EP2256859A1

EP2256859A1 - Antenna arrangement, method for tuning an antenna arrangement and apparatus with antenna arrangement

Info

Publication number: EP2256859A1
Application number: EP09160029A
Authority: EP
Inventors: Anthony Kerselaers
Original assignee: ST Ericsson SA
Current assignee: ST Ericsson SA
Priority date: 2009-05-12
Filing date: 2009-05-12
Publication date: 2010-12-01

Abstract

Two antennas are described operating in different frequencies, e.g. GPS and Bluetooth frequency, form a combo antenna consisting of two antenna elements that are capacitive coupled. Each of the antenna elements has two connecting ports, one ground element and one feeding element. Both ground elements are closer to each other than the distance between the feeding elements, while the ground elements are close to the capacitive coupling position. Any suitable antenna may be used in the arrangement like a PIFA-type, a F-type or a loop-type. The antennas are located in a separate plane, which can be overlapping with the ground plane, or can be located aside of the ground plane forming an angle with it.

According to an embodiment of the invention, a feeding structure is provided that has tuning elements suitable for tuning an impedance load as well as an inductive load on the respective antenna elements, and thereby allowing it to adapt the antenna arrangement to various mobile devices. Furthermore a method is provided that allows to adjust the input impedance and the resonating frequency of a respective antenna.

Description

The present invention relates to an antenna arrangement which builds very small and consists of two antennas that operate at different frequencies and an associated apparatus including the same. The present invention further relates to a method for tuning an antenna arrangement.

Technical Background

In recent years wireless access and wireless communication is becoming increasingly important. Even in business and office environments the use of wireless communication is widespread. For example, to perform money transactions often RFID chips are used that communicate identification data or respectively pricing information that is attached and associated to goods to be purchased.
In the area of mobile devices it is increasingly common to equip them with Bluetooth for short range communication as well as a receiver to access a satellite navigation system e.g. the global positioning system in order to be able to execute location dependent applications such as traffic routing and traffic guidance as well e.g. as providing up-to-date map information for hikers or mountain bikers.
In order to be able to perform wireless communication efficient antennas are needed that are cheap to manufacture and reliable in their operation. With the necessity of increased integration, it is also attractive for manufacturers to integrate two functions such as Bluetooth communication and access to the global positioning system in one integrated component in order to be able to meet the demand for combined applications with a competitive product.
In the European patent application EP 180732 A1 an antenna assembly and radio communication apparatus employing the same is disclosed. In particular there an antenna device is discussed including a first planar inverted F antenna (PIFA) operating at a first frequency and a second PIFA operating at a second frequency that is higher than the first frequency and disposed in a state in which it is insulated from the first PIFA. The antenna device has an antenna element in which a first short circuit lead wire and a second short circuit lead wire are coupled to a ground terminal provided on a substrate, a first feeding lead wire is coupled to a first feeding terminal provided on a substrate via a first matching circuit, and a second lead wire is coupled to a feeding terminal provided on the substrate via a second matching circuit. The radiator elements of both antennas are disposed on one spacer surface and the respective supply leads are disposed in close proximity to each other on one lateral side of a spacer spacing the radiating elements parallel to the associated ground plane.
The purpose of this antenna device is to be able to match each radiating element independently from each other with a separate matching circuit in order to avoid unwanted side effects that appear, once one matching circuit is used to tune a combined antenna element.

Summary of the invention

It is an object of the present invention to provide an antenna arrangement and an apparatus employing the same that is easy to manufacture, uses as few resources as possible, and is as simple as possible in its technical configuration while minimizing the return losses of both antennas. Furthermore a method for tuning an antenna arrangement is provided.
This object is achieved by an antenna arrangement according to claim 1, a method for tuning an antenna arrangement according to claim 13 and an apparatus including an antenna arrangement according to claim 15.
Advantageous further developments of the invention are demonstrated at the dependent claims.
Of particular advantage is an antenna arrangement according to the present invention having two antennas arranged with respect to a ground plane in a radiator plane, whereby each antenna is located in a first and a second antenna area on the radiator plane separated by a longitudinal gap and having a particular configuration of the first and second ground element with respect to the first and second feeding elements of the respective antennas. In this manner a double antenna, respectively a dual feed antenna is provided, which allows for capacitive coupling and at the same time for the construction of a configuration, where at one side of the two antennas close to the supply elements a low emission level zone is created and on the distant side thereof a high emission area is created. The particular configuration of the ground elements with respect to the feeding elements provides for a good shielding of the respective feeding element against the respective other antenna without extra measures.
Advantageously according to one further development of the antenna arrangement according to the present invention the radiator plane is arranged in parallel overlapping the ground plane, whereby a compact antenna structure can be built that allows for small devices incorporating the antenna arrangement.
Expediently a further development of the arrangement according to the present invention allows to use the total area of the ground plane as printed circuit board, because the radiator plane is located aside of the ground plane forming an angle with it and thus complex devices can be built using up a minimum amount of printed circuit board material.
Beneficially according to a further development of the arrangement according to the present invention the ground elements and the feeding elements are arranged in close proximity to each other and to the longitudinal gap and thus an optimum shielding of the respective feeding elements against respectively the other antenna will be achieved, whereas at the same time all of the connectors can be located closed to each other and thus be connected easily to a small integrated device incorporating for instance a Bluetooth and a GPS transmit /receive section.
Beneficially, according to a further development, a mounting position of feeding elements and ground elements is located at the border of the respective antenna area which allows for antennas having an area of low emission level close to the ground elements and at the same time having an area of high emission level far away from the ground elements.
Advantageously according to a further development of the arrangement according to the present invention a distance between a feeding port and a respective ground port can be dimensioned in such a manner, that it produces a certain input impedance which leads to minimum acceptable return losses for both antennas. Favourably this dimensioning functionality is available for both antennas independent of each other.
In a particular advantageous manner the radiator plane may be arranged at the small side of a rectangular shaped ground plane. This allows for instance to build mobile devices where the radiator plane is located next to the ear of a user and is not covered by the fingers, whereas at the same time the antenna does not interfere with the electronic circuitry that may be arranged on the ground plane.
Beneficially according to a further development of an embodiment according to the present invention a feeding structure is provided in the antenna arrangement, that includes at least two tuning elements between a feeding element and a respective ground element connecting them while they are arranged in running in a parallel manner. Preferably more such tuning elements can be provided depending on the needs and the required tuning range, as well as the available space. In this manner by such an arrangement a standardized component can be provided that may be used in a plurality of mobile devices. This standardized structure can then be easily adapted to the current environment by adjusting the required impedance load successively in removing the tuning elements one by one by scratching them or using any other suitable e.g. mechanical or chemical means to remove them, for instance drilling in order to adapt the circuitry of the antenna to the current housing and printed circuit board.
Advantageously according to a further development of an embodiment of the present invention the antenna arrangement comprises second tuning elements built in the area of a transmission line that effects the inductive loading of the respective antenna element, where at least two of those second tuning elements are provided and accordingly as required by the actual design and the housing more of those tuning elements may be provided depending on the available respectively required frequency range and space. In this manner a flexible tuning structure is provided that allows adapting the frequency range of a standard antenna element to a current housing and circuitry of the mobile device it is built in. An adaptation can be easily performed by adjusting the antenna in removing in a mechanical or chemical manner the respective tuning elements one by one until a desired predefined resonating frequency of the respective antenna element is achieved, in adjusting the inductive load affecting the antenna element.
Expediently according to a further development of an embodiment of the present invention the transmission line and the respective feeding and ground elements are arranged orthogonal to each other on a printed circuit board, because in this manner a design is provided that can be easily manufactured in a standard environment and is simple and cost-effective, while providing enough space to provide for a location of first and second tuning elements for two antennas at the same time.
In a particular advantageous manner according to a further development of an embodiment of the present invention the antenna arrangement provides the radiator plane and the feeding structure with a rectangular angle. In this manner advantageously the frequency depending structure which is highly influencing the tuning of the antenna is provided orthogonal to the printed circuit board and orthogonal to the antenna element, and under the prerequisite that the antenna is placed during manufacturing and design in the area of an earpiece of a mobile phone for instance behind a display, the feeding structure by such an arrangement is placed near the upper edge of the mobile phone and thus will almost never be covered by the hand of a user, which ensures that during operation of the mobile phone for instance GPS and Bluetooth are always available because no detuning of the antenna can happen favoured by the special arrangement.
Of particular advantage is a method according to the present invention according to which a tuning of an antenna arrangement can take place by first adjusting an impedance load of the antenna, in measuring the respective impedance load on an antenna element and subsequently removing a corresponding tuning element until a predefined impedance load is achieved and adjusted, and then in a second step adjusting the resonating frequency of the antenna in measuring the resonating frequency and removing associated second tuning elements to adjust a desired resonating frequency. The method is preferably performed in this sequence, because the adjustment of the impedance load again shifts the resonating frequency by about 20 to 40 MHz. Such a method provides for an easy adaptation of a standard antenna element that can be manufactured for a plurality of mobile devices such as organizers, personal digital assistants and mobile phones, and then after having being built into the device can be adjusted by removing the respective tuning elements to optimize the actual design solution.
In a particular advantageous manner according to a further development of the method according to the present invention the resonating frequency can be tuned respectively to a Bluetooth frequency and respectively to a GPS frequency for two antennas in this manner, which are applications that are widespread and used in many mobile devices with increasing demand for cheap and reliable solutions.
Favourably the antenna arrangement according to the present invention allows for very small building antennas respectively only occupying a volume of 10 x 32 x 6 mm. Such very small antennas contrary to the expectations in present antenna physics surprisingly work fine.
In a particular advantageous fashion according to a further development of the antenna arrangement of the present invention planar inverted F antennas (PIFA) can be used which are known to be small building taking their respective operating frequency into account and are easy to manufacture with little material.
In a particular advantageous manner according to a further development of a planar inverted F antenna arrangement according to the present invention one such antenna at least is equipped with a notch element, which allows to further lower the resonance frequency of the respective antenna element.
In a particular advantageous manner according an arrangement making use of a PIFA type antenna incorporates a radiating element that is folded back to form an open loop in order to allow an adaptation of the antenna to a lower resonance frequency.
Advantageously other antenna elements such as F antennas or loop antennas may be used, and thus the arrangement is very flexible in terms of adapting it to technologies in use.
Advantageously an apparatus including the antenna arrangement of the present invention allows for versatile and small building devices, having for instance a combined functionality of Bluetooth communication and access to the global positioning system.
Further below examples of the present invention are further discussed by way of examples and embodiments.

Brief Description of the figures

Fig. 1 shows a basic schematic of an arrangement according to an embodiment of the present invention;
Fig. 2 shows an example of an antenna arrangement having two PIFA elements;
Fig. 3 shows a simulated return loss and isolation of the example of Fig. 2;
Fig. 4 shows another example of an antenna arrangement having two F elements;
Fig. 5 shows a measured return loss and isolation of an antenna arrangement with PIFA elements;
Fig. 6 shows the insulation in a practical case where a Bluetooth antenna is driven by a Bluetooth transmitter where at the same time a GPS receiver is connected to a second antenna;
Fig. 7 shows an example of an antenna board according to an embodiment of the present invention;
Fig. 8 shows an example of an embodiment of a feeding structure according to an embodiment of the present invention;
Fig. 9 shows an assembly of an antenna board and a feeding structure according to a further development of the present invention;
Fig. 10 depicts the dependency of an input impedance and tuning element of a Bluetooth antenna;
Fig. 11 depicts the dependency of a resonance frequency of a Bluetooth antenna and tuning elements;
Fig. 12 depicts the dependency of an input impedance on tuning elements of a GPS antenna;
Fig. 13 shows the dependency of a resonating frequency of a GPS antenna and tuning elements;
Fig. 14 shows details of an antenna board according to an embodiment of the present invention; and
Fig. 15 gives an example of details of a feeding structure of an embodiment of the present invention.

Detailed description of the illustrative embodiments

Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness.
Although, the present invention will be described with respect to particular embodiments and with reference to certain drawings, the invention is not limited thereto but only by the claims. The drawings described are only schematic and are nonlimiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.
Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. Similarly, it is to be noticed that the term "connected", also used in the claims, should not be interpreted as being restricted to direct connections only, although "connected" includes a direct connection which may be advantageous. The term "coupling" should also be interpreted as not being limited to direct connections. Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
Fig. 1 shows a basic configuration of an embodiment of an antenna arrangement according to the present invention. Here two antenna elements 201 and 202 can be identified in an arrangement 100. Also identified at the drawing can be a first and a second feeding element 203 and 206 as well as a first and second ground element 204 and 205 associated respectively to the first and second antenna. The two antennas 201 and 202 can also be described as a dual feed antenna. The two antennas 201 and 202 are separated by a longitudinal gap or spacing G1. The gap may be considered to be linear in a generally straight direction when considering the fact that it separates two more or less rectangular antenna areas that are occupied by the resonating elements of a respective antenna. It is important to understand here that the gap serves the purpose to provide suitable galvanic insulation of the antenna elements against each other in a region where they are particularly close, while at the same time it allows for capacitive coupling of the two different antenna elements. A linear gap is not necessarily to be understood as being symmetrical nor is it required to have constant width. Linear in this context only means a generally straight direction of extension of the gap in a very wide sense of interpretation. A suitable configuration allows the two antennas to be capacitive coupled although they have no direct galvanic connection to each other.
In arranging the ground elements 204 and 205 in proximity to each other and in proximity to a position of a capacitive coupling, the electrical field at the antenna is strongly attenuated at the edge of the respective opposite antenna element. This effect is achieved due to the presence of the grounding element of the opposite antenna element. Thereby the field strength is strongly attenuated at the respective feeding element, whereby a sufficient insulation between the two feeding elements 203 and 206 is achieved. In practice it is easy to achieve at least an insulation of 20 dB between the two feeding elements. This will be further demonstrated at the representation shown in Fig. 6. The particular arrangement of the feeding elements and the ground elements near the linear gap G1 leads to a low emission area CLA in the area of capacitive coupling of the combined antenna in proximity of the feeding and the ground elements, and contrary to that to a respective high emission area HEA of the respective antennas located at the antenna opposite to the feeding and the ground elements.
In case such an arrangement is mounted in a mobile phone next to the earpiece of the mobile device such a configuration helps avoiding that the user covers the high emission area of the antenna with his hands. Such an antenna arrangement may for instance be used in combination with a combined IC which has the functionality of GPS and Bluetooth, and due to its property featuring the close proximity of the feeding and ground elements allows to be connected to a small integrated device having the combined functionality. In addition as this basic configuration shows, any type of suitable antenna may be used with the arrangement according to the present invention be it a planar inverted F antenna an F antenna or a loop antenna or any other suitable antenna.
Fig. 2 shows an example of an embodiment of an arrangement according to the present invention having a ground plane EP. In this case it may be particularly important to have a full conducting ground plane without any cut-ins in order to be able to equip it with as many components as possible in case this ground plane is used as a printed circuit board. Two antennas can be easily identified in the drawing. A first antenna PIFA1 and a second antenna PIFA2 embodied as planar inverted F antennas are located on a radiator plane AB. Both antennas are characterized by radiating elements that are located respectively in antenna area AR1 and antenna area AR2 which are separated by a longitudinal respectively linear gap G2. The respective ground elements E1 and E2 of antenna 1 and antenna 2 as well as the respective feeding elements F1 and F2 to feed the respective antenna with electric energy may also easily be recognized in the representation.
In this case the radiator plane AB is shown to be overlapping the ground plane EP separated from it by a certain gap in a parallel configuration. A respective antenna area AR1, here for instance preferably forms a volume of 10 x 32 x 6 mm together with the distance to the ground plane. Also easily identified may be the notches N1 and N2 of respective radiator elements R1 and R2 of antenna 1 and antenna 2. Although the radiating elements look similar in their design there is no restriction regarding the shape of each one and thus they can be totally different. These notches for instance help to lower the resonating frequency of the respective antennas, to adapt it to a longer transmit and receiving wavelength as required. In a particular advantageous manner the distance between the first ground element E1 and the first feeding element F1 respectively the second ground element E2 and the second feeding element F2 can be used to fine-tune the antenna, in that the distance serves the dimensioning of the input impedance which can be dimensioned in such a manner, that return losses with regard to both antennas PIFA1 and PIFA2 are minimized. The antenna arrangement according to the present invention is also suitable to form the basis for a plug in antenna to additionally connect en external antenna to it. For that purpose it would then only require an additional plug in socket.
Furthermore the tuning of an inductive loading of a respective ground element E1, E2 is individually possible by removing conductive lines subsequently, which for that purpose are provided placed running in parallel in connection with a respective element until a desired load is reached. Of course by such means also the coupling between a ground pin and a signal pin may be changed. It is self explanatory that such measures are also usable with a single antenna.
Fig. 3 shows a simulated return loss and isolation of the antenna arrangement of Fig. 2. The simulated return loss and isolation are shown in [dB]. Usual frequencies for the operation of global positioning systems are in the range of 1.575,42 MHz which corresponds to a wavelength of 19,05 cm and in the range of 1.227,6 MHz which corresponds to a wavelength of 24,45 cm. Contrary to that common Bluetooth operating frequencies are between 2.400 and 2.483,5 MHz in Europe which corresponds to a wavelength of 12,5 cm.
This, when taking the dimensions of the two antennas into account indicates, that the antenna PIFA1 with the shorter radiator element R1 is suitable for Bluetooth transmission and reception whereas the antenna PIFA2 of Fig. 2 with its radiating element R2 being longer than R1 is capable of receiving global positioning signals.
It can also be seen from Fig. 3, that around 1.5 GHz there is a minimum in the return losses in the GPS feed RLGPS, whereas around 2.4 GHz there is a minimum in the return losses of the Bluetooth feed RLBT. Also shown in the drawing of Fig. 3 is the insulation between the Bluetooth feed and the GPS feed which is indicated by ISBFD.
Of course Bluetooth and GPS only serve as examples here and any other frequency combination apart from the ones suitable for reception and transmission of Bluetooth respectively reception of GPS signals are conceivable and feasible. From the diagram in Fig. 3 one can also easily deduce, that the insulation between Bluetooth and GPS antennas amounts to more than 30 dB at Bluetooth frequencies, contrary to 10 dB in most existing solutions. Consequently the arrangement according to the present embodiment of the present invention provides a solution where less or even no extra filtering is required in order to meet co-existence requirements between an Bluetooth transmitter and a GPS receiver, which leads to cheaper devices and to reduced manufacturing costs and placement efforts in the manufacturing of associated devices using the antenna arrangement. It can also be seen from Fig. 3, that by selecting the appropriate distance between the feeding elements and the ground elements a good return loss behaviour can be achieved for the frequency bands of interest.
Fig. 4 shows another example of an antenna arrangement according to the present invention. Here a ground plane BD4 is shown and a radiator plane AB4 which is located next to the ground plane BD4. Associated to a second antenna are a feeding element F42 and a ground element E42 as well as a radiator element R42, whereas associated to a first antenna are a feeding element F41 and a ground element E41 as well as a radiator element R41. Also shown in the drawing is the linear gap G4 between the areas occupied by the two antennas. Close to the linear gap are close regions of the respective antennas CR1 and CR2 indicating that the respective resonating elements there are close to each other and are subject to capacitive coupling, whereas on the other hand in a far distance from the feeding and the ground elements the emitting outer regions EOR1 and EOR2 of the respective antennas are located. In the area of the close regions CR1 and CR2 a low emission level may be achieved whereas in the area of the emitting outer regions EOR1 and EOR2 high emission levels may be achieved. As the radiator plane AB4 of this embodiment of the antenna arrangement does not cover the ground plane BD4 the ground plane may be used as a total area for placement of components to build up a device using the antenna arrangement.
It is also shown in the drawing that the radiator elements R41 and R42 of the respective first and second antenna are folded back, in order to further lower the resonance frequency of the respective antenna. This allows for instance an antenna to be built within the area of 8 x 32 mm on FR4 material. When a mobile device is designed, for example a mobile phone, it is preferable to place the area of the radiator plane AB4 next to the ear of a user in order to prevent the user from covering the antenna with his fingers, also assuming that an appropriate dimensioning of the ground plane is chosen.
Fig. 5 shows an example of a measured return loss and insulation [dB] on a practical sample of an embodiment of an antenna arrangement for instance in a configuration as shown in Fig. 2 with two PIFA elements whereas the dimensions of the antenna were 10 x 32 mm on FA4 material in a distance of 6 mm above the ground plane.
The return loss of the GPS feed is identified by RLGPS5 whereas the return loss of the Bluetooth feed is identified by RLBT5. The lower curve shows the insulation between the two feeds marked by ISBDF5.
It is evident from the representation in the drawing that the insulation between the Bluetooth and GPS section in this example amounts to more than 22 dB. It can also be seen in the same drawing that a good behaviour of the return loss can be achieved, in a case of an example where a Bluetooth and a GPS antenna are integrated. In comparison to presently available antenna technology the antenna arrangement according to the present invention features a 3 dB better sensitivity.
Fig. 6 shows the insulation capability of the arrangement according to an embodiment of the present invention as shown in Fig. 2. Here for instance a Bluetooth antenna is shown having a feeding element F61 and a ground element E61, whereas a GPS antenna has a feeding element F62 and a ground element E62.
Different shades of grey indicate the field strength respectively being on a similar level per shade at the antennas, having their respective outer emitting regions EOR61 and EOR62 and also on a ground plane BD6. In a qualitative manner one can easily deduce, that the black coloured Bluetooth antenna emits with a high field strength, whereas due to the arrangement of the feeding elements and the ground elements F62, E62 and F61 and E61 in a configuration where the ground elements are inside of the feeding elements, this allows for a very good insulation indicated by almost no field strength that is shown at the GPS antenna. In the example given in the drawing this amounts to a 20 dB insulation between the feeding port, in case where the Bluetooth antenna is driven by a Bluetooth transmitter, where at the same time a GPS receiver is connected to the lower antenna in the drawing, while the Bluetooth power is attenuated with 30 dB at the GPS receiver at F62.
As Fig. 7 shows a radiator plane AB according to an embodiment of the present invention may be implemented as a printed circuit board, which incorporates a first antenna area, which here is presented to be smaller and thus suits due to the higher resonating frequency the space requirements of a Bluetooth antenna in the antenna area AR1 as well as a second antenna area AR2, which is larger than the antenna area AR1 and thus suits the implementation and space requirements of a GPS antenna, which has a lower resonating frequency and thus requires longer resonating structures.
Furthermore an extension of the radiator plane BEXT is demonstrated, which may be introduced in a supporting hole for instance in the feeding structure which will be demonstrated later. The extension of the antenna board or a radiator plane AB shows three soldering contacts SA1, SA3 and SA2 in order to connect the feeding elements and the ground elements of the antenna to the printed circuit board respectively to the feeding structure and to the ground plane optionally containing circuitry of a mobile device.
Fig. 8 gives an example of a feeding structure TB or tuning board according to a further development of an embodiment of the present invention. For instance, two feeding lines F81 and F82 of respectively first and second antenna elements are demonstrated that are associated to two ground elements E81 and E82 respectively. It is fairly easy to recognize that respectively feeding element F81 and F82 as well as ground elements E81 and E82 arranged running parallel to each other.
Furthermore the example given in Fig. 8 depicts first tuning elements ITB11, ITB12 and ITB13 as well as ITB21, ITB22 and ITB23 respectively associated to a feeding structure of the first and second antenna. With these tuning elements a tuning of an impedance load of the respective antenna can be performed. The first tuning elements serve for instance the tuning of a Bluetooth antenna, whereas the second tuning elements serve the tuning of a GPS antenna. Tuning is preferably required, because the resonance frequency of the antenna is decreased by for instance the substrate material of the printed circuit board. FR4 as material for instance in this case, due to the mutual coupling between the antennas influences the resonating frequency. The plastic material of a wireless terminal, in which the antenna may be integrated, introduces a loading effect on the antenna, which has a consequence to further decrease the resonating frequency. An adaptation of the impedance load effected on the respective antennas can be achieved by removing the respective first tuning elements one by one until the prescribed and desired impedance load is adjusted. Furthermore in addition to the first tuning elements between respectively a feeding element and a ground element in addition second tuning elements FTB11, FTB12 and FTB13 for instance for a Bluetooth antenna feeding structure are provided as well as second tuning elements FTB21, FTB22 and FTB23 for GPS antenna feeding structure are provided.
The example of Fig. 8 prominently demonstrates a transmission line having an upper part TRU1 and lower part TRL1 in the area of a feeding structure for a first or Bluetooth antenna and an upper part TRU2 and a lower part TRL2 in the area of a feeding structure of a second antenna respectively a GPS antenna. In between the upper part and the lower part short circuiting second tuning elements are arranged, as mentioned above. By removing the respective second tuning elements one by one starting with FTB11 or respectively FTB21 and moving to higher numbers, the resonating frequency of a connected Bluetooth respectively GPS antenna can be adjusted to a desired value, in adjusting the impedance load of the respective antenna by removing respectively as much as second tuning elements as are required to adjust to the desired resonating frequency of the respective antenna.
Fig. 9 shows an assembly of a resonating plane or antenna board AB, which contains the two antennas and a feeding structure TB that are connected at respective contact areas which are provided on the one hand on the antenna board SA1, SA3 and SA2 and on the feeding structure TB as STB1, STB3 and STB2. Hereby, if an extension BEXT of the antenna board is pushed through a hole in the tuning structure TB, the respective contact areas come into contact and only need to be soldered to provide a permanent connection.
Also Fig. 9 explicitly shows that the antenna board AB and the feeding structure TB form a rectangular angle Ω with each other. This is particular important, in a case, where the antenna arrangement is built into a mobile device and the radiator plane is parallel to the ground plane. In this case, if the antenna board AB is mounted in the area of an earpiece of a mobile device behind the display, the feeding structure TB, which highly influences the tuning of the antenna lies parallel to the upper housing edge of a housing of the mobile device, which is almost never covered by the hand of a user while the antennas need to be operated and thus during operation provide reliable conditions for Bluetooth and GPS reception and respectively transmission. It can also well be recognized in the shown representation, that the transmission line and the ground element respectively feeding element are orthogonal to each other.
Fig. 10 shows an example of a diagram showing the input impedance of for instance a Bluetooth antenna in dependency of tuning elements that are removed. In this case, referring for instance to the first tuning elements as demonstrated in Fig. 8 by reference numerals ITB11 to ITB13. Here the real part of the impedance RPBT and the imaginary part of the impedance ITBT are shown in the drawing. On the lower axis the number of removed tuning elements is listed, and on the rising axis the impedance in Ohm is listed. In this case it is easy to recognize, that the more tuning elements are removed, the higher the impedance RPBT is rising, while the imaginary part ITBT is decreasing. In this manner in small steps, by removing one by one the first tuning elements, the impedance load of the antenna respectively first antenna can be adjusted to a desired level. In case of the present invention this has the advantage that an adaptation can be performed by a trained worker or even an automated machine and does not have to be done by an RF engineer. Furthermore for variations of mobile phones no additional design or redesign effort is required, as the standard design can be used and can be adapted according to the method of the present invention by measuring and removing the tuning elements.
Tuning will preferably always be required, because the placement on the printed circuit board and the housing of the mobile device as well as switches that are placed in various locations, by capacitive coupling reduce the resonating frequency of the antenna.
The example given in Fig. 10 has been measured in an actual phone design. Here it can be seen, that the impedance can be varied in the range of 30 Ohms. As opposed to standard antennas that may be delivered by providers that are active on the mobile market, the present antenna arrangement can also be conforming to other impedances than the standard 50 Ohm, and thus do not always require matching circuitry to adapt them to a given design.
Fig. 11 shows an example of a resonating frequency for a Bluetooth antenna RFBT where on the lower axis removed tuning elements are listed, and on the rising axis the frequency in MHz is listed. As can be seen, by removing up to 15 second tuning elements that are for instance marked by reference numerals FTB11 to FTB13 in Fig. 8 it is possible to vary the resonating frequency of a connected antenna between 2.000 and 2.500 MHz. Thus the feeding structure according to the embodiment of the present invention allows for a wide range of adaptation of the frequency of the respective antenna.
Fig. 12 shows in correspondence to Fig. 10 the input impedance in dependency of removed tuning elements of a second antenna respectively a GPS antenna. The real part of the input impedance is shown as RPGP and the imaginary part as IPGP; both are shown in a curve. As can be seen in the graph, it is possible to increase the input impedance in the range from 25 to over 60 Ohms at RPGP and to reduce the imaginary part IPGP from 20 to almost -30 Ohms. As in Fig. 10 on the horizontal axis the removed tuning elements are listed and on the rising axis the impedance in Ohms is listed.
Corresponding to Fig. 11, Fig. 13 shows the resonance frequency in dependence of removed tuning elements of a GPS antenna respectively second antenna RFGP. These tuning elements are for instance marked by reference numerals FTB21 to FTB23 in Fig. 8. Here it is demonstrated, that the resonating frequency which is listed in MHz on the rising axis can be varied by removing 20 tuning elements which are listed on the horizontal axis in a range from 1650 to almost 1300 MHz. Thus a wide range for adaptation of the antenna resonating frequency to environmental effects is possible which allows a precise tuning of a standard antenna element, respectively an antenna arrangement according to the present invention which contains two antennas resonating at a respective different frequency to desired values.
Fig. 14 shows an example giving detailed dimensions of an antenna board, respectively radiator plane AB according to an embodiment of the present invention which has also been shown in Fig. 7. Here antenna areas AR1 and AR2 are shown allowing respectively space for a Bluetooth antenna for instance and a GPS antenna. Also contact areas suitable for soldering are shown identified by reference signs SA1 to SA3. From the numbers given in Fig. 14 it can be seen, that very small building antenna arrangements can be provided by the present invention and that the adaptation of the impedance and the inductive loading allows it to use smaller resonating elements that would be normally required in order to resonate in the range of the Bluetooth frequency respectively the GPS frequency for the respective antennas.
Fig. 15 gives an example of dimensions for a feeding structure or tuning board TB according to an embodiment of the present invention, which is also shown in Fig. 8. To facilitate the reference an upper part of the transmission line TRU1 opposite TRU2 and a lower part of the transmission line TRL1 opposite TRL2 is shown at the feeding structure TB as well as contact area STB1 to STB3 and feeding elements F81 as well as F82 associated to ground elements E81 and E82 are depicted. The respective antenna board AB or feeding board respectively feeding structure TB can be built by an FR4 4 layer printed circuit board having a thickness of 1 mm and a copper layer in the thickness of 0.018 mm. The associated dielectric constant may be typically 4.4 at 1 GHz.

Claims

Antenna arrangement (100) having
- a ground plane (EP),

- a radiator plane (AB),

- a first and a second antenna (PIFA1), (PIFA2) respectively operating at a first and at a second frequency and associated radiating elements (R1, R2),

- a first and a second antenna area (AR1, AR2) on the radiator plane separated by a linear gap (G1),

- a first and a second feeding element (F1, F2) associated to the respective first and second antenna for supplying electrical power,

- a first and second ground element (E1, E2) respectively associated to the respective first and second antenna for connecting them to the ground plane,
wherein in the first antenna is arranged extending in the first antenna area and the second area is arranged extending in the second antenna area;
wherein in the first and the second radiating elements (R1, R2) in the area of the linear gap (G1) are arranged in such a manner that they allow capacitive coupling between the first and second antenna (PIFA1, PIFA2);
wherein a distance between the first and the second feeding element (F1, F2) is larger than a distance between the first and the second ground element (E1, E2); and
wherein the radiator plane (AB) is located in a fixed geometrical relationship to the ground plane (EP).
Arrangement (100) according to claim 1,
wherein the fixed geometrical relationship is overlapping and substantially parallel.
Arrangement (100) according to claim 1, wherein the fixed geometrical relationship is non-overlapping and angular.
Arrangement (100) according to any of the previous claims, wherein the ground elements (E1, E2) and the feeding elements (F1, F2) are arranged at a mounting position in close proximity to each other and to the longitudinal gap (G2).
Arrangement (100) according to any of the previous claims, wherein the distance between the first ground element (E1) and the first feeding element (F1) and/ or between the second ground element (E2) and the second feeding element (F2) is dimensioned in such a manner that a minimum return loss is achieved for the first and second antenna.
Antenna arrangement (100) according to any of the previous claims, wherein respectively the first feeding element (F81) and the first ground element (E81) and the second feeding element (F82) and the second ground element (E82) form a feeding structure (TB);
wherein respective feeding elements (F81, F82) and ground elements (E81, E82) are arranged as at least partially parallel conductors; and
wherein the feeding structure (TB) comprises at least two first tuning elements (ITB11...ITB13; ITB21,...ITB23) connecting a respective parallel feeding element (F81, F82) to the associated ground element (E81, E82); and
whereby the impedance load of a respective associated antenna (PIFA1, PIFA2) is adjustable by respectively removing at least one of the tuning elements (ITB11...ITB13; ITB21,...ITB23).
Antenna arrangement (100) according to claim 6, wherein the feeding structure (TB) comprises at least a first and a second transmission line comprised of an upper conductor (TRU1, TRU2) and an associated lower conductor (TRL1, TRL2) respectively arranged parallel to each other and connecting respectively the first feeding element (F81) and first ground element (E81) to a first antenna (PIFA1) and the second feeding element (F82) and the second ground element (E82) to the second antenna (PIFA2), wherein the first and the second transmission line respectively comprise at least two second tuning elements (FTB11-FTB13, FTB21-FTB23) connecting respectively an upper conductor (TRU1, TRU2) and a lower conductor (TRL1, TRL2), whereby the resonance frequency of the respective antenna (PIFA1, PIFA2) is adjustable by removing at least one of the second tuning elements (FTB11-FTB13, FTB21-FTB23) and thereby changing an inductive loading.
Antenna arrangement (100) according to claim 7, wherein a respective transmission line (TRU1, TRU2, TRL1, TRL2) and the respective parallel feeding (F81, F82) and ground elements (E81, E82) are arranged orthogonal to each other on a printed circuit board (TB).
Antenna arrangement (100) according to claim 8 in combination with at least claim 2 wherein the radiator plane (AB) and the printed circuit board comprising the feeding structure (TB) form a rectangular angle (Ω).
Arrangement (100) according to any of the previous claims, wherein the ground plane (EB) and the radiator plane (AB) have a rectangular shape; and
wherein the long side of the radiator plane is arranged along the short side of the ground plane.
Arrangement (100) according to any of the previous claims, wherein at least the first or the second antenna (PIFA1, PIFA2) is a planar inverted F antenna.
Arrangement (100) according to claim 11, wherein at least one radiating element (R1, R2) has a notch (N1, N2).
Method for tuning an antenna arrangement according to claim 8 or any claims dependent on claim 8, wherein in a first step an impedance load of a respective antenna (PIFA1, PIFA2) is adapted by measuring the respective impedance load and subsequently removing a first tuning element (ITB11...ITB13; ITB21,...ITB23) until a desired predefined value is adjusted; and
in a second step a resonating frequency of the respective antenna (PIFA1, PIFA2) is adapted by measuring the resonating frequency of the respective antenna and subsequently removing a second tuning element (FTB11-FTB13, FTB21-FTB23) until a predefined resonating frequency is adjusted.
Method according to claim 13, wherein the first antenna (PIFA1) is tuned adjusting it to a GPS resonating frequency and the second antenna (PIFA2) is tuned adjusting it to a Bluetooth frequency.
Apparatus including an antenna arrangement according to any of the claims 1 to 12;
wherein the ground plane (EP) is equipped with at least one component in order to build a circuitry of the apparatus.