The present invention relates to an antenna arrangement and to a method for controlling such an antenna arrangement. Background

Antennas continue to have increasingly strict performance requirements as the communications technology development continues. Especially, the mobile industry continues to develop new techniques to improve the data rate of the mobile devices. This requires the use of new frequencies and wider bandwidths. This means that the antenna must be operated at different frequencies. Obtaining efficient operation over all the required frequencies is challenging, especially with the limited space available for the antennas in the mobile device.

An antenna of a mobile device does not have to function at all operating frequencies simultaneously, making it possible to circumvent the bandwidth requirements via frequency reconfigurability. Instead of covering all the operating frequencies simultaneously, only the required bands are covered at a time.

Existing antenna arrangements which provide frequency reconfigurability include matching networks with tunable capacitors and switchable matching networks. These antenna arrangements have separate matching circuits for the separate frequency bands, and the matching circuit is selected via switching. Multiple matching networks require lots of space on the circuit board. They also introduce power losses to the system. Furthermore, there are no matching networks that tune both low and high frequency bands independently. Independent tuning is needed for realizing intra-band carrier aggregation. Alternatively, the antenna element itself can be made reconfigurable by modifying the antenna geometry. Positive Intrinsic Negative (PIN) diodes are commonly used to redirect the flow of the currents in the antenna, therefore modifying the operation.

It is often necessary to fit several antennas on the same mobile device for Multiple-Input and Multiple-Output (MIMO) operation or for different wireless communication systems. Fitting all these antennas on the small device reduces the volume available for a single antenna, which further reduces their bandwidth. This also results in the additional requirement of adequate isolation between the antenna elements. The isolation is often increased via the use of specific decoupling networks. However, existing decoupling networks do not allow tunability of the isolation. Summary

An objective of the present invention is to provide an antenna arrangement which provides frequency reconfigurability and which diminishes the problems with conventional solutions.

A further objective of the present invention is to provide an antenna arrangement which provides frequency reconfigurability without having separate matching circuits for the separate frequency bands.

The above objectives are fulfilled by the subject matter of the independent claims. Further advantageous implementation forms of the present invention can be found in the dependent claims. According to a first aspect of the present invention an antenna arrangement is provided. The antenna arrangement comprises an antenna array that comprises a first antenna element including a first feed point, and a second antenna element including a second feed point. The first antenna element and the second antenna element have different physical dimensions. The antenna arrangement also comprises a signal processing device configured to receive an input signal, obtain a first complex weight, obtain a second complex weight, generate a first feed signal based on the input signal and the first complex weight, generate a second feed signal based on the input signal and the second complex weight, provide the first feed signal to the first feed point and provide the second feed signal to the second feed point so as to control the frequency characteristic of the antenna array. The frequency characteristics of an antenna arrangement according to the first aspect of the present invention may be controlled without the need for matching networks and decoupling networks.

In a first possible implementation form of an antenna arrangement according to the first aspect, the first feed signal and the second feed signal differ only in phase and amplitude. This means that signals having the same shape are fed to the different antenna elements. This makes the output signal from the antenna array predictable and easy to control.

In a second possible implementation form of an antenna arrangement according to the first possible implementation form or to the first aspect as such, the first feed signal and the second feed signal comprise a common carrier frequency, and the first complex weight and the second complex weight depend on the common carrier frequency. By having the first complex weight and the second complex weight dependent on the common carrier frequency the control of the frequency characteristic of the antenna array may be made more precise. In a third possible implementation form of an antenna arrangement according to the second possible implementation form, a mutual distance between the first antenna element and the second antenna element is smaller than the wavelength of the common carrier frequency. By having such a mutual distance between the first antenna element and the second antenna element an electromagnetic coupling between the first antenna element and the second antenna is ensured.

In a fourth possible implementation form of an antenna arrangement according to any of the possible implementation forms or to the first aspect as such, the first complex weight and the second complex weight are based on an electromagnetic scattering between the first antenna element and the second antenna element. The scattering between the first antenna element and the second antenna element defines the electromagnetic coupling between the first antenna element and the second antenna element. Thus, by basing the first complex weight and the second complex weight on the electromagnetic scattering a good control of the antenna arrangement is possible. In a fifth possible implementation form of an antenna arrangement according to the fourth possible implementation form, the signal processing device is configured to provide a first pilot signal to the first feed point and receive first pilot return signals at the first feed point and the second feed point, provide a second pilot signal to the second feed point and receive second pilot return signals at the first feed point and the second feed point. The signal processing device is also configured to determine the electromagnetic scattering by determining corresponding scattering parameters based on the first pilot signal, the second pilot signal, the first pilot return signals, and the second pilot return signals. By determining the scattering parameters by such a measurement a precise control of the frequency characteristics of the antenna arrangement may be achieved. In a sixth possible implementation form of an antenna arrangement according to the fifth possible implementation form, the provision of the first feed signal to the first feed point and the second feed signal to the second feed point results in a first return signal at the first feed point and a second return signal at the second feed point, wherein the first return signal and the second return signal are determined by the scattering parameters. Furthermore, the signal processing device is configured to choose the first complex weight and second complex weight, and thereby the first feed signal and the second feed signal, so that the sum of the first return signal and the second return signal is below a predetermined threshold value. By configuring the signal processing device in this way the frequency characteristics of the antenna arrangement may easily be optimized. In a seventh possible implementation form of an antenna arrangement according to the fifth or sixth possible implementation form, the signal processing device is configured to provide the first pilot signal and the second pilot signal in different time periods. The measurement of the scattering parameters is more reliable when the first pilot signal and the second pilot signal are provided in different time periods.

Irrespective of whether the signal processing device is configured to measure the scattering parameters or not the complex weights may be stored in a memory. Thus, in an eighth possible implementation form of an antenna arrangement according to any of the possible implementation forms or to the first aspect as such, the signal processing device is configured to retrieve the first complex weight and the second complex weight from a memory. The operation of the signal processing device is fast when the first complex weight and the second complex weight may be retrieved from a memory.

In a ninth possible implementation form of an antenna arrangement according to any of the possible implementation forms or to the first aspect as such, the first antenna element and the second antenna element each has a length in the interval 5 mm to 100 mm, and preferably in the interval 10 mm to 50 mm. The length of the antenna elements may be chosen so that they have a resonance frequency in or close to a frequency band used in mobile communications and/or so that they fit inside a mobile device, such as a cellular phone. The length is a total length of the first antenna element and the second antenna element. Alternatively, the whole mobile device may operate as the antenna. In this case individual antenna elements are not resonant without the device. The first antenna element and the second antenna element do not have to be straight but can have a bent configuration.

In a tenth possible implementation form of an antenna arrangement according to any of the possible implementation forms or to the first aspect as such, the signal processing device may comprise at least a first transceiver associated with the first feed point, and a second transceiver associated with the second feed point. By having a separate transceiver for each feed point the antenna arrangement is more easily controlled compared to when the same transceiver is used for two or more antenna elements.

In an eleventh possible implementation form of an antenna arrangement according to any of the possible implementation forms or to the first aspect as such, the signal processing device comprises a printed circuit board with a top plane and a bottom plane, wherein the first antenna element extends from the top plane and the second antenna element extends from the bottom plane. By having the antenna elements extending from different planes a better separation of the antenna elements is provided.

According to a second aspect of the present invention a (e.g. mobile) communication device is provided, which (mobile) communication device comprises an antenna arrangement according to any of the possible implementation forms.

According to a third aspect a method for an antenna arrangement comprising an antenna array is provided. The antenna array comprises a first antenna element including a first feed point, and a second antenna element including a second feed point. The method comprises receiving an input signal, obtaining a first complex weight, obtaining a second complex weight, generating a first feed signal based on the input signal and the first complex weight, and generating a second feed signal based on the input signal and the second complex weight. The method also comprises providing the first feed signal to the first feed point and providing the second feed signal to the second feed point so as to control the frequency characteristic of the antenna array. With a method according to the third aspect the frequency characteristics of the antenna arrangement may be controlled without the need for matching networks and decoupling networks.

In a first possible implementation form of a method according to the third aspect, the first feed signal and the second feed signal differ only in phase and amplitude. This means that the signals having the same shape is fed to the different antenna elements. This makes the output signal from the antenna array predictable and easy to control.

In a second possible implementation form of the method according to the first possible implementation form or to the third aspect as such, the first feed signal and the second feed signal comprise a common carrier frequency. Furthermore, the first complex weight and the second complex weight depend on the common carrier frequency. By having the first complex weight and the second complex weight dependent on the common carrier frequency the control of the frequency characteristic of the antenna array may be made more precise.

In a third possible implementation form of the method according to any of the first and second possible implementation forms or to the third aspect as such, the first complex weight and the second complex weight are based on an electromagnetic scattering between the first antenna element and the second antenna element. The scattering between the first antenna element and the second antenna element defines the electromagnetic coupling between the first antenna element and the second antenna element. Thus, by basing the first complex weight and the second complex weight are based on the electromagnetic scattering a good control of the antenna arrangement is possible.

In a fourth possible implementation form of the method according to the third possible implementation form, the method comprises providing a first pilot signal to the first feed point and receiving first pilot return signals at the first feed point and the second feed point, providing a second pilot signal to the second feed point and receiving second pilot return signals at the first feed point and the second feed point. The method also comprises determining the electromagnetic scattering by determining corresponding scattering parameters based on the first pilot signal, the second pilot signal, the first pilot return signals, and the second pilot return signals. By determining the scattering parameters by such a measurement a precise control of the frequency characteristics of the antenna arrangement may be achieved.

In a fifth possible implementation form of the method according to the fourth possible implementation form, the method comprises providing the first feed signal to the first feed point and the second feed signal to the second feed point, resulting in a first return signal at the first feed point and a second return signal at the second feed point, wherein the first return signal and the second return signal are determined by the scattering parameters. The method also comprises choosing the first complex weight and the second complex weight, and thereby the first feed signal and the second feed signal, so that the sum of the first return signal and the second return signal is below a predetermined threshold value. This method provides for an easy optimization of the frequency characteristics of the antenna arrangement.

In a sixth possible implementation form of the method according to the fourth or fifth possible implementation forms, the first pilot signal and the second pilot signal are provided in different time periods. The measurement of the scattering parameters is more reliable when the first pilot signal and the second pilot signal are provided in different time periods.

According to a fourth aspect a computer program with a program code is provided for performing a method according to the third aspect as such or to the method according to any of the first to sixth possible implementation forms, when the computer program runs on a computer.

A number of antenna arrangements according to any of the first to the seventh implementation forms of the first aspect or to the first aspect as such may be configured in the same device on the same frequency to realize the a multiple-input multiple-output (MIMO) system. Short description of the drawings

Fig. 1 shows schematically a signal processing arrangement for a transmitter according to an embodiment of the present invention.

Fig. 2 shows schematically an antenna arrangement according to another embodiment. Fig. 3 shows schematically an antenna arrangement according to another embodiment.

Fig. 4 shows schematically an antenna arrangement according to a further embodiment.

Fig. 5a is a perspective view of a part of an antenna arrangement according to a further embodiment.

Fig 5b is a plan view of the antenna arrangement in Fig. 5a. Fig. 6 shows schematically the efficiency as a function of the frequency for an antenna arrangement according to Fig 3.

Fig. 7 shows schematically the efficiency as a function of the frequency for an antenna arrangement according to Fig 3.

Fig. 8 is a flow diagram illustrating a method according to an embodiment. Fig. 9 shows schematically a communication device in a wireless communication system. Detailed description

In the following description embodiments of the invention the same reference numerals will be used for the same features in the different drawings.

Fig 1 shows schematically an antenna arrangement 100 according to an embodiment of the present invention. The antenna arrangement 100 comprises an antenna array 102 comprising a first antenna element 104a including a first feed point 106a, and a second antenna element 104b including a second feed point 106b. The first antenna element 104a and the second antenna element 104b have different physical dimensions as is shown by their different lengths in Fig. 1 . The first antenna element 104a and the second antenna element 104b each has a length L _a , U in the interval 5 mm to 100 mm, and preferably in the interval 10 mm to 50 mm. The different physical dimensions of the first antenna element 104a and the second antenna element 104b mean that they have different electromagnetic resonance frequencies. The antenna arrangement 100 comprises a signal processing device 108 having an input 1 14. The signal processing device 108 is configured to receive an input signal Sin on the input 1 14. The signal processing device 108 is configured to obtain a first complex weight wi, and to obtain a second complex weight w ₂ . The first complex weight wi and the second complex weight w ₂ may be obtained in one of many different ways as will be described in more detail below. The signal processing device 1 08 is further configured to generate a first feed signal a^ based on the input signal Sin and the first complex weight wi, to generate a second feed signal a ₂ based on the input signal Sin and the second complex weight w ₂ , to provide the first feed signal a^ to the first feed point 1 06a and provide the second feed signal a ₂ to the second feed point 1 06b so as to control the frequency characteristic of the antenna array 102.

Thus, the first complex weight wi and the second complex weight w ₂ are chosen to achieve the desired frequency characteristics of the antenna array. A portion of the signal from the first antenna element 1 04a will reflect back and another portion of the signal from the first antenna element 104a couples to the second antenna element 1 04b. The signal from the first antenna element 104a also interfere with the signal from the second antenna element 104b. Also, a portion of the signal from the second antenna element 104b will reflect back and another portion of the signal from the second antenna element 104b couples to the first antenna element 1 04a. Thus, by controlling the first complex weight wi and the second complex weight w ₂ the signal from the antenna array 102 may be controlled. According to the described embodiment the first feed signal a^ and the second feed signal a ₂ differ only in phase and amplitude. This is advantageous for control of the total signal from the antenna array 102.

According to the described embodiment the first feed signal a^ and the second feed signal a ₂ comprise a common carrier frequency fc. As the antenna elements each have a specific resonance frequency the first complex weight wi and the second complex weight w ₂ depend on the common carrier frequency fc. In other words, to achieve the desired frequency characteristic the choice of the first complex weight wi and the second complex weight w ₂ are made in dependence of the common carrier frequency.

As the antenna arrangement according to the described embodiment relies on the electromagnetic coupling between the antenna elements the mutual distance should not be too large. According to the described embodiment the mutual distance d between the first antenna element 1 04a and the second antenna element 1 04b is typically smaller than the wavelength of the common carrier frequency fc. The coupling between the antenna elements depend on the mutual distance between the first antenna element 1 04a and the second antenna element 1 04b. Depending on the configuration the mutual distance between the antenna elements may vary along the length of the antenna elements. The distance referred to may be a minimum distance between the first antenna element 104a and the second antenna element 104b.

The electromagnetic reflections and coupling between the first antenna element 104a and the second antenna element 104b may be expressed as the scattering between the first antenna element 104a and the second antenna element 104b. According to the described embodiment the first complex weight wi and the second complex weight w ₂ are based on the electromagnetic scattering between the first antenna element 104a and the second antenna element 104b. The scattering is the sum of the reflections back to the first antenna element 104a and the second antenna element 104b and the mutual coupling between the first antenna element 104a and the second antenna element 104b. The scattering may be expressed using scattering parameters Sy, which describe the scattering between the i:th antenna element to the j:th antenna element. Thus, e.g., the scattering parameter Sn describes the reflection from the first antenna element 104a back to the first antenna element 104a and s ₂ i describe the electromagnetic coupling from the second antenna element 104b to the first antenna element 104a. The scattering parameters S together form a scattering matrix S. The first feed signal a^ and the second feed signal a ₂ together form a feed signal vector a. If a feed signal vector a in the form of a first feed signal a^ and a second feed signal a ₂ is applied on the first feed point 106a and the second feed point 106b, respectively, this will result in a first return signal bi on the first feed point 106a and a second return signal b ₂ on the second feed point 106b. The first return signal bi and the second return signal b ₂ form a return signal vector b. The return signal vector b depends on the scattering matrix and the feed signal vector in the following way: b=Sa

Thus, when the scattering matrix S is known the feed signal vector can be determined for which the return signal vector is below a desired level.

The scattering matrix may be determined in one of many different ways. The scattering matrix is e.g. dependent on the physical configuration of the antenna array and on the environment in which the antenna array operates. The scattering parameters Sy of the scattering matrix may be calculated or measured during the construction phase of the antenna arrangement or measured in an initializing step for the antenna arrangement. The first complex weight wi , and the second complex weight w ₂ which give the desired return signal may then be determined and the first complex weight wi and the second complex weight w ₂ may be stored in the memory 1 10 (see for example Fig. 2). When the antenna arrangement operates the signal processing device 108 is configured to retrieve the first complex weight wi and the second complex weight w ₂ from the memory 1 10 and provide the first feed signal a^ based on the input signal Sin and the first complex weight wi, and to provide the second feed signal a ₂ based on the input signal Sin and the second complex weight w ₂ . The antenna arrangement 1 00 may also be configured to adapt the first complex weight wi and the second complex weight w ₂ to the environment in which the antenna arrangement operates. To this end, in the described embodiment, the signal processing device 1 08 is configured to measure the scattering parameters S for example in operation. The measurement is done by the signal processing device 108 being configured to measure the scattering parameters Sy, the signal processing device 1 08 is configured to provide a first pilot signal ai _p to the first feed point 1 06a and receive first pilot return signals bi _p at the first feed point 106a and the second feed point 1 06b. The first pilot return signal received at the first feed point 106a is denoted bi _p i , while the first pilot return signal received at the second feed point 106b is denoted bi _p2 . The signal processing device 1 08 is also configured to provide a second pilot signal a _2p to the second feed point 106b and receive second pilot return signals b _2p at the first feed point 106a and the second feed point 106b. The second pilot return signal received at the first feed point 106a is denoted b _2p i, while the second pilot return signal received at the second feed point 1 06b is denoted b _2p2 . The signal processing device is configured to determine the electromagnetic scattering parameters Sy using the following equation: In order to get a proper measurement of the first pilot return signals bi _p , and the second pilot return signals b _2p the signal processing device 1 08 is configured to provide the signal processing device 1 08 is configured to provide the first pilot signal ai _p and the second pilot signal a _2p in different time periods. The pilot signals % are signals used only when measuring the scattering parameters Sy. Once the scattering parameters Sy are chosen the antenna arrangement is prepared for sending out signals.

Providing a first feed signal a^ to the first feed point 106a and a second feed signal a ₂ to the second feed point 1 06b results in a first return signal bi at the first feed point 1 06a and a second return signal b ₂ at the second feed point 106. The first return signal bi and the second return signal b ₂ are determined by the scattering parameters Sn, Si ₂ , S ₂ i, S ₂₂ . The signal processing device 1 08 is configured to choose the first complex weight wi and second complex weight w ₂ , and thereby the first feed signal a^ and the second feed signal a ₂ , so that the sum of the first return signal bi and the second return signal b ₂ is below a predetermined threshold value. The first feed signal a^ and the second feed signal a ₂ are determined from the above mentioned equation b=Sa, where the vector a describes the input signal. For example, if a = [1 1 1 1 ], then each port is fed the same amount of power. Vector b then describes how much power returns back to the ports due to reflections and mutual coupling. Theoretically, it is desirable to minimize the vector b to make the antenna arrangement 100 as efficient as possible. In the ideal case b =

[0 0 0 0], so that no power is returned and the efficiency is 100%.

The scattering matrix S describes the reflections and mutual coupling among the feed ports of the antenna. If we have three antenna elements 104a, 104b, 104c, the scattering matrix is where S gives the relation between a and b according to

We then calculate the eigenvalues of D, which is related to S according to D=I-S ^H S. We select the largest eigenvalue. Each eigenvalue has a corresponding eigenvector, so we find the eigenvector of D that corresponds to the largest eigenvalue. This eigenvector of D corresponds to the optimal weight vector a. The values of a are complex numbers. As stated above the first feed signal ai is based on the input signal Sin and the first complex weight wi , and the second feed signal a ₂ is based on the input signal Sin and the second complex weight w ₂ . Thus, the first complex weight wi and the second complex weight w ₂ may be calculated when the desired feed signals ai , a ₂ , are known. The forming of the first feed signal ai and the second feed signal a ₂ from the input signal Sin will be described in more detail below. The weights may be stored in a memory 1 10.

The first feed signal ai , the second feed signal a ₂ , the third feed signal a ₃ , and the scattering parameters Si ₂ , Si ₃ , S ₂ i , S ₂₃ , S ₃ i , S ₃₂ are illustrated in Fig. 4 which is described in detail below.

Fig. 2 shows schematically an antenna arrangement 100 according to another embodiment. The antenna arrangement 100 comprises an antenna array 102 comprising a first antenna element 104a, a second antenna element 104b, a third antenna element 104c, and a fourth antenna element 104d. The antenna arrangement 100 also comprises a signal processing device 108. The signal processing device 108 comprises an input 1 14 configured to receive an input signal Sin. The signal processing device 108 also comprises a first feed point 106a connected to the first antenna element 104a, a second feed point 106b connected to the second antenna element 104b, a third feed point 106c connected to the third antenna element 104c, and a fourth feed point 106d connected to the fourth antenna element 104d. The signal processing device 108 comprises a first transceiver 1 12a associated with the first feed point 106a, a second transceiver 1 12b associated with the second feed point 106b, a third transceiver 1 12c associated with the third feed point 106c, and a fourth transceiver associated with the fourth feed point 106d. The first transceiver 1 12a comprises a first modulator 1 18a and a first phase/amplitude shifter 120a. The second transceiver 1 12b comprises a second modulator 1 18b and a second phase/amplitude shifter 120b. The third transceiver 1 12c comprises a third modulator 1 18c and a third phase/amplitude shifter 120c. The fourth transceiver 1 12d comprises a fourth modulator 1 18a and a fourth phase/amplitude shifter 120a. Each transceiver 1 12a, 1 12b, 1 12c, and 1 12d, is connected to the input 1 14 and is configured to receive the input signal Sin. The function of the transceivers will now be explained using the first transceiver 1 12a as an example. The function of the other transceivers 1 12b, 1 12c, 1 12d, is equivalent to the function of the first transceiver 1 12a. The signal processing device 108 is configured to obtain a carrier frequency f _c and a first complex weight wi . The first complex weight is retrieved from a memory 1 10. The first modulator 1 18a modulates the input signal Sin to the carrier frequency f _c . The first phase/amplitude shifter 120a multiplies the modulated input signal with the first complex weight wi to provide the first feed signal a^ , which is then fed to the first antenna element 104a from the first feed point 106a. The second transceiver 1 12b, the third transceiver 1 12c, and the fourth transceiver 1 12d work in the corresponding way. It is of course possible to change place on the first modulator 1 18a and the first phase/amplitude shifter 120a. Correspondingly, it is possible to change place on the modulator 1 18b, 1 18c, 1 18d, and the corresponding phase/amplitude shifter 120b, 120c, 120d, in each one of the second transceiver 1 12b, the third transceiver 1 12c, and the fourth transceiver 1 12d.

Fig. 3 shows schematically an antenna arrangement 100 according to a further embodiment. The antenna arrangement 100 comprises an antenna array 102 comprising a first antenna element 104a, a second antenna element 104b, and a third antenna element 104c. The antenna arrangement 100 also comprises a signal processing device 108. The signal processing device 108 comprises an input 1 14 configured to receive an input signal Sin. The signal processing device 108 comprises a first input multiplexer 128a, a second input multiplexer 128b and a third input multiplexer 128c. The first input multiplexer 128a, the second input multiplexer 128b and the third input multiplexer 128c are all connected to the input 1 14. The signal processing device 108 also comprises a first feed point 106a connected to the first antenna element 104a, a second feed point 106b connected to the second antenna element 104b, and a third feed point 106c connected to the third antenna element 104c. The antenna arrangement comprises a first transceiver group 122a, a second transceiver group 122b, and a third transceiver group 122c. The antenna arrangement also comprises a first multiplexer 126a including a first feed point 106b, a second multiplexer 126b including a second feed point 106b, and a third multiplexer 126c including a third feed point 106c. The first transceiver group 122a comprises a first subtransceiver 124a for a first carrier frequency fi , a second subtransceiver 124b for a second carrier frequency f ₂ , and a third subtransceiver 124c for a third carrier frequency f ₃ . The first input multiplexer 128a is connected to the first transceiver group 122a and is configured to divide the input signal Sin between the first subtransceiver 124a, the second subtransceiver 124b, and the third subtransceiver 124c. The first subtransceiver 124a, the second subtransceiver 124b, and the third subtransceiver 124c are all connected to the first multiplexer 126a. The first multiplexer 126a connects the first subtransceiver 124a, the second subtransceiver 124b and the third subtransceiver 124c to the first feed point 106a.

The second transceiver group 122b comprises a fourth subtransceiver 124d for a first carrier frequency fi , a fifth subtransceiver 124e for a second carrier frequency f ₂ , and a sixth subtransceiver 124c for a third carrier frequency f ₃ . The second input multiplexer 128b is connected to the second transceiver group 122b and is configured to divide the input signal Sin between the fourth subtransceiver 124d, the fifth subtransceiver 124e, and the sixth subtransceiver 124f. The fourth subtransceiver 124d, the fifth subtransceiver 124e, and the sixth subtransceiver 124f are all connected to the second multiplexer 126b. The second multiplexer 126b connects the fourth subtransceiver 124d, the fifth subtransceiver 124e and the sixth subtransceiver 124f at a time to the second feed point 106b.

The third transceiver group 122c comprises a seventh subtransceiver 124g for a first carrier frequency fi , an eighth subtransceiver 124h for a second carrier frequency f ₂ , and a ninth subtransceiver 124i for a third carrier frequency h- The third input multiplexer 128c is connected to the third transceiver group 122c and is configured to divide the input signal Sin between the seventh subtransceiver 124g, the eighth subtransceiver 124h, and the ninth subtransceiver 124i.The seventh subtransceiver 124g, the eighth subtransceiver 124h, and the ninth subtransceiver 124i are all connected to the third multiplexer 126c. The third multiplexer 126c connects the seventh subtransceiver 124g, the eighth subtransceiver 124h and the ninth subtransceiver 124i at a time to the third feed point 106c.

The operation of the antenna arrangement 100 in Fig. 3 will now be described. An input signal Sin is inputted to all of the first input multiplexer 128a, the second input multiplexer 128b and the third input multiplexer 128c. The first input multiplexer 128a divides the input signal Sin between the first subtransceiver 124a, the second subtransceiver 124b and the third subtransceiver 124c. The second input multiplexer 128b divides the input signal Sin between the fourth subtransceiver 124d, the fifth subtransceiver 124e, and the sixth subtransceiver 124f. The third input multiplexer 128c divides the input signal Sin between the seventh subtransceiver 124g, the eighth subtransceiver 124h and the ninth subtransceiver 124i. The signal processing unit 108 will retrieve all relevant complex weights wi, w ₂ , w ₃ , from the memory 1 10.

In the first transceiver group 122a, the first subtransceiver 124a modulates the input signal to the first carrier frequency fi and multiplies the modulated input signal Sin with the first complex weight wm , for the first carrier frequency fi to provide the first feed signal ai(fi). The second subtransceiver 124b modulates the input signal Sin to the second carrier frequency f ₂ and multiplies the modulated input signal Sin with the first complex weight wi _f2 , for the second carrier frequency f ₂ , to provide the first feed signal ai(f ₂ ). The third subtransceiver 124c modulates the input signal Sin to the third carrier frequency f ₃ and multiplies the modulated input signal Sin with the first complex weight wi _f3 , for the third carrier frequency f ₃ to provide the first feed signal ai(f ₃ ).

In the second transceiver group 122b, the fourth subtransceiver 124d modulates the input signal Sin to the first carrier frequency fi and multiplies the modulated input signal Sin with the second complex weight w ₂ n , for the first carrier frequency fi to provide the second feed signal a ₂ (fi). The fifth subtransceiver 124e modulates the input signal Sin to the second carrier frequency f ₂ and multiplies the modulated input signal Sin with the second complex weight w _2f2 , for the second carrier frequency f ₂ , to provide the second feed signal a ₂ (f ₂ ). The sixth subtransceiver 124f modulates the input signal Sin to the third carrier frequency f ₃ and multiplies the modulated input signal Sin with the second complex weight w _2f3 , for the third carrier frequency f ₃ , to provide the second feed signal a ₂ (f ₃ ).

In the third transceiver group 122c, the seventh subtransceiver 124g modulates the input signal Sin to the first carrier frequency fi and multiplies the modulated input signal with the third complex weight w ₃ n , for the first carrier frequency fi to provide the third feed signal a ₃ (fi). The eighth subtransceiver 124h modulates the input signal to the second carrier frequency f _C 2 and multiplies the modulated input signal with the third complex weight w ₃ f2, for the second carrier frequency f ₂ to provide the third feed signal a ₃ (f ₂ ). The ninth subtransceiver 124i modulates the input signal Sin to the third carrier frequency f ₃ and multiplies the modulated input signal with the second complex weight w ₃ f3 , for the third carrier frequency f ₃ , to provide the third feed signal a ₃ (f ₃ ).

The first multiplexer 126a, the second multiplexer 126b, and the third multiplexer 126c combine the feed signals from the subtransceivers 124a-i to which they are connected. Thus, the first multiplexer 126a combines the first feed signal ai(fi) for the first carrier frequency fi , the first feed signal ai(f ₂ ) for the second carrier frequency f ₂ and the first feed signal ai(f ₃ ) for the third carrier frequency f ₃ , and feeds the combined signal to the first antenna element 104a. The second multiplexer 126b combines the second feed signal a ₂ (fi) for the first carrier frequency fi , the second feed signal a ₂ (f2) for the second carrier frequency f ₂ and the second feed signal a ₂ (f ₃ ) for the third carrier frequency f ₃ , and feeds the combined signal to the second antenna element 104b. Finally, the third multiplexer 126c combines the third feed signal a ₃ (fi) for the first carrier frequency fi , the third feed signal a ₃ (f ₂ ) for the second carrier frequency f ₂ and the third feed signal a ₃ (f ₃ ) for the third carrier frequency f ₃ , and feeds the combined signal to the third antenna element 104c.

Fig. 4 shows schematically an antenna arrangement 100 according to a further embodiment. The antenna arrangement 100 comprises an antenna array 102 comprising a first antenna element 104a, a second antenna element 104b, and a third antenna element 104c. The antenna arrangement 100 also comprises a signal processing device 108. The signal processing device 108 comprises an input 1 14 configured to receive an input signal Sin. The signal processing device 108 also comprises a first feed point 106a connected to the first antenna element 104a, a second feed point 106b connected to the second antenna element 104b, and a third feed point 106c connected to the third antenna element 104c. The signal processing device 108 comprises a first transceiver 1 12a associated with the first feed point 106a, a second transceiver 1 12b associated with the second feed point 106b, a third transceiver 1 12c associated with the third feed point 106c. The dotted double arrow denoted S ₂ i , Si ₂ , illustrates the coupling between the first antenna element 104a and the second antenna element 104b. The dotted double arrow denoted S ₃₂ ,S ₂₃ , illustrates the coupling between the second antenna element 104b and the third antenna element 104c. The dotted double arrow denoted S ₂ i ,Si ₂ , illustrates the coupling between the first antenna element 104a and the second antenna element 104b. The first feed signal a^ , the second feed signal a ₂ , and the third feed signal a ₃ , are fed from the first transceiver 1 12a, the second transceiver 1 12b, and the third transceiver 1 12c, respectively. A first return signal bi , a second return signal b ₂ , and a third return signal b ₃ are directed towards the first transceiver 1 12a, the second transceiver 1 12b, and the third transceiver 1 12c, from the first antenna element 104a, the second antenna element 104b, and the third antenna element 104c, respectively. During the measurement of the scattering parameters S , only one antenna element at a time is provided with a feed signal. Thus, when only the first antenna element 104a is fed with a first feed signal a^ , the first return signal bi at the first feed point 106a is equal to bi=Snai , the second return signal b ₂ at the second feed point 106b is equal to b ₂ =S ₂ iai , and the third return signal b ₃ at the third feed point 106c is equal to b ₃ =S ₃ ia1 . When all feed points 106a, 106b, 106c are fed with a respective feed signal a^ , a ₂ , a ₃ , the first return signal bi at the first feed point 106a is equal to bi=Snai+ Si ₂ a ₂ + Si ₃ a ₃ , the second return signal b ₂ at the second feed point 106b is equal to b ₂ =S ₂ iai+ S ₂₂ a ₂ + S ₂₃ a ₃ , and the third return signal b ₃ at the third feed point 106c is equal to b ₃ =S ₃ iai+ S ₃₂ a ₂ + S ₃₃ a ₃ . The design of the first antenna element 104a, the second antenna element 104b, and the third antenna element 104c, and the antenna arrangement as such may vary. The scattering parameters will depend on the physical properties of the antenna arrangement.

Fig. 5a is a perspective view of a part of an antenna arrangement 100 according to a further embodiment. Fig 5b is a plan view of the antenna arrangement 100 shown in Fig. 5a. The antenna arrangement 100 comprises an antenna array 102 comprising a first antenna element 104a, a second antenna element 104b, a third antenna element 104c, and a fourth antenna element 104d. The antenna arrangement 100 also comprises a signal processing device 108. The signal processing device 108 comprises an input 1 14 configured to receive an input signal Sin. The signal processing device 108 also comprises a first feed point 106a connected to the first antenna element 104a, a second feed point 106b connected to the second antenna element 104b, a third feed point 106c connected to the third antenna element 104c, and a fourth feed point 106d connected to the fourth antenna element 104d. As can be seen in Fig 5a the signal processing device 108 comprises printed circuit board (PCB) 170 having a top plane 130 and a bottom plane 132. The first antenna element 104a and the second antenna element 104b extend from the top plane 130 of the signal processing device 108, while the third antenna element 104c, and the fourth antenna element 104d extend from the bottom plane 132. The first antenna element 104a, a second antenna element 104b, a third antenna element 104c, and a fourth antenna element 104d all have a bent shape with a first part 134a, 134b, 134c, 134d extending from the signal processing device and a second part 136a, 136b, 136c, 136d extending at a right angle from the first part 134a, 134b, 134c, 134d. In Fig. 5b a top view is shown in which the length of the largest of the first parts 134a, 134b, 134c, 134d is denoted L1 and the length of the largest of the second parts 136a, 136b, 136c, 136d is denoted L2. The antenna elements 104a, 104b, 104c, 104d could for example also be implemented as wire traces on the PCB 170 (e.g. on the top plane 130 and the bottom plane 132).

Fig. 6 shows schematically the efficiency as a function of the frequency for an antenna arrangement according to Fig 3. Fig. 7 shows schematically the efficiency as a function of the frequency for an antenna arrangement according to Fig. 3. The x-axis shows the frequency in GHZ and the y-axis the TARC (total active reflection coefficient) in dB.

In Fig. 7 the shaded areas 140, 142, and 144, show the specifications to be fulfilled by the antenna arrangement. The solid line 146 shows the obtainable efficiency using the antenna arrangement 100. The first shaded area 140 corresponds to the low band (1 .7-2.7 GHz). The second shaded area 142 corresponds to the mid band (3.3-4.5 GHz). The third shaded area 144 corresponds to the high band (5.8-6.4 GHz). The criterion for the operation is approximately >90% matching efficiency (corresponding to < -10 dB at the desired frequencies). Fig. 6 illustrates the case that the antenna arrangement is used to transmit in two bands simultaneously using a first carrier frequency fi in the low band and a second carrier frequency in the mid band. Assuming that the scattering matrix S is known for each frequency the complex weights at those frequencies may be calculated as explained above. Using the complex weights calculated based on the first frequency fi results in an efficiency as a function of the frequency shown by the first solid line 148 in Fig. 6. Using the complex weights calculated based on the second frequency f ₂ results in an efficiency as a function of the frequency shown by the second solid line 150 in Fig. 7 The dotted line 146 shows the theoretically obtainable efficiency using the antenna arrangement 100. The efficiency is shown as TARC(dB) which is the total active reflection coefficient. TARC may be calculated using the following formula where TARC relates to efficiency η via the relation η = 1 - (TARC).

Fig. 8 is a flow diagram illustrating a method 200 according to an embodiment. The method 200 is for an antenna arrangement 100 comprising an antenna array 102 comprising a first antenna element 104a including a first feed point 106a, and a second antenna element 104b including a second feed point 106b. The method 200 comprises receiving 202 an input signal Sin, obtaining 204 a first complex weight wi , and obtaining 206 a second complex weight w ₂ . The first complex weight wi , and the second complex weight w ₂ are, according to an embodiment obtained from the memory 1 10. The method 200 also comprises generating 208 a first feed signal a^ based on the input signal Sin and the first complex weight wi , generating 210 a second feed signal a ₂ based on the input signal Sin and the second complex weight w ₂ , and providing 212 the first feed signal a^ to the first feed point 106a and providing the second feed signal a ₂ to the second feed point 106b so as to control the frequency characteristic of the antenna array 102.

Fig. 9 shows schematically a communication device 300 in a wireless communication system 400. The communication device 300 comprises an antenna arrangement 100 according to an embodiment of the invention. The wireless communication system 400 also comprises a base station 500 which may also comprise an antenna arrangement 100 according to any one of the embodiments described above. The dotted arrow A1 represents transmissions from the transmitter device 300 to the base station 500, which are usually called up-link transmissions. The full arrow A2 represents transmissions from the base station 500 to the transmitter device 300, which are usually called down-link transmissions.

The present transmitter device 300 may be any of a User Equipment (UE) in Long Term Evolution (LTE), mobile station (MS), wireless terminal or mobile terminal which is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UE may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).

The present transmitter device 300 may also be a base station a (radio) network node or an access node or an access point or a base station, e.g., a Radio Base Station (RBS), which in some networks may be referred to as transmitter, "eNB", "eNodeB", "NodeB" or "B node", depending on the technology and terminology used. The radio network nodes may be of different classes such as, e.g., macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network node can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).