EP2798698B1

EP2798698B1 - An antenna on a removable card

Info

Publication number: EP2798698B1
Application number: EP12820938.4A
Authority: EP
Inventors: Miroslav Florek; Libor MAJER
Original assignee: SMK Corp
Current assignee: SMK Corp
Priority date: 2011-12-28
Filing date: 2012-12-27
Publication date: 2018-11-21
Anticipated expiration: 2032-12-27
Also published as: EP2798698A1; WO2013098784A4; SK288756B6; WO2013098784A1; SK500582011A3

Description

Field of invention

The invention refers to an antenna and a removable card (above all a memory card) that can be inserted into a slot of a mobile communication device such as a mobile phone, in which, due to its antenna, the removable card acts as hardware for additionally created contactless communication channel i.e. of the NFC (near field communication) type. The solution is intended mostly for use with payment applications designed primarily for mobile communication devices. In principle, however, the new emission method and the new type of transmitter, as these are described in this invention, can be used even with other applications and in other devices, above all in those, in which there is not sufficient space to enlarge the emitting antenna and in which the antenna is shielded by surrounding elements.

Present technology status

The placement of an antenna directly into a removable memory card that is designed to be inserted into a mobile communication device, is known from the published patent files e.g. DE 10252348 A1 , WO 03/043101 A3 . These publications describe a general use of an antenna on a card; however they do not contains its sufficient specification in cases, in which the removable memory card is shielded by surrounding parts of a mobile communication device i.e. a mobile phone. The published Logomotion patent applications describe the configuration of the antenna and of the individual layers of the removable memory card in order to set the antenna emitting and receiving features, so that it would be possible to establish a reliable communication channel even in cases when card slot is shielded in various ways. The technical task, defined in this way, lead us to create several technical solutions, which however lead to satisfactory results only in some mobile phones; subsequently the development followed the direction of larger, additional antennas in the mobile phone body outside the shielded areas. These additional antennas ( CN201590480 U ), e.g. in the form of stickers, can be connected to the basic antenna on the card in a contactless way; nevertheless, this kind of configuration remains non-universal and an average user may find the complexity using it awkward.
An antenna located directly on a removable card can be of very limited size. Mobile phones have card slots of the microSD format, a fact that substantially limits the size of the antenna that can be placed directly onto the card. In case a removable card is inserted into a very shielded slot, e.g. under a mobile phone battery, the card emitting conditions worsen. The usage of rectifying layers, foils has only a narrow, specific influence and it is not universal for purpose of usage in various mobile phone configurations.

The subject matter of the invention

The mentioned deficiencies are to a large extent eliminated by an antenna on a removable card, which is used to establish an additional contactless communication channel from a mobile communication device such as a mobile phone; the removable memory card being intended for insertion into the extending slot of a mobile communication device. The subject matter of the antenna described in this invention is based on the fact that the emitting antenna is created out of a high-frequency transformer with oblong ferrite kernel with resonantly tuned primary winding L1. The signal emitted from the antenna according to this invention is received by a standard receiving device within a given frequency range. E.g. in case the antenna is intended for a NFC transmission between a mobile phone and a POS terminal reader, the antenna on the side of the mobile phone will be in the form of a high-frequency transformer with a ferrite kernel while on the POS terminal NFC reader side it will be in the form of a common receiving antenna. It is exactly the conformity with existing, standard devices that is important since it is not necessary to replace hardware that is widely used on the side of POS terminals. The change in mobile phone hardware is reached exactly and only by inserting the removable card (primarily of the microSD format) into the existing slot of the mobile phone.
The extending slot of the mobile communication device is a slot for the card that does not influence the basic communication function of the device; so, it is mainly, however, not exclusively a slot for a removable memory card of the microSD format.
The resonant tuning of the primary winding L1 can be achieved by using capacity elements, e.g. using a capacitor or using two capacitors symmetrically connected into a circuit that connected to the primary winding L1. The resonant tuning can be achieved even by a suitable coiling of the primary winding L1 through which a required capacity of the winding itself is reached. The resonant tuning can be reached even through a connection with the secondary winding L2 on which the capacity is suitably dimensioned in accordance with the L1 and L2 winding transformation ratio or even by using an electromagnetic connection with the surrounding elements.
The output of the secondary winding L2 is left without load; it does not have a contact load, which means that on the outputs of the secondary winding L2, no contact ohm circuit is connected and the voltage at the output can reach values up over 100Vpp. The absence of load on the output of the secondary winding L2 is a situation when there is no closed circuit either created or connected via contacts through which the current would flow in the secondary winding L2. In reality, the load can exist in the form of impedance emitted into the environment (air + neighboring elements) or in the form of other electromagnetic connections to the surrounding elements. This kind of indirect load can exist in the real environment of the removable card that is inserted into the slot of a mobile communication device; however it will not have a significant influence on electrical voltage on the output of the secondary winding L2. The output or even both outputs from the secondary winding L2 can be connected to other card parts e.g. those for grounding, powering or other parts of the card or through an interface to other parts in the mobile communication device; however, the elements connected in this way do not create a circuit that closes the secondary winding L2 in a contact way. Through this connection with surrounding parts, the current, and subsequently even magnetic part of the field, can be created in the secondary winding L2. The interconnection of other parts with the output of the secondary winding will engage even other metal parts of the mobile communication device into the emission of the electric field and subsequently even of the magnetic field.
The usage of a high frequency transformer that uses the open circuit secondary winding L2 as an emitting element provides us with various possibilities of L1 and L2 winding configuration. By selecting the L1 and L2 winding ratio we can set different ratio of magnetic and electric parts within the emitted electromagnetic field. The primary winding L1 can have a smaller number of conductor loops than the secondary winding L2. The emitted signal is brought to the primary winding L1, the electric field of the emitted signal is emitted through outputs C-D of the secondary winding L2 and the magnetic field of the emitting signal flows through the ends of the kernel. In this kind of configuration a strong electromagnetic field is created since the electric part is amplified by the influence of a transformer and the magnetic part is amplified by the influence of the ferrite kernel. The secondary winding L2 does not take part explicitly in the creation of the magnetic part of the field since practically no current goes through this winding when in a configuration without a relevant load.
The secondary winding L2 can be formed even by one coiling i.e. with one incomplete coiling. In this kind of configuration the primary winding L1 does not have smaller number of conductor loops than the secondary winding L2. The coiling of the secondary winding L2 can be in the form of a flat conductor that is bent into the form of a pipe that compasses the isolated coiling of the primary winding L1 with the ferrite kernel. In the transverse plane, the pipe, which is in the in the form of a letter "C", is divided by an oblong dividing gap. The coiling made out of e.g. conductive foil or from a metal plate can cover the entire length of the ferrite kernel and in the same time it shields and directs the flux of the magnetic field. This coiling of the secondary winding L2 can represents a magnetic cannon that directs the field in such a way that this one is emitted from the pipe mouth very strongly. The wave-guiding pipe is in reality created and connected as a coiling of the secondary winding L2. This configuration enables to optimize the course of lines of power of the magnetic field when close to individual conductors of the coiling of the primary winding L1. The pipe can have different ground plans e.g. in the shape of the letters L or M. The secondary winding L2 can be even formed by a spiral coiling of the flat conductor so that this one is in the form of a pipe with several coil loops. The layers that are on top of each other are isolated in between the individual layers. The spiral coiling can have several layers, the connection of the output driver with primary winding L1 goes through the openings in between these layers. The flat material of the conductor used for the coiling should not shield the magnetic field in the first layer so that even subsequent layers (the outer layers) could be in the kernel magnetic field. The material can be non-homogeneous or perforated or it can encompass a structure of conductive paths. Subsequently, several layers on top of each other create even the magnetic cannon effect.
The signal emitted from the output driver is brought to the first winding L1 in points A-B. The capacity elements in the first winding L1, e.g. in the form of C2, C2' capacitors; are dimensioned so that they can create the selected resonant frequency e.g. between 13 MHz - 15 MHz, which corresponds to the band of the antenna emitting frequency. A strong electric field that is emitted by the C-D ends of the secondary winding is created on the secondary winding L2 within the mentioned frequency range. The resonant features on the primary winding L1 can be reached by setting the conductor location and size so that the winding itself has a suitable capacity or the entire set of the conductor windings (primary and all secondary ones) has the suitable capacity, possibly even including electromagnetic connections of the surrounding parts.
The outputs of the secondary winding L2 can end in dipole having the length between 0 mm and 15 mm, possibly even more depending on spacial possibilities on the card and depending on the required emission effect. The length of dipoles is limited above all by the card size; it is suitable for the dipoles to be away one from another as much as possible. The oblong kernel (mostly in the shape of a rod) emits magnetic field. A very strong electric field is being emitted from the ends of the secondary winding C-D, or possibly from dipoles. The emission of the electric field is improved by dipoles, however in principle the field is emitted even without dipoles - without its conductive outputs. Dipoles can be in the form of stubs or other shapes and other forms. Dipole can be in the form of variously shaped conductive surfaces, e.g. in the form of conductive foil on the card's surface. Various dielectrical materials can be connected to dipoles.
The electromagnetic field created in a high-frequency transformer according to this invention can permeate through even small gaps in the mobile communication device spacial structure. The flat gaps e.g. between the card and the card slot or between the battery body and the adjacent mobile phone body are sufficient for the electromagnetic field to emanate out of the mobile phone body. The electromagnetic field emitted from the high-frequency transformer will be received on the second side of the communication channel by a common antenna, e.g. in the form of POS terminal reader.
The antenna in the form of a high-frequency transformer that is on the card can have the primary and the secondary winding L1, L2 placed coaxially. The windings can be independent, galvanically separate or the high-frequency transformer can be in the form of an autotransformer with one winding and bifurcations of the primary and secondary circuit L1, L2. In that kind of case, the windings will not be galvanically separate, which however is not a problem; on the contrary, this kind of solution will simplify the production of a transformer.
The high-frequency transformer will be basically used to send signal from the removable memory card body. The communication in the opposite direction, when the signal is being received by the removable memory card, does not normally present a problem with the intensity of the electromagnetic field since antennas emitting in this direction are not limited in size. Therefore, in principle it is not necessary to optimize the transmission path in the direction towards the card. The antenna can also have an auxiliary winding L3 with outputs E - F for reception of signal, which can be both in the form of independent winding or in the form of auto-transformer winding bifurcations. The input amplifier and preferably also the C1 capacity element tuned to the frequency of 12 MHz -16 MHz are connected to the E-F outputs of the auxiliary L3 winding.
From the point of view of voltage ratio optimalization on the auxiliary winding L3, it is suitable if the center of the L3 auxiliary winding is grounded.
In a different configuration the high-frequency transformer can be supplemented with an independent NFC antenna that is coiled in a standard way; this antenna is used to receive signal in the direction towards the removable card.
The winding L1, L2, L3 can also create a shielding cover or it can be connected to a shielding cover electrically.
It would be suitable if the kernel length (the parameter of the kernel in direction of winding axes) was as long as possible within the card size possibilities. This would enable to have the longest magnetic field lines of power and only the smaller part of the magnetic flow would be closed in short lines of power within the phone. The transformer kernel will be in the shape of a rod of rectangular or round cross-section. The kernel thickness will be of up to 1 mm, the width will be of up to 5 mm and the length of the kernel will be mostly up to 15 mm or more depending on the spatial possibilities on the card. The kernel ferrite should have a relative permeability between 100 and 200. The permeability of the kernel will be set according to the technological possibilities of maximally permitted saturation and size possibilities of the kernels cross section. The term ferrite must be understood as any material that strengthens the features and properties of the magnetic field.
The kernel can even be bent, e.g. in the shape of L or U so it would be possible to form the longest distance possible between the kernel ends for the placement of the high-frequency transformer. In case a direct kernel on the microSD card is used one with a rectangular cross section would be suitable - thickness up to 0,5mm, width up to 1 mm and length up to 11mm. The loops, coils of the winding can exceed the kernel parameters and they can be shaped into various ground view shapes - e.g. shape L, U and similarly.
It is not important how the transformer kernel is oriented within the removable memory card; in principle it can be placed at the edge of the removable card that is opposite to the edge with card interface contact field. That being the case, the length of ferrite kernel will not exceed 11 mm. Dipoles can be lead along the edges of the removable memory card.
The maximal effective current from the output driver can be in the range from 0,1 to 0,2 Arms, while the maximal allowed current load is set by the card interface standard. The output driver is part of the final level of power amplifier. The current in the primary coil A-B does not exceed the 0,8 Arms value. The input resistance of a low-noise input amplifier is higher than the minimal load value of the auxiliary winding L3, e.g. more than 10kOhm. The output resistance of the output driver in case of this kind of configuration and powering on the microSD card can be lower than 10 Ohm. The specific value of impedance can be changed depending on the preset voltage, currents and performances ratio.
Since the high-frequency transformer with the structure and features according to this invention does not exist, not even for use in different configurations, it could be advantageous from the production point of view if the high-frequency transformer is made out several independent coils with ferrite kernels on a printed circuit or other substrate. The coils are placed next to each other, kernels touching and the coils are connected in series circuits or parallel circuits or series-parallel combination circuits by its conductor outputs. Contact areas - interconnecting bridges are prepared on the circuit board for this connection. Inputs and outputs A, B, C, D possible even E, F are connected to these contact areas. The row of interconnected coils can be covered by a conductive cover, e.g. metal cover that shields the magnetic field. The row of interconnected coils will be connected to the output driver as one unit but in principle, individual reels or groups of reels can be connected to special output drivers.
One antenna set on the removable card as described in this invention can encompass several high frequency transformers according to the above mentioned description. These transformers can be connected with variously oriented kernels, in various combinations, in different axes and with different phases.
The antenna on the card according to this invention has excellent transmission features in slots of various mobile communication devices and that even if the slot is located under a battery. The measurements proved that the mobile phone with a removable memory card with an antenna according to this invention can create a reliable NFC communication channel while it is not important how the phone is placed to the NFC reader. The influence of different mobile phone constructions on the reliability of the additionally created contactless channel is suppressed.

Figures

The solution is explained in more detail in the figures 1 to 11. The used scale and the size ratio of individual elements does not have to correspond with the description in examples and the depicted size measurements cannot be considered as narrowing the scope of protection.
On the figure 1 there is a scheme displaying how the antenna is connected to modulation and demodulation elements on the removable card in the configuration, in which the antenna that is in the form of a high-frequency transformer is intended for both emission and reception of a signal.
On the figure 2 there is a scheme displaying the emitting antenna in the form of a high-frequency transformer and the common antenna for the reception of the signal. On the figure 3 there is a scheme showing the configuration of a high-frequency transformer with independent galvanically separate windings.
The upper part of the figure 4 displays the cross-section of the high-frequency transformer construction with independent galvanically separate windings. The lower part of the figure displays how the contacts are placed on the antenna flat surface.
Figure 5 contains examples of four frequency settings of the antenna in the NFC emitting band. The resonance curve is displayed in full line. The peak of the resonance curve is the resonance frequency f_R of the antenna and it can be identical to the emitting f1 frequency or to the f2 receiving frequency or it can only form the peak of the curve that features the used bands of frequencies. The f1 emitting frequency is shown in broken line. The receiving frequency f2 is shown in dash dot line. The y axis represents the input current into the antenna.
The figure 6 is an axonometric view on an example of how the high-frequency auto-transformer with one winding and with symmetrically created bifurcations is constructed.
The figure 7 displays the example of how the antenna with dipoles is placed on the removable microSD memory card.
Figure 8 shows an example of a different placement of the antenna with dipoles on the edges of the removable microSD memory card.
Figure 9 displays a high-frequency transformer based on a PCB (printed circuit board) board made from six independent windings that are connected in series and that have kernels that are in contact with one another.
In the upper part of the figure 10 there is an axonometric view and in the lower part there is a magnified cross-section of a high-frequency transformer that has a secondary winding created in the form of one coiling forming magnetic cannon pipe.
Figure 11 displays dipoles in the form of conductive areas on the opposite outer surfaces of the microSD card, where the conductive areas have edges in a zigzag shape that is adjusted for better emission of the electric field.

Examples

Example 1

In this example depicted in the figures 1, 5, 6 and 7 there is a description of removable memory card 1 configuration. The removable memory card 1 is in the microSD format and within its body it contains an antenna in the form of a high-frequency transformer 2. The transformer 2 has three windings L1, L2, L3 that are physically created by one coil on the kernel 3 made of ferrite. The windings are created by symmetrically going bifurcations of the first, secondary and auxiliary circuit L1, L2, L3. So, the transformer 2 is in the form of an auto-transformer. The kernel 3 is in the shape of a rod with rectangular cross-section; in this example it is 0,5 mm thick, 1 mm wide and 5 mm long. The windings L1, L2, L3 are not galvanically separate in this example.
The emitted signal from the output driver 6 is brought to points A-B on the primary winding L1, to which the capacity elements C2, C2' that are tuned to the resonance frequency of 13,56 MHz are symmetrically connected. The electrical field is emitted from the C-D ends of the secondary winding L2, which in these examples is ended by two direct conductors that are 5 mm long. This ending creates a dipole 4 which strengthens the emission of the electrical field and which can also influence the magnetic field. The winding in this example is formed by a conductor 5 with a rectangular cross-section of 70 um x 30 um and the gaps between the windings are approx. 30 um.
The auxiliary winding E-F is set to receive the signal emitted in direction towards the removable card 1. The capacity element C1 and the input amplifier 7 are connected to the outputs E-F. The center of the L3 winding is grounded.
The removable card 1 with an antenna according to this example is intended for insertion into a mobile phone. Thanks to this card an additional NFC channel is created in the mobile phone. The slot for the microSD card is under the battery. Between the metal elements of the phone and the battery there are gaps through which the electromagnetic fields flow basically in all possible directions.
The antenna according to this example has excellent transmission features in slots of different mobile communication devices even if the slot is located under the battery. The primary winding A-B has induction of 0,5 - 1,5 µH and quality Q = 10 -20 in case of 13 - 15 MHz frequency. The secondary winding C-D has induction 5 - 10 µH and quality Q = 20 - 40 in case of 13 - 14 MHz frequency. The auxiliary winding E-F has induction of 50 - 100 nH and quality Q = 10 - 20.
In case the input conditions on the primary winding L1 have values U_L1 = 36Vpp@14,4 MHz and I_L1 = 700 mApp, the secondary winding L2 has values U_L2 = 110Vpp@14,4 MHz and I_L2 = 0,12 mApp, The maximal value of the magnetic field in the ferrite kernel 3 is under 100A/m.
In case of transmitting its own signal the values on the output of the auxiliary winding L3 are U_L3 = 10Vpp@14,4 MHz.

Example 2

In this example according to figures 2, 5, 8 and 9 there is a high-frequency auto-transformer 2 that is complemented with a receiving antenna 8 for the reception of a signal. This antenna is in the form of a common flat NFC antenna that substitutes the function of the auxiliary winding L3 described in example 1.
The high-transformer 2 is made out of the six independent coils 9 with a ferrite kernel 3, which are connected to a printed circuit. The coils 9 are placed practically as close to each other as possible so their kernels 3 would touch. This creates a compact kernel 3; existing air gaps between the kernels 3 do not have any significant influence on the flux of the magnetic field. The field of six coils 9 is covered by a conductive, shielding cover that improves the emission of the electromagnetic field. This cover is technologically helpful during assembly and it increases mechanical stability of the configuration. The shielding cover is not shown on the figure 9.
The dipoles 4 are created by a conductive paint on the edges of the removable microSD 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 independent windings L1, L2, L3. The secondary winding L2 is coiled first round the ferrite kernel 3 of rectangular cross section with relative permeability 125. This secondary winding L2 runs symmetrically to both ends of the kernel 3. After the isolation layer is applied to the kernel 3 with the secondary winding L2, the L1 primary winding and the auxiliary winding L3 are applied. The operation frequency of the antenna is 14,4 MHz. The windings have flat contacts brought out to the wider area of the outer surface of the antenna for the purpose of SMD assembly. The primary winding L1 with contacts A-B has 8 loops of the conductor 5 and induction of approx. 540nH +-10%. The secondary winding L2 with outputs C-D has 46 loops of the conductor 5 and induction of approx. 7µH +-10%. The auxiliary winding L3 with outputs E-F has 3 loops of the conductor 5 and induction of approx. 72 nH +-10%. The conductors 5 have 50um in diameter and windings are 30 um apart.

Example 4

In this example according to figures 5 and 11, the dipoles 4 are created as conductive facettes made out of foil. These facettes are located on the opposite surfaces of the removable memory card 1. The foil edge is of zigzag shape - made out of sharp triangles. On the surface, on which there is contact interface on the removable memory card 1 the foil is located next to the edge opposite to the contacts. On the opposite surface of the removable memory card 1 the foil is located directly opposite the contacts. On the figure 11, this foil that is opposite the contacts on the other surface is shown in broken lines.

Example 5

In this example according to the figures 5 and 10 there is a secondary winding L2 created by only one loop, one coil, which has the width of the conductor 5 that exceeds the length of the kernel 3. Basically, the coil is formed by rounding the thin conductive metal sheet, so that the "C" profile would not be closed conductively. Within the secondary winding L2 there is a kernel 3 with a primary winding L1. The secondary winding L2 also forms a shielding cover that directs the flux of the magnetic field which then comes out of the secondary winding L2 pipe ends. In another example the secondary winding L2 can have several coils of flat conductor 5 formed into a spiral while the individual layers are isolated one from another.
It is also possible to build an antenna set encompassing two or even more high-frequency transformers 2 combining the above listed examples. These transformers 2 can be connected with differently oriented kernels 3 in various combinations, in various axes and they can also be mutually phased.

Industrial usability

The industrial usability is obvious. This solution enables to produce, industrially and repeatedly, an antenna with high emitting power that is located directly on a removable memory card.

List of related symbols

1- removable card
2- high-frequency transformer
3- kernel
4- dipole
5- conductor
6- output driver
7- input amplifier
8- receiving antenna
9- coil
L1, L2, L3 inductions
C2, C2', C1 - capacity elements
A - B inputs of primary winding
C - D outputs of secondary winding
E - F outputs of auxiliary winding
f1 - emitting frequency
f2 - receiving frequency
I (A) - input current into antenna
F (MHz) - frequency
f_R- resonant frequency
PCB - printed circuit board
NFC - near field communication

Claims

An antenna on a removable card (1) for the creation of an additional contactless communication channel of a mobile communication device such as a mobile phone, where the removable card (1) i.e. a removable memory card (1) is intended for insertion in an extending mobile communication device slot and where a signal emitted from the antenna is received by a standard receiving device characterized by the reacts that the antenna is formed by a high-frequency transformer (2) with a oblong ferrite kernel (3), with the primary winding L1's inputs A - B and a secondary winding L2's outputs C - D , the oblong ferrite kernel (3) is located in parallel to the surface of the removable card (1), the primary winding L1 is resonantly tuned within the antenna frequency band, the primary winding L1 has a smaller or equal number of conductor (5) loops than the secondary winding L2, the outputs C-D of the secondary winding L2 are in open circuit, without a contact closed load circuit, and while an emitted signal is brought from an output driver (6) to inputs A - B of the primary winding L1, the electric field of the emitted signal is emitted mainly through the outputs C - D of the secondary winding L2 and the magnetic field of the emitted signal runs mainly through the kernel (3) ends.
An antenna according to the claim 1, further characterized by the fact that it contains at least two high-frequency transformers (2) with ferrite kernels (3) while the axes of the kernels (3) are oriented differently, preferably the high-frequency transformers (2) being phased differently.
An antenna according to the claim 1 or 2, further characterized by the fact that the primary winding L1 is resonantly tuned, preferably in the range between 13 MHz to 15 MHz, through at least one capacity element C2, C2' that is connected to the primary winding L1 and/or through a corresponding capacity of the primary winding L1 conductor (5) windings itself and/or through capacity of conductors (5) of all windings L1, L2 and/or through electromagnetic connections with its surroundings.
An antenna according to any of the claims 1 to 3, further characterized by the fact that the secondary winding L2 is formed from one coiling of the flat conductor (5) that is in the shape of a pipe with "C" form profile, the arms of this "C" profile being not conductively connected, the primary winding L1 with a kernel (3) being within the pipe and the length of the pipe corresponding to or exceeding the length of the kernel (3).
An antenna according to any of the claims 1 to 3, further characterized by the fact that the secondary winding L2 is formed by a coil of flat conductor (5) that is coiled spirally into a pipe; the flat conductor (5) layers being put one above the other and conductively isolated; the primary winding L1 with a kernel (3) being within the pipe and the length of the pipe corresponding to or exceeding the length of the kernel (3).
An antenna according to any of the claims 1 to 5, further characterized by the fact that the outputs C-D of the secondary winding end in dipole (4), preferably the dipole (4) being placed on the edge of the removable memory card (1).
An antenna according to any of the claims 1 to 5, further characterized by the fact that the outputs C-D of the secondary winding end in dipole (4); whereby the dipole (4) is formed by a conductive facette on the outer surface of the removable memory card (1); and the conductive surface has preferably sharp edges for the emission of the electric field.
An antenna according to any of the claims 1 to 7, further characterized by the fact that the output or both outputs of the secondary winding L2 are connected to the grounding and/or the powering and/or with a removable card (1) interface and/or with another element on the removable card (1).
An antenna according to any of the claims 1 to 8, further characterized by the fact that the high-frequency transformer (2) has a primary and secondary winding L1, L2 that is placed on the kernel (3) coaxially and the windings L1, L2 are independent, galvanically separate.
An antenna according to any of the claims 1 to 3 and 6 to 9 further characterized by the fact that the high-frequency transformer (2) is an auto-transformer with one winding and bifurcations of the primary and secondary circuit L1, L2.
An antenna according to any of the claims 1 to 10, further characterized by the fact, that the high-frequency transformer (2) has an auxiliary winding L3 for the reception of a signal in direction towards the removable card (1), the auxiliary winding L3 being connected with the input amplifier (7); the capacity element C1 being preferably connected to the auxiliary winding L3, preferably the center of the auxiliary winding L3 being grounded.
An antenna according to any of the claims 1 to 11, further characterized by the fact, that the kernel (3) is in the form of an oblong rod with a rectangular or round cross-section with thickness up to 1 mm, width of up to 5 mm and length of up to 15 mm, preferably the kernel (3) having a rectangular cross-section with thickness up to 0,5mm, width of up to 1 mm and length of up to 11 mm.
An antenna according to any of the claims 1 to 12, further characterized by the fact, that the high-frequency transformer (2) is made out of several independent coils (9) with ferrite kernels (3), coils (9) being placed next to each other so that the kernels (3) touch and the coils (9) are outputs of conductors connected in series circuit and/or parallel circuit and/or series-parallel circuit.
An antenna according to any of the claims 1 to 13, further characterized by the fact that the high-frequency transformer (2) is within a shielding cover with openings for the emission of the magnetic field, preferably the shielding cover being interconnected with some of the windings L1, L2, L3.
An antenna according to any of the claims 1 to 14, further characterized by the fact that some of the windings L1, L2, L3 form a shielding cover inside of which there is a kernel (3) with other windings.