TECHNICAL FIELD

The present invention relates to the field of antennas used for wireless communications, and particularly to antennas that fit into tight spaces in electronic devices built with electrically conductive frames. Furthermore the invention relates to antenna arrangements that comprise a plurality of antennas, and to electronic devices that comprise an antenna or antenna arrangement.

BACKGROUND

Antennas are needed in all electronic devices that communicate using radio waves. Many such devices are meant to be portable, easily usable, and aesthetically appealing to users. As a consequence their size, design, overall appearance, mechanical robustness, and efficiency in radio communications may pose difficult and possibly mutually contradicting requirements to antenna design.

One example of such an electronic device is a portable communications and/or computing device such as a smartphone, a tablet computer, or a laptop computer. Such a device may be relatively flat and somewhat elongated in form and have two ends, two side edges, as well as a front side and a back side. A large majority portion of the front side is often reserved for a touch-sensitive display. The back side may be covered by a back cover made of plastic, but in many cases the back side comprises a layer of glass and/or metal. The circumference along said ends and side edges may also comprise a metallic frame. The device may be only some millimeters thick, and the ends and side edges may measure from a few centimeters to some decimeters. The physical dimensions of an antenna have certain relation to the wavelength of communications, which means that if an antenna is to be used for communications at wavelengths below 6 GHz, it must have physical dimensions in the order of some centimeters. It is difficult to design an antenna of that size so that on one hand it would enable efficient communications and high data throughput but on the other hand it would fit easily within a portable communications device.

Prior art suggests various antenna structures that may make use of the metallic or otherwise conductive structural parts of the electronic device. However, it has been found that antenna performance is not always optimal over the whole required frequency range and/or all frequency bands on which the electronic device should operate.

SUMMARY

It is an object of the invention to provide an antenna that is compact in size, applicable in portable electronic devices, robust against many kinds of operating conditions, and combinable with other antennas comprised in an electronic device. Another object of the invention is that the antenna could be implemented in a confined space among other parts and structures of an electronic device, and yet have good performance. Yet another object of the invention is to provide an electronic device that includes at least one antenna of said kind.

The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms and advantages are apparent from the depending claims, the description and the figures.

According to a first aspect, an electronic device is provided. The electronic device comprises a housing having a first side and a second side, a dielectric cover on said second side, and an electrically conductive peripheral structure along edges of said first and second sides. The electronic device comprises also an antenna feed coupled to a portion of said peripheral structure for using said portion as a radiating antenna element. Additionally the electronic device comprises a conductive member on (e.g. attached on an inner side or an outer side of) said dielectric cover. Alternatively, the conductive member may be arranged underneath said dielectric cover (e.g. on a further support structure inside the housing). Said conductive member has a first dimension along a longitudinal direction of said portion and extending inwards from said portion - with reference to said peripheral structure - by a second dimension, said second dimension being less than twice said first dimension. The electronic device comprises an electric coupling between said portion and that part of said conductive member that extends along said longitudinal direction of said portion. The conductive member forms an antenna extender and hence can also be called an antenna extender. The purpose of the conductive member i.e. the antenna extender eis to enlarge the surface area where the electric field is distributed on. In other words, the antenna extender increases the antenna aperture for radiation. It will improve the chassis mode excitation at desired frequency band(s). The antenna extender can be used to 1) improve radiation efficiency, 2) adjust resonant frequency, 3) increase impedance bandwidth, and 4) modify current distributions and radiation patterns to control e.g. the effect of the user.

The antenna extender allows making an antenna of compact in size in particular in portable electronic devices in which there is little space, because it improves the impedance bandwidth and efficiency of the antenna without requiring more antenna clearance (i.e. more distance between radiating antenna element and ground). The improvement in impedance bandwidth and efficiency also increase robustness against suboptimal operating conditions, because they provide more marginal before the performance of the antenna would fall below acceptable limits. The antenna extender does not reserve such space that would otherwise be needed for other antennas in the same device, which makes the solution very compatible with other antennas. The antenna may even share some structures with other parts of the electronic device, which further emphasizes its suitability for confined spaces.

In a first implementation form of the electronic device, said dielectric cover is a dielectric plate and said conductive member is mechanically supported by said dielectric plate. This involves the advantage that the mechanical structure can be made robust and relatively easy to manufacture. It involves also the advantage that the distance between the conductive member and a grounded part of the electric device, such as a display, can be made as large as possible. This improves the impedance bandwidth and efficiency.

In a further implementation form of the electronic device, said dielectric plate is made of plastic, glass, ceramic, wood, or other dielectric substance and has an inner surface and an outer surface, and said conductive member is a piece of conductive material fixedly attached to the inner surface of said dielectric plate. This involves the advantages that the outer appearance of the device can be made very appealing, and that the mechanical structure can be made robust and relatively easy to manufacture.

In a further implementation form of the electronic device, said dielectric plate is transparent or translucent and comprises a decorative layer on said inner surface, and said conductive member is indirectly attached to the inner surface of said dielectric plate through being attached to said decorative layer. This involves the advantage that the advantageous outer appearance of the device does not need to be compromised even if a conductive member of this kind is used as an antenna extender. In a further implementation form of the electronic device, the electronic device comprises a dielectric support structure inside said dielectric cover, and said conductive member is mechanically supported by said dielectric support structure. This involves the advantage that the design and mechanical structure of the antenna extender can be particularly well tailored according to operating frequencies and other affecting factors, and/or that some dielectric part inside the electronic device can efficiently double as a support structure for the antenna extender.

In a further implementation form of the electronic device, said electric coupling is a galvanic coupling comprising at least one of: a direct contact between said portion and said conductive member; a coupling through a conductive gasket between said portion and said conductive member; a coupling through two or more discrete contact members between said portion and said conductive member; a weld-, solder-, or glue joint between said portion and said conductive member. This involves the advantage that a secure electric coupling can be made in a wide variety of alternatives concerning the parts and materials in the surrounding structure.

In a further implementation form of the electronic device, said electric coupling is a non- galvanic coupling comprising at least one of: a capacitive coupling, an inductive coupling. This involves the advantage that no direct contact needs to be made between certain parts, which makes it easier to design and assemble the structure and helps to avoid any problems that suboptimal contacts could cause.

In a further implementation form of the electronic device, a crossover frequency of said non-galvanic coupling is in the order of tens to hundreds of megahertz. This involves the advantage that sufficient electromagnetic connection can be made at frequencies that are useful taken the other dimensions of the antenna structure.

In a further implementation form of the electronic device, said portion constitutes a radiating antenna element of an antenna structure that is one of the following: monopole antenna, dipole antenna, folded dipole antenna, capacitive coupling element antenna, inverted-F antenna, loop antenna, slot antenna. This involves the advantage that the most suitable antenna type can be selected for a particular implementation. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates a CCE antenna,

Figure 2 illustrates an inverted-F antenna,

Figure 3 illustrates a monopole or inverted-F antenna,

Figure 4 illustrates certain structural parts of an electronic device,

Figure 5 illustrates a cross section of the structure of figure 4,

Figure 6 illustrates some structural parts of an electronic device with an antenna extender, Figure 7 illustrates a cross section of the structure of figure 6,

Figure 8 illustrates some structural parts of an electronic device with an antenna extender, Figure 9 illustrates a cross section of the structure of figure 8,

Figure 10 illustrates the dimensioning of an antenna extender,

Figure 11 illustrates the dimensioning of another antenna extender,

Figure 12 illustrates an equivalent circuit of an antenna extender,

Figure 13 illustrates an antenna extender with a contact member,

Figure 14 illustrates examples of shapes of antenna extenders,

Figure 15 illustrates some structural parts of an electronic device with an antenna extender, and

Figure 16 illustrates measured performance of antennas with and without antenna extenders.

DETAIFED DESCRIPTION

An electronic device may comprise an inner part enclosed in an outer cover. Typically the inner part or chassis comprises the electronic components needed for the operation of the electronic device, while the role of the outer cover is to provide mechanical support and protection as well as an appealing outer appearance. If the electronic device is equipped for wireless communications, it must have one or more antennas built into it. The provision of an electrically conductive peripheral structure, such as the so-called ring or outer frame that constitutes a part of the structure and outer appearance of many sophisticated smartphones, allows using one or more sections of said electrically conductive peripheral structure as radiating antenna elements. According to established vocabulary, a radiating antenna element is a structural part to which an oscillating electric current of high frequency is coupled for transmitting a radio signal, and/or to which a received radio signal induces an oscillating electric current of high frequency that can in turn be converted into the received signal.

Figures 1, 2, and 3 illustrate electronic devices that comprise an inner part or chassis 101 and a radiating antenna element, which may be a portion of an electrically conductive peripheral structure. It is typical to the inner part or chassis 101 that it comprises a relatively extensive ground plane, for which reason it may be considered as a grounded region that has an effect on the performance of the radiating antenna element.

In fig. 1 the radiating antenna element 102 is a straight portion of the electrically conductive peripheral structure, the whole length of which is located at a distance 103 from a straight edge of the inner part or chassis 101. An antenna feed 104 is at or close to a middle point of the radiating antenna element 102. Neither of these (antenna element being straight; antenna feed being close to the middle) is a strict requirement, and variations are possible. The antenna of fig. 1 could be called a CCE (Capacitive Coupling Element) antenna.

In fig. 2 the radiating antenna element 201 is otherwise located at a distance 202 from a straight edge of the inner part or chassis 101, but at one end of the radiating antenna element 201 there is a direct contact to the (ground plane of the) inner part or chassis 101. A ground contact of this kind could be located anywhere along the length of the antenna element 201. In fig. 2 an antenna feed 203 is closer to that end of the radiating antenna element 102 that has said contact than to its free end. Again, variations to all these features are possible. The antenna of fig. 2 is an IFA (Inverted-F Antenna).

In fig. 3 the radiating antenna element 301 is located at a distance 302 from a straight edge of the inner part or chassis 101. An antenna feed 303 is located at one end of the radiating antenna element 301, which makes the antenna a monopole or an ILA (inverted-L antenna).

Figures 4 and 5 are further illustrations of a structure that may follow the principle of fig. 1 above. The radiating antenna element 102 is a portion of an electrically conductive peripheral structure of the electronic device. The inner part or chassis 101 is illustrated in a simplified manner as a thick slab, a portion of which is shown in figs. 4 and 5. A first dielectric cover 401 covers a first (front) side of the electronic device, and a second dielectric cover 402 covers a second (back) side of the electronic device. In the assembled configuration the slightly inwards curved outer edges of the first 401 and second 402 dielectric covers come against respective grooves in the radiating antenna element 102, so that a streamlined outer appearance of the electronic device is achieved. The distance 103, 202, or 302 at which the radiating antenna element is located from an adjacent grounded structure can be called the ground clearance or antenna clearance. The optimal magnitude of a ground clearance depends on the operating frequency and bandwidth. As a general rule on the operating frequencies smaller than 6 GHz that are common in smartphones and other widely used wireless communications devices a ground clearance of 5 to 10 millimeters could be close to an optimum. However, it may be desirable to cover a whole side surface, for example a front surface, of an electronic device with a (touch-sensitive) display. A display needs an associated ground plane, and this ground plane may define the effective outer dimensions of what is considered as the inner part or chassis 101 in figs. 1 to 3. As a consequence there may be as little as 1 to 2 millimeters, or even less, available as the ground clearance.

Figure 6 illustrates some parts of an electronic device according to an embodiment of the present invention in an exploded view. Figure 7 is a cross section of these parts along a plane that goes through the antenna feed 601. The electronic device comprises a housing having a first side and a second side. The first side is the lower side in figs. 6 and 7, and the second side is the upper side. The electronic device comprises a dielectric cover 602 on the second side, and an electrically conductive peripheral structure along edges of the first and second sides. A portion 603 of said electrically conductive peripheral structure is seen in figs. 6 and 7. The antenna feed 601 is coupled to said portion 603 of the electrically conductive peripheral structure for using said portion 603 as a radiating antenna element.

As a difference to figs. 4 and 5, the electronic device of figs. 6 and 7 comprises a conductive member 604 covered by and arranged on the dielectric cover 602. In this example the conductive member 604 is arranged on the inside (the inner surface) of the dielectric cover 602. However, in a furhter embodiment the conductive member 604 may be arranged on the outside (the outer surface) of the dielectric cover 602. The conductive member 604 has a first dimension 605 along a longitudinal direction of the portion 603 of the electrically conductive peripheral structure that is used as a radiating antenna element. The conductive member 604 extends inwards from said portion 603 by a second dimension 606. Here “inwards” is defined as inwards with reference to said peripheral structure of the electronic device; in other words,“inwards” means towards the center of the electronic device.

Of the dimensions of the conductive member 604, the second dimension 606 is less than twice the first dimension 605. The significance of these dimensions will be discussed in more detail later. The conductive member 604 can be alternatively called an antenna extender. The expressions conductive member and antenna extender are used interchangeably in this text.

An electric coupling exists between the portion 603 of the electrically conductive peripheral structure that is used as a radiating antenna element and that part of the conductive member 604 that extends along the longitudinal direction of said portion. In the structure of figs. 6 and 7 one long edge of the conductive member 604 is in direct mechanical contact with a part of the portion 603, which ensures said electric coupling. Other ways of making such an electric coupling are discussed in more detail later.

In the structure of figs. 6 and 7 the dielectric cover 602 is a dielectric plate, and the conductive member 604 is mechanically supported by said dielectric plate. In particular, the dielectric plate that constitutes the dielectric cover 602 can be made of e.g. plastic or glass, and it may have an inner surface and an outer surface. The conductive member 604 may be fixedly attached to the inner surface of the dielectric cover 602 for example by glueing or by ultrasonic welding. The conductive member 604 could also be attached in other ways, like being embedded in the material of the dielectric cover 602. The actual way of attaching has little practical significance. Fixed attaching of this kind is based on an assumption that the conductive member 604 is a piece of conductive material, such as a piece of a metal foil or plate. An alternative would be to form the conductive member 604 on some surface of the dielectric cover 602 using conductive paint or other substance that is not in the form of a discrete, solid piece of conductive material before becoming attached to the dielectric cover 602.

Using the dielectric cover 602 as a mechanical support for the conductive member 604 involves the advantage that no other structural parts are needed for that purpose. It may also enable easy assembling of the electronic device, because the conductive member 604 may be attached to the inner surface of the dielectric cover 602 first, so that when at a later assembling stage the dielectric cover 602 and the electrically conductive peripheral structure are brought together, the electric coupling between the conductive member 604 and the portion 603 that is used as a radiating antenna element is automatically made. An electrically conductive gasket can be used to ensure the electric coupling, but this is not necessarily required. The use of plastic, glass, ceramic, wood, or other dielectric material as the material of the dielectric cover 602 may enable achieving a very appealing outer appearance of the electronic device at a reasonable level of manufacturing costs. Plastic as the material involves the additional advantage that ultrasonic welding, moulding, or other known method based on partly melting some of the plastic substance are available for fixedly attaching the conductive member 604 to the dielectric cover 602.

Figs. 8 and 9 illustrate parts of an electronic device according to a further embodiment that comprises a housing having a first side and a second side, and a dielectric cover 602 on said second side. The electronic device comprises an electrically conductive peripheral structure along edges of the first and second sides, and an antenna feed 601 coupled to a portion 603 of said peripheral structure for using said portion 603 as a radiating antenna element.

The electronic device of figs. 8 and 9 comprises a conductive member 804 covered by and arranged underneath the dielectric cover 602. In particular, the electronic device comprises a dielectric support structure 801 underneath the dielectric cover 602, and the conductive member 804 is mechanically supported by said dielectric support structure 801. Hence, the conductive member 804 is in this embodiment not arranged on the dieletric cover 602 but on the separate dielectric support structure 801 arranged underneath the dieletric cover 602. The dielectric support structure 801 may be part of (or may in turn be supported by) any other part of the electronic device, like a wall of a battery compartment, a conductive shielding can of high-frequency parts, a speaker box, or the like.

The conductive member 804 has a first dimension 605 along a longitudinal direction of the above-mentioned portion 603 of the peripheral structure of the electronic device. The conductive member 804 extends inwards from said portion 603 by a second dimension 606, so that again the“inwards” direction is taken with reference to said peripheral structure. The second dimension 606 is less than twice said first dimension 605. There is an electric coupling between said portion 603 of the peripheral structure and that part of the conductive member 804 that extends along the longitudinal direction of said portion.

In the embodiment of figs. 8 and 9 said electric coupling comprises an elastic, electrically conductive gasket 901 located between said portion 603 of the peripheral structure and that part of the conductive member 804 that extends along the longitudinal direction of said portion. An electrically conductive gasket of this kind could be used also in the embodiment of figs. 6 and 7, or in any other embodiment. The electrically conductive gasket 901 may be held in place by glue, or by locking it into a groove or the like, or by any other means that ensure both holding in place and making an electric coupling. Other alternatives for making the desired electric coupling may involve at least one of soldering, welding, or glueing with electrically conductive glue.

Figs. 10 and 11 illustrate the concept of the dimensions of the conductive member. In figs. 10 and 11 the portion 603 of the conductive peripheral structure that is used as the radiating antenna element is shown schematically as a horizontal bar. Figs. 10 and 11 illustrate embodiments in which there is a ground connection at one end of the portion 603, but there are also embodiments in which there is no such ground connection. The first dimension 605 of the conductive member is its dimension along a longitudinal direction of the portion 603. The conductive member extends inwards (with reference to said peripheral structure) from said portion by a second dimension 606. In fig. 10 the second dimension 606 is about twice the first dimension 605, while in fig. 11 the first dimension 605 is significantly larger than the second dimension 606. If there is a ground connection like in figs. 10 and 11, it may be advantageous to place the conductive member so that its distance from the ground connection in the longitudinal direction of the portion of the conductive peripheral structure is the largest possible.

Fig. 12 illustrates an equivalent circuit in which point 1201 represents the radiating antenna element and point 1202 represents a conductive member of the kind described above. Point 1203 represents the“open” end of the conductive member, i.e. that part that is furthest away from the radiating antenna element. The so-called open-end impedance Z between point 1203 and the local ground potential is typically large, in the order of at least 100 ohms, or even at least 1 kilo-ohm.

The electric coupling between the radiating antenna element and the conductive member is represented by a contact member 1204 in fig. 12. In general, the electric coupling may be considered to take place over an area A across a distance d through a material, the dielectric constant (or relative permittivity) of which is _r (epsilon-subscipt-r). If the electric coupling is a direct galvanic coupling through for example a direct metal-to-metal contact, the value of _r is very large or infinite.

Fig. 13 shows how the elements of fig. 12 may be considered in practice. The contact member 1204 is located between the portion 603 of the conductive peripheral structure used as the radiating antenna element and the conductive member, for which the reference designator 604 is used in fig. 13; this is an example only and not meant to limit the consideration to only those kinds of conductive members that are similar to the conductive member 604 of the embodiment in fig. 6. The area A is proportional to the dimension of the conductive member 604 in the longitudinal direction of the portion 603. If there are two or more discrete contact members between said portion and said conductive member, like two or more discrete conductive gaskets distributed along the longitudinal direction of the electric connection, the area A is proportional to the distance between the two discrete contact members farthest away from each other.

If the electric coupling is a non-galvanic coupling, it may comprise at least one of a capacitive coupling or an inductive coupling. An exemplary calculation can be made for a capacitive coupling. For example, if the contact area A is 1.5 mm x 12 mm, the distance d is 0.1 mm, and the material in between is air, the contact capacitance would be about 1.7 pF. That would correspond to a crossover frequency of about 90 MHz, assuming that the open end impedance is 1 kW. This means that a sufficient electromagnetic coupling between the radiating antenna element and the conductive member is achieved at frequencies higher than 90 MHz. In general a crossover frequency of a non-galvanic coupling of said kind may be in the order of tens to hundreds of megahertz.

In the embodiments described so far the antenna extender or conductive member has a rectangular shape. This is not a requirement, but the conductive member may take a wide variety of shapes. Fig. 14 illustrates some examples of such shapes, which include various rectangles, polygons with less or more comers than four, diamond shapes, trapezoidal shapes, shapes obtained by cutting a portion out of some otherwise regular shapes, partly round or curved shapes, and irregular shapes. The shape may be selected for example based on the shape of an available space for the antenna extender in the electronic device. The small white circles in the shapes of fig. 14 may be considered as examples of discrete contact members, or they may be examples of weld-, solder-, or glue joints between the conductive member and the portion of the conductive peripheral structure that is used as a radiating antenna element.

Fig. 15 illustrates an embodiment in which a dielectric cover 602 on a second side of an electronic device comprises a dielectric plate that is transparent or translucent and comprises a decorative layer 1501 on its inner surface. The conductive member 604 is indirectly attached to the dielectric plate through being attached to the decorative layer 1501. A conductive gasket 901 ensures the electric coupling between the conductive member 604 and the portion 603 of the conductive peripheral structure that is used as a radiating antenna element. Yet another possible embodiment could involve a conductive member made as a transparent electrically conductive layer on an outer surface of a dielectric plate that constitutes (a part of) a dielectric cover on the second side of the electronic device.

Fig. 16 illustrates measured total efficiencies of systems in which an electronic device comprises an antenna, the radiating antenna element of which is a portion of the conductive peripheral structure along sides of the electronic device. In each case the solid line illustrates the measured total efficiency when no antenna extender of the kind described was used. The corresponding dashed line illustrates the measured total efficiency when an antenna extender of the kind described was used. The general improvement in the system’s peak total efficiency was in the order of 1 dB, when the antenna extender was used. This is believed to be a result of the so-called chassis mode excitation improving and the antenna resonant frequency being optimized for the desired frequency band. In these measurements a rectangular antenna extender was used, and the dimensioning of the antenna extender was such that its dimension in the longitudinal direction of the radiating antenna element was about twice its dimension in the perpendicular direction.

The selection of the type of the radiating antenna element of the antenna structure is not limited by the invention. As an example, the antenna structure may be one of the following: monopole antenna, dipole antenna, folded dipole antenna, capacitive coupling element antenna, inverted-F antenna, loop antenna, slot antenna.

The invention has been described in conjunction with various embodiments herein. However, 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 description and claims the word “comprising” does not exclude other elements and steps, and the indefinite article“a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined in the appended claims. Although the invention has been described with reference to specific features and embodiments thereof, it is evident that various modifications and combinations can be made thereto without departing from the spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded simply as an illustration of the invention as defined by the appended claims, and are contemplated to cover any and all modifications, combinations, or equivalents that fall within the scope of the invention.