Orthogonal Antenna Arrangement and Method

The present invention is related generally to multi-axis antenna arrangements and more particularly to an orthogonal multi-axis antenna arrangement in which the center of the overall antenna pattern is established with a relatively high degree of precision at a known point of intersection along two or three antenna axes. An associated method is disclosed.

Establishing the location of an electromagnetic signal source is important in a range of different applications including, but not limited to locating an underground boring tool using a locating signal which is transmitted from the boring tool. Generally, in such applications, antennas such as, for example, dipole antennas are used to measure the signal strength of the locating field along orthogonally opposed axes at one or more above ground locations. The measured signal strengths are then used to calculate the position of the boring tool. Unfortunately, however, locating applications which contemplate high levels of precision are typically limited by inaccurate signal strength measurements when prior art multi-axis antenna arrangements are used. The inaccuracy can be attributed to two significant sources: (1) it is inherently difficult to establish the origin/center of the antenna pattern of these prior art antenna arrangements in a very precise way and (2) particularly in the instance of a three axis orthogonal antenna arrangement, it is improbable that the three antenna axes actually intersect at one point such that electromagnetic field measurements taken by the arrangement actually represent, as nearly as possible, the electromagnetic field strength at a single point. In fact, when three dipole antennas are used, it is submitted that intersection of the three antenna axes at a single point which also comprises the center point of the antenna pattern of each of the dipoles is not possible.

The above incorporated U.S. application discloses a number of embodiments of a highly advantageous locating system for use in not only locating, but tracking an underground boring tool. In each of these embodiments, one or more above ground receivers include antenna clusters which are used to receive the dipole electromagnetic locating signal that is emanated from the underground location of the boring tool. In order to satisfy the need for an accurate orthogonal antenna, a highly advantageous cubic antenna arrangement is disclosed for use as the antenna cluster in the above ground receivers.

While the cubic antenna arrangement disclosed in the above incorporated application remains highly effective in solving the problems encountered in precision measurement of locating signal strength, the present invention discloses another highly advantageous and heretofore unseen antenna arrangement which also provides for precise measurement of a locating field at a single point and which further provides for remarkable ease of manufacture; high levels of manufacturing repeatability; highly stable, consistent performance; and reduced complexity in associated signal conditioning circuitry.

As will be described in more detail hereinafter, there is disclosed herein an antenna arrangement and associated method. The antenna arrangement comprises a first support member defining a first through hole having a first predetermined configuration. The first support member includes a first conductive pattern surrounding the first through hole and serving as a first antenna defining a first axis which which extends through the first through hole. A second support member includes a second conductive pattern serving as a second antenna defining a second axis. In accordance with the present invention, the second support member is positioned in the first through hole of the first support member in a way which arranges the first and second axes of the antenna patterns orthogonally with respect to one another.

In one aspect of the present invention, the antenna arrangement may include a third support member defining a second through hole having a second predetermined configuration. The third support member also includes a third conductive pattern surrounding the second through hole and serving as a third antenna defining a third axis which extends through the second through hole. In addition, the second predetermined configuration of the second through hole is such that the first and second support members are received in the second through hole of the third support member in a way which arranges the third axis of the third antenna orthogonal to the first and second axes of the first and second antennas.

In another aspect of the present invention, an antenna member is disclosed that is configured such that an orthogonal antenna arrangement may utilize two or three identical ones of the disclosed antenna member. Accordingly, the antenna member includes a support member defining a through hole which includes a predetermined configuration. Furthermore, an arrangement of conductive members is supported by the support member and surrounds the through hole such that an antenna pattern is defined along an axis which extends through the through hole. The predetermined configuration of the through hole is such that a two orthogonal axis antenna subassembly may be formed by receiving a first one of the antenna members in the predetermined configuration of the through hole of a second one of the antenna members in a way which arranges the axes of the first and second antenna members orthogonally with respect to one another. Thereafter, a three axis orthogonal antenna assembly may be formed by receiving the two orthogonal axis antenna subassembly in the predetermined configuration of the through hole of a third one of the antenna members in a way which positions the axis of the antenna pattern defined by the third antenna member orthogonally with respect to the axes of the antenna patterns defined by the first and second antenna members.

In still another aspect of the present invention, an antenna arrangement is made up of two or three antenna members. Each antenna member includes an arrangement of conductors defining an antenna pattern which includes a respective axis. The overall antenna arrangement is configured such that the respective axes of the antenna patterns intersect at a particular point.

The present invention may be understood by reference to the following detailed description taken in conjunction with the drawings briefly described below.

FIG. 1 is a diagrammatic elevational view of an antenna member of the present invention shown here to illustrate details of its construction.

FIG. 2 is a schematic diagram illustrating the electrical configuration of the antenna member of FIG. 1.

FIG. 3 is diagrammatic plan view illustrating the layout of a conductive pattern which comprises one layer of the antenna member of FIGS. 1 and 2.

FIG. 4 is diagrammatic illustration showing an orthogonal antenna subassembly comprised of two of the antenna members of FIG. 1 such that a two axis orthogonal arrangement is formed.

FIG. 5 is diagrammatic illustration showing the orthogonal antenna subassembly comprised of the two antenna members of FIG. 4 in conjunction with an additional antenna member such that a three-axis orthogonal arrangement is formed.

FIG. 6 is diagrammatic perspective view showing the orthogonal antenna arrangement of FIG. 5.

Attention is immediately directed to FIG. 1 which illustrates an antenna member manufactured in accordance with the present invention and generally indicated by the reference numeral 10. Antenna member 10 includes a multi-layer printed circuit board 12 defining an opening 13 having a predetermined configuration which includes first, second and third pairs of opposing notches 14, 16 and 18, respectively. The notches are configured having a width (not indicated) which is equal to or slightly less than the thickness (not shown) of printed circuit board 12 such that an appropriate edge of a similar board is slidably receivable in the notches, as will be seen. Antenna member 10 further includes an outer peripheral edge 20 which defines first and second opposing pairs of stops 22 and 24, respectively. For purposes of clarity, the discussion relating to FIG. 1 describes antenna member 10 in the orientation of FIG. 1, however, it should be appreciated that this language is not intended to be limiting in any way.

Continuing with a description of antenna member 10, a lower edge 26 includes a width A which is substantially equal to the distance defined between first pair of opposing notches 14 and second pair of opposing notches 16, as indicated. Width A is maintained in the vertical direction along antenna member 10 up to the position of first pair of opposing stops 22. Thereafter, along the remaining height of the antenna member, its width is significantly greater than A. A side edge 28 of antenna member 10 includes a width B which is substantially equal to the distance defined between third pair of opposing notches 18, as indicated. Width B is maintained horizontally along antenna member 10 up to the position of second pair of opposing stops 24. Along the width of the antenna member to the left of stops 24 in the figure, its width is significantly greater than B. The purpose of the dimensional relationships just described will become apparent within the context of a subsequent discussion.

Having described the antenna member of the present invention with regard to specific attributes of its dimensions, a description of printed circuit board 12 will now be provided. As mentioned above, printed circuit board 12 comprises a multi-layer board. In the present example, a six layer board is used. In FIG. 1, layer 1 is disposed on the front (visible) side of printed circuit board 12, as indicated by the reference numeral 30, and is configured as a conductive plane. Layer 6 (not shown) is identical to layer 1 (when seen through the thickness of printed circuit board 12) and is disposed directly behind layer 1 on the back side of printed circuit board 12 such that layers 1 and 6 are in a confronting relationship with layers 2-5 positioned therebetween. Moreover, layers 1 and 6 each define a slot 32 which breaks the conductive planes such that a shorted loop or turn is not formed. In this manner, layers 1 and 6 serve as electrostatic shields which cooperate to protect the inner layers from any external electric fields while allowing the reception of magnetic fields.

Turning to FIG. 2 in conjunction with FIG. 1, the arrangement and electrical interconnection of layers 1-6 are illustrated. Normally, layers 1 and 6 are electrically connected with the grounded shield of a coaxial cable (not shown). Layers 2-5 comprise inductive patterns which are electrically interfaced using a series of vias X1-X5 in a manner which is known in the art. Specifically, vias X2-X4 are used to connect layers 2-5 in series while a signal input/output is provided between X1 and X5.

Referring to FIGS. 3, layer 2 is diagrammatically illustrated as an orthorectangular conductive pattern 34 which defines three inductive loops 36. It should be appreciated that only three loops have been shown for illustrative purposes and that many more turns or loops may readily be provided. In an actual working embodiment, approximately 50 turns were used per layer with excellent results in the intended receiving application. Moreover, it should also be appreciated that any suitable number of layers may be used. As described above, pattern 34 of layer 2 is disposed directly between layer 1 and layer 6 whereby to take advantage of the electrostatic shielding provided by these outermost layers. Layers 3-5 (shown schematically in FIG. 2) comprise conductive patterns which are essentially identical in appearance with pattern 34 of layer 2 except, of course, for their individual interconnection with vias X1-X5. For this reason, these patterns are not shown individually and will not be described for purposes of brevity. However, it should be appreciated that the pattern of each layer is arranged such that induced current flows in the same direction with respect to the induced current flow in the other layers such that the layer currents are additive in conjunction with their electrical interconnection.

It should be appreciated that the present invention is not limited to the use of a printed circuit board configured in the form of an antenna, but contemplates the use of any suitable form of antenna in accordance with the teachings herein. However, the printed circuit board antenna implementation is particularly advantageous in view of the accuracy and consistency with which printed circuit boards are typically manufactured. These characteristics translate directly into consistent positional orientation and uniformity in the antenna pattern from one antenna member to the next. In applications such as, for example, underground locating where it is desirable to measure the strength of a locating signal at a single, known point along a number of orthogonal axes, the antenna member of the present invention is highly advantageous.

Turning to FIG. 4 and having described antenna member 10 in sufficient detail, the formation of a multi-orthogonal axis antenna arrangement, generally indicated by the reference numeral 40, using three identical ones of antenna members 10 will be described. To that end, first and second antenna members are designated by the reference numerals 10a and 10b, respectively. For purposes of simplicity, the various features of antenna members 10a and 10b (and any subsequently recited antenna members) are referred to by appending an appropriate letter to the reference numbers originally applied in FIG. 1. For example, the opening in antenna member 10a is referred to as opening 13a.

Still referring to FIG. 4, lower edge 26b of antenna member 10b is slidably received in opposing slots 14 of antenna member 10a such that stops 22b (not visible) are engaged against the back side of antenna member 10a. In other words, edge 26b of antenna member 10b is first engaged with slots 14a from behind antenna member 10a and, thereafter, inserted through opening 13a in a direction toward the viewer until stops 22b engage the back surface of antenna member 10a. In addition, edge 28b of antenna member 10b is facing downward in the orientation of FIG. 4 such that stops 24b (only one of which is visible) are facing downward. Thus, antenna members 10a and 10b are arranged such that a central axis 41a (seen as a point in the representation of FIG. 4) of the antenna pattern of antenna member 41a is orthogonal to and intersects a central axis 41b of the antenna pattern of antenna member 10b at a point 42. It should be mentioned that the subassembly of antenna members 10a and 10b may be used as a dual orthogonal axis antenna arrangement with the provision of appropriate electrical connections.

Referring to FIG. 5 in conjunction with FIG. 4, antenna members 10a and 10b are assembled, as described (viewed from below in the orientation of FIG. 4) having edges 26a and 28b, respectively, facing the viewer. Further, an antenna member 10c is arranged such that assembled antenna members 10a and 10b are inserted in opening 13c of antenna member 10c by first engaging edge 26a of antenna member 10a with notches 16c of antenna member 10c while simultaneously engaging edge 28b of antenna member 10b with notches 18c of antenna member 10c. Thereafter, the subassembly of antenna members 10a and 10b is slidably urged in the direction of the viewer such that stops 22a of antenna member 10a and stops 24b of antenna member 10b engage the back surface of antenna member 10c. In this manner and due to the predetermined positions of stops 22a and 24b, an axis 41c (visible as a point in the present figure) of antenna member 10c is arranged in an orthogonal orientation with respect to axes 41a and 41b such that axis 41c also passes through point 42. The antenna members may be secured with respect to one another in any suitable manner. For example, epoxy may be applied where the stops of one antenna member abut against another antenna member or, as another example, the edges of the antenna members may be configured to include a catch arrangement 62 (see FIG. 1) indicated as a dashed line which allows an edge (not shown) of another antenna member to initially slide only in the direction indicated by an arrow 64, thereby providing a one-way locking feature. After the three antenna members are co-arranged, electrical connections may be made in any suitable manner with a receiver and/or transmitter package (not shown).

Thus, a highly advantageous three axis orthogonal antenna arrangement has been provided which features (1) consistency of the antenna pattern along each axis, (2) precise location of the center of the antenna pattern along each axis at a single, common point and (3) an inexpensive and well known manufacturing format.

Turning to FIG. 6, completed antenna arrangement 40 using antenna members 10a-c is illustrated in a perspective view. It is mentioned once again that the present invention utilizes three identical antenna members in arrangement 40 which are configured in a highly advantageous way. However, it is to be understood that these three members are not required to be identical in accordance with the teachings herein. Moreover, it is noted that opening 13b in antenna member 10b is not needed. Therefore, opening 13b may be eliminated with no discernable influence on the characteristics of the overall arrangement provided that any conductive material (i.e., copper cladding) is removed from layers 1-6 in the area in which the opening would have been formed.

With regard to the use of the antenna arrangement of the present invention in locating applications such as, for example, underground location of a boring tool, the antenna arrangement is well suited for use in "walk-over" detectors similar to that described in U.S. Pat. No. 5,337,002 which is incorporated herein by reference. In addition, the antenna arrangement of the present invention is equally well suited for use in stationary receiver applications such as described in above incorporated U.S. patent application Ser. No. 08/835,834 (Attorney Docket No. DCI-P006).

It should be appreciated that the antenna arrangement of the present invention may be used as an orthogonal axis transmitting antenna. In this regard, in one application where the transmission of a rotating magnetic field is required, the antenna members can be driven in sequence to generate a three dimensional field as described in copending U.S. patent application Ser. No. 08/643,209 (attorney docket no. DCI 1P008) entitled METHOD AND ARRANGEMENT FOR DETECTING A BURIED CABLE BY AN INGROUND BORING DEVICE, which is incorporated herein by reference. In another application, each orthogonal antenna member of a first antenna arrangement may transmit at a different frequency to a second, receiving orthogonal antenna arrangement so as to determine the position or orientation of either antenna arrangement. (See U.S. Pat. No. 4,054,881 as one instance of an application which benefits from the present disclosure.)

One other advantage of the present invention mentioned only briefly above resides in reducing the need for conditioning circuitry which drives the antenna arrangement. This advantage results, at least in part, due to a high degree of repeatability in manufacturing.

Because the orthogonal antenna arrangement and antenna member disclosed herein may be provided in a variety of different configurations and modified in an unlimited number of different ways, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit of scope of the invention. For example, in certain applications, a locating signal may be received along two orthogonal axes rather than three. In this instance, two antenna members may be appropriately used without the need for a third antenna member. As another example, the antenna arrangement may be designed such the antenna pattern axes of the various antennas do not intersect. Therefore, the present examples and methods are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.