WO2004097976A2 - Tuneable antenna - Google Patents

Tuneable antenna Download PDF

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Publication number
WO2004097976A2
WO2004097976A2 PCT/GB2004/001796 GB2004001796W WO2004097976A2 WO 2004097976 A2 WO2004097976 A2 WO 2004097976A2 GB 2004001796 W GB2004001796 W GB 2004001796W WO 2004097976 A2 WO2004097976 A2 WO 2004097976A2
Authority
WO
WIPO (PCT)
Prior art keywords
antenna
element
tuneable
frequency
antenna element
Prior art date
Application number
PCT/GB2004/001796
Other languages
French (fr)
Other versions
WO2004097976A3 (en
Inventor
Gert Frolund Pedersen
Original Assignee
Itt Manufacturing Enterprises, Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to GB0309640.1 priority Critical
Priority to GB0309640A priority patent/GB2402265A/en
Priority to GB0321222A priority patent/GB2406217A/en
Priority to GB0321222.2 priority
Application filed by Itt Manufacturing Enterprises, Inc filed Critical Itt Manufacturing Enterprises, Inc
Publication of WO2004097976A2 publication Critical patent/WO2004097976A2/en
Publication of WO2004097976A3 publication Critical patent/WO2004097976A3/en

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Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04Resonant antennas
    • H01Q9/0407Substantially flat resonant element parallel to ground plane, e.g. patch antenna
    • H01Q9/0442Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular tuning means
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q23/00Antennas with active circuits or circuit elements integrated within them or attached to them
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04Resonant antennas
    • H01Q9/30Resonant antennas with feed to end of elongated active element, e.g. unipole

Abstract

A tuneable antenna suitable for mobile telecommunications or small terminal applications comprises an electrically conductive antenna element (6) and a tuning element (8) proximate to the antenna element, wherein the tuning element is movable or switchable between at least two positions relative to the antenna element to tune the tuneable antenna to corresponding different resonant frequencies.

Description

TUNEABLE ANTENNA

This invention relates to a tuneable antenna. More particularly, but not exclusively, this invention relates to a tuneable antenna for use with mobile telecommunication equipment operating on at least two frequency bands.

Mobile telecommunication equipment or small terminal equipment such as a mobile, or cellular, telephone will typically have an antenna that is used for the wireless transmission and receipt of electromagnetic signals. In a mobile telephone, this antenna is used to communicate with the base transceiver station for the cell in which the telephone is operating.

The frequency band in which the mobile telephone and base transceiver station communicate depends on the communications standard to which the mobile network, of which the base transceiver station is a part, conforms. For example, The GSM (Global System for Mobile communications) standard used throughout Europe and Asia defines two alternative frequency bands, 900MHz and 1800MHz, more exactly EGSM from 880MHz to 960MHz, GSM1800* from 1710MHz to 1880MHz . In North America several systems are used, including PCS (Personal Communications Service), which operate in frequency bands around 850MHz and 1900MHz respectively, for example GSM850 from 824MHz to 894MHz, and PCS from 1850MHz to 1990MHz.

Further frequency bands have been defined for the UMTS (Universal Mobile Telephone Standard) "third generation" standard, and for other radio communications applications such as GPS.

Antennas for mobile telephones are well known. Early mobile telephones were designed to operate in single, fixed frequency bands, and were therefore only compatible with mobile networks operating in that frequency band. Antenna designs for these mobile telephones were resonant around a single, fixed frequency. Capacity constraints and different bandwidth allocations in different countries have resulted in the use of a variety of frequency bands. To deal with these multiple bands, mobile telephones that are capable of operating in two or three frequency bands were developed. Antenna designs for these mobile telephones must therefore be capable of operating in at least two defined frequency bands.

A number of antenna designs that are capable of operating in at least two defined frequency bands have been proposed. One approach for providing a multiple band antenna is to use separate antennas, each corresponding to a different frequency band. For example, EP 1109251 and WO 01/03238 disclose antenna arrangements in which two antennas for emitting two independent frequencies are used.

It is more usual however to use a single antenna capable of resonance in a plurality of frequency bands.

US 6452551 discloses a capacitor loaded planar antenna that is capable of operating in two defined frequency bands. A high band antenna stub is attached to a low band antenna.

US 6346919 discloses an antenna capable of operating on two or more unrelated frequencies. The antenna has a number of notches in a patch element so as to provide more than one resonant frequency.

EP 1168495 discloses an antenna that is capable of operating in two defined frequency bands. An antenna element is parallel to, and connected at one end to, an earth plate. An electrical switch that is capable of making a low impedance connection between the opposite end of the antenna and the earth plate allows the antennae to operate at two alternative resonant frequencies.

However, there remains a need for improved multiple band antennas.

According to a first aspect of the invention there is provided a tuneable antenna comprising: an electrically conductive antenna element having at least one antenna element portion having a respective communications frequency for radiating or receiving radio signals at the respective communications frequency; and a tuning element switchable between at least a first operation state and a second operation state relative to the antenna element, the tuning element including a capacitance element, a dielectric or a conductive tuning element arranged to couple to at least one antenna element portion to tune the communications frequency or frequencies of at least one antenna element portion to different communications frequencies corresponding to the tuning element states.

By providing a switchable tuning element in this way, the communications frequency or frequencies of the tuneable antenna can easily be altered.

Normally, the communications frequency or frequencies of an antenna element portion will be given by the resonant frequency or frequencies of the antenna element, especially at the frequencies used for mobile telephony. However, the skilled person will appreciate that it is possible, for example using suitable impedance matching techniques, to transmit and receive signals away from resonance. In this example, the communications frequency of the antenna element will be given by the antenna element in combination with the impedance matching components.

The invention is particularly applicable to a multiband antenna having at least two antenna element portions, each of the at least two antenna element portions having a different respective communication frequency, the tuneable antenna having a first plurality of communication frequencies with the tuning element in the first state and a second plurality of communications frequencies with the tuning element in the second state, the first and second plurality of communications frequencies being different. The inventors have realised that a highly versatile multiple band antenna can be provided in this way. In a preferred aspect there is provided tuneable antenna comprising: an electrically conductive antenna element having at least one antenna element portion having a respective communications frequency for radiating or receiving radio signals at the respective communications frequency; and a tuning element movable between at least a first position and a second position relative to the antenna element, the tuning element being a dielectric or conductive tuning element arranged to electromagneticaliy couple to at least one antenna element portion to tune the communications frequency or frequencies of at least one antenna element portion to different communications frequencies corresponding to the tuning element positions.

The antenna element portions corresponding to each frequency may be defined by a number of longitudinal and lateral notches.

The invention may be applied to different types of antenna. In particular, the invention may be applied to a planar antenna with or without a ground plane. Thus, the antenna element preferably extends laterally. The antenna element portions are preferably planar. In embodiments, the tuneable antenna also comprises an electrically conductive ground element proximate to the antenna element likewise extending laterally.

The motion of the tuning element may be lateral or vertical.

In preferred arrangements, the or each respective communications frequency varies by no more than 15% as the tuning element is moved between the first and the second positions. By requiring only relatively small variation of frequencies in a multiband antenna it becomes practical to realise the invention without requiring the tuning element to. be excessively large. The prior designs all provide antennas that are capable of operating on two widely disparate frequency bands. The inventors have realised that the resonant frequency of an antenna can be made adjustable or tuneable between relatively close frequency bands by incorporating a moveable element within the structure of the antenna. In particular, the tuning element may be moveable between a first position adjacent to a first antenna element portion and a second position adjacent to a second antenna element portion.

In a particularly useful embodiment, the first antenna element portion may have a resonant frequency in the EGSM frequency band of 880MHz to 960MHz when the tuning element is in the second position and at a lower frequency in the GSM 850 frequency band of 824MHz to 894MHz when the tuning element is in the first position, and the second antenna element portion may have a resonant frequency in the PCS1900 frequency band of 1850 to 1990 MHz when the tuning element is in the first position and a lower frequency in the GSM1800 frequency band of 1710MHz to 1880MHz when the tuning element is in the second position. Thus, in the second position the antenna can operate at the GSM frequencies used in Europe and some other countries, whereas in the first position the antenna operates at the frequencies particularly used in the US.

The tuning element may be a piece of dielectric material. Movement of a piece of dielectric material into close proximity with an antenna element portion causes the resonant frequency of the antenna element portion to be reduced by the proximity of the dielectric, in particular the introduction of dielectric between the antenna element portion and the ground plane.

Lateral relative motion of the tuning element works particularly well with dielectric tuning elements in which a relatively large body of dielectric needs to be moved.

Alternatively, the tuning element may be a piece of electrically conductive material. In this case, movement of a piece of electrically conductive material into close proximity with an antenna causes a change in capacitive loading of the antenna. This change in capacitive loading leads to a corresponding change in resonant frequency of the antenna. It is particularly convenient to move electrically conductive tuning elements vertically, since this produces easily determinable results. However, it is not excluded to use lateral motion in this case also, particularly where the gap between ground and antenna elements is insufficient to allow sufficient vertical motion.

An electrically conductive tuning element may be electrically connected to the ground element. This connection may be by direct or indirect connection, or even direct contact.

In embodiments, a ground element is provided extending in the lateral direction of the antenna element. Such a ground element may in a mobile telephone be provided between the antenna element and the display and thus shield a user from the radio transmissions of the mobile telephone. However, such ground elements are not essential and alternative embodiments may omit such ground elements, especially but not exclusively for mobile communications terminals not intended for operation close to the human body.

The position of the ground element in relation to the antenna element may be fixed. In this way, only the tuning element is movable to provide tuning. Alternatively, the ground element may be movable ith the tuning element or independently of the tuning element. The ground element may advantageously be disposed on one side of a printed circuit board for ease of manufacture.

The tuneable antenna may further comprise a switching element that is associated with the tuning element. The switching element can be used to move the tuning element between the at least two positions relative to the antenna element.

The switching element may comprise a manual mechanical switch, such as a slider mechanism linked to the tuning element. In this case, manual effort at the input to the linkage causes movement of the tuning element. The switching element may alternatively. comprise an electromagnetic actuator, such as a solenoid actuator. In this case, the electromagnetic actuator applies a force on the tuning element that causes the tuning element to move.

Where the at least two positions of the tuning element have been predetermined, the switching element may further comprise a means to maintain the tuning element in one of the at least two predetermined positions.

A control circuit may provide control signals to the electromagnetic device so that the position, of the tuning element may be controlled. The control circuit may, for example, provide the control signals automatically in response to the electromagnetic signals that it detects, under the control of a computer program.

Preferably, the antenna element further comprises a fixed antenna element portion for a constant communications frequency. This fixed antenna element portion may be used for a communications service with a fixed or worldwide frequency. One example of such a frequency is that of the Universal Mobile Telephone Standard (UMTS), for use with UMTS networks. Other fixed antenna element portions may be used for other fixed frequency services, such as the global positioning system (GPS).

According to another preferred aspect of the invention there is provided a multi- band tuneable antenna comprising: an electrically conductive antenna element having a plurality of antenna element portions for radiating at respective first communications frequency bands, the plurality of respective first communications frequency bands including a plurality of different frequency bands; a capacitance element adjacent to and coupled to a respective antenna element portion; and a switch switchably coupling the capacitance element to ground to tune the communications frequency of the respective antenna element portion to a respective second communications frequency different to the first communications frequency.

Note that any dc voltage acts as ground to RF frequencies. The chosen ground may conveniently be the ground plane of the mobile device in which the antenna is installed.

By arranging a capacitance element adjacent to an individual antenna element portion, to couple predominantly to that portion, or a plurality of capacitance elements adjacent to respective individual elements, the change in frequency of the individual element or elements can be individually controlled. Thus, by adjusting the size and location of the capacitance elements it is straightforward to design an antenna in which each antenna element portion can be switched between precisely determined frequencies.

The inventors are aware of a document in which a capacitance element is used in a multiple antenna element portion system, namely EP 1109251. This document is concerned not with multiple frequency bands but with enlarging a single frequency band. Moreover, this document teaches using a control electrode coupled to two element portions to controllably couple the ends of the element portions together. Thus this prior art arrangement offers much less design flexibility. In particular, the frequencies of both element portions are shifted together. This is suitable in the application envisaged in EP1109251 , for broadening a single frequency band, but unsuitable for switching between different frequency bands at well-defined frequencies, as is readily achieved using the present invention.

Normally, the communications frequency or frequencies of an antenna element portion will be given by the resonant frequency or frequencies of the antenna element, especially at the frequencies used for mobile telephony. However, the skilled person will appreciate that it is possible, for example using suitable impedance matching techniques, to transmit and receive signals away from resonance. In this case, the communications frequency of the antenna element will be given by the antenna element in combination with the impedance matching components. Another way to obtain resonance of an antenna which is electrically too small is to employ capacitative loading at the end of the element whereby the element electrical becomes longer.

The invention may be applied to different types of antenna. In particular, the invention may be applied to a planar antenna with or without a ground plane. Thus, the antenna element may extend laterally. The antenna element portions may be planar. The antenna element portions corresponding to each frequency may be defined by a number of longitudinal and lateral notches.

In embodiments, the tuneable antenna also comprises an electrically conductive ground element extending parallel to the antenna and spaced from it. Preferably, the capacitance element or elements is or are arranged closer to the antenna element portions to which they are adjacent than the distance of the ground plane to the antenna element portion.

The antenna may in particular include first and second antenna element portions and respective first and second capacitance elements adjacent to the first and second antenna elements respectively, and a common switch arranged to connect the first capacitance element leaving the second capacitance element floating in a first position and the second capacitance element portion in a second position leaving the first capacitance element floating. In this way the frequency of a switchable one of the first and second elements is adjusted by its adjacent capacitance element.

In preferred arrangements, the or each respective communications frequency varies by no more than 30% as the capacitance element is switched. By requiring only relatively small variation of frequencies in a multiband antenna it becomes practical to realise the invention without requiring the capacitance element or elements to be excessively large. In a particularly useful embodiment a first antenna element portion having a respective first capacitance element switchably connected to ground, the first antenna element portion having a resonant frequency in the EGSM frequency band of 880MHz to 960MHz when a the first capacitance element is not connected to ground and a lower frequency in the GSM 850 frequency band of 824MHz to 894MHz when the switch is connected to ground; and a second antenna element portion having a respective second capacitance element switchably connected to ground, the second antenna element portion having a resonant frequency in the PCS1900 frequency band of 1850 to 1990 MHz when the second capacitance element is not connected to ground and a lower frequency in the GSM1800 frequency band of 1710MHz to 1880MHz when the second capacitance element is connected to ground.

In this way the antenna can operate at the frequencies presently most common in Europe and North America.

A single switch may be used to switch one or the other of the capacitance plates to ground. Thus, in a first state the antenna operates at the frequencies particularly used in North America, whereas in a second state the antenna can operate at the GSM frequencies used in Europe and some other countries.

Note that this change in frequencies of bands does not occur in the arrangement of EP1109251 which describes a method of broadening a single band. Moreover, in the arrangement of EP1109251 the frequency of each element portion is switched in the same direction using a single switch, rather than increasing one frequency and decreasing another.

In a particularly preferred embodiment the or each antenna element is a planar element and each respective capacitance element is a planar element spaced perpendicularly from and extending substantially parallel to the respective antenna element. In alternative embodiments the capacitance elements may be coplanar with the antenna elements. Alternative arrangements are also considered possible.

A control circuit may provide control signals to the electromagnetic device so that the position of the switch or switches may be controlled. The control circuit may, for example, provide the control signals automatically in response to the electromagnetic signals that it detects, under the control of a computer program.

In a further arrangement, the antenna element further comprises a fixed antenna element portion for a constant communications frequency. This fixed antenna element portion may be used for a communications service with a fixed or worldwide frequency. One example of such a frequency is that of the Universal Mobile Telephone Standard (UMTS), for use with UMTS networks. Other fixed antenna element portions may be used for other fixed frequency services, such as the global positioning system (GPS).

The invention also provides mobile communications apparatus comprising the tuneable antenna described above, such as a mobile telephone, or other mobile communication equipment or small terminal equipment.

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 shows a sectional front view of a first embodiment of the tuneable antenna with the tuning element in a first position;

Figure 2 shows a plan view of the first embodiment of the tuneable antenna with the tuning element in a first position;

Figure 3 shows a plan view of the first embodiment of the tuneable antenna with the tuning element in a second position; Figure 4 shows a sectional front view of the first embodiment of the tuneable antenna with the tuning element in a second position;

Figure 5 shows a mobile telephone comprising the first embodiment of the tuneable antenna; Figure 6 shows a schematic view of a second embodiment of the tuneable antenna;

Figure 7 shows a plan view of a third embodiment of the tuneable antenna;

Figure 8 shows a sectional front view of a fourth embodiment of the tuneable antenna;

Figure 9 shows a sectional front view of a fifth embodiment of the tuneable antenna;

Figure 10 shows a top view of the embodiment of Figure 9;

Figure 11 shows a. sectional view of a further embodiment of the tuneable antenna including ground plane, spacer frame and antenna;

Figure 12 shows a top view of another embodiment;

Figure 13 shows a detail top view of the antenna elements of the embodiment of Figure 12;

Figure 14 shows the antenna elements mounted on the frame in the embodiment of Figure 12; and

Figure 15 shows a side view of the arrangement of Figure 12.

It should be noted that the figures are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these figures have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings.

Referring firstly to figures 1 to 4, a first embodiment of the tuneable antenna 2 comprises a ground element 4, an antenna element 6, and a tuning element 8.

The ground element 4 is a thin planar layer of conductive material, such as copper, disposed on one side of a printed circuit board 10 in a lateral plane. This form of ground element is easy to manufacture. It is also easy to package within the casing of mobile telecommunications equipment since it is planar. However, in alternative embodiments of the tuneable antenna the ground element could take the form of any electrically conductive material. For example, the ground element could take the form of the electrical shielding for other electrical components on a printed circuit board. The antenna element 6 is a thin, planar, rigid sheet of electrically conductive material, such as copper, mounted adjacent to the printed circuit board 10 to extend parallel with the ground element 4 in a lateral plane. The . antenna element 6 is of irregular shape and has a number of notches that will be described later. Typical overall dimensions for the antenna element 6 are 30mm x 40mm. The antenna element 6 is held by a supporting frame 12.

As will be appreciated by those skilled in the art, the form of the antenna element may vary as required. For example, the antenna element could be formed so as to fit within a given space in the casing of portable communications equipment; in this case it may not be flat.

The supporting frame 12 is a moulded plastic component that attaches to the printed circuit board 10 and rigidly locates the antenna element 6 so that the planar surface of the antenna element 6 is parallel to the planar surface of the ground element 4. The supporting frame 12 may be attached to the printed circuit board 10 using adhesive, or else by some other means such as mechanical fixings. Suitable fixing methods will be well known to persons skilled in the art. Although the embodiment shown in figures 1 to 4 includes a supporting frame, this is not essential and other suitable ways of supporting the structure will be known to those skilled in the art, for example by directly fixing the antenna element to the casing of mobile communications apparatus.

Tuning element 8 is a thin, rigid sheet of dielectric material that is disposed between the ground element 4 and the antenna element 6. In the embodiment of the tuneable, antenna shown in figures 1 to 4, the tuning element 8 is flat. However, in other embodiments, the tuning element may take other forms. For example, the tuning element may be shaped so as to correspond to elaborately shaped ground and antenna elements.

The dielectric material of the tuning element preferably has low dielectric losses. A number of different types of material are suitable. In the embodiment described, the tuning element does not have to vary the resonant frequencies of the antenna element by more than 15% and so it is not necessary to use expensive and exotic materials with high dielectric constants. Plastics are particularly convenient and suitable plastics will be. known to the skilled person. However, the skilled person will appreciate that there may be applications where a ceramic dielectric or other suitable dielectric is more appropriate, particularly if greater variation of resonant frequency is required, or if very small size is required.

Tuning element 8 is slidably located for lateral motion between the ground element 4 and the antenna element 6 by the supporting frame 12. The supporting frame 12 maintains a constant clearance between the planar surfaces of the tuning element 8 and the planar surfaces of the ground element 4 and the antenna element 6 respectively. The mounting of the tuning element 8 within the supporting frame 12 allows lateral movement of the tuning element 8 only, relative to the antenna element. In the embodiment of figures 1 to 4, the ground element 4 and the antenna element 6 are in fixed positions, while the tuning element 8 is movable.

Alternative mounting arrangements are of course possible provided that the tuning element is always movable relative to the antenna element. For example, the ground element and tuning element could be movable together relative to a fixed antenna element, or the ground element and tuning element could be fixed and the antenna element movable.

To allow the tuneable antenna 2 to transmit and receive electromagnetic signals, the antenna element 6 is connected to a feed line 14. The feed line 14 comprises a microstrip, or stripline. The microstrip is connected to the antenna element 6 and the ground is connected to the ground element 4. Typically, the tuneable antenna will be assembled on the opposite side of a printed circuit board to the components of an electronic circuit feeding the tuneable antenna, and the microstrips will lead directly from the circuit to the antenna element and ground element. In other embodiments of the tuneable antenna, the feed line may take the form of a coaxial cable.

The slidably located tuning element 8 is connected to a manual switch comprising a slider mechanism 16 which is itself located in a recess in the casing of the equipment in which the tuneable antenna 2 is located. The structure and operation of the slider mechanism 16 will be described later. The function of the slider mechanism 16 is to allow a user to manually move the position of the tuning element 8 in a lateral direction.

Referring now to figure 2, which shows a plan view of the embodiment shown in Figure 1 , the antenna element 6 is shown with the tuning element 8 in a first lateral position 8A. For the sake of clarity, the printed circuit board 10 and the supporting frame 12 are not shown, and the ground element 4 is shown in ghost form.

The outer periphery of the antenna element 6 is substantially rectangular, with minor variations in shape to meet packaging constraints. In practice, the outer periphery of the antenna element, and the tuneable antenna itself, can be virtually any shape, and will, be designed to fit into a given space in the equipment in which it is mounted.

The antenna element 6 comprises first, second and third antenna element portions 6A, 6B, 6E. The first and second antenna element portions 6A, 6B are substantially separated by notches 6C, 6D.. The first and second antenna element portions 6A, 6B are designed to provide two alternative electrical lengths, corresponding to resonant frequencies of approximately 900MHz and 1900MHz (without the presence of the tuning element) respectively.

The third antenna element portion 6E is designed to be a Universal Mobile Telephone Standard (UMTS) antenna element portion, for use with a UMTS mobile network, and provides an electrical length corresponding to the appropriate resonant frequency. In other embodiments, alternative or further fixed frequency antenna element portions may be provided, for example for a GPS service.

In other embodiments of the tuneable antenna, the antenna element may not be separated into antenna element portions, or else may be separated into several antenna element portions. The antenna element portions may be separated, or defined, by any combination of notches or any other features which achieve the equivalent effect, as will be understood by persons skilled in the art.

In position 8A, it can be seen that the tuning element 8 is substantially adjacent to the first antenna element portion 6A. In this position, the tuning element causes the resonant frequency corresponding to the first antenna element portion 6A to reduce from approximately 900MHz to approximately 850MHz. This reduction in resonant frequency is due to the introduction of a piece of dielectric material adjacent to the first antenna element portion. . For high antenna efficiency, the dielectric in this embodiment has a low dielectric loss. The resonant frequency corresponding to the second antenna element portion 6B is largely unaffected when the tuning element 8 in position 8A. The resonant frequency corresponding to the third (UMTS) antenna element portion 6E is also unaffected. With the tuning element 8 in position 8A, the tuneable antenna therefore has resonant frequencies of 850MHz, 1900MHz, and a fixed resonant frequency appropriate for a UMTS mobile network. Thus, with the tuning element 8 in position 8A the antenna is suitable for use with mobile networks based in North American territories.

Figures 3 and 4 show the same two views of the first embodiment as are shown in figures 2 and 1 respectively, but with the tuning element 8 in a second lateral position 8B. In position 8B, it can be seen that the tuning element 8 is substantially adjacent to the second antenna element portion 6B of the antenna element 6. In this position, the tuning element causes the resonant frequency corresponding to the second antenna element portion 6B to be reduced from approximately 1900MHz to approximately 1800MHz. This reduction in resonant frequency is caused by the dielectric material being close to the second antenna element portion 6B. The resonant frequency corresponding to the first antenna element portion 6A is unaffected when the tuning element 8 in position 8B. Again, the resonant frequency corresponding to the third (UMTS) antenna element portion 6E is also unaffected. With the tuning element 8 in position 8B, the tuneable antenna therefore has resonant frequencies of 900MHz, 1800MHz, and a fixed resonant frequency appropriate for a UMTS mobile network. With the switch in this position the antenna is suitable for mobile networks based in European and many Asian territories.

Referring again to figures 2 and 3, the structure of the slider mechanism 16 can be seen. The slider mechanism 16 is slidably located in a recess in the casing 18 of the equipment in which the tuneable antenna 2 is mounted. If necessary, the slider mechanism 16 may be replaced with any other form of mechanical linkage appropriate to the application. The slider mechanism 16 has a handle 17 which is used to manually move the position of the tuning element 8 between position 8A and position 8B. In the embodiment shown in figures 1 to 4, the slider mechanism 16 also includes means 20 to maintain, the tuning element 8 in position 8A or position 8B, but not in intermediate positions. Since suitable mechanical arrangements are known, they are not shown in detail in the Figures. In alternative embodiments, the means 20 may maintain the tuning element 8 any one of more than two positions.

Figure 5 shows a mobile telephone 26 comprising the tuneable antenna 2 described above. The slider mechanism 16 mounted within the casing 18 is clearly visible.

The tuneable antenna is mounted in the casing with the ground plane 4 towards the display of the mobile telephone to shield the user of the mobile telephone from transmitted radio signals in use.

In a second embodiment of the tuneable antenna 28, shown in figure 6, the slider mechanism 16 is replaced by an electromechanical switch 22, in the example, a solenoid actuator. In this second embodiment, the position of the tuning element 8 may be controlled electronically. A control circuit 24 is provided which drives the electromagnetic device 22, and thus moves the tuning element 8, in response to detected electromagnetic signals. The signals detected may be in particular be received signals from a beacon, which may transmit information relating to the frequencies used in a particular environment in a manner known to those skilled in the art of mobile telephony.

In other arrangements, the control circuit may drive the electromagnetic device 8 in response to other criteria, such as the frequency of signals selected by a user. The control circuit may run under the control of a computer program.

In use, the resonant frequencies of the tuneable antenna 2, 28 are changed by laterally moving the tuning element 8. In the first embodiment shown in figures 1 to 4, this change is effected when the user manually moves the handle 17 of the slider mechanism 16 so that the tuning element 8 is shifted between positions 8A and 8B. In the second embodiment shown in figure 6, this change is effected automatically by the control circuit 24, which operates under the control of a computer program. In this case, the control circuit drives the electromagnetic device 22 in response to the detection of electromagnetic signals in different frequency bands. Movement of the tuning element 8 causes one of the resonant frequencies of the tuneable antenna to increase slightly, and another of the resonant frequencies to reduce slightly, as described above.

The first and second embodiments described above provides a tuneable antenna having a total of five resonant frequencies, although only three resonant frequencies are available with the tuning element 8 in any one position (either 8A or 8B). One of the three available resonant frequencies, corresponding to the third (UMTS) antenna element portion 6E, is the same in either position, while two of the available resonant frequencies vary slightly depending on the position of the tuning element 8. Other embodiments of the tuneable antenna 2 may have a different number of antenna element portions, a different number of tuning element positions and different corresponding resonant frequencies. Persons skilled in the art will be able to alter the resonant frequency-of the tuneable antenna 2, by varying the size, thickness, material and relative positions of the antenna element 6 and the tuning element 8-

In this way, a mobile telephone can be designed to operate with mobile networks that conform to different communications standards in different territories (for example, GSM900 and GSM1800), as well as with different generation mobile networks (for example GSM and UMTS).

In a third embodiment of the tuneable antenna 30, shown in figure 7, the antenna element 6 comprises first and second antenna element portions 6A, 6B. Unlike the previously described embodiments the antenna element 6 does not have an antenna element portion designed for use with a fixed frequency service such as the UMTS mobile network.

A feed line 32 is used to introduce signals to and from the antenna.

ln'the above embodiments, the tuning element is a piece of dielectric material. However, it is also possible to use a metallic tuning element, as illustrated by a fourth embodiment of the tuneable antenna 34, shown in figure 8.

In this embodiment, a pair of tuning elements 8A, 8B are arranged adjacent to corresponding antenna element portions 6A, 6B between the antenna element 6 and the ground plane 4. Each tuning element is a metal sheet electrically connected to ground by connection 36. The tuning elements are tuned using vertical movement (i.e. perpendicular to the lateral plane) of the tuning elements 8, as shown by arrow 38.

In this embodiment, the varying capacitative loading of the antenna element portions 6A, 6B caused by the tuning elements 8A and 8B changes the resonant frequency of those portions as the respective tuning elements 8A, 8B are moved and accordingly changes the corresponding resonant frequency. The separate tuning elements 8A, 8B may be controlled separately. However, in a preferred arrangement the tuning elements 8A, 8B are arranged such that that one of the tuning elements 8A, 8B is brought closer to the respective antenna element portion 6A,6B as the other tuning element is brought away. Suitable mechanical arrangements for doing this are known - for example the tuning elements may be mounted on a rocker frame with a pivot arranged between the tuning elements.

The use of such metallic tuning elements gives a number of advantages over dielectric elements. Firstly, metallic plates may be provided cheaply. Secondly, the volume taken up by a thin metallic plate is very small as is the weight of the plate and this is important in small light apparatus such as mobile telephones.

It will be appreciated that the technique of using vertical movement of the tuning element and the provision of a pair of tuning elements is not limited to the case of a metallic tuning element and the same techniques may be used also with dielectric tuning elements 8 such as those discussed above.

In a fifth embodiment of the invention, illustrated in Figures 9 and 10, the antenna element is in the form of a substantially planar "antenna element 6 defining a plurality of antenna element portions 6A, 6B directly mounted onto a circuit board 10. The ground plane 4 is laterally adjacent to the antenna element on the same side of the circuit board as the planar antenna element 6. Thus, the shield between the antenna element and the user is omitted. This kind of antenna is very suitable in cases where the mobile communications apparatus is a personal digital assistant (PDA) or other apparatus not intended for use close to a user's body. A particular benefit is that the antenna arrangement can have larger bandwidth than antenna arrangements with parallel ground planes. A tuning element 8 is provided, in this example moveable laterally to couple to one or other of the antenna element portions 6A,6B to change the resonant frequency of the adjacent antenna element portion 6A,6B and so to tune the communications frequencies of the antenna element 6.

It will be appreciated that the features of the above embodiments may be combined with one another as required. For example, it is possible to arrange a metallic tuning element 8 (as in the example shown in Figure 8) between the ground plane 4 and antenna element 6, as in the example of Figures 1 to 4.

The tuneable antenna of the invention is suitable for incorporation into a mobile telephone. However, it will be obvious to persons skilled in the art that the invention is suitable for use in other applications, such as incorporation into other forms of mobile communications equipment or small terminal equipment, for example personal digital assistants (PDAs).

Further, the antenna element is also suitable in other applications where a number of different frequency ranges are required, and the skilled person will be aware of a number of such alternatives. For example, a tuneable antenna according to the invention may be used in antenna systems for wireless LAN,

• to switch between 2.4GHz and 2.5GHz frequencies.

Referring to Figure 11 , a mobile telephone according to another embodiment of the invention includes a circuit board 102 defining a ground plane 104, an insulating spacer frame 106 and an antenna 108. The spacer frame 106 is associated with a number of further components, represented in Figure 11 schematically as a capacitance plate element 110 extending substantially adjacent to and parallel to part of the antenna and a switch 112 arranged to switchably connect the capacitance plate element 110 to ground.

Figure 11 also shows schematically a signal source 114 feeding into a feed point 116 on the antenna 108 as well as a direct connection of a ground point 117 on the antenna 108 to ground. Note that the ground connection shown in Figure 11 is optional and in some alternative embodiments may be omitted. A housing 118 is provided, shown schematically by a dotted line.

Thus, in this embodiment adjustment of frequency is provided by switchable instead of moving capacitance plate elements.

Figures 12 to 15 show a further embodiment using switches. Figure 12 shows a top view with the antenna element 108 removed. Spacer frame 106 is formed of insulating plastics in the specific embodiment. The spacer frame 106 comprises a number of ribs 120 for supporting the antenna 108 away from the ground plane 104. In the specific embodiment shown the ribs are 5mm-9mm in the direction perpendicular to the ground plane, though this may vary depending on the available space within the mobile telephone housing.

Figure 12 also shows a number of components associated with the spacer frame. An electrically controlled actuator 124 is held in a hole 126 defined in one of the ribs 120. The actuator 124 is connected to a flexible switch foil 127 of metal connected in turn to a stud 128 for connection to the ground plane 104.

A pair of capacitance plate elements 110, comprising first capacitance , plate element 130 and second capacitance plate element 132, are supported on insulating capacitance plate support rib 136 (Fig. 14). The actuator 124 is connected to the switch foil 127 by rod 134 which passes under the second capacitance plate element 130 and which is arranged to move the switch foil 127 from a first position (shown dotted in Figure 13) in contact with and electrically connecting the first capacitance plate element 130 to a second position (shown in a full line) in contact with and electrically connecting the second capacitance plate element 132. In this way, either of the first and second capacitance plate elements 130, 132 can be connected to ground.

As shown in Figure 13, the antenna 108 includes a feed point 116. A first antenna element portion 140 made up of first arm 142 and second arm 44 separated by notch 146 extends in one direction from feed point 116. A second antenna element portion 148 in the form of an "L" extends in another direction from feed point 116. The ground connection 117 is made at the location indicated by reference numeral 1 17, opposite the feed point 116. Note that although the feed point 116 and ground 117 are indicated to be between the two antenna elements, it is also possible for the skilled person to arrange for different feeding and grounding points.

The mobile telephone is assembled within housing 118 with antenna 108 spaced from ground plane 102 as shown in Figure 15. Note that the first and second capacitance plate elements 130, 132 are in fact arranged parallel to and closely spaced from, the ends of the first and second antenna elements 140,148 to couple to individual elements. By arranging the plates adjacent to the ends significant frequency shifts are most easily achieved. Stud 128 is connected to ground plane 104. Note that in the configuration shown second capacitance plate element 132 is switched to ground and first capacitance plate element 130 is floating.

The use of parallel closely spaced capacitance plates 130, 132 allows significant changes in frequency without using excessively large plates. In the specific embodiment, the plates may be of linear dimension 2mm by 4mm to 6mm by 6mm, depending on the available space and frequency shift required. As the skilled person will appreciate, the capacitance of a plate of area A spaced by a distance I from the antenna element is indicated by C=εε0 A/I. Thus, a closer spacing between the capacitance plates and the antenna elements may allow smaller linear dimensions to be used, and the converse is also true. Larger or smaller plates may also be used if necessary to achieve the required frequency shifts.

In use, actuator 124 switches one of the capacitor plate elements 130,132 to connect it to ground, leaving the other floating. When the capacitance element is grounded, the capacitance is effectively on and this capacitative loading on the antenna element causes a drop in frequency. In the described embodiment, both plates 130,132 are controlled by the action of a single switch which grounds the first plate 130 in a first position and the second plate 132 in its second position. 5

In this embodiment, the first antenna element 140 has a resonant frequency in the EGSM frequency band of 880MHz to 960MHz when the switch is in a second position so that the first capacitance plate 130 is not grounded and at a lower frequency in the GSM 850 frequency band of 824MHz to 894MHz when 10 the switch is in a first position so that the first capacitance plate 130 is grounded.

The second antenna element 148 has a resonant frequency in the PCS1900 frequency band of 1850 to 1990 MHz when the switch is in the first position so 15 that the second capacitance plate 132 is not grounded and a lower frequency in the GSM1800 frequency band of 1710MHz to 1880MHz when the switch is in the second position so that the second capacitance plate 132 is grounded.

In this way the antenna operates at the frequencies suitable for North America 20 with the switch in the first position and at frequencies suitable for Europe with the switch in the second position.

The invention is not limited to the embodiments described above and the skilled person will be aware of alternative possibilities for implementing many of the 25. features.

The number of frequency bands is not restricted to two and three or more frequency bands may be provided if required.

30 In alternative embodiments, each of the capacitance plates 130,132 is connected by separate switches 112 to ground. Instead of the switch described, any alternative switching arrangement may be used.

For example, MEMS switches may be used, i.e. a small electronic switch defined on a piece of silicon. It is presently quite difficult to make a MEMS switch reliable over a large number of duty cycles, making them unsuitable for some applications. However, the number of times that the switch in the present invention is actuated is rather small, making the MEMS switch highly suitable for this application.

Alternatively, PIN diode switches may be used. These are slightly non-linear leading to some harmonic distortion, but this can be reduced by correct design as will be appreciated.

The antenna 108 may include an arm of fixed frequency, for example for a fixed band.

In less preferred embodiments the capacitance elements may be arranged elsewhere than at the ends of the antenna element arms.

The above described embodiments use an essentially planar antenna but in embodiments the antenna elements may be, for example, at different levels or not planar. The elements may be shaped to conform to the inside of the housing in which they reside.

Although the embodiments described above use a spacer to separate the antenna element from the ground plane, a spacer is not necessary, and the antenna element may simply be fixed to the inside of the housing, or otherwise.

In the present application, the term mobile telephone or mobile phone is used to cover all mobile communications devices, including for example, PDAs, cordless telephones, and other wireless communications devices.

Claims

CLAIMS:
1. A tuneable antenna comprising: an electrically conductive antenna element having at least one antenna element portion having a respective communications frequency for radiating or receiving radio signals at the respective communications frequency; and a tuning element switchable between at least a first operation state and a second operation state relative to the antenna element, the tuning element including a capacitance element, a dielectric or a conductive tuning element arranged to couple to at least one antenna element portion to tune the communications frequency or frequencies of at least one antenna element portion to different communications frequencies corresponding to the tuning element positions.
2. The tuneable antenna of claim 1 , wherein the tuneable antenna is multiband antenna having at least two antenna element portions, each of the at least two antenna element portions having a different respective communication frequency, the tuneable antenna having a first plurality of communication frequencies with the tuning element in the first position and a second plurality of communications frequencies with the tuning element in the second position, the first and second plurality of communications frequencies being different.
3. A tuneable antenna according to claim 1 or 2 wherein the tuning element is a dielectric conductive tuning element arranged to electromagnetically couple to at least one antenna element portion and moveable between first and second positions corresponding to first and second operation states.
4. The tuneable antenna of claim 3, wherein the or each respective communications frequency varies by no more than 15% as the tuning element is moved between the first and the second positions.
5. The tuneable antenna of claim 3 or 4, wherein the first position is adjacent to a first antenna element portion and a second position adjacent to the second antenna element portion.
6. The tuneable antenna of claim 5, wherein the first antenηa element portion has a resonant frequency in the EGSM frequency band of 880MHz to 960MHz when the tuning element is in the second position and at a lower frequency in the GSM 850 frequency band of 824MHz to 894MHz when the tuning element is in the first position, and the second antenna element portion has a resonant frequency in the PCS1900 frequency band of 1850 to 1990 MHz when the tuning element is in the first position and a lower frequency in the GSM1800 frequency band of 1710MHz to 1880MHz when the tuning element is in the second position.
7. The tuneable antenna of any preceding claim, wherein the antenna element extends laterally, and wherein the tuning element is laterally movable between the at least two positions relative to the antenna element.
8. The tuneable antenna of any of claims 1 to 6, wherein antenna element extends laterally and the tuning element is movable between first and second positions in a vertical direction substantially perpendicular to the plane of the laterally extending antenna element.
9. The tuneable antenna of any preceding claim, wherein the tuning element is a piece of dielectric material.
10. The tuneable antenna of any of claims 1 to 7, wherein the tuning element is a piece of electrically conductive material.
11. The tuneable antenna of any one of the preceding claims, further comprising an electrically conductive ground element extending laterally adjacent to the antenna element.
12. The tuneable antenna of claim 11 , wherein the tuning element is disposed between the ground element and the antenna element.
13. The tuneable antenna of claim 12, wherein the tuning element is electrically connected to the ground element.
14. The tuneable antenna of any one of claims 11 to 13, wherein the ground element is disposed on one side of a printed circuit board.
15. The tuneable antenna of any one claims 2 to 14, further comprising a manual mechanical switch connected to move the tuning element between the at least two positions relative to the antenna element.
16. The tuneable antenna of any of the claims 2 to 14, further comprising a control circuit for detecting the frequency of received electromagnetic signals, wherein the control circuit provides control signals to switch the switching element to move the tuning element between the at least two positions in response to the frequency of electromagnetic signals detected.
17. The. tuneable antenna of any one of the preceding claims, wherein the antenna element comprises a Universal Mobile Telephone Standard (UMTS) antenna element portion for use with UMTS mobile networks.
18. A tuneable antenna according to claim 1 or 11 : wherein the electrically conductive antenna element include a plurality of antenna element portions for radiating at respective first communications frequency bands, the plurality of respective first communications frequency bands including a plurality of different frequency bands; and the tuning element includes a capacitance element adjacent to and coupled to a respective antenna element portion; and a switch switchably coupling the capacitance element to a supply voltage to tune the communications frequency of the respective antenna element portion to a respective second communications frequency different to the first communications frequency.
19. A tuneable antenna according to claim 18 having a plurality of capacitance elements adjacent to and coupled to respective antenna element portions, the capacitance elements being switchably coupled to the ground by at least one switch.
20. A tuneable antenna according to claim 18 or 19 wherein each antenna element portion is a planar element and the or each capacitance element is a planar element spaced perpendicularly from and extending substantially parallel to the respective antenna element portion.
21. A tuneable antenna according to any one of claims 18 to 20 wherein the antenna element portions corresponding to each frequency are defined by a number of longitudinal and lateral notches.
22. A tuneable antenna according to claim 18 when dependent on claim 11 wherein each capacitance element is arranged closer to the antenna element than the ground element.
23. A tuneable antenna according to any of claim 18 to 22 wherein the or each first communications frequency of each respective antenna element portion differs by no more than 30% from the respective second communications frequency of the same antenna element portion.
24. A tuneable antenna according to claim 18 comprising: a first antenna element portion having a respective first capacitance element switchably connected to ground, the first antenna element portion having a resonant frequency in the EGSM frequency band of 880MHz to 960MHz when a the first capacitance element is not connected to ground and a lower frequency in the GSM 850 frequency band of 824MHz to 894MHz when the switch is connected to ground; and a second antenna element portion having a respective second capacitance element switchably connected to ground, the second antenna element portion having a resonant frequency in the PCS 1900 frequency band of 1850 to 1990 MHz when the second capacitance element is not connected to ground and a lower frequency in the GSM 1800 frequency band of 1710MHz to 1880MHz when the second capacitance element is connected to ground.
25. Mobile communications apparatus comprising the tuneable antenna of any of the preceding claims.
PCT/GB2004/001796 2003-04-28 2004-04-28 Tuneable antenna WO2004097976A2 (en)

Priority Applications (4)

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GB0309640.1 2003-04-28
GB0309640A GB2402265A (en) 2003-04-28 2003-04-28 Tuneable antenna
GB0321222A GB2406217A (en) 2003-09-10 2003-09-10 Tuneable antenna
GB0321222.2 2003-09-10

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US7924226B2 (en) 2004-09-27 2011-04-12 Fractus, S.A. Tunable antenna
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EP3364498A1 (en) 2017-02-21 2018-08-22 Vestel Elektronik Sanayi ve Ticaret A.S. Tuneable antenna and method for usage of such a tuneable antenna

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