WO2013060683A1

WO2013060683A1 - Antenna system for portable wireless device

Info

Publication number: WO2013060683A1
Application number: PCT/EP2012/070976
Authority: WO
Inventors: Aleksander Krewski; Werner Schroeder; Jan Vercruysse
Original assignee: Option Nv
Priority date: 2011-10-23
Filing date: 2012-10-23
Publication date: 2013-05-02

Abstract

An antenna system is described device comprising: a first casing part; a second casing part which is connected to the first casing part, wherein there is a slot between the first casing part and the second casing part, the first casing part and the second casing part being electrically conductive; electrical interconnecting elements between the first casing part and the second casing part for providing an electrically conductive loop between the first casing part and the second casing part; a first coupling element between the first casing part and the second casing part; a second coupling element, physically offset from the first coupling element along a longitudinal axis of the slot, a first node located on, or adjacent to, the first coupling element; circuitry for connecting the first node with at least one transmit/receive module.

Description

ANTENNA SYSTEM FOR PORTABLE WIRELESS DEVICE

FIELD OF THE INVENTION

This invention relates to an antenna system for a wireless device, e.g. a portable wireless device, such as a laptop computer, a PDA a smartphone, a mobile phone, a tablet, and to a portable wireless device incorporating the antenna system.

BACKGROUND OF THE INVENTION

The design of wireless devices is constrained by a number of design parameters. Users require a device which is lightweight and robust. It is also necessary to provide an antenna system which will support wireless connectivity across one or more frequency bands.

One design approach for portable wireless devices is to provide a metal unibody casing, also known as a monocoque. The outer metal casing provides structural rigidity for the device. A laptop computer is formed as two separate unibody casing parts: a first (base) part which accommodates components such as the keyboard, processor, memory and storage; and a second (lid) part which accommodates the screen. The unibody approach can provide robustness combined with low weight, especially when a material such as aluminium is used. However, a disadvantage of the unibody design is that it can hinder the provision of wireless connectivity.

One approach to providing a wireless antenna within a laptop casing is to locate antenna elements at the top of the lid. Where the laptop casing is a unibody part, an opening in the local region of the antenna elements is required. This opening will reduce the strength of the unibody casing. This is a widespread conventional solution.

Another approach is to provide an antenna which can fold out, or extend beyond, the unibody casing. This has a disadvantage that the antenna must be manually operated between a storage position and an operational position. Also, the antenna is prone to damage.

Other approaches are to mount an antenna on the frame of the optical drive opening, or behind the manufacturer's logo. These approaches are limited to high-band antennas for operation such as in the Industrial, Scientific and Medical (ISM) band at 2.4GHz or for instance E-UTRA 3GPP band 1 and 7. EP 1 962 372B1 describes a broadband antenna with inductive chassis mode coupling which is intended for use with a folder-type mobile phone.

There is an increasing demand in portable wireless devices to provide an antenna system which will support wireless connectivity across one or more frequency bands, such as the Industrial, Scientific and Medical (ISM) band at 2.4GHz used for Wireless Local Area Network (WLAN) and Personal Area Network (PAN) connectivity, and the GSM/Long Term Evolution (LTE) bands. There is also demand to support Multiple Input-Multiple Output (MIMO) operation across multiple frequency bands. MIMO operation typically requires at least two independent antenna elements, which further complicates incorporating an antenna system in a wireless device.

The present invention seeks to provide an antenna system for a wireless device having conductive casing parts.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternative antenna system for a wireless device such as a portable wireless device, such as a laptop computer, a PDA, a smartphone, a mobile phone, a tablet and a portable wireless device incorporating the antenna system.

An aspect of the present invention provides an antenna system according to any of the claims 1 to 44 wherein each dependent claim defines a separate embodiment of the present invention. A further aspect is a terminal or wireless device including the antenna system as defined in any of the claims 1 to 44. The present invention provides a portable wireless device comprising an antenna system as described above. The portable wireless device can be a smartphone, a laptop, a tablet, a PDA, a mobile phone, for example.

The casing parts can be unibody or monocoque parts, which are manufactured from a conductive material such as metal (e.g. aluminum) or a conductive plastic material. Casing parts of electronic devices comprises always a layer or coating of conductive material for Electromagnetic Compatibility (EMC) reasons. The parts may be moveable with respect to each other, e.g. hinged as with a conventional laptop, or one can be a sleeve for the other for example. Advantageously, there is a slot (opening) provided inside or between the casing parts. A number of conductive couplers can be placed in the slot connecting both casing parts. These placements realize a novel way to excite characteristic modes or linear superpositions thereof on the chassis of a wireless device.

Advantageously, circuitry is arranged to provide an in-phase excitation of the characteristic mode and further connection between the feed port with its first and second terminals and one wireless TX/RX (transmit/receive) module. The antenna system couples inductively to the chassis of the portable wireless device, e.g. to the laptop's chassis (inductive coupler). This arrangement can be used in one of the operating frequency bands, such as a low-band frequency range.

Advantageously, when there are two couplers in the slot, specifically in case of symmetric placement, then in-phase and out-of-phase excitation are a way to excite two different superpositions of characteristic modes on the chassis. But the general case is to have N couplers and to use N properly chosen superpositions of feed-port signals so as to excite N different superpositions of characteristic modes which will give us N different radiation patterns and thereby a N-port (MIMO) antenna system (or alternatively a multiband system or something in between).

Advantageously, the antenna system supports multi-band operation.

Advantageously, the present invention allows providing at least a further conventional antenna system comprising an antenna element placed at the top of one of the casing's parts such as a lid. In an embodiment of the invention these present conventional antenna solutions are capacitive couplers while in accordance with embodiments of the present invention the primary antenna system is an inductive coupler.

Advantageously, the present invention may provide a further complementary second antenna system with similar features but supporting another frequency band other than the primary antenna system. Commonly a mixture of first, second and conventional antenna systems will be implemented in future wireless devices. Amongst other reasons the combined system allow for connectivity when the casing is closed or not sufficiently open.

The antenna system can as a way of example support SISO antenna operation in a portion of the operating frequency range (e.g. a low band) and MIMO operation with two independent antenna ports in another portion of the operating frequency range (e.g. mid-band and ISM frequency band). As a way of example by means of switching a single antenna operation in a low frequency band is provided and MIMO operation in a mid-band and in a higher frequency range with two independent antennas. Primary and standard antenna systems can support multi-band operation thus providing at least two independent antennas for MIMO in defined low-band and up to four antennas in defined mid-band and for a higher frequency band.

Alternatively stated an aspect of the invention relates to an antenna system for a portable wireless device comprising a first casing part, a second casing part which is connected to the first casing part, wherein there is a slot between the first casing part and the second casing part, the first casing part and the second casing part being electrically conductive, at least two interconnecting elements between the first casing part and the second casing part for providing an electrically impedance between the first casing part and the second casing part, a first coupling element in the slot providing a further electrically impedance between the first casing part and the second casing part, a second coupling element in the slot, physically offset from the first coupling element along a longitudinal axis of the slot, providing a further electrically impedance between the first casing part and the second casing part; a first node located on, or adjacent to, the first or second coupling element; a second node located anywhere on the antenna system, and circuitry for connecting the first node and the second node with at least one transmit/receive module, more in particular the physical (width) and electrical (impedance) parameters of the elements, their position in the slot and the location of the first and second node are being selected to excite at least two characteristic modes of the system defined by the first and second casing part.

In an embodiment thereof at least one of said two characteristic modes of the system defined by the first and second casing part is a higher order mode thereof.

In a further aspect of the invention an antenna system for a portable wireless device comprising a first casing part, a second casing part which is connected to the first casing part, wherein there is a slot between the first casing part and the second casing part, the first casing part and the second casing part being electrically conductive, at least two interconnecting elements between the first casing part and the second casing part for providing an electrically impedance between the first casing part and the second casing part, N>2 coupling elements in the slot providing a further electrically impedance between the first casing part and the second casing part; each of said coupling elements being physically offset from each other along a longitudinal axis of the slot, M, preferably equal to N, nodes, of which at least part are located on, or adjacent to said coupling elements, and the other being located anywhere on the antenna system; circuitry for connecting the nodes with at least one transmit/receive module, wherein preferably the system is being adapted to excite at least N characteristic modes of the system defined by the first and second casing part. In yet another embodiment the circuitry is being capable of exciting M>1 characteristic modes, each supporting a portion of the frequency spectrum, preferably M equals N, the amount of couplers.

Another aspect of the invention relates to method of computer assisted designing an antenna system as described, the method comprising the steps of loading required antenna behavior in a computer system, adapting one or more of the amount of electrical interconnecting and coupling elements, the physical (width) and electrical (impedance) parameters of those electrical elements and their position in the slot, and the location of the first and second node in a computer model of the antenna system; simulating the computer model with the amounts, parameters, positions and locations of the previous step, comparing the obtained behavior and repeating steps 2 or 3 till the required antenna behavior is achieved.

Another aspect of the invention relates to the use, in portable wireless device, having a first casing part and a second casing part which is connected to the first casing part, wherein there is a slot between the first casing part and the second casing part, the first casing part and the second casing part being at least partly electrically conductive, of elements within the slot between the first and second casing part, to selectively excite one or more of at least two characteristic modes of the casing parts, by modifying the current paths within the casing parts, preferably at least one of said two characteristic modes of the system defined by the first and second casing part is a higher order mode thereof.

It is worth noting that a portable wireless device comprising an antenna system according to any one of the embodiments, may comprise of a second antenna system, either a classical one or again one in accordance with one of the embodiments of the invention. Such combined antenna system may support multi-band operation thus providing at least two independent antennas for MEVIO in defined low-band and up to four antennas in defined mid-band and for a higher frequency band.

In an embodiment of the invention at least one of said conductive coupling element includes a mode matching network. Alternatively one can state that in the antenna system the physical (width) and electrical (impedance) parameters of the elements, their position in the slot and the location of the first and second feed port are being selected to achieve matching of the antenna in a predefined frequency band. In summary it can be stated that the invention relates to antenna systems, the method of use of those and methods and related software to design such systems and determine suitable ways of us thereof, all those various aspects are characterized in that one or more of the antenna element (such as couplers) are placed in the slot between two casing parts of a (wireless) device (such as a laptop), such placement being selected to enable to excite characteristic modes on the chassis of a laptop. The invention provides for use of any number N of couplers (and related terminals or ports) into the slot in order to selectively excite N different superpositions of characteristic modes, preferably also higher order modes, on the chassis of the device to thereby create an N-port antenna arrangement which in principle allows for N-antenna MIMO transmission, preferably with addition of necessary matching circuitry. The invented design method allows for co-design of the location of the hinges (having at least an electrical impedance for instance being conductive) and the locations of the feed ports, in particular by placement of further electrical impedances, for example further conductive connections or couplers ("links", "strips") between the base part and lid and by choice of the width of the connections (which determines the impedance such as the inductance). Also additional elements such as L-shaped stubs, can be introduced, to aid in resonance tuning of some frequency bands. The invention provides also for use of the above systems or systems arising from the design method for MIMO applications, especially by providing that in one of the embodiments N ports, which can be used simultaneously in the same frequency band, are introduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a portable wireless device and position of ports of an antenna system;

Figure 2 shows connections between a lid and a base of the portable wireless device; Figure 3 shows return loss for the antenna system when first and second ports are used in-common mode;

Figure 4 shows modal excitation coefficients for characteristic chassis modes of the portable wireless device;

Figure 5 shows positioning of additional antenna elements in the slot between the lid and base of the portable wireless device;

Figure 6 shows a first embodiment of circuitry for connecting antenna ports to wireless transmit/receive modules;

Figure 7 shows a second embodiment of circuitry for connecting antenna ports to transmit/receive modules;

Figure 8 shows return loss and isolation for one of the symmetric ports of the antenna system;

Figure 9 shows return loss when using the circuitry of Figure 6 to provide in- common ∑ and differential mode Δ connections between a wireless MiMo transmit/receive module and the antenna ports;

Figure 10 shows return loss and isolation when using one of the symmetric antenna ports in the ISM band;

Figure 11 shows an example position of element of a second antenna system on the portable wireless device;

Figures 12A shows circuitry connecting the antenna systems and transmit/receive modules;

Figures 12B and 12C show the circuitry of Figure 12A for different operating frequency bands.

Figure 13 gives an arrow representation of the surface current density of the strongest characteristic mode at 900 MHz, defined low band.

Figure 14 shows the layout for a three port MIMO antenna system

Figure 15 shows the return loss and isolation for a three port MEVIO antenna system

Figure 16A shows for a single port penta-band antenna system

Figure 16B and 16C shows the return loss versus frequency for a single port penta-band antenna system

Figure 17: (a) Structure of a simple one-port dual-band antenna, b) Return loss versus frequency. Figure 18: (a) Structure of one-port LTE low-band / mid-band antenna, (b) Return loss versus frequency.

Figure 19: (a) Structure of two-port MIMO LTE mid-band antenna system, (b) Return loss and isolation versus frequency.

Figure 20: (a) Structure of antenna system with 3 ports, (b) RL and isolation versus frequency.

Figure 21: (a) Structure of two-port multi-band MIMO antenna system, (b) Return loss and Isolation versus frequency.

Figure 22: (a) Structure of the primary antenna (second antenna not shown), (b) Return loss and isolation of the combined 2-port antenna system.

Figure 23: (a) Structure of the primary antenna system (second antenna not shown), (b) Return loss and isolation of the combined 3-port antenna system.

Figure 24: (a) Two-port antenna structure under investigation, (b) Modal return loss versus frequency

Figure 25: Common mode return loss versus frequency for different port locations described by horizontal distance d from the center of the slot. Colors of the graphs correspond to d £ { 10,30,50,70,90} mm. The height of the slot is fixed at h = 15mm.

Figure 26: Common mode return loss versus frequency for different values of the height h of the slot between the lid and the base part. Colors of the graphs correspond to h £ { 15,12.5,10,7.5} mm. Port locations are fixed at distances of d = 65mm from the centre of the slot.

DETAILED DESCRIPTION OF AN EMBODIMENT

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Those skilled in the art will recognize that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention.

Furthermore, the terms primary, first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Multiple Input-Multiple Output (MIMO) transmission modes are a feature of many wireless communication systems. They are used in wireless communication standards such as Evolved Universal Terrestrial Radio Access (E-UTRA), Long Term Evolution (LTE), Worldwide Interoperability for Microwave Access (WiMAX) and High-Speed Packet Access (HSPA) and are also used in Wireless Local Area Network (WLAN) communications and in other applications. Explanations of MIMO transmission modes can be found in "Introduction to space-time wireless communications" by Paulraj et.al, ISBN 0 521 82615 2. A summary of MIMO operation will be provided before describing embodiments of the invention.

So as to support MIMO transmission modes such as Receive Diversity (RD) and Spatial Multiplexing (SM), it is necessary for a wireless device to be equipped with at least a two port antenna system, and in the general case a multi-port antenna which is designed to receive (or transmit, respectively) signals from different ports independently of each other in the same frequency band. For receive mode "independently" means that the different ports of the multiport antennas are capable of receiving different superpositions of incoming multi-path components which requires that their polarimetric complex radiation patterns are sufficiently distinct. A quantitative measure of this capability is the correlation between signals received at different antenna ports in a given reference propagation scenario. Figures 1 and 2 show a portable wireless device 10 in the form of a portable computer (e.g. laptop, notebook or netbook) or other device having one, two or more casing parts 1, 2: a base part 2 and a lid part 1. The portable wireless device can be a laptop, smartphone, mobile phone, PDA, tablet etc. One part of the portable wireless device may be a lid or cover, e.g. a sleeve. In the following the two parts of the portable wireless device will be described as a lid and a base, but it will be understood that these relates to first and second parts of the portable wireless device. In this embodiment the lid 1 and base 2 are physically interconnected by hinges 11, 12 but the present invention is not limited thereto. The lid 1 can be moved between a storage configuration in which the lid 1 lies parallel to the base 2, against the base 2, and an operational configuration in which the lid 1 lies at an angle to the base, such as an angle in the range between 50° and 150°. Relative movement of the two parts is not necessary, provided a slot is provided between the two parts as described below. Figure 1 shows the device in an operational configuration. Figure 2 shows the device in plan view, with the lid fully opened, to clearly show the connections between the lid 1 and base 2. Advantageously, the casing parts 1, 2 are unibody parts formed from metal (e.g. aluminum). A unibody is also known as a monocoque. It is a casing with a shell that is the principal source of its structural strength, which is designed and constructed to serve that purpose. A unibody can be a frame made from a single block of aluminum but other material, such as polycarbonate, can be used. A "unibody laptop" can be considered as an electrically uniform frame contrary to its mechanical construction for which three or more separate pieces can be distinguished. Electrically uniform means that surface currents can move freely. The casing can be a conductive plastic casing or a non-conductive material (e.g. plastic) with a conductive layer which is formed on, or as part of, the plastic casing, thus creating a casing which has a conductive layer. For a portable wireless device 10 in the form of a laptop computer, the base 2 typically accommodates components such as the keyboard, track pad, processor, memory and storage and the lid 1 typically accommodates the screen. The lid 1 and base 2 are separated by a slot 18. The width of the slot is defined by the hinges 11, 12.

The portable wireless device 10 can comprise a primary antenna system. The primary antenna system can comprise two aspects:

(a) an inductive coupler, which can excite at least one strong characteristic mode in the casing parts 1, 2; or alternatively, N > 1 inductive couplers are placed, which can excite N different superpositions of characteristic modes. If the N feed ports of the N couplers do not have yet orthogonal patterns we can achieve orthogonality by a mode matching network (MMN) constructed by a modal matching criterion, e.g. TMRL.

(b) optionally one or two parasitic elements are mounted in the slot 18 between the casing parts 1, 2. In an embodiment this can comprise one, or a pair of, parasitic elements positioned at locations 21, 22 in the slot 18. The elements can be L-shaped stubs.

The primary antenna system can provide a sufficiently wide bandwidth to cover the whole low-band frequency range in a Single Input - Single Output (SISO) configuration without using any switching. Also, the whole mid-band frequency range can be covered in a Multiple Input - Multiple Output (MEVIO) configuration (with switching). If the two additional parasitic element(s) are mounted in the slot 18, these can be used to expand the coverage to the 2.4GHz ISM band, used for WLAN, in a MEVIO configuration. The LTE low band is defined from 704MHz up to 960MHz, which is from the 3GPP band number- 17 to band number- 8. The LTE mid frequency band is defined and ranged from 1710 MHz up to 2170 MHz. It is from 3GPP band number-3 to band number- 1.

Optionally, the portable wireless device 10 can comprise a conventional antenna system. The conventional antenna system can comprise an antenna element positioned, for example, at the top of the lid 1. The conventional antenna system can couple capacitively to the chassis. If the conventional antenna system is mounted within a metallic unibody casing part, the unibody shell will require an opening in the local region of the second antenna system.

PRIMARY ANTENNA SYSTEM

The primary antenna system uses the casing parts 1, 2 themselves as part of its radiating structure. Each feed port has two terminals. A first feed port 15 has its terminals connected to parts 1 and 2 at a first position along the longitudinal axis of the slot 18. . The feed port 15 connects to its first terminal where the second terminal connects the same feed port by means of a conductive link 13. A second feed port 16 has its terminals connected to parts 1 and 2 by means of a conductive link 14 at a second, different, position along the longitudinal axis of the slot 18 compared to that of the first port 15.. Figure 2 shows the ports 15, 16 on the base 2 side of the slot 18. Through each feed port 15, 16 the lid 1 and base 2 of the device 10 are electrically connected in a well-defined lid-base location area, along the longitudinal axis of the slot.

In an embodiment the conductive links, for example 13, 14 can be carried out as a complex impedance. These complex impedances construct the mode matching circuit. By default, excitation occurs on the terminals of the ports. With both terminals excited in-phase, higher than 7 dB return loss can be achieved in the complete defined low- band frequency range. A superposition of the primary few characteristic modes with low radiation quality factors is excited giving, as a result, around 30% relative bandwidth.

The operation of the primary antenna system will be described for reception of an incoming electromagnetic wave. The casing parts 1, 2 serve as part of an antenna, with the slot 18 being part of the antenna structure. The hinges 11, 12 serve as interconnecting elements which provide an electrically conductive path between the casing parts 1, 2.

An incoming electromagnetic wave induces a current density on the casing parts 1, 2 of the device 10 that can be decomposed into characteristic chassis modes. Part of the induced current is passing through the hinges. By providing conductive links 13, 14 which contain resp. the feed ports' 15, 16 terminals in proper positions, which are obtained from the analysis of the characteristic modes, the remaining part of the induced current is diverted through the conductive links and feed ports.

The current gives rise to a surrounding magnetic field. Due to the induced magnetic flux enclosed by the loop comprising the hinges 11, 12, links 13, 14 and parts 1, 2, a voltage is induced on the feed ports' 15, 16 both terminals. Several characteristic modes are usually induced simultaneously. How the superposition as a linear function of characteristic modes is composed depends on the position of the links 13 and 14 along the longitudinal axis. Due to its inductive functionality, the principle of the described arrangement is referred to as an inductive coupler. The conducting link 13, 14 can comprise a single wire, the shield of a coaxial cable, or a strip line for example. Transmission of an electromagnetic wave is achieved by a reversal of the steps just described.

In one embodiment one of the characteristic modes shown in Figure 4 is particularly strongly excited (characteristic mode 3, high modal excitation coefficient in the frequency range 850MHz - 960MHz. For the mid-band the primary antenna system or arrangement will result in two or more independent, uncorrelated ports. For the low-band, the two ports 15, 16 can be driven in a common mode to produce a SISO antenna system. If additional L-shaped stubs are used, MIMO operation is possible in the WLAN band. In an embodiment these parasitic elements aid in tuning to the frequency band of interest for the primary antenna system.

Table 1 summarizes the possible configurations:

Table 1: Design arrangement for primary, not operational for lid closed, & conventional antenna system.

(*) single antenna will further be designated as SISO.

(°) only 1 feed port is needed for the conventional Antenna system. The "lid open" state is defined as an angle between the lid and base of between 50° and 150° degrees. In the "lid closed" configuration the primary antenna system is not operational and only the conventional antenna system can be used.

The electrical connections between the lid 1 and base 2 of device 10 can be realized by individual conductive strips, such as the shield of coaxes or multiconductor lines, or by a flexible carrier, such as a flexible printed circuit board (PCB) which is connected to the lid 1 and base 2. Advantageously, the PCB is thin and formed from low permittivity, low-loss, thin flexible PCB laminate. The PCB can carry the links 13, 14 which interconnect the lid 1 and base 2. The optimum location of the links 13, 14 along with the resp. feed ports 15, 16 for the defined low-band antenna can be identified from surface current distribution of the strongest characteristic mode at the frequency of interest, here in the lower band at 750MHz. Figure 13 gives an arrow representation of the surface current density of the strongest characteristic mode at 900 MHz, defined low-band. Advantageously, links 13, 14 along with ports 15, 16 are placed along the longitudinal axis where the surface current density is a maximum. The PCB does not have to fill the whole Open air' slot 18. The PCB can carry the L-shaped stubs at positions 21, 22. In the closed position, the flexible PCB or conductive strips are slightly bent or are folded between the lid 1 and the base 2. The additional parasitic element 21 is electrically connected to one of the terminals of port 15. The additional parasitic element 22 is electrically connected to one of the terminals of port 16.

MULTI-BAND ANTENNA DESIGN

The primary antenna system can be operated across multiple bands. Three bands are considered. There is a low band, a higher band, or a lower band and higher band such as a mid-band and a high band:

(i) a low-band (700 MHz up to 1 GHz, e.g. LTE low band);

(ii) a mid-band (1 GHz up to 2.2 GHz, e.g. LTE mid band);

(iii) WLAN band, e.g. IEEE 802.11 implementing a wireless local area network (WLAN) computer communication in the 2.4, 3.6 or 5 GHz frequency bands.

In Figure 5, for the WLAN band, parasitic elements 21, 22 provide additional antenna resonance at the WLAN frequency range and connect to the feed ports 15, 16. The antenna system can therefore be matched at the 2.4 GHz ISM band. Parasitic elements 21, 22 are shown as L-shaped strips or stubs. For the defined low-band frequency range only a common mode impedance is matched. In the defined mid-band frequency range the common and differential mode impedances are matched using series capacitance. A matching criterion of a TMRL of 7dB over the whole bandwidth of the frequency range can be used. In the primary antenna system symmetric matched and uncorrelated ports are produced. ). The primary antenna system provides a 2-port MEVIO operation for the defined mid-band or WLAN. Two embodiments of matching and connecting circuitry are shown in Figures 6 and 7.

Figure 6 shows matching circuitry and provides switching between all three frequency bands (the defined low-band, the defined mid-band and WLAN). 1. When the switches are in position 1, the diodes are in the conducting state and the common mode output is connected to the defined low-band Rx/Tx. A graph of return loss in this position is shown in Figure 3.

2. When the switches are in position 2, the diodes are in open state. Therefore, a capacitance Cm necessary for antenna matching in the defined mid-band is placed in series with the circuit. A graph of return loss and isolation in this position is shown in Figure 8. Note that if a broadband 180° "rat-race" coupler is used optionally at the symmetric ports for the defined mid-band then a DL- MEVIO might be realized more effectively with the return loss characteristics shown in Figure 9.

3. When the switches are in position 3 and diodes in the conducting state the parasitic elements 21, 22 operate in the WLAN band. A graph of return loss and isolation using one of the symmetric ports is shown in Figure 10. Figure 7 shows matching circuitry and provides switching between two states.

The first state (switches in position 1) is for both the defined low-band and WLAN. The second state (switches in position 2) is for the defined mid-band. The first state uses a dual-band 180° "rat-race" coupler. The defined low-band is covered by the common mode output port from the dual band 180° coupler with similar response to that shown in Figure 3. As in figure 6, connecting a coupler to the output of the defined mid-band matching network (in position 2) the frequency response on Δ and∑ ports is given in Figure 9, without the 180° coupler, the response on one of the symmetric ports in Figure 8.

Usage of a 180° coupler in both figures is optional and depends on the relation between modal bandwidths (or maximum achievable bandwidth in the sense of TMRL bandwidth), which both depends on the size of a device, and bandwidth requirements/isolation requirements. The 180° coupler makes the ports of the antenna system asymmetrical, but the performance criteria in the lower part (Tx portion) of the frequency band, is met more relaxed on the Δ-port. The trade-off is that MEVIO operation is only possible for the DL LTE mid-band (e.g. 3GPP band numbers-3 and - 4).

CONVENTIONAL ANTENNA SYSTEM A conventional antenna system can be provided in addition to the primary antenna system, known as inductive coupler. Advantageously, the conventional antenna system couples capacitively to the chassis of the device 10, the capacitive coupler. This ensures that both sets of the superposition of the characteristic modes are orthogonal. Cables (e.g. coaxes) connect matching/mode decomposition circuitry to the conventional antenna system 40. Figure 11 shows an example placement of such an antenna system 40 on the top edge of lid 1. Advantageously the conventional antenna system 40 is mounted on the outer face of the lid 1 so that this antenna system can be used when the lid 1 is closed.

Figure 12A shows apparatus provided in the portable wireless device 10. A primary antenna system 5 has feed ports 15, 16. Matching and switching circuitry 31, 32 connects the ports 15, 16 to TX/RX modules 33, 34. Two TX/RX modules are shown, for 2 port MIMO operation. For SISO operation, only one TX/RX module is used. A conventional antenna system 40 has feed ports 45, 46. Matching (and switching) circuitry 41 connects the antenna ports 45, 46 to TX/RX modules 43, 44. Two TX/RX modules are shown, for 2-port MIMO operation. For SISO operation, only one TX/RX module is used.

Figures 12B and 12C show the apparatus of Figure 12A for different operating frequency bands. Figure 12B shows defined low-band operation. Referring back to Table 1, for LTE low-band operation with the lid open, single antenna operation is supported by the primary antenna system 5, using TX/RX module 33 and (optionally) single antenna operation is supported by the conventional antenna system 40, using TX/RX module 43. Overall, the wireless device 10 supports 2-port MIMO operation: one port via the inductive coupler 5 and one port via the capacitive coupler 40. Ports 15 and 16 are connected in common mode to TX/RX module 33.

Figure 12C shows defined mid-band or WLAN band operation. For LTE mid- band or WLAN operation with the lid open, 2-port MIMO operation is supported by the inductive coupler 5, using TX/RX modules 33, 34, and (optionally) 2-port MIMO operation is supported by the capacitive coupler 40, using TX/RX modules 43, 44. Overall, the wireless device 10 supports 4-port MIMO operation. Ports 15 and 16 are each connected to a respective TX/RX module 33, 34. Both ports 15, 16 operate at the same frequency band as one another, but provide independent transmit/receive paths as the inductive coupler induces/excites orthogonal characteristic modes to the casing parts. Single Port Multi-band antenna design

A single port antenna system optimized for the DL defined LTE low-band and complete LTE mid-band (UL and DL) is shown in Fig. 16A with the return loss vs. frequency in Fig. 16B and Fig. 16C. Fig. 16A shows the top view of the PCB located between lid and base part and connections between them. This antenna system is designed by removing the second feed port (16, Fig. 5) but, keeping the second conducting strip, and by further optimization of the strip lines.

The L-shaped strips had to be extended to get the resonance which was before at WLAN frequency range lowered to upper part of defined-mid band. Widening the second strip gives better match in defined mid-band. (Fig. 16B)

As a result a penta-band single port antenna is achieved, (the solution reported in EP'372 requires two ports). Three-Port Multi-band antenna design

A 3-port antenna system optimized for the defined mid-band (UL and DL) is shown in Fig. 14. Feed port 2 is added in the middle of the slot. A proper matching network designed using the TMRL matching algorithm will make all ports "truly" independent which results in a 3-port MIMO antenna system. S-parameters of the matched 3-port antenna are presented in Fig. 15. Isolation is better than 10 dB and return loss is better than 7 dB in the whole LTE mid-band frequency range.

Further examples are now provided below.

In an embodiment of the invention a one-port dual-band antenna is provided. As an example Fig. 17a shows the structure of a simple one-port antenna which can be used in LTE low-band and shows some potential also for use in mid-band. The sketch in Fig. 17a represents the slot region (between base and lid of the laptop). The wide strips may be identified with conductive hinges. The narrow strips are added to achieve the desired behavior. The left narrow strip is connected at its upper end to the lid. Its lower end serves as one of the two terminals of the feed port. The other terminal of the feed port is directly at the base part. The dot indicates the location of either a source or a load (connected to the two terminals of the port). The right narrow strip is just a shunt connection. The two narrow strips may e.g. be realized using flexible PCB material. Please note that the interpretation of the wide strips as conductive hinges is not mandatory. Of relevance is only the presence of the conductive connection. In a further embodiment a further improved one-port dual antenna is disclosed. As an example Fig. 18a shows the structure of a one-port, dual-band antenna which has been optimized for use in LTE low-band and mid-band. The return loss is shown in Fig. 18b. This antenna is derived from the previous example (Fig. 17a) by placing a parasitic element close to either of the narrow strips. The parasitic element is a L- shaped strip which is connected with one of its end to the base part of the laptop. The other end is open. The parasitic element enhances operation of the antenna in mid-band because it exposes a quarter-wave resonance there. Note that the L-shape strip is connected to the base part of the laptop but NOT connected to the strips between base and lid. Note that base and lid may in principle be exchanged in Fig. 18a. The L- shaped strip is an optional feature of the invention for matching at frequencies above ~ 1GHz. Other methods may exist.

In another embodiment of the invention a two-port (MIMO) mid-band antenna is provided. For example Fig. 19a shows a two-port mid-band antenna. This antenna supports MEVIO operation in mid band. There are 3 wide strips connecting base and lid of the laptop. Any number of them may be identified with a conductive hinge (if so desired), the others with intentionally added wide strips. The two narrow strips connect the lid to the feed ports. The return loss (note the symmetry with respect to the two ports) and isolation are given in Fig. 19b. Note the excellent isolation between the two ports.

In yet another embodiment a two-port (MIMO) low-band and one-port mid-band antenna is presented. As an example Fig. 20a shows an antenna system with 3 ports which qualifies as two-port (MIMO) system in low-band and one-port mid-band antenna but also supports 3-port Downlink (DLJ-MIMO operation in E-UTRA band number 1 and DL-MIMO in band number 4 (AWS). The antenna was optimized for MIMO LTE in low-band using ports 1 and 3 and a single antenna operation in LTE mid-band using port 2. Return loss and isolation are shown in Fig. 20b. Isolation between all ports is better than 24 dB in the intended frequency ranges. Note that the symmetry of the antenna system implies that the return loss seen at ports 1 and 3 is the same.

Another embodiment presents a two-port (MIMO) multi-band antenna system. As an example thereof Fig. 21a shows a two-port (MIMO) multi-band antenna system optimized for LTE low-band, mid-band and the 2:4 GHz ISM band. The two wide strips in the center may be identified with conductive hinges but may also be purposely introduced strips. Non-conductive hinges may be present anywhere. The narrow strips connect to the feed ports as before. The L-shaped quarter-wave stubs support operation in the ISM band (WLAN, Bluetooth). The arrangement allows for excitation of common and differential modes in all bands. Isolation between ports is better than 20 dB return loss within the 7dB matching criterion for all bands of interest (Fig. 21b).

Yet another embodiment relates to a two-port (MIMO) dual-band solution by combination with conventional antenna. Any of the antenna systems according to the present invention can be combined with an additional conventional laptop antenna system. In this example the one-port, dual-band antenna system after Fig. 18a, which is shown again in Fig. 22a is combined with a conventional antenna system (not shown) at the top of the lid. The second antenna system which has been assumed for the simulation in Fig. 22b is a prior-art system. The combination of both antennas amounts to a two-port (MIMO), dual-band antenna system optimized for LTE low- band and mid-band as shown in Fig. 22b. The return loss is better than 6 dB and isolation is higher than 25 dB.

Yet another embodiment relates to a 3-port (MIMO) multi-band solution by combination with conventional antenna. Fig. 23b shows simulation results for another combination of an antenna system according to the present invention (primary antenna system, Fig. 23a) and a conventional antenna placed at the top of the lid of the laptop (second antenna). The second antenna is a prior art design. The combination of the first antenna system with the second antenna amounts to a 3-port (MIMO) antenna system which supports 3-port MIMO operation in LTE low-band and mid-band and in addition 2-port MIMO operation in the 2:4 GHz ISM band. The current densities which are excited on the chassis by feeding the 3 different ports are mutually orthogonal as can be seen from the high isolation between all 3 ports. Isolation between the ports of the first antenna system is better than 22 dB and isolation against the second antenna better than 25 dB. Return loss is within the 7 dB specification for all bands of interest for the first antenna system and within 6 dB for the second antenna.

The present invention further relates to a design approach, now illustrated as the design procedure and optimization of the response considering the common mode as an example in the design of Figure 24, but equally applicable to other modes. Two design parameters are considered. The first parameter is the distance d of the feed ports from the geometrical center of the slot (horizontal distance). The second parameter is the height h of the slot between the lid and the base part of the laptop. The results of corresponding parameter sweeps are shown in Figs. 25 and 26. It can be seen from Fig. 25 that the frequency range over which the common mode is matched in low-band can be adjusted by choice of d, which is the horizontal distance from the center of the slot. Colors of the graphs correspond to d £ { 10,30,50,70,90} mm. The height of the slot h, between the lid and the base part is fixed at h = 15mm. Fig. 26 illustrates the influence of slot height h. Colors of the graphs correspond to h £ { 15,12.5,10,7.5} mm. Port locations are fixed at distances of d = 65mm from the centre of the slot. In general a slot of larger height allows for higher return loss and larger bandwidth of the common mode. In conclusion one may state that the invention provides for an antenna system for devices like laptops realized by at least a first impedance connecting the conductive shell of the base part and the lid part, respectively, and at least one further connection between the base and the lid part containing an impedance and the two terminals of a feed port. Either of the impedances may be just a conductive strip. Preferably further the locations of the connections containing only an impedance and the location of the connections containing an impedance and a feed port are adjusted so as to achieve match of the antenna in some frequency band(s). Preferably further the values of the impedances are adjusted so as to achieve match of the antenna in some frequency band(s). Even more preferably the width and thickness of conductive strips are adjusted so as to obtain the desired impedances of the connections. Any of the systems designed with the above one or more steps of the procedure either alone or combination with classical antenna system are part of the invention, in particular those with N > 1, preferably N>2 connections containing feed port terminals and any number of connections without feed ports, where locations and impedances of the connections are chosen so as to excite different superpositions of characteristic modes on the conductive parts of the laptop when feeding different ports, again preferably the system is so designed so that the different superpositions of characteristic modes (corresponding to different ports) are mutually (nearly) orthogonal, i.e. that isolation between feed ports is high over some desired frequency band(s).

Other design considerations are that at least two of the different feed ports expose high return loss and high mutual isolation in some desired frequency band(s) allowing for MEVIO operation in these frequency bands, hence the systems might have N feed ports and allowing for N-port MIMO operation in some desired frequency band(s). Further elements can be additional parasitic elements, e.g. L-shaped quarter-wave stubs connected to either the lid or the base part of a laptop, for the purpose of improving match of the antenna system in one or more frequency bands. The invention also provides for a combined antenna system for laptops consisting of a first antenna system with N ports following the present invention and having in addition a second antenna system with M ports placed in a different location on the laptop's chassis both designed and located so as to achieve excitation of K > max(M,N) different radiation patterns in some desired frequency band(s), allowing for K-port MIMO operation in these band(s), wherein preferably the K radiation patterns are orthogonal radiation modes.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. An antenna system for a portable wireless device comprising:

a first casing part;

a second casing part which is connected to the first casing part, wherein there is a slot between the first casing part and the second casing part, the first casing part and the second casing part being electrically conductive;

at least two interconnecting elements between the first casing part and the second casing part for providing an electrically impedance between the first casing part and the second casing part;

a first coupling element in the slot providing a further electrically impedance between the first casing part and the second casing part;

a second coupling element in the slot, physically offset from the first coupling element along a longitudinal axis of the slot, providing a further electrically impedance between the first casing part and the second casing part;

a first feed port with its terminals located on, or adjacent to, the first or second coupling element;

circuitry for connecting the first feed port with at least one transmit/receive module.

2. The antenna system of claim 1, further comprising

a second feed port located on, or adjacent to, the other coupling element; and circuitry for connecting the second feed port with at least one transmit/receive module.

3. The antenna system of claim 2, whereby the physical (width) and electrical (impedance) parameters of the elements, their position in the slot and the location of the first and second feed port being selected to excite at least two characteristic modes of the system defined by the first and second casing part.

4. The antenna system of claim 3, whereby at least one of said two characteristic modes of the system defined by the first and second casing part is a higher order mode thereof.

5. The antenna system of any of the preceding claims, wherein the circuitry being capable of existing M>1 characteristic modes defined by the first and second casing part, each supporting a portion of the frequency spectrum.

6. The antenna system of any of the preceding claims, wherein the two interconnecting elements between the first casing part and the second casing part are electrically interconnecting and provide an electrically conductive loop between the first casing part and the second casing part.

7. The antenna system of any of the preceding claims wherein the first coupling element provides a further electrically conductive path between the first casing part and the second casing part.

8. The antenna system of any of the preceding claims, wherein the second coupling element provides a further electrically conductive path between the first casing part and the second casing part.

9. The antenna system of any of the preceding claims, wherein at least one of said conductive coupling elements is included as part of a mode matching network.

10. The antenna system of any of the preceding claims 2 to 9, wherein a second feed port being located on, or adjacent to, the other one of the first or second coupling elements, not being connected to the first feed port.

11. The antenna system of any of the preceding claims 2 to 10, whereby the first and second feed port operate at the same frequencies.

12. The antenna system of any of the preceding claims, wherein either one of the coupling elements being inductive.

13. The antenna system of any of the preceding claims, wherein either one of the coupling elements being capacitive.

14. The antenna system of any of the preceding claims 2 to 13, wherein the first or second coupling element, not being connected to the first feed port, being either at least conductive or connected to a second feed port.

15. The antenna system of any of the preceding claims, wherein the first or second coupling element, being connected to the first feed port, being not conductive.

16. An antenna system according to any of the preceding claims, wherein one feed port aligned with one or more coupling elements is arranged to provide an inductive coupling to generate at least one characteristic mode, or set of characteristic modes, of the casing parts.

17. An antenna system according to any of the preceding claims wherein the circuitry is arranged to provide an in-phase excitation or out-of-phase excitation or a linear superposition of excitations received at its feed ports and further connection between the first and second feed ports and one transmit/receive module.

18. An antenna system according to any one of the preceding claims wherein the circuitry is selectively operable in a first operational mode in which the circuitry is arranged to provide an in-phase connection between the first and second feed ports and one transmit/receive module and a second operational mode in which the circuitry is arranged to provide a connection between the first feed port and a transmit/receive module and an independent connection between the second feed port and another transmit/receive module.

19. An antenna system according to claim 18, wherein the first operational mode is associated with a first portion of an operating frequency range and the second operational mode is associated with a second portion of the operating frequency range.

20. An antenna system according to claim 18 or 19 wherein, in at least one of the operational modes, the circuitry includes a matching impedance.

21. An antenna system according to any one of the preceding claims further comprising at least one parasitic element positioned in the slot between the first casing part and the second casing part.

22. An antenna system according to claim 21 wherein the at least one parasitic element is arranged to operate at a frequency band which is different but expanding a frequency band of the characteristic modes of the casing parts.

23. An antenna system according to claim 21 or 22 wherein the at least one parasitic element is mounted on a flexible carrier connected between the first casing part and the second casing part.

24. An antenna system according to claim 23 wherein the first coupling element and the second coupling element are mounted on the flexible carrier.

25. A antenna system according to any one of the preceding claims comprising at least one further antenna element positioned on one of the chassis parts.

26. An antenna system according to claim 25 wherein the at least one further antenna element is arranged to provide a capacitive coupling with the casing part on which it is positioned.

27. An antenna system according to claim 25 or 26 further comprising circuitry for connecting the at least one further antenna element with at least one further transmit/receive module.

28. An antenna system according claim 26 or 27, for which the capacitive coupling is orthogonal to the inductive superpositions of the characteristic modes excited by the inductive coupling.

29. An antenna system according to any of the preceding claims which by means of switching supports single antenna operation in a low frequency band and MIMO operation in a mid-band and in a higher frequency range with two independent antennas.

30. An antenna system according to any of the preceding claims 21 to 29 wherein the antenna system support multi-band operation thus providing at least two independent antennas for MIMO in defined low-band and up to four antennas in defined mid-band and for a higher frequency band.

31. An antenna system according to any one of the preceding claims wherein the electrical interconnecting element comprises a hinge for hingedly connecting the first casing part to the second casing part.

32. A portable wireless device comprising an antenna system according to any one of the preceding claims.

33. The portable wireless device of claim 32, further comprising a second antenna system.

34. The portable wireless device of claim 33, wherein the second antenna system being an antenna system in according to any of the preceding claims 1-24.

35. A portable wireless device according to claim 32, 33 or 34 being a smartphone, a laptop, a tablet, a PDA, a mobile phone.

36. A method of computer assisted designing an antenna system in accordance with one of the claims 1 to 24, the method comprising the steps of:

loading required antenna behavior in a computer system;

adapting one or more of the amount of electrical interconnecting and coupling elements, the physical (width) and electrical (impedance) parameters of those electrical elements and their position in the slot, and the location of the first and second feed port in a computer model of the antenna system;

simulating the computer model with the amounts, parameters, positions and locations of the previous step;

comparing the obtained behavior and repeating steps 2 or 3 till the required antenna behavior is achieved.

37. A computer program product comprising code segments that when executed on a suitable processing engine implement the steps of the method of claim 36.

38. A machine readable signal storage medium, storing the computer program product of claim 37.

39. Use, in portable wireless device, having a first casing part and a second casing part which is connected to the first casing part, wherein there is a slot between the first casing part and the second casing part, the first casing part and the second casing part and connection between both being at least partly electrically conductive, use of elements within the slot between the first and second casing part, to generate at least one characteristic mode, or set of characteristic modes, of the casing parts.

40. The use of claim 39, whereby at least one of said two characteristic modes of the system defined by the first and second casing part is a higher order mode thereof.

41. An antenna system for a portable wireless device comprising:

a first casing part;

N>2 coupling elements in the slot providing a further electrically impedance between the first casing part and the second casing part; each of said coupling elements being physically offset from each other along a longitudinal axis of the slot;

M feed ports, which are located on, or adjacent to said coupling elements;

circuitry for connecting the feed ports with at least one transmit/receive module.

42. The antenna system of claim 41, being adapted to excite at least N characteristic modes of the system defined by the first and second casing part.

43. The antenna system of claim 42, being adapted to provide matching to thereby allow for M independent signals at an equal number M of feed ports.

44. The antenna system of claim 41 to 43, being adapted so that the interconnecting elements and/or coupling elements are included as part of a mode matching network.