Technical Field
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The present invention relates to antenna devices, and in particular to multiband, modularised, antenna devices that can be used for a wide range of different communication and navigation applications.
Summary of the Invention
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The present invention provides a versatile antenna device comprising an outer housing enclosing a first antenna module with an active antenna element mounted within the outer housing, the active antenna element being adapted to receive electromagnetic signals transmitted by positioning satellites, and a second antenna module with a passive whip (or vertical) antenna element mounted outside the outer housing.
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As used herein, the term 'active' refers to an antenna element which is connected to an active circuit and the term 'passive' refers to an antenna element which is simply connected to an external device by means of a suitable cable, either directly or by means of a suitable impedance matching circuit. For example, the active antenna element that is adapted to receive electromagnetic signals transmitted by positioning satellites can be connected to an active filter and amplifier circuit that forms part of the first antenna module. An input of the active filter and amplifier circuit is connected to the active antenna element and an output is connected to an external navigation device by means of a suitable cable. The external navigation device also provides an input dc voltage (typically 5 V) to the active filter and amplifier circuit.
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The antenna device of the present invention can be configured for different applications. For example, the first antenna module can be configured to support any suitable global navigation satellite system (GNSS) including: global positioning system (GPS), GLONASS and Galileo.
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Similarly, the second antenna module can be configured or optimised for any suitable communication network such as Terrestrial Trunked Radio (TETRA), ISM, GSM/GPRS, 3G and Wi-Fi, for example. In practice this can be achieved by using a whip antenna element with a length that is substantially matched to the frequency band of the particular communication network (e.g. 380 - 450 MHz for TETRA).
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The antenna device can optionally further include a third antenna module with a passive antenna element mounted within the outer housing. The passive antenna element can also be configured or optimised for any suitable communication network such as 3G and Wi-Fi, for example. The third antenna module can be used to allow the antenna device to transmit and/or receive other electromagnetic signals and the second and third antenna modules will typically be configured or optimised for different communication networks.
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The outer housing can further enclose a printed circuit board (PCB). The PCB can optionally be fixed to the outer housing (typically a base part thereof - see below) by mechanical fixings such as screws. The PCB acts as a ground plane for the antenna elements.
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The electronic components of the active filter and amplifier circuit are preferably mounted on the PCB. The electronic components can be enclosed by a shield, e.g. a metallic box which can be soldered to the electrical ground on the PCB.
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The PCB can include interfaces for connecting the various antenna elements to a respective cable.
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The outer housing of the antenna device can be a two-part housing with a base and a cover releasably secured together, e.g. with mechanical fixings such as screws. The outer housing can be made of any suitable, substantially rigid, material, but a plastics material will typically be preferred. To maintain a water-tight seal between the base and the cover of the outer housing a silicone seal or nitrile o-ring seal can be positioned between their respective peripheral edges. O-rings can also be provided around the mounting points for the mechanical fixings that are used to releasably secure the base and the cover together.
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The whip antenna element can be releasably or permanently secured or mounted to the cover of the outer housing. In one arrangement, a base part of the whip antenna element can include an external screw thread and the outer housing can include a mounting block made of metal or other electrically conductive material with a complementary internal screw thread for releasably receiving the base part. The cover of the outer housing can be over-moulded around the mounting block.
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A compressible (or spring) contact can be provided on the PCB to provide a reliable electrical contact between the interface for the whip antenna element and the mounting block, and hence with the base of the whip antenna element. The compressible contact can include a coil with one or more resilient turns that are compressed slightly when the cover is properly secured to the base of the outer housing. The coil can be spaced above the PCB surface by a spacer. When compressed, the turns of the coil are not in direct physical contact with each other (i.e. they are not 'shorted') so the impedance of the compressible contact remains substantially constant both when the cover is properly secured to the base of the outer housing - when the coil is compressed - and when it is removed - when the coil is not compressed. The impedance of the coil is substantially matched by a passive matching circuit which can form part of the interface for the whip antenna element. It will be readily appreciated that other forms of compressible contact can be used.
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The whip antenna element will typically be located within a protective sleeve. Preferably, the whip antenna element extends substantially vertically relative to the PCB which defines a ground plane.
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The outer housing can include a mounting means for selectively securing or mounting the antenna device to external equipment or surfaces. The mounting means can take the form of a screw-threaded part (e.g. a marine standard 1 inch - 14 TPI thread that allows it to be mounted on top of a mast or pole) or a bracket attachment that can be screwed onto the screw-threaded part and which allows the antenna device to be secured or mounted to any flat surface, typically using mechanical fixings such as screws or bolts. The antenna device is particularly suitable for marine use but it will be readily appreciated that other fixed-site and portable uses are possible.
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The outer housing can further comprise a gland or elastomeric moulding through which the various cables pass to maintain a water-proof seal. If the antenna device is secured directly on the top of a mast or pole then the cables can feed through the centre of the mast or pole. If the bracket attachment is used then the cables can feed through the centre of the bracket.
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The present invention also provides an antenna device comprising: a two-part outer housing with a base and a cover, wherein the cover includes a mounting block for receiving a whip (or vertical) antenna element; and a printed circuit board (PCB) fixed to the base and which defines an interface for the whip antenna element, the interface including a compressible contact (e.g. the coil described above) that is in electrical contact with the mounting block when the cover is properly secured to the base.
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The interface will typically include an impedance matching circuit. Other optional features of the antenna device are generally as defined above.
Drawings
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- Figure 1 is a side view of an antenna device according to the present invention;
- Figure 2 is a cross-section view through the antenna device of Figure 1;
- Figure 3 is a detail view of the spring contact of the antenna device of Figure 1; and
- Figure 4 is a plan view of the printed circuit board (PCB) mounted within the outer housing of the antenna device of Figure 1.
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With reference to Figures 1 to 4, an antenna device 1 according to the present invention includes a shaped outer housing 2 made of a plastics material such as acrylonitrile styrene acrylate (ASA). The housing consists of a base 4 and a cover 6 which are fixed together at internal fixing points 8, 10 using screws. An o-ring 12 is received in a groove at the peripheral edge of the base 4 to provide a seal between the base and the cover 6. Additional o-rings (not shown) can be provided between the fixing points 8, 10 so that the outer housing 2 remains substantially water-tight or weatherproof in use.
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The cover 6 contains an over-moulded metallic threaded insert or mounting block 14 into which a base part 16a of a whip antenna element 16 is screwed. The whip antenna element 16 is adapted for use with the TETRA communication network and is located within a suitable protective outer sleeve 18.
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The housing 2 contains a printed circuit board (PCB) 20 that is fixed into the base 4 by screws. The whip antenna 16 extends vertically relative to the PCB 20.
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The PCB 20 includes an interface 22 for the whip antenna element 16. A spring contact 24 is provided on an upper surface of the PCB 20 and includes a coil 26 with resilient turns. When the cover 6 is secured to the base 4, the coil 26 is in contact with the mounting block 14 as shown in Figure 3 and the resilient turns are compressed slightly. The spring contact 24 provides a reliable electrical contact between the interface 22 and the mounting block 14, and hence with the whip antenna element 16 that is screwed into the mounting block. The interface 22 is connected to an external communication device (not shown) by a cable C1 (Figure 4).
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An active antenna element 28 is mounted on the upper side of the PCB 20 and is connected to the input of an active filter and amplifier circuit 30. The active antenna element 28 can be in the form of a ceramic patch antenna that is adapted to receive electromagnetic signals transmitted by positioning satellites. The electronic components defining the active filter and amplifier circuit 30 are mounted on the underside of the PCB 20 (Figure 4) and are encased by a metallic shield box 32 which is soldered to the electrical ground on the PCB 20. It will be readily appreciated that the shield box 32 has been omitted from Figure 4 so that the electronic components can be seen.
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The output of the active filter and amplifier circuit 30 is connected by a cable C2 to an external navigation device (not shown), e.g. an external global navigation satellite system (GNSS) receiver that uses the output signals to determine position in a known manner. The active antenna element 28 can be adapted or configured to support any suitable GNSS options including: global positioning system (GPS), GLONASS and Galileo, for example. The active antenna element 28 is positioned adjacent the upper side of the PCB 20 which acts as a ground plane. The active antenna element 28 and the active filter and amplifier circuit 30 can be described as a satellite positioning unit.
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The size of the active antenna element 28 can be selected depending on operational criteria such as gain and axial ratio, for example.
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An optional passive antenna element (not shown) can be mounted adjacent the active antenna element 28 and can be electrically connected to an input interface 34 (Figure 4) provided on the PCB 20. The optional passive antenna element can be adapted or configured for use with any suitable communication network such as 3G mobile communication or Wi-Fi wireless networking.
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A base part of the housing 2 includes a screw-threaded part 36 which enables the housing to be screwed directly to a mast or pole, for example. In Figures 1 and 2, an optional bracket 38 is shown to be screwed into the part 36. The optional bracket 38 includes a mounting portion 40 with openings that allow it to be secured or mounted to a flat surface using screws or bolts. The various cables that are connected to the PCB 20 pass through a gland 42 which maintains a substantially water-tight or weatherproof seal and then either feed through the centre of the mast or pole, or through the bracket 38.
