TECHNICAL FIELD

The present disclosure relates to an antenna and an antenna array, and more particularly but not exclusively, to an antenna and an antenna array for millimetre-wave wireless communication.

BACKGROUND

Antennas with high gain and wideband features are in demand. This is particularly so in millimetre wave wireless applications, such as point to point wireless 5G applications, because millimetre waves suffer high atmospheric propagation loss and have limited transmission power. However, considering the increasing loss of transmission lines and the small dimensions of millimetre wave antennas and components, the realization of a large-size antenna array with a wide operating band and high gain performance simultaneously is a challenging task in millimetre wave antenna design.

For a large size array consisting of many radiating elements, the maximum achievable gain of the array is mainly restricted by the insertion loss of the feed network. Although a shorter length of the transmitting path with lower loss can be obtained by a series feed network, the corresponding narrow bandwidth is not acceptable for wideband millimetre wave applications. As a result, parallel feed networks comprising various transmission line structures have been widely applied to millimetre wave antenna arrays.

Existing antenna designs do not provide a satisfactory solution. For example, in one case, a microstrip line with a substrate integrated waveguide were found to be more suitable for feeding small arrays due to the existence of dielectric loss in the substrate. Even when a low loss substrate such as Roger 5880 printed circuit board (PCB) laminates were employed, the radiation efficiency for a 16 x 16 antenna array is no higher than 50% which is too low.

A further existing work employs an air-filled waveguide feed network for its low attenuation in the millimetre wave bands to achieve better radiation efficiency and gain performance. However, such waveguide feed network has complicated three-dimensional (3D) structures which are hard to realize precisely in the millimetre wave band through conventional mechanical fabrication technology. Furthermore, there may be air gaps existing in the fabricated multi-layered array configuration that is assembled with screws which will lead to degradation of the radiation characteristics of the antenna array significantly.

Diffusion bonding techniques have been introduced in the fabrication of millimetre wave antenna arrays to overcome such issues. However, the fabrication process of bonding a series of thin metallic laminates is complex, which requires the use of radiating elements that are easy to realize. In this regard, applied slot radiating elements are commonly used but such designs have a narrow band feature which results in the antenna array having relatively narrow bandwidths of less than 15%. In another existing work, air-filled ridges and groove gap waveguides were applied to construct the feed networks of millimetre-wave slot antenna arrays due to their ability to prevent undesirable power leakage since they do not require electrical contact between metallic layers. However, the fractional bandwidth of the resulting antenna array is still no more than 20%.

Therefore, it is desirable to provide an antenna and/or an antenna array that addresses at least one of the problems mentioned in existing prior art and/or to provide the public with a useful alternative. SUMMARY

Various aspects of the present disclosure are described here. It is intended that a general overview of the present disclosure is provided and this, by no means, delineate the scope of the invention. According to a first aspect, there is provided a dipole antenna including a ground plane having a feeding aperture and two magneto-electric dipole elements electrically connected to the ground plane. Each of the magneto electric dipole elements includes an electrically conductive patch and an electrically conductive wall element arranged to support and space the electrically conductive patch from the ground plane. The feeding aperture is positioned between the two magneto-electric dipole elements and configured to excite the two magneto-electric dipole elements. In a described embodiment, the dipole antenna advantageously exhibits characteristics of high gain, high radiation efficiency and wideband capabilities in the millimetre waveband making it suitable for use in millimetre wave applications. Preferably, a length of the feeding aperture may be substantially longer than a width of the feeding aperture. In one example, a length of the feeding aperture may be more than half an operating wavelength of the antenna.

Preferably, the electrically conductive patch may have four edges; and in one example, the four edges may be of equal length.

Preferably, the electrically conductive wall element may extend from at least one of the edges of the electrically conductive patch. In a specific configuration, the electrically conductive wall element may be perpendicular to the electrically conductive patch.

Preferably, the electrically conductive wall element may include a first side element and a second side element. The first and second side elements may be coupled to two corresponding edges of the electrically conductive patch. In a specific configuration, the first side element may be coupled to the second side element to form an L-shaped configuration.

According to a second aspect, there is provided an antenna array including a plurality of dipole antennas according to the first aspect. The antenna array advantageously exhibits improved characteristics of higher gain, higher radiation efficiency and greater wideband capabilities compared to the dipole antenna from the first aspect making it a useful alternative to the dipole antenna. Preferably, the antenna array may further include a parallel feed network coupled to the corresponding feeding apertures of the plurality of antennas and arranged to guide an excitation wave to excite the respective magneto-electric dipole elements. Preferably, the parallel feed network may include an input port for generating the excitation wave, an array member comprising an air-filled cavity in fluid communication to each of the feeding apertures of the plurality of dipole antennas, and a waveguide arranged to guide the excitation wave to the air- filled cavity to distribute the excitation wave to each of the feeding apertures of the plurality of dipole antennas.

Preferably, the input port may be connected to a tapered portion of the waveguide. Preferably, the waveguide may include an opening in a middle portion of the air- filled cavity, thereby enabling an even distribution of the excitation wave to the feeding apertures. In a specific example, the antenna array may further include 64 dipole antennas, and may have a gain of 28.5dBi.

According to a third aspect, there is provided a method of manufacturing the dipole antenna according to the first aspect, or the antenna array according to the second aspect. The method includes obtaining an electronic file representing a configuration of the dipole antenna or the antenna array, including a surface configuration or a volume configuration of the dipole antenna or the antenna array, and controlling an additive manufacturing apparatus to manufacture, over one or more additive manufacturing steps, the dipole antenna or the antenna array according to the configuration of the product represented in the electronic file.

According to a fourth aspect, there is provided another method of manufacturing the dipole antenna according to the first aspect or the antenna array according to the second aspect. The method includes obtaining an electronic file comprising computer executable instructions that, when executed by a processor, cause the processor to control an additive manufacturing apparatus to manufacture the dipole antenna or the antenna array, and controlling the additive manufacturing apparatus to manufacture, over one or more additive manufacturing steps, the dipole antenna or the antenna array according to the computer executable instructions.

BRIEF DESCRIPTION OF FIGURES

Exemplary embodiments will be described with reference to the accompanying drawings in which:

Figure 1 is an exploded view of a first antenna array according to a first embodiment;

Figure 2A is an enlarged view of a portion of the radiating structure of the first antenna array illustrated in Figure 1 ;

Figure 2B is a top view of the portion of the radiating structure illustrated in Figure 2A;

Figure 3 is a flowchart for a method of manufacturing a dipole antenna formed from the portion of the radiating structure illustrated in Figure 2A; and Figure 4 is a frequency response graph for Sn and gain of the dipole antenna described in association with Figure 3;

Figure 5 is a polar plot of a radiation pattern of the dipole antenna described in association with Figure 3;

Figure 6A is a perspective view of a network of air-filled waveguides for a second antenna array comprising 16 first antenna arrays illustrated in Figure 1 according to a second embodiment;

Figure 6B is a top view of the network of air-filled waveguides illustrated in Figure 6A; Figure 7 is a frequency response graph for Sn and gain of the second antenna array described in association with Figure 6A;

Figure 8 is a rectangular plot of a radiation pattern of the second antenna array described in association with Figure 6A;

Figure 9 is a perspective view of an alternative portion of the radiating structure illustrated in Figure 2A according to a third embodiment.

DETAILED DESCRIPTION

The following description contains specific examples for illustrative purposes The person skilled in the art would appreciate that variations and alterations to the specific examples are possible and within the scope of the present disclosure. The figures and the following description of the particular embodiments should not take away from the generality of the preceding summary.

Figure 1 illustrates a first antenna array 100 according to a first embodiment with its various components shown spaced apart for illustrative purposes. The first antenna array 100 includes a radiating structure 1 10 and a parallel feed network 150 coupled to the radiating structure 1 10. The parallel feed network 150 includes an input port for generating an excitation wave, although this is not depicted in Figure 1. The parallel feed network 150 is arranged to feed the excitation wave generated by the input port to the radiating structure 110. The radiating structure 1 10 includes a ground plane 120 having four feeding apertures 140, and sixteen magneto-electric (ME) dipole elements 130 that are electrically connected to the ground plane 120. The four feeding apertures 140 are arranged to receive the excitation wave from the parallel feed network 150 and to excite the ME dipole elements 130. Each of the ME dipole elements emit electromagnetic radiation for wireless communication when excited by the excitation wave.

Specifically, the sixteen ME dipole elements 130 are arranged on the ground plane 120 in a 4x4 configuration such that there are four rows of four ME dipole elements. The sixteen ME dipole elements 130 are further formed into four groups of four ME dipole elements 130 with each group being referred to as a subunit 102. Each subunit 102 has four respective ME dipole elements 130 arranged in a 2x2 configuration. The four feeding apertures 140 are positioned in the ground plane with each feeding aperture 140 configured to feed the excitation wave to the corresponding four ME dipole elements 130 in each subunit 102.

Each feeding aperture 140 is rectangular shaped with a length of the feeding aperture 140 longer than a width of the feeding aperture 140. In this embodiment, the length of each feeding aperture 140 is more than half an operating wavelength of the antenna array. In each subunit 102, two of the ME dipole elements 130 are positioned along the length on both sides of the feeding aperture 140. In other words, each of the feeding apertures 130 is surrounded by four ME dipole elements 130, and arranged to receive the excitation wave from the parallel feed network 150 and to excite their respective four ME dipole elements 130. The parallel feed network 150 includes a waveguide structure 160, and an array member 170 having inner walls 171 defining an air-filled cavity 172. The array member 170 is sandwiched between the radiating structure 1 10 and the waveguide structure 160. The inner walls 171 include a first inner wall 173, a second inner wall 174, a third inner wall 175 and a fourth inner wall 176. The inner walls 171 are arranged to form a rectangle with the first inner wall 173 being opposite the second inner wall 174, and the third inner wall 175 being adjacent to the first and second inner walls 173,174, and opposite the fourth inner wall 176. The first inner wall 173 includes a stepped indentation 177 that runs along most of the first inner wall’s length. The second inner wall 174 has a similar configuration as the first inner wall 173. The third inner wall 175 includes a protrusion 178 having two sloped edges 179 that start at opposing ends of the third inner wall 175, and join at a midpoint of the third inner wall. The fourth inner wall has a similar configuration as the third inner wall. The inner walls 171 improve impedance matching (and reduce reflection coefficient) of the first antenna array 100. In this way, power may be transferred to the ME dipole elements 130 more efficiently.

The waveguide structure 160 includes an open-ended waveguide 162 that is positioned at a center of the waveguide structure 160 and is perpendicular to the ground plane 120. The open-ended waveguide 162 includes a proximal end 164 that is closer to the array member 170, and a distal end 166 that is further away from the array member 170 and connected to the input port (not depicted in Figure 1 ). The proximal end 164 includes an opening 164a that is in fluid communication with the air-filled cavity 172 of the array member 170. Furthermore, the opening 164a of the open-ended waveguide 162 is aligned to a middle portion of the air-filled cavity 172.

In addition to being in fluid communication with the opening 164a of the open- ended waveguide 162, the air-filed cavity 172 is also in fluid communication with the four feeding apertures 140 of the radiating structure 1 10. Effectively, the open-ended waveguide 162, the air-filled cavity 172 and the four feeding apertures 140 form a channel to deliver the excitation wave from the input port to the ME dipole elements 130.

In operation, the excitation wave is generated by the input port and transmitted to the distal end 166 of the open-ended waveguide 162. The excitation wave is guided through the open-ended waveguide 162 from the distal end 166 to the proximal end 164 and into the air-filled cavity 172 of the array member 170. The air-filled cavity 172 then distributes the excitation wave to the four feeding apertures 140 of the radiating structure 1 10. Advantageously, since the opening 164a is aligned to the middle portion of the air-filled cavity 172, electromagnetic power of the excitation wave could be divided equally among the four feeding apertures 140 and fed to their respective ME dipole elements 130 in their respective subunits 102 simultaneously. Due to the even distribution of the excitation wave’s electromagnetic power, all sixteen ME dipole elements 130 are equally excited by the excitation wave, thus resulting in the sixteen ME dipole elements 130 emitting electromagnetic radiation that is consistent across the first antenna array 100.

It should be noted that the description of the first embodiment above is not meant to be limitative. For example, it is not essential for the open-ended waveguide 162 to be positioned at the center of the waveguide structure 160 as long as the opening 164a is in fluid communication with the air-filled cavity 172. It is also possible for the excitation wave to be fed to the radiating structure 1 10 via a series feed network, rather than the parallel feed network 150.

Although the first antenna array 100 is described as having sixteen ME dipole elements 130 (i.e. four subunits 102 arranged in a 2x2 configuration), the first antenna array 100 may include any number of subunits 102. For example, the first antenna array 100 may include sixty-four ME dipole elements 130 (i.e. sixteen subunits 102 arranged in a 4x4 configuration). The subunit 102 is described in more detail in the following section with reference to Figures 2A and 2B.

Figure 2A illustrates an enlarged view of a portion 1 10a of the radiating structure 1 10 having one subunit 102, which is generally called a dipole antenna 200. As illustrated in Figure 2A, the dipole antenna 200 includes the ground plane 120 having the feeding aperture 140, and a first ME dipole element 130a, a second ME dipole element 130b, a third ME dipole element 130c, and a fourth ME dipole element 130d. Figure 2B is a top view of the dipole antenna 200 of Figure 2A. The first ME dipole element 130a, and the second ME dipole element 130b are positioned along the length 142 of the feeding aperture 140 and on one side 140a of the feeding aperture 140, while the third ME dipole element 130c, and the fourth ME dipole element 130d are also positioned along the length 142 of the feeding aperture 140 but on an opposing side 140b of the feeding aperture 140. The feeding aperture 140 is thus configured to feed the excitation wave to the first ME dipole element 130a, the second ME dipole element 130b, the third ME dipole element 130c, and the fourth ME dipole element 130d simultaneously to excite them into emitting electromagnetic radiation for wireless communication.

With reference to the first ME dipole element 130a in Figure 2A, the first ME dipole element 130a includes an electrically conductive patch 132, and an electrically conductive wall element 134 arranged to support and space the electrically conductive patch 132 from the ground plane 120. One end of the electrically conductive wall element 134 is connected to the ground plane 120 while an opposing end of the electrically conductive wall element 134 is connected to the electrically conductive patch 132. Additionally, the electrically conductive wall element 134 is perpendicular to the electrically conductive patch 130 such that a space is formed between the electrically conductive patch 132 and the ground plane 120.

The electrically conductive patch 132 has four edges 132a,132b,132c,132d that are of equal length. The electrically conductive wall element 134 includes a first side element 134a and a second side element 1 134b that are coupled to two corresponding edges 132a, 132b of the electrically conductive patch 130. The first side element 134a is facing an opposing side element (hidden from view in Figure 2A) of the ME dipole element 130c, while the second side element 134b is facing an opposing side element (hidden from view in Figure 2A) of the second ME dipole element 130b.

The first side element 134a extends from the edge 132a towards the ground plane 120 while the second side element 134b extends from the edge 132b towards the ground plane 120. Furthermore, the first side element 134a is adjacent to the second side element 134b, and the first side element 134a is coupled to the second side element 134b to form an L-shaped configuration.

The second ME dipole element 130b, the third ME dipole element 130c, and the fourth ME dipole element 130d have a similar configuration as the first ME dipole element 130a, and are therefore not described in further details.

It should be noted that the description of the subunit 102 of the radiating structure 110 should not be construed to be limitative as well. For instance, the first side element 134a is described as being adjacent to the second side element 134b, and the first and second side elements 134a, 134b are described as forming an L-shaped configuration. However, this is not necessary. The first and second side elements 134a, 134b may extend from any of the edges 132a,132b,132c,132d. For instance, the first side element 134a may extend from the edge 132a while the second side element 134b may instead extend from the edge 132c such that the first side element 134a is opposite the second side element 134b. It is also possible for the first and second side elements 134a, 134b to extend from an underside of the electrically conductive patch 132 towards the ground plane 120, instead of extending from the two corresponding edges 132a, 132b of the electrically conductive patch 132 towards the ground plane 102.

Furthermore, the electrically conductive wall element 1 14 may include the first side element 134a only. Notably, whichever configuration the first ME dipole element 130a has, the second ME dipole element 130b, the third ME dipole element 130c, and the fourth ME dipole element 130d have a similar configuration to the first ME dipole element 130a to maintain some degree of antenna symmetry.

The first antenna array 100 may include exactly one subunit 102, which may be referred to as a dipole antenna 200. In a specific embodiment, the dipole antenna 110a includes the portion 1 10a of Figure 2A and a parallel feed network coupled to the portion 1 10a. The parallel feed network includes the input port for generating the excitation wave and the waveguide structure 160 having the open-ended waveguide for guiding the excitation wave to the feeding aperture 1 140. Notably, the array member 170 is not necessary in this embodiment since there is only one feeding aperture 140, and thus the excitation wave need not be divided.

An exemplary method 300 of manufacturing the dipole antenna 200 using 3D printing techniques is illustrated in Figure 3. Specifically, the method 300 employs metal laser sintering technology to manufacture the dipole antenna. At step 310, a 3D model of the dipole antenna 200 is obtained using a 3D modelling software. The 3D model is in the form of an electronic file representing a surface configuration or a volume configuration of the dipole antenna. At step 320, computer-executable instructions for 3D printing the dipole antenna are obtained by slicing the 3D model using a 3D slicing software. The computer-executable instructions are fed to a processor to control a 3D printer and includes the horizontal and vertical positions of a laser of the 3D printer, and 3D printer settings such as temperature, layer height, and printing speed. At step 330, the computer-executable instructions are fed to the 3D printer to control the 3D printer to manufacture, over one or more additive manufacturing steps, the dipole antenna according to the computer executable instructions.

The method illustrated in Figure 3 may be adjusted according to specific applications or scenarios. For example, at step 310, obtaining the 3D model of the dipole antenna may be done by obtaining the 3D model directly from a 3D model repository, instead of using the 3D modelling software. Likewise, at step 320, the computer executable instructions may be obtained directly from another repository, in which case, step 310 is not necessary.

Additionally, some additive manufacturing apparatus may have a built-in 3D slicing software. In such cases, step 820 may be omitted, and step 830 may simply include controlling the 3D printer to manufacture, over one or more additive manufacturing steps, the dipole antenna according to the 3D model.

Needless to say, the method 300 is also suitable for manufacturing the first antenna array 100, as well as any other described embodiments. Furthermore, the method 300 may be performed by any suitable additive manufacturing apparatus, other than a 3D printer, or using other suitable 3D printing technologies, other than metal laser sintering.

On the other hand, the dipole antenna 200, the first antenna array 100, and any other described embodiments may also be fabricated by conventional mechanical fabrication technology.

Figure 4 is a frequency response graph 400 of the dipole antenna 200. Specifically, Figure 4 shows the return loss (|Sn |) 410 and gain 420 of the dipole antenna 200 over an extremely high frequency (XFIF) range of 26GFIz to 40GFIz. Within the XFIF range, the dipole antenna 200 has a maximum gain of 10.5dBi at an operating frequency of 35GHz. Furthermore, at the operating frequency of 30GHz, the dipole antenna 200 is able to achieve a gain 420 of 9dBi while the return loss (|Sn |) 410 of the dipole antenna 200 drops to -33dB. In other words, the dipole antenna 200 is able to achieve high radiation efficiency while maintaining high gain in the XHF range.

Importantly, a fractional (impedance) bandwidth that is wider than 40% is still achievable with the dipole antenna 200 operating at a return loss (|Sn |) 410 of less than -10dB. Advantageously, the dipole antenna 200 is able to achieve wideband capabilities while maintaining high radiation efficiency. In summary, the dipole antenna 200 exhibits characteristics of high gain, high radiation efficiency and wideband capabilities in the millimetre waveband making it suitable for use in millimetre wave applications. Figure 5 is a polar plot 500 of a radiation pattern 510 of the dipole antenna 200. In particular, Figure 5 shows a co-polarization in E-plane 520 and a co polarization in FI-plane 530 of the radiation pattern 510. As can be seen, the radiation pattern 510 is symmetrical for the co-polarization in E-plane 520, and the co-polarization in FI-plane 530.

In addition, both the co-polarization in E-plane 520 and the co-polarization in FI- plane 530 has a Front to Back Ratio (F/B ratio) of more than 22dB which enables the dipole antenna 200 to produce the radiation pattern 510 with high directivity. Furthermore, the cross polarization level (not shown in Figure 5) of the dipole antenna 200 is less than -30dB which ensures the dipole antenna 200 experiences low interference between the co-polarization and the cross polarization in respective E-planes and H-planes of the radiation pattern 510. Advantageously, the dipole antenna 200 is able to achieve a wide bandwidth of more than 40%, a maximum gain of 10.5dBi, while exhibiting a stable radiation pattern 510 with low cross polarization levels.

To further illustrate the scope of the present disclosure, a second antenna array 600 according to a second embodiment is described. The second antenna array 600 includes sixteen first antenna arrays 100 arranged in a 4x4 configuration. To guide the excitation wave from the input port to the sixteen first antenna arrays 100, the parallel feed network of the second antenna array 600 further includes a network of air-filled waveguides 605 which is illustrated in Figures 6A and 6B.

The network of air-filled waveguides 605 is shown in Figure 6A to be coupled to the input port 610, and is configured to guide the excitation wave from the input port 610 to the distal ends 166 of the respective open-ended waveguides 162The distal ends 2166 indicate where the open-ended waveguides 162 (and the remaining components of the sixteen first antenna arrays 100) are positioned in the second antenna array 600. The network of air-filled waveguides 605 include shorted ends 620 which are electrically connected to the corresponding distal ends 166 of the open-ended waveguides 162 to transmit the excitation wave to the open-ended waveguides 162.

Referring to Figure 6B which illustrates a top view of the network of air-filled waveguides 605, it can be seen that the network of air-filled waveguides 605 further includes a short section of a tapered waveguide (tapered portion 630) which is coupled to the input port 610 so that a standard waveguide can be used for feeding the second antenna array 600.

Figure 7 is a frequency response graph 700 of the second antenna array 600. Specifically, Figure 7 shows the return loss (|Sn |) 710 and gain 720 of the second antenna array 600 over the extremely high frequency (XFIF) range of 26GFIz to 40GFIz. Within the XFIF range, the second antenna array 600 has a maximum gain of 28.5dBi at the operating frequency of 35.6GFIz. Furthermore, at the operating frequency of 34.7GFIz, the second antenna array 600 records a gain 720 of 4dBi while the return loss (|Sn |) 710 drops to -35dB. Advantageously, the second antenna array 600 is able to achieve a higher gain than the dipole antenna 200. The second antenna array 600 also has a higher radiation efficiency than the dipole antenna 200 while still maintaining a positive gain in the XFIF range. Importantly, a fractional (impedance) bandwidth of 33.5% is still achievable with the second antenna array 600 operating at a return loss (|Sn |) 710 of less than -10dB. For calculating the fractional bandwidth of the second antenna array 600, the second antenna array 600 is taken to have an operating bandwidth from 28.2GHz to 39.7GHz when operating at the return loss (|Sn |) 710 of less than -

10dB. The operating bandwidth does not take into consideration the operating frequency of 27GHz where the return loss briefly dipped below -10dB. Advantageously, the second antenna array 600 achieves greater wideband capabilities than the dipole antenna 200 while maintaining similarly high radiation efficiency. In summary, the second antenna array 600 exhibits characteristics of higher gain, higher radiation efficiency and greater wideband capabilities in the millimetre waveband than the dipole antenna 200, making it a useful alternative for millimeter wave applications. Figure 8 is a rectangular plot 800 of a radiation pattern 810 of the second antenna array 600. In particular, Figure 8 shows the co-polarization and cross polarization in respective E-planes 820,840 and in respective H-planes 830,850 of the radiation pattern 710. As can be seen, the radiation pattern 810 is symmetrical for both the co-polarizations and the cross-polarizations in respective E-planes 820,840 and respective H-planes 830,850.

In addition, the second antenna array 600 has a relatively high directivity considering that the first side lobes 820a, 820b of the co-polarization in E-plane 820 (as well as the co-polarization in H-plane 830) has a magnitude of -14dB. Furthermore, the cross polarization level of the second antenna array 600 is less than -45dB which ensures the second antenna array 600 experiences low interference between the co-polarization and the cross-polarization in respective E-planes 820,840 and respective H-planes 830,850 of the second antenna array 600. Advantageously, the second antenna array is able to achieve a wide bandwidth of 33.5%, a maximum gain of 28.5dBi, while exhibiting a stable radiation pattern 810 with low cross polarization levels.

The described embodiments thus propose multiple configurations for the dipole antenna 200, the first antenna array 100, and second antenna array 600 that are capable of achieving high gain, high radiation efficiency and wideband capabilities for wireless communication, particularly in the millimetre waveband i.e. the XHF band. Needless to say, the described embodiments are not limited to millimetre wave applications. For example, the dipole antenna 200, the first antenna array 100, and second antenna array 600 may also be suitable to operate in other frequency bands such as the Ultra High Frequency band, with modifications to the designs that will be apparent to the skilled person, if necessary. It should also be clear that although the present disclosure has been described with reference to specific exemplary embodiments, various modifications may be made to the embodiments without departing from the scope of the invention as laid out in the claims. For example, referring to Figure 2A, although the electrically conductive patch 132 is described as having four edges of equal length (i.e. a square patch), this is not necessary. For instance, it is possible for the electrically conductive patch 132 to be a rectangular patch. Furthermore, it is also possible for there to be only one ME dipole element 130 along each of the two lengths 142 of the feeding aperture 140. This is illustrated in Figure 9 which shows an enlarged view of a portion 1 110a of the radiating structure 1 10 having one subunit 102, referred to herein as a second dipole antenna 1200. The second dipole antenna 1200 has a similar structure as the first dipole antenna 200 and thus, like components in the third embodiment uses the same reference numerals with an addition of 1000. In the third embodiment, the second dipole antenna 1200 includes a ground plane 1 120 having a feeding aperture 1 140, and an alternative first ME dipole element 1 130a, and an alternative second ME dipole element 1 130b that are electrically connected to the ground plane 1 120. The feeding aperture 1140 is positioned between the first alternative ME dipole element 1 130a, and the second alternative ME dipole element 1 130b. The first alternative ME dipole element 1 130a includes an electrically conductive patch 1 132 that is rectangular shaped, and an electrically conductive wall element 1 134 having one side element 1 134a that is arranged to support and space the electrically conductive patch 1 132 from the ground plane 1 120. The second alternative ME dipole element 1 130b has a similar configuration as the first alternative ME dipole element 1 130a, and is therefore not described in further details.

Further, various embodiments as discussed above may be practiced with steps in a different order as disclosed in the description or using any other means available to the skilled person without departing from the scope of the invention as laid out in the claims. Modifications and alternative constructions apparent to the skilled person are understood to be within the scope of the disclosure.