Global positioning system antenna location

Abstract: A vehicle (1) including a GPS antenna(3) , the vehicle (1) including an air intake grill cover (5) including vents through which air is taken into the vehicle and extending across the vehicle between the base of its windscreen (7)and the rear edge of its bonnet (9), in which the GPS antenna is mounted directly beneath the air intake grill cover.

Description: Field of the invention The invention relates to an improved location for a global positioning system (GPS) antenna assembly. Such a GPS antenna assembly is used increasingly within in-car navigation (route guidance) systems and emergency messaging systems. This allows for absolute determination of position where signals are obtained from orbiting satellites. The location of the GPS antenna on the vehicle is of great importance as the GPS signals from the orbiting satellites are of a very poor level (-160dBw minimum at the earth's surface, which is below the noise floor) and GPS relies upon line-of-sight reception of signals from at least four satellites in order to provide a valid position. A typical requirement for optimum GPS reception is that the antenna can receive signals from 20° above the horizon through 360°. This can be difficult to achieve in a vehicle. There can also be problems caused by attenuation of signals by interposing material such as glass or composite; or from lying water. The signals can also be subject to multi-path reflections from the vehicle structure if the antenna is mounted within the car. As the use of in-car navigation systems increases a number of positions within a vehicle have been proposed for the mounting of the GPS antenna. One proposed position has been on the roof of the vehicle. This is most likely to have an unobstructed view of the sky but is in an exposed position with a high risk of accidental damage and insecurity from vandalism and theft. Positions have been proposed within the car such as within the boot or under the parcel shelf of the car but these positions can suffer from reflections or interference from the rest of the vehicle structure or from the attenuation of signals by the interposing material. There can also be problems caused by a limited view of the sky. There is known from US-A-5 144 318 to locate a GPS antenna at various places of a vehicle. In the following specification the term GPS antenna will be used to describe the antenna and pre-amplifier as a unit, since they are typically all mounted together as a sealed unit. Summary of the Invention According to the invention there is provided a vehicle including a GPS antenna, the vehicle including an air intake grill cover including vents through which air is taken into the vehicle and extending across the vehicle between the base of its windscreen and the rear edge of its bonnet, in which the GPS antenna is mounted directly beneath the air intake grill cover. This has proved to be an ideal position for the GPS antenna since it provides a good view of the sky and is secure from vandalism and theft and safe from accidental damage. Typically the air intake grill cover includes intake vents which do not extend across its width so that it includes a non-vented area under which the GPS antenna may be mounted. Typically the GPS antenna is mounted under an area of the air intake grill cover which is smooth and homogeneous. Preferably the cover, at least in the area overlying the antenna is of constant thickness which provides minimum attenuation or distortion of the signals. Typically the thickness is substantially 2mm. Preferably the air intake grill cover is not exactly horizontal so that there is little likelihood of water or debris accumulating on its surface. This helps reduce the possibility of attenuation or distortion of signals. Preferably the antenna is mounted at an angle of between plus and minus 5° to the horizontal and preferably it is substantially parallel to the air intake cover. Preferably the surface of the air intake grill cover is a fine grained surface which reduces the possibility of the water forming beads, which is particularly problematic. The air intake grill cover is typically of a plastic material which does not attenuate the signals being fed to the antenna. One example of a suitable plastic is acrilonitryl butadiene styrene (ABS). The position under the air intake grill cover is such that there is little risk of obstruction due to articles being placed over the air intake grill cover so this further minimises the risk of signal distortion. The antenna is protected from the outside environment and is in a position where it is secure from vandalism and theft since the air intake grill cover is not readily removed by a thief. However the removal of the cover is straightforward for a mechanic carrying out servicing of the vehicle and so access for repair and maintenance of the antenna is relatively simple. Preferably the GPS antenna is of a high gain patch design such as that sold by JRC of 1-1, Shimorenjaku 5-chome, Mitaka - shi, Tokyo 181, Japan under the mark NAY-3520xx. Preferably the antenna is mounted upon a ground plate which typically is made of mild steel. The ground plate is preferably flat and forms part of the antenna to reflect the signals. Preferably the ground plate has an area of substantially 100cm 2 and its shape can be chosen to fit within the area under the air intake grill cover. The position under the air intake grill cover does not interfere with the passage of air through the vehicle. Preferably the GPS antenna is mounted within the duct through which air is passed from the vents to the interior if the vehicle. The air passing over the surface of the GPS antenna ensures that if for any reason water has managed to reach the surface of the antenna it is readily evaporated. This is an extra precaution to ensure accuracy of readings from the antenna. Brief description of the drawings A vehicle including a GPS antenna will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic section through part of the front of the vehicle; Figure 2 is a more detailed view of the section; and Figure 3 is an isometric view of the ground plate of the antenna. Description of the preferred embodiment A vehicle 1 includes a GPS antenna 3. The vehicle 1 includes an air intake grill cover 5 including vents (not shown) through which air is taken into the vehicle and extending across the vehicle between the base of its windscreen 7 and the rear edge of its bonnet 11. The GPS antenna 3 is mounted directly beneath the air intake grill cover 5. The vents do not extend along the length of the air intake grill cover 5 so that it includes a non-vented area shown in Figures 1 and 2, under which the GPS antenna 3 is mounted. Thus the vents do not interfere with the operation of the antenna 3. The air intake grill cover 5 is of ABS (Acrilonitryl Butadiene Styrene) which is homogeneous and smooth and has a fine grained surface. In the non-vented area the cover has a substantially uniform thickness so that there is little distortion of signals passing through the cover. The cover lies at an angle to the horizontal of in the region of 5°. This means that water will not accumulate on the surface. Also in the non vented area overlying the antenna the cover is of substantially constant cross section, of thickness 2mm. It will be appreciated by the skilled addressee of the specification that there are many different designs of air intake grill covers for different vehicles. However in the majority of cases no modification of the cover will be required for the effective installation of the antenna 3. As can be seen in Figure 2 the antenna is mounted within duct 13. This duct conveys air from the vents to the rest of the vehicle for it to be used in the ventilation systems of the vehicle. The constant passage of air through the duct 13 (at least when the vehicle is moving) ensures that water droplets cannot accumulate on the surface of the antenna to distort the signals. The GPS antenna is a NAY-3520xx as sold by JRC of 1-1, Shimorenjaku 5-chome, Mitaka - shi, Tokyo 181, Japan. The antenna is a high gain patch design. The antenna is mounted upon ground plate 15 the exact shape of which can be seen in Figure 3. The plate is planar in its working area at the centre of the plate and includes four tongues 17 cut from the plate and bent upwards through 90°. The tongues are positioned such that they define four edges of the antenna 3 so that the antenna can be placed on the plate 15 between the tongues 17 which located it. The antenna has a magnet mounted on its base so that it is attracted to the ground plate 15 which is steel. One edge 19 is bent downwards to form a flange having two L-shaped projections 21 used for mounting the ground plate in position. Each projection 21 includes a bore 23 through which a bolt may be passed for fixing. A further edge 25 of the plate includes an indented area 27 allowing the edge to be pushed under a rim in the vehicle for further fixing the plate in position.

Claims: A vehicle including a GPS antenna, the vehicle including an air intake grill cover including vents through which air is taken into the vehicle and extending across the vehicle between the base of its windscreen and the rear edge of its bonnet, in which the GPS antenna is mounted directly beneath the air intake grill cover. A vehicle according to claim 1, in which the grill cover includes a non-vented area under which the antenna is mounted. A vehicle according to claim 1 or 2, in which the antenna is mounted beneath an area of the grill cover which is smooth and homogeneous. A vehicle according to claim 3, in which the antenna is mounted beneath an area of the grill cover which is of substantially constant thickness. A vehicle according to any one of the preceding claims, in which, the air intake grill cover is not horizontal. A vehicle according to any one of the preceding claims in which the air intake grill lies at up to 5°to the horizontal. A vehicle according to any one of the preceding claims, in which the air intake grill cover has a fine grained surface. A vehicle according to any one of the preceding claims, in which the antenna is mounted at up to 5°to the horizontal. A vehicle according to any one of the preceding claims, in which the antenna is mounted upon a ground plate. A vehicle according to any one of the preceding claims, in which the antenna is mounted in a duct through which air is passed from the vents to the vehicle.

Inventors: PEDLAR CHRISTOPHER E, PEDLAR, CHRISTOPHER E.
Applicants: FORD GLOBAL TECH INC, FORD GLOBAL TECHNOLOGIES, INC.
Application year: 1997
Main classification: H01Q1
IPC codes: H01Q1