WO2013107921A1

WO2013107921A1 - Antenna structure for mobile device

Info

Publication number: WO2013107921A1
Application number: PCT/FI2012/050047
Authority: WO
Inventors: Mario FALIERO; Olivier Pajona; Zlatoljub Milosavljevic
Original assignee: Amphenol Finland Oy
Current assignee: Amphenol Finland Oy
Priority date: 2012-01-19
Filing date: 2012-01-19
Publication date: 2013-07-25
Anticipated expiration: 2014-07-19

Description

Antenna Structure for mobile device

Field of the Invention

The present invention relates to antenna structures and particularly antenna structures for wireless communication devices having metal cover. Background of the Invention

Different small embedded antennas are used in portable wireless communication devices such as in radio telephones, personal base stations, portable handsets, personal digital assistants, MP3 players, and video players. The number of antennas in each device is increasing as well as the number of available wireless services such as Global System for Mobile Communications (GSM), Distributed Control System (DCS), Personal Communications Service (PCS), UW, Digital Video Broadcasting-Terrestrial/Handheld (DVB-T/H), Wireless Fidelity (Wifi), BT, Worldwide Interoperability for Microwave Access (Wimax), Long Term Evolution (LTE), Global Positioning System (GPS) etc. To ensure small sizes for the devices, embedded antennas need to be small but also have high performance. In addition to small size needs the portable wireless communication devices to be robust, compact and lightweight. In addition to the use of small embedded antennas, the use of metal as cover material for wireless communication devices allows the devices to be thinner and in addition more robust than when plastic is used as cover material. However, metallic covers of mobile devices affects disadvantageously to antenna performances and thus the use of metal as cover material has had to restrict.

Nowadays, there are different kinds of antenna solutions for wireless communication devices having at least partially metal covers. In these solutions the antennas performances are often based on a trade-off between the size of metalized cover area and the whole device enclosure area.

There is, therefore, a need for an antenna structure, for wireless communication device with a metal back cover providing high radiation efficiency and higher immunity to the losses created by the head and hand effect when the portable device is used e.g. beside the head.

Summary of the Invention

The present invention relates to an antenna structure for a device with metal cover. The antenna structure comprises at least one driven antenna radiator and at least one parasitic antenna radiator which are arranged between a metal plate of the device and the metal cover. Various aspects of the invention include a wireless communication device with a metal cover including the antenna structure, which is characterized by what is stated in the independent claim. Various embodiments of the invention are disclosed in the dependent claims. A wireless communication device may be a mobile phone or any other portable wireless communication devices such as radio telephones, personal base stations, portable handsets, personal digital assistants, MP3 players, a mobile computer, a mobile collaboration, a mobile internet device, a smart phone, a tablet computer, a tablet PC, a personal digital assistant, a handheld game console, a portable media player, a digital still camera (DSC), a digital video camera (DVC or digital camcorder), a pager, or a personal navigation device (PND).

The term "metal cover" refers, in this context, to a cover plate or a structure of a wireless communication device, for example, to a back cover of a mobile device, wherein the cover is a uniform i.e. continuous surface that is entirely made of metal and wherein the metal substantially covers the whole back side of the mobile device without slits. The metal cover may be a visual back coating of the wireless communication device. In this invention, the metal cover is Radio frequency (RF) disconnected by a slot from a metal plate of the mobile device. The metal plate is a part of the wireless communication device and may consist of mechanical and electrical printed circuit boards (PCB), sub-circuit/s, display/s and/or other components both active and passive of the device, electrically connected or grounded together. The sub-circuits may be, for example, e.g. a switch circuit, a diode, a varactor, a capacitor bank, a simple load, or a Micro Electrical Mechanical System (MEMS). The metal plate may be used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. The metal plate may also be called as a printed wiring board (PWB). Metal plate may act as a ground plane for the antenna.

The antenna structure with the metal cover provides high radiation efficiency and higher immunity to the losses created by the head and hand effect when the portable device is used e.g. beside the head. The metal cover, the Radio frequency disconnection between the metal cover and the ground (earth) or other sub-circuit on the metal plate, the simple antenna structure without any other complex antenna feeding or grounding structures, are the main advantages of the this invention.

According to a first aspect of the invention, there is provided an apparatus for a wireless communication device, wherein the apparatus comprises a metal cover, a metal plate and an antenna structure, wherein the metal cover and the metal plate forms an enclosure around the antenna structure comprising at least one driven antenna radiator and at least one parasitic antenna radiator, and wherein said antenna radiators are formed onto the metal plate and wherein there is a slot in the enclosure for radio frequency (RF) disconnecting the metal plate and the metal cover.

According to an embodiment, said at least one driven antenna is connected to a radio frequency (RF) source of the wireless communication device. According to an embodiment, said at least one parasitic antenna is connected to a ground plane by a matching circuit or other electric sub circuit of the wireless communication device. According to an embodiment, the metal cover is a back cover of the device. According to an embodiment, the slot is arranged around the metal cover so that the metal plate forms sides of the metal enclosure. According to an embodiment, the slot is arranged around the metal plate so that the metal cover forms sides of the metal enclosure. According to an embodiment, the slot is arranged to side area of the enclosure. According to an embodiment, the metal plate forms part of one side of the enclosure. According to an embodiment, said at least one driven antenna radiator is formed on to a first end of the metal plate and said at least one parasitic antenna radiator is formed on to a second end of the metal plate. According to a second aspect of the invention, there is provided a wireless communication device comprising an antenna structure, a metal cover and a metal plate, wherein the metal cover and the metal plate forms an enclosure around the antenna structure comprising at least one driven antenna radiator and at least one parasitic antenna radiator, and wherein said antenna radiators are formed onto the metal plate and wherein there is a slot in the enclosure for radio frequency (RF) disconnecting the metal plate and the metal cover.

According to an embodiment, the metal cover is a back cover of the wireless communication device. According to an embodiment, the slot is arranged around the metal cover so that the metal plate forms sides of the metal enclosure. According to an embodiment, the slot is arranged around the metal plate so that the metal cover forms sides of the metal enclosure. According to an embodiment, the slot is arranged to side area of the enclosure. According to an embodiment, the metal plate forms part of one side of the enclosure. According to an embodiment, said at least one driven antenna radiator is formed on to a first end of the metal plate and said at least one parasitic antenna radiator is formed on to a second end of the metal plate. According to an embodiment, the wireless communication device is a mobile phone. Description of the Drawings

In the following, various embodiments of the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 a shows an example of a metal enclosure with a slot from the front according to an embodiment of the invention; Fig. 1 b shows the metal enclosure with the slot of fig. 1 a from the back;

Fig. 2 shows the metal plate with a driven antenna and a parasitic antenna of figs. 1 a and 1 b;

Fig. 3 shows an example of a full metal cover of figs. 1 a and 1 b;

Fig. 4 shows an example of a driven antenna according to an example embodiment;

Fig. 5 shows an example of a parasitic antenna according to an example embodiment;

Fig. 6 shows an example of a driven antenna schematic block antenna according to an example embodiment; and

Fig. 7 shows an example of a parasitic antenna schematic block antenna according to an example embodiment; Fig. 8a shows an example of a metal enclosure with a slot from the front according to an embodiment of the invention;

Fig. 8b shows the metal enclosure with the slot of fig. 8a from the back; Fig. 9a shows an example of a metal enclosure with a slot from the front according to an embodiment of the invention;

Fig. 9b shows the metal enclosure with the slot of fig. 9a the back;

Fig. 1 0a shows an example of a metal enclosure with a slot from the front side according to an embodiment of the invention;

Fig. 1 0b shows the metal enclosure with the slot of fig. 1 0a from the back side;

Fig. 1 1 shows a return loss curves for an antenna structure of a device with a metal cover according to an embodiment of invention; and

Fig. 1 2 shows a three-dimensional (3D) radiation pattern of an antenna structure according to an embodiment of invention in free space and beside a head of a user. Detailed Description of the Embodiments

An antenna system according to this invention comprises at least two antennas, wherein the first antenna is a driven antenna radiator, and the second antenna is a parasitic antenna radiator. The antenna system is arranged onto an electrically conductive metal plate of a mobile wireless communication device so that the antenna system stays between the metal plate and a metal back cover of the device. Thus the metallic plate with metal cover forms a full metal enclosure enclosing the antenna system. The metal cover and the metallic plate are RF disconnected by a slot i.e. there is no RF connection between the metal plate and the metal cover. The metal cover may be electrically disconnected from the ground plane and disconnected from RF. However, the metal cover may also be direct current (DC) connected or correspondingly connected to ground plane to provide electrical static discharge (ESD) protection. In that case, some RF chokes, or ESD protection devices (diode, etc.), are used to make the metal cover electrically floating. Thus, the metal cover part is RF not connected to the metal plate.

Antenna system located inside the metal enclosure comprises at least one driven antenna that is connected to Radio frequency (RF) source and at least one parasitic antenna that is not connected to RF source. The parasitic antenna may be connected to the ground or to a sub circuit, such as a switch circuit, a diode, a varactor, a capacitor bank, or a Micro Electrical Mechanical System (MEMS) or a simple load, wherein the simple load may be a resistor, an inductor, a capacitor, a short end or an open end. Antenna structures may be realized in any kind of known antenna technology, for example, as flex circuit technology, metal sheet, Laser Direct Structuring (LDS), two shot MID etc.

The metal plate may consists of the mechanical and electrical printed circuit boards (PCB), sub circuits, displays and/or other components both active and passive of the device, electrically connected or grounded together.

The metal cover is a back cover for a mobile wireless communication device, so that the whole back side surface of the device is completely made of metallic material, for example, of aluminium or copper. The metal cover is not RF connected to a RF power or to ground level by matching circuit or to other electronic sub-circuit. The metal cover may have any shape depending of the shape and form of the device, it may be for example, rectangular or circular. In addition, the thickness of the metallic part is not restricted. However, the thinner cover is lighter than thicker, but the weight also depends on the used material.

The driven antenna radiator of the antenna system may be connected to a radio frequency source i.e. to a radio circuit or other sub circuit of the device by a matching circuit, which may be, for example, any combination of RF lumped or distributed components active or passive. These circuits may be located on one of the sub assembly of the electrically conductive plate. The driven antenna may be, for example, an inverted L-shape antenna or an Inverted F shape antenna. The parasitic antenna radiator may be connected to the ground of the metal plate by a matching circuit. The parasitic antenna radiator may be, for example, a loop antenna or the combination of parasitic element that is connected to the ground. The driven antenna radiator and the parasitic antenna interact with each other inside the metallic enclosure, and with the metallic enclosure and the slot separating the metal cover from the metal plate, so that a directional radiation pattern and very localized near field electromagnetic (EM) distribution and far field EM distribution are created. This makes possible to create a quite directive radiation pattern, which could be tuned to have the maximum gain in a specific direction. And thus, for example, in a case of a mobile phone, the radiation towards the head of the used can be reduced. The benefits of this specific directional radiation pattern and near field distribution are thus as discussed above a reduction of the power absorbed by a head or hand of a user of the wireless communication device when the device is positioned against the head (the electrical conductive plate being the side of the device the closest to the head) and an increased radiation efficiency of the overall device. Radiation efficiency refers to the efficiency of a radiator wherein the matching of the radiator has been taken into account.

The typical bands covered by an internal antenna for full metal devices are, for example, GSM frequency bands: 850, 900, 1 800 or 1 900 MHz, Wideband Code Division Multiple Access (WCDMA) bands: 21 1 0 to 2170 MHz (Bands I), 1 930 to 1 990 MHz (Band I I), 869 to 894 MHz (Band V), or 925 to 960 MHz (Band VI I I), and Long Term Evolution (LTE) bands: 4, 1 7 1 , 3, 7, 8, or 20. In the following, several embodiments of the invention will be described in the context of an antenna structure for a mobile wireless communication device with a metal cover, wherein the antenna structure comprising at least one driven antenna element and at least one parasitic antenna element. And wherein the antenna structure is arranged into a metallic enclosure divided in two part, the metal cover and a metal plate, that are RF disconnected by a slot. It is to be noted, however, that the invention is not limited to mobile devices only. The invention is either limited to an enclosure geometry, a slot geometry, a slot number, a number of driven and parasitic antenna or type or number of matching circuits. In fact, the different embodiments may have applications widely in any environment where a metal cover for a wireless communication device is advantageous solution. Fig. 1 a shows a metal enclosure with slot structure 1 0 for a device according to an embodiment of the invention from the front i.e. from the direction of a metal plate. The device may be for example a mobile phone. The metallic enclosure 1 0 comprises a metal plate 1 1 , a metal cover 1 2, and a slot 1 3 on the edge area of the metal enclosure. Area of the metal cover 1 2 is larger than the area of the metal plate 1 1 so the slot 1 3 is formed around the edge area of the metal plate 1 1 i.e. around the metal plate 1 1 and on the metal cover 1 2. In addition the metal cover 1 2 forms also the sides of the metal enclosure 1 0. The metal cover 1 2 is a uniform i.e. one-piece metal surface. The metal plate 1 1 is connected to the ground or other sub circuit of the wireless communication device. The metal plate 1 1 may be formed from a metal sheet, a Printed Circuit Board (PWB), a display and also other elements i.e. parts of the mobile phone structure (not shown). However, for example, the display and layers of the PWB may be on that side of the metal plate 1 1 that is not against the metal cover 1 2. The layers may, however, also be on the metal cover side. The metal cover 1 2 is RF disconnected from the conductive metal plate 1 1 . A driven antenna radiator 1 4 and a parasitic antenna radiator 1 5 are arranger onto the metal plate 1 1 and between the metal plate 1 1 of the device and the metal cover 1 2 as shown in fig. 2. Fig. 1 b shows the metal enclosure with slot structure 1 0 of fig. 1 a from the back side i.e. from the direction of the metal cover 12.

Fig. 2 shows a perspective view of the metal plate 1 1 with antennas according to an embodiment of the invention. A carrier 16 of a driven antenna radiator 14 is arranged under the driven antenna radiator 14 i.e. between the metal plate 1 1 and the driven antenna radiator 14 and a carrier 17 of a parasitic antenna radiator 15 is arranged under the parasitic antenna radiator 15 i.e. between the metal plate 1 1 and the parasitic antenna radiator 15. The driven antenna radiator 14 may be e.g. an Inverted L shape Antenna (ILA) that may be connected to a radio frequency source or other sub circuit of the wireless communication device by a matching circuit. The parasitic antenna radiator 15 may be e.g. a parasitic loop antenna. The parasitic antenna radiator 15 may be connected to a ground level or other sub circuit of the wireless communication device by a matching circuit. The radiators 14 and 15 comprise a signal feeding point to connect radiators to a matching circuit or other electronic sub-circuit. Fig. 3 shows a perspective view of a metal cover 30 without a metal plate or antenna structure according to an embodiment of the invention. The metal cover 30 may have open box geometry and it may be e.g. a copper or aluminium back cover of a mobile phone, made of aluminium.

Fig. 4 shows a perspective view of an Inverted L shape Antenna (ILA) structure 40 of an antenna structure for a device according to an embodiment of the invention. The ILA radiator structure 40 comprises a feed part 41 and a radiator arm 42. The ILA feed part 41 may be connected to a radio frequency source or other sub circuit of the wireless communication device by a matching circuit. By adjusting the electric length, and shape of the ILA arm part 42, high band (GSM 1800, GSM 1900) resonances may be created and tuned, also the low band (GSM900) may be created e.g. e.g. at least two resonances may be created and tuned by using a driven antenna element, a parasitic loop antenna and one matching circuit. Fig. 5 shows a perspective view of a parasitic loop antenna structure 50 of an antenna structure for a device according to an embodiment of the invention. The parasitic loop antenna radiator structure 50 comprises two electric termination parts 51 , 55, and a loop arm 52, wherein the loop arm 52 comprises, for example, an edge flaps part 53, and edge flaps part 54. The electric terminations parts 51 and 55 are connected to the ground or other sub circuit of the wireless communication device by a matching circuit. By adjusting the electric length of the parasitic loop arm part 52, size of the edge flap parts 53 and 54 and/or the matching circuit, the low band (GSM 850, GSM 900) resonances may be created and tuned, e.g. at least two resonances may be created and tuned by using an parasitic loop antenna 50 and one matching circuit.

Fig. 6 shows a schematic block of a driven antenna radiator 14 and a sub circuit 60 according to an embodiment of the invention. The driven antenna radiator 14 may be an ILA structure and the sub circuit 60 may be for example a series capacitor of e.g. 1 .2pF.

Fig. 7 shows a schematic block of a parasitic antenna 23 and two sub circuits 70 and 71 according to an embodiment of the invention. The parasitic antenna radiator 23 may be e.g. a parasitic loop antenna structure and two matching circuits 70 and 71 , for example, a parallel inductor and capacitor circuit of e.g. 5.6nH and 5.6pF.

Fig. 8a shows a metal enclosure 80 with slot structure for a device according to an embodiment of the invention from the front i.e. from the direction of a metal plate. The metallic enclosure 80 comprises a metal plate 81 , a metal cover 82, and a slot 83 on the side of the metal enclosure 80. The slot 83 is formed around the metal enclosure structure 80 so that the metal plate 81 and the metal cover 82 are RF disconnected by the slot 83. Fig. 8b shows the metal enclosure 80 with slot structure for a device of fig. 8a from the back i.e. from the direction of the metal cover 82. Fig. 9a shows a metal enclosure 90 with slot structure for a device according to an embodiment of the invention from the front i.e. from the direction of a metal plate. The metallic enclosure 90 comprises a metal plate 91 , a metal cover 92, and a slot 93. In this embodiment the slot 93 is formed on the metal plate 91 side of the enclosure. The metal cover 92 forms the whole back side and all sides of the enclosure 90, but also a part of the front side i.e. a metal plate 91 side of the enclosure 90 as can be seen from the fig. 9a. Antennas are formed onto the metal plate 91 and the metal plate 91 and the metal cover 92 are RF disconnected by the slot 93.

Fig. 9b shows the metal enclosure 90 with slot structure for a device of fig. 9a from the back i.e. from the direction of the metal cover 92. From the back the metal plate 91 may not be seen.

Fig. 1 0a shows a metal enclosure 1 00 with slot structure for a device according to an embodiment of the invention from the front i.e. from the direction of a metal plate. The metallic enclosure 1 00 comprises a metal plate 1 01 , a metal cover 1 02, and a slot 1 03 on the edge area of the metallic enclosure 1 00. Area of the metal cover 1 02 is smaller than the area of the metal plate 1 01 so the slot 1 3 is formed around the edge area of the metal cover 1 02 i.e. around the metal cover 1 02 and on the metal plate 1 01 . In addition the metal plate 1 01 forms also the sides of the metal enclosure 1 00. Also the metal cover 1 02 is a uniform i.e. one-piece metal surface. The slot 1 03 RF disconnects the metal plate 1 01 and the metal cover 1 02.

Fig. 1 0b shows the metal enclosure 1 00 with slot structure of fig. 1 0a from the back i.e. from the direction of the metal cover 1 02. A driven antenna radiator and a parasitic antenna radiator are arranger onto the metal plate 1 01 and between the metal plate 1 01 and the metal cover 1 02. Fig. 1 1 shows a return loss curves for an antenna structure of a device with a metal cover according to an embodiment of invention. Free space (FS) curve 1 1 0 discloses a return loss curve for position wherein the device is in a free space, not on or near users head, beside head right (BH R) curve 1 1 1 discloses a return loss curve for position wherein the device is on or near a users head on the right side and beside head left (BHL) curve 1 1 2 discloses a return loss curve for position wherein the device is on or near a users head on the left side. As can be seen from fig. 1 1 , the antenna structure with the full-metal cover has high immunity to the head presence, i.e. impedance remains stable when the device is used e.g. on or near i.e. beside the head of the user. In addition, the antenna structure with the full-metal cover has high immunity to the head presence when the device with the antenna structure and full- metal cover is held by user's hand.

Fig. 1 2 shows a three-dimensional (3D) radiation pattern of an antenna structure according to an embodiment of the invention in free space and beside a head of a user at 900MHz. Radiation patterns are quite directive, which is not a typical behavior of an ordinary antenna solution. In addition, they have no any or very little absorption loss in beside head use case. This can be observed looking at free space radiation pattern 1 20 and beside head radiation pattern 1 21 , in boresight direction 1 22. A metal cover, a metal plate, a slot and the antenna structure according to this invention may have any shape necessary to comply with the dimensional requirements of the device in which the antenna structure is adapted to be used. The antenna radiators and the switch circuit may also have any shape necessary to comply with the functional and electrical requirements of the wireless communication device in which the antenna structure is suitable to be used.

It should also be noted that both antenna elements, the driven and the parasitic antenna elements, can be placed fully on top of ground plane or off-ground, wherein ground plane has at least partly removed beneath the antennas. It is obvious that the present invention is not limited solely to the above- presented embodiments, but it can be modified within the scope of the appended claims.

Claims

Claims:

1 . An apparatus for a wireless communication device, wherein the apparatus comprises a metal cover, a metal plate and an antenna structure, wherein the metal cover and the metal plate forms an enclosure around the antenna structure comprising at least one driven antenna radiator and at least one parasitic antenna radiator, and wherein said antenna radiators are formed onto the metal plate and wherein there is a slot in the enclosure for radio frequency (RF) disconnecting the metal plate and the metal cover.

2. An antenna structure according to claim 1 , wherein said at least one driven antenna is connected to a radio frequency (RF) source of the wireless communication device.

3. An apparatus according to claim 1 or 2, wherein said at least one parasitic antenna is connected to a ground plane by a matching circuit or other electric sub circuit of the wireless communication device.

4. An apparatus according to claim 1 , 2 or 3, wherein the metal cover is a back cover of the device.

5. An apparatus according to any of the claim 1 -4, wherein the slot is arranged around the metal cover so that the metal plate forms sides of the metal enclosure.

6. An apparatus according to any of the claim 1 -4, wherein the slot is arranged around the metal plate so that the metal cover forms sides of the metal enclosure.

7. An apparatus according to any of the claim 1 -4, wherein the slot is arranged to side area of the enclosure.

8. An apparatus according to any of the claim 1 -4, wherein the metal plate forms a part of one side of the enclosure.

9. An apparatus according to any of the claim 1 -8, wherein said at least one driven antenna radiator is formed onto a first end of the metal plate and said at least one parasitic antenna radiator is formed onto a second end of the metal plate.

1 0. A wireless communication device comprising an antenna structure, a metal cover and a metal plate, wherein the metal cover and the metal plate forms an enclosure around the antenna structure comprising at least one driven antenna radiator and at least one parasitic antenna radiator, and wherein said antenna radiators are formed onto the metal plate so that and wherein there is a slot in the enclosure for radio frequency (RF) disconnecting the metal plate and the metal cover.

1 1 . A wireless communication device according to claim 1 0, wherein the metal cover is a back cover of the wireless communication device.

12. A wireless communication device according to claim 1 0 or 1 1 , wherein the slot is arranged around the metal cover so that the metal plate forms sides of the metal enclosure.

13. A wireless communication device according to claim 1 0 or 1 1 , wherein the slot is arranged around the metal plate so that the metal cover forms sides of the metal enclosure.

14. A wireless communication device according to claim 1 0 or 1 1 , wherein the slot is arranged to side area of the enclosure.

15. A wireless communication device according to claim 1 0 or 1 1 , wherein the metal plate forms part of one side of the enclosure.

1 6. A wireless communication device according to any of the claim 1 0 to 1 5, wherein said at least one driven antenna radiator is formed on to a first end of the metal plate and said at least one parasitic antenna radiator is formed on to a second end of the metal plate.

17. A wireless communication device according to any of the claim 10o 15, wherein the wireless communication device is a mobile phone.