WO1995012223A1

WO1995012223A1 - Antenna system

Info

Publication number: WO1995012223A1
Application number: PCT/GB1994/002368
Authority: WO
Inventors: Keith Geoffrey Batey; William Hope; Andrew Budd
Original assignee: Galtronics (U.K.) Limited; Sixtel S.P.A.
Priority date: 1993-10-28
Filing date: 1994-10-28
Publication date: 1995-05-04
Also published as: GB9322200D0

Abstract

An antenna system for facilitating the communication of data between computers (10, 12) which have R.F. or microwave transmitters or receivers (18, 20) is described which consists of external antennae (22, 24) coupled to the R.F. or microwave transmitter/receiver (18, 20) which uses a cable (34) as a former and is adapted to be coupled to an existing cable. The antennae can have a dipole (30, 32) or monopole (48) antenna radiating element(s) and has a flexible screened lead (26) or leads which are conveniently coupled using clip means (36) to an existing computer cable, typically a screened cable (34). This arrangement allows digital data to be simply and reliably transferred between the two computers (10, 12) or other signal handling stations provided with R.F. or microwave transmitter/receiver (18, 20) means by R.F. (radio frequency) or microwave transmission.

Description

ANTENNA SYSTEM

The present invention relates to an antenna system suitable for transferring data between computers and the like, antenna apparatus for use in such a system, and to a method of providing an antenna system for transferring data between computers.

With the increasing use of computers and the multiplicity of different types of computers being used by people at different times, including desktop, laptop, palmtop and pocket computers as well as so called personal communicators, there is a regular and increasing need for transferring data back and forth between such different types of computers using interconnections usually referred ro as "networks". There are a considerable number of different standards used for "wired" interconnection systems and a feature of such system is the necessity for a physical connection between each element on such a network. Interconnecting cables impose severe restrictions on the freedom of movement of the computer user which can be a particular problem with the increasing use of hand held computers for on-site stocking, sales etc. where the user may require to move freely across a large area. It is desirable to provide an antenna structure to provide a radio frequency "link" required for 'wireless' communication systems.

There have previously been used R.F. modems w_hich, when connected to a computer, can send and receive VHF or VHF radio wave data transmissions. These use either conventional external rod antennae which require careful positioning and tend to interfere with use of the apparatus, or internal antennae which are relatively inefficient due to the screening thereof by the modem housing.

There is accordingly a need for an improved, convenient and reliable form of antenna for communicating data between computers.

It is also an object of the present invention to avoid or minimise one or more of the above disadvantages.

This is achieved by using an external antenna coupled to the R.F. or microwave transmitter/receiver which use_ a cable as a former and is adapted to be coupled to an existing cable. The antenna can have a dipole or monopole antenna radiating element(s) and has a flexible screened lead or leads which are conveniently coupled using clip means to an existing computer cable, typically a screened cable.

This arrangement allow- digital data to be simply and reliably transferred between two computers or other signal handling stations provided with R.F. or microwave transmitter/receiver means by R.F. (radio frequency) or microwave transmission.

According to one aspect of the present invention there is provided an antenna system suitable for use between a first signal handling station and a second signal handling station, said signal handling station having an R.F. or microwave transmitter/receiver means, said signal handling station having at least one flexible cable-type means coupled thereto, said antenna system comprising an antenna having a first end coupled to said R.F. or microwave transmitter/receiver, flexible antenna lead means coupled between said first end and an antenna radiating element, said flexible lead means and said antenna radiating element being adapted to be coupled to said cable-type means along its length so that said cable-type means acts substantially as a former for said antenna.

Preferably, said signal handling station is a computer and said cable-type means is a screened cable connected to said computer, and which is external to said computer, and the antenna element is coupled adjacent to said screened cable substantially along"its length. The antenna lead is a constant impedance coaxial transmission line carrying the R.F. or microwave signal.

The antenna radiating element is preferably a pair of linear dipoles separated by a short circuit to minimise coupling between dipoles. The radiating elements are nominally one quarter wavelength of the predetermined R.F. microwave transmit/receive frequency but may be smaller than one-quarter wavelength when a host computer cable is used aε the support cable because of the distributed capacitance between the host cable and the antenna. At least one of said antenna radiating elements are formed and arranged relative to the screening element of said data transfer cable so that the radiating elements may be tuned for optimum input impedance (50 ohm) at the predetermined operating frequency.

In this way it has been possible to obtain the advantages of an external antenna whilst at the same time effectively concealing the antenna lead radiating elements by integrating them with any convenient data transfer cable and, preferably that may already be connected to the computer. This could, conveniently, be a cable connected the first computer to its R.F. or microwave modem. Where an internal "card" modem is used then any other insulated screened cable connected to the computer could be used, including serial printer cables, networking cables, serial leads for connecting to various peripherals such as scanners, bar code readers etc.

The antenna may also be coupled to the data transfer cable in various ways though generally there is provided some specific support means formed and arranged for maintaining a securely held predetermined spatial relationship. Thus for example there may be used releasable clip means or the like for holding the antenna element(s) against the side of the data transfer cable. Alternatively the antenna element could be integrally formed with the data transfer cable, e.g. embedded in part of the outer insulating sheath or cover of the data transfer cable.

The "tuning" of the antenna is primarily dependent on the capacitance between the data cable screen and .the antenna elements concerned. This in turn depends on the size and form of the antenna elements and their separation from the data cable screen. This separation is primarily dependent on the thickness and dielectric characteristics of the outer insulating sheath of the data transfer cable each of which in practice may be subject to significant manufacturing variations. Accordingly, it is generally preferred that an initial "coarse tuning" of the antenna is effected by choice of an antenna element length (and/or width, shape etc.) appropriate to the antenna mounting and geometry, followed by a "fine tuning" of the antenna in individual installations using suitable test apparatus e.g. a scalar/vector analyser. Adjustment may be effected in any convenient manner e.g. by using mechanical adjustment means, such as a screw or the like, to displace the antenna element(s) towards or away from the screening element.

Whilst the antenna radiating element would normally be disposed so as to extend alongside the screened data cable, the antenna radiating elements may be disposed of in various different ways and can extend orthogonally to the cable depending on particular requirements. Where an internal modem is used and the antenna lead juxtaposed with another data cable, possibly by clipping or clamping together therewith, then the antenna lead would normally be lead in towards the data cable at an angle thereto, e.g. at right angles thereto.

Whilst at least of the first and second signal handling stations will require to have an R.F. or microwave transmitter and the other R.F. or microwave receiver, it will be appreciated that usually each will have both a transmitter and receiver to allow two-way communications.

The system of the present invention may be used with various different signal handling stations including diverse computer and data processing apparatus, monitoring and data collection apparatus, telecommunications apparatus including portable telephones and so-called personal communicators etc. , which include and/or are provided with R.F. or microwave transmitter and/or receiver means.

In a further aspect the present invention provides an antenna suitable for use in a data transfer antenna system of the present invention, which antenna comprises an antenna lead having a connector means for connection, in use, to an R.F. or microwave transmitter receiver connected to a first signal handling station, and at least a first antenna radiating element connected to said connector means by an antenna lead cable, said antenna lead being adapted to be coupled to a former externally to said signal handling station and to substantially follow the shape of the former.

The.antenna is preferably coupled or adjacent to a screened data transfer cable alongside substantially the length of the antenna lead so as to effectively conceal and integrate it with the existing screened cable.

The antenna preferably has radiating elements in the form of a pair of dipoles. Alternatively, a single dipole or monopole radiating element can be used.

Various forms of antenna radiating elements may be used including rod, strip and coil which may have various forms such as helical or conical. The preferred form of juxtaposition may depend on the nature of the antenna element. In the case of a rod or strip form, the antenna radiating elements would usually extend substantially parallel to the longitudinal axis of the data transfer cable. With a coil form, the antenna elements would preferably be wound around the longitudinal axis of the data transfer cable.

In one arrangement the dipoles of the radiating element are provided by two planar microstrip elements orthogonally oriented to minimise crosstalk, each microstrip element being coupled to an antenna feed and each element having variable capacitance means allowing the antenna impedance to be tuned to its own antenna feed. A relatively wide range of frequencies and corresponding antenna lengths may be used whilst maintaining acceptable antenna dimensions and signal transmission efficiencies.

According to another aspect of the present invention there is provided a method of arranging an antenna system for transferring data between a first signal handling station and a secnd signal handling station, each station having an R.F. or microwave transmitter/receiver, said method comprising the steps:- coupling a flexible antenna lead with an antenna radiating element to said R.F. or microwave transmitter/ receiver providing a support structure in the form of a cable-like means for said antenna lead external to said signal handling station, and coupling said antenna lead to said cable-like means such that said cable-like means acts as a former to said antenna lead substantially along the length of the lead.

Preferably, the method includes the step of coupling the flexible antenna lead to a screened cable coupled to said signal handling station and tuning the radiating elements of said antenna lead for optimum input impedance at a predetermined operating frequency.

These and other aspects of the invention will become apparent from the following description when taken in combination with the accompanying drawings in which:-

Fig. 1 is a diagrammatic representation of an antenna system according to an embodiment of the invention implemented in two computers;

Fig. 2 depicts, to an enlarged scale, an alternative embodiment of antenna lead to that shown in Fig. 1;

Figs. 3 to 7 are detailed diagrammatic views of the coupling between an antenna radiating element and the data transfer support cable for a variety of antenna radiating elements, and

Figs. 8.1 to 8.5 are detailed views of conical and helical antenna radiating elements.

Reference is first made to Fig. l of the drawings which depicts two signal handling stations implemented by a personal computer (PC) 10 and a remote palmtop computer (PCT) 12. PC 10 is connected to a printer 14 by a screened printer cable 16. Both computers 10,12 are coupled to respective R.F. modems 18,20 located in modem housings 21 and 23 respectively for transmitting/ receiving data via respective antennae systems generally indicated by reference numerals 22,24 as will be later described in detail. It will be understood that the antenna systems 22,24 are identical and only one, 22, will be described in the interests of clarity.

Antenna 22 consists of two screened antenna leads 26,27 for connection to the modem 18 by connectors 28,29 respectively. The leads 26,27 are also connected to two dipole antenna radiating elements 30 and 32 (Fig. la) respectively at the end remote from the connectors 28,29. The flexible screened leads 26,27 and dipole elements 30 and 32 extend externally of the housing 21 of the modem 18 and are secured to cable 34 which extends from the computer 10 to the modem 18 for the purpose of carrying digital data from the computer to the modem for transmission by the antenna 22. The cable 34 is a coaxial screened cable of a type normally associated with computers. The printer cable 16 is also a typical screened cable. The antenna lead 26 is being flexible, and is secured to the cable 34 at intervals along its length by resilient clips 36. The cable 34 acts as e former and support structure for the antenna 22 and allows the antenna 22 to be located externally to the housirg in an unobtrusive and efficient manner. Similarly, the PCT 12 is coupled to the modem 20 by data connector cable 37 which also acts as a former and support structure for antenna 24 in the same way as cable 34.

It will be seen that the antenna radiating elements 30 and 32 are linear dipoles which facilitates the coupling of the antennas 22,24 to cables 34 and 37. In this embodiment the antenna leads 26 and 27 are separate but it will be appreciated that the antenna leads 26,27 and dipoles 30 and 32 may be integrated in a single clip-on cable structure 38 as best seen in Fig. 2 of the drawings. This means that the antenna has a single outer sheath which facilitates tuning of the antennae during manufacture.

Thus, it will be seen that the antenna shown, being external to the modem housing, are not restricted by any screening due to the housing and the antenna leads, being flexible, are readily coupled to cables 34,36 substantially along the length of the antenna lead such that the cables 34 and 36 acts as formers and support structures for the antenna. It will be understood that with regard to computer 10 the antenna could also be coupled to printer cable 16.

Reference is now made to Fig. 3 of the drawings which shows a screened data cable 34 with one of the dipole radiating elements 30 remaining adjacent thereto. It will be understood that the antenna lead 26 is a conventional coaxial lead with a central data carrying conductor 40, as best seen in Fig. 3a, surrounded by an insulator 42 which has a mesh screen element 44 surrounding it with an outer insulating cover or sheath 46. The first dipole element 48 is coupled to the central conductor 40 and the second dipole element 50 is connected to the antenna screen 44 and each element has a length LI, L2 corresponding approximately to one-quarter of the wavelength ( A/4) of the signal for transferring data between the two computers 10 and 12. The length of the dipole element is nominally one quarter wavelength; in practice the length is slightly less than one-quarter wavelength because of the capacitive coupling between the dipole element 48 and 50 and the screen in the data carrying cable 34. In some cases, one of the length of the dipole element may be entirely eliminated as shown in Fig. 4. In this case, the length L2 = 0 and this is achieved by effectively utilising the screen element of the coaxial antenna lead which should, in this case, also extend alongside the screen data cable 34 and having a length corresponding approximately to a suitable multiple of the half wavelength of the R.F. signal, especially where the data cable screen is connected directly to the antenna lead screen at one or more positions. Conveniently, two connections are made at a spacing of K/2. As also shown in Fig. 4, the dipole 50 is advantageously held in place adjacent the cable 34 by one of the resilient clips 36 which are, of course, releasable. However, cable tie means can also be used.

Reference is now made to Fig. 5 of the drawings which is somewhat similar to the arrangement shown in Fig. 3 except that the dipole elements 60 and 62 are implemented in a pseudo-microstrip transmission line form with an arcuate cross-section which is complementary to the outer surface 64 of the screen cable 34 so as to fit closely around the surface as best seen in Fig. 6 of the drawings. It will be understood that the antenna dipole elements could be simply secured in position by any suitable clip fastener means. It will also be appreciated that the antenna radiating elements shown in Figs. 3, 4 and 5 may be moulded within an outer sheath similar to that shown in Fig. 2 so as to be permanently secured in place.

Reference is now made to Fig. 7 of the drawings which depicts a further embodiment of an antenna radiating element in accordance with the present invention. In this ca e, the dipoles 30 and 32 are implemented by microstrip elements 66 and 68 which consist of basically an insulating circuit board element covered with conductive material, as will be describee in order to provide an appropriate dipole structure. The microstrips 66 or 68 are orthogonally arranged to minimise crosstalk between the signal on different conductors. Each microstrip element 66,68 is substantially identical and only element 66 will be described in the interests of clarity. The microstrip element 66 receives the antenna feed, generally indicated by reference numeral 70, which passes along one side of the microstrip element and the central conductor is then passed through the microstrip element 66 and fed back in the other side shown by the dotted line 72 to form the line radiator. The outer conductor of the feed is connected to a copper pad dipole 74. A trimming capacitor 76 is coupled between the dipoles 72,74 and this allows the antenna impedance to be matched to its own connecting cable, i.e. the antenna feed. The equivalent circuit diagram for this is shown in Fig. 7a. Although this structure forms a right angle in cross-section, it may be conveniently coupled by tape or clips to the cable 34 as with the other structures or else it may be embedded in a cylindrical structure which can be snap-fitted or closed over the cable 34. The advantage of this structure is that the antenna performance is substantially independent of coupling between the antenna element and the data transfer cable.

Reference is now made to Figs. 8.1 to 8.5 of the drawings which depict a variety of radiating element structures which can be used with the antenna according to the present invention. For example, the dipole arrangement shown in Fig. 8.1 may be used for each radiating element 30 or 32. In this case, one of the dipoles is linear and the other dipole is provided by a coiled radiating element. In Fig. 8.2 a single coiled arrangement is used, whereas in Fig. 8.3 both elements of the dipole are coiled/helical. In Fig. 8.4 it will be seen that the coiled arrangement is in fact conical rather than cylindrical and again a single coil can be used as shown in Fig. 8.5 similar to the structure in Fig. 8.2.

It will be appreciated that various other modifications may be made to the embodiments described above without departing from the scope of the invention. For example, in order to improve signal transmission and especially omnidirectional efficiency, two more antennae may be provided with the respective antennae elements longitudinally spaced apart along the screen data lead preferably angular offset from each other. The antenna elements may be spaced apart by an integral number of half wavelengths. As shown in Fig. 1 the data connecting cable can be provided with an annular conductor for substantially isolating antenna elements of the antenna from each other and minimising the susceptibility of accidental de-tuning of the antenna in use due to the proximity of other apparatus. The antenna/data cable can be susceptible to de-tuning effects caused by currents being induced in the antenna cables because of the position in the antenna "near field" conducting bands acting as R.F. shorted turns or the use of lossy material, such as ferrite, may be secured at points along the cable to minimise this effect. It will also be understand that, whilst it is desirable that the antenna leads should be substantially flexible to allow flexibility of routing of the data cable and antenna lead, the antenna radiating elements should have a substantially stable geometric configuration. This may be readily achieved by the use of rigid or semi-rigid antenna elements and/or use of rigid or semi-rigid supports for the antenna elements. It should also be understood that although the antenna elements are described in these embodiments for use with screened data cable, it should be understood that the antenna elements may be used around any suitable former whether or not a screen cable or even a cable carrying data signal, although this is the most convenient arrangement because these cables are already present in the available computer structure. It will be understood that a separate flexible structure such as a pliable polymer, may be coupled to the housing or to the computer which is not a cable and which does not have a screen and the antenna simply arranged and formed around this structure to provide a suitable support structure. It will, of course, be appreciated that when the screening does not occur with respect to the data cable, then there will be minimal capacitive coupled between the radiating elements and the support structure with the result that the radiating elements are likely to be very close to the theoretical quarter wavelength of the signal which is being transmitted from the particular station.

The principal advantage of the invention is that it allows an external flexible antenna to be used which can be concealed and coupled to an existing cable. This allows flexibility in the positioning of the antenna and it overcomes the disadvantage of having a rigid antenna located in the housing or extending from the housing where it is susceptible to mechanical contact which affects the antenna performance. Use of the antenna with a screened cable allows reduction in the length of the radiating elements and the radiating elements themselves can be tuned to maximise the capacitive coupling with the screen of support to fine tune the attena for the particular impedance used with the antenna lead for the particular signals being transmitted. The concept for the flexible antenna lead using a cable as a support structure can be implemented with a variety of radiating elements which can be either monopole of dipole and the antenna can be integrated into a unit which can be simply clipped on to an existing cable to facilitate installation.

Claims

CLAIMS :

1. An antenna system for use between a first signal handling station and a second signal handling station, said signal handling station having an R.F. or microwave transmitter/receiver means, said signal handling station having at least one flexible cable-type means coupled thereto, said antenna system comprising an antenna having a first end coupled to said R.F. or microwave transmitter/receiver, flexible antenna lead means coupled between said first end and an antenna radiating element, said flexible lead means and said antenna radiating element being adapted to be coupled to said cable-type means along its length so that said cable-type means acts substantially as a former for said antenna.

2. An antenna system as claimed in claims 1, wherein said signal handling station is a computer and said cable-type means is a screened cable connected to said computer, and which is external to said computer, and the antenna radiating element is coupled adjacent to said screened cable substantially along its length.

3. An antenna system as claimed in claim 1 or 2, wherein the antenna radiating element is a constant impedance coaxial transmission line carrying the R.F. or microwave signal.

4. An antenna system aε claimed in any preceding claim, wherein the antenna radiating element is a pair of linear dipoles separated by a short circuit to minimise coupling between dipoles.

5. An antenna system as claimed in claim 4, wherein the radiating element is nominally one quarter wavelength of the predetermined R.F. microwave transmit/receive frequency.

6. An antenna system as claimed in claim 4, wherein the radiating element is smaller than one-quarter wavelength when a host computer cable is used as the support cable because of the distributed capacitance between the host cable and the antenna.

7. An antenna system as claimed in any preceding claim, wherein at least one antenna radiating element is formed and arranged relative to the screen of said data transfer cable so that the radiating element is tuned for optimum input impedance (50 ohm) at the predetermined operating frequency.

8. An antenna system as claimed in any preceding claims, wherein the antenna is coupled to a data transfer cable via support means formed and arranged for maintaining a securely held predetermined spatial relationship.

9. An antenna system aε claimed in claim 8, wherein the support means is a releasable dip meanε.

10. An antenna system as claimed in claim 8, wherein the support means is provided by integrally forming the antenna with the insulating sheath or cover of the data transfer cable.

11. An antenna system as claimed in any preceding claim, wherein the antenna system includes tuning means for moving the antenna element relative to the screening element.

12. An antenna system as claimed in claim 11, wherein the tuning means is provided by mechanical adjustment means.

13. An antenna system as claimed in any preceding claim, wherein the antenna element is disposed alongside the screened data cable.

14. An antenna system as claimed in any preceding claim, wherein the antenna element iε disposed at an angle relative to the screened data cable.

15. An antenna system as claimed in any preceding claim, wherein each of said first and εaid second signal handling stations have a transmitter and a receiver to allow two-way communication.

16. An antenna for use on a data transfer system, said antenna comprising an antenna lead having a connector means for connection, in use, to an R.F. or microwave transmitter receiver connected to a first signal handling station, and at least a first antenna radiating element connected to said connector means by an antenna lead cable, said antenna lead cable being adapted to be coupled to a former externally to said signal handling station and to substantially follow the shape of the former.

17. An antenna as claimed in claim 16, wherein the antenna is coupled adjacent to a screened data transfer cable alongεide substantially the length of the antenna lead so as to effectively conceal and integrate it with the existing screened cable.

18. An antenna as claimed in claim 16 or 17, wherein the antenna has radiating elements in the form of a pair of dipoles.

19. An antenna as claimed in claim 16 or 17, wherein the antenna has a single monopole radiating element.

20. An antenna as claimed in any one of claims 16 to 19, wherein the antenna radiating elements are selected from the group of rod, strip and coil elements.

21. An antenna as claimed in claim 20, wherein the radiating element is a rod or strip arranged to extend substantially parallel to the longitudinal axis of the data transfer cable.

22. An antenna as claimed in claim 20, wherein the radiating element iε a coil, the element is wound around the longitudinal axiε of the data tranεfer cable.

23. An antenna aε claimed in claim 21, wherein dipoleε of the radiating element are provided by two planar microεtrip elements orthogonally oriented to minimise crosεtalk, each microstrip element being coupled to an antenna feed and each element having variable capacitance means allowing the antenna impedance to be tuned to its own antenna feed.

24. A method of arranging an antenna system for transferring data between a first signal handling station and a second signal handling station, each station having an R.F. or microwave transmitter/receiver, said method comprising the steps:- coupling a flexible antenna lead with an antenna radiating element to said R.F. or microwave transmitter/ receiver providing a support structure in the form of a cable-like means for said antenna lead external to said signal handling station, and coupling said antenna lead to said cable-like means such that said cable-like means acts as a former to said antenna lead substantially along the length of the lead.

25. A method as claimed in claim 24, wherein the method includes the step of coupling the flexible antenna lead to a screened cable coupled to said signal handling station and tuning the radiating elements of said antenna lead for optimum input impedance at a predetermined operating frequency.