EP2937933A1

EP2937933A1 - Low-profile wideband antenna element and antenna

Info

Publication number: EP2937933A1
Application number: EP14305603.4A
Authority: EP
Inventors: Martin Gimersky
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2014-04-24
Filing date: 2014-04-24
Publication date: 2015-10-28
Anticipated expiration: 2034-04-24
Also published as: EP2937933B1

Abstract

A low-profile wideband antenna element and antenna comprising multiple antenna elements are disclosed. An antenna element comprises: two elongate arms mounted on and at a distance from a ground plate such that they lie in a plane above a surface plane of the ground plate. The two elongate arms are angled with respect to each other and are formed of a conductive material and form the radiating elements of the antenna element. The antenna element has at least one conductive connecting member connecting a conductive surface of the ground plate to at least one of the arms; and at least one feed probe for feeding an input signal to the two arms, the at least one feed probe being spaced apart from the at least one conductive connecting member.

Description

FIELD OF THE INVENTION

The present invention relates to the field of antennas and antenna elements and in particular, to low profile wideband antenna and antenna elements suitable for use in the field of wireless communication.

BACKGROUND

Wireless communication networks are known and are generally arranged in a cellular system where radio coverage is provided to user equipment, for example, mobile telephones, by geographical area. Those geographical areas of radio coverage are known as cells. A base station or network node is located in each geographical area to provide the required radio coverage. As new standards used to transmit signals are added, new frequencies are required for transmitting the new signals required by the new standards which in their turn require antennas with different properties. The mounting of multiple antennas on base station sites creates interference between the antennas and maybe both costly and unsightly.
One way of addressing some of these issues has been to consolidate the multiple antennas into a single antenna. A popular type of radiating antenna elements for this purpose is a log-periodic dipole antenna in which a number of dipoles of differing lengths are mounted on a vertical post, each dipole providing a different frequency bandwidth of operation. A drawback of such an antenna is it is bulky and not amenable to low profile solutions.
It would be desirable to provide an antenna with a low antenna profile and wide bandwidth of operation.

SUMMARY

A first aspect of the present invention provides an antenna element comprising: two elongate arms mounted on and at a distance from a ground plate arranged such that they lie in a plane at a distance from a surface plane of said ground plate, said two elongate arms being angled with respect to each other; said two elongate arms being formed of a conductive material and forming radiating elements of said antenna element; at least one conductive connecting member connecting a conductive surface of said ground plate to at least one of said arms; and at least one feed probe for feeding an input signal to said two arms, said at least one feed probe being spaced apart from said at least one conductive connecting member.
The present invention addresses the competing problems of providing antenna elements of a low size and profile and yet with a wide bandwidth of operation. It has found that by combining the basic form of a dipole antenna having two arms and yet mounting and feeding it in a way similar to that of a planar inverted-F antenna (PIFA), an antenna which combines the advantages of each type of antenna element is provided, giving an antenna element with a wide bandwidth of operation as is provided by PIFA antenna elements yet with a reduced footprint. The reduced footprint arises due to the replacement of the PIFA's patch part with two elongate arms. This can be done without unduly affecting performance as in a PIFA the majority of the current flows around the edge of the patch and thus, changing the patch to elongate arms reduces the footprint while having only a slight effect on operation.
It should be noted that the ground plate may be a metallic plate or a plate with a conductive layer. It may have a number of forms, for example it may have a continuous planar form or it may form a plane with some portions being absent, such that a circumferential hollow shape is provided. Furthermore, where the ground plate consists of a conductive layer on a surface of another material such as a substrate, the conductive layer may cover the whole of the surface of the other material or it may just cover a portion of the surface. The conductive connecting member connects to the conductive surface allowing current to flow between the arms and the ground plate.
It should be noted that the arms lie in a plane at a distance from the surface of the ground plate. In preferred embodiments the plane is substantially parallel to the surface of the ground plate, preferably at an angle of less than 10° to the surface. In this regard an angle of up to 40° would provide an antenna element with suitable properties, however, its profile would be larger than were the plane parallel to the ground plate, thus in preferred embodiments the arms are substantially parallel to the ground plate.
In some embodiments, said conductive connecting member connects said two elongate arms to said ground plate at a vertex of said two elongate arms where said two elongate arms meet.
Although the conductive connecting member may connect the two elongate arms to the ground plate at a number of places, connecting them at the vertex of the elongate arms where the elongate arms meet provides a conductive connection to both arms by a single structure and also provides a structurally sound support for the arms making the antenna element robust.
In some embodiments, said feed probe comprises two feed lines extending towards a point on each of said two elongate arms such that each of said elongate arms receive said input signal.
For the antenna element to operate efficiently it is desirable if the input signal is fed to both arms, thus in preferred embodiments the feed probe comprises two feed lines to feed a signal to both arms. In some cases, this feed probe has the form of a fork such that a single signal line diverges into two equal length feed lines which feed equal signals to the two arms of the antenna element.
In some embodiments, said two elongate arms are substantially identical.
Although, the antenna element may function quite well if the elongate arms are not the same, generally a more efficient antenna element is achieved if they are substantially identical both radiating in a similar way.
Where the two elongate arms are substantially identical, it may be advantageous if the feedlines are arranged to supply a substantially identical signal to each of the elongate arms at a substantially same point on each of the arms. In this way, the two arms will radiate in the same way and cooperate to provide an efficient antenna.
In some embodiments, said two elongate arms have a substantially planar rectangular form.
Although the elongate arms may take a number of forms, a substantially planar rectangular form was found to be both spatially efficient and form an antenna element with a high performance.
In some embodiments, said two elongate arms are arranged at between 70° and 110° with respect to each other. Arranging the arms with these sorts of angles provides an antenna element which takes advantage of the dipole type shape of the element and produces an efficient radiation beam. In some cases, 90° maybe preferable and this may be the case where the antenna element is being used within circuitry that is formed substantially of squares such that these types of elements will fit well within available space. In this regard having arms arranged at such angles makes it practical to nest other components within the arms leading to an efficient use of space.
A second aspect of the present invention provides an antenna comprising two antenna elements according to any preceding claim, mounted on said ground plate facing each other, such that a same line substantially bisects an angle between said two elongate arms of each of said antenna elements.
Although, antenna elements as described previously may be used on their own to form antennae, they may also be used in pairs. If they are arranged facing each other, in order for their signals to add together they should be arranged such that the bisection line of the angle between the two arms is substantially the same line for each of the antenna elements. In this regard although a slight offset between symmetry lines of the antenna elements may be possible, it will reduce the performance of the antenna and is not desirable. Thus, where the lines bisecting the angles of the two antenna arms are not the same line, the two bisecting lines should be close together, at a distance of less than a half of a length of one of the elongate arms, and they should be substantially parallel to each other (less than 20° out of alignment), such that spatial power combination can take place between the signals transmitted from each antenna, thus providing a single linearly polarised beam pattern with low cross polarisation.
In some embodiments, said ground plate has a substantially quadrilateral outer form and said two antenna elements are mounted at or adjacent to diagonally opposing corners of said ground plate, said elongate arms of each of said antenna elements being arranged such that said arms extend over said ground plate.
Although the ground plate can have a number of forms, in some embodiments it will have a substantially quadrilateral outer form with the two antenna elements being mounted at or close to diagonally opposing corners. The antenna elements are arranged so that the arms extend out over the top of the ground plate. The quadrilateral outer form is a form that is easy to manufacture and place within protective casings and fits conveniently with other elements that antennae may be used in conjunction with. Placing the antenna elements at or close to diagonally opposing corners provides the arrangement of the antenna elements required for the beams to constructively interfere with each other. Furthermore, by placing these antenna elements close to the edge of the ground plate, the ground plate size does not increase the overall size of the antenna and an antenna with a smaller footprint can be achieved. In some embodiments the quadrilateral may be square, allowing the antenna elements to face each other, have a 90° angle between the arms thereby fitting well into a corner.
In some embodiments, said antenna further comprises an input signal feed distribution line configured to feed said input signal as a differential input signal to each feed probe of said two antenna elements, such that each antenna element receives said input signal with a phase difference of substantially 180° when operating at or close to a central frequency of a bandwidth of said antenna with respect to said other antenna element.
In order for the different antenna elements to constructively interfere such that the beams generated by each add up rather than cancel each other out, a phase difference of substantially 180° between the two input signals will achieve suitable constructive interference. In this regard, as these antenna elements are designed to operate across a bandwidth, generally the phase difference is calculated with respect to a signal operating at or close to a central frequency of the bandwidth. In this way, signals at either edge of the bandwidth will not be too far from this preferred phase difference and an efficient antenna where signals from each antenna element combine constructively will be obtained.
In some embodiments, said ground plate is a conductive area mounted on a substrate sheet, said input signal feed distribution line lying on an outer surface of said substrate sheet opposing a surface on which said ground plate is mounted.
The ground plate may be a conductive area or indeed a conductive layer mounted on a substrate sheet. A substrate sheet acts to conductively insulate the input signal feedline form the conductive area.
In some embodiments, said antenna comprises two further antenna elements according to a first aspect of the present invention, said two further antenna elements being mounted facing each other such, that a same line substantially bisects an angle between said two elongate arms of each of said two further antenna elements, wherein said lines bisecting said angle between said arms of said two antenna elements and said arms of said two further antenna elements intersect at an angle of between 70° and 110°, preferably at an angle of substantially 90°.
Although two antenna elements facing each other provide an antenna operating with linear polarisation, if four antenna elements are arranged mounting such that pairs face each other and the lines that bisect the angle cross each other at or close to 90°, then an antenna providing dual linear polarisation is generated and an antenna that can handle a high bandwidth of signals can be formed with a small footprint making good use of much of the surface area of the ground plate.
In some embodiments, said ground plate has a substantially quadrilateral outer form and said four antenna elements are mounted at or adjacent to corners of said ground plate, said elongate arms of each of said antenna elements being arranged such that said arms extend over said ground plate.
Where four antenna elements are mounted in this way, a particularly effective wide bandwidth, low profile antenna is produced where the ground plate has a quadrilateral outer form with the antenna elements mounted on each corner.
Where there are two pairs of antenna elements, then there should be two input signal feed distribution lines which are configured to feed differential input signals to each feed probe of diagonally opposing antenna elements, such that each diagonally opposing antenna element receives the input signal with a phase difference of substantially 180° with respect to the other diagonally opposing antenna element, where the antenna elements are being feed with signals at or close to the central frequency of their bandwidth.
Although the antenna elements may be mounted anywhere on the ground plate, in some embodiments they are mounted at or close to a circumferential edge of the ground plate. In this regard, mounting them close to the edge of the ground plate enables a ground plate of a small size to be used. Furthermore, there is an area towards the centre of the ground plate that can be used for mounting other elements that the antenna may be cooperating with. These elements may be other antennae or they may be further electronic circuitry.
In some embodiments, said antenna further comprises a radiation shielding element mounted on said ground plate and forming a hollow lateral enclosure with said antenna elements being arranged outside of said enclosure.
Providing some radiation shielding lowers interference between the radiation elements and also in some cases helps to direct the beam by reducing signals emitted parallel to the ground plate rather than projected away from it. The lateral enclosure may consist of side walls that extend out of the ground plate substantially perpendicular to it and form a fence-type structure that encloses a central section. This central section maybe used to mount other things such as electronic circuitry which will be shielded from the antenna elements. It should be noted that the ground plate may be a continuous area and the central portion may contain the ground plate and on this electronic circuitry may be mounted. Alternatively, the ground plate may have a hollow type structure such that there is a hole in the middle and some further element maybe placed within this. In this regard, there may be a solid plate-like substrate with a conductive layer mounted around the edge of it but not in the central portion.
In some embodiments, said antenna comprises a further antenna element configured to operate at a different frequency bandwidth to said antenna elements mounted at said circumferential edge of said ground plate, said further antenna element being arranged spaced apart from said circumferential edge antenna elements and being within said enclosure formed by said radiation shielding element.
The configuration of the antenna element of the first aspect of the present invention lend themselves well to being outer elements in a multiple element antenna with further antenna elements operating at different frequencies being mounted within the outer elements. In this way, a nested structure is provided and an antenna with a high bandwidth and yet low footprint is provided. In this regard although the frequency of operation of the inner antenna element may have any suitable value it may be appropriate to put a higher frequency antenna element here as it will generally be smaller.
Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.
Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows an antenna element according to an embodiment of the present invention;
Figure 2 shows an antenna comprising antenna elements according to an embodiment of the present invention mounted on opposing corners of a ground plate;
Figures 3 and 4 show views of either side of a radiating antenna in accordance with an embodiment of the present invention;
Figure 5 shows an alternative embodiment of an antenna comprising a plurality of radiating antenna elements according to an embodiment of the present invention mounted on a circular hollow ground plate;
Figure 6 shows a hybrid antenna in accordance with an embodiment of the present invention;
Figure 7 shows a frequency dependence plot of scattering parameters for an antenna according to an embodiment of the present invention;
Figure 8 shows plot of co-polarised far-field gain radiation pattern for an exemplary antenna element in accordance with an embodiment of the present invention; and
Figure 9 shows a plot of cross polarised far-field gain radiation pattern of an exemplary radiating antenna element in accordance with an embodiment of the present invention at 800 Hz.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided.
Embodiments of the present invention seek to provide a wideband low-profile antenna element or antenna formed of multiple such antenna elements. Each antenna element has two angled arms which are conductively connected to a ground plate and lie in a plane at a distance from the ground plate, preferably substantially parallel to it, thereby providing a low-profile antenna.
In embodiments the arms are substantially identical and are fed by a signal using a two-prong fork feeding structure such that each arm receives a same signal at a same point. Where multiple antenna elements are used together they may be mounted towards a circumferential edge of the ground plate providing a circumferential topology with a spatial vacancy allowing for the nesting of other components and providing an antenna with a small footprint. The multiple antenna elements are arranged in pairs facing each and fed with signals with a phase difference of substantially 180° such that they provide a single linear co-polarised beam pattern.
Figure 1 shows an antenna element 20 according to an embodiment of the present invention. Antenna element 20 comprises a radiator 1 comprising two identical conductive arms 2 mounted via a metallic shorting post 3 on a ground plate 4. Each of the radiating arms 2 is fed by means of a feeding metallic fork 5. The fork has two prongs with one prong feeding one radiating arm 2 of the pair and the other prong feeding the other radiating arm 2. In this embodiment, the prongs are connected directly to the radiating arms although in other embodiments the prongs may not be directly connected but may be proximity coupled to the arms. The input signal is provided to the feeding fork via a feedline (not shown) which runs on the opposing surface of a substrate 6 on which the ground plate 4 is mounted.
The antenna element 20 may be used as a single antenna element or it may be mounted on the ground pate 4 as one of a pair of opposing antenna elements which act together as an antenna as is shown in Figure 2.
Figure 2 shows an antenna comprising two antenna elements mounted at opposing corners of a quadrilateral ground plate. In this embodiment the ground plate is a rectangle so that the antenna elements which are facing each other are not exactly aligned with the corners. The feeding of the input signal to the respective antenna elements is provided via a feedline on the reverse side of the substrate 6 on which the ground plate 4 is mounted. The feedline is arranged such that the input signal to one of the antenna elements 20a is 180° out of phase with the signal input to the other antenna element 20b. By providing the signals out of phase with respect to each other, then the signals transmitted by the antenna which are facing in towards each other and thus emit signals in different directions are generally in phase and combine to provide an increased signal as opposed to acting to cancel each other out. In this regard, the antenna elements 20a and 20b operate effectively across a bandwidth and the 180° phase shift is calculated for a frequency close to the centre of the bandwidth.
Figures 3 and 4 show views from above and below of an antenna having four radiating antenna elements in accordance with an embodiment of the present invention. In these figures, radiating elements comprising four sequentially rotated identical radiators 1 are placed close to the corners of a substantially square shaped standard radio frequency/ microwave substrate sheet material 6. Each of the four radiators 1 include two metallic radiating arms 2 mutually arranged at a 90° angle, thereby forming a 90° V-shape. The radiating arms 2 are of substantially equal length. Each pair of radiating arms 2 runs in a plane parallel to and an elevated over a metallic ground plane 4. In this embodiment, the metallic ground plane extends across the whole surface of a substrate 6, while in other embodiments it may form a frame type arrangement extending around the edge of the square. In this regard, it is advantageous if it extends under the radiating arms.
A metallic shorting post 3 electrically connects the vertex of each pair of radiating arms 2 to the ground plate 4. Each pair of radiating arms 2 is fed by means of a feeding metallic fork 5. The fork has two prongs with one prong feeding one radiating arm of the pair and the other prong feeding the other radiating arm 2. The prongs of the feeding fork 5 can be either directly connected to the radiating arms 2 or proximity coupled to the radiating arms 2. The feeding fork 5 is substantially symmetrical and its placement with respect to the pair of radiating arms 2 is substantially symmetrical so that the prongs of the feeding fork 5 feed the radiating arms 2 with radio frequency signals of substantially equal power and phase. The common end of each of the radiating forks can be connected to a conventional metallic micro-strip line signal distribution network 7 shown on the reverse surface of the substrate in Figure 4. In this embodiment, there are two signal distribution networks 7 on the bottom surface of the substrate sheet 6. The signal distribution network provides differential feeding to the two opposing diagonally placed radiators 1, the pair of which radiates electro-magnetic waves with one linear (+45° or -45° slant) polarisation. Differential feeding provides radio frequency signals of equal amplitude and 180° phase shift compensating for the mutual 180° rotation of the radiators and providing one polarisation.
It should be noted that where the term metallic is used for parts of electrically conducting surfaces, the parts may be manufactured in several ways, for example, as solid or sheet metals, electrically conducted plastics or metalised plastics.
Figure 5 shows an alternative embodiment of a four antenna elements, antenna 30 having four opposing radiating elements 20a, 20b, 20c and 20d mounted on a circular ground plate 4 with a hollow centre. Each of the antenna elements 20 are arranged such that the line bisecting the angle between the arms of diagonally opposing antenna elements 20 is a single line that runs through both the diagonally opposing pairs. Furthermore, the bisecting lines of the two pairs intersect with each other at substantially 90°. It should be noted that this is also the case for the four antenna element antenna of Figures 3 and 4 where they are mounted on the corner of a square ground plate.
Figure 6 shows a hybrid (nested) multiple band/ultra-wide band radiator consisting of radiating antenna elements 1 in accordance with embodiments of the present invention mounted on each corner of a square ground plate 4 with a higher frequency radiating element 9 mounted in the centre. This higher frequency radiating element 9 may have different forms but owing to its higher frequency of operation, is generally smaller than the lower frequency antenna elements 1 mounted on the outside making it convenient to nest it within the centre. The shape of the outer antenna elements also lend themselves to this nesting arrangement.
It should be noted that there is a fence-type shielding element 8 between the higher frequency antenna 9 shown in this Figure to shield the radiation emitted by the inner and outer elements from each other.
The radiating shielding element 8 of Figures 3 and 6 can also be used where there is no high frequency antenna placed in the middle but where other electronic circuitry is placed here.
The shielding element 8 may additionally act to better direct the beam and improve the performance of the antenna element.
As seen from the embodiment of figure 6 one way of producing multiband/ultra-wideband radiators, which maybe required for applications where low antenna profile is of essence (e.g., metrocell base stations), is by nesting a higher-frequency component radiator within low-profile lower-frequency component radiators according to an embodiment of the invention. Another way of looking at the arrangement is that the higher-frequency component radiator is surrounded by the lower-frequency component radiator. Owing to their angled arm form, radiating elements according to embodiments of the present invention are particularly well suited for use as the lower-frequency component radiator in such (nested) hybrid radiating elements.
The antenna elements according to embodiments of the invention, such as those shown in Figures 2 -4 and 6, have a square footprint and consist of radiators mounted in the corners of the square. The radiating element are suitable for operation with dual (±45°-slant) linear polarization, whereby each polarization is produced by two diagonally positioned radiators fed differentially, i.e., the feeding radio-frequency signals to the radiators are of equal amplitudes, and there is a 180° phase shift between the signals. Typical sizes for such an arrangement are a 15cm x 15 cm ground plate with a profile of less than 3cm.
The four individual radiators of the radiating elements according to the embodiments of Figures 3 - 6 are of identical design and sequentially rotated by 90°. The concept of each of the four radiators has some properties of the V dipole and some of the planar inverted-F antenna (PIFA). The V dipole itself is a derivative of the half-wave dipole and was introduced to address a property of the half-wave dipole's far-field radiation pattern: the far-field radiation pattern of the half-wave dipole in free space is doughnut-shaped, with pronounced minima (theoretically nulls) along the direction of the dipole arms; to fill out these minima, several configurations were proposed, whereby either the outer ends of the dipole arms (such as in the broken-arrow dipole) or the entire dipole arms (the V dipole) are bent at an angle.
The radiating element according to the embodiments of the present invention, however, addresses very different performance issues from the V dipole. The PIFA is derived from the quarter-wave half-patch antenna and is widely applied as a low-profile compact antenna design, especially in mobile phones, since the antenna typically has good specific-absorption-rate properties and can have a quasi-omnidirectional radiation pattern, depending on the size of the ground plane and the antenna's position on the ground plane.
PIFAs are typically rectangular in footprint. The radiating element according to the principles of the present invention utilizes the concept of a PIFA, but it combines it with the V shape. Since the radiating surface of each radiator is V-shaped, consisting of two arms with substantially equal lengths, radio-frequency feeding is applied to the radiator by means of a two-pronged fork (in contrast, PIFAs use a single feeding probe).
The layouts of the embodiments of Figures 2 -4 and 6 yield a square topology with a square-shaped spatial vacancy in the centre. The vacancy may be filled by a higher-frequency radiating element 9 (Figure 6), such as that disclosed in co-pending European patent application 14360005.4 to Alcatel Lucent filed on 18 March 2014 . When a hybrid multiband/ultra-wideband radiating element is formed by nesting a higher-frequency radiator inside a lower-frequency radiator, a level of radio-frequency isolation between the radiators is provided by spatial separation alone. For increased radio-frequency isolation, i.e., lower electromagnetic interference, between the radiating element according to embodiments of the present invention and the higher-frequency radiating element, a radio-frequency fence 8 between the higher-frequency radiating element such as is shown in Figures 3 and 6 may be provided. The radio-frequency fence 8 can be seen as an enclosure of the higher-frequency radiating element 9 and can in some embodiments have a lid that acts to mechanically protect the higher-frequency element and to inhibit the ingress of dirt.
Preliminary results indicate that for an antenna such as is shown in Figures 3 and 4, an input-impedance match of about 14 dB is achievable over a relative bandwidth of 25.7% with the radiating element footprint of 0.348 wavelengths by 0.348 wavelengths at the lowest design frequency (0.450 wavelengths by 0.450 wavelengths at the highest design frequency) and a radiating element height of 0.067 wavelengths at the lowest design frequency (0.087 wavelengths at the highest design frequency). A port-to-port isolation of about 27.5 dB is feasible over the same relative bandwidth. Further improvement of input-impedance match can be achieved by increasing the volume of the radiating element, i.e., the footprint and/ or the height of the radiating element.
A full-wave analysis software tool has been utilized to calculate the scattering parameters and far-field gain radiation patterns of the radiating element depicted in Figures 3, 4 and 6. Ohmic losses are included in the simulations; copper (Cu) has been considered for all metallic parts.
Figure 7 shows the frequency-dependence plot 21 of the magnitudes of the input reflection coefficient 22 (|S₁₁|) and the forward transmission coefficient 23 (|S₂₁|); the scattering parameters S₁₁ and S₂₁ refer to a two-port device, where one port corresponds to the +45°-slant polarization and the other to the -45°-slant polarization. The radiating element has been designed for the operating frequency band of 695-900 MHz (i.e., a relative bandwidth of 25.7%), which is delimited by the markers f₁ and f₂ in the plot 21.
Figures 8 and 9 show the typical plots 31 and 41 of the respective co- and cross-polarized far-field gain radiation patterns of the radiating element in the E-, mid- and H-planes. Co-polarized beam integrity and good polarization purity are observed throughout the design operating frequency band. The results demonstrate the radiating element is suitable for utilization in antenna arrays as well as standalone hybrid (nested) multiband/ultra-wideband antennas.
The functions of the various elements shown in the Figures, including any functional blocks labelled as "processors" or "logic", may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which maybe shared. Moreover, explicit use of the term "processor" or "controller" or "logic" should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage. Other hardware, conventional and/or custom, may also be included. Similarly, any switches shown in the Figures are conceptual only. Their function may be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the implementer as more specifically understood from the context.
It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention.
The description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.

Claims

An antenna element comprising:
two elongate arms mounted on and at a distance from a ground plate such that they lie in a plane at a distance from a surface plane of said ground plate, said two elongate arms being angled with respect to each other;

said two elongate arms being formed of a conductive material and forming radiating elements of said antenna element;

at least one conductive connecting member connecting a conductive surface of said ground plate to at least one of said arms; and

at least one feed probe for feeding an input signal to said two arms, said at least one feed probe being spaced apart from said at least one conductive connecting member.
An antenna element according to claim 1, wherein said conductive connecting member connects said two elongate arms to said ground plate at a vertex of said two elongate arms where said two elongate arms meet.
An antenna element according to any preceding claim, wherein said feed probe comprises two feed lines extending towards a point on each of said two elongate arms such that each of said elongate arms receive said input signal.
An antenna element according to any preceding claim, wherein said two elongate arms are substantially identical and said feed lines are arranged to supply a substantially identical signal to each of said elongate arms at a substantially same point on each of said arms.
An antenna element according to any preceding claim, wherein said plane that said two elongate arms lie in is substantially parallel to said surface plane of said ground plate.
An antenna element according to any preceding claim, wherein said two elongate arms have a substantially planar rectangular form.
An antenna element according to any preceding claim, wherein said two elongate arms are arranged at between 70° and 110° with respect to each other, preferably at 90° to each other.
An antenna comprising two antenna elements according to any preceding claim, mounted on said ground plate facing each other, such that a same line substantially bisects an angle between said two elongate arms of each of said antenna elements.
An antenna according to claim 8, further comprising an input signal feed distribution line configured to feed said input signal as a differential input signal to each feed probe of said two antenna elements, such that each antenna element receives said input signal with a phase difference of substantially 180° when operating at or close to a central frequency of a bandwidth of said antenna with respect to said other antenna element.
An antenna according to claim 9, wherein said ground plate is a conductive area mounted on a substrate sheet, said input signal feed distribution line lying on an outer surface of said substrate sheet opposing a surface on which said ground plate is mounted.
An antenna according to any one of claims 8 to 10, said antenna comprising two further antenna elements according to any one of claims 1 to 7, said two further antenna elements being mounted facing each other such, that a same line substantially bisects an angle between said two elongate arms of each of said two further antenna elements, wherein said lines bisecting said angle between said arms of said two antenna elements and said arms of said two further antenna elements intersect at an angle of between 70° and 110°, preferably at an angle of substantially 90°.
An antenna according to claim 11, wherein said ground plate has a substantially quadrilateral outer form and said four antenna elements are mounted at or adjacent to corners of said ground plate, said elongate arms of each of said antenna elements being arranged such that said arms extend over said ground plate.
An antenna according to any one of claims 8 to 12, wherein said antenna elements are mounted at or close to a circumferential edge of said ground plate.
An antenna according to any one of claims 8 to 13, said antenna further comprising a radiation shielding element mounted on said ground plate and forming a hollow lateral enclosure with said antenna elements being arranged outside of said enclosure.
An antenna according to claim 14, said antenna comprising a further antenna element configured to operate at a different frequency bandwidth to said antenna elements mounted at said circumferential edge of said ground plate, said further antenna element being arranged spaced apart from said circumferential edge antenna elements and being within said enclosure formed by said radiation shielding element.