EP0371562A1 - Coil antenna device - Google Patents
Coil antenna device Download PDFInfo
- Publication number
- EP0371562A1 EP0371562A1 EP89203011A EP89203011A EP0371562A1 EP 0371562 A1 EP0371562 A1 EP 0371562A1 EP 89203011 A EP89203011 A EP 89203011A EP 89203011 A EP89203011 A EP 89203011A EP 0371562 A1 EP0371562 A1 EP 0371562A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- loop
- antenna device
- symmetry
- loop antenna
- junctions
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/12—Supports; Mounting means
- H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
- H01Q1/2208—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems
- H01Q1/2216—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems used in interrogator/reader equipment
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q5/00—Arrangements for simultaneous operation of antennas on two or more different wavebands, e.g. dual-band or multi-band arrangements
- H01Q5/30—Arrangements for providing operation on different wavebands
- H01Q5/307—Individual or coupled radiating elements, each element being fed in an unspecified way
- H01Q5/342—Individual or coupled radiating elements, each element being fed in an unspecified way for different propagation modes
- H01Q5/35—Individual or coupled radiating elements, each element being fed in an unspecified way for different propagation modes using two or more simultaneously fed points
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q5/00—Arrangements for simultaneous operation of antennas on two or more different wavebands, e.g. dual-band or multi-band arrangements
- H01Q5/50—Feeding or matching arrangements for broad-band or multi-band operation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
Definitions
- This invention relates to a loop antenna device for a two-frequency electromagnetic detection system, such device serving to generate an electromagnetic interrogation field for detecting responders comprised by said system.
- Loop antennas for electromagnetic detection systems serving to generate an interrogation field for detecting responders associated with the system are known in the art.
- One known antenna of this kind is, for example the single loop antenna, the antenna coil of which has the shape of an O.
- Another known loop antenna is eight-shaped.
- An eight-shaped loop antenna has the advantage over and above the O-shaped antenna that it has a minimum sensitivity to interfering external radiofrequency signals. As a consequence, the risk of picking up spurious signals is quite small.
- the radiation to the so-called distant field is minute, so that there is little chance of interference with other transmitting and/or receiving set-ups.
- One disadvantage of the known loop antennas is that they are only suitable for one single pre-determined signal frequency or for a single pre-determined signal frequency range.
- Two-frequency detection systems it is desirable to have an antenna that is suitable for two different frequencies (or frequency ranges).
- Two-frequency systems are used, for example, to detect attempts at tampering with a responder.
- the first signal frequency serves to detect the presence of a responder in an interrogation zone
- the second signal frequency serves to detect fraud with a responder.
- a system is described, for example, in US-A-4,742,341. It is also possible, to use a first frequency for detection purposes and a second frequency for the transfer of energy to a responder, for example, for charging a power accumulator of a responder.
- antennas for two frequencies are produced by using for example two antenna coils which are alternately connected in a parallel and a non-parallel configuration for given periods of time.
- the field of operation of the antenna is changed periodically between two predetermined frequencies or frequency ranges.
- each change in frequency will cause a transitional period during which a responder cannot be detected, or fraud with a responder cannot be detected, or a power accumulator of a responder cannot be charged. Also, special switching means are required.
- a loop antenna device of the above kind is characterized by comprising a closed loop built up of four adjoining sections having substantially equal impedances, the junction between each pair of adjoining sections together with the junction between the complementary pair of adjoining sections forming a connection port so that two connection ports are provided which in operation are available for two independent signals having different frequencies.
- detection system includes identification systems, which have responders detected similarly to the responders of detection systems.
- responders of an identification system and those of a detection system is in fact that the responders of an identification system when detected can additionally be individually recognized by a coded signal.
- Fig. 1 shows schematically an O-shaped antenna coil 1 with two terminals 2 and 3.
- Such an antenna coil after being tuned with, for example, a suitable capacitor, is only suitable for a single frequency or a single frequency range. Also, an O-shaped antenna is sensitive to spurious signals.
- Fig. 2 illustrates schematically an eight-shaped antenna 4 with two superimposed, substantially congruent loops 5 and 6 and two junctions 7,8 located on an axis of symmetry 9 of these loops.
- Such eight-shaped antennas are rather insensitive to interference by external radio signals and provide minimum radiation in the distant field.
- These eight-shaped antennas are also only suitable, after being tuned, to function at a single pre-determined frequency or a single predetermined frequency range.
- Fig. 3 shows schematically an embodiment of an antenna configuration according to the present invention.
- the loop antenna device shown comprises a loop 10, which is square in this example, and has four vertices A, B, C and D. From the vertices, branches 11,12,13 and 14 extend inwardly, coinciding with the diagonals of the square and terminating in two sets of connection points 31,33 and 32,34, each set of connection points forming a connection port.
- an eight-shaped antenna can be constructed in two ways. Unlike the eight-shaped antenna of Fig. 2, there are now two axes of symmetry joining the vertices of the square. The axes of symmetry are perpendicular to each other. The two eight-shapes in the square are turned through 90° relative to each other.
- the first antenna consists of two halves, i.e., triangle ABC and triangle ADC, which halves are separated by axis of symmetry AC. Rotation through 90° gives the second antenna, consisting of halves BCD and BAD with axis of symmetry BD.
- the eight-shaped antennas are not electrically coupled together.
- the operation of the antenna configuration is as follows.
- the first eight-shaped antenna is fed by connecting a source of A.C. voltage between terminals or connection points 31 and 33, which together form a connection port.
- A.C. voltage Through the application of the A.C. voltage, a current I1 will start to run. At the vertices A and C, this current will be equally distributed over branches ABC and ADC.
- the impedances of the antenna sections AB, BC, AD and DC are all identical, the potentials in points B and D will be equal to each other. As a consequence, there can be no difference in voltage between connection points 32 and 34. Also, no voltage can be generated through induction.
- connection points 32 and 34 If, similarly, a voltage is applied between connection points 32 and 34, then, as a result of the symmetrical construction, no voltage differential is formed between connection points 31 and 33. Therefore, if a voltage is applied to the four connection points, two antennas are active which, electrically, are fully uncoupled from each other.
- the two antennas can generate different resonant frequencies by means, for example, of capacitors.
- a capacitor not shown can be applied across connection point 31 and 33, as a result of which the resonance frequency of the first eight-shaped antenna will assume a value of 2 MHz, while across connection points 32 and 34 a capacitor can be provided which leads to a resonance frequency of, for example, 8 MHz of the second eight-shaped antenna.
- the resonance frequencies can be freely selected.
- the antenna device illustrated in Fig. 3 forms two electrically independent antennas which, however, mechanically are virtually fully integrated and essentially use the same conductors.
- connection points 31,33 and 32,34 could be closer to vertices A.C and B.D respectively, or even coincide with them. In that case, except for the location of the connection points, the two antennas are physically fully identical.
- sections AB, BC, CD and DA may have any curved and/or bent shape.
- the important feature is that the impedances of the sections should be equal, and that the magnetic fields caused by the A.C. currents which in operation flow through two successive sections (e.g. AD and DC) eliminate each other at an intermediate branch (e.g. 14,13).
Landscapes
- Near-Field Transmission Systems (AREA)
- Details Of Aerials (AREA)
- Magnetic Resonance Imaging Apparatus (AREA)
- Aerials With Secondary Devices (AREA)
- Burglar Alarm Systems (AREA)
- Radar Systems Or Details Thereof (AREA)
- Variable-Direction Aerials And Aerial Arrays (AREA)
Abstract
Description
- This invention relates to a loop antenna device for a two-frequency electromagnetic detection system, such device serving to generate an electromagnetic interrogation field for detecting responders comprised by said system.
- Loop antennas for electromagnetic detection systems, serving to generate an interrogation field for detecting responders associated with the system are known in the art. One known antenna of this kind is, for example the single loop antenna, the antenna coil of which has the shape of an O. Another known loop antenna is eight-shaped. An eight-shaped loop antenna has the advantage over and above the O-shaped antenna that it has a minimum sensitivity to interfering external radiofrequency signals. As a consequence, the risk of picking up spurious signals is quite small. Also, with an eight-shaped antenna coil, the radiation to the so-called distant field is minute, so that there is little chance of interference with other transmitting and/or receiving set-ups.
- One disadvantage of the known loop antennas is that they are only suitable for one single pre-determined signal frequency or for a single pre-determined signal frequency range.
- For two-frequency detection systems, however, it is desirable to have an antenna that is suitable for two different frequencies (or frequency ranges). Two-frequency systems are used, for example, to detect attempts at tampering with a responder. In such a system, the first signal frequency serves to detect the presence of a responder in an interrogation zone, and the second signal frequency serves to detect fraud with a responder. Such a system is described, for example, in US-A-4,742,341. It is also possible, to use a first frequency for detection purposes and a second frequency for the transfer of energy to a responder, for example, for charging a power accumulator of a responder.
- According to the prior technique, antennas for two frequencies are produced by using for example two antenna coils which are alternately connected in a parallel and a non-parallel configuration for given periods of time. The field of operation of the antenna is changed periodically between two predetermined frequencies or frequency ranges.
- When two frequencies are used and the system is alternately adjusted to one and the other frequency, each change in frequency (range) will cause a transitional period during which a responder cannot be detected, or fraud with a responder cannot be detected, or a power accumulator of a responder cannot be charged. Also, special switching means are required.
- It is an object of the present invention to overcome the disadvantages outlined above and, in general, to provide an effective and simple loop antenna device for a two-frequency electromagnetic detection system.
- For this purpose, according to the present invention, a loop antenna device of the above kind is characterized by comprising a closed loop built up of four adjoining sections having substantially equal impedances, the junction between each pair of adjoining sections together with the junction between the complementary pair of adjoining sections forming a connection port so that two connection ports are provided which in operation are available for two independent signals having different frequencies.
- It is noted that the term "detection system" as used herein includes identification systems, which have responders detected similarly to the responders of detection systems. The only difference between responders of an identification system and those of a detection system is in fact that the responders of an identification system when detected can additionally be individually recognized by a coded signal.
- One embodiment of the invention will now be described, by way of example, with reference to the accompanying schematic drawings. In said drawings,
- Fig. 1 illustrates a known O-shaped antenna coil;
- Fig. 2 shows a known eight-shaped antenna coil; and
- Fig. 3 shows an embodiment of a loop antenna device according to the present invention.
- Fig. 1 shows schematically an O-shaped antenna coil 1 with two
terminals - Fig. 2 illustrates schematically an eight-shaped antenna 4 with two superimposed, substantially
congruent loops junctions - Fig. 3 shows schematically an embodiment of an antenna configuration according to the present invention. The loop antenna device shown comprises a
loop 10, which is square in this example, and has four vertices A, B, C and D. From the vertices,branches connection points - From the square shown, an eight-shaped antenna can be constructed in two ways. Unlike the eight-shaped antenna of Fig. 2, there are now two axes of symmetry joining the vertices of the square. The axes of symmetry are perpendicular to each other. The two eight-shapes in the square are turned through 90° relative to each other. The first antenna consists of two halves, i.e., triangle ABC and triangle ADC, which halves are separated by axis of symmetry AC. Rotation through 90° gives the second antenna, consisting of halves BCD and BAD with axis of symmetry BD.
- As will be described below, the eight-shaped antennas are not electrically coupled together. The operation of the antenna configuration is as follows. The first eight-shaped antenna is fed by connecting a source of A.C. voltage between terminals or
connection points 31 and 33, which together form a connection port. Through the application of the A.C. voltage, a current I₁ will start to run. At the vertices A and C, this current will be equally distributed over branches ABC and ADC. As the impedances of the antenna sections AB, BC, AD and DC are all identical, the potentials in points B and D will be equal to each other. As a consequence, there can be no difference in voltage betweenconnection points 32 and 34. Also, no voltage can be generated through induction. Normally, in the antenna sections formed by the conductor betweenconnection points 32 and vertex B (branch 13) and the conductor between connection point 34 and vertex D (branch 14), a voltage would be induced by the magnetic fields which, in turn, are generated through the voltage applied betweenconnection points 31 and 33 and the currents flowing as a consequence. However, by reason of the fact thatbranches - If, similarly, a voltage is applied between
connection points 32 and 34, then, as a result of the symmetrical construction, no voltage differential is formed betweenconnection points 31 and 33. Therefore, if a voltage is applied to the four connection points, two antennas are active which, electrically, are fully uncoupled from each other. - The two antennas can generate different resonant frequencies by means, for example, of capacitors. Thus, for example, a capacitor not shown can be applied across
connection point 31 and 33, as a result of which the resonance frequency of the first eight-shaped antenna will assume a value of 2 MHz, while acrossconnection points 32 and 34 a capacitor can be provided which leads to a resonance frequency of, for example, 8 MHz of the second eight-shaped antenna. As the antennas are not electrically coupled together, the resonance frequencies can be freely selected. - Accordingly, the antenna device illustrated in Fig. 3 forms two electrically independent antennas which, however, mechanically are virtually fully integrated and essentially use the same conductors.
- It is noted that, in principle,
connection points - Furthermore, sections AB, BC, CD and DA may have any curved and/or bent shape. The important feature is that the impedances of the sections should be equal, and that the magnetic fields caused by the A.C. currents which in operation flow through two successive sections (e.g. AD and DC) eliminate each other at an intermediate branch (e.g. 14,13).
- These and similar modifications will readily occur to those skilled in the art after reading the above disclosure, and should be considered to fall within the scope of the present invention.
Claims (8)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
NL8802914 | 1988-11-28 | ||
NL8802914A NL8802914A (en) | 1988-11-28 | 1988-11-28 | ANTENNA CONFIGURATION FOR TWO FREQUENCIES. |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0371562A1 true EP0371562A1 (en) | 1990-06-06 |
EP0371562B1 EP0371562B1 (en) | 1995-02-08 |
Family
ID=19853291
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP89203011A Expired - Lifetime EP0371562B1 (en) | 1988-11-28 | 1989-11-27 | Coil antenna device |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0371562B1 (en) |
AT (1) | ATE118291T1 (en) |
DE (1) | DE68921048T2 (en) |
NL (1) | NL8802914A (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5254974A (en) * | 1990-09-28 | 1993-10-19 | N.V. Nederlandsche Apparatenfabriek Nedap | Deactivating device |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3902177A (en) * | 1972-09-19 | 1975-08-26 | Taiyo Musen Co Ltd | Antenna for direction finders |
US4012742A (en) * | 1975-12-29 | 1977-03-15 | International Telephone And Telegraph Corporation | Multimode loop antenna |
DE2921225A1 (en) * | 1979-05-25 | 1980-12-04 | Helge Bothfeld | Directional aerial for over 100 MHZ range - has radiator consisting of two four-pole elements, using part of electric conductor length, according to preferred polarisation plane |
US4260990A (en) * | 1979-11-08 | 1981-04-07 | Lichtblau G J | Asymmetrical antennas for use in electronic security systems |
GB2071424A (en) * | 1980-03-03 | 1981-09-16 | Pioneer Electronic Corp | Antenna array system usable for am/fm receiver |
EP0186483A2 (en) * | 1984-12-21 | 1986-07-02 | Senelco Limited | Transponder systems |
-
1988
- 1988-11-28 NL NL8802914A patent/NL8802914A/en not_active Application Discontinuation
-
1989
- 1989-11-27 DE DE68921048T patent/DE68921048T2/en not_active Expired - Fee Related
- 1989-11-27 AT AT89203011T patent/ATE118291T1/en active
- 1989-11-27 EP EP89203011A patent/EP0371562B1/en not_active Expired - Lifetime
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3902177A (en) * | 1972-09-19 | 1975-08-26 | Taiyo Musen Co Ltd | Antenna for direction finders |
US4012742A (en) * | 1975-12-29 | 1977-03-15 | International Telephone And Telegraph Corporation | Multimode loop antenna |
DE2921225A1 (en) * | 1979-05-25 | 1980-12-04 | Helge Bothfeld | Directional aerial for over 100 MHZ range - has radiator consisting of two four-pole elements, using part of electric conductor length, according to preferred polarisation plane |
US4260990A (en) * | 1979-11-08 | 1981-04-07 | Lichtblau G J | Asymmetrical antennas for use in electronic security systems |
GB2071424A (en) * | 1980-03-03 | 1981-09-16 | Pioneer Electronic Corp | Antenna array system usable for am/fm receiver |
EP0186483A2 (en) * | 1984-12-21 | 1986-07-02 | Senelco Limited | Transponder systems |
Non-Patent Citations (1)
Title |
---|
PATENT ABSTRACTS OF JAPAN, vol. 1, no. 72, page 696E77, 13th juli 1977; & JP-A-52 008 754 (DENKI KOGYO) 22-01-1977. * |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5254974A (en) * | 1990-09-28 | 1993-10-19 | N.V. Nederlandsche Apparatenfabriek Nedap | Deactivating device |
Also Published As
Publication number | Publication date |
---|---|
ATE118291T1 (en) | 1995-02-15 |
EP0371562B1 (en) | 1995-02-08 |
DE68921048T2 (en) | 1995-06-01 |
DE68921048D1 (en) | 1995-03-23 |
NL8802914A (en) | 1990-06-18 |
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