GB2463536A

GB2463536A - Tuneable antennas suitable for portable digital television receivers

Info

Publication number: GB2463536A
Application number: GB0902307A
Authority: GB
Inventors: Brian Collins
Original assignee: Antenova Ltd
Current assignee: Antenova Ltd
Priority date: 2008-09-22
Filing date: 2009-02-12
Publication date: 2010-03-24
Anticipated expiration: 2029-02-12
Also published as: GB0902307D0; WO2010032066A1; GB2463536B; TWI523333B; GB0817237D0; TW201025730A

Abstract

An antenna system comprises an electrically conductive antenna element 3 and at least first and second lines for connecting the antenna element 3 to ground 1. The first and second lines are connected to the antenna element 3 at different positions. A third line 10 is provided for connecting the antenna element to a radio apparatus. The first and second lines are respectively provided with first 13 and second 14 circuit components each having an adjustable capacitive and/or inductive reactance (e.g. MEMs, capacitors, inductors or combinations thereof) thereby allowing the antenna system to be tuned. Also disclosed are details for a circuit board comprising the antenna system as defined, a dielectric substrate with a ground plane printed thereon where there is a predetermined area where the ground plane is not printed. A radio communication device comprising the disclosed antenna system and/or the disclosed circuit board could also be produced.

Description

TUNEABLE ANTENNAS SUITABLE FOR PORTABLE DIGITAL TELEVISION

RECEIVERS

The present invention relates to antennas for a small portable radio terminal such as a mobile radio handset, or personal television receiver.

BACKGROUND

While there are numerous international standards for digital television broadcasts, many transmissions take place in the internationally assigned frequency bands, for example 174 -240MHz and 470 -860MHz.

An antenna suitable for use in a mobile receiver is frequently required to be able to be tuned to provide operation over this entire frequency range, the ratio of the maximum frequency to the minimum frequency being approximately 5:1. Small antennas are known to have bandwidths which are limited by their dimensions, so one solution for this application is to tune the antenna to optimally receive signals in some sub-band such as that occupied by the desired television or radio channel. The present invention relates to the design and tuning of an antenna for operation in this manner.

One known low-profile antenna suitable for use in a small portable terminal is the inverted-L antenna shown in Fig 1, in which a feed element 2 is connected to an extended conducting member 3. A transmitter or receiver is connected between the feed member 2 and the groundplane 1.

While it is known that the operating frequency of an inverted-L antenna can be adjusted by means of a variable tuning capacitor 4 located at or close to its open-circuit end as in Fig. 2 (see Chapter 27 of Antenna Engineering Handbook, 3rd Ed, Mc Graw-Hill 1993, page 27-2 1), it is not possible to obtain a close impedance match by this method over a frequency range as wide as 5:1. Fig. 2 shows an inverted-L antenna similar to that of Fig. 1 but having a variable capacitor 4 connected between the upper elongate conducting member 3 and the groundplane 1. The tuned frequency is changed by adjusting the value of the capacitor 4. A transmitter or receiver is connected between the feed member 2 and the groundplane 1.

A second known antenna configuration is shown in Fig. 3, in which the extended top conductor 3 of the inverted-L antenna is excited by means of a second conductor 10 attached to the top conductor 3. Such a configuration is described as an inverted-F antenna. The conductive member 2 connects the elongate conducting member 3 to the groundplane 1. A transmitter or receiver is connected between the feed member 10 and the groundplane 1.

A combination of these configurations shown in Fig. 3 provides another potential solution to an antenna tuneable over an extended frequency band. When considering the impedance matching of an inverted-F antenna it is known that matching can be effected by the control of two different parameters (Chapter 2 of Antennas for Portable Devices, Zhi Ning Chen (Editor), John Wiley, 2007). The resonant frequency is controlled by the length of the extended top conductor of the inverted-F antenna combined with the effective capacitance between the open circuit end of the said conductor and ground. The magnitude of the resistive component of the input impedance may be controlled by changing the position of the feed conductor relative to the position of the short-circuit end of the antenna, even to the extent of moving the feed conductor to the extreme opposite end of the antenna as shown in Figure 4, where the feed member 12 is connected to one end of the elongate member 3 and the connection to ground 11 is positioned between the feed 12 and the open circuit end of the elongate member 3.

When applied to an antenna which is required to operate over a restricted frequency band, for example the mobile phone band 880 -960MHz, the connection 11 between the elongate conducting member 3 and the ground 1 is positioned such that acceptable performance is achieved over the whole band. However when the antenna is to be tuned over a wide frequency range it is usually necessary to change the position of the ground connection 11 in order to obtain a satisfactory impedance match, specifically a value of the resistive component of the input impedance close to a desired value. It is not possible to obtain the required tuning range by using a fixed grounding position and a single variable reactance.

To provide multiple grounding positions, it is possible to use multiple switched ground connections, but no continuous means of adjustment is so provided. Further the capacitive loading created by multiple switches, their connections and their control circuits is likely to impair the RF performance of the antenna.

BRIEF SUMMARY OF THE DISCLOSURE

According to a first aspect of the present invention, there is provided an antenna system comprising an electrically conductive antenna element, at least first and second lines for connecting the antenna element to ground, the first and second lines being connected to the antenna element at different positions, and a third line for connecting the antenna element to a radio apparatus, wherein the first and second lines are respectively provided with first and second circuit components each having an adjustable capacitive and/or inductive reactance, thereby to allow the antenna system to be tuned.

The third line is typically adapted for connection to an RF output of a radio transmitter and/or an RF input of a radio transmitter.

The first line may be considered in some embodiments to be a loading line, the second line to be a tuning line, and the third line to be a feeding line.

The antenna system is preferably a monopole antenna system for use with a conductive groundplane acting as a counterpoise.

In exemplary embodiments, the circuit components may be configured as varactors (components having variable or adjustable capacitance) or as capacitors forming part of MEMS (microelectromechanical systems) devices, or as MEMS devices having adjustable reactances. However, it will be understood that any type of component or device that allows capacitance and/or inductance to be adjusted, controlled and/or varied according to requirements may be used. Preferably, such components or devices may be controlled or adjusted or varied electronically, but in some embodiments manual control may be appropriate. Any type of switched or continuously variable inductor and/or capacitor could be used in either the first or the second lines or both.

The first or second (or both) circuit components may be configured as, effectively, a capacitor, an inductor, a capacitor connected in parallel with an inductor, or a capacitor connected in series with an inductor, in each case optionally together with at least one resistor in series or in parallel or both.

In some preferred embodiments, the antenna element is an inverted F antenna element having an elongate conductive radiating/receiving component with first and second ends, a grounding leg and a feed line connecting the input/output of the antenna to the associated radio transmitting/receiving apparatus. The first line comprises the grounding leg with the first circuit component connected in series, and the third line is the feed line. The first and third lines are advantageously provided close to each other at the first end of the elongate conductive radiating/receiving component, while the second line, which serves as a tuning line with the second circuit component connected in series, is preferably connected between ground and a point at or close to the second end of the elongate conductive radiating/receiving component.

The first line may be located between the third line and the second line, or the third line may be connected between the first line and the second line. In other words, the facility of wide-band tuning is retained if the relative positions of the third line and the adjacent first line are interchanged.

Additional lines connecting the antenna element to ground, and each connected in series with a circuit component having a reactance, preferably a variable reactance, may be provided. The additional lines may include switching means to allow them to be switched in or out.

The conductive antenna element may be substantially planar, and preferably substantially parallel to a groundplane when installed. Where the conductive antenna element is elongate, it may extend in a substantially straight line, or may be bent or formed into any appropriate shape, including regular or irregular meander patterns and/or spiral patterns. The conductive antenna element in some embodiments may double back on itself or be folded or otherwise shaped or convoluted.

It is found that a coupling factor of the antenna system may be varied by controlling the value of a capacitive or inductive reactance placed in series with the first (grounding or loading) line. From the foregoing, it is found that the antenna system can be effectively matched over the required frequency range by providing both a variable reactance at or close to the open circuit end of the conductive radiating/receiving component and a second variable reactance in series with a conductor forming a grounding connection connected to the conductive radiating/receiving component.

While it is found that there is some interaction between the actions of these two reactances, the effects are sufficiently separate to allow the correct values to be rapidly chosen to tune the antenna system to a required channel. In a practical application the activity of tuning the antenna system by controlling the values of the tuning reactances may be carried out by a microprocessor operating under the control of a software program embodying a simple control algorithm or a look-up table of circuit element values for any desired operating frequency The tuning circuits comprising variable reactances and optional switches may be controlled by a microprocessor which during the tuning process or optionally also at other times receives information from an associated receiver to which the antenna system is connected, for example information in analog or digital form relating to the level of the signal at the receiver input or the quality of the receiver output.

While the starting point for the tuning process can be stored within the receiver or associated memory circuits, the frequency of local radio or television transmissions may be unknown, especially if the receiver has been transported between locations while it has been switched off. The process of searching for signals while at the same time optimising the tuning of the antenna is non-trivial and may occupy a considerable period of time, stepping through all available channels and attempting to tune a signal. When attempting to tune on an empty channel (i.e. most channels at an arbitrary location), the process will take longer than on an occupied channel, so most of the tuning time is spent in vain. The tuning process can be aided by the provision of a subsidiary receiver whose function is to determine the location of the receiving apparatus by reference to a satellite positioning system, for example a Global Navigation Satellite System (GNSS) such as the Global Positioning System (GPS). Such receivers are small and available at low cost. In a preferred embodiment the receiving apparatus is provided with a satellite navigation receiver and a communications means such as a mobile telephone or wireless local area connection and by this means communicates with an information server connected to Internet. On receipt of an enquiry from the receiving apparatus, specifying the geographical position of the receiver, an information server responds with a list of the frequencies at which usable signals are expected to be found at the location of the receiver. The receiver then attempts to tune the antenna system only on those frequencies at which signals are likely to be found. As a further refinement the Internet server may optionally provide information enabling the receiver to display to the user a list of the broadcast sources (for example television channels by name) and optionally a list of the broadcast content available from those sources.

An alternative method by which the receiver may obtain information to identify the locally available radio or television broadcast channels is by identifying the number of a mobile radio cell in which the receiving apparatus is currently located and sending that information to the information server. The server would then respond in the same way.

This method is more complex than obtaining a satellite-based geographical position because of the requirement to maintain an international database of all cell identities and positions for all operators. The direct transmission of geographical coordinates has the advantage that it does not require updating as mobile radio networks are expanded or modified.

In a particularly useful embodiment, the second line, which is configured as a tuning line, may comprise a printed or etched or otherwise-formed conductive track or element that is configured to couple electromagnetically with the antenna element, but which is not galvanically connected to the antenna element itself.

The conductive track of the second line may be directly connected to RF ground, or may be connected to RF ground by way of at least one circuit component having an adjustable capacitive and/or inductive reactance.

In currently preferred embodiments, a part of the antenna element that is configured for electromagnetic coupling with the second line is configured with a meander pattern defining at least one, and preferably at least two inlets or interstices or gaps into which at least one, and preferably at least two fingers or extensions of an electrically conductive RF ground connection member may respectively extend.

According to a second aspect of the present invention, there is provided an antenna system comprising an electrically conductive antenna element, at least first and second lines for connecting the antenna element to ground, the first and second lines being connected to the antenna element at different positions, and a third line for connecting the antenna element to a radio apparatus, wherein the first line is provided with at least one circuit component having an adjustable capacitive and/or inductive reactance, and wherein the second line comprises an electrical conductor that is not galvanically connected to the electrically conductive antenna element, but is configured to couple electromagnetically therewith.

The second line may additionally include at least one circuit component having an adjustable capacitive and/or inductive reactance through which it connects to RF ground, or it may connect directly to RF ground. Where at least one adjustable reactance circuit component is provided between the second line and RF ground, this can be used to tune the resonant frequency of the antenna over a wide range of frequencies.

In embodiments where the electrically conductive antenna element is formed as a conductive track formed on a dielectric substrate, the part of the antenna element configured for electromagnetic coupling may be meandered on the substrate so as to define the required inlets or interstices or gaps, and the electrically conductive RF ground connection member may also be formed as a conductive track on the substrate, with fingers of this track being formed so as to extend into the inlets or interstices or gaps (hereinafter simply referred to as inlets). The inlets generally have parallel sides defined by the meandered portion of the antenna element, although it will be understood that the inlets need not be straight, but may be curved or be formed with corners.

By adjusting the respective widths of each of the fingers and the inlets, it is possible to arrange the extent of electromagnetic coupling so that any effect of a minimum capacitance of the variable reactance circuit component(s) has a reduced or minimal effect on the resonant frequency of the antenna as a whole, while increasing the capacitance of the variable reactance circuit component(s) progressively to its maximum allows tuning across the required frequency band.

As in the first aspect, the first line may be located between the third line and the second line, or the third line may be connected between the first line and the second line. In other words, the facility of wide-band tuning is retained if the relative positions of the third line and the adjacent first line are interchanged.

According to a third aspect of the present invention, there is provided a system according to the first or second aspects in combination with the radio apparatus to which the antenna element is attached.

The radio apparatus may comprise a radio frequency (RF) integrated circuit.

According to a fourth aspect of the present invention, there is provided a circuit board comprising a dielectric substrate including an electrically conductive ground plane and a predetermined area in which the ground plane is not present, further comprising an antenna system of any preceding aspect, the electrically conductive antenna element being formed or printed on the dielectric substrate in the predetermined area thereof.

The circuit board may comprise a printed circuit board (PCB) or printed wiring board (PWB), which may be of standard or custom design. Typically, such a circuit board comprises a dielectric substrate with an electrically conductive groundplane formed on one surface or both surfaces. Alternatively, the circuit board may comprise a laminate structure with one or more groundplanes sandwiched between dielectric layers.

At least one of the circuit components (such as the first, second, third or further circuit components, and optionally also any switches) is disposed in the predetermined area.

In some embodiments, all of the circuit components are disposed in the predetermined area.

Where a microprocessor is provided, this may also be disposed in the predetermined area.

In embodiments including the radio apparatus, for example in the form of an RF integrated circuit, the radio apparatus may be disposed within the predetermined area thereof.

Such radio apparatus may itself optionally be provided with the capability of controlling the tuning signals fed to the antenna.

In this way, a discrete radio module, comprising an antenna, a radio apparatus and optionally a control means, may be formed, the module being suitable for fitting to a variety of different communications devices such as mobile telephone handsets, mobile television or radio devices, portable computers such as notebooks, netbooks, personal digital assistants and the like.

Moreover, valuable space on the main part of the circuit board (where the ground plane is present) is thereby saved, allowing for compact design.

The radio apparatus may be disposed on a first surface of the predetermined area, and the antenna element may be printed or formed on a second surface of the predetermined area opposed to the first surface. This helps to save even further space or estate on the circuit board.

According to a fifth aspect of the present invention, there is provided a radio communications device including an antenna system of the first or second aspect.

According to a sixth aspect of the present invention, there is provided a radio communications device including a circuit board of the fourth aspect.

In some embodiments of the antenna system of aspects of the present invention, the electrically conductive antenna element and (where provided) the RF ground connection member are folded along one or more lines generally parallel to a long axis of the antenna system. This may be done by forming the relevant conductive elements as etched or printed or other tracks on a flexible substrate, or by stamping and folding the relevant conductive elements from a metal sheet, or by printing the relevant conductive elements onto a supportive insulating former or by other means.

In some embodiments of the second aspect of the present invention, the antenna system may be configured with a conductive ground plane extending under parts or areas of the antenna system on which no conductive tracks or elements are formed. In this way, other electronic components, e.g. an RF receiver, may be located here and thereby help to save valuable PCB real estate. The RF feed point and/or the first line may be connected to an edge part of the extended ground plane area.

It will be understood that conductive tracks or lines and other conductive components of the antenna system may be formed by a number of different ways. On a typical PCB or PWB, conductive tracks are formed by an etching process, but on other substrate, particularly flexible substrates, tracks may be formed by printing with a conductive ink.

Other techniques include sputtering and spraying. All of these and other suitable techniques may be used in embodiments of the present invention, and reference to one technique in the context of any given embodiment is not intended to exclude other techniques unless clearly incompatible.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how it may be carried into effect, reference shall now be made by way of example to the accompanying drawings, in which: FIGURE 1 shows a conventional inverted-L antenna; FIGURE 2 shows an inverted-L antenna as in Fig. 1 but provided with a tuning capacitor; FIGURE 3 shows a conventional inverted-F antenna FIGURE 4 shows an alternative configuration of the inverted-F antenna of Fig. 3; FIGURE 5 shows a first embodiment of the present invention in schematic form; FIGURE 6 shows a second embodiment of the present invention in schematic form; FIGURE 7 shows a third embodiment of the present invention in schematic form; FIGURE 8 shows a fourth embodiment of the present invention in schematic form; FIGURE 9 shows a currently preferred exemplary embodiment of the present invention making use of printed circuit techniques; FIGURE 10 shows a further currently preferred exemplary embodiment of the present invention making use of printed circuit techniques and integrated signal lines to tuning components; FIGURE 11 shows an embodiment in which an RF integrated circuit providing for the reception or transmission of radio signals is positioned within the outline of the conductive members; FIGURE 12 shows an embodiment in which the area of the groundplane has been extended to provide accommodation for an RF integrated circuit on a projection from the groundplane; FIGURE 13 shows a simple embodiment in which one branch of the antenna element is meandered and then directly connected to RF ground by way of a variable tuning component; FIGURE 14 shows a development in which the meandered branch of the antenna element is not directly connected to RF ground, but is provided with an indirect RF ground connection member with fingers that project into inlets formed by the meander, such ground connection member being connected to RF ground by way of a variable tuning component; FIGURE 15 shows the embodiment of Figure 14 with a fold line about which the antenna system may be folded; FIGURE 16 shows a variation of the embodiment of Figure 14 with the conductive groundplane extended into the area occupied by the antenna system; FIGURE 17 shows a variation of the embodiment of Figure 14 with the conductive groundplane extended into the area occupied by the antenna system and the RF feed point connected to an edge of the extended groundplane; and FIGURE 18 shows a practical circuit arrangement for tuning embodiments of the present invention.

DETAILED DESCRIPTION

Fig. 5 shows a first embodiment of the present invention in which a variable reactive circuit element 13 is connected between a point on the elongate conducting member 3 and the groundplane 1 and a second variable reactive circuit element 14 is placed in series with the conductive member 2.

Fig. 6 shows a second embodiment of the present invention in which a variable reactive circuit element 13 is connected between a point on the elongate conducting member 3 and the groundplane 1 and a second variable reactive circuit element 14 is placed in series with the conductive member 11.

In one exemplary embodiment the variable reactive circuit element 13 is a variable capacitor or varactor diode and the length of the conducting member 3 is of the order of one quarter wavelength at the highest operating frequency.

Fig. 7 shows an embodiment of the present invention in which a plurality of reactive circuit elements 13, 14, 15, 15', 15" are connected in parallel and provided with switch means 16, 17 by which selected reactive circuit elements 15, 15', 15" may be connected or disconnected in accordance with control signals. Such switches 16, 17 may by way of example be micro electromechanical (MEM5) switches operated by signals from a controlling microprocessor (not shown).

The application of the invention is not limited to an embodiment in which the conductive members forming the antenna are disposed in a simple F-configuration. By way of example the elongate conductor 3 may be folded as shown in Fig. 8 or may be meandered or convoluted to provide an antenna having smaller overall dimensions.

Fig. 9 shows an embodiment of the invention in which the conductive members 32, 33, 34, 37 are co-planar conductors formed using printed circuit techniques on a laminate comprising at least one conductive layer and one dielectric layer. In this embodiment the variable reactive components or MEMS devices 35, 36 are fed with control voltages by conductors 40, 41 and a return path for the control signals is provided by a conventional decoupling circuit connected to the feed conductor, for example at 40.

The variable reactive component or MEMS device 36 may be located at any selected position along the conductor 37 between the junction of conductors 33 and 37 and the proximate edge of the groundplane conductor 30. Signals controlling the variable reactive components or MEMS devices 35, 36 may be connected by means of wires or circuit traces 41, 42 which require no special decoupling means.

Fig. 10 shows a further arrangement whereby control voltages can be conveyed to variable capacitance (varactor) diodes or MEMS devices without impairing the operation of the antenna. In this exemplary embodiment a pattern of conductors is etched on a double-sided or multi-layer printed circuit laminate 31. The antenna is formed from the conductive members 32, 33, 34 on the same face of the laminate as the ground plane and the projecting conductive member 37. Control signals to the varactor diodes 35, 36 are conveyed by traces 38, 39 which are preferably formed on the opposite face of the laminate from the conductive element 33. These conductors are connected through decoupling networks 40, 41, 42, 43 which comprise a series inductor and parallel capacitor in accordance with known practice. The dimension of the projection 37 and the corresponding projection of the conductive member 36 may be chosen for convenience. The conductive member 32 forms the antenna input in the form of a microstrip or co-planar waveguide transmission line. It will be understood that additional conductors and decoupling circuits may be added in order to control MEMS devices or multiple varactor diodes connected in series or in parallel.

In order to minimise or at least reduce the area or volume occupied by the antenna and its associated control circuits, the control circuits may be positioned within the area defined by the edge of the groundplane 30 and the conducting members 37, 33, 34, 32.

The dashed line 100 indicates the extent of the printed circuit laminate 31, from which it can be seen that the groundplane 30 stops short of this edge, leaving an area of substrate that can be occupied by the antenna and its associated control circuits, and optionally other components.

In an alternative implementation the control circuits are positioned within the area defined by the conducting members themselves and mounted on the opposite face of the printed circuit board to the said conductors. The precise widths and shapes of these conductors are not critical for antenna performance, so the shapes may be adjusted to provide sufficient accommodation for the control circuits, for example at the junction of conducting members 33 and 34. In an implementation of this form the DC supply lines and input data lines to the controller are decoupled at the point of connection to the antenna feed 32.

Fig. 11 shows a further embodiment the wherein shapes of the conducting members 32, 33, 34 are adapted such that, in addition to performing their function as antenna conductors, an RF integrated circuit providing for the reception or transmission of radio signals is positioned within the outline of these said conductive members. The feed from the antenna to the RF circuit is provided by the traces 52 and 53 connected respectively to the conducting members 54 and 55. Additional layers may be added to the printed circuit board in order to provide for further traces associated with the integrated circuit and additional decoupling components may be added to prevent the loss of radio frequency energy at the point of connection between the antenna-mounted devices and circuits and those located on the groundplane 30.

Fig. 12 shows an embodiment in which the area of the groundplane has been extended to provide accommodation for an RF integrated circuit 50 on a projection from the groundplane. Here the RF microcircuit is connected to the antenna structure by the connection 56 and to ground by the connection 57.

It will be seen that other locations for the RFIC are possible within the antenna configuration without departing from the general concept.

In all the above examples the distance between the elongate conductive member and the groundplane is typically less than one tenth of a wavelength in the centre of the operating frequency band and the length of the elongate member is typically less than one quarter wavelength at the same frequency. Because electrically very small antennas have poor efficiency and limited bandwidth the minimum usable dimensions are determined by the efficiency and bandwidth required for a particular application.

The arrangements here described may also be applied to a PIFA antenna in which the elongate conductive member 33 is replaced by a planar conductor lying in a plane parallel with the ground plane and spaced from it by a small fraction of a wavelength at the mid-band frequency.

In implementing the tuning system described above, it was found that the range of capacitance, and in particular the large value of minimum capacitance of low-voltage variable capacitance diodes (varactor diodes), can create a significant constraint on the performance of the antenna. This constraint particularly affects the tuning capacitor at the end of the meandered section of the antenna.

A solution to this has been found by indirectly coupling the tuning circuit to the longer section of the antenna.

Figure 13 shows an embodiment (of the second aspect of the present invention) in which a longer section or branch of the antenna conductor 3 has been meandered to reduce the space which it occupies (cf. the Figure 8 embodiment in which a single exemplary meander is shown). Figure 13 also shows the conductive member 2, a feed member 21 and first and second variable reactance circuit members 13, 14 on lines connecting the antenna conductor to the groundplane 30.

Figure 14 shows an embodiment incorporating indirect loading of the meandered section. In this arrangement, a pattern of conductive members in the form of an electrically conductive RF ground connection member 20 having fingers 200 is placed such that the it couples electromagnetically to the meandered conductor 3. The fingers 200 extend into inlets 300 defined by the meanders of the meandered conductor 3. By connecting a variable reactance 13 to that end of the RF ground connection member 20 which is proximate to ground, the resonant frequency of the antenna may be tuned over a wide range of frequencies. In the example shown the variable reactance 13 is in the form of a varactor diode. By adjusting the respective widths of each of the fingers 200 and the inlets 300 it is possible to arrange the extent of coupling such that the effect of the minimum capacitance of the varactor diode has minimal or at least little effect on the resonant frequency of the antenna, while increasing the capacitance of the varactor diode progressively to its maximum allows tuning across the required frequency band, for example 470-860MHz. As before, the value of the coupling control reactance 14 is adjusted in order to provide a low VSWR at the required frequency of operation.

In a further embodiment shown in Figure 15 the antenna is folded along one or more lines 201 parallel with its long axis. An example of such a fold line 201 is shown in Figure 15. A practical embodiment incorporating such a fold may be made using a flexible printed circuit, by stamping and folding the antenna from a metal sheet, by printing the conductors onto a supportive insulating former or by other means. A single fold could, for example, change the overall dimensions of the antenna structure from a typical 50mm x 15mm x 1mm to 50mm x 10mm x 5mm. Further options include forming the antenna around a tube, the tube being either round, elliptical rectangular or any desired shape in cross-section. A variation in which the antenna elements are printed with conductive ink could offer a wider variety of 3D shapes with curvature in all planes.

In a further embodiment shown in Figure 16 the area occupied by the conductive groundplane 30 is extended into an area 22 lying between the conductive elements forming the antenna in order to provide accommodation for other electronic components, for example the receiver.

In a further embodiment shown in Figure 17 the area occupied by the conductive groundplane 30 is further extended and the feed point 21 of the antenna is moved to a convenient position on the extended ground area 22. The grounded end of the varactor diode 14 may optionally also be located on the extended ground area 22.

Figure 18 illustrates a practical circuit arrangement for tuning the antenna. In this exemplary arrangement two varactor diodes 36, 36' are connected in series to form a variable tuning capacitor in order to reduce the value of the minimum capacitance that can be obtained using low voltage diodes. The variable coupling capacitor 35 is provided by a single diode. Inductor 62 provides a DC path to ground from the coupling structure 20 and also provides a susceptance to ground the value of which may be chosen to co-operate with the tuning diodes 36, 36', while the inductors 60, 61 form RF chokes in the DC bias control lines. In the exemplary embodiment illustrated, the DC bias voltages Vt and Vc are each provided by a voltage doubling circuit comprising a charge pump and an operational amplifier connected to the control outputs of the receiver.

Claims

CLAIMS1. An antenna system comprising an electrically conductive antenna element, at least first and second lines for connecting the antenna element to ground, the first and second lines being connected to the antenna element at different positions, and a third line for connecting the antenna element to a radio apparatus, wherein the first and second lines are respectively provided with first and second circuit components each having an adjustable capacitive and/or inductive reactance, thereby to allow the antenna system to be tuned.
2. A system as claimed in claim 1, wherein the first and/or the second circuit component comprises at least one varactor diode.
3. A system as claimed in any preceding claim, wherein the first and/or the second circuit component comprises at least one microelectromechanical (MEMS) device.
4. A system as claimed in any preceding claim, wherein the first and/or the second circuit component is provided with electronic means for adjusting its capacitance and/or inductance.
5. A system as claimed in any claim 4, wherein the electronic means includes a tuning controller.
6. A system as claimed in any preceding claim, wherein the first and/or second circuit component is configured as, effectively, a capacitor, an inductor, a capacitor connected in parallel with an inductor, or a capacitor connected in series with an inductor, in each case optionally together with at least one resistor in series or in parallel or both.
7. A system as claimed in any preceding claim, further comprising at least a fourth line for connecting the antenna element to ground, the fourth line being provided with a third circuit component having an adjustable capacitive and/or inductive reactance.
8. A system as claimed in any preceding claim, wherein the antenna element is an inverted F antenna element having an elongate conductive radiating/receiving component with first and second ends.
9 A system as claimed in claim 8, wherein the first and third lines are connected adjacent to each other at or towards the first end of the antenna element.
10. A system as claimed in claim 9, wherein the second line is connected at or towards the second end of the antenna element.
11. A system as claimed in claim 10, wherein the lines are connected in an order, from the first to the second end of the antenna element, of third line, first line, second line.
12. A system as claimed in claim 10, wherein the lines are connected in an order, from the first to the second end of the antenna element, of third line, second line, first line.13. A system as claimed in claim 10 depending through claim 7, wherein the fourth line is connected between the second line and the first end of the antenna element.12. A system as claimed in any preceding claim, wherein the antenna element is substantially planar.
13. A system as claimed in any preceding claim, wherein the antenna element is elongate.
14. A system as claimed in claim 13, wherein the antenna element extends in a substantially straight line.
15. A system as claimed in claim 13, wherein the antenna element is bent, or has a regular or irregular meander or spiral pattern.
16. A system as claimed in claim 13, wherein the antenna element doubles back on itself or is folded.
17. A system as claimed in any preceding claim, wherein at least one of the lines includes switch means operable to connect or disconnect the line between ground and the antenna element.
18. A system as claimed in any preceding claim, further comprising at least one microprocessor operable to control or adjust the reactance of at least one of the circuit components so as to tune the antenna system.
19. A system as claimed in claim 18 depending from claim 17, wherein the at least one microprocessor is operable to operate the switch means.
20. A system as claimed in claim 18 or 19, wherein the at least one microprocessor is configured to receive data from the radio apparatus.
21. A system as claimed in any one of claims 18 to 20, in combination with a Global Navigation Satellite System (GNSS) or Global Positioning System (GPS) receiver, wherein a location of the system as determined by the GNSS or GPS receiver is used in order to determine an appropriate starting point for tuning the antenna system by obtaining data relating to broadcast frequencies in the location from a remote server.
22. A system as claimed in any one of claims 18 to 20, in combination with a receiver adapted to identify a mobile radio cell in which the system is located, wherein a location of the system as determined by the identify of the mobile radio cell is used in order to determine an appropriate starting point for tuning the antenna system by obtaining data relating to broadcast frequencies in the location from a remote server.
23. A system as claimed in any preceding claim, in combination with the radio apparatus to which the antenna element is attached.
24. A system as claimed in claim 23, wherein the radio apparatus comprises a radio frequency (RF) integrated circuit.
25. A system as claimed in any preceding claim, wherein the second line comprises a conductive track or element that is configured to couple electromagnetically with the antenna element, but which is not galvanically connected to the antenna element itself.
26. A system as claimed in claim 25, wherein the conductive track or element of the second line is directly connected to RF ground.
27. A system as claimed in claim 25, wherein the conductive track or element of the second line is connected to RF ground by way of at least one circuit component having an adjustable capacitive and/or inductive reactance.
28. A system as claimed in any one of claims 25 to 27, wherein at least a part of the antenna element is configured with a meander pattern defining at least one, and preferably at least two inlets or interstices or gaps into which at least one, and preferably at least two fingers or extensions of an electrically conductive RF ground connection member may respectively extend.
29. A system as claimed in claim 28, further comprising the electrically conductive RF ground connection member.
30. A system as claimed in claim 28 or 29, wherein the inlets have parallel sides defined by the meandered portion of the antenna element.
31. A circuit board comprising a dielectric substrate including an electrically conductive ground plane and a predetermined area in which the ground plane is not present, further comprising an antenna system as claimed in any preceding claim, the electrically conductive antenna element being formed or printed on the dielectric substrate in the predetermined area thereof.
32. A circuit board as clamed in claim 31, wherein at least one of the circuit components is disposed in the predetermined area.
33. A circuit board as clamed in claim 31, wherein all of the circuit components are disposed in the predetermined area.
34. A circuit board as claimed in claim 32 or 33, wherein the antenna system is as claimed in claim 17, and wherein the switch means is disposed in the predetermined area.
35. A circuit board as claimed in claim 32 or 33, wherein the antenna system is as claimed in any one of claims 18 to 20, and wherein the microprocessor is disposed in the predetermined area.
36. A circuit board as claimed in any one of claims 31 to 33, further comprising an antenna system as claimed in claim 23 or 24, wherein the radio apparatus is disposed within the predetermined area thereof.
37. A circuit board as claimed in claim 36, wherein the radio apparatus is disposed on a first surface of the predetermined area, and wherein the antenna element is printed or formed on a second surface of the predetermined area opposed to the first surface.
38. A radio communications device including an antenna system as claimed in any one of claims 1 to 30.
39. A radio communications device including a circuit board as claimed in any one of claims 31 to 37.
40. An antenna system substantially as hereinbefore described with reference to or as shown in Figures 5 to 18 of the accompanying drawings.
41. A circuit board substantially as hereinbefore described with reference to or as shown in Figures 5 to 18 of the accompanying drawings.
42. An antenna system comprising an electrically conductive antenna element, at least first and second lines for connecting the antenna element to ground, the first and second lines being connected to the antenna element at different positions, and a third line for connecting the antenna element to a radio apparatus, wherein the first line is provided with at least one circuit component having an adjustable capacitive and/or inductive reactance, and wherein the second line comprises an electrical conductor that is not galvanically connected to the electrically conductive antenna element, but is configured to couple electromagnetically therewith.
43. A system as claimed in claim 42, wherein at least a part of the antenna element is configured with a meander pattern defining at least one, and preferably at least two inlets or interstices or gaps into which at least one, and preferably at least two fingers or extensions of an electrically conductive RF ground connection member may respectively extend.
44. A system as claimed in claim 43, further comprising the electrically conductive RF ground connection member.
45. A system as claimed in claim 43 or 44, wherein the inlets have parallel sides defined by the meandered portion of the antenna element.
46. A system as claimed in claim 44 or claim 45 depending from claim 44, wherein the electrically conductive RF ground connection member has an end that is directly connected to RF ground.
47. A system as claimed in claim 44 or claim 45 depending from claim 44, wherein the electrically conductive RF ground connection member has an end that is connected to RF ground by way of at least one circuit component having an adjustable capacitive and/or inductive reactance.
48. A system as claimed in any one of claims 1 to 31 and 42 to 47, wherein the electrically conductive antenna element and (where provided) the RF ground connection member are folded along one or more lines generally parallel to a long axis of the antenna system.
49. A system as claimed in claim 48, wherein the conductive elements are configured as printed or etched tracks on a flexible substrate, or by stamping and folding the relevant conductive elements from a metal sheet, or by printing the relevant conductive elements onto a supportive insulating former.
50. A system as claimed in any one of claims 42 to 49, wherein the system is configured with a conductive ground plane extending under parts or areas of the antenna system on which no conductive tracks or elements are formed.
51. A system as claimed in claim 50, wherein the RF feed point and/or the first means is connected to an edge part of the extended ground plane area.Amendments to the claims have been filed as followsCLAIMS1. An antenna system comprising an electrically conductive inverted-F antenna element, at least first and second lines for connecting the antenna element to ground, the first and second lines being connected to the antenna element at different positions, and a third line for connecting the antenna element to a radio apparatus, wherein the first and second lines are respectively provided with first and second circuit components each having an adjustable capacitive and/or inductive reactance, thereby to allow the antenna system to be tuned.2. A system as claimed in claim 1, wherein the first and/or the second circuit component comprises at least one varactor diode.3. A system as claimed in any preceding claim, wherein the first and/or the second circuit component comprises at least one microelectromechanical (MEMS) device. 0*)4. A system as claimed in any preceding claim, wherein the first and/or the second 0') circuit component is provided with electronic means for adjusting its capacitance and/or inductance.C\J 20 5. A system as claimed in any claim 4, wherein the electronic means includes a tuning controller.6. A system as claimed in any preceding claim, wherein the first and/or second circuit component is configured as, effectively, a capacitor, an inductor, a capacitor connected in parallel with an inductor, or a capacitor connected in series with an inductor, in each case optionally together with at least one resistor in series or in parallel or both.7. A system as claimed in any preceding claim, further comprising at least a fourth line for connecting the antenna element to ground, the fourth line being provided with a third circuit component having an adjustable capacitive and/or inductive reactance.8. A system as claimed in any preceding claim, wherein the inverted-F antenna element includes an elongate conductive radiating/receiving component with first and second ends.9 A system as claimed in claim 8, wherein the first and third lines are connected adjacent to each other at or towards the first end of the antenna element.10. A system as claimed in claim 9, wherein the second line is connected at or towards the second end of the antenna element.11. A system as claimed in claim 10, wherein the lines are connected in an order, from the first to the second end of the antenna element, of third line, first line, second line.12. A system as claimed in claim 10, wherein the lines are connected in an order, from the first to the second end of the antenna element, of third line, second line, first line.13. A system as claimed in claim 10 depending through claim 7, wherein the fourth line is connected between the second line and the first end of the antenna element.12. A system as claimed in any preceding claim, wherein the antenna element is substantially planar.13. A system as claimed in any preceding claim, wherein the antenna element is elongate.14. A system as claimed in claim 13, wherein the antenna element extends in a substantially straight line.15. A system as claimed in claim 13, wherein the antenna element is bent, or has a regular or irregular meander or spiral pattern.16. A system as claimed in claim 13, wherein the antenna element doubles back on itself or is folded.17. A system as claimed in any preceding claim, wherein at least one of the lines includes switch means operable to connect or disconnect the line between ground and the antenna element.18. A system as claimed in any preceding claim, further comprising at least one microprocessor operable to control or adjust the reactance of at least one of the circuit components so as to tune the antenna system.19. A system as claimed in claim 18 depending from claim 17, wherein the at least one microprocessor is operable to operate the switch means.20. A system as claimed in claim 18 or 19, wherein the at least one microprocessor is configured to receive data from the radio apparatus.21. A system as claimed in any one of claims 18 to 20, in combination with a Global Navigation Satellite System (GNSS) or Global Positioning System (GPS) receiver, wherein a location of the system as determined by the GNSS or GPS receiver is used in order to determine an appropriate starting point for tuning the antenna system by obtaining data relating to broadcast frequencies in the location from a remote server.22. A system as claimed in any one of claims 18 to 20, in combination with a receiver adapted to identify a mobile radio cell in which the system is located, wherein a location of the system as determined by the identify of the mobile radio cell is used in order to determine an appropriate starting point for tuning the antenna system by obtaining data relating to broadcast frequencies in the location from a remote server.23. A system as claimed in any preceding claim, in combination with the radio apparatus to which the antenna element is attached.24. A system as claimed in claim 23, wherein the radio apparatus comprises a radio frequency (RF) integrated circuit.25. A system as claimed in any preceding claim, wherein the second line comprises a conductive track or element that is configured to couple electromagnetically with the antenna element, but which is not galvanically connected to the antenna element itself.26. A system as claimed in claim 25, wherein the conductive track or element of the second line is directly connected to RF ground.27. A system as claimed in claim 25, wherein the conductive track or element of the second line is connected to RF ground by way of at least one circuit component having an adjustable capacitive and/or inductive reactance.28. A system as claimed in any one of claims 25 to 27, wherein at least a part of the antenna element is configured with a meander pattern defining at least one, and preferably at least two inlets or interstices or gaps into which at least one, and preferably at least two fingers or extensions of an electrically conductive RF ground connection member may respectively extend.29. A system as claimed in claim 28, further comprising the electrically conductive RF ground connection member.30. A system as claimed in claim 28 or 29, wherein the inlets have parallel sides defined by the meandered portion of the antenna element.31. A circuit board comprising a dielectric substrate including an electrically conductive ground plane and a predetermined area in which the ground plane is not present, further comprising an antenna system as claimed in any preceding claim, the electrically conductive antenna element being formed or printed on the dielectric substrate in the predetermined area thereof.32. A circuit board as clamed in claim 31, wherein at least one of the circuit components is disposed in the predetermined area.33. A circuit board as clamed in claim 31, wherein all of the circuit components are disposed in the predetermined area.34. A circuit board as claimed in claim 32 or 33, wherein the antenna system is as claimed in claim 17, and wherein the switch means is disposed in the predetermined area.35. A circuit board as claimed in claim 32 or 33, wherein the antenna system is as claimed in any one of claims 18 to 20, and wherein the microprocessor is disposed in the predetermined area.36. A circuit board as claimed in any one of claims 31 to 33, further comprising an antenna system as claimed in claim 23 or 24, wherein the radio apparatus is disposed within the predetermined area thereof.37. A circuit board as claimed in claim 36, wherein the radio apparatus is disposed on a first surface of the predetermined area, and wherein the antenna element is printed or formed on a second surface of the predetermined area opposed to the first surface.38. A radio communications device including an antenna system as claimed in any one of claims I to 30.39. A radio communications device including a circuit board as claimed in any one of claims 31 to 37.40. An antenna system substantially as hereinbefore described with reference to or 0) as shown in Figures 5 to 18 of the accompanying drawings.0) 41. A circuit board substantially as hereinbefore described with reference to or as ° shown in Figures 5 to 18 of the accompanying drawings.C\J 20 C\I 42. An antenna system comprising an electrically conductive inverted-F antenna element, at least first and second lines for connecting the antenna element to ground, the first and second lines being connected to the antenna element at different positions, and a third line for connecting the antenna element to a radio apparatus, wherein the first line is provided with at least one circuit component having an adjustable capacitive and/or inductive reactance, and wherein the second line comprises an electrical conductor that is not galvanically connected to the electrically conductive antenna element, but is configured to couple electromagnetically therewith.43. A system as claimed in claim 42, wherein at least a part of the antenna element is configured with a meander pattern defining at least one, and preferably at least two inlets or interstices or gaps into which at least one, and preferably at least two fingers or extensions of an electrically conductive RF ground connection member may respectively extend.44. A system as claimed in claim 43, further comprising the electrically conductive RF ground connection member.45. A system as claimed in claim 43 or 44, wherein the inlets have parallel sides defined by the meandered portion of the antenna element.46. A system as claimed in claim 44 or claim 45 depending from claim 44, wherein the electrically conductive RF ground connection member has an end that is directly connected to RF ground.47. A system as claimed in claim 44 or claim 45 depending from claim 44, wherein the electrically conductive RF ground connection member has an end that is connected to RF ground by way of at least one circuit component having an adjustable capacitive and/or inductive reactance.48. A system as claimed in any one of claims 1 to 31 and 42 to 47, wherein the electrically conductive antenna element and (where provided) the RF ground connection member are folded along one or more lines generally parallel to a long axis of the antenna system.49. A system as claimed in claim 48, wherein the conductive elements are configured as printed or etched tracks on a flexible substrate, or by stamping and folding the relevant conductive elements from a metal sheet, or by printing the relevant conductive elements onto a supportive insulating former.50. A system as claimed in any one of claims 42 to 49, wherein the system is configured with a conductive ground plane extending under parts or areas of the antenna system on which no conductive tracks or elements are formed.51. A system as claimed in claim 50, wherein the RF feed point and/or the first means is connected to an edge part of the extended ground plane area.