Efficient and accurate antenna for horizontal directional drilling positioning system

Abstract

The invention relates to an efficient and accurate antenna for a horizontal directional drilling positioning system, and discloses a three-dimensional antenna, which comprises a first pair of rods and at least a first pair of coils for limiting a first magnetic field measurement position, and a second pair of rods and a second pair of coils for limiting a second magnetic field measurement position, wherein the first magnetic field measurement location and the second magnetic field measurement location are at least substantially aligned with each other. The three-dimensional antenna may also include a third pair of coils, wherein the first pair of rods, the first pair of coils, and the third pair of coils define a first magnetic field measurement location. The three-dimensional antenna may also include a switch for connecting adjacent ones of the first and third pairs of coils in series or parallel to each other, and for connecting the first and third pairs of coils in series or parallel to each other.

Description

Technical Field

[0001] The present invention relates to directional drilling technology, in particular to a high-efficiency and precise antenna for a horizontal directional drilling (HDD) positioning system. Background Art

[0002] Directional drilling technology can be used to drill tunnels to install underground utility lines, pipelines, cables, service ducts, etc.

[0003] The positioning system typically includes an underground transmitter (e.g., located inside the drill bit) and an above-ground locator. The transmitter transmits data and positioning dipole signals at a specific frequency. The locator receives the data and positioning dipole signals, for example, using a set of three (3) orthogonal antennas. Depending on the ambient noise level and / or the positioning environment, different frequencies can be used to achieve the desired results, such as positioning accuracy, maximum operating depth, etc. For example, for high passive interference locations (e.g., under reinforced concrete), very low frequencies, such as frequencies below one thousand Hertz (1kHz), can be used. For deep underground drilling, higher frequencies, such as frequencies up to fifty kilohertz (50kHz), can be used. Typically, the positioning system can use frequencies in the range of approximately three tenths of a kilohertz (0.3kHz) to approximately forty-five kilohertz (45kHz). This provides a ratio of approximately one hundred and fifty to one (150:1) between the highest and lowest frequencies.

[0004] Typically, antennas for low-end frequencies, such as those less than approximately 20 kilohertz (<20 kHz), have relatively high inductance, for example, between 50 and 500 millihenries (50-500 mH), while antennas for high-end frequencies have relatively low inductance, for example, between approximately 1 and 10 millihenries (1-10 mH). Currently, receiver antennas used in positioning systems are configured as air-core antennas or ferrite rod antennas, using either a single coil or two coils in a differential configuration. These antennas have different inductances and frequency ranges, such as those selected for the low-end or high-end frequencies described above. However, such antennas do not cover the entire frequency band, for example, only covering the range of 0.3 kHz to 45 kHz.

[0005] Furthermore, when a three-dimensional antenna uses three separate ferrite rods, they are spatially separated, thereby measuring the three components of the magnetic field at different points in three-dimensional space. Hollow-core printed circuit board (PCB) antennas can be made so that the three antennas intersect each other and can accurately measure the three components of the magnetic field at the same point in three-dimensional space. However, in practice, hollow-core PCB antennas have low inductance (e.g., due to production cost, size, etc.). For example, the inductance of hollow-core PCB antennas is typically less than 5 millihenries (5mH), and these antennas perform poorly at the lower end of the frequency range, such as at sub-kilohertz frequencies. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a high-efficiency and accurate antenna for a horizontal directional drilling positioning system in view of the above-mentioned deficiencies in the prior art.

[0007] The technical solution adopted by the present invention to solve the above technical problems is: a three-dimensional antenna, comprising:

[0008] a first pair of rods that are at least substantially parallel to each other and spaced apart from each other;

[0009] a first pair of coils, each coil of the first pair of coils being disposed on one of the first pair of rods;

[0010] a second pair of coils, each coil of the second pair of coils being disposed on one of the first pair of rods; the first pair of rods, the first pair of coils, and the second pair of coils defining a first magnetic field measurement location;

[0011] a second pair of rods that are at least substantially parallel to each other and spaced apart from each other;

[0012] a third pair of coils, each coil of the third pair of coils being disposed on one of the second pair of rods;

[0013] a fourth pair of coils, each coil of the fourth pair of coils being disposed on one of the second pair of rods; the second pair of rods, the third pair of coils, and the fourth pair of coils defining a second magnetic field measurement location;

[0014] a third pair of rods that are at least substantially parallel to each other and spaced apart from each other;

[0015] a fifth pair of coils, each coil of the fifth pair of coils being disposed on one of the third pair of rods; and

[0016] a sixth pair of coils, each coil of the sixth pair of coils being disposed on one of the third pair of rods; the third pair of rods, the fifth pair of coils, and the sixth pair of coils defining a third magnetic field measurement position; and characterized in that:

[0017] The first magnetic field measurement location, the second magnetic field measurement location, and the third magnetic field measurement location are at least substantially aligned with each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of a pair of rods for a three-dimensional antenna according to an exemplary embodiment of the present invention, the pair of rods being at least substantially parallel to each other and spaced apart from each other, wherein each of a first pair of coils and a second pair of coils is wound around each of the pair of rods such that each rod in the pair of rods is wrapped in two adjacent coils, and wherein the pair of rods, the first pair of coils, and the second pair define a magnetic field measurement location at a three-dimensional point in the space between the coils in the rods.

[0019] Figure 2 is a top view of a three-dimensional antenna having a pair of rods according to an example embodiment of the present invention, the pair of rods being at least substantially parallel to each other and spaced apart from each other, wherein each of a first pair of coils and a second pair of coils is wound around each of the pair of rods such that each rod in the pair of rods is wrapped in two adjacent coils, and wherein the pair of rods, the first pair of coils, and the second pair of coils define a magnetic field measurement location at a three-dimensional point in the space between the rods.

[0020] Figure 3 is a perspective view of a three-dimensional antenna having three pairs of orthogonal rods, each rod having two adjacent coils, and defining magnetic field measurement locations that are at least substantially the same for each pair of rods and corresponding coils according to an example embodiment of the present invention.

[0021] Figure 4 is a schematic diagram of a circuit having two pairs of coils for a three-dimensional antenna according to an exemplary embodiment of the present invention, wherein the three-dimensional antenna, for example Figure 2 and Figure 3 , where all four coils in two pairs of coils are connected in series.

[0022] Figure 5 is a schematic diagram of a circuit having two pairs of coils for a three-dimensional antenna according to an exemplary embodiment of the present invention, wherein the three-dimensional antenna, for example Figure 2 and Figure 3 As shown in , the two coils of the two pairs of coils are connected in series, and the two coils of the two pairs of coils are connected in parallel.

[0023] Figure 6 is a schematic diagram of a circuit having two pairs of coils for a three-dimensional antenna according to an exemplary embodiment of the present invention, wherein the three-dimensional antenna, for example Figure 2 and Figure 3 As shown in , the two coils of the two pairs of coils are connected in parallel, and the two coils of the two pairs of coils are connected in series.

[0024] Figure 7 is a schematic diagram of a circuit having two pairs of coils for a three-dimensional antenna according to an exemplary embodiment of the present invention, wherein the three-dimensional antenna, for example Figure 2 and Figure 3 , where all four coils in two pairs of coils are connected in parallel.

[0025] Figure 8 is a schematic diagram of a circuit according to an exemplary embodiment of the present invention having a set of switches for two pairs of coils of a three-dimensional antenna, wherein the three-dimensional antenna is, for example, Figure 2 and Figure 3 As shown in .

[0026] Figure 9is a diagram of inductance options for a set of switches for two pairs of coils of a three-dimensional antenna according to an example embodiment of the present invention, where the switch set is, for example, Figure 8 As shown in . DETAILED DESCRIPTION

[0027] The following describes a detailed description with reference to the accompanying drawings. The use of the same reference numerals in different cases in the specification and the drawings may represent similar or identical technical features.

[0028] refer to Figures 1 to 9 , shows a three-dimensional antenna 100 for a positioning system, such as a positioning system for horizontal directional drilling. In order to provide antenna configurations over a wide frequency range, the inductance of the three-dimensional antenna 100 can be varied. Having multiple inductance options allows the three-dimensional antenna 100 to be configured for specific frequency sub-bands over the full frequency range. In addition, to improve accuracy, the three pairs of rods of the three-dimensional antenna 100 can measure the magnetic field at the same point in three-dimensional space. For example, to measure the magnetic field at the same point, an antenna with a symmetrical structure can be used. As described in some embodiments, two ferrite rods can be used, each ferrite rod having two coils in each measurement direction, for example a total of six (6) ferrite rods. As described above, the two parallel rods can be electrically combined to operate as a single antenna coil. The two signals from a set of antenna rods can be added together to provide a more accurate measurement of the magnetic field between the two antenna rods.

[0029] The three-dimensional antenna 100 includes a first pair of rods 102 that are at least substantially parallel to each other and spaced apart from each other. In some embodiments, the first pair of rods 102 may be ferrite rods. The three-dimensional antenna 100 also includes coils (e.g., a first pair of coils 104), wherein each coil in the first pair of coils 104 is disposed on (e.g., coiled or wound around) one of the first pair of rods 102. For example, each rod in the first pair of rods 102 is wound around a corresponding coil. In some embodiments, the three-dimensional antenna 100 also includes additional coils (e.g., a second pair of coils 106), wherein each coil in the second pair of coils 106 is disposed on (e.g., coiled or wound around) one of the first pair of rods 102. For example, each rod in the first pair of rods 102 is also wound around a corresponding coil in the second pair of coils 106. In some embodiments, the two coils wound around each rod are positioned adjacent to each other, for example, as shown in the accompanying figures. As described above, the first pair of rods 102 and the first pair of coils 104 (and possibly the second pair of coils 106) define a first magnetic field measurement location 108 at a three-dimensional point in space. For example, the first magnetic field measurement position 108 is located at the center of the first pair of bars 102 .

[0030] The three-dimensional antenna 100 also includes a second pair of rods 110 that are at least substantially parallel to each other and spaced apart from each other. In some embodiments, the second pair of rods 110 may be ferrite rods. The three-dimensional antenna 100 also includes coils (e.g., a third pair of coils 112), wherein each coil in the third pair of coils 112 is disposed (e.g., coiled or wrapped) around one of the second pair of rods 110. For example, each rod is wrapped around a corresponding coil. In some embodiments, the three-dimensional antenna 100 also includes additional coils (e.g., a fourth pair of coils 114), wherein each coil in the fourth pair of coils 114 is disposed (e.g., coiled or wrapped) around one of the second pair of rods 110. For example, each rod in the second pair of rods 110 is also wrapped around a corresponding second coil in the fourth pair of coils 114. In some embodiments, the two coils wrapped around each rod are positioned adjacent to each other, for example, as shown in the accompanying figures. As described above, the second pair of rods 110 and the third pair of coils 112 (and possibly the fourth pair of coils 114) define a second magnetic field measurement location 116 at a three-dimensional point in space. For example, the second magnetic field measurement position 116 is located at the center of the second pair of bars 110 .

[0031] In some embodiments, the three-dimensional antenna 100 includes a third pair of rods 118 that are at least substantially parallel to each other and spaced apart from each other. In some embodiments, the third pair of rods 118 may be ferrite rods. The three-dimensional antenna 100 also includes coils (e.g., a fifth pair of coils 120), wherein each coil in the fifth pair of coils 120 is disposed (e.g., coiled or wound) around one of the third pair of rods 118. For example, each rod is wound with a corresponding coil. In some embodiments, the three-dimensional antenna 100 also includes additional coils (e.g., a sixth pair of coils 122), wherein each coil in the sixth pair of coils 122 is disposed (e.g., coiled or wound) around one of the third pair of rods 118. For example, each rod in the third pair of rods 118 is also wound with a corresponding coil in the sixth pair of coils 122. In some embodiments, the two coils wound around each rod are positioned adjacent to each other, for example, as shown in the accompanying figures. As described above, the third pair of rods 118 and the fifth pair of coils 120 (and possibly the sixth pair of coils 122) define a third magnetic field measurement location 124 at a three-dimensional point in space. For example, the third magnetic field measurement position 124 is located at the center of the third pair of bars 118 .

[0032] In an embodiment of the present invention, the first magnetic field measurement location 108 and the second magnetic field measurement location 116 (and possibly the third magnetic field measurement location 124) are at least substantially aligned with each other. For example, the first magnetic field measurement location 108 and the second magnetic field measurement location 116 (and possibly the third magnetic field measurement location 124) may be at least substantially the same location in three-dimensional space (e.g., Figure 3). In other embodiments, the magnetic field measurement locations can be close to each other, but not necessarily at the same location. As described above, the first pair of rods 102 can define a first plane 126, the second pair of rods 110 can define a second plane 128 (e.g., with each rod lying in its respective plane), and the first plane 126 and the second plane 128 can be at least substantially orthogonal to each other. For example, the planes defined by the first pair of rods 102, the second pair of rods 110, and possibly the third pair of rods 118 can all be at least substantially orthogonal to each other.

[0033] As described above, when the rod includes multiple coils (e.g., first and second pairs of coils 104, 106, third and fourth pairs of coils 112, 114, and fifth and sixth pairs of coils 120, 122), the coils can be connected to each other in various combinations of series and parallel connections. For example, the three-dimensional antenna 100 includes a first set of switches 130 for connecting adjacent coils of the first and second pairs of coils 104, 106 in series or in parallel with each other, and for connecting the first set of coils 104 and the first pair of coils 106 in series or in parallel with each other. The three-dimensional antenna 100 may also include a second set of switches for connecting adjacent coils of the third and fourth pairs of coils 112, 114 in series or in parallel with each other, and for connecting the second and fourth pairs of coils 112, 114 in series or in parallel with each other. Furthermore, the three-dimensional antenna 100 may include a third set of switches for connecting adjacent coils of the fifth pair of coils 120 and the sixth pair of coils 122 in series or in parallel with each other, and for connecting the fifth pair of coils 120 and the sixth pair of coils 122 in series or in parallel with each other. As described above, for each antenna formed by a pair of rods and the first and second pairs of coils, there are four possible parallel and series connections while maintaining antenna symmetry.

[0034] See also Figure 4 Each of the first pair of coils 104 and the second pair of coils 106 wound around the periphery of the first pair of rods 102 can be connected together, for example, using a first set of switches 130, such that all four coils of the first pair of coils 104 and the second pair of coils 106 are connected in series. In this embodiment, the inductance of the antenna formed by the first pair of rods 102, the first pair of coils 104, and the second pair of coils 106 is sixteen times (16x) the inductance of one of the coils (when each coil has the same inductance). In this embodiment, the antenna configured in this manner can be used in a frequency range between three tenths of kilohertz (0.3 kHz) and two kilohertz (2.0 kHz).

[0035] See also Figure 5For example, using the first set of switches 130, each of the first pair of coils 104 and the second pair of coils 106 wound around the circumference of the first pair of rods 102 can be connected together, such that the two coils of the first pair of coils 104 and the second pair of coils 106 are connected in series, and the two coils of the first pair of coils 104 and the second pair of coils 106 are connected in parallel. In other words, the two adjacent coils on each rod are connected in series, and then the two sets of coils connected in series are connected in parallel. In this embodiment, the inductance of the antenna formed by the first pair of rods 102, the first pair of coils 104, and the second pair of coils 106 has four times (4x) the inductance of one coil (when each coil has the same inductance). In this embodiment, the antenna configured in this manner is usable in a frequency range between two kilohertz (2.0 kHz) and nine kilohertz (9.0 kHz).

[0036] See also Figure 6 For example, using the first set of switches 130, each of the first pair of coils 104 and the second pair of coils 106 wound around the periphery of the first pair of rods 102 can be connected together so that the two coils of the first pair of coils 104 and the second pair of coils 106 are connected in parallel, and the two coils of the first pair of coils 106 and the first pair of coils 104 are connected in series. In other words, the two coils of the first pair of coils 104 are connected in parallel, the two coils of the second pair of coils 106 are connected in parallel, and then the two sets of coils (the first pair of coils 104 and the second pair of coils 106, respectively) are connected in series. In this embodiment, the inductance of the antenna formed by the first pair of rods 102, the first pair of coils 104, and the second pair of coils 106 have an inductance that is four times (4x) the inductance of either coil (when each coil has the same inductance). In this embodiment, the antenna configured in this manner is usable in a frequency range between two kilohertz (2.0 kHz) and nine kilohertz (9.0 kHz).

[0037] See also Figure 7 Each of the first pair of coils 104 and the second pair of coils 106 wrapped around the periphery of the first pair of rods 102 can be connected together, for example, using the first set of switches 130, such that all four coils of the first pair of coils 204 and the second pair of coils 106 are connected in parallel. In this embodiment, the inductance of the antenna formed by the first pair of rods 102, the first pair of coils 104, and the second pair of coils 106 is the same as the inductance of one of the coils (when each coil has the same inductance). In this embodiment, the antenna configured in this manner can be used in a frequency range between nine kilohertz (9.0 kHz) and forty-five kilohertz (45.0 kHz).

[0038] See Figure 8 and Figure 9As shown, metal oxide semiconductor field effect transistor (MOSFET) analog switches can be used to connect the various coils in the above configuration. However, MOSFET analog switches are provided only as an example and are not meant to limit the present invention. In other embodiments, different switches can be used to connect the various coils in series and parallel configurations. Figure 9 "S" means series connection, "P" means parallel connection. For example, 2P2S means two coils are connected in series and two in parallel.

[0039] Although the subject matter has been described in language specific to structural features and / or process operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. A three-dimensional antenna, comprising: a first pair of rods that are at least substantially parallel to each other and spaced apart from each other; a first pair of coils, each coil of the first pair of coils being disposed on one of the first pair of rods; a second pair of coils, each coil of the second pair of coils being disposed on one of the first pair of rods; the first pair of rods, the first pair of coils and the second pair of coils defining a first magnetic field measurement location; a second pair of rods that are at least substantially parallel to each other and spaced apart from each other; a third pair of coils, each coil of the third pair of coils being disposed on one of the second pair of rods; a fourth pair of coils, each coil of the fourth pair of coils being disposed on one of the second pair of rods; the second pair of rods, the third pair of coils and the fourth pair of coils defining a second magnetic field measurement location; a third pair of rods that are at least substantially parallel to each other and spaced apart from each other; a fifth pair of coils, each coil of the fifth pair of coils being disposed on one of the third pair of rods; and A sixth pair of coils, each coil of the sixth pair of coils is arranged on one of the third pair of rods; the third pair of rods, the fifth pair of coils and the sixth pair of coils define a third magnetic field measurement position; characterized in that: The first magnetic field measurement location, the second magnetic field measurement location and the third magnetic field measurement location are at least substantially aligned with each other.

2. The three-dimensional antenna according to claim 1, characterized in that: Also includes: a first set of switches for connecting adjacent coils in the first pair of coils and the second pair of coils in series or in parallel with each other, and for connecting the first pair of coils and the second pair of coils in series or in parallel with each other; a second set of switches, for connecting adjacent coils in the third pair of coils and the fourth pair of coils in series or in parallel with each other, and for connecting the third pair of coils and the fourth pair of coils in series or in parallel with each other; as well as The third group of switches is used to connect adjacent coils in the fifth pair of coils and the sixth pair of coils in series or in parallel with each other, and to connect the fifth group of coils and the sixth group of coils in series or in parallel with each other.

3. The three-dimensional antenna according to claim 1, characterized in that: The first magnetic field measurement location, the second magnetic field measurement location and the third magnetic field measurement location are at least substantially the same.

4. The three-dimensional antenna according to claim 1, characterized in that: The first pair of rods, the second pair of rods, and the third pair of rods include ferrite rods.

5. The three-dimensional antenna according to claim 1, characterized in that: A first set of switches is also included for connecting adjacent coils of the first pair of coils and the second pair of coils in series or in parallel with each other, and connecting the first pair of coils and the second pair of coils in series or in parallel with each other.

6. The three-dimensional antenna according to claim 5, characterized in that: A second set of switches is also included, which is used to connect adjacent coils in the third pair of coils and the fourth pair of coils in series or in parallel with each other, and to connect the third pair of coils and the fourth pair of coils in series or in parallel with each other.

7. A three-dimensional antenna, comprising: a first pair of rods that are at least substantially parallel to each other and spaced apart from each other; at least a first pair of coils, each coil of the first pair of coils being disposed on one of the first pair of rods; the first pair of rods and the first pair of coils defining a first magnetic field measurement location; a second pair of rods that are at least substantially parallel to each other and spaced apart from each other; at least a second pair of coils, each coil of the second pair of coils being disposed on one of the second pair of rods; The second pair of bars and the second pair of coils define a second magnetic field measurement location; a third pair of rods that are at least substantially parallel to each other and spaced apart from each other; as well as At least a third pair of coils, each coil of the third pair of coils being disposed on one of the third pair of rods; the third pair of rods and the third pair of coils defining a third magnetic field measurement location; characterized in that: The first magnetic field measurement location, the second magnetic field measurement location and the third magnetic field measurement location are at least substantially aligned with each other.

8. The three-dimensional antenna according to claim 7, characterized in that: Also includes: a fourth pair of coils, each coil of the fourth pair of coils being disposed on one of the first pair of rods; the first pair of rods, the first pair of coils and the fourth pair of coils defining a first magnetic field measurement position; a fifth pair of coils, each coil of the fifth pair of coils being disposed on one of the second pair of rods; the second pair of rods, the second pair of coils and the fifth pair of coils defining a second magnetic field measurement location; and A sixth pair of coils, each coil of the sixth pair of coils is arranged on one of the third pair of rods; the third pair of rods, the third pair of coils and the sixth pair of coils define a third magnetic field measurement position.

9. The three-dimensional antenna according to claim 8, characterized in that: Also includes: a first set of switches, for connecting adjacent coils in the first pair of coils and the fourth pair of coils in series or in parallel with each other, and for connecting the first pair of coils and the fourth pair of coils in series or in parallel with each other; a second set of switches, for connecting adjacent coils in the second pair of coils and the fifth pair of coils in series or in parallel with each other, and for connecting the second pair of coils and the fifth pair of coils in series or in parallel with each other; as well as The third group of switches is used to connect adjacent coils in the third pair of coils and the sixth pair of coils in series or in parallel with each other, and to connect the third pair of coils and the sixth pair of coils in parallel or in series with each other.

10. The three-dimensional antenna according to claim 7, characterized in that: The first magnetic field measurement location, the second magnetic field measurement location and the third magnetic field measurement location are at least substantially the same.

11. The three-dimensional antenna according to claim 7, characterized in that: The first pair of rods, the second pair of rods, and the third pair of rods include ferrite rods.

12. The three-dimensional antenna according to claim 7, characterized in that: A fourth pair of coils is also included, each coil of the fourth pair of coils is arranged on one of the first pair of rods; the first pair of rods, the first pair of coils and the fourth pair of coils define a first magnetic field measurement position.

13. The three-dimensional antenna according to claim 12, characterized in that: A fifth pair of coils is also included, each coil of the fifth pair of coils is arranged on one of the second pair of rods; the second pair of rods, the second pair of coils and the fifth pair of coils define a second magnetic field measurement position.

14. A three-dimensional antenna, comprising: a first pair of rods that are at least substantially parallel to each other and spaced apart from each other; at least a first pair of coils, each coil of the first pair of coils being disposed on one of a first pair of rods, the first pair of rods and the first pair of coils defining a first magnetic field measurement location; a second pair of rods that are at least substantially parallel to each other and spaced apart from each other; as well as At least a second pair of coils, each coil of the second pair of coils being disposed on one of the second pair of rods, the second pair of rods and the second pair of coils defining a second magnetic field measurement location; characterized in that: The first magnetic field measurement location and the second magnetic field measurement location are at least substantially aligned with each other.

15. The three-dimensional antenna according to claim 14, characterized in that: Also includes: a third pair of rods that are at least substantially parallel to each other and spaced apart from each other; as well as At least a third pair of coils, each coil of the third pair of coils is disposed on one of the third pair of rods, the third pair of rods and the third pair of coils define a third magnetic field measurement location, the third field measurement location being substantially aligned with at least the first magnetic field measurement location and the second magnetic field measurement location.

16. The three-dimensional antenna according to claim 14, characterized in that: Also includes: a third pair of coils, each coil of the third pair of coils being disposed on one of the first pair of rods; The first pair of rods, the first pair of coils, and the third pair of coils define a first magnetic field measurement location; and A fourth pair of coils, each coil of the fourth pair of coils is disposed on one of the second pair of rods; the second pair of rods, the second pair of coils and the fourth pair of coils define a second magnetic field measurement position.

17. The three-dimensional antenna according to claim 16, characterized in that: Also includes: a first set of switches for connecting adjacent coils of the first pair of coils and the third pair of coils in series or in parallel with each other, and connecting the first pair of coils and the third pair of coils in series or in parallel with each other; and The second group of switches is used to connect adjacent coils in the second pair of coils and the fourth pair of coils in series or in parallel with each other, and to connect the second pair of coils and the fourth pair of coils in series or in parallel with each other.

18. The three-dimensional antenna according to claim 14, characterized in that: The first field measurement location and the second field measurement location are at least substantially identical.

19. The three-dimensional antenna according to claim 14, characterized in that: The first pair of rods and the second pair of rods include ferrite rods.

20. The three-dimensional antenna according to claim 16, characterized in that: A first set of switches is also included for connecting adjacent coils in the first pair of coils and the third pair of coils in series or in parallel with each other, and connecting the first pair of coils and the third pair of coils in series or in parallel with each other.

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