WO2007090041A2

WO2007090041A2 - Rf communication device and method of operation of the device

Info

Publication number: WO2007090041A2
Application number: PCT/US2007/061095
Authority: WO
Inventors: Aviv Shachar; Maksim Berezin; Motti Elkobi; Yonatan Kemelman; Gad Noor
Original assignee: Motorola, Inc.; Gabay, Jacob
Priority date: 2006-01-31
Filing date: 2007-01-26
Publication date: 2007-08-09
Also published as: WO2007090041A3; GB2434697A; GB0601895D0; GB2434697B

Abstract

An RF communication device (100) includes a radiating member comprising an electrically conducting portion having therein a first slot (123) operable as a slot RF radiator, wherein the radiating member comprises at least part of a casing (103) of the device. The device may further include a feed member such as a circuit board (101) for feeding RF signals to and from the radiating member, the feed member having an electrically conducting area (201) forming at least part of a radiator ground plane. The electrically conducting area may have a gap (203) therein providing a second slot operable to provide RF energy coupling with the first slot. The device may further include, attached to the radiating member, a dielectric member (105), e.g. a dielectric cap, which in operation increases the electrical length, compared with the actual length, of at least the feed member.

Description

RF COMMUNICATION DEVICE AND METHOD OF OPERATION OF THE

DEVICE

FIELD OF THE INVENTION

The present invention relates to an RF communication device and a method of operation of the device. In particular the invention relates to a portable communication device having a radiator for transmission and receipt of RF radiation by the device.

BACKGROUND OF THE INVENTION

Monopole antennas are widely used as RF radiators in portable communication devices such as cellular telephones and portable radios. However, the communication devices are becoming more complex, e.g. by the incorporation of additional functional components such as cameras and advanced loudspeakers, and this has led to extra functional requirements from the antenna system. There is also an ongoing search for ways to reduce the overall size and weight of such devices.

Thus, it is expected that the space available in a portable communication device for the antenna will decrease, since the overall size of the device will continue to decrease and/or the device will have to accommodate other functional components at the expense of the antenna. However, reducing the antenna size is done at the expense of antenna gain and bandwidth. This follows from the fact that an antenna is used to transform a bounded wave into a radiating wave. However, when the dimensions of the antenna are much smaller than the wavelength of the RF radiation to be transmitted, the antenna performs this transformation with only a poor efficiency. The loss in antenna gain can to some extent be compensated for by amplification. However, this causes a greater energy drain, e.g. from a battery of the device.

Another challenging task is that the distance available between the antenna and other components of the communication unit, such as a camera or an advanced loudspeaker, is likely to be reduced as well. This requires careful selection of where components are placed in the communication device to give suitable operation of the antenna. Thus there is a need for a new radiator (antenna) form which addresses the above problems.

SUMMARY OF THE INVENTION

According to the present invention in a first aspect there is provided an RF communication device including a radiating member comprising an electrically conducting portion having a first slot therein operable as a slot RF radiator, wherein the radiating member comprises at least part of a casing of the device. The radiating member may form at least part of a radiator ground plane.

The device may include a feed member for feeding RF signals to and from the radiating member, the feed member having an electrically conducting area forming at least part of a radiator ground plane. The electrically conducting area may have a second slot therein operable to provide RF energy coupling with the first slot. The second slot may itself be capable of operating as an RF slot radiator when not attached to the radiating member. The first slot and the second slot may be aligned to face one another to provide coupling of RF energy between the two. The first slot may be larger than the second slot at its sides and ends.

The conducting portion of the radiating member and the conducting area of the feed member may include substantially flat portions which may respectively include the first and second slots facing one another, and the substantially flat portions may be arranged in operation to be contiguous to facilitate electrical coupling between the conducting portion of the radiating member and the conducting area of the feed member.

The device may include a feed conductor which is near to or bridges the second slot. The feed conductor may be connected to an RF feed line, e.g. a stripline or microstrip conductor, connected in turn to an RF transceiver of the communication device. The feed conductor and the feed line may be attached to a conducting land, e.g. by a welded joint.

The second slot may have an open end and a closed end and may thereby be capable of operation as a quarter wave monopole slot radiator. The feed conductor in this case may be located nearer to the closed end than the open end of the second slot. The first slot may have a corresponding open end and a closed end and may provide in operation a quarter wave monopole slot radiator. The open and closed ends of the first slot may be aligned to face the open and closed ends respectively of the second slot.

Alternatively, the second slot may have two closed ends and may be capable of providing a half wave dipole slot radiator. In this case, the communication device may include a feed conductor which is near to or bridges the slot of the conducting portion of the feed member, wherein the feed conductor is located mid-way between the ends of the second slot. The first slot may also have two closed ends and may be capable of providing in operation a half wave dipole slot radiator.

The communication device according to the first aspect of the invention may include, attached to the radiating member, a dielectric member which in operation increases the electrical length, compared with the actual length, of at least the second slot. This increase may be by a factor which approaches (ε_r)^1/2 , where ε_r is the relative permittivity of the dielectric material of the dielectric member. The dielectric member may conveniently comprise a cap which is adapted to fit on the radiating member thereby covering the first slot.

The device according to the first aspect of the invention may include conducting connectors by which the feed member is attached to the radiating member and which provide conducting paths between the feed member and the radiating member, the conducting connectors being galvanically connected to the electrically conducting area. The feed member may include a plurality of holes each of which has a conducting wall electrically connected to the conducting area, the conducting connectors occupying the holes to attach and electrically connect the conducting area of the feed member to the conducting portion of the radiating member. The conducting connectors may for example comprise fasteners. The feed member may conveniently comprise a circuit board having the conducting area formed as a sheet layer on a surface of the circuit board.

The radiating member may comprise at least part of a casing made of a metallic material, e.g. comprising an alloy containing at least 80 per cent by weight magnesium. The radiating member may for example comprise a top cover part of a casing of the device.

The device according to the first aspect of the invention may be adapted to transmit and/or receive RF signals in a frequency band which is above 100 MHz, e.g. in a band which includes 2.4 GHz (especially 2.44 GHz) for use in a number of applications of current commercial interest. The device may be a portable or hand held unit and may for example comprise a portable radio, a mobile telephone, a personal digital assistant, a data communication device or the like.

According to the present invention in a second aspect there is provided a method of operation of a device according to the first aspect which includes operating the radiating member as a slot radiator to receive and/or transmit RF radiation signals.

A slot radiator or antenna is known per se. However, the provision of a slot radiator in a communication device as described herein in relation to the present invention has not previously been disclosed or suggested. The benefits of such a radiator are described later.

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective exploded view of three component parts of a handheld communication unit embodying the invention.

FIG. 2 is a plan view of a circuit board which is one of the component parts shown in FIG 1.

FIG. 3 is a side cross-section of the components parts shown in FIG. 1 when fitted together.

FIG. 4 is a plan view of a front end of an alternative circuit board for use in an alternative handheld communication unit embodying the invention.

FIG. 5 is a plan view of a front end of a cover for use with the printed circuit board of FIG. 4 in an alternative handheld communication unit embodying the invention

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 is a perspective exploded view of three component parts of a handheld communication unit 100 embodying the present invention. In particular, the unit 100 includes, as shown separately in FIG. 1, a shaped printed circuit board 101, a conducting top cover 103 and a dielectric cap 105. The circuit board 101 includes, mounted thereon in a known manner, a plurality of interconnected electronic processors and components to provide radio communications and other functions of the unit 100 in a known manner. The circuit board 101 has a shape which facilitates housing in the unit 100 particularly inside a casing formed by the top cover 103. The circuit board 101 is used for (amongst other things) feeding RF signals to and from the top cover 103 which provides a radiating member as described in more detail later. The detailed shape of the circuit board

101 and of the top cover 103 as shown in the drawings is illustrative and is not critical to operation of the embodiment of the invention.

A curved recess 107 is provided in an edge of the circuit board 101 at one end of the circuit board 101. The circuit board 101 also has four attachment holes 109 and four smaller attachment holes 110. The recess 107 and the attachment holes 109 serve to facilitate attachment of the printed circuit board 101 to the top cover 103 as described later. The attachment holes 110 serve to facilitate attachment of the printed circuit board 101 to the top cover 103 via the dielectric cap 105 in a sandwich structure, as described later. The attachment holes 109 and the attachment holes 110 also facilitate providing electrical connection of the circuit board 101 to the top cover 103 as described later.

The unit 100 has a casing which is formed from the top cover 103 and a bottom cover portion which are fitted together to form the completed casing after incorporation of the circuit board 101 and other components required in the enclosure formed between them. The top cover 103 is the only part of the casing shown in the drawings since the bottom cover portion is not material to the embodiment of the invention being described. The top cover 103 is made of a conducting material which may suitably be a strong, lightweight conducting material such as a metallic alloy, e.g. an alloy comprising mainly magnesium, aluminium or titanium. Use of a magnesium alloy, e.g. one which includes at least 80% by weight of magnesium, e.g. the alloy known by the industry standard name AZ91D, is for example suitable in view of the common use and availability for use of such material in the electronics industry. The top cover 103 includes a body portion 111 which includes speaker apertures 113 formed therein. The top cover 103 also includes, projecting from one end of the body portion 111, a head portion 115 which has a reduced thickness and is substantially flat. A shoulder 119 is formed at an end of the body portion 111 where the head portion 115 projects from the body portion 111. The head portion 115 is formed integrally with the body portion 111 and defines together with the body portion 111 a suitable outer design shape for the unit 100. The head portion 115 includes a hole 117 which is adapted to align with the recess 107 of the circuit board 101 to allow the head portion 115 and the circuit board 101 to be fastened together, e.g. by a fastening screw (as shown in FIG. 3) . The head portion 115 also includes holes 121 adapted to align with the holes 110 of the circuit board 101 to facilitate attachment to the circuit board 101 via the holes 110 as illustrated later with reference to FIG. 3.

The head portion 115 further includes a slot 123 extending along an axis which is perpendicular to an axis of symmetry X-X of the top cover 103. The slot 123 is described in more detail later.

The dielectric cap 105 has a shape which is adapted to fit over the head portion 115 and thereby abut against the shoulder 119 of the body portion 111 to provide a smooth outer surface profile together with the outer surface of the body portion 111. The dielectric cap 105 may be made of a non-porous, lightweight, dielectric material, e.g. a moulded plastics material such as a polycarbonate material, to provide a waterproof and dustproof cover for the head portion 115. In addition, the cap 105, the top cover 103 and the circuit board 101 have electrical properties which combine to provide a radiator and receiver of RF radiation at the slot 123 in a desired frequency band as described later.

FIG. 2 is a plan view of the circuit board 101 showing more detail of the circuit board 101 on an upper surface of the circuit board 101, i.e. a surface which faces a lower (inner) surface of the top cover 103 when attached in use to the top cover 103. The circuit board 101 has an axis of symmetry X-X which matches the axis of symmetry X-X of the top cover 103. The circuit board 101 includes on its upper surface a conducting sheet 201 forming a conducting area which covers all of the upper surface apart from a gap 203 formed in the conducting sheet 201 and areas where the holes 109 and 110 are provided. The gap 203 has a shape in the form of a narrow, elongate strip adapted to provide a slot which, when the circuit board 101 is attached to the top cover 103, aligns with and faces the slot 123 (FIG. 1) . The gap 203 has an outer end 205 at a side edge of the circuit board 101 and has an inner end 207 inside the conducting area 201. The outer end 205 is ^Λoρen' , i.e. conducting material of the conducting sheet 201 is not bridged at the outer end 205. In contrast, the inner end 207 is ^λclosed' , i.e. conducting material of the conducting sheet 201 is bridged around the gap 203 at the inner end 207.

The conducting sheet 201 encloses the holes 110 and the holes 109. Conducting material also coats the side walls of the holes 110 and the holes 109. The circuit board 101 is attached to the top cover 103 by metallic fasteners (one of which is shown in FIG. 3) which fit though the holes 110 and the holes 109 thereby forming conducting bridges between the circuit board 101 and the top cover 103, the conducting bridges all being galvanically connected to the conducting sheet 201. In addition, as noted earlier, the head portion 115 of the top cover 103 and the conducting sheet 201 of the circuit board 101 are flat and lie against one another when the circuit board 101 is attached to the front cover 103 thereby forming a further galvanic connection between the circuit board 101 and the front cover 103.

A conducting via 219 (lead through connector) extends through the circuit board 101 from a lower surface (on a face opposite that shown in FIG. 2) and emerges in the upper surface to contact the conducting sheet 201 near to the gap 203 at a point part-way along the gap 203. The via 219 is connected on the lower surface of the circuit board 101 to a conducting land 221, e.g. by a soldered weld. The land 221 is indicated by a dashed line in FIG. 2. An RF feed microstrip 223 on the lower surface of the circuit board 101 (and also indicated by a dashed line in FIG. 2) is galvanically connected to the land 221, e.g. by a soldered weld, and to RF transceiver circuitry 225 (indicated by a dashed line) on the lower surface. The feed microstrip 223 is therefore galvanically connected to the conducting sheet 201 by the land 221, and the via 219 and is thereby galvanically connected in turn to the top cover 103. The dimensions, especially the widths, of the land 221 and the microstrip 223 are selected in a manner well known to those skilled in the art to give a suitable input impedance, e.g. 50 ohms. The via 219 has a small offset, determined by experimentation, from the gap 203 to maximise RF feed efficiency. The via 219 could however be located without an offset to emerge (from the rear surface of the circuit board 101) in the gap 203 thereby bridging the conducting material of the conducting sheet 201 across the gap 203.

The conducting sheet 201 on the upper surface of the circuit board 101 which may be made of any suitable conducting material known in the art for use in producing conductors on circuit boards. For example, the conducting sheet 201 may be a copper or a copper based alloy formed in a known manner on the circuit board 101. For example, the conducting sheet 201 may be formed by depositing a coating of copper on a circuit board substrate material and using a known computer controlled cutting operation applied to the coated substrate material to remove copper and to leave the desired gap 203 and the areas where the holes 109 and 110 are formed uncovered.

The circuit board 101 includes, mounted on its lower surface, a plurality of interconnected electronic processors and components to provide radio communications and other functions of the unit 100 in a known manner. These processors and components, apart from the transceiver circuitry 225, the feed microstrip 223 and the land 221, are not material to the invention and so for the sake of clarity are not shown or further described. The circuit board 101 has outer straight sides 213 which define a width of the sheet 201 (referred to later) .

FIG. 3 is a side cross-section, taken on an axial vertical plane (a plane perpendicular to the axis X-X in FIG. 1) , of the components parts shown in FIG. 1 when fitted together in the unit 100. A metallic fastener screw 301 is shown holding the cap 105 to the top cover 101. The screw 301 is fitted through the recess 107 of the circuit board 101 and through the hole 117 of the head portion 115. In addition, a metallic fastener screw 302 is shown holding the circuit board 101 to the top cover 103. The screw 302 is fitted through one of the holes 110 and one of the holes 121 and thereby provides galvanic connection between the circuit board 101 and the top cover 103. The screw 302 also attaches the dielectric cap 105 to the top cover 103 via a shaped intermediate member 303 engaged inside the cap 105. The cap 105 has a shaped internal profile to facilitate holding the intermediate member 303 and an end part of the top cover 103. In use, when the circuit board 101, the top cover 103 and the dielectric cap 105 are fitted together, a monopole slot radiator is provided by a combination of the gap 203 in the conducting area 201 of the printed circuit board 101 and the slot 123 in the front cover 103. The slot 123 forms the first slot referred to earlier and the gap 203 forms the second slot referred to earlier. The dielectric properties of the cap 105 affect the radiative properties of the monopole slot radiator. The conducting sheet 201 including the gap 203 is capable itself of providing an RF slot radiator if operated separately from the top cover 103, but in the combination with the top cover 103 may be considered to be an RF launcher which couples RF energy into the top cover 103 causing the top cover 103 to emit (or receive) an RF radiation pattern at the slot 123. The conducting area 201 and the top cover 103 which are galvanically connected as described earlier provide together a conducting radiator ground plane of sufficient surface area, as required in accordance with known electromagnetic radiation theory, to provide an efficient RF radiator.

Further desirable detailed properties of the slot radiator provided by the unit 100 and its operation will now be provided. The gap 203 in the conducting sheet 201 of the circuit board 101, particularly the length of the gap 203, is designed to provide a quasi quarter-wave slot radiator which itself is capable (before attachment to the top cover 103) , of radiating omnidirectionally when the ground plane provided by the conducting sheet 201 has a sufficiently large surface area. From known ground plane theory, a minimum surface area will be approximately (λ/4)² m². where λ is a wavelength or radiation emitted or received by the radiator. A suitable actual length for the gap 203 to provide a monopole slot radiator between the ends 205 and 207 is between λ/4 and λ/6. The length of the gap 203 required to provide a slot radiator at a particular wavelength will depend upon a number of other factors, for example the thickness and dielectric properties of the circuit board 201 and of the cap 105.

The position of the via 219 is also significant, since this determines the size of a conducting loop formed in the conducting material of the conducting sheet 201 with the inner end 207 of the gap 203. This in turn affects the operational feed impedance. Thus the feed impedance may be adjusted by selecting a suitable position of the via 219 along the gap 203 as well as a suitable offset distance (if any) from the gap 203. Desirably, the via 219 is positioned nearer the inner end 207 than the outer end 205 of the gap 203.

The width of the gap 203 (measured along the axis X-X) affects the impedance and bandwidth of the slot radiator provided by the gap 203 and also may be correctly chosen so that harmonics of the required resonance will be matched to the required band. Desirably, the width of the gap 203 is selected to be between about λ/10 and about λ/50.

When the circuit board 101 as shown in FIG. 2 is placed on a horizontal surface and itself is operated as a radiator, a radiation pattern is obtained around the outer end 205 of the gap 203. The radiation pattern is omnidirectional and the polarisation of the radiation is principally orthogonal to the plane of the circuit board 101, i.e. vertical. The dimensions of the circuit board 101, particularly the conducting sheet 201 thereon, determine the radiator (antenna) gain obtained. Desirably the dimensions are selected so that the gain obtained is at least +3dBi. As noted earlier, the slot 123 in the top cover 103 is arranged to face the gap 203 when the circuit board 101 and the top cover 103 are fitted together. RF energy is thereby coupled between the circuit board 101 at the gap 203 and the top cover 103 at the slot 123. The top cover 103 thereby acts as a quasi quarter-wave slot radiator .

The dimensions of the slot 123 in the top cover 103 are designed to be marginally larger than those of the gap 203 to ensure that all of the gap 203 is beneath the slot 123, i.e. so that in production it will not be possible for any of the gap 203 to be beneath the metallic material of the top cover 103 taking into account the tolerances applied in manufacture of the top cover 103 including the slot 123 and of the circuit board 101 including the gap 203. The slot 123 at its ends and its sides thus overlaps the gap 203. The dimensions of the slot 123 are also selected to give suitable impedance matching between the gap 203 and the slot 123.

The dielectric cap 105 when fitted to the top cover 103 attached to the circuit board 101 provides fine tuning of the operational resonance band of the slot radiator provided by the combination of the circuit board 101, the top cover 103 and the dielectric cap 105. In particular, the relative permittivity ε_r of the dielectric material of the cap 105 is selected so that it provides an appropriate capacitive loading, thereby beneficially allowing the actual slot dimensions of the slot radiator to be reduced, to achieve a desired electrical length of λ/4 for the slot 123 (and the gap 203) . Also, the loss factor (loss angle tangent value) , tan δ, of the dielectric material affects energy losses obtained by use of the dielectric cap 105 which in turn affect the quality (Q) factor of the radiator resonance. Desirably tan δ of the dielectric material of the cap 105 is not greater than 0.02 (although a greater value could be tolerated with increased losses) .

A specific example of the unit 100 embodying the invention was produced to operate in a frequency band including 2.44 GHz, i.e. radiating or receiving at a target wavelength λ of about 122 mm. The unit 100 in this case had the following specific properties:

1) The circuit board 101 had a length (longest dimension) of 58.6 mm and a width (distance between the outer straight sides 213) of 40.95 mm. The circuit board 201 was made of the industry standard material FR4 having a thickness of 1.6 mm, and dielectric properties of ε_r = 4.5 and tan δ = 0.019. The conducting sheet 201 on the circuit board 101 was made of copper having a thickness of 0.018 mm.

2) The length of the gap 203 was 20.65 mm. 3) The width of the gap 203 was 0.5 mm.

4) Thus, the length to width ratio of the gap 203 was 41.3.

5) The distance of the via 219 to the inner end 207 of the gap 203 was 9.8 mm (λ/12) . 6) The length of the land 221 was 7.34 mm.

7) The width of the land 221 was 3.03 mm.

8) The front cover 103 was made of the industry standard magnesium alloy AZ91D.

10) The dimensions of the slot 123 were: length 27 mm; width 1.7 mm.

11) The dielectric cap 105 was made of moulded polycarbonate material (produced from the polycarbonate resin commercially available from GE Advanced Materials under the trade name LEXAN 500R) . This material has a relative permittivity of 2.9 at 2.4 GHz and a tan δ value of 0.0085. Consequently, the dielectric cap 105 caused the gap 203 to have an effective electrical length greater than its actual length, by a factor m. The factor m is approaching (ε_r)^1/2 where ε_r is the relative perimittivity of the dielectric material of the dielectric cap 105, where (ε_r)^1/2 is about 1.7. However, the factor m is reduced somewhat below (ε_r)^1/2 owing to the curvature of the cap 105. In practice, the effective electrical length is about 30.5 mm giving the required target value of wavelength λ of 122 mm. The specific example of the unit 100 made with the specific properties listed above gave suitable radiator (antenna) operation in a band including 2.4 GHz. RF radiation emitted was omnidirectional with a directivity of 5.1 dBi and a gain of 3.56 dBi. The VSWR (voltage standing wave ratio) at 2.40 GHz was 1.41 and at 2.48 GHz was 1.28 indicating a suitable resonance band extending from 2.40 GHz to 2.48 GHz (at least). The specific example of the unit 100 is therefore suitable for use in applications operating at about 2.4 GHz

(especially 2.44 GHz), e.g. communications in accordance with the WLAN (Wireless Local Area Network) 802.11 (b) and 802.11 (g) standards defined by the IEEE (Institute of Electrical and Electrical Engineers) as well as applications using the unlicensed ISM (Industrial

Scientific and Medical) band from 2.40 to 2.48 GHz, e.g. Bluetooth™.

FIG. 4 is a plan view of a front end of an alternative circuit board 401 for use an alternative handheld communication unit embodying the invention. The circuit board 401 has the same shape as the circuit board 101 of FIGS 1 and 2 and includes the recess 107 and holes 110 (and holes 109 not shown) for the same purposes as in the circuit board 101. The circuit board 401 includes on its upper surface a conducting sheet 402 similar to the conducting sheet 201. However, a gap 404 forming a slot is provided in the conducting sheet 402 which is different from the gap 203 in the sheet 201. The gap 404 is closed at both of its ends, i.e. both ends are enclosed within conducting material of the conducting sheet 402. A conducting via 403 extends from a rear surface of the circuit board 401. The via 403 contacts the conducting sheet 402 at a location which has a small offset from the gap 404 and is level with a point mid-way along the gap 404. The via 403 contacts a conducting land (not shown) on the lower surface of the circuit board 401, which in turn is connected to transceiver circuitry (not shown) via a microstrip conductor (not shown) in a manner similar to that in which the via 219 is connected to the conducting land 221, the RF feed microstrip 223 and the RF transceiver circuitry 225 as described earlier with reference to FIG. 2.

FIG. 5 is a plan view of a front portion 415 of a cover 405 for use with the printed circuit board of FIG. 4. The cover 405 has a shape similar to that of the cover 101 of FIG. 1 and is made in a similar manner using a lightweight metallic material. The front portion 415 of the cover 405 includes the same holes 121 and 117 as the front portion 115 of the cover 103. The slot 123 of the front portion 115 of the cover 103 is replaced by a slot 407 in the front portion 415 of the cover 405. The slot 407 is closed at both ends.

In use, the circuit board 401 and the cover 405 are fitted together in a similar manner to the circuit board 101 and the cover 103 of the unit 100 of FIGS. 1 to 3, together with a dielectric cap (not shown) . The gap 404 is covered by the slot 407 directly above the gap 404. The via 403 provides an RF feed at a point level to a point mid-way along the slot formed by the gap 404, thereby forming a dipole slot radiator which couples RF energy to and from the slot 407 in the cover 405. RF signals are thereby radiated from or picked up by the radiator formed by the slot 407. Since a unit comprising the circuit board 410 and the cover 405 provides a dipole radiator, in contrast to the monopole radiator of the unit 100, the unit operates at a shorter wavelength than the unit 100 (approximately half that of the unit 100) if the dimensions (including the slot dimensions) are the same as for the unit 100. Alternatively, the dimensions of the unit comprising the circuit board 410 and the cover 405 (including the slot dimensions) may be scaled up to provide the same operating wavelength as the unit 100.

The communication unit 100 and the alternative unit including the circuit board 401 and the cover 405 (FIGS. 4 and 5) provide examples of a novel radiator form which may, beneficially, be made in a suitably compact and lightweight form even with additional components typically used in a communication unit, such as a camera and an advanced loudspeaker, included in the unit. This may be achieved without unduly compromising bandwidth and the gain of the slot radiator provided by the communication unit. Efficient radiator operation may be obtained in a selected high frequency band, e.g. including 2.4 GHz. It is not necessary to use excessive amplification to compensate for any radiator gain loss and this avoids the need for an excessive energy drain, e.g. from a battery of the unit 100.

Claims

1. An RF communication device including: a radiating member comprising an electrically conducting portion having a first slot therein operable as a slot RF radiator, wherein the radiating member comprises at least part of a casing of the device.

2. A device according to claim 1 further including a feed member for feeding RF signals to and from the radiating member, the feed member having an electrically conducting area forming at least part of a radiator ground plane.

3. A device according to claim 2 wherein the electrically conducting area has a gap therein providing a second slot operable to provide RF energy coupling with the first slot.

4. A device according to claim 3 wherein the first slot and the second slot are aligned to face one another.

5. A device according to claim 4 wherein the first slot is larger than the second slot, and the first slot overlaps the second slot at its sides and ends.

6. A device according to claim 5 wherein the conducting portion of the radiating member and the conducting area of the feed member include substantially flat portions which respectively include the facing slots and the substantially flat portions are arranged in operation to be contiguous.

7. A device according to claim 6 wherein the second slot has an open end and a closed end and is capable of providing a quarter wave monopole slot radiator.

8. A device according to claim 7 including a feed conductor which is near to or bridges the second slot, the feed conductor being located nearer to the closed end than the open end of the second slot.

9. A device according to claim 6 wherein the first slot has an open end and a closed end and provides in operation a quarter wave monopole slot radiator, the open and closed ends of the first slot facing the open and closed ends respectively of the second slot.

10. A device according to claim 6 wherein the second slot has two closed ends and provides in operation a half wave dipole slot radiator, the device including a feed conductor which bridges or is close to the slot of the conducting portion of the feed member, the feed conductor being located mid-way between the ends of the slot of the conducting portion.

11. A device according to claim 10 including, attached to the radiating member, a dielectric member which in operation increases the electrical length, compared with the actual length, of at least the second slot.

12. A device according to claim 11 wherein the dielectric member comprises a cap which is adapted to fit on the radiating member thereby covering the first slot .

13. A device according to claim 12 including conducting connectors by which the feed member is attached to the radiating member and which provide conducting paths between the feed member and the radiating member, the conducting connectors being galvanically connected to the electrically conducting area.

14. A device according to claim 13 wherein the feed member includes a plurality of holes each of which has a conducting wall electrically connected to the conducting area, the conducting connectors occupying the holes to attach and galvanically connect the conducting area of the feed member to the conducting portion of the radiating member.

15 . A device according to claim 14 wherein the conducting connectors comprise fasteners .

16. A device according to claim 15 wherein the feed member comprises a circuit board having the conducting area formed as a sheet layer on a surface of the circuit board.

17. A device according to claim 16 wherein the radiating member comprises at least part of a casing made of a metallic material.

18. A device according to claim 17 wherein the metallic material comprises an alloy containing at least 80 per cent by weight magnesium.

19. A device according to claim 18 which is adapted to transmit and/or receive RF signals in a frequency band which includes 2.4 GHz.

20. A device according to claim 19 which is a portable or hand held device and comprises a portable radio, a mobile telephone, a personal digital assistant, or a data communication device.