Patent Publication Number: US-2023136183-A1

Title: Antenna for a wireless communication device and such a device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/089436, filed on May 9, 2020, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to wireless communications in general. More specifically, the present disclosure relates to an antenna for a wireless communication device as well as such a wireless communication device. 
     BACKGROUND 
     The wireless fidelity (Wi-Fi) protocol was developed to provide services to numerous users at arbitrary locations within the coverage area of a Wi-Fi access point (AP; also referred to as base station). In order to enable an access point to cover a large region of its environment, its antenna should have an omnidirectional radiation pattern. Moreover, for improving the multiple-input multiple-output (MIMO) performance of an access point, it is known to provide an access point with vertically and horizontally polarized antennas (also known as V-Pol and H-Pol antennas). 
     Access points used, for instance, in offices (also known as enterprise APs) are often installed on the ceiling of a respective office room. In order to decrease the number of APs in an office deployment, each AP needs to cover a large area. Consequently, such an AP needs to have a low radiating angle so that clients underneath the AP are provided with a sufficient signal strength. This requirement faces considerable challenges for low profile APs, i.e., APs having a small build height. In such an AP due to the limited vertical dimensions of the housing of the AP the radiation elements must be placed at a very small distance from the AP&#39;s ground plan, which causes the radiation beam to tilt perpendicularly to the ground plan. Consequently, these radiation elements provide a high radiation angle (above the ground) and small coverage area. The requirements of a compact form-factor, a low profile and a low radiation angle are partially conflicting and therefore difficult to achieve with a horizontal dipole array. Moreover, the antenna(s) of an AP should have a high gain (&gt;4 dBi). However, reducing the height of an antenna also reduces its gain, because the area covered by the antenna increases. 
     Thus, there is a need for an improved antenna with a low radiating angle and a small build height as well as a for a wireless communication device comprising such an antenna. 
     SUMMARY 
     The present disclosure provides an improved antenna for a wireless communication device with a low radiating angle and a small build height as well as a wireless communication device comprising such an antenna. 
     The implementations of the present disclosure are achieved by the subject matter of the independent claims. Further implementations are apparent from the dependent claims, the description and the figures. 
     According to a first aspect an antenna for a wireless device is provided. The antenna comprises an electrically conductive radiation structure for generating electromagnetic waves, a feeding network for feeding a radio frequency (RF) signal to the electrically conductive radiation structure for generating the electromagnetic waves and a grounding structure for guiding the electromagnetic waves generated by the electrically conductive radiation structure. The electrically conductive radiation structure defines a plurality of radially extending radiation slots. Each of the plurality of radially extending radiating slots has an open outer end at a perimeter of the electrically conductive radiation structure and defines a radiation portion of the electrically conductive radiation structure. The feeding network comprises a plurality of feeding arms configured to feed the RF signal into each of the plurality of radiation portions of the electrically conductive radiation structure for exciting each of the radiation portions and the radially extending radiation slots to emit electromagnetic waves. The grounding structure defines an electrically conductive grounding surface, wherein the electrically conductive grounding surface is spaced from and faces the plurality of radiation portions of the electrically conductive radiation structure for guiding the electromagnetic waves emitted by the plurality of radiation portions. Thus, advantageously, an improved antenna with a low radiating angle and a small build height is provided. 
     In a further possible implementation of the first aspect, the plurality of radiation portions of the electrically conductive radiation structure are at least partially coplanar, i.e., extend at least partially in the same plane. 
     In a further possible implementation of the first aspect, the electrically conductive grounding surface extends at least partially in parallel to the plurality of radiation portions of the electrically conductive radiation structure. 
     In a further possible implementation of the first aspect, the electrically conductive radiation structure is radially symmetric. 
     In a further possible implementation of the first aspect, the electrically conductive radiation structure defines at least three radially extending radiation slots, wherein the at least three radially extending radiation slots define at least three radiation portions of the electrically conductive radiation structure. 
     In a further possible implementation of the first aspect, the plurality of radially extending radiation slots and the plurality of radiation portions are uniformly distributed around a centre of the electrically conductive radiation structure. 
     In a further possible implementation of the first aspect, each of the plurality of feeding arms is arranged and configured such that at least a feeding arm portion of each feeding arm is inductively or galvanically coupled to a respective radiation portion of the electrically conductive radiation structure for exciting the respective radiation portion to emit electromagnetic waves. 
     In a further possible implementation of the first aspect, each feeding arm portion extends substantially perpendicular to a respective radially extending radiation slot. 
     In a further possible implementation of the first aspect, the antenna further comprises an electrically non-conductive substrate, wherein the electrically conductive radiation structure and the feeding network are arranged on different sides of the non-conductive substrate and wherein electrically non-conductive material of the electrically non-conductive substrate at least partially fills the plurality of radially extending radiation slots. 
     In a further possible implementation of the first aspect, each radially extending radiation slot extends from its open outer end at the perimeter of the electrically conductive radiation structure to an inner end having a finite radius. In other words, for each radially extending radiation slot there is a finite distance between the inner end of the respective slot and the centre of the electrically conductive radiation structure, which is filled by the material of the electrically conductive radiation structure. 
     In a further possible implementation of the first aspect, the electrically conductive radiation structure further defines a plurality of radially extending de-coupling slots for de-coupling the plurality of radiation portions of the electrically conductive radiation structure, wherein each of the radially extending de-coupling slots has an open outer end at the perimeter of the electrically conductive radiation structure. 
     In a further possible implementation of the first aspect, the electrically conductive radiation structure further defines a respective recess at a respective inner radius of a radially extending de-coupling slot, wherein each recess has a width larger than a width of the respective radially extending de-coupling slot. 
     In a further possible implementation of the first aspect, each radially extending de-coupling slot is arranged half-way between two adjacent radially extending radiation slots. 
     In a further possible implementation of the first aspect, for each radially extending de-coupling slot the antenna further comprises one or more metal strips, wherein the one or more metal strips are arranged to extend radially adjacent to a respective radially extending de-coupling slot. 
     In a further possible implementation of the first aspect, for each feeding arm the antenna further comprises a switch in series, wherein all of the plurality of radiation portions of the electrically conductive radiation structure are excited by the RF signal provided by the feeding network for providing omni-directional electromagnetic waves, when all of the plurality of switches are closed, and wherein only a subset of the plurality of radiation portions of the electrically conductive radiation structure are excited by the RF signal provided by the feeding network, when a subset of the plurality of switches are open for providing directional electromagnetic waves. Advantageously, this allows to selectively provide different radiation patterns with the antenna. 
     In a further possible implementation of the first aspect, for each feeding arm the antenna further comprises a switch in parallel electrically connected to the electrically conductive grounding surface, wherein all of the plurality of radiation portions of the electrically conductive radiation structure are excited by the RF signal provided by the feeding network for providing omni-directional electromagnetic waves, when all of the plurality of switches are open, and wherein a subset of the plurality of radiation portions of the electrically conductive radiation structure are excited by the RF signal provided by the feeding network, when a subset of the plurality of switches are closed for providing directional electromagnetic waves. Advantageously, this allows to selectively provide different radiation patterns with the antenna. 
     According to a second aspect a wireless communication device is provided comprising one or more antennas according to the first aspect. 
     In a further possible implementation of the second aspect, the wireless communication device is a Wi-Fi access point or base station. 
     Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which: 
         FIG.  1    is a perspective view of an antenna according to an embodiment; 
         FIG.  2    is a more detailed perspective view a portion of the antenna of  FIG.  1   ; 
         FIG.  3    is a bottom view of the antenna portion of  FIG.  2   ; 
         FIG.  4    is a top view of the antenna portion of  FIG.  2   ; 
         FIG.  5   a    is a perspective view of a radiation pattern of an antenna according to an embodiment; 
         FIG.  5   b    is a cross-sectional view of the radiation pattern of  FIG.  5   a    for a constant elevation angle; 
         FIG.  6   a    is a top view of a feeding network of an antenna according to an embodiment including switches in parallel; 
         FIG.  6   b    is a more detailed view of a portion of the feeding network of  FIG.  6     a;    
         FIGS.  7   a - d    show for the embodiment of the feeding network of  FIGS.  6   a  and  6   b    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant azimuth angle, a cross-sectional view of the radiation pattern for a constant elevation angle and a graph illustrating the antenna matching as a function of frequency; 
         FIG.  8    shows the feeding network of  FIG.  6   a    with two switches closed and the other switches open; 
         FIGS.  9   a - d    show for the embodiment of the feeding network of  FIG.  8    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant azimuth angle, a cross-sectional view of the radiation pattern for a constant elevation angle and a graph illustrating the antenna matching as a function of frequency; 
         FIG.  10    shows the feeding network of  FIG.  6   a    with three switches closed and the other switches open; 
         FIGS.  11   a - d    show for the embodiment of the feeding network of  FIG.  10    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant azimuth angle, a cross-sectional view of the radiation pattern for a constant elevation angle and a graph illustrating the antenna matching as a function of frequency; 
         FIG.  12   a    is a top view of a feeding network of an antenna according to an embodiment including switches in series; 
         FIG.  12   b    is a more detailed view of a portion of the feeding network of  FIG.  12     a;    
         FIGS.  13   a - d    show for the embodiment of the feeding network of  FIGS.  12   a  and  12   b    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant azimuth angle, a cross-sectional view of the radiation pattern for a constant elevation angle and a graph illustrating the antenna matching as a function of frequency; 
         FIG.  14    shows the feeding network of  FIG.  12   a    with four switches closed and the other switches open; 
         FIGS.  15   a - d    show for the embodiment of the feeding network of  FIG.  14    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant azimuth angle, a cross-sectional view of the radiation pattern for a constant elevation angle and a graph illustrating the antenna matching as a function of frequency; 
         FIG.  16    shows the feeding network of  FIG.  12   a    with three switches closed and the other switches open; and 
         FIGS.  17   a - d    show for the embodiment of the feeding network of  FIG.  16    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant azimuth angle, a cross-sectional view of the radiation pattern for a constant elevation angle and a graph illustrating the antenna matching as a function of frequency. 
     
    
    
     In the following identical reference signs refer to identical or at least functionally equivalent features. 
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, exemplary aspects of embodiments of the present disclosure or exemplary aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims. 
     For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of exemplary method steps are described, a corresponding device may include one or a plurality of units, e.g., functional units, to perform the described one or plurality of method steps (e.g., one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if an exemplary apparatus is described based on one or a plurality of units, e.g., functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g., one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise. 
       FIG.  1    shows a perspective view of an embodiment of an antenna  100  for a wireless communication device, such as a Wi-Fi access point (sometimes also referred to as base station). Such a Wi-Fi access point may include in addition to the antenna  100  a housing for housing the antenna as well as electronic components for controlling the antenna  100 . In an embodiment, such a Wi-Fi access point may be configured to be mounted on the ceiling of a room in order to communicate with Wi-Fi stations within the room, i.e., underneath the Wi-Fi access point. For such an embodiment,  FIG.  1    shows a perspective view of the antenna of such an Wi-Fi access point from below. 
     The antenna  100  comprises a first main portion  101  in the form of an electrically conductive grounding structure  101  and a second main portion  110 , which is illustrated in more detail in  FIGS.  2 ,  3  and  4    and which comprises an electrically conductive radiation structure  120  and a feeding network  130 . As can be taken from  FIGS.  1  and  2   , the second main portion  110  of the antenna  100  may further comprise an electrically non-conductive substrate  140 , wherein the electrically conductive radiation structure  120  and the feeding network  130  are arranged on different sides of the electrically non-conductive substrate  140 , which may comprise, for instance, an electrically non-conductive plastic material. In the embodiment shown in  FIGS.  1  and  2   , the electrically non-conductive substrate  140  substantially has the shape of a circular disk. In an embodiment, the thickness of the electrically non-conductive substrate  140  may be, for instance, in the range from 0.5 to 1.5 mm. In an embodiment, the diameter of the disc-shaped electrically non-conductive substrate  140  may be, for instance, in the range from 40 to 60 mm. 
     As can be taken in particular from  FIGS.  2 ,  3  and  4    and as will be described in more detail below, the second main portion  110 , including the electrically conductive radiation structure  120 , the feeding network  130  and the electrically non-conductive substrate  140 , may be substantially radially symmetric, wherein the symmetry axis is defined by the central axis of the circular disk-shaped electrically non-conductive substrate  140 . 
     Generally, as will be described in more detail below, the electrically conductive radiation structure  120  is configured to generate electromagnetic waves, the feeding network  130  is configured to feed an RF signal to the electrically conductive radiation structure  120  for generating the electromagnetic waves and the grounding structure  101  is configured to guide the electromagnetic waves generated by the electrically conductive radiation structure  120 . 
     In the embodiment shown in  FIG.  1    the guiding function is provided by an electrically conductive grounding structure  101  in the form of a square-shaped metal plate  101 , which defines an electrically conductive grounding surface facing the second main portion  110  of the antenna  100 . In other embodiments, the shape of the electrically conductive grounding structure  101  and or the shape of the electrically non-conductive substrate  140  may be different to the shapes shown in  FIGS.  1  and  2   . For instance, the electrically conductive grounding structure  101  may have a circular disk shape as well. As will be appreciated from  FIG.  1   , the electrically conductive grounding structure  101  may have substantially larger dimensions than the disc-shaped electrically non-conductive substrate  140 . 
     In the perspective view of  FIG.  1    the second main portion  110 , including the electrically conductive radiation structure  120 , the feeding network  130  and the electrically non-conductive substrate  140 , is illustrated above the electrically conductive grounding surface defined by the electrically conductive grounding surface  101  in the form of the square-shaped metal plate  101 . More specifically, the central axis of the circular disk-shaped electrically non-conductive substrate  140 , which as described above may also be the symmetry axis of the electrically conductive radiation structure  120  and/or the feeding network  130 , extends through the center of the square-shaped electrically conductive grounding structure  101 . In an embodiment, the distance between the electrically non-conductive substrate  140  and the second main portion  110 , including the electrically conductive radiation structure  120 , the feeding network  130  and the electrically non-conductive substrate  140 , along the symmetry axis may be, for instance, in the range from 12 to 30 mm. 
     As will be described in more detail below, the antenna  100  is configured to emit electromagnetic waves primarily in the direction of the space relative the electrically conductive grounding surface of the electrically conductive grounding structure  101  where the second main portion  110 , including the electrically conductive radiation structure  120 , the feeding network  130  and the electrically non-conductive substrate  140 , is located and beyond. Thus, in an embodiment, where the antenna  100  is a component of a Wi-Fi access point mounted on the ceiling of the room, the antenna is configured to emit electromagnetic waves primarily in the direction of the room below the Wi-Fi access point. 
     As can be taken in particular from  FIGS.  2  and  3   , the electrically conductive radiation structure  120  comprises, i.e., defines a plurality of radially extending radiation slots  121   a - f . In the exemplary embodiment shown in the figures, the electrically conductive radiation structure  120  comprises six radially extending radiation slots  121   a - f . However, in other embodiments the number of radially extending radiation slots  121   a - f  may be smaller or larger than 6. In an embodiment, the electrically conductive radiation structure  120  comprises at least three radially extending radiation slots  121   a - f.    
     In the embodiment shown in the figures the six radially extending radiation slots  121   a - f  are uniformly distributed around the center  125  of the electrically conductive radiation structure  120 , which defines the symmetry axis of the second portion  110  of the antenna  100 . In other words, for the embodiment with six radially extending radiation slots  121   a - f  two respective adjacent slots define a respective angle of about 60° therebetween. For instance, a first radially extending radiation slot  121   a  and a second radially extending slot  121   b  is about 60°. In other embodiments, however, the radially extending radiation slots  121   a - f  may be distributed around the center  125  of the electrically conductive radiation structure  120  in a non-uniform manner. 
     Each of the plurality of radially extending radiating slots  121   a - f  has an open outer end at a perimeter  127  of the electrically conductive radiation structure  120 . In the embodiment shown in  FIGS.  1  to  4   , each slot does not extend from its open outer end at the perimeter  127  of the electrically conductive radiation structure  120  completely inward, i.e., up to the center  125  of the electrically conductive radiation structure  120 , but to an inner end thereof having a finite inner radius. In an embodiment, the ratio between the maximal outer radius of the perimeter to the inner radius of the inner end of a respective slot  121   a - f  may be, for instance, in the range from 2 to 5. As illustrated, for instance, in  FIG.  3   , electrically non-conductive material of the electrically non-conductive substrate  140  may fill at least partially the plurality of radially extending radiation slots  121   a - f  defined by the electrically conductive radiation structure  120 . Moreover, in an embodiment, the electrically non-conductive substrate  140  may define the outer boundary, i.e., the perimeter  127  of the electrically conductive radiation structure  120 . 
     As can be taken in particular from  FIG.  3   , each radially extending radiation slot  121   a - f  defines a radiation portion of the electrically conductive radiation structure  120 . For instance, the first radially extending radiation slot  121   a  defines a first radiation portion  122   a  of the electrically conductive radiation structure  120 , which in the top view of  FIG.  3    is bounded by the notional lines A and B. For the sake of clarity only the radiation portion  122   a  defined by the first radially extending radiation slot  121   a  is illustrated in  FIG.  3   . As will be appreciated, however, five additional radiation portions are defined by the other radially extending radiation slots  121   b - f . In the embodiment shown in the figures, the plurality of radiation portions of the electrically conductive radiation structure  120  are coplanar, i.e., extend in the same plane. As can be taken from  FIG.  1    this plane, i.e., the common plane of the plurality of radiation portions of the electrically conductive radiation structure  120 , may be substantially parallel to the electrically conductive grounding surface defined by the electrically conductive grounding structure  101 . Thus, the electrically conductive grounding surface defined by the electrically conductive grounding structure  101  is spaced from and faces the plurality of radiation portions of the electrically conductive radiation structure  120  for guiding the electromagnetic waves emitted by the plurality of radiation portions, such as the radiation portion  122   a  of the electrically conductive radiation structure  120 . 
     In an embodiment, the electrically conductive radiation structure  120  further defines a plurality of radially extending de-coupling slots  123   a - f  for de-coupling the plurality of radiation portions, such as the first radiation portion  122   a  of the electrically conductive radiation structure  120 . For instance, a first radially extending de-coupling slot  123   a  and a second radially extending de-coupling slot  123   b  de-couples the radiation portion  122   a  bounded by the notional lines A and B from the neighbouring radiation portions defined by the radially extending radiation slots  121   b  and  121   f , respectively. As can be taken from  FIG.  3   , like the plurality of radially extending radiation slots  121   a - f  the plurality of radially extending de-coupling slots may be distributed uniformly around the centre  125  of the electrically conductive radiation structure  120 . Thus, in the embodiment shown in  FIG.  3    with six radially extending de-coupling slots  123   a - f  two respective adjacent slots define a respective angle of about 60° therebetween. Thus, the embodiment shown in  FIG.  3   , each radially extending de-coupling slot  123   a - f  is arranged half-way between two adjacent radially extending radiation slots  121   a - f.    
     In the embodiment shown in the figures, each of the radially extending de-coupling slots  123   a - f  has an open outer end at the perimeter  127  of the electrically conductive radiation structure  120  and extends to a finite inner radius. As can be taken, for instance, from  FIG.  3   , the inner radius of each of the plurality of radially extending de-coupling slots  123   a - f  may be similar to the inner radius of each of the plurality of radially extending radiation slots  121   a - f . In an embodiment, the inner radius of the plurality of radially extending de-coupling slots  123   a - f  may be, for instance, in the range from 5 to 8 mm. In an embodiment, the inner radius of the plurality of radially extending radiation slots  121   a - f  may be, for instance, in the range from 6 to 9 mm. 
     As illustrated in  FIG.  3   , the width of each of the plurality of radially extending de-coupling slots  123   a - f  may be smaller than the width of each of the plurality of radially extending radiation slots  121   a - f . In an embodiment, the width of each of the plurality of radially extending de-coupling slots  123   a - f  may be, for instance, in the range from 0.3 to 1 mm. In an embodiment, the width of each of the plurality of radially extending radiation slots  121   a - f  may be, for instance, in the range from 0.5 to 1.2 mm. 
     In an embodiment, the electrically conductive radiation structure may further define a respective recess  124   a - f  at a respective inner radius of a respective radially extending de-coupling slot  123   a - f , wherein each recess  124   a - f  has a width larger than a width of the respective radially extending de-coupling slot  123   a - f . As in the case of the plurality of radiation slots  121  electrically non-conductive material of the electrically non-conductive substrate  140  may fill at least partially the plurality of radially extending de-coupling slots  123   a - f  defined by the electrically conductive radiation structure  120 , including the plurality of recesses  124   a - f  defined at the inner ends thereof. In an embodiment, the dimensions of each respective recess  124   a - f  may be, for instance, in the range from 0.2 to 2 mm. 
     The feeding network  130 , which is illustrated in more detail in  FIG.  4   , comprises a plurality of feeding arms  131   a - f  configured to feed a RF signal into each of the plurality of radiation portions, such as the radiation potion  122   a , of the electrically conductive radiation structure  120  for exciting each of the radiation portions and, thus, the radially extending radiation slots  121   a - f  to emit electromagnetic waves based on the RF input signal. As can be taken from  FIG.  4   , the plurality of feeding arms  131   a - f  are connected at a common center, i.e., a feeding port of the feeding network  130 , which in the embodiment shown in the figures is arranged on the symmetry axis of the antenna  100 . Further electronic components of the antenna  100  (not shown in the figures) feed the RF input signal into the feeding port at the center of the feeding network  130 . From there the RF input signal propagates along the respective feeding arms  131   a - f  in an outward direction. As the RF signal travels from the feeding port at the center along the respective feeding arms  131   a - f  outwards it is coupled into the respective radiation portion of the electrically conductive radiation structure  120  and, thereby, excites the respective radiation portion, such as the radiation portion  122   a  to emit electromagnetic waves based on the RF signal. In other words, each of the plurality of feeding arms  131   a - f  may be arranged and/or configured such that at least a feeding arm portion of each feeding arm  131   a - f  is inductively or galvanically coupled to a respective radiation portion of the electrically conductive radiation structure  120  for exciting the respective radiation portion to emit electromagnetic waves. 
     As can be taken from  FIG.  2   , each feeding arm  131   a - f  may have a feeding arm portion, which extends substantially perpendicular to a respective radially extending radiation slot  121   a - f  and is configured to couple the RF signal into the respective radiation portion of the electrically conductive radiation structure  120  and thereby excite the respective radiation portion. For instance, in the perspective view shown in  FIG.  2   , the feeding arm  131   a  has a portion extending underneath of and perpendicular to the radially extending radiation slot  121   a . Although material of the electrically non-conductive substrate  140  is located between the feeding arm  131  and the radiation portion  122   a  defined by the radially extending radiation slot  121   a , the feeding arm  131  inductively couples the RF signal into the radiation portion  122   a  defined by the radially extending radiation slot  121   a . Thereby, the radiation portion  122   a  defined by the radially extending radiation slot  121   a  is excited to emit electromagnetic waves in response to the RF signal. As already described above, the electromagnetic waves generated by the radiation portion  122   a  (as well as the other radiation portions of the electrically conductive radiation structure  120 ) in response to the RF signal are guided, in particular reflected by the electrically conductive grounding surface defined by the electrically conductive grounding structure  101  in the form of the square-shaped metal plate  101 . 
     As illustrated in  FIG.  4   , at the respective outer end of each of the plurality of feeding arms  131   a - f  a respective grounding contact  132   a - f  may be provided. The purpose of the respective grounding contact  132   a - f  is to connect the respective feeding arm  131   a - f  to the ground. 
     In an embodiment, the antenna  100  may further comprise for each radially extending de-coupling slot  123   a - f  one or more metal strips  137   a - f ,  137   a ′-f, which are arranged to extend radially adjacent to a respective radially extending de-coupling slot  123   a - f . As can be taken from the embodiment shown in  FIG.  4   , the antenna  100  may comprise two metal strips for each radially extending de-coupling slot  123   a - f , which are affixed to the substrate  140  on the same side as the feeding network  130 . Thereby, the metal strips  137   a - f ,  137   a ′-f may improve the de-coupling effect provided by the plurality of radially extending de-coupling slots  123   a - f  of the electrically conductive radiation structure  120 . 
     As can be taken from  FIG.  2   , in an embodiment, the antenna  100  may further comprise for each radially extending radiation slots  121   a - f  a plurality of electrically conductive guiding elements  141   a - f  configured to guide the electromagnetic waves emitted by the plurality of radiation portions of the electrically conductive radiation structure  120 . In the embodiment shown in  FIG.  2   , a respective guiding element  141   a - f  is arranged along the radially outward extension of a respective radially extending radiation slot  121   a - f . Each guiding element  141   a - f  may be arranged at the outer rim of the substrate  140  and on the same side of the substrate  140  as the electrically conductive radiation structure  120 . 
       FIG.  5   a    is a perspective view of a radiation pattern of the antenna  100  described above in the context of  FIGS.  1  to  4   .  FIG.  5   b    is a cross-sectional view of the radiation pattern of  FIG.  5   a    for a constant elevation angle, i.e., an azimuth pattern at an angle of 60° relative to the vertical axis. 
     In further embodiments shown in the following figures, the feeding network  130  may further comprise a plurality of switches which allow to selectively couple or de-couple one or more of the plurality of radiation portions of the electrically conductive radiation structure  120  to/from the feeding network  130  and, thereby, produce a more directed radiation pattern in comparison to the radiation pattern shown in  FIGS.  5   a  and  5   b   , which is substantially constant with respect to the horizontal azimuth angle (as can be taken from  FIG.  5   b   ). 
     A first embodiment of the feeding network  130  using a plurality of switches  138   a, b  in parallel for selectively generating different directional radiation patterns is illustrated in  FIGS.  6   a  and  6   b   , which show a bottom view of the feeding network  130  of the antenna  100  arranged on one side of the support  140  and a more detailed view of a portion thereof (illustrated by the rectangle in  FIG.  6   a   ). For the sake of clarity  FIGS.  6   a  and  6   b    only explicitly shows two switches  138   a, b  for two of the feeding arms  131   a, b . It will be appreciated, however, that according to an embodiment a switch, such as the switches  138   a, b  explicitly shown in  FIGS.  6   a  and  6   b   , may be provided for each of the feeding arms  131   a - f  of the feeding network  130 .  FIGS.  7   a - d    show for such an embodiment of the feeding network of  FIGS.  6   a  and  6   b   , i.e., where a switch is provided for each of the feeding arms  131   a - f  and all switches are open, i.e., inactive, a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant elevation angle, a cross-sectional view of the radiation pattern for a constant azimuth angle and a graph illustrating the antenna matching as a function of frequency. 
     For the embodiment shown in  FIGS.  6   a  and  6   b    each switch, including the switches  138   a, b  explicitly shown, is electrically connected to the electrically conductive grounding surface  101 , e.g., by means of a grounding pad in parallel to a respective feeding arm  131   a - f  of the feeding network  130 . In other words, in case a switch  138   a, b  is closed, i.e., active, the RF signal is shortened via the respective switch  138   a, b  to the grounding structure  101  and, thus, does not propagate along the respective feeding arm  131   a - f  so that consequently the respective feeding arm  131   a - f  does not excite the respective radiation portion of the radiation structure  120 . Thus, in an embodiment, all of the plurality of radiation portions, including the radiation portion  124   a  of the electrically conductive radiation structure  120  are excited by the RF signal provided by the feeding network  130 , when all of the plurality of parallel switches  138   a, b  are open (as shown in  FIGS.  7   a - d   ), wherein only a subset (as will be described in more detail further below in the context of the embodiment shown in  FIGS.  8  and  9     a - d ) of the plurality of radiation portions of the electrically conductive radiation structure  120  are excited by the RF signal provided by the feeding network  130 , when a subset of the plurality of parallel switches  138   a, b  are closed, i.e., active. Each switch  138   a, b  may comprise, for instance, a diode. 
       FIG.  8    shows the feeding network  130  of  FIG.  6   a    with two switches  138   a, b  closed and the other switches open.  FIGS.  9   a - d    show for the embodiment of the feeding network  130  of  FIG.  8    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant elevation angle, a cross-sectional view of the radiation pattern for a constant-azimuth angle and a graph illustrating the antenna matching as a function of frequency. As will be appreciated, because only two of the switches, namely the switches  138   a, b  are closed, the radiation patterns shown in  FIGS.  9   a - c    are more directive than the radiation patterns shown for the “omni-directional” case in  FIGS.  7   a   - c.    
       FIG.  10    shows the feeding network  130  of  FIG.  6   a    with three switches  138   a - c  closed and the other switches open.  FIGS.  11   a - d    show for the embodiment of the feeding network  130  of  FIG.  10    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant elevation angle, a cross-sectional view of the radiation pattern for a constant azimuth angle and a graph illustrating the antenna matching as a function of frequency. As will be appreciated, because half of the switches, namely the switches  138   a - c  are closed, the radiation patterns shown in  FIGS.  11   a - c    are more directive than the radiation patterns shown for the “omni-directional” case in  FIGS.  7   a - c   , but less directive than the radiation patterns shown in  FIGS.  9   a - c    for the case of two switches  138   a, b  closed. 
     A further embodiment of the feeding network  130  using a plurality of switches  139   a - f  not in parallel (as in the previous embodiments), but in series for selectively generating different directional radiation patterns is illustrated in  FIGS.  12   a  and  12   b   , which show a bottom view of the feeding network  130  of the antenna  100  arranged on one side of the support  140  and a more detailed view of the central portion thereof.  FIGS.  13   a - d    show for the embodiment of the feeding network of  FIGS.  12   a  and  12   b    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant elevation angle, a cross-sectional view of the radiation pattern for a constant azimuth angle and a graph illustrating the antenna matching as a function of frequency. 
     For the embodiment shown in  FIGS.  12   a  and  12   b    each switch  139   a - f  is arranged in series between the feeding port at the center of the feeding network  130  and a respective feeding arm  131   a - f . In other words, in case a switch  139   a - f  is closed, i.e., active, the RF signal propagates along the respective feeding arm  131   a - f  so that consequently the respective feeding arm  131   a - f  excites the respective radiation portion of the radiation structure  120 , as described in great detail further above. Thus, in an embodiment, all of the plurality of radiation portions, including the radiation portion  124   a  of the electrically conductive radiation structure  120  are excited by the RF signal provided by the feeding network  130 , when all of the plurality of switches  139   a - f  are closed, i.e., active, while only a subset of the plurality of radiation portions of the electrically conductive radiation structure  120  are excited by the RF signal provided by the feeding network  130 , when a subset of the plurality of switches  139   a - f  are open (as will be described in more detail further below in the context of the embodiment shown in  FIGS.  14  and  15     a - d  as well as the embodiment shown in  FIGS.  16  and  17     a - d ). Each switch  139   a - f  may comprise, for instance, a diode. 
       FIG.  14    shows the feeding network  130  of  FIG.  12   a    with four switches  139   a - d  closed and the other switches  139   e ,  139   f  open.  FIGS.  15   a - d    show for the embodiment of the feeding network  130  of  FIG.  14    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant elevation angle, a cross-sectional view of the radiation pattern for a constant azimuth angle and a graph illustrating the antenna matching as a function of frequency. As will be appreciated, because four of the switches, namely the switches  139   a - d  are closed, the radiation patterns shown in  FIGS.  15   a - c    are more directive than the radiation patterns shown for the “omni-directional” case in  FIGS.  13   a - c   , namely in the directions defined by the switches  139   a - d.    
       FIG.  16    shows the feeding network  130  of  FIG.  12   a    with three switches  139   a - c  closed and the other switches  139   d - f  open.  FIGS.  17   a - d    show for the embodiment of the feeding network  130  of  FIG.  16    a perspective view of the radiation pattern, a cross-sectional view of the radiation pattern for a constant elevation angle, a cross-sectional view of the radiation pattern for a constant azimuth angle and a graph illustrating the antenna matching as a function of frequency. As will be appreciated, because only half of the switches, namely the switches  139   a - c  are closed, the radiation patterns shown in  FIGS.  17   a - c    are more directive than the radiation patterns shown for the “omni-directional” case in  FIGS.  13   a - c    and the radiation patterns shown in  FIGS.  15   a - c    for the case of four switches  139   a - d  closed. 
     The person skilled in the art will understand that the “blocks” (“units”) of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual “units” in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit=step). 
     In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms. 
     The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments. 
     In addition, functional units in the embodiments of the present disclosure may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.