GB2476087A

GB2476087A - Compact laminated ultra-wideband antenna array

Info

Publication number: GB2476087A
Application number: GB0921675A
Authority: GB
Inventors: Lye Whatt Chua
Original assignee: Thales Holdings UK PLC
Current assignee: Thales Holdings UK PLC
Priority date: 2009-12-10
Filing date: 2009-12-10
Publication date: 2011-06-15
Also published as: GB0921675D0

Abstract

An ultra-wideband (UWB) antenna 170, or its method of manufacture, comprises a first laminar dielectric substrate 104 with first and second opposing planar surfaces with a radiating element 102,with a signal feedpoint 105, being formed on the first surface of the substrate 104. A second laminar dielectric substrate is provided with a plurality of conductive elements 154 formed on a first planar surface and a ground element 156 formed on a second opposing planar surface. At least one or more of the said conductive elements 154 is electrically connected to the ground element 156 by at least one conductive via path 154. The first surface of the second substrate is substantially coupled to the second surface of the first substrate. A signal transmission element 180 is substantially arranged orthogonal to the first planar surface of the first substrate 104 and is connected to the feedpoint 105 of the radiation element 102. A plurality of radiating elements may be arranged in a regular or irregular compact array formation. Further conductive elements may be formed on the first surface of the first substrate 104 adjacent the feedpoint 105 to improve the impedance matching.

Description

An Ultra Wideband Antenna

Field of the Invention

The present invention relates to antennas, and more particularly to antennas for radiating ultra wide bandwidth (UWB) pulses.

Background of the Invention

Pulsed electromagnetic (elm) energy transmission and reception systems typically possess wide-band or UWB transmission spectral bandwidths. This UWB characteristic stems from the pulsed nature of the e/m energy transmitted and received by systems. The shape of such energy pulses in the time domain is typically one of any number of approximations to a delta function, and generally has the property that the width of the frequency spectrum of such impulse increases as the time domain "length" or duration of the pulse decreases. Thus, the shorter the pulse of radiation is, the broader is its spectral bandwidth.

UWB was previously defined as an impulse radio technology, but those skilled in the art now view it as an available bandwidth set with an emissions limit that enables coexistence without harmful interference. One of the challenges of the implementation of UWB systems is the development of a suitable antenna that would enhance the advantages promised by a pulsed communication system. UWB systems require antennas that cover up to an octave bandwidth in order to transmit pulses on the order of a sub-nanosecond in duration with minimal distortion.

The UWB performances of antennas result from excitation by impulse or non-sinusoidal signals with rapidly time-varying performances. Thus, when an antenna is used employing such pulses in UWB applications, it is often found that the time-domain behaviour of the antenna is critical to the operation of the antenna. In particular, if an impedance mismatch or discontinuity occurs in such an antenna (such as at the open circuit end of the antenna), the consequence is often the unwanted generation of a standing wave of e/m energy within the antenna's radiating element(s) caused by reflections within the antenna of the e/m energy to be transmitted.

This trapped energy not only reduces the efficiency of the transducer of which the antenna forms a part, but also masks, obscures or interferes with signals received by the transceiver while the trapped energy is still present within the antenna.

Thus, in any resonant structure, such as a dipole antenna, an impulse signal injected at the antenna input will typically be partially reflected from the open-circuited end of the dipole causing a residual reflected return signal to appear at the antenna input.

This return reflection is often referred to as "ringing" or may be referred to as "aperture clutter" since it clutters/obscures the aperture of the antenna.

Pulsed UWB transceivers are often employed in applications such as short-distance positioning, or length measurement and so on, where a pulse e/m signal is transmitted from the transceiver and its reflection is subsequently received after a very brief time period. Such an application requires that the entire e/m signal pulse has exited the antenna of the transceiver before any reflection of that signal is expected to be received. This aims to ensure that the transmitted signal does not interfere with its received reflections and thereby obscure the positioning/measurement process.

However, ringing/aperture clutter results in just such obscurement and is highly undesirable.

Prior art pulsed UWB transceiver systems have attempted to overcome this problem by adding e/m signal absorbing material to the ends of the dipole antennas thereof or by loading the antennas with a distributed series of resistors along their length in an attempt to dampen or attenuate the standing waves therein which cause aperture clutter. However, such solutions are generally of little effect or most likely result in undesirably excessive attenuation of received/transmitted signal energy.

Furthermore, short-range positioning antennas are most desirably small in physical size so as to be not only portable but also useable at close quarters and in confined spaces. This requires the antenna to be as small as possible. However, reducing the size of an antenna has, in prior art, typically resulted in a corresponding reduction of bandwidth.

US5812081 relates to a time domain communications system in which a pulse-responsive antenna is employed to translate an applied DC impulse into a monocycle signal. Essentially, US5812081 discloses a dipole antenna which is completely the reverse of the conventional "bat wing" antenna and wherein two triangular elements of the dipole are positioned with their bases closely adjacent but DC isolated.

W00161784 relates to a bowtie antenna for use as ground penetrating radar in geometrical applications searching for metal or determining groundwater level, or determining the presence of pipes or electrical wiring. The bowtie antenna comprises a feedpoint for radiating energy, and flat mutually opposing arms that in use radiate the energy supplied at the feedpoint, wherein the feedpoint is positioned in between the opposing arms. Each of the arms comprises a carrier and an electrically conductive element attached to the carrier. Usually the carrier is a substrate to which the conductive element is attached.

Essentially, the above prior art examples disclose antennas that are suitable for ultra wideband applications. However, neither of these prior art examples discloses antennas which produce a substantially shallow radiation null along the direction of the geometrical symmetry axis of the antenna.

A physically small broadband UWB antenna with low ringing time is described in GB2406220. That UWB antenna demonstrates good impedance match from 3.5 GHz to 18 GHz which ensures very low ringing from harmonics of the impulse frequency. It also produces a wide elevation beam width of radiated signals and a shallow radiation null along the direction of the geometrical symmetry axis of the radiating element, which one would not expect from a conventional monopole antenna (as one would expect a complete, zero-signal null along the axis of symmetry).

Although the ground plane of the UWB antenna in GB2406220 provides excellent screening of the associated active circuit from the radiating aperture and may be formed by metallisation of the inter-compartment partition of a hand-held transceiver, the antenna, as a stand-alone component, is a 3-D structure.

Therefore, a small planar antenna structure is desirable for applications which require easy integration of the antenna on a user's clothing or on a PCMCIA PC card for WIFi, Bluetooth and UWB simultaneous applications. Such a small planar antenna structure is described in GB24391 10. Different configurations of the small planar antenna are also described in the same document. Generally, the small planar antennas provide similar performance as the UWB antenna described in GB2406220. The antennas also provide omnidirectional characteristics in their azimuthal direction of radiation and a shallow radiation null along its geometrical symmetry axis of the radiating element.

In some applications, it is desirable to provide an antenna with a unidirectional characteristic. This allows the antenna to radiate greater power in a wanted direction of communication to increase performance, and to reduce interference from unwanted sources.

As shown in figure 1, reflectors are commonly used to modify the radiation pattern of an antenna 62. This is usually achieved by placing a flat sheet reflector 60 of sufficiently large dimension in the plane in the direction of unwanted radiation.

Therefore, the "backward" radiation 64 from the antenna can be significantly reduced (or eliminated) and substantial gain in the "forward" radiation 66 can be increased.

The person skilled in the art would appreciate that the radiation pattern (or the gain in the forward radiation) is determined by the distance, d, between the antenna 62 and the reflector 60. Typically, the reflector 60 is placed one quarter wavelength from the antenna 62. Therefore, the overall size/thickness of the antenna structure 70 would be dependent on the distance, d, and the frequency in which the antenna operates.

In some applications, especially for antennas that are integrated on a user's clothing, it is essential to reduce the overall size/thickness of the antenna.

GB2453778 describes a small planar antenna structure having a photonic circuit element coupled thereto to allow the antenna to form a substantiaHy unidirectional radiation profile, with reduced spacing between the antenna and the reflector.

Figure 2 shows a front surface of the planar antenna element 10 comprising a radiating element 12, a transmission line 19 and a ground plane element 27 printed on a dielectric substrate 14. The transmission line 19 has a signal feed point 15 to provide (and to receive) signal to and from the radiating element 12. As shown in figure 2, the ground plane element 27 is printed on the same surface as the radiating element 12. In order for the antenna to operate over a wide frequency range, the ground plane element 27 comprises a plurality of slots 26 along its longitudinal edges 28. In this configuration, the slots are essentially series inductance that functions as RF choke to attenuate unwanted signals. The ground plane element 27 is extended for a length that is greater than the dimensions of the radiating element 12. Similarly, the transmission line 19 is also extended in the same length as the ground plane element 27.

Figure 3 shows a front surface of a photonic circuit element 50 comprising a plurality of conductive elements 54 printed on one surface of the dielectric substrate 52, and a ground plane (not shown) printed on an opposing surface of the dielectric substrate.

As illustrated in figure 3, the conductive elements 54 are arranged in an array and are spaced from each other at regular intervals. Conductive vias 58 are provided through the dielectric substrate 52 to electrically connect each of the conductive elements 54 to the ground plane.

Figure 4 illustrates a side view of a planar antenna structure 75 assembled from the antenna element 10 of figure 2 and the photonic element 50 of figure 3 positioned under the antenna element 10. As described in GB2453778, this configuration provides an antenna that produces a unidirectional, linearly polarised, radiation characteristic.

Antenna arrays are commonly used in radio communication systems. One of the key advantages of employing an antenna array is that higher directivity can be achieved in comparison with a single antenna. Moreover, by adjusting the relative amplitude and phase of the signals emitted from each antenna element of an antenna array, the radiation pattern in the far field of the antenna array can be changed. This allows the radiation pattern of the antenna array to be tailored to a particular application without mechanical movement of the antenna array. Figure 5 illustrates the planar antenna structure 75 of figure 4 is implemented in a planar antenna array 80 having a plurality of the planar antenna structures 75 arranged in a matrix arrangement.

In order to operate over a wide frequency range, the antenna structures of the array are arranged such that the spacing between each of the radiating element of the antenna structures is less than half wavelength at the highest operating frequency of the planar antenna array 80. As shown in figure 5, the horizontal spacing 82 between the radiating elements 12 can be easily arranged to meet this requirement.

As a result, this allows the antenna array to be able to steer the radiation pattern in the azimuth (x-y plane) with maximum gain across the whole frequency range. In this example, the y axis in figure 5 is pointing out of the page.

However, due to the presence of the ground plane 27 on each of the antenna structure 70, it is impossible to arrange the antenna structures such that the vertical spacing 84 between the radiating elements 12 are less than half wavelength at the highest operating frequency. Consequently, the radiation pattern at the highest end of the operating frequency range could be distorted when the radiation pattern of the antenna array is steered in the x-z plane.

The present invention provides a small planar antenna structure which can be implemented in an antenna array to provide maximum gain in the elevation and the azimuth plane of the antenna array.

Summary of the Invention

In a first aspect of the invention, there is provided an antenna for use in ultra wideband communications, the antenna comprising: a laminar dielectric substrate layer defining first and second opposing planar surfaces; a radiating element formed on said first planar surface, said radiating element comprising a signal feedpoint; a further laminar dielectric substrate, defining first and second opposing planar surfaces, a plurality of conductive elements formed on said first planar surface of said further laminar dielectric substrate and a ground element formed on said second planar surface of said further laminar dielectric substrate, said further laminar dielectric substrate having at least one conductive path for providing electrical connection between at least one of said plurality of conductive elements and said ground element of said further laminar dielectric substrate, wherein said first planar surface of said further laminar dielectric substrate is substantially coupled with said second planar surface of said first laminar dielectric substrate such that said radiating element is operable to form a substantially unidirectional radiation profile; and a transmission element including a signal component for passing therethrough signals transmitted to and/or received by means of said radiating element, said signal component being connected to said signal feedpoint, and a ground component connected to said ground element of said further laminar dielectric substrate, wherein said transmission element is positioned substantially orthogonal to said first planar surface of said laminar dielectric substrate.

Positioning the transmission element substantially orthogonal to said first planar surface of said laminar dielectric substrate allows the transmission element to be grounded to the ground element of the further laminar dielectric substrate, thereby allowing the ground plane of the antenna structure to be omitted. This is advantageous because the overall size of the antenna structure can be significantly reduced, thereby allowing the antenna to be position close to each other in an array arrangement. Such an antenna array is therefore capable of providing maximum gain in the elevation and azimuth plane of the antenna array.

The radiating element may be substantially tapered towards a narrow end thereof connected with said signal feedpoint, the distal wider end thereof having formed therein a substantially v-shaped notch thereby defining two lobes which diverge with increasing distance from said signal feedpoint, wherein outer edges of said lobes have formed therein a plurality of serrations to inhibit propagation of signal waves at said outer edges.

The v-shaped notch may be extended into said radiating element with an apex angle less than 90 degrees thereby substantially suppressing transverse signal modes of said radiating element.

The serrations may be log-periodically distributed such that said radiating element is operable over a wide bandwidth of signal frequencies without increasing size of the radiating element.

The serrations may be formed to enable an enhanced rate of radiative energy loss along said edge thereby reducing reflection signal travelling back along said edge.

The serrations may be formed such that each serration tip is formed by the convergence of two serration edges.

The convergence of said two serration edges may be formed at an angle of between approximately 75° and 105°.

The serrations may be distributed such that corresponding dimensions of successive serrations increase log-periodically whereby the ratio of said corresponding dimensions in respect of successive serrations has constant predetermined ratio value.

The serrations of said opposing edges may be arranged axially symmetrically about an axis extending through the radiating element from said transmission line and between said two edges.

The conductive elements may be arranged in an array on said first surface of said surface of said further laminar dielectric substrate.

The conductive elements may be substantially geometrically similar.

Alternatively, the conductive elements may be substantially geometrically non identical.

The conductive elements of said array may be spaced at regular intervals.

Alternatively, the conductive elements of said array may be spaced at irregular intervals.

Each of said conductive elements may be formed of regular or irregular structures.

The conductive path may be provided between each of said conductive elements and said ground element of said further laminar dielectric substrate.

The transmission element may include a coaxial cable having a signal component connected to said signal feedpoint, and positioned through said laminar dieJectric substrate and one of said conductive paths of said further laminar dielectric substrate.

Alternatively, the transmission element may include a microstrip transmission line or a co-planar waveguide. It is further noted that a skilled person would appreciate that any other forms of transmission element may also be used depending on fabrication constraints.

In an embodiment of the above aspect, said antenna further comprising a further conductive element formed on said first planar surface of said laminar dielectric substrate, and substantially adjacent to said signal feedpoint, wherein said further conductive element include a plurality of conductive vias, thereby maintaining an impedance match between the transmission element and said signal feedpoint.

Alternatively, said further conductive element may be formed on said second planar surface of said laminar dielectric substrate, and substantially adjacent to said signal feed point, wherein said further conductive element include a plurality of conductive vias, thereby maintaining an impedance match between the transmission element and said signal feedpoint.

The further conductive element may be generally V-shaped and substantially corresponding to the extent of said tapered narrow end of said radiating element.

In a further independent aspect of the invention, there is provided a method of manufacturing an antenna structure, the method comprising: providing a laminar dielectric substrate layer with first and second opposing planar surfaces; forming a radiating element on said first planar surface, said radiating element comprising a signal feedpoint; providing a further laminar dielectric substrate with first and second opposing planar surfaces, forming a plurality of conductive elements on said first planar surface of said further laminar dielectric substrate and a ground element on said second planar surface of said further laminar dielectric substrate, and forming at least one conductive path for providing electrical connection between at least one of said plurality of conductive elements and said ground element of said further laminar dielectric substrate, coupling said first planar surface of said further laminar dielectric substrate with said second planar surface of said laminar dielectric substrate such that said radiating element is operable to form a substantially unidirectional radiation profile; and providing a transmission element including a signal component for passing therethrough signal transmitted to and/or received by means of said radiating element, said signal component being connected to said signal feedpoint, and a ground component connected to said ground element of said further laminar dielectric substrate, wherein said transmission element is positioned substantially orthogonal to said first planar surface of said laminar dielectric substrate.

Brief description of the Drawins

Embodiments of the present invention will now be described with reference to the accompanying drawings, wherein: Figure 1 shows a side view of an antenna structure having an antenna element and a reflector.

Figure 2 shows a plan view of a front surface of an antenna element of an antenna structure; Figure 3 shows a plan view of a front surface of a photonic circuit element; Figure 4 shows a side view of an antenna assembled from the antenna element illustrated in figure 2 and the photonic element illustrated in figure 3; Figure 5 shows a plan view of an array of antennas; Figure 6 shows a plan view of a front surface of an antenna element according to an embodiment of the invention; Figure 7 shows a plan view of a back surface of the antenna element of figure 6; Figure 8 shows a side view of the antenna element of figure 6; Figure 9 shows a plan view of a front surface of a photonic circuit element according to an embodiment of the invention; Figure 10 shows a back view of the photonic circuit element of figure 9; Figure 11 shows a side view of the photonic circuit element of figure 9; Figure 12 shows a side view of an antenna structure assembled from the antenna element illustrated in figures 6 to 8 and photonic circuit element illustrated in figures 9 to 11; Figure 13 shows a plan view of a front surface of an antenna element according to another embodiment of the invention; Figure 14 shows a plan view of a front surface of an antenna element according to another embodiment of the invention; and Figure 15 shows plan view of a planar antenna array according to a further embodiment of the invention.

Detailed Description

Specific embodiments of the present invention will be described in further detail on the basis of the attached diagrams.

In the following description, a number of specific details are presented in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, to a person skilled in the art that these specific details need not be employed to practice the present invention.

Figures 6 to 8 show various views of a planar antenna element 100 produced on a dielectric substrate 104. The planar antenna is capable of being utilised in transmission and reception.

Figure 6 shows a front surface of the planar antenna element 100 comprising a radiating element 102 having a signal feed point 105 to provide (and to receive) signal to and from the radiating element. The radiating element 102 is shaped as a segment having two opposed slant edges 120, which diverge outwardly from an apex 116 of the segment.

The two opposed slant edges 120 diverge with increasing distance from the signal feedpoint 105 such that the radiating element 102 tapers outwardly from the signal feedpoint 105. The radiating element 102 possesses two distal peripheral edges (101 and 103) which are arcuate and which respectively bridge the terminal outermost ends of the two opposed slant edges 120 and form curved outermost peripheries of the radiating element 102.

The radiating element 102 has two corresponding series of serrations 107 each formed within a respective one of the two opposed slant edges 120. Each serration of a given series of serrations is formed by a pair of successive angular (tapering) notches 108 which extend into the radiating element 102 from the respective slant edge 120. Each tapering notch has notch edges which converge to terminate within the radiating element 102 at a right-angled apex 108.

Each such serration, and the series of serrations 107 collectively, present a slow-wave structure to a signal propagating along the slant edge 120. Essentially, the slow-wave structure formed along the slant edge 120 of the radiating element 102 is provided with a meander which slows down the progress of a signal wave travelling along the slant edge 120. This is achieved by constraining the signal wave to progress along the longer meandering slant edge rather than to progress directly along a shorter linear slant edge. As a result, the radiating element is operable over a wide bandwidth of signal frequencies without increasing the physical size of the radiating element 102.

The meanders of the slant edge 120 are shaped such that the Q-factor of the antenna is minimised thereby reducing aperture clutter by reducing the relative magnitude of a signal reaching the terminal (open circuit) end of the slant edge 120 where signal reflection tends to occur, this being the source aperture clutter. The Q-factor of the radiating element 102 is given as: stored energy Q factor rate of energy loss Thus, the relative magnitude of a signal reaching the terminal outer edge of the slant edge (i.e. relative to the magnitude of that signal at the beginning of the slant edge) is sensitively dependent upon the rate of loss of energy from the signal during propagation along the slant edge. By suitably shaping the meanders of the slow-wave structure, the described specific embodiment of the present invention may enhance the rate of radiative energy loss of the propagating signal as it progresses along the slant edge thereby reducing aperture clutter.

Successive serrations of each series of serrations are shaped to increase in size relative to the preceding serrations in a log-period manner. Thus, the serrations in a given series have a common shape. In this example the common shape is a straight-edged serration with two tapering edges extending from the body of the radiating element 102 at predetermined angles and converging at increasing distance from the body of the radiating element 102 to a terminal right-angular serration tip or apex 108.

Each serration in a given series of serrations 107 possess two tapering edges which each extend from the body of the radiating element 102 at the same predetermined angles as occurs in respect of the edges of an adjacent serration of the series, and also converge at a right angular serration apex 108. The ratio of the lengths of the two tapering edges of any given serration is shared by all serrations in the same series since all serrations in a given series share the same general shape. However, due to log-periodic scaling, the lengths themselves increase by a predetermined scaling value such that the ratio of a serration edge length of a given serration and the corresponding edge length of the succeeding serration has a constant predetermining ratio value shared by all such neighbouring serrations.

Furthermore, each series of serrations 107 is arranged such that the distance between the location of the apex 108 of the segment of the radiating element 102 and the location of the serration increase log-periodically as one encounters successive serrations of a given series. The result is that the ratio of the aforesaid distance, as between two neighbouring (successive) serrations, is equal to a constant predetermined ratio value shared by all such neighbouring serrations. The location of the serration may be considered to be the location of the apex 108 of the tip of the serration in question, for example.

Figure 9 shows a front surface of a photonic circuit element 150 comprising a plurality of conductive elements 154 printed on one surface of the dielectric substrate 152, and a ground plane 156 printed on an opposing surface of the dielectric substrate. As illustrated in figure 9, the conductive elements 154 are geometrically similar and have octagonal structures. The conductive elements 154 are arranged in an array and are spaced from each other at regular intervals. Conductive vias 158 are provided through the dielectric substrate 152 to electrically connect each of the conductive elements 154 to the ground plane 156.

Alternatively, the conductive elements can be of different geometries and structures, and can be arranged in a different array pattern with elements spaced at irregular intervals. In fact, it is noted that this arrangement would substantially increase the operating bandwidth of the photonic circuit element.

Figure 12 illustrates a side view of the antenna 170 of the present invention including the photonic circuit element 150 of figures 9 to 11 being positioned under the antenna element 100 of figures 6 to 8. This configuration provides an antenna that produces a unidirectional radiation characteristic. It will be appreciated by the person skilled in the art that the photonic element may not be physically attached to the antenna element in order to produce a unidirectional radiation characteristic. The person skilled in the art will appreciate that the antenna would provide almost the same performance when the photonic element is positioned substantially close the antenna element. Preferably, the distance between the photonic surface element and the antenna element 100 is approximately quarter wavelength of the highest operating frequency of the antenna 170.

As illustrated in figure 12, a transmission element 180 having a signal component (not shown) connected to the signal feedpoint 105 of the antenna element 100 to provide (and to receive) signal to and from the radiating element 102. The transmission element 180 is positioned substantially orthogonal to the plane of the radiating element 102, through the antenna element 100 and one of the conductive vias 158 of the photonic circuit element 150. The transmission element 180 also includes a ground component which is grounded to the ground plane 156 of the photonic surface element 150. In this example, the transmission element is a coaxial cable, but it is noted that the person skilled in the art would appreciate that any other forms of transmission element can also be used depending on the fabrication constraints. Examples of a transmission element include a co-planar waveguide or a microstrip transmission line.

Alternative configurations of the planar antenna element 100 are shown in figures 13 and 14. Referring to figure 13, the radiating element 302 is similar to the radiating element 102 of figure 6 described above. Therefore, detailed description pf radiating element 302 will not be repeated. The antenna element 300 of figure 13 further includes a conductive element 310 formed on the same surface as the radiating element 102. The conductive element formed is adjacent to the signal feedpoint 305 of the radiating element 302, and along an edge of the antenna element 300. The conductive element 310 includes a row of conductive vias 312 to maintain an impedance match between the transmission element and said signal feedpoint.

Figure 14 illustrates the antenna element 400 including a radiating element 402 and a conductive element 410 formed on the same surface as the radiating element 402.

The conductive element 410 of antenna element 400 is V-shaped and substantially corresponds to the extent of the tapered narrow end of the radiating element 402.

The conductive element 410 includes a row of conductive vias 412, and two vias 415 offset from the row of conductive vias 412.

It is further noted that the conductive elements 310, 410 in figures 13 and 14 can also be formed on the surface opposite to the radiating element 102.

Figure 15 illustrates a planar antenna array 200 implemented using a plurality of antennas 170 of figure 12 arranged in a matrix arrangement. As shown in figure 15, the spacing between the antennas 170 can be arranged substantially closed to each other without being restricted by the length of the transmission element. Preferably, the antennas 170 are arranged such that the horizontal spacing 172 and the vertical spacing 174 are less than half wavelength of the highest operating frequency of the antenna array 200. This configuration will allow the antenna array to achieve maximum gain in the elevation plane (x-z plane) and the azimuth plane (x-y plane).

In this example, the y axis is pointing out of the page.

The present invention, for example, as shown in the above embodiments, may provide an ultra wide-band (UWB) electromagnetic impulse transceiver for applications in short range communications and/or positioning systems. The invention may be implemented in the form of a monopole antenna thereby obviating the need for a balun with the antenna circuitry. The antenna according to the present invention in any of its embodiment has the important benefit of being sufficiently small for use as a portable impulse transceiver.

Furthermore, monopole antennas structured according to the present invention in its first aspect display up to an octave bandwidth, have reduced aperture clutter with moderate signal loss and have relatively small physical size.

The antenna described above is unidirectional, having a substantially linearly polarised radiation.

The planar structure of the antenna of the specific embodiment is also easy to manufacture in large volumes. Furthermore, the associated electronics components of a PCMCIA PC card can be incorporated on the same substrate as the planar structure of the antenna. This is also useful in other applications, especially for antennas that are integrated on a user's clothing.

It will be appreciated by those of ordinary skill in the art that the invention can be embodied in other specific forms without departing from the spirit or essential character thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

CLAIMS: An antenna for use in ultra wideband communications, the antenna corn p rising: a laminar dielectric substrate layer defining first and second opposing planar surfaces; a radiating element formed on said first planar surface, said radiating element comprising a signal feedpoint; a further laminar dielectric substrate, defining first and second opposing planar surfaces, a plurality of conductive elements formed on said first planar surface of said second dielectric substrate and a ground element formed on said second planar surface of said further laminar dielectric substrate, said further laminar dielectric substrate having at least one conductive path for providing electrical connection between at least one of said plurality of conductive elements and said ground element of said further laminar dielectric substrate, wherein said first planar surface of said further laminar dielectric substrate is substantially coupled with said second planar surface of said first laminar dielectric substrate such that said radiating element is operable to form a substantially unidirectional radiation profile; and a transmission element including a signal component for passing therethrough signals transmitted to and/or received by means of said radiating element, said signal component being connected to said signal feedpoint, and a ground component connected to said ground element of said further laminar dielectric substrate, wherein said transmission element is positioned substantially orthogonal to said first planar surface of said laminar dielectric substrate.
2. An antenna according to claim 1, wherein said radiating element is substantially tapered towards a narrow end thereof connected with said signal feedpoint, the distal wider end thereof having formed therein a substantially v-shaped notch thereby defining two lobes which diverge with increasing distance from said signal feedpoint, wherein outer edges of said lobes have formed therein a plurality of serrations to inhibit propagation of signal waves at said outer edges.
3. An antenna according to claim 2, wherein said v-shaped notch is extended into said radiating element with an apex angle less than 90 degrees thereby substantially suppressing transverse signal modes of said radiating element.
4. An antenna according to claim 2 or claim 3, wherein said serrations are log-periodically distributed such that said radiating element is operable over a wide bandwidth of signal frequencies without increasing size of the radiating element.
5. An antenna according to any one of claims 2 to 4, wherein said serrations are formed to enable an enhanced rate of radiative energy loss along said edge thereby reducing reflection signal travelling back along said edge.
6. An antenna according to any one of claims 2 to 5, wherein said serrations are formed such that each serration tip is formed by the convergence of two serration edges.
7. An antenna according to claim 6, wherein said convergence of said two serration edges is formed at an angle of between approximately 75° and 105°.
8. An antenna according to any one of claims 2 to 7, wherein said serrations are distributed such that corresponding dimensions of successive serrations increase log-periodically whereby the ratio of said corresponding dimensions in respect of successive serrations has constant predetermined ratio value.
9. An antenna according to any one of claims 2 to 8, wherein said serrations of said opposing edges are arranged axially symmetrically about an axis extending through the radiating element from said transmission line and between said two edges.
10. An antenna according to any one of the preceding claims, wherein said conductive elements are arranged in an array on said first surface of said surface of said further laminar dielectric substrate.
11. An antenna according to any one of the preceding claims, wherein said conductive elements are substantially geometrically similar.
12. An antenna according to any one of claim 1 to 10, wherein said conductive elements are substantially geometrically non identical.
13. An antenna according to any one of claims 10 to 12, wherein said conductive elements of said array are spaced at regular intervals.
14. An antenna according to any one of claims 10 to 12, wherein said conductive elements of said array are spaced at irregular intervals.
15. An antenna according to any one of the preceding claims, wherein each of said conductive elements is formed of regular or irregular structures.
16. An antenna according to any one of the preceding claims, wherein said conductive path is provided between each of said conductive elements and said ground element of said further laminar dielectric substrate.
17. An antenna according to any one of the preceding claims, wherein said transmission element includes a coaxial cable having a signal component connected to said signal feedpoint, and positioned through said laminar dielectric substrate and one of said conductive paths of said further laminar dielectric substrate.
18. An antenna according to any one of claims ito 16, wherein said transmission element includes a microstrip transmission line or a co-planar waveguide.
19. An antenna according to claims 2 to 18, wherein said antenna further comprising a further conductive element formed on said first planar surface of said laminar dielectric substrate, and substantially adjacent to said signal feedpoint, wherein said further conductive element include a plurality of conductive vias, thereby maintaining an impedance match between the transmission element and said signal feedpoint.
20. An antenna according to any one of claims 2 to 18, wherein said antenna further comprising a further conductive element formed on said second planar surface of said laminar dielectric substrate, and substantially adjacent to said signal feed point, wherein said further conductive element include a plurality of conductive vias, thereby maintaining an impedance match between the transmission element and said signal feedpoint.
21. An antenna according to claim 19 or claim 20, wherein the further conductive element is generally V-shaped and substantially corresponding to the extent of said tapered narrow end of said radiating element.
22. A method of manufacturing an antenna structure, the method comprising: providing a laminar dielectric substrate layer with first and second opposing planar surfaces; forming a radiating element on said first planar surface, said radiating element comprising a signal feedpoint; providing a further laminar dielectric substrate with first and second opposing planar surfaces, forming a plurality of conductive elements on said first planar surface of said further dielectric substrate and a ground element on said second planar surface of said further laminar dielectric substrate, and forming at least one conductive path for providing electrical connection between at least one of said plurality of conductive elements and said ground element of said further laminar dielectric substrate, coupling said first planar surface of said further laminar dielectric substrate with said second planar surface of said laminar dielectric substrate such that said radiating element is operable to form a substantially unidirectional radiation profile; and providing a transmission element including a signal component for passing therethrough signal transmitted to and/or received by means of said radiating element, said signal component being connected to said signal feedpoint, and a ground component connected to said ground element of said further laminar dielectric substrate, wherein said transmission element is positioned substantially orthogonal to said first planar surface of said laminar dielectric substrate.
23. A method according to claim 22, wherein said radiating element is substantially tapered towards a narrow end thereof connected with said signal feedpoint, the distal wider end thereof having formed therein a substantially v-shaped notch thereby defining two lobes which diverge with increasing distance from said signal feedpoint, wherein outer edges of said lobes have formed therein a plurality of serrations to inhibit propagation of signal waves at said outer edges.
24. A method according to claim 23, wherein said v-shaped notch is extended into said radiating element with an apex angle less than 90 degrees thereby substantially suppressing transverse signal modes of said radiating element.
25. A method according to claim 23 or claim 24, wherein said serrations are log-periodically distributed such that said radiating element is operable over a wide bandwidth of signal frequencies without increasing size of the radiating element.
26. A method according to any one of claims 23 to 25, wherein said serrations are formed to enable an enhanced rate of radiative energy loss along said edge thereby reducing reflection signal travelling back along said edge.
27. A method according to any one of claims 23 to 26, wherein said serrations are formed such that each serration tip is formed by the convergence of two serration edges.
28. A method according to claim 27, wherein said convergence of said two serration edges is formed at an angle of between approximately 750 and 105°.
29. A method according to any one of claims 23 to 28, wherein said serrations are distributed such that corresponding dimensions of successive serrations increase log-periodically whereby the ratio of said corresponding dimensions in respect of successive serrations has constant predetermined ratio value.
30. A method according to any one of claims 23 to 29, wherein said serrations of said opposing edges are arranged axially symmetrically about an axis extending through the radiating element from said transmission line and between said two edges.
31. A method according to any one of claims 22 to 30, wherein said conductive elements are arranged in an array on said first surface of said surface of said further laminar dielectric substrate.
32. A method according to any one of claims 22 to 31, wherein said conductive elements are substantially geometrically similar.
33. A method according to any one of claim 22 to 31, wherein said conductive elements are substantially geometrically non identical.
34. A method according to any one of claims 31 to 33, wherein said conductive elements of said array are spaced at regular intervals.
35. A method according to any one of claims 31 to 33, wherein said conductive elements of said array are spaced at irregular intervals.
36. A method according to any one of claims 22 to 35, wherein each of said conductive elements is formed of regular or irregular structures.
37. A method according to any one of claims 22 to 36, wherein said conductive path is provided between each of said conductive elements and said ground element of said further laminar dielectric substrate.
38. A method according to any one of claims 22 to 37, wherein said transmission element includes a coaxial cable having a signal component connected to said signal feedpoint, and positioned through said laminar dielectric substrate and one of said conductive paths of said further laminar dielectric substrate.
39. A method according to any one of claims 22 to 37, wherein said transmission element includes a microstrip transmission line or a co-planar waveguide.
40. A method according to claims 23 to 39, wherein said antenna further comprising a further conductive element formed on said first planar surface of said laminar dielectric substrate, and substantially adjacent to said signal feedpoint, wherein said further conductive element include a plurality of conductive vias, thereby providing thereby maintaining an impedance match between the transmission element and said signal feedpoint.
41. A method according to any one of claims 23 to 39, wherein said antenna further comprising a further conductive element formed on said second planar surface of said laminar dielectric substrate, and substantially adjacent to said signal feed point, wherein said further conductive element include a plurality of conductive vias, thereby maintaining an impedance match between the transmission element and said signal feedpoint.
42. A method according to claim 40 or claim 41, wherein the further conductive element is generally V-shaped and substantially corresponding to the extent of said tapered narrow end of said radiating element.
43. An apparatus substantially as herein described with reference to figures 6 to 15.