GB2418781A

GB2418781A - Antenna with dual coaxial helical portions

Info

Publication number: GB2418781A
Application number: GB0414822A
Authority: GB
Inventors: Ovadia Grossman; Moshe Ben-Ayun; Mark Rozental
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2004-07-02
Filing date: 2004-07-02
Publication date: 2006-04-05
Anticipated expiration: 2024-07-02
Also published as: GB0414822D0; GB2418781B

Abstract

An antenna 100 comprises first and second helical portions 103, 105 which are electrically coupled such that the second portion 105 acts as a top load to the first portion 103. The said helical portions are arranged such that, in use, the magnetic flux of the said coil portions 103, 105 cancel with one another. The helical coil portions 103, 105 are wound in opposite directions to provide the said flux cancellation and to reduce the inductive coupling such that a mainly capacitive top load to the first helical portion 103 is provided. The coupling between the said portions 103, 105 may be of a galvanic or non-galvanic (ie inductive or capacitive) nature. The second helical coil portion 105 may be arranged at least partly inside or outside the first coil portion 103. The pitch of the windings, the diameter of the wound portions and the position at which the coupling occurs between the coil portions may be varied to obtain the desired operational characteristics. The antenna may include a sleeve 107 as a spacer between the coil portions and the antenna may be enclosed in moulded plastic material with an outer envelope 109. The antenna may provide a compact arrangement which may be modified to provide broadband or multiple frequency band operation for a mobile station radio communication device.

Description

241 878 1 TITLE: ANTENNA FOR USE IN A MOBILE RADIO COMMUNICATION

DEVICE

FIELD OF THE INVENTION

The present invention relates to an antenna. The antenna is for use in radio communications particularly for use in a mobile radio communications unit.

BACKGROUND OF THE INVENTION

Mobile communications are carried out using mobile radio communications units known in the art as 'mobile stations' which include a transmitter to convert messages or information of a user input mainly in the form of speech, but possibly also in the form of text data and/or visual images etc., into radio frequency (RE) signals for transmission to a distant receiver, and a receiver to convert received RF signals from a distant transmitter back into information which can be understood by the user. Many components of the transmitter and receiver are common components usually forming a single transceiver unit.

In a mobile station, the function of sending and receiving an RF signal via an air interface to and from a distant transceiver is carried out by a component referred to in the art as an antenna or aerial. In general, an antenna is a device which converts an electrical signal oscillating at RF frequency into a radiated electromagnetic energy signal and vice versa.

In modern mobile communications, such as using digital technology, the RF signals generally have a high frequency, e.g. above 30MHz. For example, for systems operating according to TETRA standard procedures, an operating frequency is in a specified range in the region of 400MHz, e.g. from 410MHz to 430MHz, centre frequency 420MHz. TETRA (Terrestrial Trunked Radio) is a set of operational industry standard procedures defined by the European Telecommunications Standards Institute (ETSI). The frequency of such systems is often referred to as 'UHF' (ultra high frequency).

Generally, antennas for use in TETRA and other UHF mobile stations are limited in frequency bandwidth.

Generally, the bandwidth becomes smaller as the size of the mobile station and the antenna is reduced at any frequency. For operation in multiple frequency bands multiple resonators are normally used and each has a bandwidth of not more than about 10% (of the operating centre frequency). However, for new wireless communication services which are currently emerging, the bandwidth required is greater than the conventional 10%. For example, there are different TETRA systems in various different geographical regions designed to operate at 380-470MHz as well as at 410430MHz and some are planned for 450-470MHz. A roaming service will enable a mobile station to be handed over seamlessly between such different systems, when moving from one geographical region to another.

The purpose of the present invention is to provide a novel antenna of a form which can be designed to provide a bandwidth greater than that of known antennas for use in mobile communications.

Antenna configurations for many different

applications are described in the prior art. GB-A-

2282487 and US-A-5216436 are mentioned as giving

examples of prior art configurations. These

configurations include a 'top hat' portion which is required to occupy a considerable volume.

In addition, GB-B-2380323 describes an antenna (for use in a radio communication device), having a length of not greater than lOOmm and including a first portion comprising a conductive helical or spiral coil extending along an axis and electrically connected to a further portion, namely a conductive capacitive portion comprising a hollow cylinder extending along the axis of the coil. The present invention is intended to give an improved bandwidth performance compared with that obtainable with the antenna of GB-B-2380323.

SUMMARY OF THE PRESENT INVENTION

According to the present invention in a first aspect there is provided an antenna for use in a radio communication device including a first portion which is a first conductive helical or spiral coil portion extending along an axis and, electrically coupled to the first portion, a second portion which comprises a conductive top load portion, the first portion and the second portion being mutually arranged to provide an electrically resonant structure, wherein the second portion comprises a second conducting helical or spiral coil portion which extends along or parallel to the axis in a configuration in which in use the instant l magnetic flux of the coil portions is mutually cancelling.

Preferably, one of the coil portions extends for part of its length coaxially inside the other coil portion. The first coil portion may have a first part and a second part wherein at least part of the second coil portion extends inside the second part but not the first part of the first coil portion. Alternatively, the first coil portion may have a first part and a second part wherein at least part of the second coil portion extends outside the second part but not the first part of the first portion.

The resonant structure provided by the antenna according to the invention may provide a plurality of electrical resonances at frequencies in a frequency band of operation of the radio communication device in which the antenna is employed. The configuration of the antenna is preferably such that (i) the first and second parts of the first coil portion contribute to one of the resonances; and (ii) the first part of the first coil portion and the second coil portion contribute to another of the resonances.

The first coil portion and the second coil portion may have a common axis. The first coil portion may comprise a single coil or multiple coils. In any case, the first coil portion may be divided into the first and second parts by the coupling to the second portion.

It is possible for the electrical coupling between the first coil portion and the second coil portion to be other than galvanic, e.g. a capacitive coupling provided by a dielectric coupling ring. However, the coupling is preferably a galvanic coupling, e.g. by use of a suitable conductive coupling ring or conducting wire connection. The coupling may be provided at either of the ends of an overlap region defined by overlap of the second coil portion and the second part of the first coil portion.

In one form of the antenna according to the invention, the second coil portion may be adjustable in position relative to the first coil portion whereby the frequency response (e.g. as measured by antenna return loss versus frequency) of the resonant structure is adjustable. The effect of adjusting the relative position is illustrated later. The relative position may be subsequently fixed after it has been optimised, e.g. by measuring frequency response for various adjusted relative positions.

In the antenna according to the invention, the first coil portion and the second coil portion may have a region of mutual overlap wherein the lateral separation (measured perpendicular to the axis of the first coil portion) of the first coil portion (in its second part) and the second coil portion is substantially constant along the region of overlap.

However, in a particular form of the antenna according to the invention, the second portion may have a variable distance of separation from the first coil portion (in its second part). The distance of separation may increase with distance from the coupling between the first coil portion and the second coil portion. In this case, the second coil portion may for example have a frusto-conical shaped envelope.

In the antenna according to the invention, the second coil portion and the second part of the first coil portion are mutually designed and arranged so that the instantaneous magnetic flux provided by each is mutually cancelling. When such cancellation occurs, the inductive effect of the two is minimised and the second coil portion behaves essentially as a capacitive top load portion. The mutual coupling is preferably controlled so that transformer elects are minimized, e.g. the return loss of the antenna obtained is less than -8dB.

The antenna according to the invention may include a further portion for connection to a conductor of the radio device. The further portion may for example comprise an elongate portion, for example a conductive linear stub portion or a coaxial cable portion. The elongate portion may have an axis which substantially co-incides with or is parallel to the axis of the first coil portion.

In another preferred form of the antenna according to the invention, the coil of the first coil portion may have a varying helical or spiral pitch. The first coil portion may include for example at least a first section having a first helical pitch and a second section having a second helical pitch. The first and second sections may be the same as the first and second parts of the first coil portion referred to earlier.

Alternatively, the second section may start at a different location on the coil from the second part of the coil, i.e. the part inside the second top load portion. For example, the second section may start in a position which is in the first part of the coil portion outside the second top load portion. Alternatively, the pitch may vary continuously in at least a part of the l first coil portion. In any case, the pitch may be longer at an end thereof nearer a conductor of the radio device and shorter where further from the conductor of the radio device.

Beneficially and surprisingly, a very wideband and satisfactory performance is provided by the antenna according to the invention yet the overall shape and size, or form factor, of the antenna does not have to be significantly greater than that of known single frequency antenna for use in a mobile station. The antenna is therefore suitable for use in a mobile station for use in radio communications, particularly where wideband performance is needed, e.g. to provide operation at two different frequencies in a given range. An antenna embodying the invention may for example provide a bandwidth which encompasses resonance components at 380MHz and 430MHz, thereby providing a compact and suitably efficient structure for operation in multiple TETRA frequency ranges.

A particular benefit of the antenna according to the invention is its simplicity of manufacture using readily available components. This is a significant benefit compared to previous antenna configurations aimed at the same functionality.

Another major improvement over previous antenna configurations, is that one set of tooling can be used to accommodate manufacture of antennas for use in different frequency ranges. This benefit can be used to eliminate significant costs associated with antenna manufacture.

According to the present invention in a second aspect there is provided a mobile station for use in radio communications which includes the novel antenna according to the first aspect of the invention. The mobile station may comprise a radio, radio telephone, data communication device or the like. The mobile station may have, apart from the antenna, a known construction and operation per se. For example it may include a RF transceiver, signal processing capability, a user dispay, a user operation interface and a source of electrical energy such as a battery. A typical mobile station arrangement is described fro example in [example to be added].

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

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. l is a side view mainly in cross-section of an antenna embodying the invention.

FIG. 2 is a side view mainly in cross-section of an alternative antenna embodying the invention.

FIG. 3 is a side view of an alternative coil for use in an antenna embodying the invention.

FIG. 4 is a side view of an alternative coil for use in an antenna embodying the invention.

FIG. 5 is a side view of an alternative coil for use in an antenna embodying the invention.

FIG.s 6 to 9 are diagrammatic representations of stages in the construction of an antenna embodying the invention, a corresponding frequency response graph being shown in each FIG. for each stage.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

As shown in Figure 1, an antenna 100 embodying the invention for use in a mobile station (not shown) has a longitudinally extending axis 102 and comprises a first conducting coil portion 103 and a second conducting coil portion 105. The antenna 100 is connected at its inner end (the left hand end as shown) to a RF signal conductor 104 connected to a RF transceiver of the mobile station (not shown). The conductor 104 is the inner conductor of a stub having a coaxial insulating sleeve 107 which is formed integrally with an end plate of a case of the antenna. The first and second coil portions 103, 105 may be made of a copper based material or other efficiently conducting material well known and used in the art. The antenna 100 is enclosed in a conventional manner in an insulating case, e.g. made of a moulded plastics material. The case is not shown in FIG. 1 but its outer envelope is indicated by a dashed line 109. The case is conventional and provides mechanical and environmental protection of the antenna 100. The case has an end plate 110 between the sleeve 107 and the first coil portion 103. The end plate 110 in use abuts against the body (not shown) of a mobile station.

The second coil portion 105 has a greater outer diameter (coil loop size) than the first coil portion 103 and the first coil portion 103 extends inside the second coil portion 105. The first coil portion 103 and the second coil portion 105 having windings which have an opposite winding sense (i.e. one is progressing like a right hand screw thread whilst the other is progressing like a left hand screw thread) so that the instantaneous magnetic flux due to current flowing in the first coil portion 103 and due to current flowing in the second coil portion 105 is mutually cancelling.

The first coil portion 103 is connected to the second coil portion 105 by a conducting coupling ring 111 at the inner end of the second portion 105 (the coupling ring could alternatively be at the outer end of the first coil portion 103). The coupling ring 111 provides galvanic connection between the first coil portion 103 and the second coil portion 105.

The coupling ring 111 thereby divides the first coil portion into a first part into a first part 119 nearer the sleeve 107 and a second part 121 further from the sleeve 107. The second part 121 of the first coil portion 103 extends along the axis 102 inside the second coil portion 105, although an outer end of the second coil portion 105 extends beyond an outer end of the second part 121.

In operation, the antenna 100 exhibits (at least) two RF electrical resonances. A first resonance is produced by the combined structure of (i) the conductor 104 and the conducting parts of the mobile station to which it is connected together with: (ii) the first part 119 of the first coil portion 103; and (iii) the second coil portion 105. A second resonance is produced by the combined structure of (i) the conductor 104 and the conducting parts of the mobile station to which it is connected together with: (ii) the first part 119 of the first coil portion 103 and the second part 121 of the first coil portion 103. The individual resonance frequencies can be measured separately, although in practice it is possible to plot an overall frequency response curve in which both resonances may be observed. If the second coil portion 105 is adjustable in lengthwise position, it is possible by moving the second coil portion 105 (e.g. by moving the position of the coupling ring 111) to determine which one of the two resonances is due to the structure including the second portion 105. Thus, the antenna 100 is a superposition or composite of two antennas, one including the second coil portion 105 and the other including the second part 121 of the fist coil portion 103, the other components of the two antennas being common.

FIG. 2 shows an alternative antenna 200 embodying the invention. Components of the antenna 200 which are the same as those of the antenna 100 of FIG. 1 are indicated by the same reference numerals. In the antenna 200, the second coil portion 105 is replaced by a further coil portion 205 which has an outer coil diameter less than that of the first coil portion 103. The further coil portion 205 extends inside the first coil portion 103. The first coil portion 103 and the further coil portion 205 are galvanically connected by a coupling ring 211 at the inner end of the further coil portion 205. The coupling ring 211 thereby divides the first coil portion 103 into the first part 119 nearer the sleeve 107 and the second part 121 further from the sleeve 107. The coupling ring could alternatively be at the outer end of the first coil portion 103.

The first coil portion 103 and the further coil portion 205 in the antenna 200 of FIG. 2 having windings which have an opposite winding sense so that the instantaneous magnetic flux due to current flowing in the first coil portion 103 and due to current flowing in the further coil portion 205 is mutually cancelling.

The antenna 200 functions in a manner similar to the antenna 100 of FIG. 1. Thus, a first resonance is produced by the combined structure of (1) the conductor 104 and the conducting parts of the mobile station to which it is connected together with: (ii) the first part 119 of the first coil portion 103; and (iii) the further coil portion 205. A second resonance is produced by the combined structure of (i) the conductor 104 and the conducting parts of the mobile station to which it is connected together with: (ii) the first part 119 of the first coil portion 103 and the second part 121 of the first coil portion 103.

The shape and the proximity of (i) the second portion 105 to the second part 121 of the first portion 103 of the antenna 100 in FIG. 1; and of (ii) the further portion 205 to the second part 121 of the first portion 103 of the antenna 100 in FIG. 2; is important in determining the overall frequency response of the antenna 100 and the antenna 200. The proper optimization of the load provided by the second coil portion 105 or further coil portion 205 is easy to estimate empirically: the smaller the residual inductance and the greater the top loading length provided by each of these portions the better, and a better resonance Q factor will be achieved. (Q factor is a measure of inverse of resonance width: a low Q factor, e.g. 4 indicates a wide resonance curve). However, in practice the optimization is not so simple. The overall length of the antenna which is usually limited by space and size design constraints within the mobile station is limited.

Nevertheless, for an antenna having an overall length of about 5cm (a typical acceptable upper limit of overall antenna length), a top load provided by the second coil portion 105 of the form illustrated in FIG. 1, or a top load provided by the further coil portion 205 of the form illustrated in FIG. 2, the top load having a length of about 2.5cm, provides a very suitable compromise.

In practice, two location points on the frequency response curve can be found which give optimum Q factor, i.e. maximum local bandwidth, such that deviation from the selected location point reduces the bandwidth. These points can be found experimentally by adjusting for the antenna the second coil portion 105 in position lengthwise relative to the first portion 103 (i.e. by adjusting the position of the coupling ring 111). Similarly, these points can be found experimentally by adjusting for the antenna 200 the further coil portion 205 in position lengthwise relative to the first portion 103 (i.e. by adjusting the position of the coupling ring 211). These two location points in each case are related to the impedance of the antenna. One point shows a simple wide resonance and is found at a frequency lower than the main coil resonance frequency, and the other with distinct dual resonance features (due to conjugate impedance coupling) and a wider resonance bandwidth is found at a higher frequency. Both optimum points can be used in practice.

The dual frequency antenna model which has been described can provide a bandwidth which is typically two to three times that of a standard coil antenna which typically has a bandwidth of about 20-25MHz at 400MHz. Furthermore the bandwidth obtained can be substantially greater than, e.g. up to 40-50MHz greater than, the bandwidth of an antenna of comparable dimensions of the form described in GB-B-2380323. However, even better results are possible with antennas embodying the invention if the loading provided by the top load coil portion and/or the distance of separation between the top load portion (e.g. second portion 105 in FIG. 1) and the part of the main coil portion inside (e.g. second part 121 of first coil portion 103) or outside it is varied along the length of the top load portion. This is because the effect can be to provide a more beneficial distributed loading rather than a locally concentrated loading. An example including such a variation is shown diagrammatically in FIG. 3. In FIG. 3, a coil 305 is shown. This has a tapered or frusto-conical shaped envelope. The coil 305 is for use in a variation of the antenna 100 of FIG. 1. In this variation the second coil 105 of FIG. 1 is replaced by the coil 305. The coil 305 is connected to the coil 103 by a galvanic coupling provided by a connection ring similar to the ring 111. This coupling is made for example at the end of the coil 305 at which the coil 305 has its smallest outer diameter (left hand end as shown in FIG. 3).

In a further embodiment illustrated diagrammatically in FIG. 4, a coil 401 is shown. The coil 401 is for use in a further variation of the antenna 100 of FIG. 1. In this further variation, the first coil portion 103 of FIG. 1 is replaced by the coil 401. The coil 401 is connected to a coil portion (not shown) similar to the second coil portion by a galvanic coupling provided by a connection ring 402 similar to the ring 111 in FIG. 1. The coil 401 has two selected pitch sections 404 and 405 respectively. In the first section 404 the coil has a long pitch. In the second section 405 which begins at the connection 402, the coil has a short pitch. The first section 404 and the second section 405 correspond respectively with the first and second parts 119, 121 of the first coil portion 103 referred to earlier.

In a further embodiment illustrated diagrammatically in FIG. 5, a further coil 501 is shown. The coil 501 is for use in a yet further variation of the antenna 100 of FIG. 1. In this yet further variation, the first coil portion 103 of FIG. 1 is replaced by the coil 501. The coil 501 is connected to a coil portion (not shown) similar to the second coil portion 105 by a galvanic coupling provided by a connection ring 502 similar to the ring 111 in FIG. 1.

The coil 501 has two selected pitch sections 504 and 505 respectively. In the first section 504 the coil has a long pitch. In the second section 505 which begins at a position 508 indicated by a dashed line the coil 501 has a short pitch. In contrast to FIG. 9, the position 508 where the pitch changes is different from the position of the connecting ring 502 In a practical example of an antenna including the coil 401 and an antenna including the coil 501, the two pitch coil had an outside diameter of 6.5mm, the long pitch section of the coil had a length of 20mm and a pitch of 4mm and the short pitch section of the coil had a length of 14.4mm and a pitch of 1.2mm. The top loading larger coil had a length of 25mm. Such an antenna gave suitable operational performance across the range 370-450MHz, e.g. it was suitable for use in multiple TETRA systems.

In the above embodiments, the effective lengths of the two coils, namely the base coil and top load coil are proportional to approximately one half wavelength and are chosen to resonate at the two main required frequencies, for instance 380 and 430 MHz.

FIG.s 6 to 9 illustrate in diagrammatic form stages in the construction and performance of an antenna similar to the antenna 200 of FIG. 2.

In FIG. 6, a first main coil portion 600 only is present. This gives a resonance 601, seen in the graph on the right side of FIG. 6 as a sharp drop in return loss.

The resonance 601 is at a frequency well above a required operational frequency range indicated as 603.

In FIG. 7, a further coil portion 605 to act as a top load portion is introduced. However, a galvanic connection between the coil portions 600 and 605, indicated as 701, is near the ends of the coil portions 600 and 605. In practice, the galvanic connection may be provided by a short conducting connection wire. The combination of the coil portions 600 and 605 gives a resonance 703 seen in the graph on the right side of FIG. 7. The resonance 703 is at a frequency below the required operational frequency range 603. A residual low energy resonance 705 is also seen at the high frequency end of the graph.

FIG. 8 shows the further coil portion 605 inserted further into the coil portion 600, and connected to it at a galvanic connection 801. A lower frequency resonance 803 indicated in the graph on the right side of FIG. 8 is provided by the combination of the two coil portions and a higher frequency resonance 805 is also obtained. Compared with the resonances 703, 705 in FIG. 7, the resonances 803, 805 are closer together but still outside the required range 603.

Finally, as shown in FIG. 9, the further coil portion 605 is inserted a sufficient distance into the coil portion 103, and connected to it at a galvanic connection 901. As seen in the graph on the right side of FIG. 9, a composite l resonance 903 is obtained by merging of the higher frequency and lower frequency resonance components (e.g. as seen in FIG.s 7 and 8). By correct engineering design, the composite resonance 903 can easily be obtained to include the required frequency range 603, for instance a range including TETRA multi- band operation at 380 MHz to 430 MHz.

Claims

1. An antenna for use in a radio communication device including a first portion which is a first conductive helical or spiral coil portion extending along an axis and, electrically coupled to the first portion, a second portion which is a conductive top load portion, the first portion and the second portion being mutually arranged to provide an electrically resonant structure, wherein the second portion comprises a second conducting helical or spiral portion which extends along or parallel to the axis in a configuration in which in use the instant magnetic flux provided in operation by the coil portions is mutually cancelling.

2. An antenna according to claim l wherein one of the coil portions extends for part of its length coaxially inside the other coil portion.

3. An antenna according to claim 2 wherein the first coil portion has a first part and a second part and at least part of the second coil portion extends inside the second part but not the first part of the first coil portion.

4. An antenna according to claim 2 wherein the first coil portion has a first part and a second part and at least part of the second coil portion extends outside the second part but not the first part of the first coil portion.

5. An antenna according to any one preceding claim wherein the antenna provides in operation multiple electrical resonance components.

6. An antenna according to claim 5 wherein the multiple resonance components are parts of a composite resonance structure.

7. An antenna according to any one of claims 3 to 6 wherein the the antenna provides in operation multiple electrical resonance components and the first and second parts of the first coil portion contribute to one of the resonance components and the first part of the first coil portion and the second coil portion contribute to another of the resonance components.

8. An antenna according to any one of the preceding claims wherein the electrical coupling between the first coil portion and the second coil portion is non-galvanic.

9. An antenna according to any one of the preceding claims wherein the electrical coupling between the first coil portion and the second coil portion is a galvanic connection.

10. An antenna according to any one preceding claims wherein the second coil portion is adjustable in position relative to the first coil portion whereby the frequency response may be adjusted.

11. An antenna according to any one preceding claim wherein the relative position between the first coil portion and the second coil portion has been fixed after it has been optimised.

12. An antenna according to any one preceding claim wherein the first coil portion and the second coil portion are coaxial and have a region of mutual overlap wherein the lateral separation, measured perpendicular to the axis of the coil portions, of the first coil portion and the second coil portion is substantially constant along the region of overlap.

13. An antenna according to any one of claims 1 to 11 wherein the first coil portion and the second coil portion are coaxial and have a region of mutual overlap wherein the lateral separation, measured perpendicular to the axis of the coil portions, of the first coil portion and the second coil portion varies along the region of overlap.

14. An antenna according to claim 13 wherein the distance of separation between the first coil portion and the second coil portion increases with distance from the coupling between the first coil portion and the second coil portion.

15. An antenna according to any one preceding claim which includes a further portion which comprises an elongate conducting portion for connection to a conductor of a radio communication device.

16. An antenna according to claim 15 wherein the further portion is coaxial with the first coil portion.

17. An antenna according to any one preceding claim wherein the first coil portion has a varying helical or spiral pitch.

18. An antenna according to claim 17 wherein the first coil portion includes at least a first section having a first helical pitch and a second section having a second helical pitch.

19. An antenna according to claim 18 wherein the first and second sections are joined at a position corresponding to a position of a coupling between the first and second coil portions.

20. An antenna according to claim 18 wherein the first and second sections are joined at a position different from a position of a coupling between the first and second coil portions.

21. An antenna according to claim 17 wherein the pitch of the first coil portion varies continuously in at least a part of the first coil portion.

22. An antenna according to any one of claims 17 to 21 wherein the pitch of the first coil portion is longer at an end thereof nearer a conductor to be connected to a radio device and shorter where further from the conductor to be connected to a radio device.

23. An antenna according to any one of the preceding claims which in operation provides a composite resonance including a bandwidth which encompasses operating frequencies at 380MHz and 430MHz.

24. An antenna according to claim l and substantially as described with reference to any one of claims 1 to 5 of the accompanying drawings.

25. A mobile station for use in radio communications which includes an antenna according to any one of the preceding claims.