The present invention relates to antennas, in particular for transmitting signals between computers on wireless local area networks (WLANs).

With the advent of WLANs , it has become necessary for computers to transmit to and receive from other computers using antennas. An antenna used for this purpose will often, by necessity, be connected protruding from the computer utilising it in order to improve reception or transmission. The antennas being used will often utilise dedicated hardware on PCcard standard cards, to which they will be attached. The invention described herein is applicable to cards according to this standard and also to other situations where an antenna plugs into but protrudes from a computer.

A concern that this raises is that physical impact on the antenna extension may cause damage to the relatively expensive hardware to which it is attached, in particular the card and the host machine.

The present invention provides means adapted to connect an externally protruding antenna to a computer such that damage caused to the computer by physical impact on the antenna is minimised. A preferred embodiment comprises a capacitative coupling between the antenna assembly and the computer. This embodiment has several advantages.

Firstly, it is very rugged, as the connection areas between the host and the antenna can be sealed in a dielectric. The capacitative coupling forms a very good high frequency contact and is much more reliable than the standard RF connectors used for connecting antennas, which frequently fail after being connected and disconnected less than 100 times.

A further advantage of this embodiment is that

it eliminates any direct electrical connection between the host machine and the antenna. The host is therefore much less susceptible to external static electricity.

Another embodiment of the invention comprises an antenna printed on a flexible circuit board, the flexible board absorbing the majority of any impact that might occur.

A further embodiment of the invention employs weakly sprung clips to attach the antenna assembly to the host machine. Impact on the antenna unit is likely _to cause the clips to disengage.

A still further embodiment of the invention comprises an optional antenna built into the host machine. If the machine on which an antenna is desired does not have one built in means are provided for attaching an antenna in accordance with another of the embodiments of the invention given. The technique may be used for special functions where laptops employing their own brand of cards can give extra performance whilst not precluding themselves from use with other types of lap top machine. An example may be that a "snap-off" external antenna may be removed when an "A" brand card is used with an "A" brand laptop computer as it is replaced with the wiper contact that accesses an antenna integral to the lap top machine.

Preferred embodiments of the invention will now be described by way of example with reference to the following drawings:

Figure 1 shows in perspective the preferred embodiment of the invention.

Figure 2 shows in perspective a second embodiment of the invention.

Figure 3 shows in perspective a third embodiment of the invention.

Figure 4 shows in perspective a fourth embodiment of the invention.

Figure 5 shows in perspective a fifth embodiment of the invention.

Figure 6a shows in plan view a sixth embodiment of the invention.

Figure 6b shows a cross section of the sixth embodiment of the invention along the line AB in Figure 7a

Figure 7 shows in perspective an seventh embodiment of the invention.

Figure 8 shows in perspective an arrangement for earthing a protruding antenna

Referring to figure 1, the preferred embodiment of the invention consists of a card 1, which is made up of a plastic card frame 2 and a Metal case 3 enclosing a rigid Printed Circuit Board 4. One edge 5 of the card consists an edge connector for the electrical connection of the card and the host machine.

A separate antenna assembly 6 has two flat conducting areas 7a,7b for RF connection to the card 1. The conducting areas 7a,7b are protected by a layer of dielectric material 27a,27b.

The card also has two flat conducting areas 8a,8b. The conducting contacts on the card 8a,8b are also protected by a layer of dielectric material 28a,28b.

The card is designed so that it engages with the antenna assembly, along the edge of the card which protrudes from the host machine 9. This is achieved by the provision of two slots 18a,18b on said edge of the card 9 said slots facing the two conducting areas 8a,8b. Tabs 17a,17b are provided on the antenna assembly containing the conducting areas 7a,7b and adapted to mate with the two slots 18a,18b on the card. When mated, the card and the assembly are held together by friction.

When mated thus, the two conducting areas 7a and 8a, and the two conducting areas 7b and 8b face one

another, the facing areas being separated by two layers of dielectric material 27,28, thus creating a capacitative contact between the card and the antenna assembly.

This capacitative contact is sufficient to transmit the RF signals between the card and the antenna assembly and in fact transmits the signal better than a standard RF connector designed for the same purpose.

An advantage of this design of contact is that it does not cause expensive damage when broken by _^ impact; a side-on impact which might be caused by somebody walking past would simply push the protruding antenna assembly out of its socket, causing no damage at all. A sharp vertical impact, although possibly snapping off the tabs on the antenna assembly would not cause any damage to the significantly more expensive card or to the host. The broken antenna assembly could be replaced very cheaply, as it comprises only cheap components.

Referring to figure 2, a second embodiment of the invention consists of a card 1, which is made up of a plastic card frame 2 and a metal case 3 enclosing a rigid Printed Circuit Board 4. One edge 5 of the card comprises an edge connector for the electrical connection of the card and the host machine. The opposite edge is attached to a flexible printed circuit board 12 on which is printed an antenna circuit. The card is in electrical contact with the flexible board for the transmission of RF signals.

The flexible circuit board 12 is reflow soldered using a "Hot Bar" reflow solder joint 23, to a small extension 19 to the card 1.

A ground connection is provided to the flexible printed circuit board 12 by way of extensions 21 to the metal case connecting to an earth contact 22 on the flexible printed circuit board 12.

Two flexible antennas 20 printed on the edge

of the flexible circuit may be used to give a diversity system. The antennas 20 are unbalanced elements which are fed via stripline lines directly from the radio electrics.

Impact occurring from any direction will be absorbed by the flexible Printed Circuit Board 12 and therefore no damage should occur to any of the components, especially the host machine connection 5.

Referring to figure 3, a third embodiment of the invention consists of a card 1, which is made up of a plastic card frame 2 and a metal case 3 enclosing a rigid Printed Circuit Board 4. One edge 5 of the card comprises an edge connector for the electrical connection of the card and the host machine.

Sprung metal antenna feed contacts 13 connect the board 4 and the metal case 3. These contacts are driven through a balanced to unbalanced transformer which connects to the radio transceiver. The end of the antenna is "capped" with a plastic plug or radome 15.

This embodiment overcomes the problem of the antenna protruding entirely, as the antenna does not extend sufficiently for impact to have an effect.

Referring to Figure 4, a fourth embodiment of the invention consists of a card 1, which is made up of a plastic card frame 2 and a metal case 3 enclosing a rigid Printed Circuit Board 4. One edge 5 of the card comprises an edge connector for the electrical connection of the card and the host machine.

The antenna assembly 6 protrudes from the slot but is a separate component held in place by "snap-on" couplings 14 integrated within the card frame. The couplings are dimensioned such that any slight blow to the radome housing the antenna causes it to break free from the card without damaging the connection to the host machine.

Referring to Figure 5, a fifth embodiment of

the invention consists of a card 1, which is made up of a plastic card frame 2 and a Metal case 3 enclosing a rigid Printed Circuit Board 4. One edge 5 of the card comprises an edge connector for the electrical connection of the card and the host machine.

The card 1 has an extension 19 along the outfacing edge on which two pairs of pads 25a,25b are printed, the pads of each pair facing away from each other on opposite sides of the extension 19. The pads of each pair are connected by three plated-thru holes _ and are connected to the device requiring external connection.

The three plated-thru holes are designed to mate with a sprung, three finger clip 26 to which the antenna element is connected (not shown in diagram for clarity) .

The spring loading is designed such that a gentle knock to the antenna elements causes the clip 26 to lose contact with the three holes in the pad 25 and fall off. In this manner any host connection is protected from strain from any external interference to a protruding antenna.

The metallic nature of the connection makes the design suitable for control and other non-RF signals as well as the carrier frequencies associated with antennas.

Referring to Figure 6a and Figure 6b, a sixth embodiment of the invention consists of a card 1, which is made up of a plastic card frame 2 and a Metal case 3 enclosing a rigid Printed Circuit Board 4. One edge 5 of the card comprises an edge connector for the electrical connection of the card and the host machine.

A small extension to the circuit board protrudes outside the existing case 3 on the outfacing edge of the card. A pad 25a on the extension of this circuit board is connected to the radio-tranceiver via a

track and plated-thru hole and exposed on the lower side. An antenna assembly 6 and plastic radome 15 is designed with a similar exposed pad 25b. The radome is designed such that the extension keys into the radome housing ensuring that the two pads are aligned. Radio frequency signals are able to feed across the pads with minimum loss thus forming an isolating feed. Small extensions to the radome moulding 16 are designed to hold the radome in place but to break contact if the radome is knocked. In this manner, any host connection is protected from strain from any external interference to the antenna.

Referring to Figure 7, a seventh embodiment of the invention consists a card 1, which is made up of a plastic card frame 2 and a metal case 3 enclosing a rigid Printed Circuit Board 4. One edge 5 of the card comprises an edge connector for the electrical connection of the card and the host machine.

In this embodiment, the problem of the protruding antenna assembly is avoided by placing the antenna 6 elsewhere in or on the host machine. It would be undesirable to connect the card and antenna 6 using the edge connector 5 as this would interfere with the standard use of these connections. Instead, a wiper contact 29 is used.

A small printed circuit board 30 containing a spring contact 29a is mounted in the machine containing the card slot such that it makes contact with the card 1 as it placed in the slot. The card requiring contact is given a special contact 29b which mates when the card is fully inserted in the slot. In this fashion the user is unaware of any difference to the card 1, yet an extra contact 29 has been made.

The technique may be used for special functions where laptops employing their own brand of cards can give extra performance whilst not precluding

themselves from use with other types of lap top machine. An example may be that a "snap-off" external antenna may be removed when an "A" brand card is used with an "A" brand laptop computer as it is replaced with the wiper contact that accesses an antenna integral to the lap top machine.

Referring to Figure 8, an arrangement is shown which can be used to earth a protruding antenna in any of the afore-mentioned embodiments. This arrangement