Patent Publication Number: US-2018048063-A1

Title: Beamforming antenna array

Description:
TECHNICAL FIELD 
     The invention relates to communications. More particularly, the present invention relates to beamforming. 
     BACKGROUND 
     In a communication network, beam transmission may be beneficial in transferring information. Providing solutions enhancing the beamforming may be beneficial for the operation of the communication network. Solutions making the used antenna array structure simplified may be an example of one such solution. 
     BRIEF DESCRIPTION 
     According to an aspect, there is provided the subject matter of the independent claims. Some embodiments are defined in the dependent claims. 
     One or more examples of implementations are set forth in more detail in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In the following embodiments will be described in greater detail with reference to the attached drawings, in which 
         FIG. 1  illustrates an example cellular communication system to which embodiments of the invention may be applied; 
         FIG. 2  illustrates an apparatus according to an embodiment; 
         FIGS. 3A to 3D  illustrate the apparatus according to some embodiments; 
         FIG. 4  illustrates an apparatus according to an embodiment; 
         FIGS. 5A to 5E  illustrate apparatuses according to some embodiments; 
         FIGS. 6 and 7  illustrate flow diagrams of methods according to some embodiments; and 
         FIG. 8  illustrates an apparatus according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SOME EMBODIMENTS 
     The following embodiments are exemplifying. Although the specification may refer to “an”, “one”, or “some” embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. 
     Embodiments described may be implemented in a radio system, such as in at least one of the following: Worldwide Interoperability for Micro-wave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), and/or LTE-Advanced. 
     The embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with necessary properties. Another example of a suitable communications system is the 5G concept. 5G is likely to use multiple input—multiple output (MIMO) techniques (including MIMO antennas), many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates. 5G will likely be comprised of more than one radio access technology (RAT), each optimized for certain use cases and/or spectrum. 5G mobile communications will have a wider range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications, including vehicular safety, different sensors and real-time control. 5G is expected to have multiple radio interfaces, namely below 6 GHz, cmWave and mmWave, and also being integradable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and 5G radio interface access comes from small cells by aggregation to the LTE. In other words, 5G is planned to support both inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6 GHz−cmWave, below 6 GHz−cmWave−mmWave). One of the concepts considered to be used in 5G networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility. It should be appreciated that future networks will most probably utilize network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into “building blocks” or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or cloud data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labor between core network operations and base station operations may differ from that of the LTE or even be non-existent. Some other technology advancements probably to be used are Software-Defined Networking (SDN), Big Data, and all-IP, which may change the way networks are being constructed and managed. 
     Some embodiments of the present invention may be applied to a cellular communication system applying beamforming to transmissions in a cell.  FIG. 1  illustrates an example of such a cellular communication system. Cellular radio communication networks, such as the Long Term Evolution (LTE), the LTE-Advanced (LTE-A) of the 3 rd  Generation Partnership Project (3GPP), or the predicted 5G solutions, are typically composed of at least one network element, such as a network node  102 , providing a cell  104 . The cell  104  may be, e.g., a macro cell, a micro cell, femto, or a pico-cell, for example. The network node  110  may be an evolved Node B (eNB) as in the LTE and LTE-A, a radio network controller (RNC) as in the UMTS, a base station controller (BSC) as in the GSM/GERAN, or any other apparatus capable of controlling radio communication and managing radio resources within the cell  104 . For 5G solutions, the implementation may be predicted to be similar to LTE-A, as described above. The network node  102  may be a base station or an access node. The cellular communication system may be composed of a radio access network of network nodes similar to the network node  102 , each controlling a respective cell or cells. Thus, in some embodiments, the cellular system of  FIG. 1  may comprise a plurality of network nodes providing cellular services. However, such system may not be necessary for benefits of the invention. 
     The network node  102  may be further connected via a core network interface to a core network  130  of the cellular communication system. In an embodiment, the core network  130  may be called Evolved Packet Core (EPC) according to the LTE terminology. The core network  130  may comprise a mobility management entity (MME) and a data routing network element. In the context of the LTE, the MME tracks mobility of the terminal devices  120  and carries out establishment of bearer services between the terminal devices  120  and the core network  130 . In the context of the LTE, the data routing network element may be called a System Architecture Evolution Gateway (SAE-GW). It may be configured to carry out packet routing to/from the terminal devices  120  from/to other parts of the cellular communication system and to other systems or networks, e.g. the Internet. 
     As described above, the network node  102  may employ beamforming in transmission of radio signals in the cell  104 . As known in the field of wireless communications, beamforming also called spatial filtering refers to directional transmission or reception. The steering of a radio beam may be achieved through digital and/or analog signal processing techniques and use of multiple antenna elements forming an antenna array. For example, the steering may be achieved by combining elements in a phased antenna array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used in a transmitter and/or in a receiver in order to achieve spatial selectivity. The spatial selectivity results in improvement compared with omnidirectional transmission/reception, wherein the improvement is called transmit/receive gain. 
     In some embodiments, the network node  102  may employ two types of radio beams: a first type of radio beam  114  that covers substantially the whole cell  104 ); and a second type of radio beam  112 ,  113  that covers a portion of the cell  104 . When the cell  104  is a sector-type of cell amongst a plurality of sectors established by the network node  102 , the first type of radio beam may be called a sector beam. Conventionally, cellular communication systems rely on the first type of radio beams for control plane transmissions (downlink synchronization, broadcast, antenna-port based common reference signals, etc.) and reception (e.g. random access channel, RACH). A system operating on higher carrier frequencies, such as a 5G system, may require higher antenna gain which may be achieved by using radio beams of the second type. In order to support cell sizes with inter-site distance of tens to hundreds meters, both common control and user plane related signaling may utilize radio beams that are narrower than the sector-wide radio beam. The second type of radio beam may provide a solution to such a situation. In general it may be said that present cellular communication systems and probably future communication systems offer multiple opportunities to improve connection speeds by utilizing beamforming. 
     As explained, the radio beams may be formed by an apparatus (e.g. beamforming apparatus comprised in the network node  102  or the network node  102 ) utilizing digital and/or analog signal processing. One aspect of utilizing analog signal processing may be the complexity of the system required. Further, at the network node side (i.e. network node  102 ) the complexity may be, at least sometimes, handled. However, at the user side (e.g. the terminal device  120 ) complexity may pose an implementation obstacle, and therefore beamforming antennas at the user side are usually mechanically tunable such that the steering of the beam direction is done at the installation phase only. To tackle at least some of these problems, there is provided an apparatus and a method for beamforming. The apparatus and the method are suitable for both uplink and downlink communication. However, the simplicity of the solution may be particularly beneficial for the user side (i.e. the terminal device  120  (may also be referred to as UE  120  at least in some embodiments). Further, the present solution may be particularly suitable for analog signal processing. 
     The terminal device  120  may be and/or comprise cellphones, tablets, laptops, computers, smart phones, user hand-held devices or wearable devices. Hence, the terminal device  120  may be used by user to transfer data in and out from the device. In some embodiments, the terminal device  120  comprises a customer end device, such as a cellular communication network device configured to cooperate with the cellular communication network. Thus, for example, the cellular communication network device may be a device that is configured to be installed to home or office and further configured to transfer data with said network and/or with other terminal devices. Thus, the cellular communication network device may be a relay device or a router configured to transfer data with said network and/or with cellphones and tablets, for example. Said cellular communication network device may provide a small cell. Said small cell may be part of and/or cooperate with the cellular communication network. Such small cell can be used, for example, in a home or office environment to enhance service for one or more terminal devices. According to an embodiment with reference to  FIG. 2 , there is provided an apparatus  200  comprising: an antenna array for generating radio beams, the antenna array comprising antenna element sub-groups  210 ,  220 ,  230  (i.e. at least two antenna element sub-groups) and each antenna element sub-group  210 ,  220 ,  230  comprising a plurality of antenna elements  212 ,  214 ,  216 ,  222 ,  224 ,  226 ,  232 ,  234 ,  236 ; signal input means (e.g. signal feed element  240  or electrical connections between a signal input and the antenna elements) for providing an input signal to each antenna element sub-group  210 ,  220 ,  230  and to the plurality of antenna elements within each antenna element sub-group  210 ,  220 ,  230  via electrical connections, wherein the plurality of antenna elements within each antenna element sub-group are consecutively electrically connected to each other such that the input signal is configured to be inputted, within each antenna element sub-group, to at least one antenna element via at least one other antenna element (e.g. via antenna element  212  to antenna element  214 , and via antenna elements  212 ,  214  to antenna element  216 ); and phase shift means (phase shift elements T 1  and/or T 2 ) for shifting a phase of the input signal between the consecutively electrically connected antenna elements within each antenna element sub-group  210 ,  220 ,  230 . 
     According to an embodiment, referring to  FIG. 2 , the apparatus  200  comprises an antenna array for generating radio beams, the antenna array comprising antenna element sub-groups  210 ,  220 ,  230  (shown in  FIG. 2  to comprise three antenna elements each), wherein the antenna element sub-groups  210 ,  220 ,  230  are electrically connected in parallel manner to each other, and wherein antenna elements within each antenna element sub-group  210 ,  220 ,  230  are electrically connected in consecutive manner (e.g. antenna elements  212 ,  214 ,  216  of antenna element sub-group  210  are connected consecutively in  FIG. 2 ). The apparatus  200  may further comprise a signal feed element  240  for providing an input signal to the antenna array, the signal feed element  240  configured to provide the input signal to each of the antenna element sub-groups  210 ,  220 ,  230  via the parallel electrical connection and to each antenna element within each antenna element sub-group  210 ,  220 ,  230  via the consecutive electrical connection between the antenna elements within each sub-group  210 ,  220 ,  230 . The apparatus  200  may further comprise at least one first phase shift element T 1  electrically connected between the signal feed element  240  and at least one antenna element sub-group  210 ,  220 ,  230  and configured to shift phase of the input signal inputted to said at least one antenna element sub-group  210 ,  220 ,  230 . Further, the apparatus  200  may comprise a plurality of second phase shift elements T 2  electrically connected between the consecutively connected antenna elements  212 ,  214 ,  216 ,  222 ,  224 ,  226 ,  232 ,  234 ,  236  and configured to shift phase of the input signal within each of the antenna element sub-groups  210 ,  220 ,  230  between the consecutively connected antenna elements  212 ,  214 ,  216 ,  222 ,  224 ,  226 ,  232 ,  234 ,  236 . 
     It needs to be understood that the consecutive electrical connection (e.g. galvanic connection) between the antenna elements within each sub-group  210 ,  220 ,  230  can be, in a way, understood as serial electrical connection. This may mean that the input signal is inputted via other antenna elements to some other antenna elements as shown in  FIG. 2 . For example, antenna elements  212 ,  214 ,  216  are serially connected signal-wise, such that the input signal is inputted to antenna element  212 , via antenna element  212  to antenna element  214 , and via antenna elements  212 ,  214  to antenna element  216 . The phase shift elements T 2  (also referred to as second phase shift elements) may shift the phase of the input signal so that the phase of the input signal may be different for each antenna element  212 ,  214 ,  216 . 
     For example looking at  FIG. 2 , the second phase shift elements T 2  are configured to shift phase of the input signal between the antenna elements  212  and  214  and between antenna elements  214  and  216 , to name a couple of examples. For example, the first phase shift elements T 1  of  FIG. 2  may be configured to shift phase of the input signal inputted to the antenna element sub-groups  220  and  230 . Further, the input signal inputted to the antenna element sub-group  230  may travel via two first phase shift elements T 1 . Later we will see how this may affect the signal phases and beamforming in the system. However, it needs to be noted that the first phase shift elements T 1  may in some embodiments be used in a different way to achieve the benefits of the invention. Therefore, later we will show different examples of how to arrange the phase shift elements T 1 , T 2  in the apparatus  200 . 
     The apparatus  200  of  FIG. 2  may be, at least in some embodiments, referred to as a radio beamforming apparatus or a beamforming apparatus. In an embodiment, the apparatus  200  comprises or is comprised in a terminal device, such as the terminal device  120 . In an embodiment, the apparatus  200  comprises or is comprised in a network node, such as the network node  102 . 
     The apparatus  200  of  FIG. 2  may provide a novel structure that allows analog beamforming that can be used for both Tx and Rx operation. For example, using the described structure it may be possible to have at least 5 different phase values for the inputted signal. Thus, directional radio beam(s) can be achieved when the input signal is outputted accordingly. Let us look at one example shown in  FIG. 3A  in which the phase shift value of the first phase shift element(s) is chosen to be −10 degrees (deg) and the phase shift value of the second phase shift elements is chosen to be +10 degrees (deg). Further, the same structure as shown in  FIG. 2  is utilized, but may not be necessary for the proposed solution. That is, the solution may be suitable for, for example, four antenna elements in two sub-groups as will be described later in more detail. 
     Let us further discuss some examples how the different antenna elements may be arranged within the antenna array. In one example, the antenna elements may be physically arranged in a line so that the horizontal beaming of the antenna array may be further enhanced. In another example, the antenna elements may be arranged into a plurality of lines (i.e. lines and columns). Let us bear in mind that the electrical connection between the sub-groups and the antenna elements may still be how it is described although a different kind of physical arranging of the antenna elements would be employed. In one preferable solution, nine antenna elements maybe suitable to be arranged in two or more lines such that the lines are at least partially overlapping. That is, arranging the antenna elements in a diamond-like formation may benefit the described serial-parallel electrical connection between the antenna elements. In one diamond-like formation, top and bottom rows would have one antenna element, middle row would have three antenna elements, and rows between the middle row and top row and middle row and bottom row would each have two antenna elements. Other structures may also be possible: for example, the antenna array may comprise two rows each having two antenna elements, three rows each having two antenna elements, four rows each having three antenna elements, four rows each having four antenna elements, to name a few examples. In general, the antenna array may have X rows at least partially on top of each other, wherein each row comprises one or more antenna elements (number per row may vary), wherein X may be a positive integral number (e.g. 1, 2, 3, 4, and so on). 
     Still referring to  FIG. 2 , the parallel connected sub-groups  210 ,  220 ,  230  may be in galvanic connection with each other. That is, the lines shown with arrows may connect the sub-groups  210 ,  220 ,  230  to each other in parallel manner. However, in some embodiments, serial connection between the sub-groups may also be used meaning that the input signal may be inputted to a sub-group via at least one other sub-group. Further, the antenna elements within a sub-group may be in galvanic connection with each other. Therefore, also the consecutive electrical connection between the antenna elements may be galvanic. Galvanic connection may be achieved using, for example, conducting wire or conductor (e.g. copper wire). Any means that are able to transmit signal to the antenna elements may be used. The phase shift elements T 1 , T 2  may also be in galvanic connection with the conducting wire. For example, conducting wire between the antenna elements  212 ,  214  may be galvanically connected to the second phase shift element T 2  (shown in  FIG. 2  between the antenna elements  212 ,  214 ). Thus, when the input signal transfers from the antenna element  212  to the antenna element  214  in the example of  FIG. 2  via the conducting element or wire, it transfers via the second phase shift element T 2  (signal phase is shifted). 
     The signal feed element  240  may comprise a signal port for receiving the input signal that is to be transferred to the antenna elements shown in  FIG. 2 . The signal feed element  240  may acquire the input signal (e.g. radio frequency (RF) signal) and transfer it to the antenna elements. The antenna elements may then resonate the input signal accordingly as electromagnetic energy via air interface. Thus, the radiated electromagnetic energy may be received by a receiver via the air-interface. 
     To further explain the transmittance of the input signal (e.g. RF signal), it may need to be understood how the input signal is distributed in points  292 - 296  of  FIG. 2 . That is, the parallel connection between the sub-groups  210 ,  220 ,  230  may require performing power splitting. One way to do this may be to use Wilkinson type power divider. However, any conventional type of power dividing may be used as long as the input signal can be inputted into each of the sub-groups  210 ,  220 ,  240 . It is clear to a skilled person how the power splitting can be achieved in different examples and embodiments of the invention. 
     Further, the consecutive electrical connection between the antenna elements may require that the antenna elements are suitable for such serial connection. Basic suitable structure may be a patch antenna element where an RF signal or input signal can be fed in from one edge of the patch antenna element, and outputted from an adjacent edge of the patch antenna element. That is in general, RF signal or the input signal should be inputted from one edge of the antenna element (e.g. antenna element  212 ) and outputted from another edge (e.g. opposite side) of said antenna element to be inputted to the next antenna element (e.g. antenna element  214 ). 
     Referring to  FIG. 3A , we can see that the inputted signal from the signal feed element  240  may have initially a phase shift of zero (0) degrees (it could potentially be already phase shifted if needed). However, using the first and second phase shift elements T 1 , T 2 , the input signal&#39;s phase may be changed. Thus, the phase shift of the input signal inputted to the first antenna element sub-group  210  may be zero degrees. Thus, the phase shift of the input signal inputted to the second antenna element sub-group  220  may be −10 degrees. Thus, the phase shift of the input signal inputted to the third antenna element sub-group  230  may be −20 degrees. Within each sub-group  210 ,  220 ,  230  the second phase shift elements T 2  may further shift the phase of the input signal. Thus, the first antenna element sub-group  210  may comprise three antenna elements to which the input signal is inputted having different phases as shown in  FIG. 3A  (i.e. 0 degrees phase shift, +10 degrees phase shift, and +20 degrees phase shift). Using this approach for each of the sub-groups  210 ,  220 ,  230  may result in inputting the input signal with −20 degrees phase shift to one antenna element, with −10 degrees phase shift to two antenna elements, with 0 degrees phase shift to three antenna elements, with +10 degrees phase shift to two antenna elements, and finally with +20 degrees phase shift to one antenna element. Therefore, in this example, total of five different phase shift values of the input signal may be outputted by the antenna elements. However, this should be understood as an example, and it may be possible to use different phase shift values with the first and/or second phase shift elements. 
     In an embodiment, the at least one first phase shift element T 1  has a first phase shift value and the second phase shift elements T 2  each have a second phase shift value. The first and second phase shift values may be of different size. One example of this was shown in  FIG. 3A  in which the first phase shift values was −10 degrees and the second phase shift value was +10 degrees. Naturally, other values may be used. For example, the second phase shift value could be +5 degrees and the first phase shift value could be −5 degrees. 
     In an embodiment, with reference to  FIG. 3B , the plurality of phase shift elements (e.g. phase shift means) comprise at least one first phase shift element and a plurality of second phase shift elements. In the example of  FIG. 3B , the phase shift of the second phase shift elements may be 10 degrees and the phase shift of the first phase shift element may be −20 degrees. Thus, connecting the antenna element sub-groups with the signal feed element  240  as shown in  FIG. 3B , the resulting phase shifts in the antenna elements may be similar as in the example of  FIG. 3A . Therefore, there can be a number of different ways to perform the connection between the antenna element sub-group (and also within antenna element sub-groups) to achieve the benefits the invention. Another example may be shown in  FIG. 3C  in which the first phase shift value is −10 degrees and second phase shift value is 10 degrees. The resulting antenna array in  FIGS. 3A to 3C  may be substantially similar with different ways of connecting the antenna sub-groups to the signal input element  240 . So in general, different phase shift values may be used than shown in the embodiments of  FIGS. 3A to 3D , for example. In some embodiments, phase shift value for each phase shift element is configurable. Thus, when, for example, 9 phase shift elements are used, there may be one or nine different phase shift values. In an embodiment, two different phase shift values are used. 
       FIG. 3D  illustrates yet another embodiment of the invention. As an example, phase shift values are illustrated, but as said before, may differ from the illustrated values. However, the general idea in the antenna array of  FIG. 3D  may be that the phase shifts of the antenna elements of the antenna array do not need to be symmetrically arranged as, for example, in  FIGS. 3A to 3C . Therefore, for example, the input signal may be zero phased on the left-most antenna element and +20 degrees phased on the right-most antenna element. However, using the example of  FIG. 3D , needed beam steering may also be achieved at least for some use cases. Further, in the example of  3 D there are now phase shift elements between the signal input and the sub-groups (e.g. phase shift elements T 2 ). However, such elements could also be used. In such case, the T 2  value should be selected such that a needed a non-symmetrical phase shift values for the antenna array would be acquired. 
       FIG. 4  illustrates the apparatus  200  according to an embodiment. Referring to  FIG. 4 , the apparatus  200  comprises a plurality of first phase shift elements T 1  (i.e. at least two first phase shift elements T 1 ) configured to shift phase of the input signal for at least two of the antenna element sub-groups  210 ,  220 ,  230 . The plurality of first phase shift elements will now be referred to as the plurality of first phase shift elements  402 ,  404 ,  406  as shown in  FIG. 4 . Thus, in an embodiment, there may be a first phase shift element  402  between the signal feed element  240  and the sub-groups  210 ,  220 ,  230  as shown in  FIG. 4 . Further, there may be total of three first phase shift elements  402 ,  404 ,  406 . Thus, for each sub-group  210 ,  220 ,  230  there may be a corresponding first phase shift element  402 ,  404 ,  406 . Looking at the embodiment of  FIG. 2 , it may be seen that there may be less first phase shift elements than shown in  FIG. 4 . 
     In an embodiment, the plurality of first phase shift elements  402 ,  404 ,  406  are arranged such that one first phase shift element  402  is connected between the signal feed element  240  and the at least one antenna element sub-group  210 ,  220 ,  230  and another first phase shift element  404  is connected between said one first phase shift element  402  and at least one antenna element sub-group  220 ,  230 . Further if there are three sub-groups  210 ,  220 ,  230  as in  FIG. 4 , there may a further first phase shift element  406  connected between said another first phase shift element  404  and the sub-group  230 . Thus, before the input signal from the signal feed  240  reaches the antenna element  232 , the first phase shift elements  402 ,  404 ,  406  may each have shifted the phase of the input signal in a serial manner. For example, if T 1 &#39;s value is −10 degrees, the inputted signal to the antenna element  232  may be −30 degrees phase shifted compared to the inputted signal by the signal feed element  240 . 
     In an embodiment, with reference to  FIGS. 2 and 4 , the at least one first phase shift element T 1  is configured such that phase of the input signal is different for each of the antenna element sub-groups  210 ,  220 ,  230 . That is, as it is shown in  FIG. 3A  for example, the phase of the input signal may be different between sub-groups when the input signal is inputted into the sub-groups  210 ,  220 ,  230 . This may be achieved using one or more first phase shift elements. For example, if there are only two sub-groups (e.g.  FIG. 5A ), the phase of the input signal may be different for each of the sub-groups  210 ,  220  by using only one first phase shift element T 1 . However, if there are at least three sub-groups  210 ,  220 ,  230 , at least two first phase shift elements T 1  may be beneficial to be used (examples in  FIG. 3A  and  FIG. 4 ). 
     In an embodiment, the antenna element sub-groups  210 ,  220 ,  230  are electrically connected to each other in parallel. Examples of this may be seen in  FIGS. 2, 3A to 3C, and 4 , for example. 
     In an embodiment, phase shift means (e.g. the first and second phase shift elements) are further configured to shift phase of the input signal for at least one antenna element sub-group. Examples of this may be seen in  FIGS. 2, 3A to 3C, and 4 , for example. In  FIGS. 5C and 5D  opposite examples may be shown, wherein for each sub-group the phase of the input signal is essentially the same, but the phase shift within each sub-group is then performed. 
     In an embodiment, the phase shift means are further configured to perform a first phase shift of the input signal for a first antenna element sub-group  220  and a second phase shift of the input signal for a second antenna element sub-group  230 , the first and second phase shifts being of different size. Examples of this may be seen in  FIG. 2 , for example. That is, the phase of the input signal inputted to sub-group  220  may be different than the phase of the input signal inputted to sub-group  230 . For sub-group  210  phase shift is not performed in the example of  FIG. 2  thus resulting in a different phase of the input signal. 
     In an embodiment, the phase shift means comprise a plurality of phase shift elements (e.g. T 1  and/or T 2 ) for shifting the phase of the input signal for the antenna element sub-groups  210 ,  220 ,  230 , said plurality of phase shift elements arranged such that at least one phase shift element  404  is configured to perform the first phase shift, and said at least one phase shift element  404  coupled with at least one other phase shift element  406  are arranged to perform the second phase shift. One example of this can be seen in  FIG. 4 . Another may be seen in  FIG. 2  in which two T 1  phase shift elements are serially connected to change the phase of the input signal. Thus, the second phase shift may be understood as being a multi-phase phase shift in which the shift of the input signal may be shifted two or more times. 
     In an embodiment, the phase shift means are configured such that a phase of the input signal is different for each antenna element sub-groups  210 ,  220 ,  230 . Examples of this may be seen in  FIGS. 2, 3A to 3C, and 4 , for example. 
     In an embodiment, the phase shift means are configured to shift phase of the input signal between each consecutively electrically connected antenna element  212 ,  214 ,  216  within each antenna element sub-group  210 ,  220 ,  230 . Examples of this may be seen in  FIGS. 2, 3A to 3C, and 4 , for example. E.g. second phase shift elements T 2  shown in  FIGS. 2 and/or 4 . 
     In an embodiment, the phase shift means are configured such that the phase of the input signal is different for each antenna element  212 ,  214 ,  216  within an antenna element sub-group  210 ,  220 ,  230 . Examples of this may be seen in  FIGS. 2, 3A to 3C, and 4 , for example. This may mean that antenna elements within one sub-group each have inputted with an input signal having a different phase. However, within the antenna array there may be antenna elements inputted with an input signal having the same phase (e.g. between sub-groups). 
     In an embodiment, with reference to  FIGS. 2 and 4 , the plurality of the second phase shift elements T 2  is configured to shift phase of the input signal between each serially connected antenna element. This may mean that there is at least one second phase shift element T 2  between each serially connected antenna element. Taking sub-group  210  as an example, there is a second phase shift element between the antenna element  212  and the antenna element  214 , and another second phase shift element between the antenna element  214  and the antenna element  216 . Similar logic may apply to each sub-group  210 ,  220 ,  230 . This may enable that the input signal has a different phase for each antenna element within a sub-group. 
     In an embodiment, the plurality of the second phase shift elements T 2  is configured to shift phase of the input signal such that phase of the input signal inputted to the serially connected antenna elements within an antenna element sub-group is different for each of said antenna elements. Thus for example, phase of the input signal inputted to the antenna elements  212 ,  214 ,  216  would be different for each antenna element. Example of this can be seen in  FIG. 3A , for example. In  FIG. 3A , the phase of the input signal is different for each of the antenna elements within a sub-group. 
       FIGS. 5A to 5B  illustrate some embodiments. Referring to  FIGS. 5A to 5B , it is noted that the solution may work with only four antenna elements  212 ,  214 ,  222 ,  224 . That is, in an embodiment, the antenna array comprises at least four antenna elements  212 ,  214 ,  222 ,  224  arranged into two antenna element sub-groups  210 ,  220  (i.e. sub-group  210  comprises elements  212 ,  214  and sub-group  220  comprises elements  222 ,  224 ). As shown in  FIG. 5A , the solution may work with only one first phase shift element  404 . In such case, it may be beneficial to arrange the first phase shift element  404  such that inputted signal has a different phase when inputted into the sub-groups  210  and  220 . That is, the phase of the input signal may be different when inputted to the sub-group  210  compared with inputting the signal to the sub-group  220 . This may be due to the position of the first phase shift element  404 . As shown in  FIG. 5B , also two first phase shift elements  402 ,  404  can be used. In both examples and/or embodiments, there may be a second phase shift element T 2  between each serially connected antenna element (e.g. between antenna elements  212  and  214 ; and between antenna elements  222  and  224 ). 
     In an embodiment, the sub-groups  210 ,  220  are inputted with an input signal having the same phase. Thus, there may not be phase shift element before the input signal enters antenna elements  212 ,  222 . In such case, it may be beneficial to arrange the T 1  phase shift element between the antenna elements  222  and  224  instead of using two T 2  phase shift elements. Thus, the antenna elements  212  and  222  could output the input signal with first phase (e.g. 0 degrees), antenna element  214  could output input signal with second phase (e.g. 0+T 2 , e.g. −10 degrees) and antenna element  224  could output input signal with third phase (e.g. 0+T 1 , e.g. +10 degrees). This kind of approach may also be applicable to antenna arrays comprising more than four antenna elements. 
     In an embodiment (one example shown in  FIG. 5A ), the phase shift means of the apparatus  200  comprise at least one first phase shift element T 1  configured to shift phase of the input signal for at least one antenna element sub-group  220  and a plurality of second phase shift elements T 2  configured to shift phase of the input signal between the consecutively electrically connected antenna elements  212 ,  214  and  222 ,  224 , the at least one first phase shift element T 1  having a first phase shift value (e.g. −10 degrees) and each second phase shift element T 2  having a second phase shift value (e.g. +10 degrees), wherein the first and second phase shift values are of different size. 
     In an embodiment (one example shown in  FIG. 5A ) the antenna array comprises at least a first antenna element sub-group  210  and a second antenna element sub-group  220 , the first antenna element sub-group  210  comprising at least a first antenna element  212  and a second antenna element  214 , the second antenna element sub-group  220  comprising at least a third antenna element  222  and a fourth antenna element  224 , wherein the signal input means  240  are configured to input the input signal to the first and second antenna element sub-groups  210 ,  220 , the first and second antenna elements  212 ,  214  being consecutively electrically connected such that the input signal is configured to be inputted to the first antenna element  212  and to the second antenna element  214  via the first antenna element  212 , and the third and fourth antenna elements  222 ,  224  being consecutively electrically connected such that the input signal is configured to be inputted to the third antenna element  222  and to the fourth antenna element  224  via the third antenna element  222 , and wherein the phase shift means T 1 , T 2  are configured to shift phase of the input signal between the first and the second antenna elements  212 ,  214  such that the phase of the input signal configured to be inputted to the first antenna element  212  is different compared with the phase of the input signal configured to be inputted to the second antenna element  214 , and such that the phase of the input signal configured to be inputted to the third antenna element  222  is different compared with the phase of the input signal configured to be inputted to the fourth antenna element  224 . 
     In an embodiment, the phase shift means T 1 , T 2  are configured such that the phase of the input signal configured to be inputted to the first antenna element sub-group  210  is different compared with the phase of the input signal configured to be inputted to the second antenna element sub-group  220 . 
     In an embodiment, the phase of the input signal configured to be inputted to the first antenna element  212  is equal to the phase of the input signal configured to be inputted to the fourth antenna element  224 . 
       FIGS. 5C and 5D  illustrate some embodiments in which the input signal is inputted to the sub-groups without shifting the phase between the sub-groups. That is, the phase of the input signal for each sub-group  210 ,  220 ,  230  may be the same. Referring to  FIG. 5C , the sub-groups  210 ,  220 ,  230  may be arranged to be consecutively electrically connected to each other as shown in the  FIG. 5C . Thus, the input signal may be inputted to antenna element  212  of sub-group  210 . Then the input signal may be inputted to antenna element  224  of sub-group  220  via antenna element  212 . Then the input signal may be inputted to antenna element  236  of sub-group  230  via antenna elements  212 ,  224 . In each of the sub-groups  210 ,  220 ,  230  the input signal may be further inputted to each antenna element in a consecutive manner described above. However, the phase shift elements T 1 , T 2  may be used such that the T 1  phase shift elements are used within the sub-group  210 , T 2  phase shift elements are used with the sub-group  230 , and both T 1  and T 2  phase shift elements are used with the sub-group  220 . In an embodiment, T 1  and T 2  phase shift elements perform a different size phase shift. 
     Referring to  FIG. 5D , another example of the apparatus  200  is shown. As illustrated, the needed phase shift may also be achieved using both T 1  and T 2  with each sub-group. Also, phase shift elements T 1  and/or T 2  may be linked to each other to achieve a needed phase shift for the input signal (e.g. input signal for antenna element  226  and antenna element  222 ). 
     In an embodiment, phase shift value of the T 1  phase shift element(s) is additive inverse of phase shift value of the T 2  phase shift value. For example, if T 1  performs a +10 degrees phase shift, T 2  performs a −10 degrees phase shift. For example, if T 1  performs a +20 degrees phase shift, T 2  performs a −20 degrees phase shift. 
     In an embodiment, with reference to  FIGS. 2 and 4 , the antenna array comprises at least nine antenna elements arranged into three antenna element sub-groups  210 ,  220 ,  230 . 
     In an embodiment, the apparatus  200  is a terminal device (e.g. terminal device  120 ) of a cellular communication system. In an embodiment, the apparatus  200  is comprised in a terminal device of a cellular communication system. 
     In an embodiment, the phase shift means (e.g. first and/or second phase shift elements T 1 , T 2 ) are configured to cause the phase shifting of the input signal by causing delay to the input signal. Different types of delays may be used. The first and second phase shift elements T 1 , T 2  may be sometimes referred also to as the first and second delay elements T 1 , T 2 . In some embodiments, the first and second phase shift elements T 1 , T 2  each comprise one or more capacitors. Further, digital processing (e.g. one or more digital components, such as digital circuitry) may be used to together with the one or more capacitors to cause delay to the input signal so that the delayed (or phase shifted) input signal may be inputted to the antenna element(s) with appropriate phase shift. 
     In an embodiment, the apparatus  200  comprises a controller for controlling phase shift means (e.g. the first and second phase shift elements T 1 , T 2 ). The controller may change the first and/or second phase shift values of the first and/or second phase shift elements T 1 , T 2 . Thus, the direction of the beam(s) may be changed. So as explained, the input signal may be an RF signal that is to be transmitted via air-interface to one or more receivers. To achieve wanted beam direction, the first and/or second phase shift values of the first and second phase shift elements T 1 , T 2  may need to be modified or controlled. For example, in the example of  FIG. 3A , the selected phase shift values (i.e. T 1 =−10 deg, T 2 =+10 deg) would result in +10 degree angled beam to right. In general, beam directing using a plurality of antenna elements and a plurality of phase shift element may be known, but the solution presented herein is novel compared to known solutions. 
       FIG. 5E  illustrates the apparatus  200  according to yet another embodiment. Referring to  FIG. 200 , apparatus  200  may be configured to output a radio beam having two or more polarizations. Thus, the antenna array may be inputted with at least another input signal having a different polarization compared with the input signal inputted via the signal feed element  240 . Said another input signal may be inputted via a second signal feed element  540  of the apparatus  200 , for example. The polarization difference between the two input signals may be, for example, 45 degrees or 90 degrees. In an embodiment, the apparatus comprises second phase shift means T 3 , T 4  for shifting the phase of the second input signal. The second phase shift means may be similar to the phase shift means described above. Thus, for example, T 1  may equal to T 3  and T 2  may equal to T 4  in the example of  FIG. 5E . However, it may be possible that the T 3  and T 4  are of different size compared with T 1  and T 2  respectively. Using the same sized phase shifting may result in a needed direction of the radio beam(s). When polarization Multiple Input Multiple Output (MIMO) is used, patch antenna structure (i.e. antenna elements are patch antenna elements) may be beneficial. Therefore, in an embodiment, the antenna elements are patch antenna elements. 
     In an embodiment, the second input signal is inputted into each antenna element from a different side compared with the first input single (i.e. input signal from the signal feed element  240 ). The second input signal may further be outputted from an antenna element to the next antenna element from opposite side of the antenna element compared with the input. For example, the second input signal may be inputted into the antenna element  214  from one side and outputted to the antenna element  224  from the opposite side. 
       FIGS. 6 and 7  illustrates a flow diagram according to some embodiment. Referring to  FIG. 6 , the method comprises: acquiring, by the apparatus  200 , an input signal for an antenna array, the antenna array comprising antenna element sub-groups  210 ,  220 ,  230  and each antenna element sub-group  210 ,  220 ,  230  comprising a plurality of antenna elements (e.g. sub-group  210  comprising elements  212 ,  214 ,  216 ) (step  610 ); providing the input signal to each antenna element sub-group  210 ,  220 ,  230  (step  620 ); within each antenna element sub-group  210 ,  220 ,  230 , inputting the input signal to a first antenna element of that antenna element sub-group (step  630 ); within each antenna element sub-group  210 ,  220 ,  230 , inputting the input signal to a second antenna element of that antenna element sub-group via said first antenna element and shifting a phase of the input signal such that the phase of the input signal inputted to the second antenna element is different compared with the phase of the input signal inputted to the first antenna element (step  640 ); and outputting, via the antenna array, at least one radio beam according to the input signal (step  650 ). 
     Referring to  FIG. 7 , a method for manufacturing an apparatus, such as the apparatus  200  is shown. Said method comprising: providing an antenna array for generating radio beams, the antenna array comprising antenna element sub-groups  210 ,  220 ,  230  and each antenna element sub-group comprising a plurality of antenna elements  212 ,  214 ,  216 ,  222 ,  224 ,  226 ,  232 ,  234 ,  236  (step  710 ); providing a signal input element  240  for providing an input signal to each antenna element sub-group  210 ,  220 ,  230  and to the plurality of antenna elements within each antenna element sub-group (step  720 ); electrically connecting the antenna element sub-groups  210 .  220 ,  230  to the signal input element  240  (step  730 ); within each antenna element sub-group, electrically connecting the plurality of antenna elements to each other in a consecutive manner such that the input signal is configured to be inputted, within each antenna element sub-group, to at least one antenna element via at least one other antenna element (step  740 ); and providing a plurality of phase shift elements T 1 , T 2  between the consecutively electrically connected antenna elements within each antenna element sub-group  210 ,  220 ,  230  for shifting a phase of the input signal (step  750 ). 
       FIG. 8  illustrates a block diagram of the apparatus  200  according to an embodiment. Referring to  FIG. 8 , the apparatus  200  may at least comprise an antenna array  860  comprising the antenna element sub-groups  210 ,  220 ,  230  (i.e. two or more sub-groups). Further, the apparatus  200  may comprise the signal feed element  240 . The signal feed element  240  may be comprised in the antenna array  860  or in the radio interface  820  of the apparatus  200 , for example. 
     In an embodiment, the apparatus  200  comprises a processing circuitry  810 . The processing circuitry  810  may be configured to perform operations, such as control the first and/or second phase shift values of the antenna array  860 . In an embodiment, the processing circuitry  810  comprises at least one processor. The at least one processor may be configured with at least one memory  830  comprising a computer program  832  to carry out one or more operations of the apparatus  200  (e.g. control the first and/or second phase shift values). 
     Referring to  FIG. 8 , the memory  830  may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The memory  830  may comprise a database  834  for storing data, such as predetermined values for the first and/or second phase shift values. 
     The apparatus  200  may further comprise radio interface (TRX)  820  comprising hardware and/or software for realizing communication connectivity according to one or more communication protocols. The TRX may provide the apparatus with communication capabilities to access the radio access network, for example. The TRX may provide the apparatus  200  connection to an X2 interface, for example. The TRX may comprise standard well-known components such as an amplifier, filter, frequency-converter, (de)modulator, and encoder/decoder circuitries and one or more antennas. Thus, in some embodiments, the antenna array  860  is comprised in the radio interface  820 . However, they may also be separate, but configured to co-operate. 
     The apparatus  200  may also comprise user interface  840  comprising, for example, at least one keypad, a microphone, a touch display, a display, a speaker, etc. The user interface  840  may be used to control the respective apparatus by a user of the apparatus  200 . 
     In an embodiment, the apparatus  200  may be or be comprised in a base station (also called a base transceiver station, a Node B, a radio network controller, or an evolved Node B, for example). The apparatus  1000  may be and/or be comprised in the network node  102 , for example. In an embodiment, the apparatus  200  is comprised in the terminal device  120  or some other terminal device. In an embodiment, the apparatus  200  is a terminal device of a cellular communication network. 
     In an embodiment, the apparatus  200  comprises a printed circuit board (PCB) (e.g. dual layer PCB). The antenna elements (e.g. elements  212 ,  214 ,  216 ,  222 ,  224 ,  226 ,  232 ,  234 ,  236 ) and/or the phase shift elements T 1 , T 2  may be printed on the PCB. Further, the signal feed element  240  may be at least partially printed on the PCB meaning that it may additionally comprise a signal port that is not printed. However, in some cases the signal feed element  240  may be printed on the PCB and connected to, for example, the processing circuitry  810  that may be configured to provide the input signal to the signal feed element  240 . If further signal inputs and/or phase shift elements are used, they may also be printed on to the PCB. 
     Let us further discuss about split loss of the described apparatus  200 . Split loss may be generally be calculated from the following equation: 
     Split loss=10 Log(Pin/Pout)=−10 Log(1/N), wherein Pin equals to power at SUM(Σ) port, Pout equals to power at any 1 of N outputs, and N equals to number of output ports. Therefore, the following table 1 may be formed: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Split loss equalling to number of output ports. 
               
            
           
           
               
               
               
            
               
                   
                 Output ports (N) 
                 Split Loss (decibel (dB)) 
               
               
                   
                   
               
               
                   
                 2 
                 3.01 
               
               
                   
                 3 
                 4.77 
               
               
                   
                 4 
                 6.02 
               
               
                   
                 5 
                 6.99 
               
               
                   
                 6 
                 7.78 
               
               
                   
                 8 
                 9.03 
               
               
                   
                 9 
                 9.54 
               
               
                   
                   
               
            
           
         
       
     
     As table 1 indicates, the path loss in parallel construction is different compared to parallel/serial construction of which numerous examples are given above. For example, nine element parallel array (e.g. nine antenna elements are arranged in parallel with each other) would have some 10 dB loss in each antenna element input. There may be some means to taper the powers, but generally the loss would be quite high. However, using the parallel/serial construction as shown for example in  FIG. 2 , the path loss due to splitting may be made smaller. That is, using nine antenna elements and arranging them as in  FIG. 2 , for example, the path loss would be about 4.77 dB for the first row (i.e. elements  212 ,  222 ,  232 ) and additional about 3 dB loss for the second row (i.e. elements  214 ,  224 ,  234 ) and further about 3 dB additional loss for the last row (i.e. elements  216 ,  226 ,  236 ). The phase shifters (e.g. T 1  and T 2 ) may generate further path loss. 
     As used in this application, the term ‘circuitry’ refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and soft-ware (and/or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of ‘circuitry’ applies to all uses of this term in this application. As a further example, as used in this application, the term ‘circuitry’ would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and/or firmware. The term ‘circuitry’ would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device. 
     In an embodiment, at least some of the processes described in connection with  FIGS. 1 to 7  may be carried out by an apparatus comprising corresponding means for carrying out at least some of the described processes. Some example means for carrying out the processes may include at least one of the following: detector, processor (including dual-core and multiple-core processors), digital signal processor, controller, receiver, transmitter, encoder, decoder, memory, RAM, ROM, software, firmware, display, user interface, display circuitry, user interface circuitry, user interface software, display software, circuit, antenna, antenna circuitry, and circuitry. In an embodiment, the at least one processor, the memory, and the computer program code form processing means or comprises one or more computer program code portions for carrying out one or more operations according to any one of the embodiments of  FIGS. 1 to 7  or operations thereof. 
     According to yet another embodiment, the apparatus carrying out the embodiments comprises a circuitry including at least one processor and at least one memory including computer program code. When activated, the circuitry causes the apparatus to perform at least some of the functionalities according to any one of the embodiments of  FIGS. 1 to 7 , or operations thereof. 
     At least some of the techniques and methods described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the apparatus(es) of embodiments may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation can be carried out through modules of at least one chip set (e.g. procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case, it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of the systems described herein may be rearranged and/or complemented by additional components in order to facilitate the achievements of the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art. 
     Embodiments as described may also be carried out in the form of a computer process defined by a computer program or portions thereof. Embodiments of the methods described in connection with  FIGS. 1 to 7  may be carried out by executing at least one portion of a computer program comprising corresponding instructions. The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. For example, the computer program may be stored on a computer program distribution medium readable by a computer or a processor. The computer program medium may be, for example but not limited to, a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example. The computer program medium may be a non-transitory medium, for example. Coding of software for carrying out the embodiments as shown and described is well within the scope of a person of ordinary skill in the art. In an embodiment, a computer-readable medium comprises said computer program. 
     Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.