HK1025696B - Radio telephone with separate antenna for stand-by mode - Google Patents

Description

Radio telephone with independent antenna for backup mode

Technical Field

The invention relates to a radio telephone for wireless telecommunication, comprising a transmitter/receiver unit, a control unit, a first antenna, the characteristics of which are optimized for use in a backup mode, and a second antenna, the characteristics of which are optimized for use in an ongoing call, said second antenna being electrically engageable and disengageable with the transmitter/receiver unit. The invention also relates to a method of controlling the establishment of incoming and outgoing calls in such a radio telephone.

Background

Wireless telecommunications is now at least as common as the more conventional wired form of telecommunications. In almost every country, more and more people use wireless, and in particular cellular, telephones in everyday life. The term "radio telephone" includes all portable devices that can be used for wireless communication, i.e. cellular telephones, so-called personal communicators or organizers or the like. Predictions for the future also indicate that such phones are used even more frequently, and that wireless telecommunication systems will become more popular than wired systems in the near future.

In mobile telephone systems, or so-called cellular telephone systems, public or commercial telephone companies provide a large number of geographically distributed base stations. Each base station is arranged to cover a specific area, a so-called cell, and the areas are selected in such a way that they together cover as wide a continuous geographical area as possible. The base stations are designed to forward incoming and outgoing calls to and from mobile stations, such as wireless or mobile telephones, present in the area, and from there each base station is connected to a public wired communication network. Mobile stations in modern telecommunication systems, such as GSM (global system for mobile services), have two main modes of operation, the first of which is to talk between the mobile station in question and a base station in high-density communication. The second mode of operation is a standby mode, i.e., when the mobile station is not providing any ongoing call, but some communication with the base station is still ongoing normally. For example, when a user turns on his mobile station, the mobile station will search for available base stations and select the one with the highest signal strength. The mobile station then reports his presence to the selected base station. The mobile station then receives information, such as frequency synchronization information, normally from the base station. A handover to the latter typically occurs if the signal strength appears to be lower than that of any other available base station (so-called handover). In addition, two-way so-called handshake communication occurs between the mobile station and the base station, when an incoming call is to be established. By means of the above it is possible to provide services like roaming (system detects and keeps subscriber records at moment of border crossing), SMS (short message service; transmission of short text messages is shown on the phone display), and CB (cell broadcast; i.e. broadcasting messages from public authorities to several mobile phones present in a cell).

Other kinds of wireless telecommunications are known which are not connected to a public wired telephone network. One example is dispatch applications, i.e. non-public wireless systems used by the taxi industry, police authorities or transportation companies. Another example is a local or global paging system, and yet another example is a cordless telephone system such as DECT (digital european cordless telephone system).

For the above-described wireless transmission of voice or data in a communication system, a transmitter and a receiver of electro-magnetic energy are required. Information is processed electronically in both the transmitter and receiver, whether in analog or digital systems. Both the transmitter and the receiver are connected to a conversion means, such as an antenna, for converting between electrical and electro-magnetic energy. Wireless information transmission is achieved by generating a radio frequency electromagnetic field around a transmitter antenna and propagating outward from the antenna and then at the speed of light to a receiver antenna.

As the antennas are heavily used during the talk and back-up modes, various requirements are placed on mobile station antennas in modern mobile telephone systems, as described above. The economic and cost effective requirements are obvious. Another common requirement is a long operating time between battery charges and the mobile station must reserve a large amount of available power to meet this requirement, thereby requiring a high antenna conversion efficiency. Generally, antenna and signal quality requirements are more stringent during ongoing calls than during backup mode.

In addition, the physical size of the mobile phone is very important. Mobile phones, which today users find useful, require a low weight, compact and rugged model; the mobile phone is preferably adapted to be placed in a jacket inner pocket, a handbag or the like, or possibly to be clipped onto a belt with a belt. The requirements for compactness and robustness also apply significantly to mobile phone antennas.

The mobile phone is generally placed in close proximity to the user during a call and, as a result, the user's hand and, in particular, head will inevitably affect the signal characteristics of the antenna. The interaction between the body and the antenna near field usually causes the antenna characteristics to deteriorate, mainly due to reflection and absorption losses. In particular, if the distance between the antenna and the body is reduced, the signal attenuation increases, and it is obviously difficult to achieve both high antenna efficiency and physical compactness and robustness.

Various antenna types are used today on mobile phones, such as half-wavelength or quarter-wavelength whip antennas, dipole antennas, helical antennas, etc. Different antenna types are suitable for different ranges when considering signal characteristics and antenna efficiency. For example, a helical antenna is often used because its helical shape can give a compact size and good resistance to damage. However, the helical antenna cannot exhibit as good antenna efficiency as a half-wave antenna.

Due to space considerations mobile phones are often also equipped with extendable whips, which in some cases are supplemented by a separate external antenna for the backup mode, since the whip is completely retracted into the metal phone housing, isolating its transmitted signal from the surroundings. International patent publication WO9301659 to Motorola discloses a radiotelephone having an antenna that is movable between retracted and extended positions. The phone has two modes of operation depending on whether the antenna is extended or not. These modes of operation may be associated with, for example, different levels of display illumination or non-illumination, keypad engagement or disengagement, or emission effects.

Summary of The Invention

The object of the present invention is to optimize the design of a mobile station antenna with respect to the above requirements and problems. It is an object of the invention, inter alia, to provide an antenna system with high performance during ongoing calls and in a backup mode. This object is achieved by using two different antennas, the first antenna having a small and compact form resistant to external mechanical stress and being used in a backup mode for the mobile station, and the second antenna being a longer antenna often used only during a conversation and having the property of physical length and position that produces insignificant signal attenuation and high antenna efficiency. In addition, the second antenna is preferably completely or partly retracted into the phone housing or folded against the housing side in other situations during periods when no call is in progress, and measures are taken according to the invention to prevent the use of the first antenna, which is often used for the backup mode, during a call.

Brief description of the drawings

The invention will be described in more detail below with reference to the accompanying drawings, in which

Fig. 1 is a schematic diagram of a radiotelephone, in which the present invention is used,

figure 2 is a block diagram of the transmitter/receiver unit of figure 1,

figures 3 and 4 are cross-sectional views of a preferred embodiment of the antenna of figure 1,

figure 5 is an equivalent circuit diagram of the components of figures 3 and 4,

fig. 6a is a front view of a radiotelephone with a front or cover open, illustrating an antenna arrangement according to a modified embodiment of the invention,

figure 6b shows the same radiotelephone with the front cover folded,

figure 6c is a cross-sectional view of the radiotelephone according to figure 6a,

fig. 7a is a front view of a radiotelephone with the front cover open, illustrating an antenna arrangement according to a second modified embodiment of the invention,

figure 7b shows the same radiotelephone with the front cover folded,

figure 7c is a cross-sectional view of the radiotelephone according to figure 7a,

fig. 8a is a front view of a radiotelephone with an open front cover, illustrating an antenna arrangement according to a second modified embodiment of the invention,

fig. 8b is a cross-sectional view of the radiotelephone according to fig. 8 a.

In fig. 1a radio telephone functioning as a mobile station is shown, in which an antenna system according to the invention is applied. The disclosed mobile phone is of the type used in modern telephone systems, such as GSM or NMT, for example, and not by way of limitation. The telephone includes a housing 6, a small antenna 1, a large antenna 2, an antenna switch 3, a transmitter/receiver unit 4, a control unit 5, and various devices and apparatuses not shown, such as a keypad, a display, a battery, an earphone, a microphone, and the like.

The small antenna 1 is often used in a backup mode for mobile phones, i.e. when no user controlled communication takes place, and the small antenna 1 therefore has a compact form suitable for this purpose. The antenna 1, which will be referred to as backup antenna in the following, preferably has a substantially short physical length compared to its electrical length, which may be achieved in connection with winding an electrical conductor into a spiral. The performance requirements of the antenna 1 are not as strict as those set forth for the antenna 2, since the antenna 1 is only used in a backup mode. For the most compact, the antenna 1 is preferably of the quarter-wave type.

The large antenna 2 is often used during a call and is therefore referred to as a call antenna in the following. The properties of the antenna make it well suited for its purpose. It has a physical length and/or position such that the influence on the signal characteristics from the user's body is small or even negligible, thereby helping to optimize the antenna efficiency. The talking antenna is preferably a half-wave antenna.

By controlling the mode of operation of the mobile station as described above, it can be ensured that the antenna most suitable for each mode of operation (backup mode and talk mode, respectively) is used.

The control unit is preferably implemented by a microprocessor and associated software programs, even though the functions described below may be performed in hardware in many different ways, for example via a digital switching network, as is readily implemented by a person skilled in the art of digital switching. To minimize costs, it is preferable to use the same Central Processing Unit (CPU) that controls the main operation of the mobile station, or any other co-processor that is already used in conventional mobile stations.

A block diagram of the transmitter/receiver unit 4 is shown in fig. 2. The transmitter/receiver unit is of substantially conventional design and therefore its operation will only be described briefly below. In the transmit mode, information is transmitted, i.e. a baseband signal 41 ("TX" baseband) arrives in digital or analog form from the control unit 5 to the modulator 42. Where the baseband signal 41 modulates an intermediate frequency signal from a transmitter local oscillator 43 and subsequently receives a clock signal from a clock circuit 44. The modulated intermediate frequency signal is then mixed in a mixer 46 by a carrier generated by a synthesizer 46. The obtained high frequency signal is amplified and filtered in an amplifier 47 and a filter 48, respectively, and then transmitted to the antenna currently selected by the antenna switch 3.

The signal received by the antenna in the receive mode is supplied to a filter 50 and an amplifier 51 for filtering and amplification. The high frequency signal is down-converted to an intermediate frequency in mixer 52 by the signal from synthesizer 45. And then filtered and amplified again in the filter 53 and the amplifier 54, respectively, and then demodulated by an intermediate frequency signal from the receiver local oscillator 56 in the demodulator 55. The resulting baseband signal 57 ("RX" baseband) may then be decoded or signal processed in circuitry not shown in a well-known manner.

Fig. 3 and 4 are cross-sectional views of preferred embodiments of the two antennas of fig. 1. The small antenna 1 in fig. 1 is implemented by a helical antenna 11a intended for the mobile station backup mode, whereas the large antenna 2 in fig. 1 is implemented by a whip antenna 10a of the half-wave type. Both antennas are mounted on the phone housing 6. The antenna 10a is also retractable into the housing, as described below. The spiral antenna 11a is surrounded by a dielectric material 11b, which provides robustness and protection against mechanical stress, which is particularly important in a backup manner, since mobile stations are often carried in pockets, bags or the like. Whip antenna 10a is disposed in cavity 11d of dielectric material 11 b. The whip antenna shown in fig. 3 is fully deployed and electrically connected to a coaxial cable 34 through an impedance matching network using a metal reed 32. The other end of the coaxial cable 34 is electrically connected to the transmitter/receiver unit 4 according to fig. 1 and 2.

The impedance matching network comprising the coil 20, the metal tube 21, the dielectric body 15 and the two ring connectors 16 and 22 is vertically displaceable between an upper engagement position according to fig. 3 and a lower engagement position according to fig. 4, respectively. In the upper engagement position according to fig. 3, the metal tube 21 is in galvanic contact with the threaded clamp 13 via the flange 24, which clamp is then screwed into the housing 6 of the mobile station, which brings the metal tube 21 to ground potential. In the joined position according to fig. 3, the impedance matching network can be considered as a so-called pi filter for the input impedance 58 (Z) at whip antenna 10a_ANT) And the output impedance 59 (Z) of the transmitter/receiver unit 4_RX/TX) To perform impedance matching therebetween. Generally, the latter is 50 Ω like the impedance of a coaxial cable, and the whip antenna of the end-fed half-wave type antenna has a theoretically infinite impedance but actually has a value of about 200 to 250 Ω. The need for impedance matching in a mobile station when using a half-wave antenna is well known. The known solutions in the past include separate placement of the filter circuits, which takes up space and increases costs.

Fig. 5 schematically shows a pi filter. The inductance 60 corresponds to the coil 20 and the capacitances 61 and 62 correspond to the charge on the coil, which is separated from the grounded metal tube 21 by the dielectric material 15. In addition, the key functions of impedance matched filters are well known to those skilled in the art and therefore will not be described further.

Whip antenna 10a is shown in a fully retracted position in fig. 4. While the impedance matching network is in a lower position and electrically disconnected with the whip antenna. Instead, the helical antenna 11a is electrically connected to the transmitter/receiver unit 4, so that the metal strip 32 is now in contact with the metal tube 21 and not with the connector 22. In this way, the metal tube 21 is no longer in any electrical contact with the clamp 13 and is therefore no longer grounded. In this position the insulating sleeve 14 separates the metal tube 21 from the clamp 13. Instead, the metal tube is in galvanic contact with the loop connector 12, which is then in galvanic contact with the helical antenna 11 a. Unlike whip antenna 10a, helical antenna 11a is not fed through a disconnected impedance matching network, as the helical antenna can be easily designed to any desired input impedance (50 Ω in this example).

A dielectric segment 10c is arranged around the upper end of whip antenna 10a and another dielectric segment 10b is arranged around the lower end of whip antenna 10a in order to avoid mutual coupling between the two antennas. On segment 10c is mounted an antenna head 10d and the antenna head is preferably formed as an integral unit.

The blocking means 10e is positioned at the lower end of the whip antenna in frictional engagement with the loop connector 22 so as to hold the antenna 10a and the impedance matching network in their respective positions in accordance with the above. In addition, flange 24 and antenna head 10d are used to engage clamp 13 and cavity 11c, respectively.

When the user of the mobile station pushes the whip antenna 10a into the phone housing 6, the lower part of the segment 10c thus comes into contact with the loop connector 16, and the impedance matching network thus shifts from its upper position to its lower position, the actual switching from the extended position of the whip antenna to its retracted position is performed. When the user grasps antenna head 10d and deploys whip antenna 10a, preventing means 10e and dielectric segment 10b are thus engaged with loop connectors 22 and 16, respectively, the impedance matching network is transferred from its lower position to its upper position in a corresponding manner.

With the antenna switching design described above, the antenna switch 3 (the function of which is shown in fig. 1 and described in more detail below) is implemented with a minimum of space requirements and a small number of components, by means of an antenna switching design comprising an impedance matching network fully integrated with the actual antenna system.

The antenna switch 3 is adapted to determine the active engagement status of the second antenna 2; 10a-e, i.e. whether the antenna is electrically connected or coupled to the transmitter/receiver unit 4. The term "electrically connected" in this case means any galvanic, capacitive or inductive coupling, or any combination thereof. Thus, according to a preferred embodiment of the invention, the antenna switch 3 is equipped with means, not shown in the figures, for determining the retracted and extended positions, respectively, of the second antenna 2; 10 a-e. The means, which may be selected from various mechanical, electrical or optical switches or sensors known to those skilled in the art, are arranged to provide the control unit 5 with a control signal 7 responsive to the detected antenna position. It is also possible to indirectly determine the electrical engagement of the second antenna by detecting the detachment of the first antenna.

The operation of a mobile station or radiotelephone in accordance with the invention will now be described. Initially, it is assumed that the mobile station is in a backup mode, so that the mobile station is not providing any ongoing calls at the time. Regular communication between the mobile station and the selected base station is via the backup antenna 1; 11a-d, a conversation antenna 2; 10a-e are simultaneously electrically disconnected and fully retracted into the phone housing 6.

When the base station informs the mobile station of an incoming call, the following occurs. The first step control unit 5 checks whether the user takes any action to answer the call, for example by pressing an appropriate key on the keypad (e.g. a "YES" or "OFF-hook" key). If so, the control unit determines whether the call antenna is fully deployed or otherwise ready to provide further call setup. If this is the case, the user is given a message to inform him of these facts. The message may be in visual, audible or perceptible form, or any combination of these forms. The immediate "antenna pull" message is preferably indicated on the display of the mobile phone. In another form, a voice signal may be emitted through a speaker of the mobile phone, or a vibration may be generated in the phone or any portion thereof. As long as the call antenna is not fully deployed or otherwise ready to provide a call, the control unit will disable a given function necessary for the mobile phone to establish a call. These are preferably accomplished by preventing the transmission of data sequences necessary for information exchange with the base station prior to establishing the call. Such precautions are readily available to those skilled in the art, wherein a microprocessor is used, as the action can be performed solely by software. The more "in-line" solution involves simply disconnecting a device such as a microphone or speaker.

As soon as the user releases the above-mentioned prohibition condition by unfolding the call antenna, the above-mentioned call prohibition function is correspondingly ended, and then a call is established in a conventional manner. In case the antenna switch 3 constitutes a separate unit, which is not the case for the preferred antenna system described above, the control unit will provide a control signal to the antenna switch, which then performs the electrical disconnection of the backup antenna 1 and at the same time also the electrical connection of the conversation antenna 2.

The simple form of the series of actions described above is as follows. Once the base station informs the mobile station of the incoming call, the control unit 5 will simply disengage the key "YES" or "OFF-hook" required by the user to answer the call. The user is then notified as described above, without engaging the "YES" or "OFF-hook" keys until the user complies with the request, and the user is then finally able to answer the call.

When the call is completed, the mobile station reverts to the backup mode. Any necessary communication is performed during the backup mode by electrically engaging the antenna at the time. Generally, a user contracts the call antenna after the call is completed, whereby the call antenna is disconnected and the backup antenna is connected, but the user can keep the call antenna connected or engaged as desired, for example, due to a bad signal environment.

When the user enters a telephone number on the keypad in an attempt to establish an outgoing call, for example by pressing the "YES" key, the control unit will detect and notify the user in a similar manner to that described above that the talking antenna must be engaged. Any given functionality necessary to establish a call is disabled from then on in a similar manner as described above. The disablement is not removed until the user does engage the talk antenna, and then a talk can be established as usual.

The preferred embodiments described above are only examples. Different embodiments may depart from the above description within the scope of the invention, as defined by the appended claims. For example, as mentioned before, the control unit functions may be implemented according to different hardware and/or software schemes, which is easily implemented by a person skilled in the art. In addition, other antenna types than those described above may be used as the backup antenna and the talking antenna. The antenna described above is extendable, but it may also be another form of collapsible housing, for example, the antenna may be folded close to the mobile telephone housing when the telephone is not providing a call.

Another form of antenna design according to an embodiment of the present invention is shown in fig. 6 a-c. As usual, the radiotelephone comprises a telephone housing 6, a display 7, a keypad 72, a speaker 73, and a microphone 74, and the radiotelephone additionally comprises a foldable front cover or cover 70 designed to fold up according to fig. 6b when no conversation is provided, thereby flipping the front side of the telephone. When an incoming call is answered, or when a call is initiated, the user releases the front cover 70 about the pivot axis 76 in a conventional manner according to fig. 6 a.

As previously mentioned, the backup antenna 1 is mounted on top of the phone housing 6. The conversation antenna 2, preferably formed of an end-fed half-wave type rotation antenna, is disposed inside the front cover 70 adjacent to one long side thereof. The antenna 2 is rotatably mounted on the same shaft 76 as the bezel 70 and follows the folding up and unfolding of the bezel when the user is using the phone. At the swivel end the antenna 2 is connected to a transmitter/receiver unit 4 by conventional electrical means, such as a coaxial cable.

By the above design, the antenna 2 will be directed downwards and away from the user's head in a direction parallel to the front cover 70 and substantially vertically downwards during a conversation, thereby obtaining a maximum distance to the head. The antenna design according to fig. 6a-c further reduces the interaction between the antenna and the user's body during the ongoing call, together with the measures described above preventing the use of the backup antenna 1, thereby reducing signal attenuation and thus improving antenna efficiency. Otherwise, the radiotelephone functionality is the same as previously described.

Another antenna design is shown in fig. 7a-c, corresponding to the antenna shown in fig. 6, except that a shorter antenna is used as the talking antenna 2. The antenna 2, which is preferably constituted by a helical antenna, is mounted at the bottom of the front cover 70 (as seen in fig. 7) and is connected to other telephone components, for example to the transmitter/receiver unit 4 by means of a coaxial cable 75 placed along one long side of the front cover 70.

The same reference numerals in fig. 7a-c as in fig. 7a-c denote the same parts and are not described in more detail. As can be seen in fig. 7b, the talking antenna 2 extends above the phone when the front cover 70 is in its upper position, but as before, in this case the user is prohibited from using the talking antenna 2.

Another antenna design is shown in fig. 8 a-b. This embodiment is essentially the same as the embodiment shown in fig. 6a-c, except that the front cover does not flip the entire phone when folded up. By virtue of these features, the display 71 is visible to the user even when the front cover 70 is folded up.

It will be obvious to the person skilled in the art that the embodiments in fig. 6-8 can be varied in various ways. For example, the conversation antenna 2 may be placed outside the front cover 70 in another manner or may be inserted into the front cover 70, and it may extend laterally across the front cover 70 instead of along one long side. In addition to being pivotally mounted about axis 76, front cover 70 can be vertically translated between an upper position, in which it covers the main portion of the radiotelephone, and a lower position, in which the radiotelephone is used for speaking. In addition, the front cover 70 is arranged to be pushed a short distance and then pivoted open. In addition, the antenna 2 may be realized by a so-called patch antenna, i.e. a metal sheet preferably having a square shape, mounted for example inside the front cover.

It is also possible within the scope of the invention to keep the backup antenna constantly engaged if the antenna system is designed in such a way that the backup antenna functions as a receiving antenna together with the talking antenna in order to obtain antenna diversity gain in the receiving mode or so-called downlink mode.

Claims (15)

1. A method of controlling the establishment of incoming and outgoing calls in a radio telephone comprising a first antenna (1; 11a-d) for a back-up mode and a second antenna (2; 10a-e) to be used during ongoing calls, characterized by the steps of:

a) determining the location of the second antenna (2; 10a-e) whether it is electrically and/or operatively connected to the transmitter/receiver unit (4) and, if this is not the case, disabling at least one function necessary for the radiotelephone to establish a call,

b) repeating the determination according to a) until the condition in a) is satisfied, and

c) as soon as the condition in a) has been fulfilled, the inhibition according to a) is released, after which the call is established.

2. A method according to claim 1, characterized by the further steps of:

a') notifying the user of the radiotelephone in a visual, audible or tactile manner when the conditions in a) have been met.

3. A method according to claim 2, characterized in that the notification according to a') is given as a text message on the display of the radio telephone.

4. A method according to claim 2, characterized in that the notification according to a') is given as an acoustic signal on the loudspeaker of the radio telephone.

5. A method according to claim 2, characterized in that the notification according to a') is given as a vibration on the radiotelephone or on a part of the radiotelephone.

6. A method according to any preceding claim, characterised in that the functions necessary to set up the call are constituted by data sequences sent from the radiotelephone for handshaking with the radio base station used to conduct the call.

7. A method according to claim 6, characterized in that the functions necessary for establishing a call are disabled by effectively disconnecting at least one key on the keypad of the radio telephone.

8. A method according to claim 6, characterized by the step of detecting the electrical engagement status of the first antenna (11; 11a-d) and using this information in the determination step according to a).

9. A radio telephone for use in radio telecommunications comprising a transmitter/receiver unit (4), a control unit (5), a first antenna (1; 11a-d) for use in a back-up mode, and a second antenna (2; 10a-e) for use during a call, said second antenna being electrically engageable with and disengageable from the transmitter/receiver unit,

characterized by an antenna switch (3) mounted to effectively electrically connect the transmitter/receiver unit (4) with the first antenna (1; 11a-d) or the second antenna (2; 10a-e), said antenna switch providing a control signal (7) to the control unit (5) responsive to an electrical engagement status of at least the second antenna, said control unit being mounted to prevent the establishment of incoming and outgoing calls as long as the second antenna is indicated as electrically disengaged in accordance with said control signal.

10. A radio telephone according to claim 9, characterized in that the first antenna (1; 11a-d) is formed by a helical antenna (11 a-d).

11. A radio telephone according to claim 9 or 10, characterized in that the second antenna (2; 10a-e) is mounted on a surface of a rotatable and/or movable front cover (70) of the radio telephone.

12. A radio telephone according to claim 11, characterized in that the second antenna (2; 10a-e) is mounted such that the antenna is directed away from the radio telephone in substantially the same plane as the front cover (70) when the front cover is opened during a call.

13. A radio telephone according to claim 11, characterized in that the second antenna (2; 10a-e) is formed by an end-fed half-wave antenna mounted in the front cover (70) along its long side.

14. A radio telephone according to claim 9 or 10, characterized in that the second antenna (2; 10a-e) is formed by a whip antenna (10a-e) which is arranged to be extended from the telephone housing (6) during a call and to be retracted into or folded along the telephone housing (6) when no call is provided.

15. A radiotelephone according to claim 14 further comprising an impedance matching network comprising a metal tube (21), a coil (20) mounted in the metal tube, a dielectric material (15) mounted between the coil and the metal tube, and first and second annular connectors (16, 22) respectively connecting first and second ends of the coil;

helical antenna (11a-d) comprising a helical electrical conductor (11a), a substantially cylindrical dielectric body (11b) surrounding the conductor, and a cavity (11c-d) extending along its length arranged centrally in the dielectric body; and

whip antennas (10a-e) mounted in cavities of the helical antennas (11a-d) and respectively deployable from and retractable into the telephone housing (6),

the impedance matching network is configured to have a first position when the whip antenna is deployed, the whip antenna thereby being electrically connected to the transmitter/receiver unit through the first loop connector (16), the coil (20) and the second loop connector (22), and a second position when the whip antenna is collapsed, the helical antenna thereby being electrically connected to the transmitter/receiver unit through the metal tube (21).