GB2464544A

GB2464544A - Bouyant global navigation satellite system antenna

Info

Publication number: GB2464544A
Application number: GB0819237A
Authority: GB
Inventors: Peter Eric Hall; Christine Anne Edwards
Original assignee: SCI TECH SYSTEMS Ltd
Current assignee: SCI TECH SYSTEMS Ltd
Priority date: 2008-10-21
Filing date: 2008-10-21
Publication date: 2010-04-28
Also published as: GB0819237D0

Abstract

A buoyant antenna comprises a body portion, with an antenna 6 which is suitable for satellite communication in a global navigation satellite system GNSS such as GPS or Galileo. The antenna 6 is located at one end of the body and a mass concentration is substantially located at the other end. The body is mounted in a rotatable manner, at a position between the said ends of the body, to a float portion 2. The float portion 2 is arranged to rotate about the body such that in use it lies on a water surface whilst the antenna 6 stays generally upright above the surface of the water. The heavy components of the device, such as the battery or electronic members, may be located at the opposite end of the body to that of the antenna 6. The antenna may provide a small and stable arrangement which can maintain good satellite reception even in heavy seas.

Description

BUOYANT GNSS ANTENNA

This invention relates to a buoyant global navigation satellite system (GNSS) antenna.

The use of GNSS signals such as GPS or Galileo signals allows position to be determined. This is achieved by receiving precisely timed signals from a plurality of satellites in different positions and then performing triangulation to determine a position in space relative to the satellites. This position may then be mapped on to a model of the earth's surface to determine a highly accurate absolute position in three dimensions, on that surface.

The signals transmitted by the satellites are necessarily of relatively low power and thus any attenuation of the signal from each satellite can have a significant impact on the ability of any GNSS receiver to accurately determine position.

It is known that water, for example, is a significant attenuator of radio frequency signals at the frequencies used by existing GNSS constellations. Accordingly in any use of GNSS receivers at sea, it is important to minimise wetting of the antenna by sea water, for example, during stormy conditions. Furthermore, in situations where the receiver may be very close to the surface of the water, for example, when used for emergency position indicating radio beacons (EPIRB) or other floating receivers such as personal alarms, that the receiver antenna is maintained clear of the surface of the water.

One solution is to make such floating beacons very tall. For example, a typical EPIRB such as the McMurdo 406 beacon "Smart Find" and "Smart Find Plus", is approximately 400mm tall. Whilst this might be an acceptable dimension for a device designed to be attached to a ship and released if the ship sinks, such dimensions are too large to practicably be worn by sailors. Any personal GNSS emergency receiver needs to be sufficiently small to be carried on the person and yet still needs to achieve good satellite reception when floating in the sea.

Accordingly, the present invention provides a buoyant GNSS antenna comprising a body portion and a float portion, the body portion including an antenna for reception of GNSS signals generally at one end and being further arranged to have a mass concentration generally at the opposite end from the antenna, the float portion being rotatably mounted to the body between the antenna and the mass concentration, the mass concentration having an effective weight in seawater greater than that of the antenna in air such that in use, the float portion rotates around the body to lie along the sea surface whilst the antenna stays generally upright above the surface of the sea.

By allowing the float portion to be rotatably mounted on the body, in use, the float forms a raft or catamaran which significantly stabilises the body portion in rolling waters. This helps to maintain the antenna portion clear of the water and helps to maintain a constant orientation which aids with signal acquisition and retention. This design is considerably more stable in high seas than prior art designs and yet typically may have dimensions of the order of 150mm. This type of GNSS receiver is therefore readily wearable by sailors.

The invention will now be described by way of example with reference to the drawings in which: Figure 1 is an elevation of a receiver in accordance with the invention; Figure 2 is a side elevation of the receiver of Figure 1; Figure 3 is a side elevation of a float portion in accordance with the invention; Figure 4 is a side elevation of a body portion in accordance with the invention; and Figure 5 is a schematic diagram of the receiver in use.

With reference to Figures 1 and 2, a buoyant GNSS antenna has a float portion 2 and a body portion 4. The body portion includes a GNSS antenna 6 and an optional transmitter antenna 8 for transmitting information to a ground or ship-based receiver.

Optionally also, the antenna 8 or 6 may be used to transmit data to satellites. The device may also be designed to operate with non-GPS GNSS constellations such as Glonass and/or Galileo. The antennas are covered with radomes 8' and 6' respectively.

The body portion houses PCBs 10-1, 10-2 and 10-3 and also a battery pack/weight 12.

The float portion 2 is fixed to the body portion 4 at hinge points 14. It is also shown in Figure 3 which shows the float portion and body portion separated.

With reference to Figure 5, it will be seen that in use, the float portion 2 is free to rotate about hinges 14 and thereby stabilises the body portion with the antennas 8 and 6 clear of the water and oriented generally vertically. This provides maximum radiated power into the sky.

By arranging for the battery/weight 12 to have its mass concentrated generally below the hinges 14, the stability of the antenna is maximised. The weight distribution may be achieved by distributing heavier electronic components towards the lower parts of the PCBs 10-1, 10-2 and 10-3 and also ensuring that the heaviest parts of the batteries etcetera are located towards the bottom of the body portion 4.

If necessary, additional weight in the form, for example of metal may be inserted towards the bottom of the body portion.

In this way, the overall dimensions of the receiver may be reduced while still retaining good stability in heavy seas and thereby maintaining good satellite reception.