SLOT ANTENNA DEVICE

Abstract: A slot antenna device for transmitting and/or receiving radio frequency (RF) waves, connectable to a radio communication device including signal processing circuitry, comprises a substantially planar conductive antenna element (23) provided with a slot (25), and with feeding and grounding points, respectively, located at opposite sides of said slot (25); a substantially planar RF ground plane conductor generally located substantially in parallel with said planar conductive antenna element; a grounding connector connecting said ground plane conductor to said grounding point; and a feeding connector connecting said signal processing circuitry to said feeding point, wherein said antenna device is connectable to said radio communication device such that said ground plane conductor will be located between said conductive antenna element (23) and said signal processing circuitry to effectively shield said circuitry from said transmitted and/or received RF waves.

Description: SLOT ANTENNA DEVICE TECHNICAL FIELD OF THE INVENTION The present invention generally relates to the field of antennas and particularly to a slot antenna device for transmitting and/or receiving radio frequency waves, and to a portable radio communication device comprising such a slot antenna device. BACKGROUND OF THE INVENTION In radio communication systems of today there is an increasing demand for availability and small sizes of user terminals thereof. This puts high requirements on the antenna devices of these user terminals to be compact and to exhibit good antenna performance . Antenna devices including a helical element in combination with an extendible whip antenna have been used for hand portable user terminals in order to achieve compact dimensions and durability, while still maintaining high radiation efficiency. Also, permanently protruding external antenna devices are used extensively. Recently, attention has also been focused on antenna devices mounted inside the housing of hand portable terminals. Thereby, protruding antenna parts are avoided, lower radiation intensity towards the user may be obtained, and possibilities for further reductions of the size of the terminals are enabled, since many of these internal antenna devices may be achieved by means of thin film technology. The US patent 5,914,693, issued to K. Takei et al., discloses a coaxial slot antenna installed in a radio communication device comprising an entire strip conductor arranged inside a flat conductive cubic, such that the strip conductor is insulated from the conductive cubic. The cubic is provided with a U- shaped slot crossing the strip conductor along the length thereof and in the height direction thereof. In one embodiment of the patent, a radio communication device is disclosed having the coaxial slot antenna device embedded in a multilayer RF circuit board (PCB) mounted in parallel with and elevated from a base band terminal PCB. Further, the antenna RF PCB is provided with RF circuitry and another circuitry. The antenna RF PCB and the terminal base band PCB are interconnected by a connector. The uppermost layer comprises the coaxial slot antenna and RF circuitry laterally separated therefrom. A second layer is provided with power supply and control circuitry, and the third layer is connected to ground. The fourth layer is provided with intermediate frequency components, which are connected to base band circuitry arranged on the terminal PCB. However, such an antenna structure is not easily made very compact, operable in multiple bands or adaptively impedance matchable. Further, it has a rather complex structure, which, due to required tolerances on the coupling with the feed, makes it difficult and expensive to manufacture, and it has no explicit shielding means around the RF circuitry. Other internally arranged antenna devices are disclosed in i.a. the following patent documents: EP 0,878, 863, A2 (T. Suesada) , EP 0,851, 531, A2 (D. Hicks et al.), EP 0,623, 967, Al (N. Erkocevic) , US 4,924,237 issued to K. Honda et al., US 5,874,920 issued to T. Araki et al., EP 0,738, 023, A2 (T. Tsuru), WO 99/13528 (G. Johnson), WO 94/15378 (L.J. Vannatta et al.), WO 98/49743 (E. Cassel) , and EP 0,752, 735, Al (D. Mϋller) , which further illustrate the background of the present invention. The smaller the terminals are manufactured, the smaller are the distances between various parts, such as base band circuitry, RF circuitry, and radiating structures of the terminal, and the more electrical disturbances and interference between the various parts are achieved. The present invention concerns a readily manufactured compact antenna device to be installed in a compact terminal, said antenna device reducing the amount of disturbances and interference in said terminal. SUMMARY OF THE INVENTION A main object of the present invention is to provide an antenna device for a radio communication device, which exhibits an overall improved performance in comparison with antenna devices of prior art. It is in this respect a particular object of the invention to provide an antenna device, which is easy and cheap to manufacture, easy to install and which enables an efficient use of the available space, and which exhibits good antenna performance. Another object of the invention is to provide an antenna device, which is insensitive to conductive portions, such as e.g. a conductive radio communication device casing or the hand of a user, in the proximate environment of the antenna device. It is a further object of the invention to provide an antenna device which when being installed in a radio communication device exhibits, together with the radio communication device, reduced losses, e.g. due to resistivity in connection lines, as compared with known radio communication devices. It is yet a further object of the invention to provide an antenna device as an easily installable module comprising processing circuitry for RF signals. It is still a further object of the invention to provide an antenna device that is small, of lightweight and reliable, particularly mechanically durable. It is an additional object of the invention to provide an antenna device suited to be used as an integral part of a radio communication device. It is yet an additional object of the invention to provide an antenna device adapted for operation in at least two different frequency bands. These objects among others are, according to the invention, attained by a slot antenna device and by a radio communication device as claimed in the appended Claims. In this disclosure it is to be understood that the antenna system of the invention is operable to transmit or receive RF signals. Even if a term is used herein that suggests one specific signal direction it is to be appreciated that such a situation can cover that signal direction and/or its reverse. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description of embodiments of the present invention given hereinbelow and the accompanying Figs. 1-4 which are given by way of illustration only, and thus are not limitative of the invention. Fig. la is a perspective view of a portable telephone without casing and Fig. lb is an exploded perspective view of the same telephone, said telephone including a slot antenna device according to one embodiment of the present invention. Figs. 2a-b are a perspective view and an exploded perspective view, repectively, of the slot antenna device of Fig. 1. Fig. 3a is an exploded perspective view of a three-layer structure comprised in the slot antenna device of Fig. 2 and Fig. 3b is a cross-sectional view of said three-layer structure. Fig. 4 displays schematically parts of slot antenna layers provided with radiation affecting components connected over the slot according to an alternative embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In the following description, for purposes of explanation and not limitation, specific details are set fourth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known devices and methods are omitted so as not to obscure the description of the present invention with unnecessary details. Fig. la and lb show a portable telephone for transmitting and receiving radio frequency (RF) waves. The telephone is shown without casing in an assembled perspective view and an exploded perspective view, respectively, as seen from behind. In the Figures reference numeral 1 is a chassis of a portable telephone. A main printed circuit board, PCB, 3 of the telephone is intended to be mounted at the front side of chassis 1. PCB 3 comprises any suitable signal processing circuitry (not shown) known in the art for the operation of the telephone. A slot antenna device 5 of the present invention is intended to be mounted at the back side of chassis 1 together with a battery 7. Antenna device 5 comprises a multilayer PCB- based antenna 9, a connector 11 for connection of an external antenna (not shown) , and a shielding box 13 mounted at the bottom surface of multilayer antenna 9 for the shielding of electronics. Further, antenna device comprises a top 15 and bottom 17 cover. The antenna can alternatively be arranged on a flexible substrate or on a MID (Molded Interconnection Device) structure (not shown in the Figures) . The inventive slot antenna device is shown more in detail in Figs. 2a and 2b. Here, Fig. 2a shows a perspective view of the slot antenna device 5 as assembled. Preferably, antenna device is provided in the form of a plug and play module, which is easily installed into the portable telephone and which may also be easily removed therefrom. With reference now to Fig. 2b some further aspects of the antenna device will be depicted. Antenna 9 and top cover 15 comprise respective apertures 19, 21 aligned to each other, wherein connector 11 is mounted such that an external antenna, such as an antenna of a car (not shown) , may be connected to the hand portable telephone. Further, antenna 9 comprises a substantially planar conductive patch 23, in which a U-shaped slot 25 is formed. The shape of slot 25 may, however, have any suitable shape, such as e.g. any of V, W, H and Ω shapes. At opposite sides of slot 25, there is arranged a feeding point 27 and a grounding point 29, respectively, where feeding point 27 is connected (not shown in Fig. 2) to signal processing circuitry arranged on PCB 3 of Fig. 1 and grounding point 29 is connected to a substantially planar RF ground plane conductor (not shown in Fig. 2) comprised in antenna 9. The antenna 9 may be adapted for transmitting and/or receiving RF waves in at least two different frequency bands, wherein the slot 25 and the extension of the conductive antenna layer 23 are designed to obtain operation in the two different frequency bands . In Fig. 3a and 3b is shown antenna 9 in more detail. Fig. 3a is an schematic exploded perspective view of antenna 9, which comprises a three-metallic-layer structure and Fig. 3b is a cross-sectional view of the three-layer structure as taken along a line crossing through the feeding and grounding points 27 and 29, respectively. The uppermost layer 23 is the above mentioned conductive patch layer provided with the slot 25, the feeding point 27 and the grounding point 29. The next conductive layer 31, preferably substantially in parallel with patch layer 23, is the above-mentioned substantially planar RF ground plane conductor. A metallic substantially vertical conductor 33 is provided, which connects, resistively or capacitively, grounding point 29 to ground plane conductor 31. Reference numeral 35 indicates the RF grounding of layer 31 which may be common ground with ground of PCB 3 in Fig. 1 (such interconnection is not explicitly shown in the Figure) or may be a separate ground. Further, there is provided an aperture 37 in layer 31 for receiving a feeding connector 39, which connects, resistively or capacitively, feeding point 27 to signal processing circuitry of the telephone PCB. Feeding connector 39 may be comprised of a coaxial line connector. The bottom layer 41 provides electrical connections to feeding connector 39 and optionally electric RF circuitry. In Fig. 3a layer 41 comprises an electrical conductor 43, which connects feeding connector 39 to a duplexer 45, which in turn is connected to a power amplifier 47 and a low noise amplifier 49 arranged in parallel. Power amplifier 47 and low noise amplifier 49 are further connected to feeding circuitry and receiving circuitry, respectively, said circuitry being arranged on the telephone PCB 3 in Fig. 1. Furthermore, aperture 19 of antenna 9 as shown in Fig. 2a is in Fig. 3a indicated by reference numerals 19a, 19b, and 19c in layers 23, 31, and 41, respectively. Electrical connection from duplexer 45 to aperture 19a is provided through connectors 51 and 53. Two dielectric layers are provided between the metallic layers to electrically insulate the conductive layers from each other (not shown in Fig. 3a for sake of simplicity) . However, in Fig. 3b, these layers are indicated with 54 and 55. The thickness of layer 54 is chosen so as to achieve suitable antenna performance of antenna 9. It shall be appreciated that the electrical connections 43, 51 and the electric components 45, 47, 49 on layer 41 are located on the bottom surface of a dielectric, which may be layer 55, but may alternatively be a dielectric thin film, such as a flexible film (not shown) . The components 45, 47, 49 and radiation shielding box 13 (see Fig. 2a) are arranged such that shielding box 13 surrounds the components in all directions except in the direction of the ground plane conductor 31. Preferably, radiation-shielding box 13 is in the form of a shielding can. The shielding box 13 can be of a conductive material or may comprise a conductive film on a surface thereof. The electric components located at the antenna device 5 may in various embodiments comprise any of a duplexer for separating transmission and reception lines, bandpass filter (s) for bandpass filtering signals fed to and/or received from the feeding point, a power amplifier for amplifying signals fed to the feeding point, at least one low noise amplifier for amplifying signals received from the feeding point, a frequency converter for frequency converting signals fed to and/or received from the feeding point, an analogue-digital converter for converting received analogue signals from the feeding point to digital form and a digital-analogue converter for converting digital signals from the signal processing circuitry to an analogue signal, which is fed to the feeding point. The interface between the antenna PCB 9 and the telephone PCB 3 may be chosen to be at any suitable location along any RF circuitry line(s); e.g. if all above components are arranged on the antenna PCB 9, the antenna device 5 has only digital ports and thus, it may be referred to as a digital controlled antenna (DCA) . The antenna device of the present invention may indeed comprise any of the various components and features incorporated in antenna devices, which are depicted and detailed in our co- pending Swedish patent applications entitled "Antenna device and method for transmitting and receiving radio waves" , "An antenna device for transmitting and/or receiving RF waves", "Antenna device and method for transmitting and receiving radio waves", and "Antenna device for transmitting and/or receiving radio frequency waves and method related thereto" , all filed on October 29, 1999, which applications hereby are incorporated by reference. It shall be noted that antenna device is installable in and connectable to the telephone such that ground plane conductor 31 will be located between conductive antenna element 23, 25 and signal processing circuitry on PCB 3 to effectively shield said circuitry from transmitted and/or received RF waves. The ground plane conductor 31 is further lying between conductive antenna element 23, 25 and any electric RF component located in layer 41 to effectively shield the electric RF component from transmitted and/or received RF waves. As can be seen from Fig. 3a, ground plane conductor 31 has an extension in its plane of extension that is substantially of the same size as the extension of conductive antenna element 23, 25 in its plane of extension. It is preferred that the ground plane conductor 31 is of at least this size to obtain good antenna performance and to shield electric circuitry from radiation. Fig. 4 displays schematically parts of an antenna layer 23' provided with radiation affecting components Ci, C 2 , Li and Di connected over a slot 25' according to an alternative embodiment of the present invention. The upper Figure shows electrical equivalent symbols connected over slot 25' and a feed device 57 for feeding slot 25' , whereas the lower Figure illustrates examples of implementations of the electric components shown in the upper Figure, and also indicates the feeding 27' and grounding 29' points. Two capacitances Ci and C 2 are connected across the slot, Ci being implemented as two notches at opposite sides of slot 25' and C 2 being implemented as three protrusions, two at one side and the third at the opposite side of slot 25' . Further, an inductance Li is connected across the slot, Li being implemented as a narrow strip across slot 25' . There is also provided an active component across the slot, here in the form of a diode D x interconnecting opposite sides of slot 25' . The design of this electric circuitry at slot 25' , together with the design of patch layer 23' and slot 25' , may be chosen in order to obtain a suitable antenna performance. The design may apparently affect any of a set of radiation related parameters, such as resonance frequency, input impedance, bandwidth, radiation pattern, gain, polarization and near-field pattern. It will be obvious that the invention may be varied in a plurality of ways. Such variations are not to be regarded as a departure from the scope of the invention. All such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the appended claims .

Claims: CLAIMS 1. A slot antenna device for transmitting and/or receiving radio frequency (RF) waves, connectable to a radio communication device, which radio communication device comprises signal processing circuitry, characterized by a substantially planar conductive antenna element (23) provided with a feeding point (27) and a grounding point (29) , respectively, and provided with a slot (25) located between said feeding point (27) and said grounding point (29); a substantially planar RF ground plane conductor (31) generally located in a plane substantially parallel with said planar conductive antenna element (23) ; - a grounding connector (33) connecting said ground plane conductor (31) to said grounding point (29) ; and - a feeding connector (39) connecting said signal processing circuitry to said feeding point (27), wherein said antenna device (5) is connectable to said radio communication device such that said ground plane conductor (31) is to be located between said conductive antenna element (23) and said signal processing circuitry to effectively shield said signal processing circuitry from said transmitted and/or received RF waves. 2. The antenna device as claimed in Claim 1, wherein said ground plane conductor (31) has an extension in its plane of extension that is at least of the same size as the extension of said conductive antenna element (23) in its plane of extension. 3. The antenna device as claimed in any of Claim 1 or 2, wherein a dielectric layer (54) of a predetermined thickness is provided between said conductive antenna element (23) and said ground plane conductor (31) . 4. The antenna device as claimed in any of the preceding Claims, wherein said grounding connector (33) is connecting said ground plane conductor (31) to said grounding point (29) resistively. 5. The antenna device as claimed in any of Claims 1-4, wherein said grounding connector (33) is connecting said ground plane conductor (31) to said grounding point (29) capacitively. 6. The antenna device as claimed in any of the preceding Claims, wherein said feeding point (27) is fed resistively. 7. The antenna device as claimed in any of Claims 1-5, wherein said feeding point (27) is fed capacitively. 8. The antenna device as claimed in any of the preceding Claims, wherein said feeding connector (39) is a coaxial line connector. 9. The antenna device as claimed in any of the preceding Claims, wherein it comprises at least one electric RF component (45-49) connected inbetween said feeding point (27) and said signal processing circuitry, and arranged such that said ground plane conductor (31) is located between said conductive antenna element (23) and said at least electric RF component (45-49) to effectively shield said electric RF component from said transmitted and/or received RF waves. 10. The antenna device as claimed in Claim 9, wherein said at least one electric RF component comprises a bandpass filter for bandpass filtering a signal fed to or received from said feeding point (27) . 11. The antenna device as claimed in Claim 9 or 10, wherein said at least one electric RF component comprises a power amplifier (47) for amplifying a signal fed to said feeding point (27) . 12. The antenna device as claimed in any of Claims 9-11, wherein said at least one electric RF component comprises at least one low noise amplifier (49) for amplifying a signal received from said feeding point (27). 13. The antenna device as claimed in any of Claims 9-12, wherein said at least one electric RF component comprises a frequency converter for frequency converting a signal fed to or received from said feeding point (27). 14. The antenna device as claimed in any of Claims 9-13, wherein said at least one electric RF component comprises an analogue-digital converter for converting a received analogue signal from said feeding point (27) to digital form and/or a digital-analogue converter for converting a digital signal from said signal processing circuitry to an analogue signal, which is fed to said feeding point (27) . 15. The antenna device as claimed in any of Claims 9-14, wherein it comprises a radiation shielding structure (13) surrounding said at least one electric RF component (45-49) in all directions except in the direction of the ground plane conductor (31) . 16. The antenna device as claimed in Claim 15, wherein said radiation shielding structure (13) is shielding can shaped. 17. The antenna device as claimed in Claim 15 or 16, wherein said radiation shielding structure (13) is made of a conductive material or comprises a conductive film on a surface thereof. 18. The antenna device as claimed in any of Claims 9-17, wherein said planar conductive antenna element, said ground plane conductor, and said at least one electric component are arranged at a multilayer board, particularly a printed circuit board (5) . 19. The antenna device as claimed in Claim 18, wherein said printed circuit board comprises a first conductive top layer (23) , in which said planar conductive antenna element (23) with the slot (25) is formed, a second dielectric layer (54) for insulating said first layer from a third conductive layer (31), in which third layer said ground plane conductor (31) is formed, and a fourth dielectric layer (55) for insulating said third layer from a fifth bottom layer, in which fifth layer said at least one electric RF component (45-49) is arranged. 20. The antenna device as claimed in any of the preceding Claims, wherein it is adapted for transmitting and/or receiving RF waves in at least two different frequency bands. 21. The antenna device as claimed in Claim 20, wherein the slot (25) and the extension of the planar conductive slot antenna element (23) are designed to obtain operation in said at least two different frequency bands. 22. The antenna device as claimed in any of the preceding Claims, wherein the slot (25) has generally the shape of anyone in the group of the characters U, V, W, H and Ω. 23. The antenna device as claimed in any of the preceding Claims, wherein the slot (25' ) is provided with impedance or resonance frequency affecting circuitry (Ci, C 2 , Li, Di) . 24. The antenna device as claimed in Claim 23, wherein said resonance frequency affecting circuitry comprises a capacitive ' (Ci, C 2 ) and/or inductive (Li) component (s) . 25. The antenna device as claimed in Claim 24, wherein said, capacitive and/or inductive component (s) (Ci, C 2 , Li, Di) is (are) connected across the slot (25'), thus interconnecting opposite sides thereof. 26. The antenna device as claimed in Claim 23, wherein said resonance frequency affecting circuitry comprises at least one active component, e.g. a diode (Di) . 27. The antenna device as claimed in any of the preceding Claims, wherein said planar conductive antenna element (23) comprises a second feeding point and the antenna device comprises a connector (11) connected to said second feeding point and arranged to be connectable to an external antenna. 28. The antenna device as claimed in any of the preceding claims, wherein said ground plane conductor (31) is connectable to a grounding conductor provided in said radio communication device. 29. The antenna device as claimed in any of the preceding Claims, wherein it comprises dielectric top (15) and bottom (17) cover parts. 30. A slot antenna device for transmitting and/or receiving radio frequency (RF) waves connectable to a radio communication device, which radio communication device comprises signal processing circuitry, characterized by - a substantially planar conductive antenna element (23) provided with a feeding point (27) and a grounding point (29), respectively, and provided with a slot (25) located between said feeding point (27) and said grounding point (29); a substantially planar RF ground plane conductor (31) generally located in a plane substantially parallel with said planar conductive antenna element (23) ; - a grounding connector (33) connecting said ground plane conductor (31) to said grounding point (29); - a feeding connector (39) connecting said signal processing circuitry to said feeding point (27); and - at least one electric RF component (45-49) connected between said feeding point (27) and said signal processing circuitry; wherein - said antenna device (5) is arranged such that said ground plane conductor (31) is located between said conductive antenna element (23) and said at least one electric RF component (45- 49) to effectively shield said at least one electric RF component (45-49) from said transmitted and/or received RF waves . 31. A radio communication device, particularly a handheld or portable radio communication device, comprising a slot antenna device (5) according to any of the preceding Claims.

Inventors: SCORDILIS THIERRY, SCORDILIS, THIERRY
Applicants: ALLGON AB, SCORDILIS THIERRY, SCORDILIS, THIERRY
Application year: 2000
Main classification: H01Q1
IPC codes: H01Q1, H01Q13, H01Q23