GB2355115A

GB2355115A - Coupling a mobile 'phone antenna feed to a remote antenna

Info

Publication number: GB2355115A
Application number: GB9923313A
Authority: GB
Inventors: Moshe Einat; Yaron Hasson; Gadi Shirazi; Moshe Bitran
Original assignee: Motorola Israel Ltd
Current assignee: Motorola Solutions Israel Ltd
Priority date: 1999-10-01
Filing date: 1999-10-01
Publication date: 2001-04-11
Anticipated expiration: 2019-10-01
Also published as: GB9923313D0; GB2355115B

Abstract

A method for coupling electromagnetic radiation from a mobile 'phone to a remote antenna comprises coupling the radiation from the antenna feed 16 of the mobile 'phone to the remote antenna and shielding a major portion of the radiation from the mobile 'phone antenna 17. The shield may be a U-shaped member (Figure 4) or a hollow cylindrical shield (Figure 7) and the coupling to the antenna feed may be via a pin 21 which passes through the mobile 'phone case and which is connected to the external antenna via a matching circuit (51, Figure 5). The method allows a mobile 'phone to be used inside a car having an externally mounted antenna and the shielding of the mobile 'phone antenna ensures good coupling between the mobile 'phone antenna feed and the external antenna by minimising the radiation radiated from the 'phone antenna.

Description

2355115 A Method and Apparatus for Coupling A Radio Device

FIELD OF THE INVENTION

The present invention is in the general field of electromagnetic energy coupling, and in particular it concerns radio antenna applications such as cellular telephones, which require coupling of Radio Frequency (RF) energy from the internal antenna of the telephone to an external device BACKGROUND OF THE INVENTION

In many applications, it is required to couple electromagnetic io energy from an internal antenna of a radio to an external device. A specific known appli cation of electromagnetic coupling is a vehicle adapter for a cellular telephone. As is well known, receiving and transmitting RF energy through the internal antenna of a cellular telephone in a vehicle introduces relatively high losses of the RF signal due to shielding by the metallic body of the vehicle.

It is therefore customary to couple the RF energy via an adapter to an external antenna that is fitted, say, on the vehicle's roof. In contrast to the telephone's internal antenna located in the vehicle, the external antenna can be relatively large, grounded and capable of receiving and transmitting energy to and from the environment with greater efficiency. Consequently, by using an external antenna, the RF signal quality (e.g.

RF power) is substantially improved as compared to the alternative of using the internal antenna.

In order to route the RF energy to the external antenna, it must first be coupled to the vehicle adapterby, by typically, using an RF switch.

The RF switch has inherent limitations. For example, the actual switching involves loss of energy, which naturally reduces the RF signal quality. Moreover, RF switches tend to have relatively large physical dimensions and its incorporation into the telephone enlarges the unit, contrary to the present trend of making the unit as compact as possible.

Another known approach for coupling the energy to an external device is by electromagnetic coupling of the antenna radiation. More specifically, U.S. patent no. 5,668,561 Assigned to Motorola Inc., U.S.A.

discloses so-called "capacitance coupling" for accomplishing the specified energy routing. In accordance with this approach, a metal plate is placed close to the radiating antenna. The plate and antenna together form a capacitor.

The electromagnetic coupling solution has some clear advantages over the RIF switch. For one, it does not involve physical contact with the antenna so that when the telephone unit is not fitted to the vehicle adapter energy losses are reduced. The electromagnetic coupling solution is more reliable and extends the product life span. Lastly, since the capacitance coupling device resides externally to the telephone unit (unlike the RF switch), it does not affect the unit's dimensions.

Notwithstanding this, the electromagnetic coupling has some inherent limitations and in particular it involves losses of at least 2.5 - 5 dB which, in some applications, may be intolerable.

There is accordingly a need in the art to provide for a method and device which facilitate electromagnetic energy coupling with relatively low losses of energy.

SUMMARY OF THE INVENTION

The invention provides for a method for coupling electromagnetic radiation from a radio device to an external device; the radio device including a radiation path coupled to a radio antenna for conveying the electromagnetic radiation to the antenna; the method comprising the steps of: (a) coupling the electromagnetic radiation from the radiation path to the external device; and (b) shielding a major portion of the radiation radiated from the antenna.

The invention further provides for a system for coupling electromagnetic radiation from a radio device to an external device; the radio device including a radiation path coupled to a radio antenna for conveying the electromagnetic radiation to the antenna; the system comprising:

(a) a coupler coupled to said path and to said external device, for coupling the electromagnetic radiation from said path to the external device, and (b) a shield for shielding at least a major portion of the radiation radiated from the antenna.

Still further, the invention provides for a system for coupling electromagnetic radiation from a telephone radio device to a vehicle adapter; the telephone radio device includes a radiation path that is coupled to a radio antenna for conveying the electromagnetic radiation to the antenna radiation path which system comprising:

(a) a coupler that includes an inductive coupling pin coupled to said radiation path and to said external device, for coupling the electromagnetic radiation from said path to the external device, and (b) a shield associated for shielding at least a major portion of the radiation radiated from the antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of nonlimiting example only, with reference to the accompanying drawings, in which:

Fig. 1 illustrates schematically an antenna fitted to a cellular telephone unit.

Fig. 2 illustrates schematically an antenna coupler in accordance with the invention for coupling electromagnetic energy form the telephone io to the vehicle adapter.

Fig. 3 illustrates schematically a radiation shield member in accordance with one embodiment of the invention.

Fig. 4 illustrates schematically the radiation shield member of Fig. 3, applied to the antenna of the cellular telephone unit.

Fig. 5 illustrates schematically a generalized tuning net circuitry for matching impedance between the telephone unit and the vehicle adapter.

Fig. 6 illustrates schematically a radiation shield member applied to the telephone unit in accordance with another embodiment of the invention; and Fig. 7 illustrates schematically a radiation shield member applied to the telephone unit in accordance with yet another embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

For convenience of explanation, the invention is described for the specific embodiment of a cellular telephone unit, vehicle adapter, and RF range utilised in cellular telephony. Those versed in the art will readily appreciate that the invention is, likewise, applicable to other radio devices and/or other external devices, and/or other ranges of electromagnetic radiation.

Bearing this in mind, attention is first directed to Fig. 1 illustrating schematically a radio antenna (17) fitted to a cellular telephone unit (10) operating at, say, about 400 MHz. The invention is not bound to this operational range. The cellular telephone unit (10) includes a case (111) accommodating a printed circuit board (PCB) (12), bearing the electronic circuitry of the unit, and a battery (113) serving as the power source of the lo unit.

The telephone unit (10) further accommodates a radiation path often called a hot section (14) that conducts the electromagnetic radiation from the PCB to the antenna. By the specific embodiment of Fig. 1 the hot section includes a hot line (15) connected at the one end thereof to the PC13 (12) and at the second end thereof to an antenna receiving socket (16), which is capable of snuggly receiving the antenna (17). By the specific example of Fig. 1 the antenna is threaded to the receiving socket (16).

In accordance with a preferred embodiment (see Fig. 2), a coupling member (being by this example a conductive thin pin (21)) passes through (18) (see Fig. 1). the plastic casing of the cellular unit so as to contact the antenna receiving socket (18), which, as recalled, constitutes part of the hot section that conducts electromagnetic radiation to the antenna. The pin (21) is also coupled to a circuitry (not shown in Fig. 2) in the vehicle adapter-designated generally as (22). The invention is not confined to any specific manner of coupling the coupling member to the hot section and likewise not to any specific coupling member. Additionally, the coupling member may be fixedly attached to either the hot section or to the vehicle adapter, all as required and appropriate depending upon the particular application.

In operation, when the cellular telephone is placed in the vehicle adapter (see Fig. 2), the pin (21) contacts the receiving socket (16). As a result, some of the energy that would otherwise be conveyed to the antenna is now coupled to the adapter through the pin. This connection by itself is incapable of directing most of the energy to the external device, because the antenna (17) is still operative, so that only a portion of the energy will actually be directed to the external device.

There is accordingly a need to shield substantially a major portion of the energy radiated from the antenna and thereby assure that the major lo portion of the electromagnetic energy will be coupled to the external device (and therefrom to the external antenna in a known per se manner).

To this end, a conductive shield e.g. a shield member formed in a "U" shape (see 30 in Fig. 3) is employed. The shield member (30) is preferably shorted to ground (not shown) and due to its conductivity and placement (see Fig. 4), it shields the radiation from the antenna. By the specific example of Fig. 4 the shield surrounds major portion of the antenna on three sides and has the following dimensions: length 40mm, width 20 mm and height 20 mm. By the specific example of Fig. 4, for antenna of 10 mm diameter and 50 mm length, the distance between the antenna and the side walls of the shield member is 5 mm, respectively.

In order to radiate, the antenna (17) has to develop currents that create an electric field around it. In the presence of the shield (30) this field does not develop and the internal antenna does not radiate. Consequently, a significant portion of the energy is coupled through the pin (21) to a tuning net (designated generally as 51 in Fig. 5) which matches the impedance of the telephone unit to that of the vehicle adapter, all as known per se. The coupled energy is now directed (52) to the designated destination, e. g. an antenna fitted on the vehicle's roof (not shown).

Figs. 6 and 7 illustrate another two non-limiting examples of shield members (U-Iike shape member (60) and hollow cylinder member (70), respectively). The structure, size and operational specification of the shield (e.g. placement vis-a-vis the antenna) may vary depending upon the particular application. In particular, the specific structure and use of the shield is not bound to the members shown in Figs 3,4,6 and 7.

In accordance with the invention the coupling is done without a connector or switch and therefore the inherent drawbacks associated therewith are avoided.

In one embodiment, the signal loss in the presence of a shield in accordance with the invention was determined experimentally better than 1 dB over a 60 MHz bandwidth at operating frequency of 420 MHz, so it is superior to prior art coupling devices.

The present invention has been described with a certain degree of particularity, but those versed in the art will readily appreciate that various alterations and modifications may be carried out without departing from the scope of the following claims:

Claims

CLAIMS:

A method for coupling electromagnetic radiation from a radio device to an external device; the radio device includes a radiation path coupled to a radio antenna for conveying the electromagnetic radiation to the antenna; the method comprising the steps of:

(a) coupling the electromagnetic radiation from the radiation path to the external device; and (b) shielding a major portion of the radiation radiated from the antenna.

lo
2. The method according to Claim 1, wherein said electromagnetic radiation is in the radio-frequency (RF) range.
3. The method ac cording to Claim 1 or 2, wherein said radio device is a cellular telephone.
4. The method according to claim 3, wherein said external device is a vehicle adapter.
5. A system for coupling electromagnetic radiation from a radio device to an external device; the radio device includes radiation path coupled to a radio antenna for conveying the electromagnetic radiation to the antenna; the system comprising: (a) a coupler coupled to said radiation path and to said external device, for coupling the electromagnetic radiation from said radiation path to the external device, and (b) a shield associated with said external device, for shielding at least a major portion of the radiation radiated from the antenna.
6. The system according to Claim 5, wherein said electromagnetic -9radiation is in the radio-frequency (RF) range.
7. The system according to Claims 5 or 6, wherein said radio device is a cellular telephone.
8. The system according to Claim 7, wherein said external device is a vehicle adapter.
9. For use in a system according to anyone of Claims 5 to 8, a radio io and a coupler fixedly attached thereto.
10. For use in a system according to anyone of Claims 5 to 8, an external device and a coupler fixedly attached thereto.
11. A system for coupling electromagnetic radiation from a telephone radio device to a vehicle adapter; the telephone radio device includes a radiation path that is coupled to a radio antenna for conveying the electromagnetic radiation to the antenna; the system comprising: (a) a coupler that includes an inductive coupling pin coupled to said radiation path and to said external device, for coupling the electromagnetic radiation from said radiation path to the external device, and (b) a shield associated with said external device, for shielding at least major portion of the radiation radiated from the antenna.
12. The system according to Claim 11, wherein said shield is a longitudinal member having a U shaped lateral cross section; the shield surrounding said antenna from three directions.
13. The system according to Claim 11, wherein said shield being a longitudinal member having a U-like shaped lateral cross section; the shield surrounding said antenna from three directions.
14. The system according to Claim 11, wherein said shield being a cylindrical shield member surrounding at least a major portion of said antenna.