EP3387706A1

EP3387706A1 - Antenna and radiating element for antenna

Info

Publication number: EP3387706A1
Application number: EP16715555.5A
Authority: EP
Inventors: Juan Segador Alvarez; Ignacio Gonzalez; Tao TANG; Bruno BISCONTINI
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2016-04-12
Filing date: 2016-04-12
Publication date: 2018-10-17
Anticipated expiration: 2036-04-12
Also published as: CN109690871B; BR112018067753A2; ES2973634T3; CN109690871A; BR112018067753B1; EP3387706B1; WO2017178037A1

Abstract

The invention relates to a radiating element comprising a conductive element comprising a lower plane, sidewalls extending from edges of the lower plane, at least a first and a second non-conductive slot each extending at least partly in the lower plane and along the sidewalls from the lower plane to upper edges of the sidewalls, wherein the radiating element is configured to be arranged on a reflector of an antenna by a support structure holding the lower plane in a predefined distance to the reflector; and an antenna for a base station including a reflector and multiple of the radiating elements of any of the previous claims wherein the lower planes of the conductive elements of the multiple radiating elements are supported in the predefined distance to the reflector.

Description

ANTENNA AND RADIATING ELEMENT FOR ANTENNA

TECHNICAL FIELD

The present invention relates to a radiating element and an antenna including a plurality of such radiating elements. In particular, the antenna may be an antenna of a base station.

BACKGROUND

With the growing demand for a deeper integration of antennas with Radios, such as Active Antenna Systems (AAS) for base stations, a reduction of the depth of ultra-broad band antennas is being requested without compromising antenna key performance indicators.

The antenna-radio integration leads to highly complex systems and strongly influences the antenna form factor which is fundamental for commercial field deployment. In this context one of the dominant limiting technological factors is the height of the antenna. Reducing the antenna height means to strongly simplify the overall deploying process of AAS and traditional passive antenna systems.

When thinking about the radiating element performance, a reduction in the height naturally implies a reduction in the relative bandwidth than can be covered with acceptable RF performance. To cover the standard operating bands in modern base station antenna systems maintaining the same RF performance, and with a lower height in the radiating element, new con- cepts/architectures different from the legacy technology must be developed.

Besides the low profile/broadband characteristics, the new radiating elements should be suitable to work in a multiband environment which means that the geometry must be transparent for the rest of the bands. In the particular case of the lower frequency band (from 690 to 960 MHz), in order to maximize the utilization of the available space in the antenna aperture, it is desirable to combine the radiating elements of different operating bands such as the lower frequency band with the higher frequency bands, e.g. from 1400 to 2700 MHz. However, if the radiating elements of different frequency bands are combined in single antenna systems, the structure, in particular for feeding the radiating elements become complex and the overall height remains a problem. Thus, there is still a demand for a radiating element that has ultra-broadband characteristic (which means a bandwidth more than 30%), an ultra-low profile characteristic and a suitable shape for combining radiating elements of different frequency bands. Moreover, the feeding structure of the radiating element should be simplified.

SUMMARY OF THE INVENTION The objective of the present invention is to provide a radiating element and an antenna wherein the radiating element and the antenna overcome one or more of the above-mentioned problems of the prior art.

A first aspect of the invention provides a radiating element comprising:

a conductive element comprising:

a lower plane, sidewalls extending from edges of the lower plane, at least a first and a second non-conductive slot each extending at least partly in the lower plane and along the sidewalls from the lower plane to upper edges of the sidewalls,

wherein the radiating element is configured to be arranged on a reflector of an antenna by a support structure holding the lower plane in a predefined distance to the reflector. In particular, the conductive element having the lower plane and the sidewalls provide a cup-shaped form which allows to include further radiating elements for a higher frequency band inside the conductive element. Thus, the radiating element is usable for a multiple frequency band antenna. Moreover, by providing the predetermined distance to the reflector, the capacity to ground is lowered which provides broadband characteristics of the radiating element. A relative bandwidth of more than 30% can be achieved.

In a first implementation of the radiating element according to the first aspect, the radiating element further comprises the support structure configured to support the radiating element on the reflector with the predefined distance between the lower plane and the reflector. The support structure provides for the predetermined distance to the reflector. The support structure may include two or more distance holders, e.g. arranged at the corners of the radiating element. The distance holders can be made from a dielectric material or any other isolating material. Alternatively, the support structure may also include the one single piece preferably arranged in the center, and may also be comprise conductive material. The support structure may include one or more printed circuit boards which may, according to further preferred implementations, also include microstrip lines of a feeding system of the radiating element. In a second implementation of the radiating element according to the first implementation of the first aspect, the support structure is configured such that the predefined distance is at least 1 25 wherein Xc is the wavelength at the center frequency of the operating band of the conductive element. Simulation results show that the predefined distance of 25 to the ground plate (e.g. the reflector board), more preferably λο/15, is suitable to maintain the broadband characteristics of the radiating element.

In a third implementation of the radiating element according to the first aspect and any of the implementations of the first aspect, the lower plane has a minimum area of 25% or preferably more than 40% of the total area of an upper plane of the radiating element at the upper edges of the sidewalls. A minimum for the lower plane of 25% of the area of the upper plane provides a suitable impedance along the slot in the lower plane. Thus, with having a lower plane of 25% of the area of the upper plane, the feeding points for the slots can be arranged in a flat layer close to the lower plane. In a fourth implementation of the radiating element according to the third implementation of the first aspect, the slots further extend along the upper plane. With the slots extending in the upper plane, a shortcircuit of the slots is avoided.

In a fifth implementation of the radiating element according to the first aspect and any imple- mentations of the first aspect, the radiating element has at least two electrical feeding points crossing the slots in the area of the lower plane, preferably in an area closer to the edges of the lower plane than to the center of the lower plane. Arranging the feeding points crossing the slots in the lower plane has the advantage that the feeding system can be provided in a flat plane which simplifies the construction of the feeding system. In particular, the feeding lines can be arranged on a flat PCB mounted e.g. on a bottom side of the lower plane of the conductive element. Preferably, the feeding points are arranged closer to the edges of the lower plane than the center of the lower plan as the impedance along the slot increases when moving away from the center of the lower plane. In a sixth implementation of the radiating element according to the fifth implementation of the first aspect, the radiating element further comprises a first transmission line crossing the first slot to form a first electrical feeding point of the at least two electrical feeding points; and a second transmission line crossing the second slot to form a second electrical feeding point of the at least two electrical feeding points. The construction is easy to manufacture because the feeding points are provided by separated transmission lines which cross the slots and it is not necessary to make any soldering on the conductive element for building the feeding points. For example, in another implementation, cable feeding can be used. The inner conductors of the cable are soldered to a small tab connected to one side of the slot and the outer conductor of the cable is soldered to the opposite side of the slot. However, the cable solution is more expensive because the soldering is difficult to be automated. Furthermore, the conductive element would need to be made of solderable material or plated to be solderable which increases the costs.

In a seventh implementation of the radiating element according to the sixth implementation of the first aspect, the radiating element further comprises a printed circuit board, PCB, arranged at the lower plane, wherein the PCB includes a first microstrip line forming the first transmission line and a second microstrip line forming the second transmission line. According to this implementation, the feeding system is arranged on a PCB which is mechanically connected to the lower plane. This solution is cost efficient because a flat PCB can be used rather than handling cables which must be fixed and electrically connected to the conductive element as mentioned before.

In an eighth implementation of the radiating element according to the seventh implementation of the first aspect, the PCB includes a ground plane on the opposing side of the microstrip lines, the ground plane being capacitively coupled to the lower plane. The radiating element is acting as a subreflector for a higher frequency radiating element inside the (cup-shaped) conductive element of the radiating element. To ground a higher frequency radiating element disposed inside the conductive element, the ground plane on the PCB can be used. In a ninth implementation of the radiating element according to the first aspect and any implementations of the first aspect, the conductive element further comprises flaps extending from edges of the upper plane in a direction to the level of the lower plane, wherein the slots extend into the flaps. The flaps in the corners of the radiating element make the radiating element very compact, thereby reducing the shadow and interference of other bands when the radiating element is used in a multiband antenna configuration.

In a tenth implementation of the radiating element according to the first aspect and any im- plementations of the first aspect the conductive element is made from a single piece, preferably a bended aluminum sheet. In this implementation, the radiating element can easily be manufactured as it includes only a single bent metal sheet. Aluminum is preferred due to low weight, cost efficiency, easy manufacturability, and good electrical properties. In an eleventh implementation of the radiating element according to the first aspect and any implementations of the first aspect the lower plane has a central opening. The central opening of this implementation can be used for including the support structure of the feeding system inside the (cup-shaped) conductive element to support a further inner radiating element. Moreover, the opening may also be used for the support structure for the conductive element in order to keep the predetermined distance to the reflector.

In a twelfth implementation of the radiating element according to the first aspect and any implementations of the first aspect, the radiating element further comprises an inner second radiating element inside the conductive element, wherein the conductive element is constructed to operate in a first frequency band while the inner radiating element inside the conductive element is constructed to operate in a second frequency band higher than the first frequency band. By including the higher frequency radiating element inside the lower frequency radiating element, the total arrangement is optimally space saving. Moreover, the low -band radiating element outside may also act as a reflector for the inner radiating element at the higher frequency.

In a thirteenth implementation of the radiating element according to the twelfth implementation when depending on the eleventh implementation of the first aspect the inner radiating element includes a support structure that extends through the opening in the lower plane. Thus, the opening in the lower plane provides the advantage that the inner radiating element is mechan- ically supported and at the same time, the opening may also be used to pass through the feeding lines for the inner radiating element.

In a fourteenth implementation of the thirteenth implementation of the first aspect the support structure of the inner radiating element includes at least one, preferably two crossed PCBs wherein the one or two PCBs includes feeding lines for the conductive element and/or for the inner radiating element. The two crossed PCBs have the advantage that they may provide at the same time feeding system for the outer lowband radiating element and for the inner high frequency radiating element.

In a fifteenth implementation of any of the twelfth to the fourteenth implementation of the first aspect the inner radiating element comprises a further PCB arranged in a further predefined distance (in an opposite direction than the first predefine distance) from the lower plane and preferably parallel to the lower plan. Or in other words, when the radiating element is arranged on a reflector board, the lower plane is typically arranged between the reflector and the further PCB of the inner radiator. Furthermore, in a preferred embodiment, the reflector, lower plan and further PCB are arranged parallel to each other.

In a sixteenth implementation of any of the twelfth to the fifteenth implementation the inner radiating element has a dipole structure substantially in the same level of the upper plane or below the upper plane. Arranging the dipole structure of the inner radiating element in the same level as the upper plane or below the upper plane of the outer lowband radiating element provides the advantage of a minimum height over the reflector. The term "substantially" may be used to indicate that the respective layers do deviate no more than ±10 mm.

A second aspect of the invention refers to an antenna for a base station including a reflector and multiple of the radiating elements of any of the previous implementations of the first aspect wherein the radiating elements are arranged on the reflector such that the lower planes of the conductive elements of the multiple radiating elements are supported in the predefined distance to the reflector. The advantage of the antenna is that it can be used in a multiple frequency band configuration with an ultra-broadband characteristic (relative bandwidth >30%) of a low frequency band and an ultra-low profile characteristic. The shape of the radiating element is suitable to fit a higher frequency radiating element inside while the feeding system is simplified.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate the technical features of embodiments of the present invention more clearly, the accompanying drawings provided for describing the embodiments are introduced briefly in the following. The accompanying drawings in the following description are merely some embodiments of the present invention, but modifications on these embodiments are possible without departing from the scope of the present invention as defined in the claims.

FIG. 1 shows a perspective view of a radiating element of a first embodiment of the invention.

FIG. 2 shows a side elevation view of a radiating element of a second embodiment located on a reflector.

FIG. 3 shows a side elevation view of a conductive element of a radiating element of

FIG. 1 or FIG. 2.

FIG. 4 shows a perspective view of the conductive element of FIG. 3 indicating the evolution of the impedance along the slots.

FIG. 5 shows a perspective view of an embodiment of a radiating element from the bottom side including a feeding system in form of PCBs.

FIG. 6 shows a perspective view of a further embodiment of the invention forming a dual band radiating element.

FIG. 7 shows a top view of an antenna of a further embodiment of the invention including radiating elements of FIG. 6.

Detailed Description of the Embodiments

FIG. 1 shows a first embodiment of a radiating element according to the invention. The radiating element includes a conductive element 2 made from a bent metal sheet, in particular an aluminium sheet. The conductive element includes four slots 4 that are arranged every 90° in the conductive element. The slots are preferably fed 2 x 2 with the same phase and amplitude which in combination achieve dual linear polarization radiation as described below. A combination of only two inputs in two opposing slots would create one polarization and the com- bination with the other two opposing slots create the orthogonal polarization. However, other embodiments of the invention may also include only one polarization, i.e. only two slots.

As shown in FIG. 1, the conductive element is supported by a support structure, which, in this embodiment, includes four dielectric distance holders 6 configured to support the conductive element 2 on a surface of a reflector (not shown in FIG. 1) of an antenna configuration. The support structure is configured to hold the conductive element 2 in a certain distance from a reflector plate. FIG. 2 shows a second embodiment of a radiating element included in a reflector 10 to create an antenna wherein the conductive element 2 is similar to the conductive element 2 of the first embodiment. In this case, a single support is used to hold the radiating element on top of the reflector 10. In general, the support structure can be formed by any isolating material which is configured to hold the radiating element in a certain distance to the reflector surface. Fur- thermore, the support structure ion Fig. 2 could also be used to feed the radiating element. E.g. the support structure could be a PCB or MID. Furthermore, to give the embodiment in Fig. 2 a higher stability dielectric distance holders 6 as shown in Fig. 1 , could be added to the embodiment shown in Fig. 2. The total height of the radiating element in this example from the reflector plate is only around 0.125 x λ wherein λ is the wavelength at the lowest operating frequency of the radiating element. Thus, a voltage standing wave ratio (VSWR) below 1.35 in a relative bandwidth of 32% can be achieved. FIG. 3 shows the conductive element 2 of the first and second embodiments in FIGs 1 and 2 as a single part. It includes a lower plane 12 and an upper plane 14 connected by sidewalls 11 (respectively formed by conductive material of the conductive elements and conductively connected to each other). In this way, the conductive element 2 takes the form of a cup which allows to arrange a further radiating element inside the structure as described below in con- nection with FIG. 6.

Typically the radiating element will be fed across the slots 4. As shown in FIG. 4, the impedance of the radiating element changes when shifting the feeding points along the slots 4. Moving the feeding points to the center of the radiating element, the impedance decreases reaching a short circuit value in the very beginning of the slot at the center. On the other hand, when moving the feeding points to the outer part of the radiating element closes to the edges of the lower plane 12, the impedance increases progressively.

In order to have a reasonable value of impedance, the radiating element is fed at a certain distance from the beginning of each slot 4 (and therefore also at a certain distance from the center of the lower plan 12). For simplifying the feeding system, it is preferred in the embodiments of the invention to arrange the four feeding points located in a common flat surface, i.e. in a plane parallel to the lower plane 12. To meet these conditions, the embodiments of the radiating element have a minimum area in the lower plane 12 with respect to the total area of the upper plane 14. Preferably, the minimum value of 25% or preferably more than 40% is used for the area of lower plane 12 with respect to area of upper plane 14. In order to be able to feed the radiating elements in the lower plane 12 and to achieve ultra broadband characteristics, there is a certain distance provided between the lower plane 12 of the radiating element from the reflector 10. As the minimum area in the lower plane is 25% of the upper plane 14, there is a big conductive area close to the reflector 10 and therefore a strong capacity to ground. However, to achieve a broadband characteristic of the radiating element, this capacity should be lowered. Since the minimum area of the lower plane 12 is limited by 25%o, the capacity to ground is reduced by lifting up the radiating element over the reflector using a suitable support structure. Preferably, a minimum distance between the lower plan 12 and the reflector 10 of λ_</25 or preferably J15 is used in the embodiments of the invention wherein λε is a wavelength at the center frequency of the operating frequency band of the ra- diating element.

With reference to FIG. 5 a feeding system of the radiating element is described. The feeding system includes three printed circuit boards (PCBs) arranged together. Two crossed PCBs 20 act as grounding, mechanical support and contain the feeding lines for the radiating element. A third PCB 22 is arranged orthogonal to crossed PCBs 20 and attached to but DC isolated from the lower plane 12 of the conductive element. The third PCB 22 has four microstrip lines 24. Each of the microstrip lines 24 crosses and feeds one of the slots 4 above. As can be seen from FIG. 5, each the microstrip line 24 crosses its slot 4 in an outer region of the slots 4 in the lower plane 12. In particular, the microstrip lines cross the slots 4 in the second outer half of the slots in the lower layer 12. The cross sections between the microstrip lines 24 and the slots 4 define the feeding points as mentioned above in the context of FIG. 4. The microstrip lines 24 on the third PCB 22 are connected to microstrip lines 26 on the two crossed PCBs 20. On the crossed PCBs 20, the microstrip lines 26 of two opposing slots 4 are connected together and provide an electrical terminal. Thus, two opposing slots 4 can be fed by an electrical signal with the same amplitude and the same phase. For the other two slots 4 in the perpendicular orientation, the same arrangement is provided on the second of the two crossed PCBs 20 in a symmetrical manner. The crossed PCBs 20 extend through a central opening 18 in the lower plane 12 of the conductive element 2. As shown in FIG. 6, the two crossed PCBs 20 can carry another PCB 30 which is arranged orthogonally to the crossed PCBs 20. The PCB 30 forms a further inner radiating element which is arranged inside the cup-shaped conductive element 2. Preferably, the PCB 30 is arranged in substantially the same layer as the upper plane 14 of the conductive element. The PCB 30 includes conductive portions composing a higher frequency radiating element which is fed through the microstrip lines 32 which are also provided on the two crossed PCBs 20. The PCB 30 acts as a radiating element in a frequency band which, due to the dimension of the conductive elements on the PCB 30, is higher than the frequency band of the conductive element 2. For example, the conductive element 2 may be operated in a low band from 690 to 960 MHz, while the inner radiating element 30 may be operated in an intermediate band from 1427 to 2400 MHz. Further details of the inner radiating element are described in the parallel pending European patent application of the same applicant with the title "Ultra Broad Band Dual Polarized Radiating Element for a Base Station Antenna".

For further details to the inner radiating element reference is made to the disclosure of this application which is incorporated by reference. The higher frequency radiating element can be of any kind: dipole, patch, lock periodic antenna, etc.

In the embodiment of the dual-band radiating element as shown in FIG. 6, it is obvious that the lower frequency radiating element, i.e. the conductive element 2, is acting as well as a subre- flector for the higher frequency radiating element, i.e. the PCB 30. To ground the higher fre- quency radiating element to its subreflector, the PCB 22 is used. The PCB 22 includes a conductive ground layer which is grounded and which is arranged opposing the layer of the microstrip lines 24. Furthermore the ground layer of the PCB 22 is capacitive coupled to the lower plane 12. Typically the protective cover on the ground layer of PCB 22 can serves as a dielectric between the lower plane 12 and the ground layer to avoid galvanic contact between the ground layer of PCB 22 and the lower plane 12. Nevertheless an isolating sheet can be provided between PCB 22 and the lower plane 12 of the conductive element 2. The reason why the PCB 22 is DC isolated/capacitively coupled to the lower plane 12 is to avoid intermodulation products that are generated when having a non-stable metal junction.

As mentioned above, the radiating elements previously described are intended to work in a multiband antenna architecture, which means that within the same antenna several radiating elements working in different frequency bands are provided. FIG. 7 shows an embodiment of an antenna including a multi-band arrangement of radiating elements.

The multi-band arrangement of the antenna includes conductive elements 2 having an inner radiating elements 30 (in from of PCB radiator) inside the (cup-shaped) conductive element 2 as described in FIG. 6. Multiple of these radiating elements are arranged on a common reflector 10. Moreover, between the conductive elements 2, the antenna includes further radiating ele- ments 30' which are constructed similar to the inner radiating elements 30 as described before. Moreover, further radiating elements 40 operating in a high frequency band from 1710 to 2690 MHz are arranged also on the reflector 10 preferably along and parallel to one or two sides of the low band and intermediate band radiating elements. It is obvious that in the multiband architecture as described in FIG. 7, the available space is very limited. In order to reduce the interference and shadow between the different frequency bands, the size of the radiating elements is minimized. To minimize the radiating elements for the low band, the conductive elements 2 further include added flaps 19 as shown in FIGs 1 to 6. By adding the flaps 19, the electrical length of the radiating element is increased while keeping small physical dimensions and minimizing the shadow that is created in the rest of the bands.

The flaps 19 are arranged on the edges of the upper plane 14 of the conductive element 2 and bent downwardly in a direction perpendicular to the upper plane 14. As shown in FIGs 1 to 4, the slots 4 extent through the flaps 19.

The foregoing descriptions are only implementation manners of the present invention, the scope of the present invention is not limited to this. Any variations or replacements can be easily made through person skilled in the art. Therefore, the protection scope of the present invention should be subject to the protection scope of the attached claims.

Claims

A radiating element comprising:

a conductive element (2) comprising:

a lower plane (12), sidewalls (11) extending from edges of the lower plane (12), at least a first and a second non-conductive slot (4) each extending at least partly in the lower plane (12) and along the sidewalls (11) from the lower plane (12) to upper edges of the sidewalls (11),

wherein the radiating element is configured to be arranged on a reflector (10) of an antenna by a support structure holding the lower plane (12) in a predefined distance to the reflector (10).

The radiating element according to claim 1, further comprising:

the support structure configured to support the radiating element on the reflector (10) with the predefined distance between the lower plane (12) and the reflector (10).

The radiating element according to claim 2, wherein the support structure is configured such that the predefined distance is at least λ_</25 wherein Xc is the wavelength at the center frequency of the operating band of the conductive element.

The radiating element of any of the previous claims wherein the lower plane (12) has a minimum area of at least 25% or more than 40% of the total area of an upper plane (14) of the radiating element at the upper edges of the sidewalls.

The radiating element of claim 4, wherein the slots (4) further extend along the upper plane (14).

The radiating element according to any of the previous claims, having at least two electrical feeding points crossing the slots (4) in the area of the lower plane, preferably in an area closer to the edges of the lower plane (12) than to the center of the lower plane (12).

7. The radiating element according to claim 6, further comprising:

a first transmission line crossing the first slot (4) to form a first electrical feeding point of the at least two electrical feeding points; and

a second transmission line crossing the second slot (4) to form a second electrical feeding point of the at least two electrical feeding points.

8. The radiating element according to claim 7, further comprising: a printed circuit board, PCB (22), arranged at the lower plane, wherein the PCB (22) includes:

a first microstrip line (24) forming the first transmission line and a second microstrip line (24) forming the second transmission line.

9. The radiating element according to claim 8, wherein the PCB (22) includes a ground plane on the opposing side of the microstrip lines (24), the ground plane being capacitively coupled to the lower plane (12).

10. The radiating element according to any of the previous claims, wherein the conductive element further comprises flaps (19) extending from edges of the upper plane (14) in a direction to the level of the lower plane (12), wherein the slots (4) extend into the flaps (19).

11. The radiating element of any of the previous claims wherein the conductive element (2) is made from a single piece, preferably a bended aluminum sheet.

12. The radiating element of any of the previous claims wherein the lower plane (12) has a central opening (18).

13. The radiating element of any of the previous claims further comprising an inner second radiating element inside the conductive element, wherein the conductive element is constructed to operate in a first frequency band while the inner radiating element inside the conductive element (2) is constructed to operate in a second frequency band higher than the first frequency band.

14. The radiating element of claim 13 when depending on claim 12 wherein the inner radiating element includes a support structure that extends through the opening (18) in the lower plane.

15. The radiating element of claim 14 wherein the support structure of the inner radiating element includes at least one, preferably two crossed PCBs (20) wherein the one or two PCBs (20) includes feeding lines for the conductive element (2) and/or for the inner radiating element.

16. The radiating element of any of claims 13 to 15, wherein the inner radiating element comprises a further PCB (30) arranged in a further predefined distance from the lower plane (12) and preferably parallel to the lower plan (12).

17. The radiating element of any of claims 13 to 16, wherein the inner radiating element has a dipole structure substantially in the same level of the upper plane or below the upper plane.

18. Antenna for a base station including a reflector and multiple of the radiating elements of any of the previous claims wherein the radiating elements are arranged on the reflector such that the lower planes of the conductive elements of the multiple radiating elements are supported in the predefined distance to the reflector.