Patent Description:
More particularly it relates to wire antennas such that those used in mobile communication equipments like smartphones, which can access to several kinds of communication links using different frequency bands.

Terminals or smartphones on board aircraft, ship, trains, trucks, cars, or carried by pedestrians, need to be connected while on the move.

These devices need both short and (very) long range communication capabilities, for voice/data and high-throughput data, as well as a low power and optimised consumption, for instance to enable users to watch/listen to multimedia content (video or audio), or participate in interactive games.

Many kinds of objects on-board vehicles or located in manufacturing plants, offices, warehouses, storage facilities, department stores, hospitals, sporting venues, or in private homes, are connected to the Internet of Things ("loT") world. By way of examples only: tags to locate and identify objects in an inventory or to keep people in or out of a restricted area; devices to monitor physical activity or health parameters of users; sensors to capture environmental parameters (concentration of pollutants; hygrometry; wind speed, etc.); actuators to remotely control and command all kinds of appliances; etc..

More generally, loT encompasses any type of electronic device that could be part of a command, control, communication and intelligence system, the system being for instance programmed to capture/process signals/data, transmit the same to another electronic device, or a server, process the data using processing logic implementing artificial intelligence or knowledge based reasoning and return information or activate commands to be implemented by actuators.

Radiofrequency communications are more versatile than fixed-line communications for connecting these types of objects or platforms. As a result, radiofrequency transmitter/receiver (T/R) modules are yet, and will be, more and more pervasive in professional and consumer applications and a plurality of T/R modules are commonly implemented on the same device.

By way of example, a smartphone typically includes a cellular communications T/R module, a Wi-Fi™/Bluetooth™ T/R module, a receiver of satellite positioning signals (from a Global Navigation Satellite System or GNSS). Wi-Fi, Bluetooth and <NUM> or <NUM> cellular communications are operated in the <NUM> frequency band (S-band) whereas GNSS receivers typically operate in the <NUM> frequency band (L-band) and RadioFrequency IDentification (RFID) tags operate in the <NUM> frequency band (UHF) or lower. Near Field Communication (NFC) tags operate in the <NUM> frequency band (HF) at a very short distance (about <NUM>).

Regarding most of these equipments, able to communicate, and that are usually small and mobile, it seems that a good compromise for "loT" connections lies in VHF or UHF bands (<NUM>-<NUM> and <NUM> to <NUM>) to get sufficient available bandwidth and range, a good resilience to multipath reflections as well as a good energy consumption balance.

However, a problem to be solved for the design of T/R modules at these frequency bands is to have antennas which are compact enough to fit with the dimensions of a connected object. Indeed, a traditional omnidirectional antenna of a monopole type, adapted, for instance for VHF bands, has a length between <NUM> and <NUM> (λ/<NUM>). An antenna of that size cannot obviously be housed, as such, in a compact connected object.

A solution to this problem of length is provided by PCT application published under n° <CIT>, which has the same inventor and is currently co-assigned to the applicant of this application. This application discloses an antenna arrangement of a bung type, where a plurality of antenna elements are combined so that the ratio between the largest dimension of the arrangement and the wavelength may be much lower than a tenth of a wavelength, even lower than a twentieth or, in some embodiments than a fiftieth of a wavelength. To achieve such a result, the antenna element which controls the fundamental mode of the antenna is wound up in a 3D form factor, such as, for example, a helicoid so that its outside dimensions are reduced relative to its length.

Most equipment mentioned above also need to be compatible with terminals which communicate using Wi-Fi™ or Bluetooth™ frequency bands and protocols. As a consequence, some stages of the T/R module have to be compatible with both the VHF and S bands; moreover, if a GNSS receiver is added, a T/R capacity in the L band is also needed. This means that the antenna arrangements of such devices should be able to communicate simultaneously or successively in different frequency bands. However, adding as many antennas as frequency bands is costly in terms of space, power consumption and materials. This creates another challenging problem for the design of the antenna.

Some solutions are disclosed for base station antennas by PCT applications published under n° <CIT> and <CIT>. But these solutions do not operate in the VHF bands and do not provide arrangements which would be compact enough for most of the loT and smart devices in these bands.

<CIT> discloses a power feed pin of a radiation electrode is disposed in the vicinity of a first end in the lengthwise direction of a dielectric substrate. A ground pin of the radiation electrode is disposed in the vicinity of a second end in the lengthwise direction of the dielectric substrate. A first location that is in the vicinity of the mid-point on the path from the power feed pin to the ground pin of the radiation electrode is close to a second location that is a point midway from the first location to the power feed pin, or a third location that is a point midway from the first location to the ground pin is close to the first location. A capacitance-forming part is configured at a position where the second location or third location and the first location are close to each other.

<CIT> presents an antenna including a grounded conducto, a shorting pin that is formed with a conductor, and a radiation conductor that has one end connected to the grounded conductor via the shorting pin <NUM>, has the other end left open, and receives power supplied from a feeding point <NUM> located at the one end. The radiation conductor is folded at a portion between the one end and the other end, and forms a lower arm closer to the grounded conductor and a folded upper arm, with at least part of the lower arm and the upper arm having a meandered portion.

<CIT> describes a system and method for wirelessly sending information electromagnetically at one of a first or a second specified operating frequency from within a biological medium, or receiving information electromagnetically at one of the first or second specified operating frequencies in the biological medium, using an implantable antenna including a switchback portion having multiple segments. The first specified operating frequency and the second specified operating frequency can be provided using the multiple segments.

<CIT> presents an antenna, antenna combination, and portable electronic device having the antenna or the antenna combination are disclosed. The antenna comprises a radiator, a grounding portion, and an arc-shaped feeding portion connected with a coaxial cable for feeding electronically. A first end of the arc-shaped feeding portion is connected with the radiator, and a second end of the arc-shaped feeding portion is connected with the grounding portion.

<CIT> provides an antenna and a wireless communication device that includes the antenna in which a high-order mode can be controlled while maintaining good radiation characteristics in both the fundamental mode and high-order mode. The antenna has a radiation electrode provided on a surface of a dielectric substrate and a branch electrode portion that branches from the radiation electrode portion at a branch point near the feeding port toward a vicinity of a position of the radiation electrode at which a maximum voltage of a high-order mode is generated.

<CIT> relates to a multiband folded loop antenna comprising a dielectric substrate, a ground plane, a radiating portion and a matching circuit. The ground plane is located on the dielectric substrate and has a grounding point. The radiating portion comprises a supporter, a loop strip, and a tuning patch. The loop strip has a length about half wavelength of the antenna's lowest resonant frequency. The loop strip has a feeding end and a grounding end, with the grounding end electrically connected to the grounding point on the ground plane. The loop strip is folded into a three-dimensional structure and is supported by the supporter. The tuning patch is electrically connected to the loop strip. The matching circuit is located on the dielectric substrate with one terminal electrically connected to the feeding end of the loop strip and another terminal to a signal source.

A purpose of the invention is to propose an antenna arrangement which can be designed and tuned in a simple manner to transmit/receive (T/R) radiofrequency signals at a plurality of frequencies, notably in the microwave or VHF/UHF domains, with an optimal compactness.

The invention advantageously fulfils this need by providing, according to a first aspect, a monopole antenna arrangement as set out in the appended independent claim <NUM>, And a a method for designing an antenna arrangement as defined in the appended independent claim <NUM>. Advantageously too, specifications for an antenna according to the invention, for frequencies bands commonly used for "loT" (i.e. VHF or UHF bands (<NUM>-<NUM> and <NUM> to <NUM>)) may be achieved with standard technologies. The antenna wire element of the invention can, for instance, conveniently be configured (folded) to radiate according to two or more frequency bands, comprising one or more bands among an ISM band, a Wi-Fi™ band, a Bluetooth™ band, a <NUM> band, a LTE band and a <NUM> band. However antennas according to the invention working at higher frequency bands may also be considered since, for higher frequencies such as those in the millimeter wave domain, state-of-the-art technologies are now available with which the invention may be implemented. For instance, semiconductor etching techniques allow the creation of ten micrometers ribbons with a precision in the micrometer range.

The multi-frequency antenna wire element of the invention may be used, either in alternate mode or in simultaneous mode on a plurality of aggregated frequencies, thus increasing significantly the bandwidth resources.

Advantageously too, due to the folding of the conductive element, the antenna of the invention may be compact, considering the lowest frequency used, which allows its integration in small packages.

Moreover, whatever the structure of the conductive element (2D or 3D wire arrangement or printed track) the antenna of the invention is simple to design, easy to connect to the printed circuit board of an electronic T/R device and easy to manufacture. It is thus of a very low manufacturing cost.

All the features and advantages of the invention will be better understood thanks to the following detailed description of some particular embodiments, given purely by way of non-limiting examples, which refers to the appended figures which show:.

In the aforementioned figures, a same functional element is referred to, as far as possible, by the same number.

<FIG> shows a monopole wire antenna <NUM> known of the prior art, made of a rectilinear conductive element <NUM>, a metallic wire, or a conductive ribbon (conductive track) for instance.

The rectilinear conductive element <NUM> has a physical length l which is defined as a function of the radiating frequency of a desired fundamental resonant mode (F<NUM>) of the antenna, as explained further down in the description.

The conductive element <NUM> is associated to a ground plane <NUM> located near its proximal end <NUM> which is adapted to be connected to a transmitter/receiver device. Such an antenna has an omnidirectional radiating pattern in the azimuth plane.

In <FIG>, the conductive element <NUM> is a wire arranged to be perpendicular to said ground plane <NUM>. The ground plane <NUM> may be thus a metallic plane through which the wire element <NUM> passes before being connected to the transmitter/receiver device, as shown on <FIG> for instance.

However, in some other existing solutions, for instance when the conductive element and the ground plane are designed as a coplanar arrangement, the plane in which the conductive element <NUM> is arranged may be parallel to the ground plane <NUM>, or may be inscribed in said ground plane.

In such an arrangement, which is discussed below, the conductive element <NUM> may be a conductive track engraved on the front side of a dielectric substrate, a PCB structure as shown on <FIG> for instance, which comprises the transmitter/receiver circuit, whereas the ground plane <NUM> may be a conductive layer arranged on the back side of the substrate, i.e. the PCB.

In a manner known by a person of the art, a monopole antenna is adapted to operate at different resonant modes that depend on its physical length l, mainly:.

<FIG> shows a graphic illustration of the various resonant modes according to which a monopole antenna as illustrated on <FIG> can operate and the respective variations of voltage along its length. It also shows the electrical characteristics of the antenna corresponding to each resonant mode. <FIG> makes it possible to highlight the various features of such an antenna which are used in the context of the invention.

As it can be seen on <FIG>, when an antenna <NUM> is used to transmit (radiate) or receive (capture) an electromagnetic wave, the value of the voltage of the corresponding electromagnetic field is varying along the length l of the conductive element <NUM> as a sinusoid, the period of which depending on the order of the resonant mode. On <FIG>, this variation is indicated by doted lines.

As shown, each of the resonant mode is thus defined by a point of maximum voltage level of the electromagnetic field (corresponding to a current node) located at the distal end <NUM> (or Open Circuit end) of the conductive element <NUM>, and by a point of zero voltage (corresponding to a voltage node) of the electromagnetic field located at its proximal end <NUM> (or Short Circuit end), the latter corresponding to a maximum current value.

Additionally, for the various higher order modes (harmonic modes), there are other current and voltage nodes alternately distributed along the length of the conductive element <NUM>. The number of nodes depends on the order of the mode.

For instance, for a conductive element with a length l = λ<NUM>/<NUM>, the third resonant mode (F<NUM> = 5F<NUM> and l = <NUM>λ<NUM>/<NUM>) shows three current nodes MX31, MX32 and MX33 whereas fundamental (first) resonant mode (F<NUM>) shows only one current node MX11.

Moreover, for each resonant mode, the distance between a current node and a neighbouring voltage node is equal to λn/<NUM>, where n is the order of the resonant mode. For instance, for the second resonant mode (first higher mode at F<NUM> = 3F<NUM>), that distance equals λ<NUM>/<NUM> with λ<NUM> = c/<NUM>F<NUM>.

As it can also be seen on <FIG>, the polarity of the voltage induced by the electromagnetic field, relative to a common reference, varies alternately between "+" and "-" along the wire antenna element <NUM>, such that two consecutive current nodes are located in areas of opposite polarities.

Thus, for instance, there are only one current node MX11 and one voltage node for the fundamental mode (F<NUM>), which are separated from each other by the length l, whereas there are two current nodes MX21 and MX22 and two voltage nodes for the <NUM>st higher order mode (F<NUM> = 3F<NUM>) each node being separated from its neighbours by a distance equal to <NUM>/<NUM> and three current nodes and three voltage nodes for the 2nd higher order mode (F<NUM> = 5F<NUM>).

The fundamental mode (F<NUM>) therefore only has one current node MX11 and a single area A11 in which the voltage of the electromagnetic field is positive ("+") and varies from a maximum value to zero whereas the first higher order mode (F<NUM> = 3F<NUM>) shows two current nodes MX21 and MX22 and two areas A21 and A22 in which the voltage of the electromagnetic field is alternately positive ("+") and negative ("-") and varies between a maximum value (MX21 or MX22) and zero.

The third higher order mode (F<NUM> = 5F<NUM>), in turn, has three current nodes MX31, MX32 and MX33 and three areas A31, A32 and A33 in which the voltage of the electromagnetic field is alternately positive ("+"), negative ("-") and positive ("+") again, and varies between a maximum value (MX31, MX32 or MX33) and zero.

As illustrated in <FIG>, it is possible to determine along the conductive element <NUM>, for each resonant frequency, particular areas where the antenna demonstrates a high electrical sensitivity, that is to say zones where the voltage of the electromagnetic field has a value still significant with respect to the maximum values MX of the nodes located in those areas.

Some of these high electrical sensitivity areas, areas <NUM>, belong to areas where the electromagnetic field shows a given polarity and some other, areas <NUM>, belong to areas where it shows the opposite polarity.

<FIG> illustrates the main structural features of a monopole antenna according to the invention.

The monopole antenna <NUM> according to the invention is designed from a conductive rectilinear element like conductive element <NUM> of antenna <NUM> of <FIG>.

As shown on <FIG>, that rectilinear conductive element is folded in order to make a conductive element <NUM> with areas <NUM>, <NUM>, called coupling areas, where some parts of the conductive element (points or segments) located along its length at particular locations are positioned facing one another.

According to the invention, these parts of the conductive element <NUM> belong to those particular areas where the antenna shows a high electrical sensitivity. Advantageously, positioning two of these particular parts facing one another creates a coupling which induces a shift in the resonant frequency of one or more of the higher order resonant modes of the antenna. Moreover, in order to achieve an efficient coupling, the parts of the conductive element <NUM> which are positioned facing each other to form a given coupling area, are located at, or at least close to, points MX corresponding to current nodes for the selected resonant mode, and anyway in those areas of the conductive element with a high electrical sensitivity.

The number of the coupling areas and their location along the conductive element <NUM> as well as the geometrical features of each coupling area are thus determined such that each of the coupling areas is intended to produce, for a given higher order resonant mode (3F<NUM>, 5F<NUM>, 7F<NUM>. ), a desired shift of the resonant frequency of the conductive element <NUM> for that resonant mode.

The strength of the coupling between two conductive elements positioned neighboring one another is proportional to the length of the area where the conductive elements face one another and inversely proportional to the size of the gap between these two conductive elements.

As shown in <FIG>, the parts of conductive element <NUM> which are positioned facing one another can either be punctual or quasi-punctual, like in coupling area <NUM>, or form segments, like in coupling area <NUM>.

According to the invention, considering the shift of resonant frequency the coupling area is adapted to provide, the geometrical features of each coupling area are determined based on the following properties:.

In that context a part of the conductive element is considered located close to a given point MX if it is located inside the area of high electrical sensitivity including that point. Indeed, insofar as the two parts remain located inside their respective corresponding area of high electrical sensitivity, a significant frequency shift remains achievable.

Advantageously, forming such coupling areas, makes it possible to design a monopole antenna with a conductive element <NUM> of a length l to operate around various given resonant frequencies, one or more of those frequencies being different from those around which a monopole antenna made of a rectilinear conductive element <NUM> of a same length is normally adapted to operate, that is to say resonant frequencies that are odd multiples of a fundamental frequency F<NUM> determined by the length l of the conductive element <NUM> forming the antenna.

A monopole antenna according to the invention can be thus designed, for instance, from a monopole antenna with a rectilinear conductive element of a given length, configured to operate around given frequencies F<NUM>, 3F<NUM>, 5F<NUM>, 7F<NUM>, etc.. , by folding the conductive element to set up coupling areas along its length in order to shift some of the resonant frequencies to adapt the antenna to operate in accordance with a particular set of frequencies F<NUM>, F'<NUM>, F'<NUM>, F'<NUM>, etc.. used in a given application and where one or more of the frequencies F'<NUM>, F'<NUM>, F'<NUM>, etc.. can differ from nominal resonant frequencies F<NUM>= 3F<NUM>, F<NUM> = 5F<NUM>, F<NUM> = 7F<NUM>, etc..

As mentioned previously, the folded antenna <NUM> according to the invention can be implemented in accordance with different kinds of embodiments.

According to one series of embodiments, illustrated by examples in <FIG>, the antenna <NUM> according to the invention can be made of a conductive wire element <NUM> folded so as to make a substantially planar folded structure arranged perpendicularly to a ground plane <NUM>, made of a metal plate for instance.

In such embodiments resonant frequency shifts can be obtained by fixing, for each frequency shift, the features of the corresponding coupling area, that is to say the locations, along the conductive element, of the parts of the conductive element forming the coupling area as well as their lengths and the width of the gap between these two parts. The locations of these parts are determined related to the respective polarities of the voltage at these locations.

In the exemplary embodiment of <FIG>, the antenna <NUM> has two punctual coupling areas <NUM> and <NUM>, adapted to induce two resonant frequency shifts. The value of each frequency shift and the sign of the shift are given by the position of the corresponding coupling area along the conductive element <NUM> and by the size of the gap e<NUM> or e<NUM> located between the two parts of the conductive element that are positioned facing each other.

<FIG> illustrates graphically the various results that can be obtained with an antenna like the exemplary antenna of <FIG> considering that the coupling areas <NUM> and <NUM> are arranged so as to shift resonant frequencies of the second and the third resonant modes to frequencies F<NUM> and F<NUM> respectively lower than 3F<NUM> and 5F<NUM>. <FIG> illustrates four different configurations of coupling respectively referenced a), b), c) and d).

The frequency shifts illustrated on <FIG> may for instance be obtained by positioning point MX33 or a point close to MX33 of element <NUM> facing point MX32 or a point close to MX32 to form coupling area <NUM>, and terminal point MX21 or a point close to MX21 facing point MX22 or a point close to MX22 to form coupling area <NUM>.

Points MX33 and MX32 belonging to areas <NUM> and <NUM> of the conductive element <NUM> for which the electromagnetic field has opposite polarities, the frequency shift caused by coupling area <NUM> results in a decrease of the resonant frequency F<NUM> with respect to initial resonant frequency 5F<NUM>.

Similarly, MX21 and MX22 belong to areas <NUM> and <NUM> of the conductive element. As a result, the frequency shift caused by coupling area <NUM> results in a decrease of the resonant frequency F<NUM> with respect to initial resonant frequency 3F<NUM>.

Configuration a) corresponds to a case where the values e<NUM> and e<NUM> of the gaps between the parts of the conductive element <NUM> forming the coupling areas <NUM> and <NUM> are such that no significant coupling appears in any of the two areas. Thus, none of the resonant frequencies 3F<NUM> and 5F<NUM> is shifted.

Configuration b) corresponds to a case where the value e<NUM> of the gap between the parts of the conductive element <NUM> forming the coupling area <NUM> is wide enough not to induce a significant coupling in that area. As a result resonant frequency 5F<NUM> is advantageously not shifted.

In contrast the value e<NUM> of the gap between the parts of the conductive element <NUM> forming the coupling area <NUM> is small enough to induce a coupling in that area. As a result, resonant frequency 3F<NUM> is shifted to a resonant frequency F<NUM> lower than 3F<NUM>.

Configuration c) corresponds to a case similar to configuration b) but where the value e<NUM> of the gap between the parts of the conductive element <NUM> forming the coupling area <NUM> is such that a coupling appears in that area, whereas the value e<NUM> of the gap between the parts of the conductive element <NUM> forming the coupling area <NUM> is such that no significant coupling appears in that area. As an interesting result, resonant frequency 3F<NUM> is not shifted and frequency 5F<NUM> is shifted to a resonant frequency F<NUM> lower than 5F<NUM>.

Configuration d) corresponds to a case where both values e<NUM> and e<NUM> of the gaps between the parts of the conductive element <NUM> forming the coupling areas <NUM> and <NUM> are such that a coupling appears in the two areas. This advantageously leads to the resonant frequency 3F<NUM> being shifted to a resonant frequency F<NUM> lower than 3F<NUM> and frequency 5F<NUM> shifted to a resonant frequency F<NUM> lower than 5F<NUM>.

<FIG> illustrates an example <NUM> useful for understanding the invention outside the scope of the claims. wherein the antenna comprises a conductive wire element <NUM>, arranged in a full planar configuration and folded in a plane. Antenna <NUM> of <FIG> comprises one coupling area <NUM> made of two parts <NUM>, <NUM> of the conductive element <NUM> positioned facing each other. The location and the length of the two parts <NUM> and <NUM> as well as the gap between them are determined so as to obtain the desired shift of the resonant frequency (3F0, 5F0,. ) of one given resonant mode. Antenna <NUM> is thus conformed to produce a single desired frequency shift.

<FIG> illustrates a further exemplary embodiment <NUM> of the antenna not according to the invention, wherein the antenna comprises a conductive wire element <NUM>, arranged in a full planar configuration and folded in a plane. Antenna <NUM> of <FIG> comprises two coupling areas: one coupling area <NUM> made of two parts <NUM> and <NUM> of the conductive element <NUM> and another coupling area <NUM> made of two other parts <NUM> and <NUM>, of the same conductive element <NUM>. The location and the length of the two parts forming a given coupling area <NUM> or <NUM>, as well as the gap between the parts forming the latter are determined so as to obtain the desired shift of the resonant frequency of one given resonant mode. Antenna <NUM> is thus conformed to produce two desired frequency shifts.

<FIG> illustrates another exemplary embodiment of the antenna according to the invention, wherein the antenna <NUM> comprises a conductive wire element <NUM>, arranged spatially in relation to three perpendicular planes: planes xOy and yOz, and a plane parallel to plane xOz comprising the distal portion <NUM> of the conductive element <NUM> linking the two coupling areas <NUM> and <NUM>. This embodiment, quite similar to the embodiment of <FIG> advantageously provides more possibilities, more degrees of freedom, to form various coupling areas along the conductive element <NUM>, either punctual coupling areas like area <NUM>, made of two points distant from one another of a gap e2, or elongated coupling areas, like area <NUM> made of two parts with a length Δl, remote from each other from a gap e1.

According to another series of examples useful for understanding the invention outside the scope of the claims, illustrated by <FIG>, the antenna <NUM>, <NUM> or <NUM> can be made of a sinuous conductive track <NUM> arranged on one side of a plane substrate <NUM>, the opposite side being partly covered by a conductive layer forming a ground plane area <NUM> located facing the end of the conductive track configured to be connected to a transmitter/receiver device.

According to this kind of arrangement, the coupling areas <NUM> are thus created by shaping the conductive track <NUM> in such a way that some parts of the track are arranged to face other parts. The overall length of the track, i.e. the part of the track extending from signal feed point <NUM> and the distal end <NUM> of the track, determines the resonant frequency of the fundamental resonant mode.

Insofar as the ground plane and the conductive element of such antennas are arranged in parallel plans formed by the two opposite sides of a same planar substrate - instead of being arranged in perpendicular plans like in arrangements comprising wire-made conductive elements - this kind of arrangement is well suited to applications implemented in relatively small or thin packages small communication devices such as smartphone or the like. However, like antennas made of a wire conductive element folded according to a plane, antennas of <FIG> for instance, the number of coupling areas that can be formed at the same time is limited by the planar bidimentional '<NUM>-D" structure of the conductive track <NUM>. As a result, the number of resonant frequencies that can be shifted at the same time, each with the desired increase or decrease, is also more limited in this configuration.

<FIG> represents the particular case of an antenna <NUM> according to <FIG>, wherein the antenna comprises a single punctual coupling area formed by points P1 and P2, and the particular case of an antenna <NUM> according to <FIG>, wherein the antenna comprises a single elongated coupling area formed by segments Z1 and Z2 of the conductive track <NUM>. It represents the variation of the frequency response of an antenna according to the invention induced by a coupling area <NUM>.

<FIG> shows three curves <NUM>, <NUM> and <NUM>, each of them representing the frequency response of the antenna in one of the three configurations A), B) and C) shown above the curves.

For configuration A), with a wide gap between the two points P1 and P2 forming coupling area <NUM>, the frequency response doesn't display any shift of the resonant frequencies F<NUM>, 3F<NUM> and 5F<NUM>, meaning that the coupling <NUM> is too weak to induce any shift.

Regarding configuration B), with a much narrower gap between the two points P1 and P2, frequency response displays a decrease of the resonant frequency F<NUM> = 3F<NUM> that shifts to a desired frequency F'<NUM>, whereas resonant frequencies F<NUM>, and F<NUM> = 5F<NUM> remain substantially unshifted. This means that, due to the low value of the gap between points P1 and P2, the coupling <NUM> induces a shift of resonant frequency F<NUM> = 3F<NUM> of the first higher resonant mode. This also means that points P1 and P2 are located on parts of the conductive track <NUM> where the voltage of the electromagnetic field has opposite polarities, parts respectively belonging to areas <NUM> and <NUM> shown on <FIG>.

Regarding configuration C), with the same gap between the two segments Z1 and Z2 as between points P1 and P2, frequency response displays a decrease of the resonant frequency F<NUM> = 3F<NUM> that shifts to frequency F'<NUM> (F'<NUM> < F<NUM>) whereas resonant frequencies F<NUM>, and F<NUM> = 5F<NUM> remain substantially unshifted. This means that, due to the low value of the gap between segments Z1 and Z2, respectively including P1 and P2, the coupling <NUM> induces a shift of resonant frequency F<NUM> = 3F<NUM> of the first higher resonant mode. This also means that, due to the extent of the coupling zone, the strength of the coupling in configuration C) is higher than that of the coupling in configuration B) for a same gap value, inducing a more important frequency shift. Illustration of <FIG> considers the particular case of an antenna according to the invention comprising a single coupling area, inducing a single frequency shift to show the influence of the geometrical features of a coupling area on the value of the resonant frequency shift.

However, it is obvious for an ordinarily skilled person that, when the antenna comprises several coupling areas, the same applies to each corresponding frequency shift.

As described in the previous paragraphs, an antenna according to the invention can advantageously optionally be built from a known monopole antenna, with a rectilinear λ<NUM>/<NUM> conductive element, by folding said conductive element in order to create coupling areas, said coupling areas inducing desired frequency shifts on resonant frequencies of the conductive element.

According to the invention, a coupling area is created by positioning two parts of the conductive element facing each other. The coupling areas are defined by the strength of the coupling provided and by the polarity of the areas of the conductive element the two parts of the conductive element belong to. The size of the gap between the two parts of the conductive element involved in the coupling area and the lengths of these two parts, determine the strength of the coupling, and thus the value of the frequency shift, whereas the sign of the shift (increase or decrease) is determined by the polarity of the areas of the conductive element the two segments belong to.

An antenna according to the invention can therefore be designed, considering those parameters, by implementing a design method comprising the following steps.

A first step consists in determining the length of the conductive element, in accordance with the lower operating frequency of the set of frequencies (F'<NUM>, F'<NUM>. , F'N) on which the designed antenna is expected to work.

In most cases, the length of the conductive element will be determined such that the frequency F<NUM> of the fundamental resonant mode of the conductive element, which cannot be shifted, will correspond to the lower operating frequency F'<NUM>, in order to operate the antenna in the most efficient manner and to simplify the design. Nevertheless, the length of the conductive element may, in some cases, be determined such that frequency F0 corresponds to another frequency, another frequency of the set of working frequencies for instance.

Indeed, as it can be noticed considering the present disclosure, and considering in particular <FIG>, the frequency F<NUM> of the fundamental resonant mode cannot be shifted, since for that resonant mode the length of the conductive element corresponds to the quarter of the fundamental wavelength λ<NUM>. That means that, for that mode, the voltage of the electromagnetic field has only one maximum MX11 and only one area of high electrical sensitivity. As a consequence, no coupling area can be created to induce any frequency shift.

As a result, F'<NUM> being determined, the length l of the conductive element may then be defined in such a way that the fundamental resonant mode appears for a frequency F<NUM> corresponding substantially to the lower frequency F'<NUM> of the set of expected frequencies (F'<NUM>, F'<NUM>. Moreover, since the length l of the conductive element is determined, both frequency F<NUM> and the resonant frequencies (F<NUM> = 3F<NUM>, F<NUM> = 5F<NUM>, F<NUM> = 7F<NUM>, etc.. ) of the higher resonant modes are also determined.

A second step consists in selecting the resonant frequency or frequencies of those of the higher order modes which are to be shifted to obtain the other desired frequency values F'<NUM>, F'<NUM>, F'<NUM>, etc.. and to determine the value of the corresponding frequency shifts as well as the sign of these shifts (increase or decrease). The values of these shifts are directly deduced from the resonant frequencies obtained with a conductive element of the length determined at the previous step.

A third step consists in determining, for each frequency shift determined at the previous step, the features of the coupling area fit to achieve that shift, said features being:.

The third step must be implemented for each resonant frequency to be shifted, considering the other coupling areas to create and the effect of the setting up of a given coupling area on potential unwanted shifts that may affect other resonant frequencies.

Indeed, as it can be noticed considering <FIG>, setting up a coupling area to shift a given resonant frequency is achieved by positioning facing one another two points of maximum voltage of the electromagnetic field located in two different areas of high electrical sensitivity, or two segments of the conductive element containing these points or located close to them. This may result in said coupling area thus created to shift other resonant frequencies at the same time, causing unwanted shifts.

Each coupling area has to be therefore designed in order to prevent, as far as possible, any unwanted frequency shift. However, if the design of a given coupling area that is adapted to induce the necessary shift of a given resonant frequency seems to induce an unwanted shift on another resonant frequency, such unwanted shift can often be cancelled by designing an additional coupling area fit to produce an opposite shift or by modifying the features of another coupling area, already fit to cause a given shift to the resonant frequency that was unwillingly modified.

Thus, implementation of the design method described here above makes it advantageously possible to design an antenna according to the invention fit to operate at a number of resonant frequencies different from those of a monopole antenna of the prior art. As a result, the method to create an antenna according to the invention comprises two steps:.

As described previously, the antenna arrangement according to the invention comprises a conductive element <NUM> configured to resonate at and above a chosen electromagnetic radiation frequency (F<NUM>) corresponding to a fundamental resonant mode.

According to the invention, the conductive element <NUM> is folded to achieve coupling areas <NUM> and <NUM> intended to modify one or more of the resonant frequencies (3F<NUM>, 5F<NUM>, 7F<NUM>. ) of the higher resonant modes of the conductive element <NUM>.

Such coupling area is formed by positioning given parts of the conductive element <NUM> facing each other in accordance with a given relative position.

The location of these parts along the conductive element <NUM>, as well as the length of these parts and as the width of the gap between them are determined so as to obtain a given strength of coupling providing a desired increase or decrease of the resonant frequency of a given resonant mode of the conductive element <NUM>.

The field of the present invention is not limited to VHF and UHF frequencies Bands, but can rather cover higher frequency bands corresponding to millimeter waves, like WiFi™ <NUM> ad Band (<NUM>-<NUM>) or <NUM> bands (<NUM>,<NUM>, <NUM>,<NUM>, <NUM>,<NUM> - <NUM>,<NUM>, <NUM> - <NUM>,<NUM>, <NUM>,<NUM> - <NUM>,<NUM>, <NUM>,<NUM> - <NUM>,<NUM>, <NUM> - <NUM>-GHz and <NUM> - <NUM> for instance), or else like WBAN (Wireless Body Area Network) band (<NUM>). The principle of design of antennas according to the invention operating at these frequencies remains the same. Only the precision of the manufacturing means necessary to produce such antennas is increased due to the small size of those antennas.

Claim 1:
A monopole antenna arrangement (<NUM>) comprising a conductive element (<NUM>) of length l, configured to resonate at or above a chosen electromagnetic radiation frequency (F<NUM>), wherein the conductive element (<NUM>) comprises at least two first parts (<NUM>) corresponding to high electrical sensitivity areas that include respective nodes of current of the chosen electromagnetic radiation for a given resonant mode selected amongst the second, third and fourth order resonant modes (3F<NUM>, 5F<NUM>, 7F<NUM>) of the conductive element, and where the voltage of the electromagnetic field has a value still significant with respect to the maximum values of the respective nodes,
the monopole antenna being characterized in that
each first part (<NUM>) faces close to one respective second part (<NUM>) of the conductive element (<NUM>) corresponding to a high electrical sensistivity area that includes one different node of current of said electromagnetic radiation having the same responant mode of the node of current of the said first part, so as to create an electromagnetic coupling area (<NUM>) configured to shift the resonant frequency of two or more of the second, third or fourth order resonant modes (3F<NUM>, 5F<NUM>, 7F<NUM>) of the node of current of the said first part while avoiding any coupling between the remaining portions of the conductive element.