Dipole antenna for radar applications

Abstract

An antenna for a ground penetrating radar system is disclosed. The antenna has a housing defining a cavity. The radiator is located on a surface of the planar substrate within the cavity. And the wear-resistant block is positioned between the radiator and the opening of the cavity and is used for providing mechanical protection for the radiator. The absorber assembly is located on a side of the radiator opposite the opening. The absorber assembly includes a microwave absorber and a first dielectric layer. The first dielectric layer is located between the radiator and the microwave absorber.

Description

[0001] This application is a divisional application of the invention patent application with the application date of July 18, 2019, named “Dipole antenna for radar applications” and application number 201980047875.8.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application is a national phase application of international patent application No. PCT / EP2019 / 069412 filed on July 18, 2019, which claims priority to UK patent application No. 1811745.7 filed on July 18, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0004] The present disclosure relates to the field of radar systems, particularly for compact, close range applications.One application is ground penetrating radar in the case of machining tools (eg, excavator buckets). Background Art

[0005] Radar systems for detecting the presence of objects in an environment are well known, including ground penetrating radar systems.

[0006] In most radar applications, the antenna needs to facilitate air coupling (for example, if the antenna is mounted on a drone intended to fly some distance above the ground) or facilitate ground coupling (for example, if the antenna is mounted to the underside of a ground-based radar measurement vehicle).

[0007] However, in some cases, such as where the antenna is to be mounted on a machining tool such as an excavator bucket, the antenna needs to facilitate both air and ground coupling. Using the example of an excavator bucket, this is because in some cases it will be directly in contact with or very close to the ground, while in other cases it will be several centimeters, tens of centimeters, or even meters above the ground.

[0008] In addition, ground penetrating radar systems require wide bandwidth antennas, often called ultra-wideband (UWB) antennas. Wide bandwidth antennas are often achieved by using biconical dipoles that promote frequency independence. In cases where a planar antenna is required, a so-called bow-tie antenna can be used. The bow-tie shape is derived from truncating and projecting onto the plane of an infinite bicone. An appropriate resistive load is also necessary.

[0009] In the case where the ground penetrating radar antenna is mounted on a processing tool such as an excavator bucket, a considerable degree of mechanical strength is required. Summary of the invention

[0010] Against this background, an antenna for ground penetrating radar applications is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0012] Figure 1 shows a schematic representation of a cross section through an antenna according to the present disclosure;

[0013] Figure 2a Shown through as Figure 1 A schematic representation of a cross section of a printed circuit board of a component part of an antenna;

[0014] Figure 2b Shows Figure 2a A schematic representation of a top view of a printed circuit board;

[0015] Figure 3 Shows Figure 2b A schematic representation of a top view of the printed circuit shown in FIG. 1 plus a balun through which the electrical connection to the radiator is made;

[0016] Figure 4 Shown include Figure 1 The dual antenna of the antenna pair of an embodiment;

[0017] Figure 5 Shows Figure 4 A top view of the dual antennas;

[0018] Figure 6 Shows Figure 1 A first alternative embodiment of the embodiment;

[0019] Figure 7 Shows Figure 1 A second alternative embodiment of the embodiment;

[0020] Figure 8 Shows Figure 1 A third alternative embodiment of the embodiment;

[0021] Fig. 9 Shows Figure 1 A fourth alternative embodiment of the embodiment;

[0022] Fig.10 Shows Figure 1 A fifth alternative embodiment of the embodiment;

[0023] Fig.11 An excavator bucket is shown with dual antennas according to the present disclosure mounted thereon;

[0024] Fig.12 shows the magnetic permeability properties of a typical microwave absorber used with the antenna assembly of the present disclosure; and

[0025] Fig.13The power loss properties of a microwave absorber used with the antenna assembly of the present disclosure are shown. DETAILED DESCRIPTION

[0026] Fig.11 The dual antenna assembly 400 is shown mounted on an excavator bucket 500 for use in a ground penetrating radar application. The excavator bucket 500 may be attached to the arm of an excavator or other machine. The excavator bucket 500 may otherwise be, for example, a conventional 12 inch (-305 mm) wide excavator bucket.

[0027] The excavator bucket 500 includes a base 510 and a side surface 530, wherein the side surface 530 defines a cavity 540 for containing excavated material. A blade 520 that can be used to cut into the ground is located in front of the base 510. The dual antenna assembly 400 is mounted to the outer surface of the base 510 of the excavator bucket 500 in the same plane as the blade 520 and behind the blade 520. One of the two antennas 470, 480 of the dual antenna assembly 400 can be used as a transmitter, and the other of the two antennas 480, 470 can be used as a receiver.

[0028] As already explained, one of the challenges surrounding antenna design for this application is the need for the antenna to couple to the ground (when the bucket is cut into or close to the ground) and the need for the antenna to couple to the air (when the bucket is elevated). Another challenge is that the antenna must have a strong and slender construction, given that the antenna is expected to be located at the base 510 of the bucket and given the bucket's purpose, the antenna will inevitably be subject to mechanical stress and strain.

[0029] Figure 1 A schematic representation of a cross section through an antenna 1000 is shown, which is similar to Fig.11 One of the antenna pairs 470 , 480 of the dual antenna assembly 400 .

[0030] Antenna 1000 includes a housing 110 defining a cavity 112 having a bottom surface 115, a plurality of side surfaces 116, and a plate 119 opposite bottom surface 115, which plate may be referred to as a healing plate 119. Plate 119 has an opening 111 that provides access to cavity 112. Housing 110 may be metal, preferably aluminum or an aluminum alloy.

[0031] The cavity 112 may contain a wear block 120, a radiator assembly 200, and an absorber assembly 300. The radiator assembly 200 is sandwiched between the wear block 120 and the absorber assembly 300, such that the wear block 120 is located at the opening 111 to the cavity, and the absorber assembly 300 is located near the bottom surface 115 of the cavity 112 and farthest from the opening 111 to the cavity 112. In this manner, the radiator assembly 200 is located between the wear block 120 and the absorber assembly 300.

[0032] The radiator assembly 200 may include a printed circuit board substrate 210 on the upper side of which is printed a metal radiator 220 described in more detail below.

[0033] The radiator 220 may be copper. The copper may be 1 ounce (28.3 g) of copper.

[0034] The radiator assembly 200 may be approximately 215 mm long and 90 mm wide. The radiator 220 may be approximately 190 mm long and 50 mm wide at the widest portion of the bow tie.

[0035] The wear block 120 is located at the opening 111 of the cavity 112 and occupies the volume between the opening 111 and the top surface of the printed radiator 220. The wear block 120 can have at least two purposes. In particular, the wear block 120 can be a material with dielectric properties that are selected to provide a match to both the air and the ground. Second, it can have particularly wear-resistant properties (hence the name wear block), while recognizing that, for example, when mounted on the underside of an excavator bucket 500, some mechanical damage may be unavoidable. Therefore, it can also be configured to withstand mechanical damage such as scratches and indentations in order to protect the radiator 220 from such damage. In this way, scratches and other mechanical damage to the wear block 120 can be prevented from affecting the operation of the antenna 1000 to any significant extent.

[0036] The relative permittivity (dielectric constant) of the ground surface that a user may wish to penetrate with the blade 520 of an excavator bucket 500 may typically be around 4.0, while the relative permittivity of air may be 1.0. Therefore, it may be appropriate to select a wear block 120 having a relative permittivity (dielectric constant) between these two values. A relative permittivity (dielectric constant) of approximately 2.7 may be most preferred as this promotes both ground and air coupling.

[0037] The wear block 120 may be plastic. For example, the wear block 120 may be polycarbonate. The wear block 120 may be a plastic having a Shore D durometer value of 60 or more. Such a wear block has a particularly wear-resistant property, as well as an appropriate dielectric constant. The wear block 120 may have a thickness of approximately 20 mm.

[0038] The absorber assembly 300 is located near the bottom surface 115 of the cavity 112 farthest from the opening 111 (at Figure 1 1 and 2. The absorber assembly 300 includes an absorber 310 at the bottom of the cavity 112 adjacent to the bottom surface 115 and a first dielectric layer 320 between the absorber 310 and the radiator assembly 200. The first dielectric layer 320 can be thick enough so that the capacitive coupling between the absorber 310 and the printed radiator 220 is negligible. The thickness of the first dielectric layer 320 can be, for example, about 20 mm, about 30 mm, about 40 mm, or any other suitable thickness. The thickness of the absorber 310 can be between 0.5 mm and 2.0 mm, preferably 0.8 mm.

[0039] The microwave absorber may comprise metal flakes distributed in a polymer resin. Alternatively, the microwave absorber may comprise graphite.

[0040] Fig.12 Typical magnetic permeability properties of microwave absorber 310 are shown. These magnetic permeability properties lead to Fig.13 Typical power losses are shown in .

[0041] In this manner, the microwave absorber 310 absorbs back reflections of microwave radiation reflected from the bottom surface 115 of the housing 110. Therefore, the back reflections absorbed by the microwave absorber 310 do not reach the radiator and / or the second antenna using the radiator as a receiver.

[0042] In an antenna using a frequency band between 500 MHz and 1300 MHz, Fig.13 It can be seen particularly clearly that the power loss provided by the microwave absorber 310 is higher in this frequency band than at lower frequencies.

[0043] An appropriate value of the relative permittivity (dielectric constant) of the first dielectric layer 320 may be between 1.0 and 4.0, and preferably is around 2.7.

[0044] The first dielectric layer 320 may be a plastic. For example, the first dielectric layer may be a polycarbonate. The first dielectric layer 320 may be a plastic that measures 60 or more on the Shore D durometer scale. This has wear resistant properties, as well as an appropriate dielectric constant. The requirement for a wear resistant plastic may not be as important in the case of the first dielectric layer 320 as in the case of the wear block 120. This is because the first dielectric layer 320 is encapsulated by the various other features of the antenna 1000 and is therefore less susceptible to direct mechanical damage.

[0045] The housing 110 may be pre-formed before the various components (including the wear block 120 , the radiator assembly 200 , and the absorber assembly 300 ) included in the completed antenna assembly 1000 , or 400 are installed.

[0046] Alternatively, in some embodiments, the wear block 120, the radiator assembly 200, and the absorber assembly 300 may be assembled first, and the housing 110 may be formed around them. In this way, the cavity 112 may be sized to enclose the exact outer form of the combination of the wear block 120, the radiator assembly 200, and the absorber assembly 300. In some embodiments, the housing 110 may be formed by a metallization process or metal coating technique known in the art, such as, but not limited to, vacuum metallization, thermal spraying, or cold spraying.

[0047] By forming the housing 110 around the wear block 120, the radiator assembly 200 and the absorber assembly 300, air gaps between the housing 110 and its contents are eliminated (or at least greatly minimized), which avoids or at least significantly reduces the resonance effects (secondary resonances) caused by such air gaps.

[0048] Figure 2a and Figure 2b Shows Figure 1 Schematic representation of the radiator assembly 200 of the antenna 1000. Figure 2a In the cross section and Figure 2b Radiator assembly 200 is shown in a plan view.

[0049] The radiator assembly 200 may be manufactured from a printed circuit board including a substrate 210 having a metal layer covering the entire area of ​​the top surface of the substrate 210. The planar bow-tie radiator 220 may be produced using conventional printed circuit board techniques involving the use of masks to distinguish between areas where the metal layer is to be retained and areas where the metal layer is to be removed. For example, unwanted areas of the metal layer are removed by selectively etching the unmasked areas, resulting in Figure 2b The bow shape shown in .

[0050] Ground penetrating radar requires a broadband antenna. Typically, the bandwidth will be roughly equal to the center frequency. This results in a high percentage bandwidth. In this application, the bandwidth is achieved by shaping (e.g., angling) the arms of the radiating element.

[0051] A common approach is a biconical dipole, which avoids resonances because an infinite cone can be defined only by angles. Since it is length independent, it is wavelength independent, and therefore frequency independent. A three-dimensional radiator is not feasible in this context. The bow-tie shape of the radiator of the present disclosure is derived from a truncated bicone projected onto a plane. This shape retains some of the frequency-independent properties of an infinite dipole, while being implementable in a planar manner at practical sizes for the intended purpose.

[0052] Figure 3 A plan view of a bow-tie radiator 220 on its substrate 210 is shown, along with a balun 240 providing electrical connection to the bow-tie radiator 220 .

[0053] The balun 240 is mounted on the substrate 210 so as to be connected to the center of the radiator bow-tie via a metal electrical connection formed by conventional means in a printed circuit board. These may be formed by etching in parallel with the process of etching the radiator geometry. The balun 240 may be mounted so that its major axis is in a plane parallel to the plane of the bow-tie radiator 220. The balun 240 may also be mounted so that its major axis is perpendicular to the major axis of the bow-tie radiator 220. In this way, it may be conveniently accommodated in the triangular space of the substrate between the two halves of the bow-tie radiator 220. In addition, the balun 240 may have an elongated form factor, making it larger in length and width relative to its thickness, which the balun 240 protrudes from the surface of the substrate 210.

[0054] The thickness of the balun 240 protruding from the surface of the substrate may be accommodated in the wear block 120 by means of a recess in the wear block 120 (not shown), the geometry and overall volume of the recess largely corresponding to the geometry and overall volume of the balun 240. By mounting the thin form factor balun 240 largely parallel to the plane of the substrate 210, and by accommodating the balun 240 in a form-fitting recess in the wear block 120, the balun 240 may withstand mechanical forces to which the antenna 1000 may be exposed, particularly when mounted to an excavator bucket 500.

[0055] Alternative mounting arrangements and orientations of the balun 240 are possible. Figure 320 is shown mounted on circuit board substrate 210 with its major axis parallel to the plane of circuit board substrate 210, but in an alternative embodiment, balun 240 may be mounted so that its major axis protrudes upward from the plane of circuit board substrate 210. In this manner, balun 240 may be recessed in a vertical wall of wear block 120. As with the location and orientation of the balun first described, the geometry and overall volume of the recess may largely correspond to the geometry and overall volume of balun 240. By mounting balun 240 in this alternative orientation, the compressive loads on balun 240 may be reduced.

[0056] One or more coaxial transmission cables (not shown) may be provided for the purpose of feeding signals to and from the balun 240. The balun 240 may be connected to the radiator 220 using a coaxial line or a printed transmission line on a flex circuit. A transformer may also be provided at or near the balun 240 or the one or more coaxial transmission cables.

[0057] In some embodiments, it may be the case that the sum of the volumes of all components listed herein housed in cavity 112 or any particular antenna is at least 90% of the volume of cavity 112, such that the cavity is at least 90% occupied without air gaps. Preferably, the 90% figure may be 95%, or more preferably 98%, or even more preferably 99%. In this way, gaps of air within the confines of housing 110, which may create resonant effects (secondary resonances), may be avoided or at least minimized. Furthermore, the range of movement of the components relative to each other is limited, which increases the mechanical strength of the overall package.

[0058] Although the antenna 1000 of the present disclosure is not limited to use with ground penetrating radar applications or actual radar applications, with such applications and others, a matched antenna pair 470, 480 is typically provided, one for transmission and one for reception. Figure 4 and Figure 5 A dual antenna assembly 400 including a matched antenna pair 470, 480 according to the present disclosure is shown. As shown, a composite housing 410 is provided to house the matched antenna pair 470, 480. The housing 410 may include two separate but matched cavities, one for each of the antenna pairs 470, 480. Each antenna 470, 480 may also be provided as described with respect to Figure 1 As shown in the embodiment of Figure 6 , Figure 7 , Figure 8 and Fig. 9 One of the alternative embodiments shown in FIG. 1 is shown in FIG. 1 and is further described below.

[0059] exist Figure 4 and Figure 5 In an embodiment of the present invention, the housing provides a central divider 498 between each of the two cavities. The central divider 498 can also provide a portion of the healing plate 419.

[0060] from Figure 5 Obviously, Figure 4 and Figure 5 The dual antenna assembly 400 may have a square footprint. The advantage of a square footprint is that it is rotationally symmetric to allow the dual antenna assembly 400 to be rotated 90° while occupying the same space (see Fig.11 The housing 410 may be provided with fixing holes 499 through which the housing 410 may be fixed to, for example, an excavator bucket using bolts. The fixing holes 499 may be selected to maintain the rotational symmetry of the footprint of the dual antennas so as to allow the user to select in which orientation the dual antenna assembly 400 is to be mounted.

[0061] Thus, in a first orientation, each of the antenna pairs 470, 480 is mounted to travel from the blade 520 to the back of the bucket 500. In a second orientation, the dual antenna assembly is rotated 90° relative to the first orientation so that each of the antenna pairs 470, 480 is mounted to travel from one side to the other relative to the bucket 500. The two different orientations can lend themselves to different uses of the bucket 500.

[0062] As will be appreciated by those skilled in the art, rotational symmetry may be provided by an enclosure having a shape other than a square. Such alternative rotationally symmetric enclosures fall within the scope of the present disclosure.

[0063] Figure 6 Shows Figure 1 Antenna 2000 is an alternative embodiment to the illustrated embodiment. Figure 6 and Figure 1 The difference is that the absorber assembly 300 is configured differently. Instead of the microwave absorber 310 being located at the bottom of the cavity, and the dielectric layer 320 being just above the microwave absorber 310, there is a pair of dielectric layers 320, 330 with the absorber 310 located therebetween. The lower dielectric layer 330 is placed at the bottom of the cavity 112, the absorber 310 is placed above the lower dielectric layer 330, and the upper dielectric layer 320 fills the space below the radiator assembly 200 above the absorber 310.

[0064] Figure 7 Shows Figure 1 Antenna 3000 is another alternative embodiment to the illustrated embodiment. Figure 7 and Figure 1The difference is that the radiator assembly 200 also includes an absorbent pad 230 located below the printed circuit board substrate and above the dielectric layer 320 for absorbing microwave radiation. The absorbent pad 230 can be applied to the underside of the printed circuit board substrate 210. Alternatively, the absorbent pad 230 can be a separate component near the underside of the printed circuit board substrate 210. The absorbent pad 230 can be graphite. The absorbent pad 230 can be capacitively coupled to the printed radiator 220 via the printed circuit board substrate 210. (This is in contrast to the microwave absorber 310 that is not capacitively coupled to the printed radiator 220.) The printed circuit board substrate 210 can have a thickness of less than 0.5 mm, preferably a thickness of between 0.2 mm and 0.4 mm, and more preferably a thickness of 0.25 mm, which can achieve capacitive coupling compared to standard printed circuit boards that tend to have a thickness of about 1.6 mm.

[0065] The absorbent pad 230 may have a resistivity between 100 Ohms / square and 1000 Ohms / square, more preferably between 400 Ohms / square and 600 Ohms / square. The absorbent pad 230 may have a constant resistance over its entire area, or the resistance may vary over its entire area. The absorbent pad 230 may be continuous, or it may be discontinuous. In the latter case, it may be shaped to interact with the radiator only in a specific area.

[0066] The absorbent pad 230 may be painted, sprayed, printed or otherwise deposited on the underside of the substrate 210. The paint, spray or print of the absorbent pad 230 may be a colloidal solution of graphite. In an alternative method, the absorbent pad 230 may be deposited on a temporary surface and then transferred to the underside of the substrate 210.

[0067] The absorption mechanism of the resistive pad may be to dissipate the current flowing in the resistive absorbing substrate as heat by means of its capacitive coupling with the radiator.

[0068] Figure 8 Shows Figure 1 Antenna 4000 is another alternative embodiment to the illustrated embodiment. Figure 8 An embodiment effectively comprises Figure 6 Additional features of the embodiments Figure 7 Combinations of additional features of embodiments.

[0069] Fig. 9 Shows Figure 1 Antenna 5000 is another alternative embodiment to the illustrated embodiment.

[0070] exist Fig. 9In the antenna 5000 of FIG. 5 , the absorber assembly 300 includes a stack of multiple dielectrics, wherein the absorber is between each pair of adjacent dielectrics in the stack. For example, it may include N dielectrics and N-1 absorbers alternating between dielectrics and absorbers. Fig. 9 A specific example is shown, where N=5. Thus, Fig. 9 The illustrated example includes an absorber assembly 300a that includes five dielectric layers 340a and four absorber layers 310a.

[0071] In another example (not shown), the absorber assembly 300 may include an upper dielectric layer 320 and an absorber 310, and instead of a lower dielectric layer 330, there may be N dielectrics and N-1 absorbers. (In other words, above the dielectric layer 320, the absorber assembly may be Figure 8 , whereas below the dielectric layer 320, the absorber assembly may be more similar to Fig. 9 ) In one particular arrangement, a 10 mm thick lower dielectric layer 330 may replace five dielectric layers 340a, each 2 mm thick, with absorber layers 310a interposed therebetween.

[0072] The absorption properties of the antenna can also be adapted by using discontinuous absorption or dielectric elements.

[0073] Fig.10 Shows Figure 8 Antenna 6000 is another alternative embodiment of the embodiment shown. Figure 8 The continuous absorber layer 310 of the antenna 4000 may have a discontinuous absorber layer 310a. (As in all appendices of this application) Figure 1 Likewise, skilled artisans appreciate the highly schematic nature of the representation of discontinuities in absorber layer 310a.)

[0074] The discontinuity in the microwave absorber layer 310a, in addition to its distance from the radiator 220, further reduces the likelihood of capacitive coupling between the radiator 220 and the microwave absorber layer 310a.

[0075] The present disclosure contemplates the use of these different absorption characteristics alone or in combination. The exact combination of absorption characteristics may be selected depending on the particular application.

[0076] As previously in Fig.11 One application of the disclosed antennas (particularly the dual antenna assembly 400) is in the context of a radar system for a machine tool such as an excavator bucket 500. (It should be noted that Fig.11 The dual antenna assembly 400 does not have the above-mentioned rotationally symmetrical mounting feature.)

[0077] In addition to the antenna assembly 400, Fig.11 The excavator bucket 500 of the embodiment may include a top cavity ( Fig.11 5 (not visible in the figure), the top cavity is enclosed within the bucket cavity 540 at the opposite side of the bucket 500 relative to the base 510. The top cavity may include a removable panel attached in place by fasteners.

[0078] The excavator bucket 500 may also include one or more conduits ( Fig.11 ), which provides a connection between each antenna 470, 480 in the dual antenna assembly 400 and the top cavity.

[0079] The top cavity may contain a radar control module. The radar control module may include one or both of a digital printed circuit board and an analog printed circuit board.

[0080] A coaxial cable (not shown) facilitates communication between each antenna 470, 480 in the dual antenna assembly 400 and the radar control module. The coaxial cable forms a channel in the conduit.

[0081] A plurality of fasteners may be employed to secure the dual antenna assembly 400 to the base 510 of the excavator bucket 500. The fasteners may be mounted so that they do not protrude below the surface of the base 510. In this way, they are less susceptible to damage. Instead, the fasteners are mounted so that they protrude above the inner surface of the bucket cavity 540. This is to allow the fasteners to be more easily ground off (e.g., with an angle grinder) in the event that the antenna assembly 400 needs to be replaced. Although releasable fasteners may be employed, using an excavator bucket for its intended purpose often means that the fasteners may become bent or damaged, which means that the most effective way to remove the fasteners may be by grinding them off.

[0082] Each fastener may include a bolt and a nut. The bolt may include a head that is flush with the surface of the base 510. The nut may be located inside the excavator bucket 500 and protrude above the inner surface of the bucket cavity 540.

[0083] although Fig.11 Not shown in the embodiment of FIG. 4 , the locations of the fixing holes may be selected to maintain the rotational symmetry characteristics of the dual antenna assembly 400 .

[0084] In this way, the orientation of the dual assembly 400 can be such that the transmitter 470 preferentially transmits in a direction toward the blade 520, and the receiver 480 preferentially receives from a direction facing the blade 520. Alternatively, by releasing the fixture and rotating the dual antenna assembly 400 90 degrees, the same fixture and fixing holes can be used to attach the antenna assembly 400 so that the transmitter 470 preferentially transmits in a direction transverse to the blade 520, and the receiver 480 preferentially receives in a direction transverse to the blade 520.

[0085] As described above, the signals are sent via a coaxial cable between the dual antenna assembly 400 and the radar control module located in the top cavity of the excavator bucket 500. Separating the radar control module from the dual antenna assembly 400 means that only those components that are important relative to the position of the cutting blade are located in this manner. In contrast, those elements that are not important relative to the position of the excavator blade 520, such as those of the radar control module, are located at a distance from the excavator blade 520. This means that they may be less susceptible to damage from the impact of the excavator blade 520 and the rest of the base 510 of the excavator bucket 500 impacting the ground or other material to be excavated.

[0086] although Fig.11 The embodiment shown in the figure relates to an excavator bucket 500, but it should be noted that the claimed antenna and wider radar system are suitable for a wider range of potential applications. For example, other applications would include other machining tools, such as drilling tools, augers, flails and mulchers.

[0087] From outside the field of machines with machining tools, other applications would include aerial vehicles, including autonomous aerial vehicles, such as drones. These embodiments may be particularly useful for applications where the objective of seeking underground contours is sought, perhaps in anticipation of construction work.

[0088] Regardless of the application, radar systems may involve acquiring geolocation data to be matched with radar system output information in order to construct a subsurface map of the area subject to analysis by the radar system.

[0089] The radar system of the present disclosure is particularly suitable for low-cost applications, such as in machining tools, where the entire range of the tool may require the system, and where the environment of the tool is such that component replacement may be more frequent than other radar applications. In addition, the radar system of the present disclosure is a low-power solution compared to many prior art radar systems, and therefore, it is suitable for applications where low power is particularly beneficial, such as in the context of small-scale autonomous aircraft with small battery packs, and where it is desired that the radar system have minimal impact on flight range.

[0090] The radar system of the present disclosure is not limited to ground penetrating applications, but it is particularly well suited for applications where the antenna position relative to the ground may move between close (where ground coupling is necessary) and far (where air coupling is necessary).

[0091] Other aspects of the disclosure are set forth in the following numbered clauses:

[0092] 1. An antenna for a ground penetrating radar system, the antenna comprising:

[0093] a housing defining a cavity having an opening, the cavity containing:

[0094] a radiator, the radiator being on a first surface of a planar substrate, the radiator being on a planar bow-tie-shaped conductive layer included on or adjacent to the first surface of the substrate;

[0095] an absorbent pad on or adjacent to a second surface of the substrate opposite the first surface;

[0096] a wear-resistant block located between the radiator and the opening to the cavity, the wear-resistant block being used to provide mechanical protection for the radiator; and

[0097] An absorber assembly is located on a side of the radiator opposite the opening, the absorber assembly including an absorber layer located between first and second dielectric layers such that the absorber layer is capacitively coupled to the radiator and to the housing.

[0098] 2. The antenna of clause 1, wherein the substrate comprises a printed circuit board substrate, and wherein the radiator is printed on the printed circuit board substrate.

[0099] 3. An antenna according to clause 1 or clause 2, wherein the absorber component comprises a layered arrangement of layers including N absorber layers and N+1 dielectric layers.

[0100] 4. An antenna according to any preceding clause, wherein the substrate has a thickness of less than 1 mm, preferably less than 0.5 mm, more preferably less than 0.25 mm.

[0101] 5. An antenna according to any preceding clause, wherein at least a portion of the absorbent pad has a resistivity between 400 Ohms / square and 600 Ohms / square.

[0102] 6. An antenna according to any preceding clause, wherein one or both of the absorptive pad and the absorber layer comprises or consists of graphite.

[0103] 7. An antenna according to any preceding clause, wherein the housing is metallic, preferably aluminium or an aluminium alloy.

[0104] 8. An antenna according to any preceding clause, wherein the housing comprises a plate having a hole, the hole providing the opening of the housing, such that the plate surrounds the opening.

[0105] 9. An antenna according to any preceding clause, wherein one or more of the wear block, the first dielectric layer and the second dielectric layer has a dielectric constant between 1.0 and 4.0, preferably a dielectric constant of 2.7.

[0106] 10. An antenna according to any preceding clause, wherein one or more of the wear-resistant block, the first dielectric layer and the second dielectric layer comprises plastic or consists of plastic, preferably comprises polycarbonate or consists of polycarbonate, more preferably comprises D60 or consists of D60.

[0107] 11. An antenna according to any preceding clause, wherein:

[0108] the sum of the volumes of the following components being at least 99% of the volume of the cavity: the wear block; the planar substrate; the radiator comprising a planar surface; the absorbent pad; and the absorber assembly,

[0109] Such that the cavity is at least 99% occupied without air gaps.

[0110] 12. An antenna according to any preceding clause, further comprising a coaxial transmission line, preferably comprising a transformer.

[0111] 13. An antenna according to any preceding clause, further comprising a balun mounted on the substrate close to the centre of the bow-tie shaped conductive layer of the radiator.

[0112] 14. An antenna according to clause 13, wherein the transmission line of the balun lies in a plane parallel to the plane of the radiator.

[0113] 15. An antenna according to any of clauses 12 to 14, wherein the wear block comprises a recess to accommodate the balun and / or the coaxial transmission line.

[0114] 16. A dual antenna assembly comprising a matched antenna pair, wherein each of the matched antenna pair is as described in any preceding clause.

[0115] 17. The dual antenna assembly of clause 16, comprising a composite housing, wherein the composite housing comprises a housing for a first antenna in the antenna pair and a housing for a second antenna in the antenna pair.

[0116] 18. The dual antenna assembly of clause 17, wherein the composite housing is rotationally symmetric such that the composite housing can be mounted with the antenna pair side-to-side or side-to-side.

[0117] 19. A dual antenna assembly according to any of clauses 16 to 18, wherein the composite housing has a square form in the plane of the radiator.

[0118] 20. An excavator bucket comprising a dual antenna assembly according to any one of clauses 16 to 19.

[0119] Industrial Applicability

[0120] The antenna of the present disclosure is suitable for a variety of industrial applications, such as those mentioned above. In particular, the antenna of the present disclosure may be suitable for ground penetrating radar applications. For example, the antenna may be suitable for a radar system used with a machining tool so that feedback can be provided to the operator in real time, which allows feedback to be provided immediately before cutting into the ground. This enables underground features to be properly discovered and / or avoided. In another example, the radar system may be suitable for surveying applications. Surveying applications may involve installing a radar system in an air vehicle or a ground vehicle, which is designed to complete the measurement of the location to be measured by perhaps systematically passing through (e.g., in rows or columns) the location to be measured.

Claims

1. An antenna for a ground penetrating radar system, the antenna include: a metal or metal-coated housing having a cavity therein; a plurality of polymer plastic dielectrics, the plurality of polymer plastic dielectrics filling the cavity; as well as a planar printed radiating element connected to a balun recessed within at least one of the polymer plastic dielectrics, wherein the housing has an opening that allows radiation to be emitted to and from the radiating element, wherein at least one of the polymer plastic dielectrics is loaded or laminated with a microwave absorbing material, wherein at least one of the polymer plastic dielectrics provides mechanical protection to the radiating element; and Wherein, at least one of the polymer plastic dielectrics has a dielectric constant between the dielectric constant of the ground and the dielectric constant of air.

2. The antenna according to claim 1, in, The radiating element has a dipole with radiating arms.

3. The antenna according to claim 2, in, The dipole originates from a truncated bipyramid projected onto a plane.

4. The antenna according to claim 2, in, The radiating arm is at least partially elliptical or circular.

5. The antenna according to claim 2, in, The microwave absorbing material is an electrically or magnetically active material.

6. The antenna according to claim 2, in, The electrically or magnetically active material includes at least one of: metal flakes and graphite.

7. The antenna according to claim 3, in, The metal housing is formed from sheet metal by a metallization process or metal coating technology.

8. An excavator bucket comprising the antenna according to any one of claims 1-7.

9. A dielectric for an antenna, the antenna being used in a ground penetrating radar system, the dielectric being characterized by: The dielectric is placed between the radiator and the opening of the antenna; The dielectric is formed of plastic having a dielectric constant between that of the ground and that of air; and The dielectric is a wear-resistant block to provide mechanical protection to the radiator.

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