, 24a, which also consist of copper foil and radially lead radially from the central region to the outside to feed from there the second coil of the respective double helix T0, R0, T90, R90.

In order to obtain a correct supply of the respective double helices T0, R0, T90, R90, the respective inner conductor 7a of the feeders 7 of a double helix T0, R0, T90, R90, as in Fig. 4 shown connected to the respective double helix T0, R0, T90, R90 belonging, diametrically opposed sector 21a, 22a, 23a, 24a and an associated line 8. This line 8 is formed in the present case in each case by the outer conductor of a coaxial cable, which, however, has no inner conductor. The outer conductor of the feed line 7 and the associated line 8 each form a λ / 4 short-circuit line for transforming the unbalanced signal of the feed line 7 into a symmetrical signal at the feed point. The line 8 extends through the cover plate 2 into the interior of the main body 1, traverses it and is conductively connected to the plate 2.

Due to the requirement that this λ / 4 short-circuit line must correspond to a quarter of the wavelength of the resonance frequency of the respective helical antenna 3,4, the position of the plate 5 and thus the geometric dimensions of the mounting cylinder 6 in the interior of the main body first result.

In the present case, the feed lines 7 and the lines 8, starting from the plate 5, are initially supported in the interior of the base body 1 by three cylinders 9 made of foam material aligned with the longitudinal axis of the base body, and separating wheels 10 arranged between these cylinders 9. The cylinders 9 in this case have an identical cross section, wherein the feed lines 7 and the lines 8 are guided in corresponding grooves in the lateral surfaces of the cylinder 9, and in through holes in the cutting discs 10. In this way, the lines 7,8 are held in their symmetrical arrangement with substantially identical distance to the longitudinal axis of the base body 1.

Following the third cutting disk 10, the lines 7, 8 are then guided in grooves in the lateral surface of a substantially conical foam body 9 a, which tapers in the direction of the cover plate 2. At this cone-shaped foam body 9a is followed by a further cutting disc 10a with a smaller radius, which in turn has passage openings for the leads through to 7,8. Finally, between the cutting disc 10a and the cover plate 2, a further cylinder 11 is arranged made of foam, which in turn has grooves in its lateral surface to accommodate the lines to be led by 7.8.

In this way, symmetrically the distance between the lines 7, 8 belonging to a double helix T0, R0, T90, R90 can be reduced, so that for a better symmetrization of the lines Fig. 4 shown, exposed area of the inner conductor 7a small compared to the wavelength λ is.

In the present case, a material which preferably has the following physical properties is used as the foam material for the cylinders 9, the conical foam body 9a and the cylinder 11: Density: <50 kg / m ³ , in particular <35 kg / m ³ dielectric constant: 1.0 - 1.1 for frequencies <26.5 GHz Dielectric loss factor: <0.002 for frequencies <10 GHz

For example, a suitable polymethacrylimide (PMI) rigid foam such as Rohacell® 31 is suitable as a commercially available foam material.

The cutting discs 10 and 10a are made in the present case of a preferably very rigid material with good breaking strength and suitable dielectric properties. For example, these requirements of polyvinyl chloride (hard PVC) are met.

Furthermore, the cylinders 9, the cone-shaped foam body 9a, the cylinder 11 and the cutting discs 10 and 10a in the present case, a central

Hole on, so that optionally centrally on the longitudinal axis of the base body 1, one or more feed lines for additional antennas, which may be mounted, for example, on the cover plate 2, can be performed.

The double helices T0, R0, T90, R90 of the two helical antennas 3, 4 are formed in the present embodiment in each case by corresponding strips of copper foil, which are wound on the lateral surface of the main body 1. Consequently, in the present case, the respective double helices are open at the ends opposite to the feed. The bands are electrically connected at the transition region between the cover plate 2 and the lateral surface of the base body 1 with the respective sectors 21,21 a, 22,22a, 23,23a, 24,24a of the double helices.

In the selected embodiment, the two helical antennas 3, 4 of the antenna system according to the invention can be operated in the two ranges of 240-270 MHz and 290-320 MHz, respectively, so that transmission and reception in the UHF Satcom system is possible. Since a resonance at a lower frequency is associated with a greater length of the corresponding double helices, it turns out Fig. 1 it can be seen that in the present case it is the helix antenna 4 which operates in the range of 240-270 MHz.

Depending on the electronics used, the two helix antennas 3, 4 in the present embodiment can be operated either in full-duplex mode or in half-duplex mode.

Due to the symmetrical arrangement according to the invention of the two helical antennas 3, 4 wound in one another, an isolation between the two antennas of greater than 15 dB can already be achieved in the present case. By additional use of filters, this decoupling can be further enhanced, for example, up to 30 dB.

The typical gain of the present antenna system with the two helical antennas 3, 4 is typically 0 dBi, but it may also reach 2 dBi become. An omni-hemispheric radiation image is generated in a right-polarized radiation. The antenna impedance is 50 ohms. The maximum operating power 200 W.

FIG. 5 shows a detailed view of a sub-area Fig.1 and represents the base portion of the antenna system with the mounting cylinder 6. In the interior of the mounting cylinder 6, an additional antenna is housed in the embodiment shown here.

This is a monopoly in the form of a rod antenna with a roof capacity. This monopole is formed in the present case by a copper ring 63, which is held by means of spacers 64 in a transverse plane of the base body 1 and which is connected directly via an insulated terminal to the base module of the antenna system.

The additional rod antenna is used in the present case for reception in the frequency ranges of 1 MHz - 30 MHz and 155 MHz - 160 MHz.

Furthermore, the two 90 ° hybrid couplings 62 for generating the phase shift for feeding in the helical antennas 3, 4 are located inside the assembly cylinder 6. These are arranged on a cover body 66 terminating the main body 1, on the outside of which the connections 65 are provided, via which the antenna system is connected to the supply unit (not shown).

The hood for protecting the antenna system against environmental influences is formed in the present embodiment of a radome made of glass fiber reinforced epoxy resin whose wall thickness depends on the use of either a submarine or over water or on land.

LIST OF REFERENCE NUMBERS

1

body

2

cover plate

3

helix antenna

4

helix antenna

5

mounting plate

6

mounting cylinder

7

feeder

7a

inner conductor

8th

management

9

foam cylinder

9a

foam cone

10

cutting wheel

10a

cutting wheel

11

small foam cylinder

21, 21 a

sectors

22, 22a

sectors

23, 23a

sectors

24, 24a

sectors

51.51 a

connections

52,52a

connections

53,53a

connections

54,54a

connections

55

screw holes

56

screw

61

Front side of 6

62

hybrid couplings

63

copper ring

64

spacer

65

connections

66

cover

T0

double helix

T90

double helix

R0

double helix

R90

double helix

Claims (10)

1. An antenna system for simultaneous operations in at least two different frequency bands, in particular for transmitting and receiving in full duplex mode, comprising at least two helix antennas (3, 4) with four coils each, wherein each of the antennas comprises two double coils (R0, R90, T0, T90) disposed in a circumferential direction a with 90° offset from one another and is excited with a 90° degree phase shift, wherein

   - the two helix antennas (3, 4) are wound about the same longitudinal axis and are rotated relative to one another with respect to their common longitudinal axis by an angle of 45°,

   - the double coils (R0, R90, T0, T90) of both helix antennas, 3, 4) respectively have the same distance from the longitudinal axis in any sectional plane transversal to the longitudinal axis;

   - each double coil (R0, R90, T0, T90) is fed through a coaxial feed conductor (7), wherein one of the coils of the respective double coil (R0, R90, T0, T90) is connected with the outer conductor of the associated feed conduit (7) and the other coil is connected with the inner conductor (7a) of the feed conductor (7),

   - the symmetric control of each double coil of the helix antennas (3, 4) is respectively performed through a short circuit conductor (8),

   - the respective short circuit conductor (8) together with the inner conductor (8a) is connected with an associated other coil;

   - all feed conduits (7) and short circuit conduits (8) are symmetrically disposed in a longitudinal direction of the antenna system at the same distance from the longitudinal axis of the helix antennas (3, 4);

   - one respective feed conduit (7) and an associated shorting conduit (8) are diametrically opposed,

   - the feed conduits (7) and the short circuit conductors (8) are substantially run at a constant distance from the longitudinal axis and the distance is only reduced proximal to the feed points; and

   - the feed conduits (7) and the shorting conduits (8) are fixated in position at least over a portion through a foam material (9, 9a, 11) configured as separate foam material elements, wherein the feed conductor (7) and the short circuit conductor (8) are supported in grooves on the enveloping surface of separate foam material elements (9, 9a, 11).
2. The antenna system according to claim 1, wherein

   - the double coils (R0, R90, T0, T90) of the two helix antennas (3, 4) are disposed on the enveloping surface of an element that is rotation symmetrical to the longitudinal axis, and

   - the rotation symmetrical element is a cylinder in particular.
3. The antenna system according to one of the preceding claims, wherein

   - the feeding for the respective helix antenna (3, 4) is performed in a plane extending transversal to the longitudinal axis, wherein the plane is disposed at an end of the respective helix;

   - feeding planes of both helix antennas, (3, 4) coincide in particular, and

   - a common feeding plane of both helix antennas (3, 4) is disposed in particular at an end of the helix antennas (3, 4) oriented towards a radiation direction.
4. The antenna system according to one of the preceding claims, wherein

   - the double coils (R0, R90, T0, T90) of at least one helix antenna (3, 4) are open at the non-excited end, or

   - the double walls (R0, R90, T0, T90) of the two helix antennas (3, 4) have the same pitch.
5. The antenna system according to one of the preceding claims, wherein

   - the double coils (R0, R90, T0, T90) of the two helix antennas (3, 4) have different lengths, so that the helix antennas (3, 4) have different resonance frequencies; and

   - in particular one helix antenna (3, 4) has a resonance frequency in a range of 210 to 300 MHz, in particular 240 to 270 MHz, and a second helix antenna (3, 4) has a resonance in a range of 260 to 350 MHz, in particular 290 to 320 MHz.
6. The antenna system according to one of the preceding claims, wherein the at least two frequency bands include frequency bands from 210 to 300 MHz, in particular from 240 to 270 MHz and from 260 to 350 MHz, in particular from 290 to 320 MHz.
7. The antenna system according to one of the preceding claims, wherein the two helix antennas (3, 4) with respect to their geometric dimensions, in particular their ratio of length to diameter, are configured, so that they include omni- hemispherical radiation characteristics for waves polarized in a right circular manner.
8. The antenna system according to one of the preceding claims, wherein

   - at least one additional antenna is provided coaxial to the two helix antennas (3, 4), and

   - in particular the at least one additional antenna is a mono-polar transmitter, in particular a rod antenna (63), which due to its geometric dimensions is usable for receiving in the frequency ranges of 0.5 to - 60 MHz and 125 - 190 MHz, in particular in the frequency ranges of 1 - 30 MHz and 155 - 160 MHz.
9. The antenna system according to one of the preceding claims, wherein the foam elements (9, 9a, 11) have a cylindrical or cone shape.
10. The antenna system according to one of the preceding claims, wherein plates (10, 10a) made from a non-flexible material are disposed between the particular foam elements (9, 9a, 11), wherein the conductors (7, 8) to be supported are run through openings in the plates.

Images