Patent Description:
Radar systems that detect the presence of objects in an environment are well known, including ground-penetration radar systems.

In most radar applications, the antenna needs either to facilitate air coupling (such as if the antenna is mounted on a drone intended to fly some distance above the ground) or to facilitate ground coupling (such as if the antenna is mounted to the underside of a ground travelling radar survey vehicle).

However, in some cases, such as where the antenna is to be mounted on a machine work tool like an excavator bucket, the antenna needs to facilitate both air and ground coupling. This is because, to use the example of the excavator bucket, it will on some occasions be in direct contact with or very close to the ground while on other occasions it will be centimetres, tens of centimetres or even meters above the ground.

Furthermore, ground-penetration radar systems need broad bandwidth antennas, often referred to as ultra-wideband (UWB) antennas. Broad bandwidth antennas are often achieved by using a bi-cone dipole which facilitates frequency independence. Where a planar antenna is required, a so-called bow-tie antenna may be used. The bow-tie shape derives from truncation and projection onto a plane of an infinite bi-cone. Appropriate resistive loading is also necessary.

Where a ground-penetration radar antenna is mounted on a work tool such as an excavator bucket, a significant degree of mechanical ruggedness is necessary.

<CIT>) relates to a wideband compact antenna of very small thickness and with dual orthogonal linear polarization operating in the V/UHF bands.

<CIT>) relates to an antenna device provided in a wireless device such as a mobile communication terminal or a wireless IC card, which is required to be thin.

<CIT> (B1) relates to planar antennas with non-dispersive, ultra wide bandwidth (UWB) characteristics.

<CIT> (A1) relates to an implement for a machine such as a bucket, and more particularly to the bucket having an integrated RADAR system.

Against this background there is provided an antenna for a ground-penetration radar application in accordance with claim <NUM>.

Embodiments of the invention are now described with reference to the accompanying drawings, in which:.

<FIG> shows a dual antenna assembly <NUM> mounted on an excavator bucket <NUM> for use in a ground-penetration radar application. The excavator bucket <NUM> may be attached to an arm of an excavator or other machine. The excavator bucket <NUM> may otherwise be, for example, a conventional 12inch (~<NUM>) wide excavator bucket.

The excavator bucket <NUM> comprises a base <NUM> and side surfaces <NUM> defining therein a cavity <NUM> for containing excavated material. A blade <NUM>, which may be used for cutting into the ground, is located at a front of the base <NUM>. The dual antenna assembly <NUM> is mounted to an outside surface of the base <NUM> of the excavator bucket <NUM> in the same plane as and behind the blade <NUM>. One of the two antennas <NUM>, <NUM> of the dual antenna assembly <NUM> may be used as a transmitter and the other of the two antennas <NUM>, <NUM> may be used as a receiver.

As already explained, one of the challenges around antenna design for such an application as this is the need for the antenna to couple to the ground (when the bucket is cutting into or proximate to the ground) and for the antenna to couple to air (when the bucket is elevated). Another of the challenges is that the antenna must be of a rugged and slim construction, given its intended located on the base <NUM> of the bucket and where it will inevitably experience mechanical stresses and strains given the purpose of the bucket.

<FIG> shows a schematic representation of a section through an antenna <NUM> similar to one of the pair of antennas <NUM>, <NUM> of the dual antenna assembly <NUM> of <FIG>.

The antenna <NUM> comprises a housing <NUM> defining a cavity <NUM> with a bottom surface <NUM>, a plurality of side surfaces <NUM>, and a plate <NUM>, which may be termed a heal plate <NUM>, opposite the bottom surface <NUM>. The plate <NUM> has an opening <NUM> providing an opening <NUM> to the cavity <NUM>. The housing <NUM> may be of metal, preferably of aluminium or aluminium alloy.

The cavity <NUM> may contain a wear-block <NUM>, a radiator assembly <NUM> and an absorber assembly <NUM>. The radiator assembly <NUM> is sandwiched between the wear-block <NUM> and the absorber assembly <NUM> such that the wear-block <NUM> is located at the opening <NUM> to the cavity and the absorber assembly <NUM> is located adjacent the bottom surface <NUM> of the cavity <NUM> and furthest from the opening <NUM> to the cavity <NUM>. In this way, with the radiator assembly <NUM> is located in between the wear-block <NUM> and the absorber assembly <NUM>.

The radiator assembly <NUM> may comprise a printed circuit board substrate <NUM> on an upper side of which is printed a metallic radiator <NUM> described in more detail below.

The radiator <NUM> may be of copper. The copper may be 1oz. (<NUM>) copper.

The radiator assembly <NUM> may be approximately <NUM> in length and <NUM> in width. The radiator <NUM> may be approximately <NUM> in length and <NUM> in width at the broadest portion of the bow-tie.

Located at the opening <NUM> of the cavity <NUM> and occupying the volume between the opening <NUM> and the top surface of the printed radiator <NUM> is the wear-block <NUM>. There may be at least two purposes of the wear-block <NUM>. In particular, the wear-block <NUM> may be of a material having dielectric properties selected to provide matching to both air and ground. Secondly, it may have particularly hard-wearing properties (hence the term wear-block) whilst recognising that some mechanical damage may be inevitable when mounted on the underside of an excavator bucket <NUM>, for example. It may therefore also be configured to sustain mechanical damage such as scratches and dents so as to protect the radiator <NUM> from such damage. In this way, scratches and other mechanical damage to the wear-block <NUM> may be prevented from affecting operation of the antenna <NUM> to any significant degree.

The relative permittivity (dielectric constant) of ground surfaces which a user may wish to penetrate with the blade <NUM> of an excavator bucket <NUM> may typically be around <NUM> while that of air may be <NUM>. Accordingly, selecting a wear-block <NUM> having a relative permittivity (dielectric constant) between these two values may be appropriate. A relative permittivity (dielectric constant) of approximately <NUM> may be most preferable as this facilitates both ground and air coupling.

The wear-block <NUM> may be of plastic. For example, the wear-block <NUM> may be of polycarbonate. The wear-block <NUM> may be of a plastic that measures <NUM>, or more than <NUM>, on the Shore D durometer scale. Such a wear-block has a particularly hard-wearing properties as well as appropriate permittivity. The wear-block <NUM> may have a thickness of approximately <NUM>.

Located adjacent the bottom surface <NUM> of the cavity <NUM> furthest from the opening <NUM> (beneath the radiator assembly <NUM> in the orientation shown in <FIG>) is located the absorber assembly <NUM>. The absorber assembly <NUM> comprises an absorber <NUM> at the bottom of the cavity <NUM> adjacent the bottom surface <NUM> and first dielectric layer <NUM> between the absorber <NUM> and the radiator assembly <NUM>. The first dielectric layer <NUM> may be sufficiently thick such that capacitive coupling between the absorber <NUM> and the printed radiator <NUM> is negligible. The thickness of the first dielectric layer <NUM> may, for example, be approximately <NUM>, approximately <NUM>, approximately <NUM>, or any other suitable thickness. The absorber <NUM> may be between <NUM> and <NUM> in thickness and preferably <NUM> in thickness.

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

<FIG> shows typical permeability properties of the microwave absorber <NUM>. These permeability properties result in typical power loss shown in <FIG>.

In this way, the microwave absorber <NUM> absorbs back reflections of microwave radiation that reflects off the bottom surface <NUM> of the housing <NUM>. Back reflections that are absorbed by the microwave absorber <NUM> do not therefore reach the radiator and/or a second antenna that uses its radiator as a receiver.

In an antenna that makes use of the frequency bank between <NUM> and <NUM>,<NUM>, it can be seen particularly clearly from <FIG> that the power loss provided by the microwave absorber <NUM> within this frequency band is high compared with at lower frequencies.

An appropriate value for relative permittivity (dielectric constant) of the first dielectric layer <NUM> may be between <NUM> and <NUM>, preferably around <NUM>.

The first dielectric layer <NUM> may be of plastic. For example, the first dielectric layer may be of polycarbonate. The first dielectric layer <NUM> may be of a plastic that measures <NUM>, or more than <NUM>, on the Shore D durometer scale. This has hard-wearing properties as well as appropriate permittivity. The requirement for a hard-wearing plastic may be less important in the case of the first dielectric layer <NUM> than in the case of the wear-block <NUM>. This is because the first dielectric layer <NUM> is enclosed by various other features of the antenna <NUM> and therefore much less susceptible to direct mechanical damage.

The housing <NUM> may be pre-formed prior to the installation of the various components (including the wear-block <NUM>, the radiator assembly <NUM> and the absorber assembly <NUM>) that the finished antenna assembly <NUM> or <NUM> contains.

Alternatively, in some embodiments, the wear-block <NUM>, the radiator assembly <NUM> and the absorber assembly <NUM> may be assembled first and the housing <NUM> may be formed around them. As such, the cavity <NUM> may be dimensioned so as to envelope the exact exterior form of the combination of the wear-block <NUM>, the radiator assembly <NUM> and the absorber assembly <NUM>. In some embodiments, it may be that the housing <NUM> is formed by a process of metallisation or a metal coating technique as known in the art such but not limited to vacuum metallisation, thermal spraying, or cold spraying.

By forming the housing <NUM> around the wear-block <NUM>, the radiator assembly <NUM> and the absorber assembly <NUM>, air gaps between the housing <NUM> and its contents are eliminated (or at least vastly minimised) which avoids or at least significantly reduces resonant effects (secondary resonances) that would result from such air gaps.

<FIG> show a schematic representation of the radiator assembly <NUM> of the antenna <NUM> of <FIG>. The radiator assembly <NUM> is shown in cross section in <FIG> and in plan view in <FIG>.

The radiator assembly <NUM> may be manufactured from a printed circuit board comprising a substrate <NUM> having a metallic layer that covers the whole area of a top surface of the substrate <NUM>. The planar bow-tie form of the radiator <NUM> may be produced using conventional printed circuit board techniques involving using a mask to distinguish between areas of the metallic layer to be retained and areas of the metallic layer to be removed. Removal of the unwanted areas of the metallic layer, such as by selective etching of unmasked areas, results in the bow-tie shape illustrated in <FIG>.

Ground-penetration radars need broadband antennas. Typically the bandwidth will be approximately equal to the centre frequency. This leads to high percentage bandwidth. In the present application, the bandwidth is achieved by shaping (e.g. angling) the arms of the radiating element.

A common approach is the bi-cone dipole which avoids resonance because an infinite cone can be defined by angle only. Since it is length independent, it is wavelength independent and therefore frequency independent. In the present context, a three-dimensional radiator is not feasible. The bow-tie shape of the radiator of the present disclosure is derived from a truncated bi-cone projected onto a plane. This shape maintains some of the frequency independent nature of the infinite dipole, whilst being realisable in a planar manner of realistic dimensions for the intended purpose.

<FIG> shows a plan view of the bow-tie radiator <NUM> on its substrate <NUM> and also shows a balun <NUM> which provides an electrical connection to the bow-tie radiator <NUM>.

The balun <NUM> is mounted on the substrate <NUM> so as to connect to the centre of the bow-tie of the radiator via metallic electrical connections formed by conventional means in the printed circuit board. These may be formed by etching in parallel with the process of etching the radiator geometry. The balun <NUM> may be mounted with its main axis in a plane parallel to the plane of the bow-tie radiator <NUM>. The balun <NUM> may also be mounted with its main axis perpendicular to the main axis of the bow-tie radiator <NUM>. In this way it may be conveniently accommodated in a triangular space on the substrate between the two halves of the bow-tie radiator <NUM>. Furthermore, the balun <NUM> may have a slim form factor such that it is larger in length and width relative to its thickness by which it protrudes from the surface of the substrate <NUM>.

The thickness of the balun <NUM> by which it protrudes from the surface of the substrate may be accommodated in the wear-block <NUM> by virtue of a recess (not shown in the figures) in the wear-block <NUM> whose geometry and overall volume largely corresponds to the geometry and overall volume of the balun <NUM>. By mounting a thin form factor balun <NUM> largely parallel to the plane of the substrate <NUM> and by accommodating the balun <NUM> in a form-fitting recess of the wear-block <NUM>, the balun <NUM> may withstand mechanical forces with which the antenna <NUM> is likely to come into contact, especially when mounted to an excavator bucket <NUM>.

Alternative mounting arrangements and orientations of the balun <NUM> are possible. While the balun <NUM> is shown in <FIG> as being mounted on the circuit board substrate <NUM> with its major axis parallel to the plane of the circuit board substrate <NUM>, in an alternative embodiment the balun <NUM> may be mounted such that its major axis projects up from the plane of the circuit board substrate <NUM>. In this way, the balun <NUM> may be recessed in the vertical wall of the wear-block <NUM>. As with the first described balun position and orientation, the geometry and overall volume of the recess may largely correspond to the geometry and overall volume of the balun <NUM>. By mounting the balun <NUM> in this alternative orientation, compressive loading on the balun <NUM> may be reduced.

One or more coaxial transmission cables (not shown) may be provided for the purpose of feeding signals to and from the balun <NUM>. The balun <NUM> may be connected to the radiator <NUM> using either co-axial lines or printed transmission lines on a flexi circuit. There may also be provided a transformer at or in the vicinity of the balun <NUM> or the one or more coaxial transmission cables.

In some embodiments it may be that the sum of the volumes of all the components listed herein as being accommodated in the cavity <NUM> or any particular antenna is at least <NUM>% of the volume of the cavity <NUM>, such that the cavity is at least <NUM>% occupied without air gaps. Preferably, the figure of <NUM>% may be <NUM> % or more preferably <NUM>% or even more preferably <NUM>%. In this way, seams of air within the confines of the housing <NUM>, which might create resonant effects (secondary resonances), can be avoided or at least minimised. Furthermore, there is limited scope for movement of components relative to one another which increases the mechanical ruggedness of the overall package.

While the antenna <NUM> of the present disclosure is not limited for use with ground-penetration radar applications, or indeed radar applications, in the case of such applications and others it is common to provide a pair of matched antennas <NUM>, <NUM> - one to transmit and one to receive. <FIG> and <FIG> show a dual antenna assembly <NUM> that comprises a matching pair of antennas <NUM>, <NUM> in accordance with the disclosure. As shown, a compound housing <NUM> is provided to accommodate a matching pair of antennas <NUM>, <NUM>. The housing <NUM> may comprise two separate but matching cavities, one for each of the pair of antennas <NUM>, <NUM>. Each antenna <NUM>, <NUM> may otherwise be as shown in respect of the <FIG> embodiment, or perhaps as shown in respect of one of the alternative embodiments shown in <FIG>, <FIG>, <FIG> and <FIG>, and as described further below.

In the embodiment of <FIG> and <FIG>, the housing provides a central divider <NUM> between each of the two cavities. The central divider <NUM> may also provide part of the heal plate <NUM>.

The dual antenna assembly <NUM> of <FIG> and <FIG> may have a square footprint, as evident from <FIG>. An advantage of a square footprint is that it is rotationally symmetric to allow for straightforward rotation of the dual antenna assembly <NUM> by <NUM>° whilst occupying the same space (see <FIG>). The housing <NUM> may be provided with fixing apertures <NUM> (through which bolts might be used to secure the housing <NUM> to, for example, an excavator bucket). The fixing apertures <NUM> may be selected to maintain the rotationally symmetric nature of the footprint of the dual antenna so as to allow a user to choose in which orientation to mount the dual antenna assembly <NUM>.

As such, in a first orientation each of the pair of antennas <NUM>, <NUM> is mounted to run from the blade <NUM> to the back of the bucket <NUM>. In a second orientation, the dual antenna assembly is rotated by <NUM>° relative to the first orientation, such that each of the pair of antennas <NUM>, <NUM> is mounted to run from side to side relative to the bucket <NUM>. The two different orientations may lend themselves to different uses of the bucket <NUM>.

As the skilled person recognises, rotational symmetry may be provided by a housing having a shape other than a square. Such alternative rotationally symmetric housings fall within the scope of the present disclosure.

<FIG> shows an antenna <NUM> of an alternative embodiment to that shown in <FIG>. <FIG> differs from <FIG> in that the absorber assembly <NUM> is differently configured. Instead of the microwave absorber <NUM> being located at the bottom of the cavity with the dielectric layer <NUM> being only above the microwave absorber <NUM>, there is a pair of dielectric layers <NUM>, <NUM> with the absorber <NUM> located therebetween. A lower dielectric <NUM> is placed at the bottom of the cavity <NUM>, the absorber <NUM> is placed above the lower dielectric layer <NUM> and an upper dielectric later <NUM> fills the space above the absorber <NUM> beneath the radiator assembly <NUM>.

<FIG> shows an antenna <NUM> of a further alternative embodiment to that shown in <FIG>. <FIG> differs from <FIG> in that the radiator assembly <NUM> further comprises an absorbing underlay <NUM> for absorbing microwave radiation located beneath the printed circuit board substrate and above the dielectric <NUM>. The absorbing underlay <NUM> may be coated onto the underside of the printed circuit board substrate <NUM>. Alternatively, the absorbing underlay <NUM> may be a separate component proximate the underside of the printed circuit board substrate <NUM>. The absorbing underlay <NUM> may be of graphite. The absorbing underlay <NUM> may be capacitively coupled to the printed radiator <NUM> via the printed circuit board substrate <NUM>. (This contrasts with the microwave absorber <NUM>, which is not capacitively coupled to the printed radiator <NUM>. ) The printed circuit board substrate <NUM> may have a thickness of less than <NUM>, preferably between <NUM> and <NUM>, more preferably <NUM>, which enables the capacitive coupling by comparison with standard printed circuit boards that tend to have a thickness of approximately <NUM>.

The absorbing underlay <NUM> may have a resistivity of between 100Ohms/square and <NUM>,000Ohms/ square, more preferably between 400Ohms/ square and 600Ohms/ square. The absorbing underlay <NUM> may have a resistance that is constant across its area or it may vary across its area. The absorbing underlay <NUM> may be continuous or may be discontinuous. In the latter case it may be shaped to interact with the radiator only in specific areas.

The absorbing underlay <NUM> may be painted, sprayed, printed or otherwise deposited on the underside of the substrate <NUM>. Painting, spraying or printing of the absorbing underlay <NUM> may be of a colloidal solution of graphite. In one alternative approach, the absorbing underlay <NUM> may be deposited on a temporary surface and then transferred to the underside of the substrate <NUM>.

The mechanism of absorption of the resistive underlay may be to dissipate as heat a current that flows in the electrically resistive absorbing underlay by virtue of its capacitive coupling to the radiator.

<FIG> shows an antenna <NUM> of a further alternative embodiment to that shown in <FIG>. The <FIG> embodiment effectively includes the additional feature of the <FIG> embodiment in combination with the additional feature of the <FIG> embodiment.

<FIG> shows an antenna <NUM> of a further alternative embodiment to that shown in <FIG>.

In the <FIG> antenna <NUM>, the absorber assembly <NUM> comprises a stack of multiple dielectrics, with an absorber between each pair of adjacent dielectrics in the stack. For example, it may comprise N dielectrics and N-<NUM> absorbers, alternating between dielectric and absorber. <FIG> illustrates a specific example where N=<NUM>. As such, the illustrated example of <FIG> includes an absorber assembly 300a that comprises five dielectric layers 340a and four absorber layers 310a.

In another example (not illustrated), the absorber assembly <NUM> may comprise an upper dielectric <NUM> and an absorber <NUM> and, in place of the lower dielectric <NUM>, there may be N dielectrics and N-<NUM> absorbers. (In other words, above dielectric <NUM>, the absorber assembly may be of the type shown in <FIG> while below the dielectric <NUM> the absorber assembly may be more like that shown in <FIG>. ) In one particular arrangement, a <NUM> thick lower dielectric <NUM> may be substituted for five dielectrics 340a, each <NUM> thick, with absorber sheets 310a interposed.

Absorption properties of the antenna may also be adapted by employing discontinuous absorption or dielectric elements.

<FIG> shows an antenna <NUM> of a further alternative embodiment to that shown in <FIG>. In place of the continuous absorber layer <NUM> of the <FIG> antenna <NUM>, there may be a discontinuous absorber layer 310a. (As with all of the figures of this application, the skilled person appreciates the highly schematic nature of the representation of the discontinuities in the absorber layer 310a.

The discontinuities in microwave absorber layer 310a may - in addition to its distance from the radiator <NUM> - further reduce the likelihood of capacitive coupling between the radiator <NUM> and the microwave absorber 310a.

The present disclosure encompasses the use of these different absorption features either separately or in combination. The precise combination of absorption features may be selected dependent upon the particular application.

As mentioned previously in the context of <FIG>, one application of the antenna (in particular the dual antenna assembly <NUM>) of the present disclosure is in the context of a radar system for a machine work tool such as an excavator bucket <NUM>. (It should be noted that the dual antenna assembly <NUM> of <FIG> does not have the rotationally symmetric mounting feature described above.

In addition to the antenna assembly <NUM>, the excavator bucket <NUM> of the <FIG> embodiment may comprise a top cavity (not visible in <FIG>), enclosed within the bucket cavity <NUM> at an opposing face of the bucket <NUM> relative to the base <NUM>. The top cavity may comprise a removable panel attached in position by fasteners.

The excavator bucket <NUM> may further comprise one or more conduits (not shown in <FIG>) within the bucket cavity <NUM> providing a connection between each antenna <NUM>, <NUM> of the dual antenna assembly <NUM> and the top cavity.

The top cavity may contain a radar control module. The radar control module may comprise one or both of a digital printed circuit board and an analogue printed circuit board.

Coaxial cables (not shown) facilitate communication between each antenna <NUM>, <NUM> of the dual antenna assembly <NUM> and the radar control module. The coaxial cables may be channelled in the conduits.

A plurality of fasteners may be employed to fasten the dual antenna assembly <NUM> to the base <NUM> of the excavator bucket <NUM>. The fasteners may be mounted such that they do not protrude beneath the surface of the base <NUM>. In this way they are less vulnerable to damage. By contrast, the fasteners may be mounted such that they do protrude above an inner surface of the bucket cavity <NUM>. This is to enable the fasteners to be ground away (for example with an angle grinder) more easily in the event of a need to substitute the antenna assembly <NUM>. While releasable fasteners may be employed, use of an excavator bucket for its intended purposes often means that fasteners may be bent or damaged, meaning that the most efficient method of removing the fasteners may be by grinding them away.

Each fastener may comprise a bolt and a nut. The bolt may comprise a head that is flush with the surface of the base <NUM>. The nut may sit inside the excavator bucket <NUM> and protrude above an interior surface of the bucket cavity <NUM>.

While not shown in the embodiment of <FIG>, the location of the fixing holes may be selected to maintain the rotationally symmetrical nature of the dual antenna assembly <NUM>.

As such, the orientation of the dual assembly <NUM> may be such that the transmitter <NUM> transmits preferentially in a direction towards the blade <NUM> and the receiver <NUM> receives preferentially from a direction facing the blade <NUM>. Alternatively, by releasing the fixings and rotating the dual antenna assembly <NUM> by <NUM> degrees, the same fixings and fixing holes may be used to attach the antenna assembly <NUM> such that the transmitter <NUM> preferentially transmits in a direction transverse to the blade <NUM> and the receiver <NUM> preferentially receives in a direction transverse to the blade <NUM>.

As discussed above, the signals are sent via coaxial cables between the dual antenna assembly <NUM> and the radar control module which is located within the top cavity of the excavator bucket <NUM>. Separating the radar control module from the dual antenna assembly <NUM> means that only those components whose location relative to the cutting blade is significant are located in that manner. By contrast, those elements whose location relative to the excavator blade <NUM> is not significant, for example those of the radar control module, are located at a distance from the excavator blade <NUM>. This means that they may be less vulnerable to damage from impact of the excavator blade <NUM> and the rest of the base <NUM> of the excavator bucket <NUM> impacting the ground or other materials to be excavated.

While the embodiment illustrated in <FIG> relates to an excavator bucket <NUM>, it should be noted that the claimed antenna and the broader radar system is applicable to a much wider range of potential applications. For example, other applications would include other machine work tools such as drilling tools, augers, flails and mulchers.

Looking outside the field of machines with work tools, other applications would include airborne vehicles, including autonomous aircraft such as drones. These embodiments may be particularly useful for applications where the aim of a subterranean profile is sought, perhaps in anticipation of construction work.

Regardless of the application, the radar system may involve the obtaining of geo-location data to be matched with the radar system output information in order to build a subterranean map of the area that is subject to the radar system analysis.

The radar system of the present disclosure is particularly appropriate for low cost applications, such as in machine work tools, where a whole range of tools may require the system and where the environment of the tool is such that component replacement may be more frequent that in other radar applications. Furthermore, the radar system of the disclosure is a low power solution by comparison with many prior art radar systems and, accordingly, it is appropriate for applications where low power is a particular benefit, such as in the context of small scale autonomous aircraft having small battery packs and where there is a desire for the radar system to have minimal impact on flying range.

The radar system of the present disclosure is not limited to ground-penetration applications though it is particularly suitable for applications where the antenna position relative to the ground is likely to move between proximate (where ground coupling is necessary) and distant (where air coupling is necessary).

Claim 1:
An antenna (<NUM>) for a ground-penetration radar system, the antenna comprising:
a housing (<NUM>) defining a cavity (<NUM>) having an opening (<NUM>), the cavity containing:
a radiator (<NUM>) on a first surface of a planar substrate (<NUM>), the radiator comprising a planar, bow-tie shaped conducting layer on or adjacent to the first surface of the substrate;
wherein the antenna further comprises:
a wear-block (<NUM>) formed of a solid dielectric located between the radiator and the opening to the cavity for providing mechanical protection to the radiator, the wear-block abutting the radiator; and
an absorber assembly (<NUM>) located on an opposite side of the radiator from the opening, the absorber assembly comprising a microwave absorber (<NUM>) and a first dielectric layer (<NUM>), wherein the first dielectric layer is located between the radiator and the microwave absorber.