RETRACTABLE TRIPOD ANTENNA

Abstract: The present invention relates to an antenna (1) with an aerial sheath (5), a body (3) and legs (11) pivotally attached to said body (3). The legs (11) can be pivoted in the body (3) from a storage position in which they are adjacent to the aerial sheath (5) to a working position in which they extend away from the body (3) in a direction opposite that of the aerial sheath (5) and can support the antenna with the aerial sheath (5) pointing upwards.

Description: RETRACTABLE TRIPOD ANTENNA Technical Field of the Invention The present invention relates to portable antennas for use with radio equipment and particularly to foldable antennas. Description of Related Art The use of portable radio receivers and transmitters has increased tremendously over the last few years. In particular there has been a large growth in the use of mobile telephones. This growth has been accompanied by a decrease in the size of mobile telephones and a corresponding decrease in the size of their built-in, internal antennas. These smaller antennas can prove inadequate in extreme conditions and when the telephone is used near to or connected to computer equipment EMC problems can occur. Therefore it is often desirable to connect the mobile telephone to a separate, external, antenna. These separate antennas are normally either magnetic foot antennas or ground plane independent desk antennas. Magnetic foot antennas require large conducting, magnetic ground planes to function which makes them large and heavy. Ground plane independent antennas are often half-wave dipoles which makes them tall and heavy. In order to be stable they need a commensurably large and heavy base which makes them even larger and heavier. These antennas often need an impedance matching network which leads to signal losses and lower antenna gain. The present invention seeks to provide a portable antenna which overcomes these problems. Summary The present invention seek to provide an antenna which is lighter and less bulky than antennas previously used as external antennas. The antenna according to the present invention comprises an aerial and three or more less which are made of a conducting material and which are in electrical contact with the earth for the aerial wire. These legs are preferably movable in relation to the aerial so that they can form a stable base when the antenna is in use and they can reduce the bulkiness of the antenna by being folded up when d e antenna is not in use. Preferably they are folded up alongside the aerial so that the total length of the antenna is reduced. When the antenna is in use the legs are folded out and project downwards at a angle from the aerial to form a stable tripod. The legs preferably comprise a ground plane for the antenna when they are folded out. By using the legs to form both the ground plane and a stable base for the antenna, there is a saving of both weight and space as there is no longer any need to provide a separate base and a separate ground plane. Brief description of the drawings The invention will be illustrated by means of drawings of one example of an embodiment of the invention, in which: Figure 1 is a side view of an embodiment of an antenna according to the invention; Figure 2 is a plane view from above of the antenna according to Figure 1; Figure 3 is a partially sectioned exploded view of the antenna shown in Figure 1 : Figure 4 is a side view of a folded antenna according to the invention. Detailed description of the embodiments. In Figure 1 a first embodiment of an antenna 1 according to the invention is shown in the folded out position. Antenna 1 has a body 3 which comprises an aerial sheath 5 on top of a leg housing 7. Body 3 is preferably made of an insulating, resilient material such as a plastic. The housing 7 has a substantially triangular horizontal cross-section and at each of the apexes of the triangle there is a hole 9. Each of these holes receives a leg 1 1 and the legs 1 1 are retained in the holes 9 by a pin or the like (not shown) which permit the legs 11 to rotate in the vertical plane. Legs 1 1 are made of a conducting material, preferably a metal such as copper, steel or aluminium. Legs 11 preferably have feet 12 made of an anti-slip material such as rubber. A coaxial antenna cable 13 is fitted into die body 3. Figure 2 shows the antenna of Figure 1 viewed from above. Figure 3 shows a vertical cross-section through body 3 though a hole 9. Hole 9 has a cavity 15 for receiving a horizontal retaining pin 17 for leg 11 '. Leg 11 ' has one curved end 19 which forms a loop 21 which co-operates with pin 17 to retain leg 11' in hole 9. The fit between pin 15 and loop 21 is sufficiently loose to allow leg 1 1 ' to pivot around pin 15. Legs 1 1 " and 11 ' " are similarly attached to body 3. The legs 11 '-11'" can be individually moved in their respective holes 9 between a fully open position pointing downwardly inclined and a closed position in which they are adjacent to, and substantially parallel to, or inclined towards, the aerial sheath 5. The profile of the holes 9 can be adapted to include holding cut-outs 16', 16" such that when die legs 11 '-11 '" are placed in die fully open or closed positions they are retained diere. In order to form a stable base for the antenna the legs should be able to be pivoted at least 90° from the closed position to the opened out position. Preferably the legs can be pivoted dirough a maximum angle which is in the range of 100°-160° from the closed position. Coaxial cable 13 comprises an insulated aerial wire 23 surrounded by an earth screen 25 which in turn is surrounded by an outer insulating cover 27. One end 28 of cable 13 is provided with a connector 29 for connecting it to a radio device (not shown). The other end 31 of cable 13 is partially stripped of earth screen 25 and outer insulating cover 27 to leave a suitable length of insulated aerial wire exposed to form an aerial of length L. The length L of aerial wire 23 exposed is adapted to d e intended frequency range that the antenna 1 is to be used with. A preferably shorter length 1 of earth screen 25 is also exposed. The lengths L and 1 are chosen such that when the exposed aerial wire 23 is placed inside aerial sheath 5 the exposed earth screen 25 is at substantially the same height as holes 9. The coaxial cable is held in the leg housing 7 by a retaining body 33. Retaining body 33 can be attached to cable 13 by means of , for example, a crimping ring 35 being crimped onto the retaining body 33 after the cable 13 has been treaded d ough it. Retaining body 33 is fastened by any suitable means, such as snap-fitting, gluing, welding, screws, bolts rivets or d e like to body 3. Retaining body 33 is made of a conducting material, or comprises conducting means, such that when it is fastened into body 3 it provided an electrically conducting path between legs l l '-H" ' and earth screen 25. In this way he folded out legs 1 1 '-1 1 ' " form a ground plane when die coaxial cable 13 is attached to a radio device. When used with a mobile telephone the length of the exposed aerial wire 23 of me antenna should preferably be between one eighth and one half of d e wavelength of the frequency used and most preferably around one quarter of the wavelength e.g. around 8 cm long for a GSM system. The length of the legs 11 is preferably chosen that when they are folded up iey do not extend beyond die end of die aerial sheath 5. Figure 4 shows an antenna in a folded condition where legs 11 '-11 '" are substantially parallel to aerial sheath 5. In another embodiment of me invention, not shown, the legs 11 are provided with magnetic feet to facilitate the use of the antenna on magnetic surfaces such as automobile bodies. In yet anotiier embodiment of me invention, not shown, legs 11 are telescopic. In a further embodiment of die invention, not shown, legs 11 are helical. In a further embodiment of the invention, not shown, die antenna comprises a helical aerial wire. In a further embodiment, not shown, the aerial sheath is made of a conducting material, is telescopic or foldable and is electrically insulated from retaining body 33 and legs 11. In a further embodiment of the invention the holes in which the legs are pivoted have friction means which resist movement of the legs so that once a leg has been placed in a particular position it is retained diere until subject to a force greater than the force provided by the friction means. This enables the legs to be inclined at different angles with respect to the body of the antenna and therefore if the antenna rests on an uneven surface it is possible to adjust d e positions of the legs so that die aerial is substantially vertical. -Although die invention has been illustrated by means of an antenna with a tripod arrangement of legs, it is also conceivable wimin the scope of the invention to vary the number of legs as required and it is also conceivable to have one or more legs which are not electrically conducting or which are not electrically connected to d e earth screen of d e aerial. It is also conceivable to provide a simplified antenna according to the invention which lacks a aerial sheatii and body housing. In tihis case the legs could be conductingly attached to a conducting body which is also provided with means for non-conductingly supporting die aerial. It is naturally possible within die scope of the invention to combine any of the above-mentioned different embodiments of the legs, housing, retaining body, aerial wire, etc. in any conceivable manner.

Claims: Claims 1. Antenna for portable radio apparatus comprising a body (3) or housing means (7) supporting an aerial wire (23) and a plurality of legs (11 '-11 '") characterised in that said legs (11 '-11'") are movably attached to said body (3) or housing means (7) and are movable through an angle of at least 90° from a collapsed position adjacent to said aerial wire (23) to a working position extending from said body (3) or housing means (7) in a direction away from said aerial wire (23). 2. Antenna for portable radio apparatus according to claim 1 characterised in diat said legs (l l'-l 1"') are movable from said collapsed position dirough a maximum angle which lies between 100° and 160°. 3. Antenna according to claim 1 or 2 characterised in mat said antenna further comprises an earth screen (25) and that at least one of said legs (H'-l l'") is : electrically conducting; and, electrically connected to said earth screen (25). 4. Antenna according to any of die previous claims characterised in mat said legs (11 '- 11'") are pivotally or telescopically connected to said body (3) or housing means (7). 5. Antenna according to any of die previous claims characterised in mat it comprises at least 3 legs (l l'-l I T")- 6. Antenna according to any of the previous claims characterised in that at least two of said legs (ll'-l 1 "') are electrically connected to each other by electrically conducting retaining means (33) which is electrically insulated from said aerial wire (23) and electrically connected to said earth screen (25). 7. -Antenna according to any of d e previous claims characterised in that said legs (l l '- i ") have feet (12) made of an anti-slip material. 8. Antenna according to any of the previous claims characterised in that it is for a mobile telephone. 9. Antenna according to any of die previous claims characterised in tihat said legs (i r-l l ' ") are suitable for supporting said antenna. 10. Ground plane for an antenna having a body (3) or housing means (7) supporting an aerial wire (23) and an earth screen (25) characterised it that it comprises legs (l l '- l 1' ") wherein said legs (l l'-l 1 "') are movably attached to said body (3) or housing means (7) and are movable d rough an angle of at least 90° from a collapsed position adjacent to said aerial wire (23) to a working position extending from said body (3) or housing means (7) in a direction away from said aerial wire (23). 11. Ground plane in accordance with claim 10 characterised in that said legs (1 I'l l' ") are movable from said collapsed position dirough a maximum angle which lies between 100° and 160°. 12. Ground plane according to claims 10 or 11 characterised in that said at least one of said legs (l l'-l 1"') is electrically conducting and electrically connected to said earth screen (25).

Inventors: LUNDBERG JOACIM, PENSJOE THOMAS, LUNDBERG, JOACIM, PENSJOE, THOMAS
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 1998
Main classification: H01Q9
IPC codes: H01Q1, H01Q9