WO2016131496A1

WO2016131496A1 - Multiport antenna element

Info

Publication number: WO2016131496A1
Application number: PCT/EP2015/053640
Authority: WO
Inventors: Haiguang Chen; Juan Segador Alvarez; Chun Wei MIN
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2015-02-20
Filing date: 2015-02-20
Publication date: 2016-08-25

Abstract

The invention refers to an antenna element comprising a cross-shaped slot on top of a metallic cavity and a plurality of metallic strips encapsulated in said cavity with a distance to said cross-shaped slot, wherein a length direction of each strip traverses an arm of the cross-shaped slot; each of said strips includes at least two terminals in electrical connection with said strip contacting the strip in areas on both sides of the respective arm which is traversed by said strip, and the at least two terminals of each strip are separated such that an electrical signal can be applied to the terminals having a defined phase-shift between the at least two terminals of the strip. Moreover, the invention refers to a method of operating the antenna element and to an antenna including one or more of these antenna elements and a signal generator.

Description

MULTIPORT ANTENNA ELEMENT

TECHNICAL FIELD

The present invention relates to the field of antenna elements and in particular to a cavity- backed slot-patch antenna with multiple inputs. Such antenna elements are usable in particular for mobile communication systems.

BACKGROUND

Mobile base station systems of the next generation require antennas which can be dynamically controlled and allow to support different modes of operations defined by various channel al- gorithms achieving an efficient integration with the hardware architecture.

An example of a compact designed antenna element in disclosed in US 4 710 775. A parasiti- cally coupled, complementary slot dipole antenna element includes a cavity-backed slot antenna element and a parasitic dipole element traverse the slot of the cavity-backed slot antenna element. The cavity-backed slot and the parasitic dipole antenna elements resonate at about a center frequency of the excitation signals supplied to the antenna element in order to generate a relative symmetrically electromagnetic signature and an increased bandwidth. According to a particular implementation, the slot antenna element is fed by striplines which are connected to first and second excitation signals, respectively. The striplines excite the slot along a first and second axis perpendicular to the arms of the slot. The first and second excitation signals may be either different or the same.

A drawback of conventional antenna designs is that typically the antenna element per polarization is excited by only one amplifier output. Such antenna elements are not able to support a configuration where the system offers multiple channels of power simultaneously to the antenna element per polarization in order to increase the signal-to-interference-plus-noise ratio (SINR) of the antenna system. Thus, in conventional systems, transmission networks designs are necessary to convert signals in different modes on transmission lines in order to be con- nected to an antenna with a single port. However, such a transition network introduces additional losses and degrades the efficiency of the system.

SUMMARY

Object of the invention is to provide an antenna element which can be highly integrated such as a system of a single mode, having a low profile and which provide a stable RF performance over a broadband. Moreover, the antenna should be able to be adapted for the mass production at low overall costs.

The foregoing and further objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. According to a first aspect, an antenna element comprises a cross-shaped slot on top of a metallic cavity and a plurality of metallic strips encapsulated in said cavity with a distance to said cross-shaped slot, wherein a length direction of each strip traverses an arm of the cross-shaped slot. Each of said strips includes at least two terminals in electrical connection with said strip contacting the strip in areas on both sides of the respective arm which is traversed by said strip. The at least two terminals of each strip are separated such that an electrical signal can be applied to the terminals having a defined phase-shift between the at least two terminals of the strip.

By offering an antenna element having a strip for each arm of the slot with at least two sepa- rated terminals, these terminals can be directly connected to RF channels of the system without the need of a transition network. Thus, the antenna element is capable of allowing more input power into the antenna element per polarization, as well as supporting various excitation schemes of input signals with a suitable arrangement of amplitudes and the phases of the RF channels.

According to a preferred implementation, the at least two terminals of each strip are allocated close to opposing shorter edges of the respective strip. Thus, for a given area of the strip, the distance of the separated terminals can be maximized. Hence, this configuration helps to minimize the overall dimension of the antenna element. According to a preferred implementation, the strips are arranged with their respective length direction perpendicular to the respective arm which is traversed. This configuration optimizes the efficiency of the parasitic coupling of the respective dipole element of the cross-shaped slot.

According to a preferred implementation, the plurality of strips is allocated in the same layer which is parallel and a defined distance from the layer in which the cross-shaped slot is arranged. This configuration is easy to manufacture e.g. when using a standard-printed circuit- board process as the strips can be surface-mounted on the same flat support layer. Moreover, the parasitic coupling efficiency for the different polarization modes is equal. According to a preferred embodiment, the distance between the cross-shaped slot and the stripes is at least 0.5 mm up to one eighth of the dielectric wavelength at the highest frequency which is of interest for the antenna element. Such frequency of interest for the antenna is preferable below 3 GHz in embodiments having an air-filled metallic cavity and above 3 GHz in embodiments having a cavity of an PCB implementation. A distance of at least 0.5 mm has the advantage that the metallic cavity can easily be fabricated using at least two printed circuit boards. Preferably, the distance between the strips and the cavity is the same as the distance between the strips and the bottom of the cavity. This ensures an optimum coupling performance at a given distance. The distance between the strips to the slot is preferably about (±10%) 0.7 to 0.9 times the length of the arm of the slot. The distance between the slot and strip shall not be too large to offer adequate coupling from the strip to the slot. The slot-to-strip distance may be the same as or less than the strip-to-cavity-bottom distance. According to a preferred implementation, the antenna element includes four of these strips and the cross-shaped slot has four arms, wherein each arm is traversed by one of said four strips. This configuration is preferred to operate the antenna element in the mode of two perpendicular linear polarizations or to generate circularly polarized waves as explained in more detail below.

According to a preferred implementation, each of the terminals includes a conductive (e.g. metallic) post being electrically connected to the strip and extending in a direction perpendicular to the layer in which the strips are arranged and facing away from a layer in which the cross-shaped slot is arranged. Preferably, the posts traverse through holes in the bottom of the metallic cavity opposing the top layer in which the cross-shaped slot is arranged. This configuration provides an optimum compact antenna design. Arranging the terminals in the layer of the strips would require more space for electrical connection of the terminals. According to a preferred implementation, the antenna element includes a conductive (e.g. metallic) patch, operating as a parasitic antenna element, in a layer parallel to the layer of the cross-shaped slot and opposing the stripes. Although it would be possible also to arrange the stripes between the layer of the cross-shaped slot and the patch, the arrangement as mentioned before provides a more compact design and an increased coupling efficiency. Preferably the patch is arranged to be in a capacitive coupling with the plurality of metallic strips.

According to a preferred implementation, the patch is square-shaped. By having a square- shaped patch an optimal coupling ratio between the patch and the metallic strips can be achieved.

According to a preferred implementation, the patch is arranged on a cladded dielectric substrate using a PCB process or machining of a metallic foil on a surface of a dielectric sheet, wherein the substrate or sheet is integrated with or bonded to the cavity on a side facing the slot and opposing the strips. Such an arrangement enables a compact low cost antenna design.

According to a preferred embodiment, the slot is etched off from a top layer of the cavity. The etching process is a manufacturing step easy to be implemented in mass production.

Further aspects of the invention refer to a method of operating an antenna element of one of the embodiments previously disclosed. The method includes the step of applying an AC signal to the terminals of the metallic strips wherein in operation the signal of each slot has an amplitude and a phase shift that propagates through the slot with a predefined phase delay between the two terminals of each strip. For example, the phase delay can be π radians between those two terminals on each strip. According to a further implementation, the phase delay can be π/2 radians between a first terminal of a first strip and a second terminal of a second strip adjacent to the first strip. This configuration is to generate circularly polarized waves when all arms of the cross-shaped slot are used all ports to be energized simultaneously. A further aspect of the invention refers to an antenna including an antenna element according to the embodiments previously described and a signal generator to generate electrical signals to be applied to the terminals of the strip. In particular, the signal generator provides signals to operate the antenna according to the methods as previously described.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and benefits of the present invention will become apparent from the following description of preferred embodiments with making reference to the attached drawings, in which:

FIGs 1 A to IE show planar views on a first embodiment of an antenna element of the invention, wherein FIG. 1 A is a top view with a patch, a slot-layer and a strip-layer, FIG. IB is a bottom view, FIG. 1C shows only the strip lay- er, FIG. ID shows only the slot layer and FIG. IE shows the slot layer with the patch on top;

FIG. 2 shows a vertical cross-sectional view of the antenna element of FIGs 1A to IE;

FIGs 3A and 3B show planar views of the antenna element of FIGs 1A to IE for different operation modes;

FIG. 4 shows a perspective view of an array of four antenna elements accord- ing to FIGs lA to IE;

FIG. 5 shows a perspective view of an antenna element of a further embodiment; and FIGs 6A and 6B show flow charts of methods for operating an antenna; and

FIG. 7 shows a symbolic diagram of an antenna including one or more antenna elements and a signal generator. DETAILED DESCRIPTION OF EMBODIMENTS

An antenna element, as shown in FIGs. 1A to IE, comprises of a slot 101 of crossed shape including four orthogonal arms on top of a closed metallic cavity. The slot 101 operates as a driven antenna element fed by four metallic strips 103 encapsulated in the cavity. The strips 103 are of rectangular form. Each of said strips 103 is attached by two metallic probes 113 on the shorter sides of the rectangular strip 103 to operate as feeding ports when connected to a signal generator. The (cavity-backed crossed) slot 101 is preferable manufactured by using a PCB processes. The design pattern of the slot 101 is deposited on one metallization layer 107 laminated on one side of a dielectric substrate, whilst there is no metallization on the other side of the dielectric substrate. The pattern of the metallic strips 103 is deposited on a side of another dielectric substrate, whilst on the other side of the dielectric substrate a metallization layer serves as the bottom 108 of the cavity. The two deposited dielectric substrates are bonded together and gone through drilling and plating processes to form the cavity structure.

Metallic sidewalls 111 of the cavity are produced by using an edge-plating process, or effectively produced by arrays of plated holes 109, where areas 112 are left blank as "stamp holes" for machining in mass production.

A metallic patch 105, operating as a parasitic antenna element can be optionally placed on top of the crossed slot 101 with a predetermined distance 209. The (parasitic) patch 105 is, according to the shown embodiment, square shaped and can be fabricated on a cladded dielectric substrate using PCB processes, or alternatively machined on metallic foils and rolled on to the surface of a dielectric sheet 117 of predetermined thickness.

A possible implementation of the antenna element as described above is shown in the cross- sectional view of FIG. 2. A radome 119 serves as the cover to enclose and protect the antenna from various weather conditions. The thickness of the radome is determined such that it is transparent to electromagnetic waves emitted from the antenna, whilst offering sufficient mechanical strength and rigidity. The spacing 118 as defined between the dielectric sheet 117 and the radome 119 is selected to minimize reflections of waves returned to the antenna so as to maintain acceptable impedance matching of the antenna. The dielectric sheet on which the one or more patches 105 is attached, is assembled on to a main board 203 through some supporting structures. Alternatively, the patch 105 can be fabricated on to the inner side of the the radome 119 facing said slot.

As illustrated in FIG. 2, the antenna element (or an array of antenna elements) is mounted, preferably by soldering 201 on a ground plane 115. The ground plane 115 offers isolation to the antenna from an interface of interconnections 207, associated feeding networks 205 and other components integrated in a dielectric substrate 203 on the side opposing the antenna element. The antenna element and all the other circuitries are integrated as a single module that can be fabricated using PCB processes in one production routine, being suitable for mass production with high precision control.

With reference to FIGs 3A and 3B, the electrical operation of the antenna is described.

Referring to FIG. 3 A, when having the antenna operate in a mode of linear polarization, -45°- polarized waves can be generated as shown with the solid arrow 307a by exciting the +45° arms of the slot with appropriate excitation arrangement on the strip ports defined as 1, 2, 3 and 4. The electromagnetic energy, which is coupled to the +45° arms of the slot, is generated by a combination of signals from the metallic strips that traverses two opposing arms of the cross-shaped slot with a predetermined distance with respect to the centre of the slot for optimum impedance matching. In operation, a signal Si with amplitude of P and a phase of 9s at port 1 propagates through the first strip, and encounters a phase delay of 0L. A signal S₂ with amplitude of P and a phase of at port 2 is constructively combined with the signal Si to generate maximum energy that is coupled to the respective arms of the cross-shaped slot. The maximum energy shall be combined by optimizing the physical length of the strip, which corresponds to the electrical length of 9L such that the two signals are added in-phase. The identical operating mechanism applies to the opposing metallic strip connected to Port 3 and Port 4 to generate maximum energy. The distance between the two opposing strips is optimized to guarantee that the coupled energy to the respective arms slot shall be combined constructively with minimum reflection to create broadside radiations.

An identical excitation scheme applies to the other two sets of strips to energize the -45° arms to generate +45°-polarized waves as shown with the dotted arrow 307b in FIG. 3A. As shown in FIG. 3A, the antenna element can be used to generate +45° and -45° linear polarized waves 307a and 307b simultaneously. However, by superimposing the two linear polarized waves, with 90° phase difference a circularly polarized wave can be produced, as shown in FIG. 3B. Referring to FIG. 3B, to generate circularly polarized waves, both slots are used with all ports being energized simultaneously. Each slot is fed using the excitation scheme as described, and with an additional phase delay of 90° (π 12 radians) on ports 5, 6, 7 and 8 with respect to the other port set 1 , 2, 3, 4. At an instant of time, waves emitted from +45° slot are in -45° polarization, followed by waves in +45° polarization emitted from -45° arms of the slot with an effective time delay of quarter wavelength (90° of π 12 radians). The combination of the waves is consequently in rotary manner with the time delay and, thus, form right-handed circular polarized waves. Left-handed circular polarized waves can be generated by applying such time delay on Ports 1 , 2, 3 and 4 with respect to the other port set. The described operation can be applied to other communication systems where circularly polarized waves are needed for propagations.

FIG. 6A shows a flow chart of a method for operating an antenna element as shown in FIG. 3 A to produce linear polarized waves. The method includes in step 601 generating a first AC signal and in step 602 applying the first AC signal on two terminals of a first strip of the an- tenna element, such as terminals 1 and 2 shown in FIG. 3A. Next, the method includes in step 603 generating a second AC signal having a phase delay of π radians with respect to the first AC signal and in step 604 applying the second AC signal on two terminals of a second strip of the antenna element such as terminals 3 and 4 shown in FIG. 3 A. With reference to FIG. 6B a method is described for operating an antenna element to produce a circularly polarized waves. The method includes the four method steps 601 to 604 as described with reference to FIG. 6A. Moreover, it includes in step 605 generating a third AC signal having a phase delay of π/2 radians to the first signal and in step 606 applying the third AC signal on two terminals of a third strip of the antenna element such as terminals 5 and 6 shown in FIG. 3B. Moreover, the method includes in step 607 generating a fourth AC signal having a phase delay of 3π/2 radians to the first AC signal and in step 608 applying the fourth AC signal on two terminals of a fourth strip of the antenna element such as terminals 7 and 8 in FIG. 3B. FIG. 7 shows a symbolic diagram of a complete antenna according to an embodiment of the present invention. The antenna includes one or more antenna elements 701 such as the antenna elements previously described. Moreover, a signal generator 702 is connected to the one or more antenna elements 701 to generate AC signals such as the AC signals described with ref- erence to FIGs 6 A and 6B.

According to a preferred implementation, an antenna includes an array of more than one, in particular four antenna elements, as shown in the configuration of FIG. 4. The array is, preferably but not limited to, of square type where rows and columns of said antenna elements are arranged to align horizontally and vertically, respectively. The array can be of alternative types, such as arranging said antenna elements in triangular array and sparse array, depending on characteristics of operating scenarios, where associated beamforming schemes are applied for optimum channel capacity. Referring to FIG. 5, an alternative antenna element is described. The antenna element includes of a metallic cavity 403, which can be either air- filled or filled with dielectric materials. On top of the cavity 403 a crossed slot 401 is machined with predetermined dimensions. The slot 401 is energized by multiple metallic strips 411 which are connected by pairs of metallic posts 413 to form connections between the antenna and the transceivers through a metallic sheet 407, serving as the ground plane for the antenna. The strips 411 are located inside the cavity and assembled using suitable supporting structures. A metallic patch 405, operating as a parasitic antenna element of at least one or more, can be optionally placed on top of the slot 401 with a predetermined distance. The patch 405 is of square shape and can be fabricated on cladded dielectric substrates using PCB processes, or alternatively machined on metallic foils and rolled on to the surface of a dielectric sheet 409 of predetermined thickness.

It is to be understood that also the embodiment of FIG. 5 can be arranged as a single antenna element or in an array of more than one antenna elements such as shown in FIG. 4.

Claims

Antenna element comprising:

a cross-shaped slot (101; 401) on top of a metallic cavity and

a plurality of metallic strips (103; 403) encapsulated in said cavity with a distance to said cross-shaped slot (101; 401), wherein a length direction of each strip (103; 403) traverses an arm of the cross-shaped slot (101; 401);

each of said strips (103; 403) includes at least two terminals (1, 2; 3, 4; 5, 6; 7, 8) in electrical connection with said strip (103; 403) contacting the strip (103; 403) in areas on both sides of the respective arm which is traversed by said strip (103; 403), and the at least two terminals (1, 2; 3, 4; 5, 6; 7, 8) of each strip (103; 403) are separated such that an electrical signal can be applied to the terminals having a defined phase- shift (9L) between the at least two terminals of the strip (103; 403).

Antenna element of claim 1, wherein the at least two terminals (1, 2; 3, 4; 5, 6; 7, 8) of each strip (103; 403) are allocated close to opposing shorter edges of the respective strip (103; 403).

Antenna element of one of the previous claims, wherein the strips (103; 403) are arranged with their respective length direction perpendicular to the respective arm which is traversed.

Antenna element of one of the previous claims, wherein the plurality of strips (103; 403) is allocated in the same layer which is parallel and in a defined distance to a layer in which the cross-shaped slot (101; 401) is allocated; and

wherein the defined distance is at least 0.5 mm and preferably the same distance to a bottom of said cavity or the layer of strips is closer to the slot than to the bottom of said cavity.

Antenna element of one of the previous claims having four of said strips (103; 403) and the cross-shaped slot (101; 401) having four arms, wherein each arm is traversed by one of said four strips (103; 403).

6. Antenna element of one of the previous claims, wherein each of the terminals (1, 2; 3, 4; 5, 6; 7, 8) includes a conductive post (113) being electrically connected to the strip (103; 403) and extending in a direction perpendicular to a layer in which the strips (103; 403) are arranged and facing away from a layer in which the cross-shaped slot (101; 401) is arranged.

7. Antenna element of claim 6, wherein the posts (113) traverse through holes in a metallic sheet below the layer in which the strips (103; 403) are arranged.

8. Antenna element of one of the previous claims having a conductive patch (105; 405), operating as a parasitic antenna element, in a layer parallel to the layer of the cross- shaped slot (101; 401) and opposing the strips (103; 403).

9. Antenna element according to claim 8, wherein the patch (105; 405) is square-shaped.

10. Antenna element according to claim 8 or 9, wherein the patch (150; 405) is arranged on a cladded dielectric substrate using a PCB process or machining of a metallic foil on a surface of a dielectric sheet, wherein the substrate or sheet is integrated with or bonded to the cavity on a side facing the slot (101; 401) and opposing the strips (103; 403).

11. Antenna element according to one of the previous claims wherein the slot ( 101 ; 401 ) is etched off from the top layer of the cavity.

12. Method for operating an antenna element of one of the previous claims including the step of

applying an AC signal to the terminals (1, 2; 3, 4; 5, 6; 7, 8) of the metallic strips (103; 403) wherein in operation the signal of each slot (101; 401) has an amplitude and a phase that propagates through the slot (101; 401) with a predefined phase delay between the two terminals (1, 2; 3, 4; 5, 6; 7, 8) of each strip (103; 403).

13. Method of claim 12, wherein the phase delay is π radians between the at least two terminals (1, 2; 3, 4; 5, 6; 7, 8) on each strip (103; 403). Method of claim 12 or 13, wherein a further phase delay is π 12 radians between a first terminal (1 , 2; 3, 4; 5, 6; 7, 8) of a first strip (103; 403) and at least a second terminal of a second strip adjacent to the first strip (103; 403).

Antenna including an antenna element according to one of claims 1 to 1 1 and a signal generator to generate electrical signals to be applied to the terminals (1 , 2; 3, 4; 5, 6; 7, 8) of the strips (103; 403) such that the signals operate the antenna according to the method of one of claims 12 to 14.