EP1941579A1

EP1941579A1 - Antenna device

Info

Publication number: EP1941579A1
Application number: EP06716912A
Authority: EP
Inventors: Carl-Gustaf Blom
Original assignee: Lite On Mobile Oyj
Current assignee: Lite On Mobile Oyj
Priority date: 2005-10-04
Filing date: 2006-02-17
Publication date: 2008-07-09
Also published as: WO2007040431A1; TW200721592A; SE528069C2; SE528069C3; SE0502185L

Abstract

An antenna (400) is provided, which comprises at least one antenna element (405) with at least one frequency arm (413, 415) and a resonator (409) for feeding the antenna element. The antenna element is arranged to be fed non- galvanic via the resonator, the resonance frequency of which is above the highest frequency in the highest frequency band the antenna is intended.

Description

ANTENNA DEVICE

Technical field

The present invention relates to an antenna for a mobile terminal unit such as a mobile telephone for operation in one or several frequency bands.

Background

Different types of multiband antennas intended for integration in mobile terminal units are known in the art. The most common type is the so-called PIFA (Planar Inverted F Antenna) antenna. These antennas normally consist of a radiator element made of metal sheet or flex-film applied to a plastic carrier mounted at a certain distance above a ground plane. The radiator element is in galvanic contact to a RF feed and to the ground plane. The radiator element is configured with one or several slots to achieve one or several resonance arms, one for each frequency band. If the distance between the radiator element and the ground plane is sufficient an antenna for several frequency bands can be accomplished. The main obstacle to achieve a good matching for both frequency arms (in the case with two frequency arms) is that there is only one common RF feed as well as one common ground feed for the two frequencies. This means that the impedance matching can be made optimal for the frequency arm where the RF feed is located.

Figure 1 shows a conventional PIFA according to older technology. The antenna element 105, which can be made of a flexfilm or thin metal sheet, is applied on a non- conductive carrier of e.g. plastic, not shown in the figure for clarity reasons. The carrier can then be mounted against a printed circuit board comprising a ground plane 109. The antenna element 105 has a galvanic connection to the ground plane in the point 107 and also a galvanic contact to RF in point 101 or 103. If RF contact is made at point 101 an optimal matching for the high frequency band using the frequency arm 111 is achieved and if contact is made at point 103 matching will be optimal in the low frequency band using frequency arm 113.

A variation of this solution is shown in GB 2403069, describing an integrated antenna unit comprising a first, dielectric antenna and a second, electrically conductive antenna, where the first and second antenna are not electrically connected to each other but configured such that the second antenna is fed by the first antenna when the first antenna is fed by a predetermined signal, where the second antenna is connected to ground, and where the first and second antenna are configured to radiate in different, non overlapping frequency ranges.

GB 2403069 requires that part of the ground plane under the dielectric antenna is removed or in another embodiment, with a complete ground plane under the dielectric antenna, that the dielectric antenna is shaped in a certain way to achieve resonance at a desired frequency.

Summary of the invention

An object of the present invention is to provide an antenna that can be built into a mobile terminal unit, henceforth exemplified with a mobile phone, that eliminates the drawbacks with prior art and to accomplish a solution with very compact outer dimensions with easy and cost effective manufacturing.

A further object of the invention is to provide an antenna making it possible with resonance in up to four or more frequency bands .

These objects are met by providing an antenna comprising at least one antenna element with at least one frequency arm and a resonator for feeding the antenna element. The antenna element is configured to be fed non-galvanic via a resonator with a resonance frequency above the highest frequency in the highest frequency band for which the antenna is intended. The term frequency arm is meant as a radiating unit that may be configured as a slot or radiating surface of conductive material.

The purpose of the resonator is only to transfer RF energy between the antenna element and the receive- and transmit-circuits of the mobile phone and to work as an impedance matching to the different frequency arms of the radiator. The resonance frequency of the resonator is thus not used in any of the frequency bands for which the antenna is intended to operate.

With this solution, henceforth called DFA-antenna (Dielectric Feed Antenna), a very manufacture-effective, compact and cost-effective antenna solution is accomplished with an optimal impedance matching in all frequency bands and thereby a good antenna function. As the resonator can be located very close to the antenna element a thin antenna design can be achieved with short distance between antenna element and ground plane. The DFA-antenna can interact with a ground plane and in one embodiment it can preferably be located above the printed circuit board of the mobile phone and use the regular ground plane of the mobile phone without any modifications. This is advantageous compared to the solutions with older technology where part of the ground plane under the ceramic element needs to be removed in order to achieve optimal function. In other embodiments of the invention interaction with the ground plane can be arranged by integrating the antenna element in the ground plane of the printed circuit board of the mobile phone. This means fewer components, compact design as well as simple and cost effective manufacturing.

Other embodiments with ground plane independent half-wave antennas do not require direct interaction with a ground plane .

Further advantages are achieved if the invention also is given one or several characteristics according to the dependent claims .

Brief description of the figures

The invention will now be described in more detail with reference to the enclosed drawings. These are.

Figure 1 shows a PIFA according to prior art.

Figure 2 shows schematically a mobile phone comprising an antenna according to the present invention

Figure 3 shows schematically transfer of RF energy

Figure 4a is a schematic top view of a DFA according to the present invention. Figure 4b is a schematic side view of the DFA in figure

4a.

Figures 5a and 5b show schematically two examples of quarter-wave resonators.

Figures 5c and 5d show schematically examples of resonators with RF feed to a metallized side.

Figure 6 shows schematically a resonance diagram for a penta-band antenna

Figures 7a and 7b are schematic top and side views of the antenna element realized as a meander according to the present invention.

Figure 8 shows schematically antenna element realized as ^-wave meander-slot in ground plane according to the present invention.

Figure 9 shows schematically a combination of two antenna elements, slot and structure according to figure 4, according to the present invention.

Figure 10 shows schematically antenna element as PILA- structure according to the present invention.

Figure 11 shows schematically antenna elements as k-wave slot in ground plane according to the present invention.

Figure 12 shows schematically antenna element and parasitic antenna element according to the present invention .

Figure 13 shows schematically two antenna elements in galvanic contact according to the present invention. Figure 14 shows schematically curved antenna elements according to the present invention.

Figures 15a and 15b are schematic top and side views of antenna elements with windows in which a resonator is located.

Figure 16 is an alternative embodiment of an antenna element with a window.

Figures 17a-17e illustrate an embodiment of an antenna comprising a flexfilm substrate.

Preferred embodiments

As seen by way of introduction the object of the invention is to accomplish an antenna with possibilities for resonance in one or several bands, called DFA- antenna, intended to be used in a mobile terminal unit such as e.g. a mobile telephone according to figure 2.

Figure 2 shows a mobile phone 201 comprising a control unit 207 configured to control communication with a mobile communication system 203. A keyboard 213, a display 215 and radio frequency circuits 209 are connected to the control unit 207 that together with an antenna 211 are arranged to establish a radio-interface 205 for communication with the mobile communication system 203.

In one embodiment the antenna is able to cover a low and a high frequency range. The low range can e.g. consist of the range 824-960 MHz, covering the GSM 800 and GSM 900 bands (GSM=Global System for Mobile communication) . The high range can e.g. consist of 1710-2170 MHz, covering the GSM 1800, GSM 1900 and UMTS (Universal Mobile Telecommunication System) bands . This means that several bands can be covered with a compact, single-fed antenna. GSM 800 and 1900 is primarily used in the USA and GSM 900 and 1800 in Europe. The UMTS frequencies are used in the so-called 3G phones (third generation phones) . One antenna can thus cover the frequency bands for both GSM and UMTS, which is desirable for phones that are required to operate in both systems.

The resonator may consist of a standard ^-wave coaxial- resonator of ceramics having a resonance frequency of approximately 2.1 GHz . The resonance frequency must be well outside of the frequency bands the antenna is intended to cover. This resonator can therefore be used to cover frequency bands up to approximately 2 GHz and can hence be used for a four band antenna covering GSM 800, 900, 1800 and 1900. If also the UMTS band shall be covered, the resonator frequency should be around 2.3 GHz or higher, which is well above the upper frequency limit of 2.17 GHz for UMTS. Resonance frequency is here used as the frequency the resonator obtains when it is mounted in the application at hand.

By using the resonator a broad band transfer of RF energy is obtained with low losses from generator to resonator, from resonator to antenna element and from antenna element to free space. Figure 3 shows the different transfers .

Between a generator 305 and a resonator 307 a galvanic connection is normally used between the RF conductor of the generator and a plated metal surface on the resonator 307. But also a capacitive connection between generator and resonator can be used. Because low losses are important, matching components should be avoided. A resonator 307 with an impedance close to 50 ohm should therefore be chosen. An antenna element 303 and RF conductor 302 are connected to a ground plane 301. From the resonator 307 to the antenna element 303 a non- galvanic, "hard", connection is used. This is controlled by choosing a resonator 307 with suitable size and dielectric constant and by the localization of the resonator 307 in relation to the antenna element 303.

For transfer to the impedance of 377 ohm for free space 309, normal antenna rules apply. A main concern is to have an antenna structure with as large loss-free conductive surface as possible.

Figure 4a shows a preferred embodiment of a DFA-antenna (Dielectric Feed Antenna) 400. The antenna 400 comprises an antenna element 405 with a ground connection 403 to a ground plane 401. The antenna element 405 can be realized by a thin metal sheet, printed circuit board, flex film or other material with good conductive properties in the frequency range in question, e.g. conductive polymer material or meta material applied to a non-conductive carrier. The carrier is not shown in the figure. The RF feed of the DFA-antenna 407 is performed through galvanic connection to a resonator 409 at point 411. The resonator 409 then couples through a non-galvanic connection via slot 417 (see figure 4b) to antenna element 405 consisting of a high frequency arm 413 and a low frequency arm 415. The advantage with this coupling principle is that RF coupling to antenna element 405 is not made by a galvanic point connection as with conventional technology but with a connection made over a surface, indicated at 410, between the two frequency arms 413, 415 on the antenna element 405, corresponding to the resonator's 409 electromagnetic field projection towards antenna element 405. With conventional technology and galvanic connection, the point of connection must be located either in a point which is optimal for the high or the low band. With a connection according to the invention a geographically distributed connection over a surface is accomplished making it possible to achieve an optimal impedance matching for both frequency bands. The impedance matching can then be fine tuned through the orientation of the resonator 409 in relation to antenna element 405 and by choosing a dielectric constant for the resonator 409 of ε~10-100. Normally a value around 20-30 is preferable but also higher or lower values can be feasible. Characterizing for the invention is also that the resonance frequency of the resonator 409 must be chosen such that it well above the highest frequency in the highest frequency band, as discussed further with reference to figure 6. A resonator 409 with high dielectric constant has a very narrow bandwidth around its resonance frequency, normally only one or a few MHz, which means that the frequency band of the resonator can be seen as a "spike" compared to the broad frequency band of 100-500 MHz of the antenna element 405. If the "spike" of the resonator 409 is located within any of the frequency bands of the antenna element 405, the antenna performance will surprisingly be deteriorated at the "spike" frequency due to circulating currents generated in the resonator at this frequency. This means that the resonator 409 does not participate to any appreciable extent in the radiation at the "spike" frequency. By choosing the resonance frequency of the resonator 409 well outside the frequency ranges of the antenna element 405 as described above, this negative effect is avoided while at the same time reaching the effect that an RF transfer is accomplished effectively via resonator 409 to both the low and high frequency arm 413, 415 i.e. within a very broad frequency range. Moreover, an optimal impedance matching is achieved for both the high and low frequency band through the "geographically distributed connection" described above.

Figure 4b shows a side view of the DFA-antenna shown in figure 4a, with the antenna element 405, the ground plane 401, the resonator 409 with longitudinal axis 410 indicated, RF feed 407 and the galvanic connection to the resonator via point 411. The ground connection 403 is not shown in this figure. The transfer between the resonator 409 and the antenna element 405 is realized with a "hard" non galvanic coupling, i.e. the gap 417 between resonator 409 and antenna element 405 is narrow, typically 0.2-0.3 mm. This further facilitates obtaining a thin antenna construction where a distance 419 between ground plane 401 and antenna element 405 can be kept short. The gap 417 can normally consist of air but also other non- conductive materials with low loss factor can be used. By varying the size of this gap 417 the degree of coupling between the resonator 409 and the antenna element 405 can be varied and both broader and narrower gaps can exist depending on application. Other ways to vary the degree of coupling between resonator and antenna element is described below in relation to figures 15 and 16.

The DFA-antenna in embodiment according to figures 4a and 4b is an antenna type called ground dependent antenna, i.e. the ground plane 401 must be available below all of antenna element 405 and even somewhat outside. The larger the ground plane 401, the better the antenna function.

The ground plane 401 is, as shown in figure 4b, substantially parallel with the antenna element 405. A mobile phone normally includes a multi layer circuit board where one of the layers consists of a ground plane. A DFA-antenna can in this embodiment advantageously be located above the circuit board and use the ordinary ground plane of the circuit board without modifications. This is advantageous compared to the solutions with older technology where part of the ground plane below the ceramic element needs to be removed in order to achieve optimal function.

The figures 5a and 5b show two examples of two embodiments of typical standard resonators 500, 500' of coaxial type that advantageously can be used in an antenna according to the invention. The material used in the resonators 500, 500' can preferably be an insulating ceramic material with high dielectric constant but also other material with high dielectric constant can be used. All sides except the bottom side 501, 501' of resonators 500, 500' are metallized. The RF signal is connected to a centre conductor 503, 503'. The resonators 500, 500'also have a channel 505, 505' through the resonators that are metallized on the inside to obtain what is known as a coaxial resonator. By choosing an appropriate diameter of the channel 505, 505', the impedance of the resonator 500, 500' can be tuned as is known in the art. Figure 5a shows a parallelepipedic quarter wave resonator 500. Typical dimensions for this resonator at a resonance frequency of 2.5 GHz and ε«20-30 is roughly 7x3x3 mm. Also lower ε-values down to approximately 10 and significantly higher values can be used. Figure 5b shows a corresponding resonator 500' in cylindrical design.

Also so-called half wave resonators can be used. These resonators are twice as long for the same e-value and have preferably non-metallized short sides. A coaxial resonator can certainly also be designed so as not to have any metallized side but only a metallized channel surrounded by a dielectric, i.e. a channel defined as a cylinder of metallized surfaces.

Also other designs than that of the coaxial resonator are possible. As an example dielectric units realized as blocks or pucks, at least partly provided with metallized sides, can be used. The RF feed to such a dielectrical unit can be provided through a galvanic connection to one of the metallized side-surfaces. Examples of such embodiments of resonators are illustrated in figures 5c and 5d. Figure 5c shows a dielectric resonator 510 designed as a block with metallized side surfaces 511 and 512. RF feed is arranged through a connection 513 to side surface 511. Figure 5d shows an alternative embodiment of a dielectric resonator 520 which, in similarity to the block embodiment of figure 5c, has metallized side surfaces 514, 515 and 516. RF feed is arranged through a feed path 517 in galvanic contact to side surface 516. The shape of the block can of course be varied in other ways than shown in figures 5c and 5d.

Figure 6 shows schematically a frequency diagram for a penta-band antenna thus covering five different frequency bands. The horizontal axis shows frequency (f) and the vertical axis reflected energy (RL=Return Loss) . When the antenna function is good, supplied energy is transferred to free space and only a small fraction of the supplied energy is reflected back to the transmitter. (The antenna function is reciprocal which means that the same applies for received energy.) Between frequencies fl-f2 and f3-f4 the reflected energy is low and here energy is hence transferred to free space. By designing the antenna element according to figure 4 with a low frequency arm 415 and a high 413, fl-f2 can be located to 824-960 MHz and thus cover the low GSM bands 800 and 900 and f3-f4 to 1710-2170 MHz for covering the high GSM bands 1800 and 1900 as well as the UMTS band. The resonance between fl and f2 is a k-wave resonance from the low frequency arm 415. To achieve the broad resonance band between f3 and f4, 460 MHz, a double resonance is used by the first part between f3 and f5 consisting of a H-wave resonance from the high frequency arm 413 and the other part between f5 and f4 consists of a ^-wave resonance from the low frequency arm 415. The resonance frequency of the ceramic resonator 409 is seen as a "spike" at f6.

The invention can also be applied within other frequency ranges than described here.

Within the frame of the principle of the invention, one, two or more frequency bands can be covered. In a preferred embodiment according to figure 4 and 6, five frequency bands can be obtained.

The resonator can also be made of other materials than ceramics . The important thing being that the material has a high dielectric constant (high ε-value) and low loss factor for the frequencies in question.

The design of the antenna element can be made substantially according to what is shown in figure 4. A requirement for the antenna element is that it is an efficient radiator. The antenna element can e.g. be a ground plane dependent ^-wave type or ground plane independent ^-wave type realized as e.g. monopoles, patches, slot antennas, meanders. The antenna element can also be equipped with one or several frequency arms. Different combinations can also exist as e.g. a non- galvanic or so-called parasitic coupling to a second antenna element, which may be a patch with one or several arms or a slot. Some examples of these alternative embodiments are shown in figures 7-14. RF feed can be realized by a coaxial cable or strip-line feed on a printed circuit board.

Figure 7a shows a top view of an antenna element in the form of a so-called meander 701 that is fed non- galvanically via a resonator 703. RF feed is accomplished through galvanic contact to the RF feed point 705 of the resonator. In this case a ground plane 707 can be in the same plane as the meander or in a plane approximately perpendicular to the meander plane. In the case where the meander 701 is in the same plane as the ground plane 707, the antenna element can be easily integrated in the PCB of a mobile phone. The meander 701 can be designed according to, for the skilled person, well known principles for resonance in one or several frequency bands thus accomplishing one or several frequency arms. By adjusting the relative position between resonator 703 and antenna element 701, here exemplified by the angle α, the antenna can be tuned to obtain an optimal combination of degree of coupling and impedance matching. With α=0° the coupling becomes maximal, i.e. a maximum of RF energy is transferred to the antenna element and with α=180° the transfer will have a minimum. By choosing an angle α approximately as shown in the figure, i.e. in this embodiment some tens of degrees, a matching can be made towards an impedance close to 50Ω, while at the same time the coupling becomes close to maximum giving an optimal transfer of RF energy.

Figure 7b is a side view of the antenna element 701 and the resonator 703 shown in figure 7a. The dashed resonator 709 shows an alternative location of the resonator to illustrate that the resonator can be located over or below the antenna element. The resonator can also be located beside the antenna element, discussed further referring to figures 10 and 12 below. The only criterion is that the resonator is located close enough to the antenna element to obtain the optimal combination of degree of coupling and impedance matching as described above. It is also advantageous to locate the resonator close to the ground contact of the antenna element or the first antenna element (in the embodiment with several antenna elements according to figures 12 and 13) .

Figure 8, also a top view, shows an antenna element as a radiating so-called meander slot 801 in a ground plane 803. RF feed is made via a resonator 805 and its RF connection 807. The meander slot 801 is here shown as an antenna type called half-wave slot, which means that the length of the slot 801 shall correspond to half of the wave length of the desired resonance frequency. A half wave slot is also characterised by that both ends of the slot 801 shall be entirely surrounded by the ground plane 803. The slot 801 can also be designed for resonance in one or several frequency bands whereby the slot 801 can be said to consist of one or several frequency arms. In this case the antenna element can thus be integrated in the ground plane of the circuit board of the mobile phone .

Figure 9 shows a combination of a slot 901 and PIFA- structure with two frequency arms 903 and 905 above a ground plane 907 having a contact point 909 with the antenna element. The slot 901 can in this embodiment be said to consist of a third frequency arm. RF feed of both the slot and the PIFA-structure is accomplished through a non-galvanic connection via a resonator 911 and its RF connection 913. Additionally there is a normal mutual coupling between the PIFA-structure and the slot.

Figure 10 shows a perspective view of an antenna element realized as a PILA-structure (Planar Inverted L Antenna) with a frequency arm 1001 above a ground plane 1003. The antenna element can also be made thread- or band-shaped and then becomes a variant of the antenna element 701 in figure 7a (a meander with only one 90° bend) where the ground plane can be located in the plane of the antenna element or in a plane perpendicular to the antenna plane. Here also, an integration of the antenna element in the circuit board of the mobile phone is possible in the case where the plane of the antenna element coincides with the ground plane. RF feed is made through a non-galvanic connection via a resonator 1005 and its RF connection 1007.

Figure 11 shows a top view of a ground plane 1101 in a circuit board to a mobile phone. The ground plane 1101 has a slot 1103, making one frequency arm, open at one end, i.e. not surrounded by the ground plane 1101. The slot 1103 thus becomes a k-wave slot that can be used in an upper frequency band. A frequency arm 1105 can be used as a ^-wave resonance in the lower frequency band. The length of the frequency arm 1105 is the distance 1107 which can be reduced as the material of the circuit board normally has a dielectric constant 8^3-4. Air used in the slot has ε=l . The shortening factor L=l/Vε. With ε=4 the shortening factor thus becomes 0.5. RF feed is made through a non-galvanic connection via a resonator 1109 and its RF connection 1111. In this case the antenna element can thus be integrated in the ground plane 1101 of the circuit board of the mobile phone.

Figure 12 shows a side view of an antenna being a variant of the antenna in figure 10, but with an antenna element with two frequency arms 1201 and 1203, both with ^-wave resonances and galvanic connection to a ground plane

1207. The arms 1201, 1203 of the antenna element feed a second antenna element 1205 through non- galvanic connection. An antenna element fed this way is usually called a parasitic antenna element. The length of the parasitic antenna element can in a preferred embodiment be configured for half-wave resonance suitable for e. g. the GPS-frequency (Global Positioning System) . RF feed is made through non-galvanic connection via a resonator 1209 and its RF connection 1211.

Figure 13 shows a similar solution as the one in figure 12 but with galvanic connection between a first 1301 and a second antenna element 1302.

The realisations according to figures 12 and 13 can also be accomplished in two- dimensional embodiment analogous to what is described for the embodiment according to figure 10. In these embodiments an integration in the printed circuit board of the mobile phone will be possible according to what is described above.

Figure 14 shows an example of an embodiment with an antenna element 1401 manufactured of, for the skilled person well-known, electrically conductive flexible so- called flex-film, applied to a non conductive carrier 1403 made of e.g. plastic with a curved surface 1404. The flex-film has a galvanic connection 1405 to a ground plane 1407. A resonator 1409 is located inside the carrier such that optimal coupling and impedance matching is obtained. RF feed is realized through resonator 1409 and its RF connection 1411. Also the ground plane can be curved. In figure 17 below a further example of an embodiment with flex-film is shown.

The figures 15 and 16 show alternative embodiments of antenna elements and RF feeding resonators. Figure 15a is a schematic top-view (xy-plane) of an antenna element 1501 in which an opening 1502, or "window" has been designed. A resonator 1503, being any of the resonators previously described, is located in the opening 1502. As seen in the cross-section view AA in figure 15b (xz- plane) , a surface 1504 of the resonator is located in the same xy-plane, i. e. with the same z-coordinate, as the antenna element 1501. Figure 15c shows the resonator 1503 in an other relative position to the antenna element 1501 where the surface 1504 is located above the plane of the antenna element 1501. i. e. the surface 1504 is located in a xy-plane having a higher value for the z-coordinate than the xy-plane in which the antenna element 1501 is located. Even if not shown in figure 15, the surface 1504 can also be positioned below the plane of the antenna element 1501. Figure 16 shows a further example of an antenna element

1601 in which an opening 1602 has been cut out. Figure 16 is a top view, similar to e.g. figure 15a, and shows a resonator 1603 located in the opening 1602.

The examples in figures 15 and 16 illustrate how the degree of coupling for a resonator 1503 and 1603 can be varied. By designing a window or opening 1502, 1602 in an antenna element a decrease of the degree of coupling can be achieved compared to the situation where the antenna element does not have an opening. The size of the opening and the positioning of the resonator in relation to the opening, i.e. the relative location in the xy-plane as well as in the xz-plane (see figures 15 and 16), can be varied such that a desired degree of coupling is achieved. A configuration as indicated in figure 15c of course gives a thin structure, advantageous in applications such as mobile phones.

It is of course also possible that the embodiments according to figure 4 and figures 7-11 and 13-16 can excite a parasitic element in a similar way as shown in figure 12.

The figures 17a-17e illustrate an embodiment of an antenna comprising an antenna element 1701, with a first frequency arm 1702, a second frequency arm 1704 and a ground connection 1708, arranged on the upper side of a substrate of flex-film 1706. In figure 17a the antenna is shown from the top and in figure 17b a cross-section A-A is shown. In figure 17b is shown that on the lower side of the flex-film substrate 1706 a layer of flexible, compressed foam plastic or other insulating material 1710 is arranged with an opening 1712 in which a RF feeding resonator is intended to be arranged. In figures 17c and

17d such a resonator 1714 is shown. The resonator 1714 is preferably a block, disc or film of dielectric material. Figure 17c shows the resonator 1714 in a top view and figure 17d show the resonator in a side view. The resonator 1714 is arranged on a metal foil 1715 being in turn arranged on a flex-film substrate 1718. The resonator 1714 can have a metallized surface facing the metal foil 1715. The metal foil 1715 has an elongated part 1716 intended for feeding of RF energy to the resonator 1714. The shape of the resonator 1714 and the design of the elongated part 1716 is such that, as shown in figure 17e, when the resonator 1714 is arranged in the opening 1712, the RF feeding elongated part 1716 is running below the ground connection 1708 of the antenna element. With this configuration a thin antenna device is obtained where RF feed and ground connection are close together giving a continuous feeding impedance and through its coaxial structure facilitating assembly in different terminal devices.

The invention is also well suited for use of what is called Meta material as antenna element as the transformation of energy to the antenna element is accomplished through a resonator the frequency of which is outside the frequency ranges for which the antenna is intended for use.

The reaction of a material when exposed to an electromagnetic field is decided by two parameters: the dielectric constant ε deciding how the material reacts to an electrical field and the magnetic permeability μ deciding how the material reacts to a magnetic field. These two parameters can be fine-tuned in meta material and in certain cases also assume negative values. Thus the material can obtain new properties enabling a minimizing of size and weight of the antenna element and at the same time providing a further increased bandwidth.

Claims

1. Antenna for mobile terminal unit comprising at least a first antenna element (405) comprising at least one frequency arm (413,415) and comprising a resonator (409) for feeding of the at least first antenna element (405), characterized in that the antenna element (405) is arranged to be fed non galvanic via the resonator (409) the resonance frequency of which is above the highest frequency in the highest frequency band for which the antenna is intended.

2. Antenna according to claim 1, where the resonator has at least one metallized surface.

3. Antenna according to claim 2, where the at least one metallized surface of the resonator is facing the antenna element.

4. Antenna according to any of claims 1-3, where the antenna element (405) is in galvanic contact with the ground plane (403).

5. Antenna according to any of claims 1-4, where the antenna element (405) is extended in a two-dimensional plane and that one axis (410) of the resonator (409) is substantially parallel with the antenna element (405) .

6. Antenna according to any of claims 1-4, where the antenna element (405, 1401) is curved in a third dimension.

7. Antenna according to any of claims 1-6, where the antenna element is provided with at least one opening (1502, 1602) and where the resonator is arranged in relation to the antenna element such that at least a part of the resonator is located within the opening from a direction of view being perpendicular to the plane of the antenna element.

8. Antenna according to any of claims 1-7, where the resonator is a coaxial resonator comprising an at least partly through-going metallized channel.

9. Antenna according to any of claims 1-7, where the resonator (510, 520) is block shaped.

10. Antenna according to claim 9, where at least one surface of the resonator is metallized.

11. Antenna according to any of claims 1-10, where the resonator is a k-wave resonator.

12. Antenna according to any of claims 1-10, where the resonator is a ^-wave resonator.

13. Antenna according to any of claims 1-12, where the resonator is of ceramic material.

14. Antenna according to any of claims 1-13, where the antenna element (405) has at least one frequency arm for high frequencies and at least one frequency arm for low frequencies.

15. Antenna according to any of claims 1-14, further comprising a parasitic antenna element (1205) and where the antenna element (1203) is arranged to excite the parasitic antenna element (1205) .

16. Antenna according to any of claims 1-14, further comprising a second antenna element (1302) and that the antenna element (1301) is in galvanic contact with the other antenna element (1302) .

17. Antenna according to any of claims 1-16, where at least one antenna element and one ground plane are extended in a two-dimensional plane.

18. Antenna according to any of claims 1-16, where at least one antenna element is extended in a two- dimensional plane being curved in a third dimension.

19. Antenna according to any of claims 1-18, where the antenna element is made of meta-material .

20. Mobile terminal unit comprising an antenna according to any of claims 1-19.

21. Mobile terminal unit according to claim 20, where at least one antenna element is integrated into a printed circuit board located in the terminal unit.