EP3841678A1

EP3841678A1 - Antenna system with at least two antennas, mainly for nfc transmission

Info

Publication number: EP3841678A1
Application number: EP19786657.7A
Authority: EP
Inventors: Emil HUBINÁK
Original assignee: Logomotion sro
Current assignee: Logomotion sro
Priority date: 2018-08-02
Filing date: 2019-08-02
Publication date: 2021-06-30
Also published as: SK500372018A3; WO2020026203A1

Abstract

Antenna system has at least one spiral antenna (1) and at least one solenoid antenna (2) with a magnetic core. The solenoid antenna (2) is placed against the flat spiral antenna (1) in such a way that the groundplan of the solenoid antenna (2) at least partially overlaps the respective strip (3) and the respective strip (3) and the groundplan of the solenoid antenna (2) are symmetrically centered in order to achieve the match of their axes without significant deviation. The solenoid antenna (2) is placed in the plane of the flat spiral antenna (1) or on the flat spiral antenna (1) or under the flat spiral antenna (1). The antenna system can include two solenoid antennas (2, 22) where the second solenoid antenna (22) is placed on the second strip (3) and mutually they form a topology shaped "II" or "L". The output from the receiving flat spiral antenna (1) is connected to the phase modulator of the transmitting solenoid antenna (2) and the transmission of the solenoid antenna (2) is synchronized with the signal simultaneously received on the receiving flat spiral antenna (1).

Description

ANTENNA SYSTEM WITH AT LEAST TWO ANTENNAS, MAINLY FOR NFC TRANSMISSION

Field of technology

The invention concerns the antenna system which has at least one transmitting solenoid antenna and one cooperating receiving antenna with the spiral winding of the conductor on the surface, whereby the antennas have a mutual spatial arrangement and connection which produces their mutual electromagnetic isolation. The antenna allows simultaneous transmission and reception and it takes few space in the available space, for example on the PCB of the mobile phone, in SiP (System in Package) module, on SD memory card, and so on.

Prior state of the art

During communication by means of an NFC platform, mainly pursuant to ISO/IEC 14443, flat spiral antennas are preferably used. In passive mode (regime) the initializer/emitter (transmitter) (PCD) offers a carrier field with an energy for the device of the transponder/receiver (PICC, for example payment card) which answers by means of a modulated carrier field (load modulation). The antenna of the receiver must be sufficiently large to bear the energy demands of the transmitter, which in this mode lacks its own power source.

In a pseudo-passive mode the transponder actively transmits the carrier frequency which is phase modulated in such a way that this frequency in sum with the carrier frequency from the initializer produces an amplitude modulation. It is necessary that the carrier frequency transmitted by the transponder is exactly in the phase or counter-phase related to the initializer.

The publication US 2001/0026244 A1 uses a flat spiral antenna inside which there is a solenoid antenna. The solenoid antenna has two separate windings; one winding is connected with the protrusions of the flat spiral antenna. This solution, however, does not create the necessary isolation between the transmitting and receiving antenna; on contrary, these antennas are electromagnetically connected. This solution is useless during miniaturization, when we try to place both antennas in small available space, for example to the removable memory card. The effective use of the small available space with a single flat spiral antenna and a single solenoid antenna is disclosed in CN103633421 , where the groundplans of the solenoid antenna and the flat spiral antenna overlap. The solenoid antenna has a very flat core which worsens its transmitting features. Similarly, in this arrangement there is not sufficient electromagnetic isolation between two antennas.

The problems with isolation are solved by the publication WO2017109681 A1 which discloses a solenoid antenna with a ferrite core and a flat spiral antenna, which are placed in the same plane, whereby they are distanced in a groundplan from each other and the magnetic center of the flat spiral antenna lies in the transversal axial plane of the solenoid antenna. This solution achieves good mutual isolation of the antennas, but it also requires relatively larger space for placement.

A solution is desired and not known, which will achieve, against the state of the art, sufficiently strong isolation of the antennas in the system of the flat spiral antenna and at least one solenoid antenna, whereby on the small available space it receives a sufficient transmitting and receiving performance of the antenna system during simultaneous transmission and reception.

Essence of the invention

The abovementioned deficiencies are significantly remedied by an antenna system with at least two antennas, mainly for NFC transmission, which includes one flat spiral antenna and at least one solenoid antenna with a magnetic core, where the antennas are placed in the same basic plane or in mutually parallel basic planes, where the flat spiral antenna has a conductor spirally wound on the surface in such a way that the winding of the conductor is delimited by four strips following each other, where the strips for a rectangular shape of the coil, and where the output of the flat spiral antenna is designed for connection to the receiving circuit and the output of the solenoid antenna is designed for the connection to the transmitting circuit according to this invention whose essence lies in the fact that the solenoid antenna is placed against the flat antenna in such a way that the transversal axis of the solenoid antenna is parallel with one of the strips of the flat spiral antenna and the groundplan of the solenoid antenna at least partially overlaps with a respective strip of the flat spiral antenna. The basic feature is a placement and orientation of the solenoid antenna against one of the strips of the flat spiral antenna in such a way that these are overlapping in the groundplan and, at the same time, the respective strip and groundplan of the solenoid antenna are symmetrically centered. The centering, that is, the matching of the transversal and longitudinal axes of the solenoid antenna and the respective strip of the flat spiral antenna in the groundplan view can have a margin of error of less than 10% of the respective dimension, that is, the length or the width of the respective strip.

The “groundplan” in this text denotes a plane identical or parallel with the surface on which the flat spiral antenna is placed. The solenoid antenna can be placed in the plane of the flat spiral antenna; in the actual realization the solenoid antenna will be placed on a flat spiral antenna or under the surface of the flat spiral antenna.

The length of the solenoid antenna is not supposed to exceed the length of the respective strip by more than 10%. The length of the solenoid antenna shall not exceed the length of the respective strip or it shall not exceed its width by more than 100%.

In this arrangement it is achieved that the antennas generate mutually orthogonal magnetic fields and between the solenoid antenna and the flat spiral antenna a partial transformer coupling is produced, where the mutual induction coupling between the windings ranges from 0,2 to 0,6.

During the transmission a magnetic field is generated by the solenoid antenna and this exists mainly in a horizontal plane, and mainly at the ends of the solenoid; thanks to the transformer coupling a part of the field is transferred by means of the flat spiral antenna to the vertical plane and the antenna system appears omnidirectional, where it transmits in both mutually perpendicular planes. Pursuant to the reciprocity principle the reception also appears omnidirectional in such a way that the received field will be mainly in the horizontal plane and this field will be mainly used by the solenoid antenna and thanks to the transformer coupling it will be transferred to the receiving flat spiral antenna and in the case of the vertical field it will be received directly by the receiving flat spiral antenna. Such arranged antennas are more effective (sensitive) than independent vertical flat spiral antennas or horizontal solenoid antennas by themselves.

The goal of the groundplan centering is the production of the magnetic symmetry between the solenoid antenna and the respective strip of the flat spiral antenna or also between the solenoid antenna and the flat spiral antenna as a whole. The margins of error from the exact dimensional centering can achieve the matching of the magnetic centers which are affected by the surrounding environment, too. The advantage of the proposed invention is the possibility to place further component inside the surface between the strips of the flat spiral antenna. These components as well as the surrounding environment can affect the magnetic axes of the antenna system and then it is preferable to move the geometric axes of the solenoid antennas against the axes of the strip of the flat spiral antenna. The dimension of movement shall not exceed 10% of the respective dimension and can be quickly and easily determined by experimenting.

The placement of the solenoid antenna inside the groundplan of the flat spiral antenna achieves a preferable use of the available space and the localization of the solenoid antenna to the center of the strip of the flat spiral antenna leads to the creation of the sufficient isolation, even if the antennas are in complete mutual proximity. The centric arrangement leads to the compensation of the induced electromagnetic field in two directions.

The term“solenoid antenna” denotes a cylindrical coil with multiple windings of the conductor where the length of the coil is usually larger than its diameter, for example, the length of the coil is more than five times its diameter. It can be also called“an antenna with a core”,“coil antenna”, and so on.

Both antennas are preferably placed on a common substrate, that is, on the identical surface, for example in a single surface of a PCT. A realization is, however, possible, too, where the antennas are on the different surfaces or on independent carriers, respectively; it is, however, important that the longitudinal axis of the solenoid antenna is in the groundplan projection identical with the longitudinal axis of the respective strip of the flat spiral antenna and that the transversal axis of the solenoid antenna is in the groundplan projection identical with the transversal axis of the respective strip of the flat spiral antenna and that there is not a significant deviation between these axes.

A“respective strip” means one of the four strips, above which the solenoid antenna is placed.

The antenna system according to this invention has mutually symmetrical and orthogonal arrangement of both antennas. In case the antennas are placed on different, mutually distant surfaces, the distance of their planes can reach up to 50% of the length of the respective strip. In practice this distance will be delimited mainly by the thickness of the respective carrier, for example by the thickness of the component or thickness of the device. In the preferable arrangement the antenna system includes two solenoid antennas with a magnetic core, which are both placed in the same base plane in which a flat spiral antenna is placed, or they are placed in mutually parallel base planes. For both solenoid antennas it holds that the solenoid antenna is placed on a flat antenna in such a way that the longitudinal axis of the solenoid antenna is parallel with one of the strips of the flat spiral antenna and the groundplan of the solenoid antenna at least partially overlaps with the respective strip of the flat spiral antenna.

The second solenoid antenna can be placed on a strip which is opposite to the strip with the first solenoid antenna; then the topology (architecture) shaped as“II” is formed, where two solenoid antennas are mutually parallel. In another arrangement the second solenoid antenna is placed on the strip which is perpendicular to the strip with the first solenoid antenna; the topology is in shape “L”, where the solenoid antennas are mutually perpendicular. A use of two or multiple solenoid antennas can increase the transmission performance. Two or more solenoid antennas can be connected to a single transmitting circuit; the antennas can be connected in parallel or in sequence. With use of multiple solenoid antennas it is preferable if these are identical or if their lengths correspond pro rata to the lengths of respective strips.

The magnetic center of the flat spiral antenna lies in the transversal axial plane of the respective solenoid antenna or these centers differ only by a value of acceptable margin of error. The magnetic center of the flat spiral antenna lies in the transversal axial plane of the solenoid antenna which runs through the magnetic center or the magnetic center of the flat spiral antenna is distanced from the transversal axial plane of the solenoid antenna by up to tenth of the respective dimension of the solenoid antenna. The magnetic center of the antenna which has a preferable, even and symmetrical construction will usually be identical with the geometric center of the antenna. However, the magnetic center can deviate under the influence of surrounding objects, mainly under the influence of metal particles in the immediate vicinity.

The dimensional and spatial configuration according to this invention ensures a selective non-sensitivity (non-responsitivity) of the receiving antenna which is capable of receiving the outside signal from the foreign source (PCD) during the active transmission from the nearby antenna within a common antenna system. It is not necessary to process or filter the receiving signal in complicated ways. The invention allows to effectively guide, direct the synchronization at pseudo-passive mode of communication. In the preferable arrangement the strips of the flat spiral antenna produce a rectangle whose larger dimension is not more than twice the smaller dimension. Two longer strips are preferably used for the placement of the solenoid antenna.

It is important that the solenoid antenna and the respective strip of the flat spiral antenna have magnetically symmetrical arrangement. Thanks to this a state is achieved where the tension on the flat spiral antenna induced from the activity of the solenoid antenna is low or zero. The fields at the ends of the solenoid antenna according to figure 6 are identical but in mutual counter-phase. If the strip of the flat spiral antenna is placed symmetrically to the solenoid antenna in such a way that the magnetic field in the left half of the flat spiral antenna is exactly opposite to the one in its right half and therefore the resulting integral through the whole surface of the spiral antenna is zero, and therefore the overall induced voltage from the solenoid antenna is zero, too. This holds for other solenoid antennas, too.

The magnetic field generated by the solenoid antenna has on the ends of the core always an opposite polarity: field lines flow out from one end and flow into on the other end. The individual vectors of the magnetic field on the figure 6 are denoted as ¹H and ²H. These vectors projected to the conductors on the flat spiral antenna themselves are denoted as ¹H_a and ¹H_b, or ²H_a a ²H_b, respectively. Each of these vectors includes an x and y component - H_ax and H_ay.

It follows from figure 6 that if the conductors are placed symmetrically against the horizontal axis of the solenoid antenna, then H_ax is identical to H _x and these components compensate each other on the conductors. If the conductor of the flat spiral antenna with length L is place symmetrically against the vertical axis of the solenoid antenna, then ¹H_ax compensates ²H_ax. The end result is then that the induced voltage on the conductor with length L placed symmetrically against the vertical and horizontal plane is zero, therefore the interference or noise from the solenoid antenna is negligible.

The deviation (tilting) of the geometrical axes of the solenoid antenna from the axes of the respective strip of the flat spiral antenna can adjust the exact tuning of the antenna system in such a way that it takes into consideration the production irregularities as well as the influence of the components and shielding in the vicinity of the antenna system. The deviation of the geometrical axes and the effect of the deviation is depicted in figures 6 and 7. Even though the solenoid antenna is placed in the close vicinity of the flat spiral antenna, the electromagnetic isolation between both antennas is increased, usually by at least 6 dB against the ration of the amplitudes of the signal transmitted by the transponder and received signal form the initializer. In practice this brings an isolation between the transmitting and receiving antenna of the transponder at least at level of 25 dB in the range 13, 56-14, 40MHz.

A maximal sensitivity of the flat spiral antenna L1 to surrounding electromagnetic fields is in the direction of the axis z, that is, in the direction perpendicular to its surface. A minimal sensitivity is in the direction of the axes x and y. The maximal level of the magnetic field generated by the solenoid antenna L2 is in the direction of x axis and the minimal is in the direction of z axis.

The arrangement according to the proposed invention achieves a sufficiently high isolation between the antennas even though these are physically placed in close vicinity, thanks to which the available space is put to good use, or all available space is used for the creation of the flat spiral antenna, respectively. The configuration according to this invention ensures great non-sensitivity of the flat spiral antenna to the transmission of the solenoid antenna; the signal from the flat spiral antenna does not need to be filtered from the transmission signal from the solenoid antenna in a complicated way. During the transmission from the solenoid antenna it is possible to receive the carrier signal from the initializer (PCD) and pursuant to its frequency and phase a transmitted signal can be continuously synchronized.

With the antenna system according to this invention the received signal from the initializer is distorted by the transmission of the transponder only negligibly, and this happens thanks to the isolation and no special synchronization circuits are necessary. Such signal received by the transponder is again transmitted back as a modulation carrier wave for the modulation of the data, which ensures that both signals are precise, exact in the frequency and the modulation of the data happens only through the change of phase (0 180°). A connection of the impedance circuits of both antennas, where the output from the receiving antenna with an information concerning the phase is connected to the phase modulator of the transmitting antenna, serves this purpose. The information concerning the phase of the received signal serves for synchronization of the transmitted modulated signal from the solenoid antenna.

The number of threads of the solenoid antenna L2 depends on the permeability of the core, but usually the resulting value of induction of L2 or L22, respectively, for NFC applications should range from 0,7 to 2,5 pH with a quality Q = 18 - 22. The receiving flat spiral antenna L1 can have 2 to 10 threads, preferably 6 to 8 threads; sufficient quality is Q = 4 - 6.

The advantage of this invention is mainly a simple arrangement of the antenna system and simple connection of the respective circuits, whereby thanks to the physical bonds between the transmitting and receiving antenna a high efficiency of the phase and frequency synchronization is achieved.

Description of drawings

The invention is further disclosed by means of drawings 1 to 12. The particular depictions of solenoid antennas, the amount of windings, threads and loops, the shape of the flat spiral antenna, the course of the field lines and the examples of mutual dimensions are all for illustration purposes only and cannot be interpreted as limiting the scope of protection.

Figure 1 depicts a placement of the solenoid antenna on a single strip of the flat spiral antenna; the arrow points to place where solenoid antenna will be placed. Figure 2 is the antenna system with a single solenoid antenna in the groundplan view. Figure 3 is side view of the antenna system with a single solenoid antenna.

Figure 4 is an arrangement of the antenna system with two solenoid antennas during their parallel arrangement into shape“II”.

Figure 5 is an arrangement of the antenna system with two solenoid antennas with their mutually perpendicular arrangement into“L” shape.

Figure 6 depicts the course of the magnetic field in the surroundings of the solenoid antenna where the vectors of the magnetic field are shown.

Figure 7 and 8 depicts the course of the deviation of the axes of the solenoid antenna from the axes of the flat spiral antenna. Figure 7 depicts options a) to f) of the deviation of the position in various directions in the plane the flat spiral antenna. The deviations are not depicted in scale so that the better readability of the figures is achieved.

Figure 8 depicts a graph with the intensity of the induced voltage on the flat spiral antenna depending on its position against the solenoid antenna according to figure 7.

Figures 9 and 10 are axonometric views of the SiP module with two solenoid antennas in“II” topology. The flat spiral antenna is placed on the bottom side of PCB; there are other electronic components of SiP module placed between solenoid antennas on PCB.

Figure 11 is cased SiP module depicted in the spatial view and figure 12 depicts this module placed in the example of a standardized plastic card.

Examples of realization of invention

Example 1

In this example according to figures 1 , 2, 3, 6 to 8 the antenna system has one solenoid antenna 2 L2 with a ferrite core and a flat spiral antenna 1 L1. Solenoid antenna 2 is 18 mm long. Both antennas 1_, 2 are placed on the same surface of a common carrier. The flat spiral antenna 1 has rectangular groundplan; its outer length is 20 mm and its inner length is 15 mm.

The flat spiral antenna 1 in this particular example has 6 threads of the conductor which are placed next to each other in strips 3 according to figures 1 and 2. Four strips 3 form the rectangle’s circumference; inside the rectangle there is a free space for the placement of other components.

Solenoid antenna 2 is placed in such a way that it is placed on the strip 3 which forms the longer side of the rectangle of the flat spiral antenna 1_.

The longitudinal axis 4 of the solenoid antenna 2 is in the groundplan projection identical with the longitudinal axis of the strip 3; the groundplan projection of the longitudinal axis 4 runs through the center of the strip 3. At the same time the transversal axis 5 of the solenoid antenna 2 is in the groundplan projection identical with the transversal axis of the strip 3; the groundplan projection of the transversal axis 5 runs through the center of the strip 2. Such geometrical arrangement represents an exact centering of the axes without deviations, which presupposes the match of the geometric and magnetic centers of the antennas 1_, 2.

The magnetic center of the flat spiral antenna 1 is in the center plane through which a transversal axis 5 runs and a magnetic center of the solenoid antenna 2 is therefore placed in a mutually symmetrical magnetic position with the magnetic center of the flat spiral antenna 1_, whereby the groundplan of the solenoid antenna 2 overlaps the strip 3.

Each antenna 1_, 2 has its own impedance circuit and impedance matching. The impedance matching of the flat spiral antenna 1 is connected with a low-noise amplified whose output runs into the phase modulator, into which the data intended for the transfer by the transmitting solenoid antenna 2 enter. The phase modulator is connected with a transmitting element, impedance matching and the solenoid antenna 2.

The resulting value of the induction of the solenoid antenna 2 in this example ranges from 0,7 to 2,5 pH and its quality is Q = 20. The receiving flat spiral antenna 1 has 6 threads and quality Q = 5.

The antenna system suppresses the noise without the need for active suppressing by means of active circuits. This solves the problems in cases of miniature NFC antennas which require active load modulation where the active signal acts from the point of view of the receiver as distortion or noise, which worsens the quality of the signal.

The antenna is suitable for use in a mobile phone, SiP modules of various devices, SD cards, even for read/write regime, and for card emulation regime.

Example 2

In this example the antenna system from the previous example has a tilted position of the solenoid antenna 2 against the center of the strip 3 which causes a deviation. The deviation of the position of the solenoid antenna 2 from the central position against the strip 3 is depicted in figure 7 in positions a) to f), where x and y represent a dimensional deviation in mm.

a) position x=0, y=0

b) position x=0, y=-0,5

c) position x=0, y=0,5

d) position x=0, y=0

e) position x=-0,5, y=0

f) position x=0,5, y=0

White lines inside the graph which form a cross on the figure 8 denote centrally symmetrical position of the solenoid antenna 2 where a single thread of the flat spiral antenna 1. runs exactly under the longitudinal axis 4 of the solenoid antenna 2 as depicted on the figure 7 d). Moving of the solenoid antenna 2 in x axis increases the induced voltage similarly as if the whole flat spiral antenna 1. moves against the solenoid antenna 2 in y direction. The darker the point on the graph of the figure 8 gets, the lower the induced voltage and the higher the isolation. Example 3

In this example according to figures 4 and 6 the antenna system has two solenoid antennas 2, 22 with basically similar construction and these are connected in parallel. Both have ferrite core or they can have ferric core (Carbonil Iron). The inductances of the solenoid antennas 2, 22 are similar, ranging from 0,7 to 2,5 pH. The mutual distance of the solenoid antennas 2, 22 led in parallel corresponds to the distances between the centers of two opposite strips 3, whereby the mutual induction coupling of the solenoid antennas 2, 22 is smaller than k = 0,1. In this example the distance of the solenoid antennas 2, 22 is equal to half its length, that is, ca. 6 mm.

Solenoid antennas 2, 22 are placed on the opposite strips 3 which form longer sides of the flat spiral antenna 1 The centers of the solenoid antennas 2, 22 match in the groundplan projection with the centers of the respective strips 3 above which they are placed.

Example 4

In this example according to figures 5 and 6 the antenna system has two solenoid antennas 2, 22 with a similar construction and these are connected in parallel. Both have a core from the magnetic material and they have identical inductances. The solenoid antennas 2, 22 in this example are placed on the neighboring, mutually perpendicular strips 3 which form the longer and shorter side of the rectangle of the flat spiral antenna.

Example 5

In this example according to figures 9 to 12 the antenna system has two solenoid antennas 2, 22 with“II” topology.

The vertical antenna is formed by the flat spiral antenna 1 with 6 - 8 threads which is placed in the bottom part of the carrier for the solenoid antennas 2, 22. The mutual position of the flat spiral antenna 1 and solenoid antennas 2, 22 is such that partial transformer coupling arises between them with a mutual induction coupling between the windings ranging from 0,2 to 0,6.

The antenna system is part of the SiP communication module. The size of the module depends on whether the communication module contains further auxiliary power circuits which would allow a transfer of the maximal performance even at power voltage lower than 5V. In such case the communication module is enhanced by the increasing voltage convertor. If communication module contains one or more Secure elements, the communication module will have contact field pursuant to standard IS07816 so that it is possible to communicate with these Secure Elements.

Communication module SiP with an antenna system according to this invention and eventually with other components within the module is mounted similarly as SMD (Surface Mount Devices) component. Further pins can serve this purpose, at least two further pins, place on the circumference of the communication module’s casing.

Example 6

In this example the flat spiral antenna 1. is formed by the rotation of the conducive path onto the PCB’s surface. The solenoid antenna 2 is produced in such a way that on the PCB there are conducive connecting strips produced, where a core is subsequently placed on these strips and the conducive connecting strips are connected to loops by means of bonding and thereby form the windings of the solenoid antenna 2.

A typical flexible conductor or flexible strip can be used for bonding.

Industrial applicability

Industrial applicability is obvious. According to this invention it is possible to industrially and repeatedly produce and use the antenna system with at least two antennas for transmission and reception of the signal where the receiving antenna is electromagnetically isolated from the transmitting antenna.

List of symbols

1 - flat spiral antenna (L1 )

2 - solenoid antenna (L2)

22 - second solenoid antenna (L22)

3 - strip

4 - longitudinal axis

5 - transversal axis x, y, z - axes of orthogonal coordinate system

NFC - Near field communication

PCB - printed circuit board

SE - Secure Element

SiP - System in Package

SMD - Surface Mount Devices

Claims

PAT E N T C LAI M S

1. An antenna system with at least two antennas, mainly for an NFC transmission, which includes one flat spiral antenna (1) and at least one solenoid antenna (2) with a magnetic core, where antennas (1, 2) are distributed in a same base plane or in mutually parallel base planes, where the flat spiral antenna (1) has a conductor spirally wound on a surface in such a way that a winding of the conductor is delimited by four sequential strips (3) which for a rectangular shape of a loop and where an output of the flat spiral antenna (1) is intended for a connection to a receiving circuit and the output of the solenoid antenna (2) is intended for the connection to a transmitting circuit is characterized by the fact, that

the solenoid antenna (2) is placed against the flat spiral antenna (1) in such a way that a longitudinal axis (4) of the solenoid antenna (2) is parallel with at least one of the strips (3) of the flat spiral antenna (1 );

a groundplan of the solenoid antenna (2) at least partially overlaps with the respective strip (3);

the respective strip (3) and the groundplan of the solenoid antenna (2) are symmetrically centered, where a deviation of a transversal axis (5) and the longitudinal axis (4) of the solenoid antenna (2) from axes of the respective strip (3) in the groundplan projection is less than 10% of a respective dimension of the strip (3), preferably less than 5% of the respective dimension of the strip (3).

2. The antenna system with at least two antennas, mainly for NFC transmission according to the claim 1 is characterized by the fact, that the solenoid antenna (2) is placed in the plane of the flat spiral antenna (1 ).

3. The antenna system with at least two antennas, mainly for NFC transmission according to the claim 1 is characterized by the fact, that the solenoid antenna (2) is placed on the flat spiral antenna (1 ) or below the flat spiral antenna (1).

4. The antenna system with at least two antennas, mainly for NFC transmission according to any of the claims 1 to 3 is characterized by the fact, that the length of the solenoid antenna (2) is less than 110% of the length of the respective strip and the width of the solenoid antenna (2) is less than 200% of the width of the respective strip (3).

5. The antenna system with at least two antennas, mainly for NFC transmission according to any of the claims 1 to 4 is characterized by the fact, that a resulting value of an induction of the solenoid antenna (2) ranges from 0,7 to 2,5 pH and a quality Q = 18 to 22.

6. The antenna system with at least two antennas, mainly for NFC transmission according to any of the claims 1 to 5 is characterized by the fact, that the flat spiral antenna (1) has 2 to 10 threads, preferably 4 to 8 threads and quality Q = 4 to 6.

7. The antenna system with at least two antennas, mainly for NFC transmission according to any of the claims 1 to 6 is characterized by the fact, that between the solenoid antenna (2) and the flat spiral antenna (1 ) there is a partial transformer coupling, where a mutual induction coupling between windings is between 0,2 and 0,6.

8. The antenna system with at least two antennas, mainly for NFC transmission according to the claim 7 is characterized by the fact, that center of the solenoid antenna (2) deviates against center of the respective strip (3) by a dimension determined by a measurement of actual magnetic centers of the antennas (1 , 2).

9. The antenna system with at least two antennas, mainly for NFC transmission according to any of the claims 1 to 8 is characterized by the fact, that the output from the receiving flat spiral antenna (1) is connected to a phase modulator of the transmitting solenoid antenna (2).

10. The antenna system with at least two antennas, mainly for NFC transmission according to the claim 9 is characterized by the fact, that the flat spiral antenna (1) is connected to an impedance matching to which a low-noise amplifier is connected.

11. The antenna system with at least two antennas, mainly for NFC transmission according to any of the claims 1 to 10 is characterized by the fact, that the transmission of the solenoid antenna (2) is synchronized with a signal simultaneously received on the receiving flat spiral antenna (1).

12. The antenna system with at least two antennas, mainly for NFC transmission according to any of the claims 1 to 11 is characterized by the fact, that it includes two solenoid antennas (2, 22) where the second solenoid antenna (22) is placed on the second strip (3), whereby the groundplan of the second solenoid antenna (22) at least partially overlaps with the second strip (3); the second strip (3) and the groundplan of the second solenoid antenna (22) are symmetrically centered where the deviation of the transversal axis (5) and the longitudinal axis (4) of the second solenoid antenna (22) from the axes of the second strip (3) in the groundplan projection is less than 10% of the respective dimension of the second strip (3), preferably less than 5% of the respective dimension of the second strip (3).

13. The antenna system with at least two antennas, mainly for NFC transmission according to the claim 12 is characterized by the fact, that the solenoid antenna (2) and the second solenoid antenna (22) are placed on the mutually opposite strips (3).

14. The antenna system with at least two antennas, mainly for NFC transmission according to the claim 12 is characterized by the fact, that the solenoid antenna (2) and the second solenoid antenna (22) are placed on the perpendicular strips (3).