WO2017098315A1

WO2017098315A1 - An antenna arrangement for portable computerised devices

Info

Publication number: WO2017098315A1
Application number: PCT/IB2016/001728
Authority: WO
Inventors: Francesco Donzelli; Daniele Piazza
Original assignee: Adant Technologies Inc.
Priority date: 2015-12-11
Filing date: 2016-12-06
Publication date: 2017-06-15

Abstract

An antenna arrangement (1) for a portable computerised device (100) having an enclosure ( 101 ) that is at least partially made of a metal material characterised in that it comprises a first radiating structure (11) that is formed by at least a metal portion of said enclosure and a feeder structure (12), which is operatively coupled to said radiating structure to provide feeding currents in the MHz and GHz range to excite said first radiating structure.

Description

AN ANTENNA ARRANGEMENT FOR PORTABLE COMPUTERISED DEVICES

DESCRIPTION

The present invention relates to an antenna arrangement for portable computerised devices, such as notebooks, laptops, tablets, smartphones, and the like.

More particularly, the present invention relates to an antenna arrangement for portable computerised devices provided with an enclosure that is at least partially made of a metallic material.

In the last years, a lot of attention has been reserved to the design of antenna arrangements for portable computerised devices due to the growing popularity of these devices and to the tight requirements for the antenna arrangements in terms of form factor, bandwidth and radiation pattern.

As is known, an emerging trend in the design of portable computerised devices consists in adopting a single monocoque (e.g. aluminum) shell in order to provide impact protection and guarantee product durability.

The adoption of a metal case, however, has raised some issues in relation to the design of an antenna arrangement for these devices. ^

Antenna arrangements, which are normally proposed for portable computerised devices with a plastic enclosure, have shown relevant drawbacks when adopted in portable computerised devices provided with a metal enclosure.

In figures 1 -2, a typical portable computerised device 500 with a metal enclosure of the state of the art is shown.

As it may be noticed, as for most of the portable computerised devices, the antenna 550 of the computerised device of Fig. 1 consists in a planar monopole or inverted F-antenna, which is adapted to be integrated in regions 501 of the screen panel or the chassis.

The antenna may be accommodated in the plastic frame at the edge of the base portion 502 of the device, e.g. behind the device logo or in a slot between the lid portion 503 and the base portion 502 of the device.

The experience has been shown that solutions of this type do not generally offer a satisfactory coverage for the radiation pattern R.

The antenna may be accommodated along the lid portion 503 of the device. However, it has been proven that this solution is characterised by severe distortions in the radiation pattern R due to the presence of the metallic shell all around the radiating structure.

In general, as shown in figure 2, in known portable computerised devices having a metal enclosure, the antenna radiation pattern R is mainly directed towards the direction of the keyboard and shows a poor coverage towards the back of the lid portion 503.

As a consequence, the coverage offered by the antenna is not satisfactory in consideration of the general requirements for these devices, which ideally foresee for the radiation pattern to be uniformly directed in all directions, taking as a reference a semi-sphere defined by the laying plane XY of the portable computerised device (figure 1 ).

The main aim of the present invention is to provide an antenna arrangement for a portable computerised device that allows overcoming or mitigating the mentioned technical problems of the state of the art.

Within the scope of this aim, an object of the present invention is to provide an antenna arrangement that allows obtaining a uniform distribution of the radiation despite of the presence of an enclosure at least partially made of metal material.

Another object of the present invention is to provide an antenna arrangement that is highly reliable in operation and relatively easy to manufacture at industrial level, at competitive costs with respect to currently available devices of similar kind.

This aim, these objects and others that will become apparent hereinafter are achieved by an antenna arrangement for a portable computerised device according to the following claim 1 and the related dependent claims.

In a further aspect, the present invention relates to a portable computerised device according to the following claim 13.

Yet in a further aspect, the present invention relates to a method for designing an antenna arrangement for a portable computerised device according to the following claim 14.

Further characteristics and advantages of the invention will become apparent from the detailed description of exemplary embodiments of the electronic protection device, which is illustrated only by way of non-limitative examples in the accompanying drawings, wherein: Figures 1 -2 are schematic diagrams showing a traditional antenna arrangement in a portable computerised device with a metal enclosure;

Figures 3-4 are schematic diagrams showing an embodiment of the antenna arrangement, according to the invention;

Figures 5-10 schematically show the operation of the embodiment of Figs. 3-4;

Figure 1 1 is a schematic diagram showing another embodiment of the antenna arrangement, according to the invention;

Figures 12- 14 are schematic diagrams showing another embodiment of the antenna arrangement, according to the invention;

Figure 15 is a schematic diagram showing another embodiment of the antenna arrangement, according to the invention.

Figure 16 schematically shows examples of operation of the embodiments of Figs. 12-15. With reference to the cited figures, the present invention relates to an antenna arrangement 1 for a portable computerised device 100.

The computerised device has a lid portion 100A, a base portion 100B and a screen l OOC. The computerised device 100 is provided with an enclosure 101 , which is at least partially made by a metal material.

According to the invention, the antenna arrangement 1 comprises a first radiating structure 1 1 that consists of at least a metal portion of the enclosure 101.

Preferably, the radiating structure 1 1 comprises a monocoque metal shell of the enclosure 101 of the computerised device 100, more preferably to the lid portion 100A of this latter.

According to the invention, the antenna arrangement 1 comprises a feeder structure 12, which is operatively coupled to the radiating structure 1 1 to provide feeding currents in the MHz and GHz range to excite the radiating structure 1 1 .

Preferably, the feeder structure 12 comprises a transmission line 121 , such as a coaxial cable or probe or a waveguide.

Preferably, the feeder structure 12 is coupled with the first radiating structure 1 1 by means of a capacitive or inductive coupling.

Preferably, the feeder structure 12 comprises a high frequency impedance structure 123 to properly confine the current distribution on the first radiating structure 1 1 and/or adjust the input impedance of the first radiating structure 1 1 .

Preferably, the antenna arrangement 1 comprises a second radiating structure 150 that may be of known type (figure 1 1).

Preferably, the feeder structure 12 is operatively coupleable to the second radiating structure 150 to excite feeding currents in the MHz and GHz range over the second radiating structure 150.

Preferably, the feeder structure 12 comprises switching means 16 configured to switch feeding currents between the first radiating structure 1 1 and the second radiating structure 150.

Referring to figures 4- 10, an embodiment of the antenna arrangement, according to the invention, in a portable computerised device 100 (e.g. a notebook) is illustrated.

The present invention allows resolving the coverage issues described above by using at least a metal portion 1 1 of the enclosure 101 as the main radiating device through the excitation of characteristic electromagnetic (EM) modes. Preferably, the radiating structure 1 1 is configured to sustain different resonant radiation modes.

As is known, the theory of characteristic modes describes a fundamental electromagnetic property of conductors to be radiating and to sustain therefore a set of surface-currents modes {λ, } ί=1..Ν excited in some places along the structure by a generic EM incident field.

Characteristic modes depend only on the shape of conductors when an EM field incident the structure. To properly excite the modes without an EM incident field a specific excitation mechanism is required.

The modes are generally numbered according to the occurrence of the respective resonance frequency at which they can be considered as effectively radiating - with different efficiency and radiating characteristics.

The modal significance is a parameter used to understand the behavior of each characteristics mode. The modal significance, MS, is normally defined as follows,

such a parameter represents the normalized amplitude of each mode (figure 5).

As is known, the modal significance is directly proportional to the efficiency of the radiated mode.

When MS = 1 , the mode corresponding is resonant.

The resonance frequency and radiating bandwidth can be obtained from the diagram of modal significance and other figures of merit (figure 5).

A half-power bandwidth can be defined according to the MS

where f_res, f_H andfL are the resonant frequency, upper band frequency and lower frequency respectively.

They are evaluated from the MS values as follows:

MS{f_res) = 1 1 1

MS(f_H) = MS{f_L) =

1 + j t

According to the claimed invention, a metal portion 1 1 (e.g. a metal monocoque shell) of the enclosure 101 (preferably of the lid portion 100A) of the computerised device 100 is adopted as a radiating structure 1 1.

Such a radiating structure 1 1 can be properly excited through particular resonant characteristic modes at a selected frequency of operation, each mode allowing for a different radiation pattern.

The feeder structure 12 is configured to excite such a radiating structure for the suitable current modes, which may be selected on the base of their radiated field behaviors.

In order to select a given current mode, a characteristic mode analysis on the radiating structure 1 1 can be performed.

To this aim, a mode tracking over frequency may be performed on a 3D model of the radiating structure 1 1 fed by an incident plane electromagnetic wave.

Modal significance curves similar to that of figure 5 can be obtained and plotted.

According to the trend of said modal significance curves, a set of characteristic modes can be identified (if resonant or close to resonance) and the respective radiated field patterns modeled and evaluated case by case.

This analysis allows selecting a current mode to excite the radiating structure 1 1 based on the resonance frequency and radiation characteristics of this latter.

The feeder structure 12 is advantageously configured to feed the radiating structure 1 1 to provide the current distribution of a selected current mode.

The feeder structure 12 preferably comprises a transmission line 121 formed by a micro- coaxial cable electrically connected to a TX-RX Module (not shown).

According to some embodiments (figures 3-1 1 ), the feeder structure 12 is advantageously configured to directly feed the radiating structure 1 1 and to confine appropriately the induced currents on this latter to preserve mode purity and to control the impedance at the same time. An embodiment of the feeder structure 12 is shown in figure 6.

Proper confinement of the excitation currents on the radiating structure 1 1 is achieved through proper design of frequency selective surfaces that can be placed on the inner side of the lid portion 100A of the computerised device 100.

Preferably, the feeder 12 comprises a laminate sheet structure 122 (e.g. multilayer apton structure) that is preferably positioned in the gap between the hidden surface of the lid portion 100A and the backside of the screen 100C of the computerised device (figure 6).

The laminate structure 122 is preferably of the multi-layer type.

Preferably, the laminate structure 122 comprises the following layers:

Layer 1 - metal layer

Layer 2 - EBG layer

The Layer I is aimed at acting as a ground-plane for the transmission line 121 (e.g. a RF-ln cable) and at the same time as a EM shield for the screen 100C itself.

Surface currents, which correspond to the selected excited characteristic mode, travel along the entire metallic surface of the radiating structure 1 1 (e.g. the monocoque shell of the enclosure 101 ).

In some embodiments, the Layer 1 can also be removed depending on the type of layer 2 selected and the EM shielding.

The Layer 2 is composed of an Electromagnetic Bandgap (EBG) structure 123 and it is used to confine the surface propagation around a certain region to properly excite the selected mode.

The EBG structure 123 may include a periodic arrangement of dielectric or metallic elements 1230 in one, two or three dimensional manners (figure 7).

The EBG structure 123 advantageously inhibits the propagation of the electromagnetic waves in a specific frequency band for all angles and for all polarization states. The band-gap formation the high impedance structure 23 is achieved through the resonances of the above mentioned periodic structure.

The EBG structure 123 may have a mushroom like configuration.

In this case, the EBG structure 123 preferably comprises a metal sheet, textured with a two- dimensional lattice of resonant elements 1230, which act as a two-dimensional filter to prevent the propagation of electric currents.

The FBG structure 171 can e intuitively described using a lumped LC circuit model that also refers to the range of frequency where EM propagation is suppressed.

The capacitance C of said LC circuit is due to the proximity of the top metal patches 1230. while the inductance L originates from the current flowing through the vias.

Thus, the behavior of the EBG structure can be adjusted by tuning the inductance or capacitance of such a LC circuit.

The EBG structure 123 may have an uni-planar configuration.

In this case, as for the mushroom-like configuration, the operational mechanism of the EBG structure 123 can be described by a lumped LC model as well. The capacitance C is provided by the edge coupling between adjacent patches 1230. Instead of using vertical vias to provide the inductance L, a thin microstrip line on the same layer of the patches is used to connect the patches 1230 together.

In order to properly arrange the EBG structure 123, the characteristic currents for the final selected current modes are plotted onto the structure to identify the locations of electric field maximums and minimums and the distribution of the currents.

The feeder structure 12 needs to be placed close to a field maximum in a way to favor the appearance of the said currents according to their physical characteristics - e.g. longitudinal currents may be easily excited by linearly polarized feeder structures such as monopoles.

According to the peculiarities of the currents, the feeder structure 12 is then properly designed to conveniently excite the selected mode on the shell: the first approach can be based on an ideal high-impedance surface in order to model the shape and extension of the feeder structure with low computational effort in the full-wave simulations.

At the same time, the geometry of the EBG structure 123 is separately designed and tuned on a fixture in order to drive the intrinsic frequency response and the bandgap extension (figure 8).

In the characteristic frequency range of the EBG structure 123, the currents coming from the transmission line 121 (e.g. a coaxial probe) and travelling along the radiating structure 1 1 are expected to be confined around a specific region and their flux controlled in the direction according to the shape of the EBG structure itself (figure 9).

Finally the feeding structure 12 is coupled to the radiating structure 1 1.

The final results are evaluated and the feeder structure 12 is optimized with respect to two different goals, a) radiated pattern, b) correct impedance match between the RF-In cable to the mode intrinsic impedance.

Figure 10 shows examples of radiation patterns of an antenna arrangement according to the claimed invention at 2.4 GHz and 5 GHz compared with radiation patterns of traditional ₍ antenna arrangements.

The antenna arrangement, according to the invention, is capable of providing a hybrid radiating configuration structure able to fill the experienced holes in coverage, typical of standard antennas solutions, towards lateral and back direction (figure 10).

An antenna selection scheme can then be adopted to select the antenna that provides best coverage in the specific use case scenario.

In view of the above, it is apparent the present invention relates also to a method for designing an antenna arrangement 1 for a portable computerised device 100 having an enclosure 101 that is at least partially made of a metal material.

According to the invention, the method comprises the following steps;

- providing a first radiating structure 1 1 that is formed by at least a metal portion of said enclosure;

- selecting suitable feeding currents to excite said first radiating structure;

- providing a feeder structure 12 to provide said feeding currents in the MHz and GHz range to excite said first radiating structure;

- coupling said feeder structure with said first radiating structure.

According to some embodiments of the invention (figures 12- 16), the antenna arrangement of the invention comprises at least an exciter structure 15 operatively coupled with the feeder structure 12 (in particular with the transmission line 121 ) and with the first radiating structure 1 1.

The exciter structure 15 is adapted to be excited by the feeding structure 12 and to emit, in response to the excitation by said feeder structure, an electromagnetic radiation to excite the first radiating structure 1 1 .

Preferably, the exciter structure 15 comprises a hollow conductive structure 1 A, 15B operatively coupled with the feeder structure 12 and provided with non-conductive portions 19, 190 emitting an electromagnetic radiation when said conductive structure is excited by the feeder structure 12.

According to an embodiment (figures 12- 14), the exciter structure 15 comprises a cavity- backed antenna 15 A.

The cavity-backed antenna 15A preferably consists of a metallic container 18 filled with air or a low-loss dielectric medium.

The cavity-backed antenna 15A is preferably coupled to the transmission line 12 1 of the feeder structure 12 by means of a probe 121 A of said feeder structure, which protrudes in the interior of the cavity backed antenna.

Preferably, the probe 121 A is adapted to operate as a monopole antenna.

The probe 121 A can be directly in contact with the metal parts of the cavity-backed antenna

15A or it could be floating inside in the interior of the cavity backed antenna.

Preferably, the cavity-backed antenna 15A comprises a plurality of slots 19 that define corresponding openings in the metallic container 18.

As an example, the slots 19 may have a length of λ/2, where L is the working frequency wavelength.

Preferably, the slots 19 have a bowtie shape or are shaped as log-periodic slots (figure 13). Although these structures typically show a resonant behavior - which is mainly conditioned by the size of the metallic container 1 8 and by the filling medium inside said container - the inventors have seen that the arrangement of a plurality of slots 19 can excite a combination of hybrid modes in addition to the natural resonant TE i oi mode inside the container.

It has been proven that such hybrid modes can surprisingly enhance the antenna bandwidth and furthermore originate a pronounced end-fire radiation lobe beyond the enclosure 101 of the portable computerised device 100.

According to another embodiment (figure 15), the exciter structure 15 comprises substrate- integrated waveguide (SIW) structure 1 5B.

Preferably, the SIW structure 1 5B comprises a planar dielectric substrate 34 (e.g. a PCB), in which multiple rows of conductive elongated elements 37 are obtained, e.g. by providing corresponding holes in said substrate and by filling said holes with electrically conductive material.

The dielectric substrate 34 has opposite surfaces (perpendicular to the extension of said conductive elongated elements) that are covered by corresponding electrically conductive layers 35, 36.

It is evident how the assembly including elongated elements 37 and the conductive layers 35, 36 is equivalent to a hollow conductive structure filled with an electrically insulating medium (the material of the substrate 34).

Said conductive structure is preferably coupled to the transmission line 121 of the feeder structure 12 by means of a probe 121 A of said feeder structure, which penetrates through the substrate 34.

At one or both of said conductive layers 35-36, the dielectric substrate 34 comprises non- conductive portions or slots 190.

The arrangements of the non-conductive portions or slots 190 provides similar advantages to those described for the exciter structure 15 A.

Preferably, the exciter structures 15A, 1 B are positioned in proximity to an edge of the first radiating structure 1 1.

Figure 16 shows examples of radiation patterns of an antenna arrangement 1 including two exciter structures 15 at opposite edges of the first radiating structure 1 1 .

In practice it has been found that the antenna arrangement 1 , according to the invention, fully achieves the intended aim and objects.

The antenna arrangement of the invention allows obtaining an optimal distribution of the radiation even if the computerised device 100 comprises an enclosure 101 including metal portions.

The antenna arrangement of the invention is highly reliable in operation and relatively easy to manufacture at industrial level, at competitive costs with respect to currently available devices of similar kind.

Claims

1 . An antenna arrangement ( 1) for a portable computerised device ( 100), said portable computerised device having an enclosure ( 101 ) that is at least partially made of a metal material, characterised in that it comprises a first radiating structure (1 1) that is formed by at least a metal portion of said enclosure and a feeder structure ( 12), which is operatively coupled to said first radiating structure to provide feeding currents in the MHz and GHz range to excite said first radiating structure.

2. An antenna arrangement, according to claim 1 , characterised in that said at least a metal portion (1 1 ) of said enclosure comprises a monocoque metal shell of said enclosure.

3. An antenna arrangement, according to one or more of the previous claims, characterised in that said first radiating structure ( 1 1 ) is capable of sustaining different resonant radiation modes.

4. An antenna arrangement, according to one or more of the previous claims, characterised in that said feeder structure (12) comprises a transmission line ( 121 ).

5. An antenna arrangement, according to one or more of the previous claims, characterised in that said feeder structure ( 12) is coupled with said first radiating structure (1 1 ) by means of a capacitive or inductive coupling.

6. An antenna arrangement, according to one or more of the previous claims, characterised in that said feeder structure ( 12) comprises a high frequency impedance structure ( 123) confining the current distribution on said first radiating structure ( I I ) and/or adjusting the input impedance of said first radiating structure.

7. An antenna arrangement, according to one or more of the previous claims, characterised in that it comprises a second radiating structure ( 150), said feeder structure ( 12) being operatively coupleable to said second radiating structure to provide feeding currents in the MHz and GHz range to excite said second radiating structure.

8. An antenna arrangement, according to claim 7, characterised in that said feeder structure ( 12) comprises at least a switch ( 16) switching said feeding currents between said first radiating structure (1 1) and said second radiating structure ( 150).

9. An antenna arrangement, according to one or more of the previous claims, characterised in that it comprises at least an exciter structure ( 15) operatively coupled with said feeder structure ( 12) and with said first radiating structure ( 1 1), said exciter structure being excited by said feeding structure and emitting, in response to the excitation by said feeder structure, an electromagnetic radiation to excite said first radiating structure.

10. An antenna arrangement, according to claim 9, characterised in that said exciter structure (1 5) comprises a hollow conductive structure ( 15A, 15B) coupled with said feeder structure (12), said hollow conductive structure being provided with non- conductive portions ( 19, 190) emitting an electromagnetic radiation when said conductive structure is excited by said feeder structure.

1 1. An antenna arrangement, according to claim 10 or 1 1 , characterised in that said exciting structure ( 15) comprises a cavity-backed antenna ( 15A).

12. An antenna arrangement, according to claim 10 or 1 1 , characterised in that said exciting structure ( 15) comprises a substrate-integrated waveguide (15B).

13. A portable computerised device ( 100) characterised in that it comprises an antenna arrangement (1), according to one or more of the previous claims.

14. A method for designing an antenna arrangement ( 1 ), according to one or more of the claims from 1 to 1 1 , characterised in that it comprises the following steps;

providing a first radiating structure ( 1 1 ) that is formed by at least a metal portion of said enclosure;

selecting suitable feeding currents to excite said first radiating structure; providing a feeder structure ( 12) to provide said feeding currents in the MHz and GHz range to excite said first radiating structure;

coupling said feeder structure with said first radiating structure.