SK288756B6 - Antenna on the removable card - Google Patents

Abstract

An antenna on a removable memory card (1) is intended for the creation of contactless communication channel of the mobile communication device. The antenna is in the form of a high-frequency transformer (2) with an oblong ferrite kernel (3) with resonantly tuned primary winding L1. The emitted signal is brought to the primary winding L1. The secondary winding L2 is left open circuited, without closing the load circuit in a contact way, without ohm load; it emits electrical field with its outputs. The high-frequency transformer (2) can be in the form of auto-transformer with one winding. The signal emitted in the direction towards the removable memory card (1) can be received through the auxiliary winding L3 or through an independent receiving antenna (8). The secondary winding L2 can have a larger number of loops than the primary winding L1 or it can be formed by only one winding in the form of a pipe.

Description

Technical field

The invention relates to an antenna and a removable card (in particular a memory card) for insertion into a slot of a mobile communication device, in particular a mobile telephone, the removable card forming thanks to the antenna hardware for an additionally formed contactless communication channel, e.g. NFC (near field communication) type. The solution is intended primarily for payment applications performed using a mobile communication device. In principle, however, the new transmission method and the new type of transmitter according to the invention can also be used in other applications and devices, especially where there is a lack of space to enlarge the transmitting antenna where the antenna is shielded by eye elements.

Prior art

The placement of the antenna directly on a removable card, which is intended to be inserted into a slot of a mobile communication device, is known from published patents, e.g. DE 10252348 A1, WO 03/043101 A3. These disclosures describe the general possibility of using an antenna on a card, but do not contain a sufficient specification of the antenna in a situation where the removable card is shielded by adjacent parts of a mobile communication device, in particular a mobile telephone. Published Logomotion patent applications describe the arrangement of the antenna and the individual layers of a removable memory card in order to adjust the radiating and receiving characteristics of the antenna so that a reliable communication channel can be established even with differently shaded card slots. The technical task defined in this way led to the creation of several technical solutions, which in turn led to satisfactory results only in some mobile phones and subsequently the development current moved towards the creation of larger, additional antennas on the mobile phone body outside shielded areas. These additional antennas (CN201590480 U), for example in the form of stickers, can be connected to the base antenna on the card by contactless, but the low versatility of such an arrangement still remains and the complexity of application in the hands of a normal user is unpleasant.

The antenna placed directly on the removable card has very limited dimensional possibilities. Mobile phones have microSD card slots, which significantly limits the size of the antenna that can be placed directly on the card. When a removable card is placed in heavily shielded slots, such as under a mobile phone battery, the conditions for transmission from the antenna on the card are significantly worsened. The use of guide layers, foils has only a narrow specific effect and is not very universal when used in various constructions of mobile phones.

The essence of the invention

These shortcomings are substantially eliminated by the antenna on the removable memory card to form an additional contactless communication channel of the mobile communication device, in particular the mobile phone, where the removable memory card is inserted into an expansion slot of the mobile communication device according to the invention. the transmitting antenna consists of a high-frequency transformer with an elongated ferrite core with a resonant-tuned primary winding L1. The signal transmitted from the antenna according to the invention is received by standard receiving means in a given frequency band. For example, if the antenna is for NFC transmission between a mobile phone and a POS terminal reader, the antenna on the mobile phone side will be a ferrite core high frequency transformer, but a conventional receiving antenna will be located on the NFC reader side of the POS terminal. It is compliance with existing, standard devices that is important so that there is no need to change the hardware widely used on the POS terminal side. The hardware change on the mobile phone side is done by inserting a removable card (especially microSD format) into the existing slot of the mobile phone.

The expansion slot of the mobile communication device is a card slot that does not affect the basic communication function of the device, so it is mainly, but not exclusively, a slot for a removable microSD memory card.

Resonant tuning of the primary line L1 can be achieved by means of capacitive elements, e.g. by means of a capacitor or by means of two symmetrically connected capacitors in a circuit connected to the primary winding LL Resonant tuning can also be provided by a suitable winding of the primary winding L1, which achieves the required capacity of the winding itself. Resonant tuning can also be achieved by coupling with the secondary winding L2, on which the capacitance is suitably dimensioned in accordance with the transformation ratio of the windings L1 and L2 or by using electromagnetic coupling with the environment

The output of the secondary winding L2 is connected empty, it is a non-contact load, ie no contact ohinic circuit is connected to the outputs of the secondary winding L2 and the voltage at the output can

With K 288756 B6 that reach values up to over 100 Vpp. The absence of a load at the output of the secondary winding L2 represents a state in which a contact closed circuit is not formed or connected at the outputs, through which the relevant current flows in the secondary winding L2. The load may in fact exist in the form of radiating impedance to the environment (air + adjacent elements), or in the form of other electromagnetic links with the environment. Such an indirect load may exist in the real environment of a removable card inserted in a mobile communication device slot, but will not significantly affect electrical voltage at the output of the secondary winding 12. The output or both outputs from the secondary winding L2 can be connected to other elements of the card, for example to ground, power supply or other elements on the card, or via an interface to other elements in the mobile communication device. the connected elements will not form a circuit contacting the secondary winding L2. Upon coupling to the environment, a current can be generated and consequently also a magnetic field component in the secondary winding L2. The connection of other elements with the output of the secondary winding will connect other metal elements of the mobile communication device to the radiation of the electric field and subsequently also of the electromagnetic field.

The use of a high-frequency transformer with an empty-ended secondary winding L2 as a transmitting element provides various possibilities for arranging the connections of the windings L1 and L2. By selecting the ratios of the windings L1 and 12, different ratios of the magnetic and electrical components of the transmitted electromagnetic field can be set.

The primary winding L1 may have fewer conductor loops than the secondary winding L2. The transmitted signal is applied to the primary winding L1, the electric field of the transmitted signal is radiated mainly through the outputs C - D of the secondary winding L2 and the magnetic field of the transmitted signal flows through the ends of the core. In this arrangement, a strong electromagnetic field is created in a small space, since the electrical component is amplified by the effects of the transformer and the magnetic component is amplified by the effects of the ferrite core. The secondary winding 12 does not participate in the formation of the magnetic component of the field, since in a circuit without a relevant load there is essentially no current passing through this winding.

The secondary winding L2 can be formed by only one winding, resp. The primary winding L1 has fewer conductor loops than the secondary winding 12. The winding of the secondary winding L2 could take the form of a flat conductor bent into a tube shape that surrounds the insulated winding of the primary winding L1 with a ferrite core pr the tube in the shape of the letter 'C' will be divided by a longitudinal dividing gap. A coil formed, for example, from a conductive foil or sheet metal can cover the entire length of the ferrite core and will at the same time create shielding and direct the magnetic flux of the field. This coil of the secondary winding L2 may be a magnetic cannon that directs the field so that it is strongly radiated from the mouth of the tube. The waveguide tube is in fact formed and connected as a coil of the secondary winding L2. With this arrangement, the waveforms of the magnetic field lines in the vicinity of the individual conductors of the winding of the primary winding LL can be optimized. The tube can have a different plan shape, e.g. in the shape of the letter L, M. The secondary winding L2 can also be formed by a spiral winding of a flat conductor into the shape of a tube with several winding loops. The superimposed layers will be interlayer insulated. The helical winding can have several layers through which the connection of the output driver with the primary winding LL will pass through the openings. The flat conductor material used for the winding should not shield the magnetic field in one layer, so that subsequent layers can be in the magnetic drive of the core. The material may be inhomogeneous or perforated, or with a conductive path structure formed. Several layers on top of each other will also create the effect of a magnetic cannon.

The transmitted signal from the output driver is fed to the primary winding L1 at points A - B. The capacitive elements in the primary winding L1, for example in the form of capacitors C2, C2 'are dimensioned to produce a selected resonant frequency, e.g. in the range 13 MHz - 15 MHz, which corresponds to the antenna's transmission frequency band. A strong electric field is generated on the secondary winding 12 in said frequency range, which is radiated in particular from the ends C - D of the secondary winding. Resonant properties on the primary winding L1 can also be achieved by adjusting the position and dimensions of the winding conductor so that the winding itself has a suitable capacity, or the whole system of all winding conductors (primary and all secondary) has a suitable capacity, possibly including electromagnetic bonds.

The outputs of the secondary winding 12 can be terminated by a dipole with a length from 0 mm to 15 mm, or even more according to the spatial possibilities on the card and according to the required radiation efficiency. The length of the dipoles will be limited mainly by the dimensions of the card, it is advisable to keep the ends of the dipoles as far apart as possible. A magnetic field radiates from the elongated core, which will be primarily rod-shaped. A particularly strong electric field radiates from the ends of the secondary winding C - D, or from the dipoles. With the help of dipoles, the radiation of the electric field is improved, but in principle the radiation also occurs without a straight line of dipoles. In addition to the shape of stumps, dipoles can have other shapes and designs. The dipole can be in the form of variously shaped conductive surfaces, for example in the form of a conductive foil on the card surface. Various dielectric materials can be connected to the dipoles.

The electromagnetic field generated in the high-frequency transformer according to the invention has the ability to penetrate even small gaps in the spatial structure of the mobile communication device. Flat gaps, for example, between a card and a card slot, then between the battery body and an adjacent mobile body

With the K 288756 B6 phone, they are sufficient to penetrate the electromagnetic field out of the body of the mobile phone. The electromagnetic field radiated from the high-frequency transformer will be received on the other side of the communication channel by a conventional antenna, for example in the form of a POS terminal reader.

The antenna on the card in the form of a high-frequency transformer may have primary and secondary windings L1, L2 located on the core substantially coaxially. The windings can be separate, galvanically separated, or the high-frequency transformer can take the form of an autotransformer with one winding and taps of the primary and secondary circuits L1, L2. In this case, the windings will not be galvanically separated, which, however, does not create any major problem and, conversely, such a solution will simplify the production of the transformer.

The high frequency transformer will in principle be used to transmit a signal from the body of the removable memory card. In the opposite direction of communication, when the signal is received on a removable memory card, there is usually no problem with the intensity of the electromagnetic field, since in this direction, the transmitting antennas are not dimensionally limited. In principle, therefore, there is no need to specifically optimize the transmission path towards the card. The antenna may have an auxiliary winding L3 with an output E-F for receiving the signal, also in the form of a separate winding or in the form of taps of the autotransformer winding. An input amplifier and preferably also a capacitive element C1 tuned to a frequency of 12 MHz-16 MHz are connected to the outputs E-F of the auxiliary winding L3. From the point of view of optimizing the voltage ratios on the auxiliary winding L3, it is suitable if the center of the auxiliary winding L3 is grounded.

In another arrangement, the high frequency transformer may be supplemented by a classically wound, separate NFC antenna to receive a signal towards the removable card.

The windings L1, L2, L3 may at the same time form a shielding cover or may be electrically connected to the shielding cover.

It is advantageous for the length of the core, i.e. the dimension of the core in the direction of the winding axis, to be as large as possible within the dimensional possibilities of the card, thus achieving the longest possible magnetic field lines and closing only a small part of the magnetic flux in a short way. The core of the transformer will in particular have the shape of a straight rod of rectangular or round cross-section. The thickness of the core will be up to 1 mm, the width of the core will be up to 5 mm and the length of the core will usually be up to 15 mm, or even more depending on the space options on the card. The core ferrite should have a relative permeability in the range of 100 to 200. The permeability of the core will be set according to the technological possibilities of the maximum allowed magnetic saturation and the dimensional possibilities of the cross-section of the core. The term ferrite is to be understood as meaning any material which enhances the characteristics of the magnetic field properties.

The core can also have a bent course, for example in the shape of an L or a U, so that the longest possible distance between the ends of the core can be extended from the free positions possible for locating the high-frequency transformer. If a straight core is used on a núcroSD card, a rectangular cross-section up to 0.5 mm thick, up to 1 mm wide and up to 11 mm long will be suitable. Loops, windings may exceed the dimensions of the core and may be formed into various planar shapes, e.g. shape L, U and the like.

The orientation of the transformer core within the body of the removable card is not essential, but in principle it can be located on the edge of the removable card opposite the edge where the contact field of the card interface, then the ferrite core length does not exceed 11 mm. The dipoles can be guided at the edges of the removable memory card.

The maximum effective current from the output driver can be in the range of 0.1 - 0.2 Arms, where the maximum permissible current load is based on the standard interface of the card. The output driver is part of the output stage of the power amplifier. The current in the primary line A - B does not exceed 0.8 Arms. The input resistance of the low-noise input amplifier is greater than the minimum load value of the auxiliary winding L3, for example more than 10 kOhm The output resistance of the output driver at such setting and power supply on the nucc card may be less than 10 Ohm The specific impedance value may vary according to the set voltage ratio. currents and powers.

Since a high-frequency transformer with the structure and properties according to the invention does not even exist for use in other circuits, it may be advantageous from a manufacturing point of view if the high-frequency transformer consists on a printed circuit board or other substrate of several separate ferrite core coils. The coils are placed side by side to touch the cores and the coils are connected in series or in parallel, or in a series-parallel combination by the output conductors. On the printed circuit board, contact surfaces are prepared for this connection - connecting bridges, to which the inputs and outputs A, B, C, D, possibly also E, F are connected. The row of connected coils can be covered with a conductive cover, e.g. a metal cover that shields the magnetic field. A series of connected coils will be connected to the output driver as a whole, but in principle individual coils or groups of coils can be connected to separate output drivers.

One antenna system on a removable card according to the present invention may also include a plurality of high frequency transformers as described above. These transformers can be connected with different core orientations, in different combinations, in different axes and different phased.

The antenna on the card according to the invention has excellent transmission properties in the slots of various mobile communication devices, even when the slot is placed under the battery. Measurements have shown that a mobile phone with a removable memory card with an antenna according to the invention is able to establish a reliable NFC communication channel, without limiting the directional orientation of the mobile phone against the NFC reader. After

With K 288756 B6, the influence of different mobile phone designs on the reliability of the additionally created contactless channel is printed.

Overview of figures in the drawings

The solution is explained in more detail with the aid of Figures 1 to 11. The display scale used and the size ratio of the individual elements may not correspond to the description in the examples, and these scales and size ratios cannot be explained as narrowing the scope of protection.

In picture no. 1 is a diagram of the connection of an antenna to modulation and demodulation elements on a removable card in a circuit, where the antenna in the form of a high-frequency transformer is intended for both transmitting and receiving a signal.

In picture no. 2 is a circuit diagram of a transmitting antenna in the form of a high-frequency transformer and a conventional antenna for receiving a signal.

In picture no. 3 shows a circuit diagram of a high-frequency transformer with separate, galvanically separated windings.

In picture no. 4 above shows a section of the construction of a high-frequency transformer with separate, galvanically separated windings. At the bottom of the figure is a view of the arrangement of contacts on the planar surface of the antenna.

Picture no. 5 contains examples of four frequency settings of antennas in the NFC broadcast band. The resonant curve is shown by a solid line. The peak of the resonant curve represents the resonant frequency Ir of the antenna and may coincide with the transmit frequency f1 or the receive frequency f2, or may form only the peak of the curve which characterizes the usable frequency band. The transmission frequency fl is indicated by a dashed line. The frequency f2 of the reception is indicated by a dotted line. The y-axis shows the input current to the antenna.

Picture no. 6 is an axonometric view of an example of the construction of a high frequency autotransformer with one winding and symmetrically formed taps.

Picture no. 7 shows an example of the location of a dipole antenna on a removable microSD format memory card.

Picture no. 8 shows an example of another location of an antenna with dipoles on the edges of a removable microSD format memory card.

Picture no. 9 shows a high-frequency transformer composed on a PCB (printed circuit board) of six separate windings, which are connected in series and the cores touch each other.

Figure 10 is a top axonometric view and a bottom enlarged cross-section of a high-frequency transformer having a secondary winding formed in the form of a single coil as a magnetic cannon tube.

Figure 11 shows dipoles in the form of conductive surfaces on opposite outer surfaces of a microSD card, where the conductive surfaces have a spike-shaped edge adapted to better radiate an electric field.

Examples of embodiments of the invention

Example 1

In this example, according to Figures 1, 5, 6 and 7, the construction of a removable microSD memory card 1 is described, which has an antenna in its body in the form of a high-frequency transformer 2. The transformer 2 has three windings L1, L2, L3 formed by a single winding ferrite core 3. The windings are formed by symmetrically guided taps of the primary, secondary and auxiliary circuits L1, L2, L3. Transformer 2 thus takes the form of an autotransformer. The core 3 has the shape of a rod with a rectangular cross-section, in this example with a thickness of 0.5 mm, a width of 1 mm and a length of 5 mm. The windings L1, L2, L3 are not galvanically separated in this example.

The transmitted signal from the output driver 6 is fed to points A - B on the primary winding L1, to which the symmetrically connected capacitive elements C2, C2 'are tuned to a resonant frequency of 13.56 MHz. The electric field is radiated mainly from the ends C - D of the secondary winding L2, which in this example is terminated by two straight conductors with a length of 5 mm. This termination creates a dipole 4 enhancing the radiation of the electric field and can also affect the magnetic field. The winding in this example is formed by a conductor 5 with a rectangular cross-section of 70 μm x 30 μm and the spacing of the winding is approximately 30 μm

The auxiliary winding E - F is set to receive the signal radiated towards the removable card 1. A capacitive element C1 and an input amplifier 7 are connected to the outputs E-F. The center of the winding L3 is grounded.

The removable card 1 with the antenna according to this example is intended to be inserted into a mobile telephone. Thanks to this card, an additional NFC channel will be created in the mobile phone. The microSD card slot is under the battery.

S K 288756 B6

There are gaps between the metal parts of the phone and the battery, through which the electromagnetic field flows in virtually all possible directions.

The antenna according to this example has excellent transmission properties in the slots of various mobile communication devices, even when the slot is placed under the battery. The primary winding A - B has an inductance of 0.5 to 1.5 pH and a quality Q = 10 - 20 at a frequency of 13 - 15 MHz. The secondary winding C - D has an inductance of 5 - 10 pH at quality Q = 20 - 40 and a frequency of 13 - 14 MHz. Auxiliary winding E - F has an inductance of 50 - 100 nH at quality Q = 10 - 20.

Under the input conditions on the primary winding L1 with the values Uli = 36Vpp @ 14.4 MHz and Ili = = 700 mApp, the values on the secondary winding L2 are the values Ul2 = 1 lOVpp @ 14.4 MHz and Il2 = 0.12 mApp. The maximum value of the magnetic field in the ferrite core 3 is below 100 A / m

When transmitting the own signal, the values Ul3 = 10 Vpp @ 14.4 MHz are output at the output of the auxiliary winding L3.

Example 2

In this example according to Figures 2, 5, 8 and 9, the high-frequency autotransformer 2 is supplemented by a separate receiving antenna 8 for receiving the signal. This is in the form of a conventional flat NFC antenna, which replaces the function of the auxiliary winding L3 described in Example 1.

The high-frequency transformer 2 is formed of six separate coils 9 with a ferrite core 3, which are connected to a printed circuit board. The coils 9 are placed substantially as close together as possible so that they touch the cores 3. This creates a seemingly solid core 3, the existing air gaps between the cores 3 do not have a significant effect on the flux of the magnetic field. The array of six coils 9 is covered by a conductive, shielding cover, which improves the radiation of the electromagnetic field, forms a technological aid during assembly and improves the mechanical strength of the mounting. The shield is not shown in Figure 9.

The dipoles 4 are formed in the form of a conductive coating on the edges of the microSD removable card 1.

Example 3

In this example according to Figures 3, 4 and 5, the high-frequency transformer 2 is in the form of a transformer with three separate windings L1, L2, L3. On the ferrite core 3 of rectangular cross-section with relative permeability 125, the secondary winding L2 is first wound, which extends symmetrically to both edges of the core 3. After applying the insulating layer to the core 3 with the secondary winding L2, the primary winding L1 and the auxiliary winding L3 are wound. The operating frequency of the antenna is 14.4 MHz. The windings have flat contacts connected to a wider area of the outer surface of the antenna, especially for SMD mounting. The primary winding L1 with contact A - B has 8 conductor loops 5 and an inductance of approx. 540 nH ± 10%. The secondary winding L2 with outputs C - D has 46 conductor loops 5 and an inductance of 7 pH ± 10%. The auxiliary winding L3 with outputs E - F has 3 conductor loops 5 and an inductance of 72 nH ± 10%. The conductors 5 have a diameter of 50 urn and the pitch is 30 μm

Example 4

In this example according to Figures 5 and 11, the dipoles 4 are formed as conductive surfaces of a foil which is placed on opposite surfaces of a removable memory card L. The foil has an edge formed into sharp triangular protrusions. On the side where the surface of the removable card 1 is provided with a contact interface, the foil is located at the opposite end to the contacts. On the opposite surface of the removable card 1, the foil is placed on the other side. In Figure 11, this film, on the other hand, is indicated as dashed.

Example 5

In this example according to Figures 5 and 10, the secondary winding L2 is formed by only one loop, one thread having a conductor width 5 exceeding the length of the core 3. In essence, the thread is formed by bending a thin conductive sheet so that the "C" profile is not conductively closed by the arms. Inside the secondary winding L2, a core 3 with a primary winding LL is located. The secondary winding L2 also forms a shielding cover, which directs the flow of the magnetic field and it flows out of the ends of the tube of the secondary winding L2. In another example, the secondary winding L2 may have a plurality of coils of flat conductor 5 in a spiral, the individual layers being insulated from each other.

It is also possible to assemble an antenna system comprising two or even more high-frequency transformers 2 according to the examples in combination with each other. These transformers 2 can be connected with different orientations of the cores 3, in different combinations, in different axes and can be phased in different ways.

Industrial applicability

Industrial applicability is obvious. According to this solution, it is possible to industrially and repeatedly manufacture and use antennas placed directly on a removable memory card with high radiation capacity.

S K 288756 B6

List of reference marks

- Removable card

- high frequency transformer

- the core

- dipole

- driver

- output driver

- input amplifier

- receiving antenna

- coil

L1, L2, L3 inductance

C2, C2 ', C1 - capacitive elements

A - B inputs of the primary winding

C - D outputs of the secondary winding E - F outputs of the auxiliary winding fl - transmitting frequency f2 - receiving frequency

I (A) - input current to the antenna

F (MHz) - frequency ir - resonant frequency

PCB - printed circuit board

NFC - nearfield communication

Claims (22)

PATENT CLAIMS An antenna on a removable card (1) for creating an additional contactless communication channel of a mobile communication device, in particular a mobile telephone, wherein the removable card (1), in particular as a removable memory card (1), is intended to be inserted into an expansion slot of a mobile communication device, and wherein the signal transmitted from the antenna is received by standard receiving means, characterized in that the antenna is formed by a high-frequency transformer (2) with a ferrite core (3), with a primary winding L1 with inputs A - B and a secondary winding L2 with outputs C - D , the primary winding L1 is resonant tuned within the frequency band of the antenna, the primary winding L1 has less or the same number of conductor loops (5) as the secondary winding L2, the outputs C - D of the secondary winding L2 are connected empty, without contact closed load circuit. the signal is fed from the output driver (6) via inputs A - B to the primary winding LL Antenna according to claim 1, characterized in that it has at least two high-frequency transformers (2) with ferrite cores (3), the axes of the cores (3) being differently oriented. Antenna according to claim 2, characterized in that the high-frequency transformers (2) are differently phased. Antenna according to any one of claims 1 to 3, characterized in that the primary winding L1 is resonant tuned, preferably in the range 13 MHz to 15 MHz, by at least one capacitive element C2, C2 'connected to the primary winding L1 and / or by a corresponding capacitor the winding of the conductors (5) of the primary winding L1 itself, and / or by the capacitances of the conductors (5) of all the windings L1, L2, and / or by means of electromagnetic coupling with the environment. Antenna according to any one of claims 1 to 4, characterized in that the secondary winding L2 is formed by one winding of a flat conductor (5) into a tube with a "C" shape, the arms of the C profile are conductively unconnected, the primary winding L1 with the core (3) is inside the tube and the length of the tube corresponds to or exceeds the length of the core (3). Antenna according to any one of claims 1 to 4, characterized in that the secondary winding L2 is formed by winding the flat conductor (5) into a helically wound tube, the superimposed flat conductor layers (5) are conductively insulated, the primary winding L1 with core ( 3) is inside the tube and the length of the tube corresponds to or exceeds the length of the core (3). Antenna according to any one of claims 1 to 6, characterized in that the outputs C-D of the secondary winding L2 are terminated by a dipole (4), preferably with a length of up to 15 mm. Antenna according to claim 7, characterized in that the dipoles (4) are located on the edges of the removable memory card (1). Antenna according to claim 7, characterized in that the dipole (4) is formed by a conductive surface on the outer surface of the removable card (1), preferably the conductive surface has sharply terminated edges for radiating an electric field. Antenna according to any one of claims 1 to 9, characterized in that the output or both outputs of the secondary winding L2 are connected to ground and / or power supply, and / or to the interface of the removable card (1), and / or to another element on the removable card. (1). Antenna according to any one of claims 1 to 10, characterized in that the high-frequency transformer (2) has primary and secondary windings L1, L2 located coaxially on the core (3) and windings L1, L2 are separate, galvanically separated. Antenna according to any one of claims 1 to 5 and 7 to 10, characterized in that the high-frequency transformer (2) is an autotransformer with one winding and taps of the primary and secondary circuits L1, L2. Antenna according to any one of claims 1 to 12, characterized in that the high-frequency transformer (2) has an auxiliary winding L3 for receiving a signal towards the removable card (1), the auxiliary winding L3 being connected to an input amplifier (7), preferably capacitive element CL connected to auxiliary winding L3 Antenna according to claim 13, characterized in that the center of the auxiliary winding L3 is grounded. Antenna according to any one of claims 1 to 14, characterized in that it is complemented by a separate receiving antenna (8) for receiving a signal towards the removable card (1). Antenna according to any one of claims 1 to 15, characterized in that the core (3) has the shape of an elongated rod of rectangular or circular cross-section up to 1 mm thick, up to 5 mm wide and up to 15 mm long Antenna according to claim 16, characterized in that the core (3) has a rectangular cross-section up to 0.5 mm thick, up to 1 mm wide and up to 11 mm long. Antenna according to any one of claims 1 to 17, characterized in that the high-frequency transformer (2) is composed of a plurality of separate coils (9) with ferrite cores (3), the coils (9) being With K 288756 B6 placed side by side in contact with the cores (3) and the coil (9), the output conductors are connected in series and / or in parallel, and / or in series-in parallel. Antenna according to claim 18, characterized in that the coils (9) are covered by a common conductive shielding cover 5 Antenna according to any one of claims 1 to 19, characterized in that some of the windings L1, L2, L3 form a shielding cover, inside which there is a core (3) with other windings. Antenna according to any one of claims 1 to 18, characterized in that the high-frequency transformer (2) is arranged in a shielding housing with openings for radiating a magnetic field. Antenna according to claim 21, characterized in that some of the windings L1, L2, L3 are connected to the shielding cover