The present invention relates to radio antennas and antenna assemblies and in particular, but not limited to, antennas and antenna assemblies for vehicles and other mobile units.
Vehicle mounted radio antennas are generally known for receiving radio broadcast signals and for two-way communication in mobile telephone applications. Vehicle mounted antenna are also known for voice communications in military applications.
In static applications, a known antenna assembly comprises an antenna array comprising several vertically stacked dipole antennas each of which operates over the same frequency band. In transmission mode, each antenna is fed the same carrier frequency signal with the signal fed to the upper and lower antennas being phase shifted relative to middle antenna to increase the concentration of electromagnetic energy in the horizontal direction.
The inventors have discovered that when transmitting at certain frequencies from a vehicle mounted antenna, the signal strength is significantly lower than expected in certain regions in close proximity to the vehicle, and that such regions of lower than expected signal strength occur particularly for higher frequencies and where the vehicle significantly shadows and scatters the signal. Thus, as the vehicle moves towards an object, such as a receiver, the signal strength fades significantly when the vehicle is in close proximity with the receiver resulting in the receiver receiving less than the desired signal strength. In some applications, the signal emitted by the antenna comprises a jamming signal and the receiver may be a receiver for a remote controlled explosive device, for example. Accordingly, fading of the jamming signal when the vehicle is in close proximity to the receiver may render the jamming signal ineffective, and enable the explosive device to be remotely detonated.
In view of the above, it would be desirable to provide an improved antenna assembly which is capable of producing adequate signal strength and coverage in close proximity to the vehicle or other support on which it is mounted.
According to one aspect of the present invention, there is provided an antenna assembly for mounting on a predetermined support structure positioned on a surface, said support structure having a peripheral edge at an elevated position above the surface, the antenna assembly comprising an antenna and a support for supporting the antenna at an elevated position above said surface, when mounted on said support structure, wherein the support is adapted to support the antenna at a sufficient height above said surface to provide a direct path for electromagnetic radiation from at least a portion of the antenna to a position on the surface external of the peripheral edge, of less than or equal to about 4.5 meters from substantially any point on the peripheral edge, or to a position on the surface at a point positioned a first predetermined distance from the front of the support structure and a predetermined distance from a side of the support structure, or to a position on the surface a predetermined distance from the center of the support structure.
Thus, where the position on the surface is less than or equal to about 4.5 meters from substantially any point on the peripheral edge, the antenna has a direct line of sight to substantially all positions along the peripheral edge spaced a distance of 4.5 meters from the peripheral edge, or less. In other words, the inner edge of the direct line of sight footprint extends around the support structure so that the inner edge is no more than about 4.5 meters away from the peripheral footprint at the surface at any position on the peripheral edge.
The inventors have determined that at certain frequencies, the vehicle's metallic shell causes significant shadowing, reflecting and scattering of electromagnetic radiation emitted by an antenna mounted on the exterior of the vehicle. Mounting the antenna at a sufficient height to provide a direct line of sight from at least a portion of the antenna to a region within close proximity to the vehicle substantially improves uniformity of the signal strength around the vehicle and reduces both the number and depth of spatial nulls. The inventors have further determined that, although interference of the direct path signal by out-of-phase, indirect path signals, for example, scattered from the vehicle surface, causes some attenuation of the direct path signal, the direct path signal is significantly stronger than the scattered multi-path signals and therefore the amount of attenuation of the direct path signal is relatively small.
For the purpose of determining the position from the peripheral edge of the support structure, the surface may be a planar surface.
Certain features of support structure are predetermined. For example, the support structure has predetermined dimensions, including length, width and possibly height above the surface, the shape of the peripheral edge and the height of different portions of the peripheral edge above the surface. Different portions of the upper surface of the support structure may be at different levels above the surface. The position on the support structure (and its height above the surface) for mounting the antenna assembly may also be predetermined.
In some embodiments, the support is arranged so that when mounted on the support structure, the antenna is positioned at a sufficient height above the surface to provide a direct path for electromagnetic radiation from at least a portion of the antenna to a position on the surface external of the peripheral edge of less than or equal to 3.6 meters from substantially any point on the peripheral edge.
In some embodiments, the antenna is configured for transmitting electromagnetic radiation over a substantially full azimuthal range of angles, i.e. over an azimuthal range of substantially 360°.
In some embodiments, the magnitude of the electromagnetic energy radiated from the antenna varies with angle of elevation of the radiated energy.
In some embodiments, the magnitude of the electromagnetic energy has a range of values between a maximum value at a first angle of elevation and a predetermined lower value at a second angle of elevation, and the longest direct path from the antenna to the position on the surface has an angle between the first and second angles, inclusive. In some embodiments, the predetermined lower value may be about 3 dB below the maximum value. Thus, in this embodiment, an upper limit is placed on the height of the antenna above the surface, so that at the predetermined position at the surface, the RF signal has a strength at or above a predetermined minimum value.
In some embodiments, the longest direct path from the antenna to the position on the surface forms an angle with the vertical greater than or equal to a predetermined minimum angle. The predetermined minimum angle may be an angle where the magnitude of electromagnetic radiation is between a maximum value and a predetermined value of less than the maximum value. The predetermined value may for example be about 3 dB below the maximum value.
In some embodiments, the antenna assembly further comprises biasing means for biasing the spread of electromagnetic radiation emitted from the antenna in a downward direction. Thus, in this embodiment, for a vertical antenna, more electromagnetic radiation emitted from the antenna is directed below the horizontal than above the horizontal. Advantageously, this arrangement may increase the amount of electromagnetic radiation received at the position on the surface.
In some embodiments, the biasing means comprises a second antenna.
In some embodiments, the antenna is configured to bias the spread of electromagnetic radiation downwardly. This may be achieved by configuring the antenna asymmetrically. For example, in the case of a dipole antenna, or where the antenna comprises two radiating elements, the lower element may be longer than the upper element, and/or an additional element may be provided which capacitively couples with the lower element more than with the upper element.
In some embodiments, the first antenna has upper and lower ends, the second antenna has upper and lower ends, and wherein the upper end of the second antenna is below the upper end of the first antenna.
In some embodiments, the antenna assembly further comprises an RF signal source coupled to the first and second antennas and for providing an RF signal having a first frequency to the first antenna and an RF signal having a second frequency to the second antenna. The first frequency may be different from the second frequency, and in some embodiments, the second frequency is below the first frequency.
In some embodiments, the second signal has a different phase to the first signal.
In some embodiments, an RF signal is applied to each of the first and second antennas such that at least one common frequency or frequency band is applied to both antennas. The common frequency or frequency band applied to the first antenna may have a different phase to the common frequency or frequency band applied to the second antenna to bias the direction of emitted radiation downwardly.
In some embodiments, the RF signal applied to the first and/or second antenna includes one or more different frequency(ies) to the frequency(ies) applied to the other of the first and second antenna.
In some embodiments, the antenna assembly further comprises control means for controlling the elevational direction of electromagnetic radiation emitted from the antenna.
In some embodiments, the antenna assembly comprises means for concentrating the elevational spread of electromagnetic radiation emitted from the first antenna. In some embodiments, the concentrating means comprises a second antenna.
In some embodiments, the area of the support within the peripheral edge is substantially opaque to electromagnetic radiation emitted from the antenna. In some embodiments, the area of the support within the peripheral edge has no direct path from the antenna to the surface.
In some embodiments, the support comprises a mobile support. The support may, for example, comprise a vehicle. In some embodiments, the vehicle comprises a military vehicle.
In some embodiments, the support has opposed ends and a center, midway between the opposed ends, and the antenna is offset from the center towards one of the ends. The opposed ends may comprise a front end and a rear end of the support, and the antenna may be offset towards the rear end.
In some embodiments, the support has opposed sides and a center between the opposed sides and the antenna is offset from the center towards one of the opposed sides.
In some embodiments, the antenna comprises a ground plane independent antenna, for example, one of a bicone antenna and a dipole antenna.
In some embodiments, the antenna is limited to operate within a predetermined frequency band, wherein the frequency band is within a range having a lower frequency of about 200 MHz. The inventors have found that for the particular type of vehicle tested whose length is about 5 m, and for frequencies of 200 MHz and above, a direct line of sight from the antenna to the position on the surface substantially increases signal strength at the position and reduces the depth of spatial nulls.
In some embodiments, the minimum frequency to be radiated by the antenna having a direct line of sight to the critical position on the surface is related to the length of the vehicle. In one embodiment, the minimum frequency is determined as that for which the ratio 1/λ is in the range 2.5 to 4, for example 3 to 3.5, where 1 is the length of the vehicle (or support) and λ is the wavelength of the RF signal.
In some embodiments, the antenna assembly further comprises a second antenna supported by the support.
In some embodiments, the support is adapted to support the second antenna at a sufficient height above the surface to provide a substantially direct path for transmission of electromagnetic radiation from at least a portion of the second antenna to a position at the surface of less than or equal to 3 meters (for example equal to or less than 2.5 meters) from substantially any point on the peripheral edge.
In some embodiments, the first antenna has opposed upper and lower ends, the second antenna has opposed upper and lower ends, and the upper end of the second antenna is positioned below the upper end of the first antenna.
In some embodiments, the upper end of the second antenna is adjacent the lower end of the first antenna. In some embodiments, the second antenna is positioned to capacitively couple with the first antenna. In some embodiments, a portion of the length of the second antenna overlaps a portion of the length of the first antenna.
In some embodiments, the first and second antennas each have a longitudinal axis and the axes are substantially coaxially aligned.
In some embodiments, the second antenna at least partially supports the first antenna.
In some embodiments, the first antenna is limited to operate over a first frequency band between first upper and first lower frequencies and the second antenna is limited to operate over a second frequency band between a second upper frequency and a second lower frequency, wherein the second upper frequency is below the first upper frequency.
In some embodiments, the first lower frequency is substantially adjacent the second upper frequency. Thus, the frequency bands may or may not partially overlap.
In some embodiments, the antenna assembly further comprises biasing means for biasing the elevational spread of electromagnetic radiation emitted from the second antenna in a downward direction.
In some embodiments, the antenna assembly further comprises means for concentrating the spread of electromagnetic radiation emitted from the second antenna.
In some embodiments, the antenna assembly further comprises a third antenna supported by the support at an elevated position above the surface.
In some embodiments, the third antenna has upper and lower ends, and the upper end of the third antenna is positioned below the upper end of the second antenna.
In some embodiments, the upper end of the third antenna is positioned substantially adjacent the lower end of the second antenna. In some embodiments, the third antenna is positioned to capacitively couple with the second antenna. In some embodiments, a portion of the length of the third antenna overlaps a portion of the length of the second antenna.
In some embodiments, the third antenna has an axis extending between its first and second ends, and the axis is substantially coaxially aligned with the axis of at least one of the first and second antennas.
In some embodiments, the third antenna at least partially supports at least one of the first and second antennas.
In some embodiments, the third antenna is limited to operate efficiently over a predetermined frequency having upper and lower frequencies, and wherein the upper frequency of the third antenna is below the upper frequency of the second antenna.
In some embodiments, the upper frequency of the third antenna is substantially adjacent the lower frequency of the second antenna.
In some embodiments, the third antenna comprises a ground plane independent antenna, e.g. a bicone antenna or dipole antenna.
The second antenna may comprise a ground plane independent antenna, e.g. a bicone antenna or dipole antenna.
In some embodiments, the support includes mounting means for mounting the antenna assembly on a vehicle.
According to another aspect of the present invention, there is provided an antenna assembly comprising an antenna, a support for supporting the antenna at an elevated position above a surface, the support having a peripheral edge positioned above the surface, wherein the support structure is adapted to support the antenna at a sufficient height above said surface to provide a direct path for electromagnetic radiation from at least a portion of the antenna to a position on the surface external of the peripheral edge, of less than or equal to about 4.5 meters from substantially any point on the peripheral edge, or to a position on the surface at a point positioned a first predetermined distance from the front of the support and/or a predetermined distance from a side of the support, or to a position on the surface a predetermined distance from the center of the support.
According to another aspect of the present invention, there is provided an antenna assembly comprising a first antenna limited to operate over a first frequency band between a first upper and a first lower frequency, the antenna having opposed upper and lower ends, a second antenna limited to operate over a second frequency band between a second upper frequency and a second lower frequency, the second antenna having opposed upper and lower ends, wherein the second upper frequency is different from the first upper frequency, and support means for supporting the first antenna at a position above the second antenna such that the upper end of the second antenna is below the upper end of the first antenna.
In some embodiments, the second upper frequency is below the first upper frequency.
In some embodiments, the antenna assembly further comprises biasing means for biasing the elevational spread of electromagnetic radiation emitted from at least one of the first and second antennas downwardly.
In some embodiments, the antenna is configured to bias the spread of electromagnetic radiation downwardly. This may be achieved by configuring the antenna asymmetrically. For example, in the case of a dipole antenna, or where the antenna comprises two radiating elements, the lower element may be longer than the upper element, and/or an additional element may be provided which capacitively couples with the lower element more than with the upper element.
In some embodiments, the biasing means comprises a controller for controlling at least one of the relative frequency and relative phase of the electromagnetic radiation emitted from at least one of the first and second antennas.
In some embodiments, the upper end of the second antenna is substantially adjacent the lower end of the first antenna.
In some embodiments, each of the first and second antennas has an axis extending between the respective opposed ends thereof, and the axis of the first and second antennas are substantially coaxially aligned.
In some embodiments, the second antenna at least partially supports the first antenna.
In some embodiments, one or more of the first and second antennas comprises a ground plane independent antenna, e.g. a bicone antenna or a dipole antenna.
In some embodiments, the antenna assembly further comprises a signal source coupled to at least one of the first and second antennas for providing a jamming signal thereto.
In some embodiments, one or more of the first and second antennas is capable of transmitting electromagnetic radiation over substantially the full range of azimuthal angles.
According to another aspect of the present invention, there is provided an antenna assembly comprising an antenna for emitting radio frequency electromagnetic radiation therefrom and biasing means for biasing the elevational spread of electromagnetic radiation emitted from the antenna downwardly.
In some embodiments, the antenna is configured to bias the spread of electromagnetic radiation downwardly. This may be achieved by configuring the antenna asymmetrically. For example, in the case of a dipole antenna, or where the antenna comprises two radiating elements, the lower element may be longer than the upper element, and/or an additional element may be provided which capacitively couples with the lower element more than with the upper element.
In some embodiments, the antenna is capable of transmitting electromagnetic radiation over substantially the full range of azimuthal angles.
In some embodiments, the biasing means comprises a second antenna.
In some embodiments, the second antenna has upper and lower ends, in which the upper end is positioned below the upper end of the first antenna.
In some embodiments, the biasing means comprises a controller for controlling at least one of the relative frequency and relative phase of electromagnetic radiation emitted from at least one of the first and second antennas.
In some embodiments, the antenna assembly further comprises concentrating means for concentrating the spread of electromagnetic radiation emitted from the antenna.
In some embodiments, the antenna assembly comprises a signal source coupled to at least one of the first and second antennas for providing a jamming signal thereto.
In some embodiments, one or more of the first and second antennas comprises a ground plane independent antenna, e.g. a bicone antenna or a dipole antenna.
According to another aspect of the present invention, there is provided an antenna assembly comprising one or more antennas including a first antenna, mounting means for mounting the antenna to a vehicle, concentrating means for concentrating the spread of electromagnetic radiation emitted from the antenna and a signal source coupled to the antenna for providing a jamming signal thereto.
In some embodiments, one or more of the antennas is configured for transmitting electromagnetic radiation over substantially the full range of azimuthal angles.
In some embodiments, the concentrating means comprises a second antenna.
In some embodiments, the concentrating means may further comprise a controller for controlling at least one of the relative frequency and relative phase of electromagnetic radiation emitted from at least one of the first and second antennas.
According to another aspect of the present invention, there is provided an antenna assembly comprising an antenna, a support for supporting the antenna at an elevated position above a surface, the support having a peripheral edge positioned above the surface, wherein the support is adapted to support the antenna at a sufficient height above said surface to provide a direct path for electromagnetic radiation from at least a portion of the antenna to any position between opposed ends of the support that is spaced at least one of (1) about 2.5 to 3 meters or (2) less than about 2.5 to 3 meters from a side of said support.
Thus, in this arrangement, the antenna has a direct line of sight at least to substantially all positions along a side of the support structure between the ends which are spaced 3 meters from the side. In other words, the inside edge of the direct line of sight footprint is no more than 3 meters from one or both sides of the support structure between the ends thereof.
In some embodiments, the antenna is positioned centrally between the two sides or offset to one side so that the direct path must traverse at least half or more than half of the width of the support structure to the critical position on the surface.
According to another aspect of the present invention, there is provided an antenna assembly comprising an antenna, a support for supporting the antenna at an elevated position above a surface, the support having a peripheral edge positioned above the surface, wherein the support is adapted to support the antenna at a sufficient height above the surface to provide a direct path for electromagnetic radiation from at least a portion of the antenna to a position on the surface external of the peripheral edge spaced about 2.5 to 3 meters from one or both ends of said support or less than about 2.5 to 3 meters from one or both ends of said support and between a side of said support and about 2.5 to 3 meters from said side.
Thus, in this arrangement, the antenna has a direct line of sight to a position spaced both 3 meters from an end and 3 meters from a side of the support structure. In other words, the direct line of sight footprint includes this position.
In some embodiments, the antenna has a direct line of sight from the antenna to all positions spaced both 3 meters from one or both ends and between one or both sides and 3 meters from a respective side.
In some embodiments, the antenna has a direct line of sight to all positions spaced both 3 meters from one or both sides and between one or both ends and 3 meters from a respective end.
In some embodiments, the antenna is positioned on the support structure either centrally between the sides and/or ends and/or offset towards a side and/or end. The direct path or line of sight may traverse at least half or more than half of the width and/or the length of the support structure to reach the or each position on the surface.
According to another aspect of the present invention, there is provided an antenna assembly for mounting on a support structure positioned on the surface and having a peripheral edge, the antenna assembly comprising an antenna and a support for supporting the antenna on the support structure wherein the support is configured to support the antenna at a sufficient height above said surface when mounted on said support structure to provide a direct path for electromagnetic radiation from at least a portion of the antenna to a position on the surface external of the peripheral edge, wherein said position comprises any one or more of the positions disclosed or claimed herein.
According to another aspect of the present invention, there is provided a method of designing an antenna support comprising selecting a support structure on which to mount the antenna, the support structure having a peripheral edge, selecting a position on the support structure on which to mount the antenna, determining a height for the antenna, when mounted at said selected position, to provide a direct path from at least a portion of the antenna to a position on a surface below the selected support structure and spaced externally of a peripheral edge of the support structure by a distance of any one or more of (1) less than or equal to about 3.6 to 4.5 meters from substantially any point on the peripheral edge, (2) a position at any point between opposed ends of said support which is spaced about 2.5 to 3 meters or less from a side of said support structure, (3) a position of about 2.5 to 3 meters or less than 2.5 to 3 meters from a side of said support structure and about 2.5 to 3 meters or less from one or both ends of said support structure and (4) a position of about 2.5 to 3 meters from an end of said support structure and between a side of said support structure and about 2.5 to 3 meters from said side, and designing a support for mounting on the support structure and for supporting the antenna at the determined height.
According to another aspect of the present invention, there is provided an antenna for radiating electromagnetic radiation having opposed ends and a structure which biases the direction of radiation emitted outwardly from the antenna towards one of said ends.
Examples of embodiments of the present invention will now be described with reference to the drawings, in which:
Referring to
The mobile structure has opposed front and rear ends 19, 21 and opposed left and right sides 23, 25. In this embodiment, the first and second antennas are located at a position which is offset from the center 27 of the mobile support structure 11 towards the rear end 21 and towards the right side 25. In other embodiments, the first and second antennas may be located at any other position on the support structure, for example at the center position 27 or at any other location.
The support 6 is configured to support the first antenna 3 at a sufficient height above the surface 9 to provide a direct path 29 for electromagnetic radiation from at least a portion of the antenna (for example, the mid or main radiating region, or region between elements of a ground plane independent antenna) to a position, P, on the surface 9 spaced from the front end of the support structure (e.g. vehicle) by a distance of less than or equal to d1 and spaced from a side 23 of the support structure by a distance of less than or equal to d2. In some embodiments, the distance d1 has any value in the range of 2.5 to 3 meters. In some embodiments, the distance d2 has any value in the range 2.5 to 3 meters.
In some embodiments, the first antenna 3 is positioned at a sufficient height above the surface 9 to provide a direct path for electromagnetic radiation from at least a portion of the antenna 3 to a position on the surface, external of the peripheral edge 13 of the support structure of less than or equal to a distance d3 from substantially any point on the peripheral edge 13. As can be appreciated from
In this embodiment, the second antenna 5 is also positioned at a sufficient height above the surface 9 to provide a direct path for electromagnetic radiation from at least a portion (e.g. the mid, or main radiating region, or region between elements of a ground plane independent antenna) of the second antenna to the position P, as defined above, and shown in
Referring to
In other embodiments, the first and second antennas may comprise any other suitable form of antenna, non-limiting examples of which include any other ground plane independent antenna (e.g. a bicone antenna) or a monopole antenna.
Providing a direct path for electromagnetic radiation emitted from the first antenna 3 to a position on the surface spaced a distance d1 in front of the mobile support structure and spaced a distance d2 from one side of the support structure has been found to significantly improve the signal strength at that position, particularly for relatively high frequencies, in comparison to other arrangements in which only indirect paths for electromagnetic radiation exist between the antenna and that position. Thus, this arrangement significantly mitigates the effects of scattering and shadowing by the support structure. Similar benefits are obtained by providing a direct path between at least a portion of the second antenna 5 and the position.
In some embodiments, a direct line of sight from either one or both of the first and second antennas 3, 5 may be provided over a range of lateral distances dw positioned at a distance d1 from the front peripheral edge of the support structure from point P (at d2) towards the side (e.g. side 23) of the support structure. The range, for example, may be the range 51 between point P and point F1 which corresponds to a lateral position at the side 23 of the support structure. In other embodiments, the range may be greater or less than the range 51. This arrangement helps to ensure that a continuous region of relatively high signal strength exists across a region in front of and proximate to the support structure, and which extends from a position P to at least the side 23 of the support structure, for example.
In some embodiments, a direct path from one or both of the first and second antennas may be provided over a range of longitudinal distances dL from point P towards the rear of the support structure spaced a distance d2 from a side 23 of the support structure. The range may extend from point P to at least to a position F2 which corresponds to the rear end 21 of the support structure or beyond the rear end 21.
This arrangement helps to ensure that a continuous region of relatively high signal strength exists along the side of the support structure and which extends at least from the front of the support structure to the rear of the support structure, and which is positioned relatively close to the side of the support structure. This enables a receiver device 53 (which in
In some embodiments, the inner edge of the direct line of sight footprint may extend substantially fully around the support structure, so that the inner edge is no more than about 4.5 meters away from the peripheral edge at any position on/along/around the peripheral edge.
Conventional dipole antennas have an antenna pattern in which the signal intensity is a maximum along a line perpendicular to the dipole axis and decreases as the elevation angle increases from the line towards the dipole axis. Thus, referring to
The antenna assembly includes a support for supporting the first antenna 103 at an elevated position above the base 109. The support may for example be provided at least partially by the second antenna 105, and/or by a housing at least partially enclosing the second antenna, and/or by some other structure upstanding from the base 109.
In this embodiment, each of the first and second antennas 103, 105 are designed to operate efficiently over a limited frequency band, in which the upper operating frequency of the first antenna 103 is above the upper operating frequency of the second antenna 105. The first antenna 103 may be designed to operate at frequencies which are readily scattered by a support structure on which the antenna assembly is or is to be mounted. Locating the first antenna at an upper position of the antenna assembly brings positions on a surface below the support structure having a direct line of sight to the first antenna closer to the support structure, so that RF signals from the antenna are relatively strong at such positions. The height of the first antenna 103 above a surface is the height above the base 109 of the antenna assembly at which the first antenna is supported plus the height of any support structure from the surface to the base 109. The antenna assembly may be configured so that the height of the first antenna 103 above the base 109 provides the desired height of the first antenna 103 above the surface when mounted on a particular support structure, e.g. a mobile structure such as a vehicle, for example, or a static support structure.
In some embodiments, the operating frequency band of the second antenna 105 may be such that the support structure on which the antenna assembly is to be mounted does not significantly scatter or shadow electromagnetic radiation emitted therefrom. At such frequencies, it has been found that the support structure does not significantly interfere with the signal strength at locations proximate the peripheral edge of the support structure. Embodiments of the invention exploit this fact by locating such an antenna at a lower position of the antenna assembly, for example below the upper antenna, thereby making use of the space between the upper antenna and the base of the antenna assembly and not lengthening the antenna assembly unnecessarily. In some embodiments, the second antenna 105 may be located so that there is no or no substantial direct line of sight between the antenna and a position on the surface spaced from the support structure where the RF signal strength emitted from the second antenna should be relatively high.
The upper operating frequency limit of the second antenna 105 may either be above, adjacent or below the lower operating frequency limit of the first antenna 103. The first antenna 103 may be any suitable antenna for emitting relatively high frequencies such as a dipole, bicone or other ground plane independent antenna, and the second antenna 105 may be any suitable antenna for operating at relatively low frequencies, such as a dipole or monopole antenna.
In this embodiment, the second antenna 205 is positioned above the third antenna 207 and the first antenna 203 is positioned above the second antenna 205. Each of the antennas operates efficiently over a limited frequency band, and in some embodiments, the upper operating frequency limit of the second antenna 205 is below the upper operating frequency limit of the first antenna, and/or the upper operating frequency limit of the third antenna 207 is below the upper operating frequency limit of the second antenna 205. In this arrangement, each of the antennas is positioned at an elevational level of the antenna assembly which increases with the operational frequency band of the antenna. Thus, the first antenna 203 which operates at the highest frequency band is the uppermost antenna, the second antenna 205 which operates at the second highest frequency is positioned below the first antenna 203 and the third antenna 207 which operates at the lowest frequency band is positioned below the second antenna 205.
The lower antenna 207 is supported by the support section 215. The second antenna 205 may be supported at least partially by the third antenna 207, and/or by a housing at least partially enclosing the third antenna 207 or by some other support structure. The first antenna 203 may be supported at least partially by the second antenna 205, by a housing of the antenna assembly at least partially enclosing the second antenna or by some other support structure.
The operating frequency band of the first antenna 203 may be such that electromagnetic radiation within the frequency band is significantly scattered by a support structure on which the antenna assembly 201 is or is to be mounted. The antenna assembly is configured so that the height of the first antenna 203, when mounted on the support structure, is at a sufficient height above the surface on which the support structure is located to provide a direct line of sight between the first antenna and a position on the surface spaced a predetermined distance from the peripheral edge of the support structure, where sufficient signal strength from the first antenna is critical.
In some embodiments, the second and/or third antenna 205, 207 may operate at frequencies which are also significantly scattered by the support structure to which the antenna assembly is or is to be mounted, and the antenna assembly is configured so that the second and/or third antenna is positioned at a sufficient height above the surface when mounted to the support structure to provide a direct line of sight between the respective antenna and a critical position on the surface spaced from the peripheral edge of the support structure. In a specific embodiment, the second antenna 205 is positioned at a sufficient height to provide a direct line of sight to the critical position on the surface, but the third antenna 207 operates at frequencies at which the electromagnetic radiation is not significantly scattered by the support structure, and is positioned at a height where there is no or substantially no direct line of sight from the third antenna to the critical position on the surface.
In some embodiments, the first and second antennas 203, 205 may be designed to operate at relatively high frequencies, and may for example comprise a bicone or dipole antenna. The third antenna 207 may be designed to operate at intermediate frequencies and may comprise any of a bicone, dipole or monopole antenna or any other form of antenna.
In some embodiments, the antenna assemblies shown in
In some embodiments, one or more of the antennas of the antenna assemblies 101, 201 of the
In some embodiments, the antennas of an antenna assembly may be positioned so that the upper end of one antenna is at an elevational level which is either at, below or above the lower end of an upper antenna. Thus, in some embodiments, the elevational position of two or more antennas may or may not overlap. In the former case, the lateral dimension of overlapping antennas may be such that each antenna does not interfere with the propagation of electromagnetic radiation emitted from another antenna at the wavelength(s) concerned. In some embodiments, one or more antennas may be arranged to capacitively couple with another, e.g. adjacent, antenna to control the direction of RF radiation, as more fully described below.
A specific example of the antenna assembly of
In this embodiment, the spacer element 137 supports the first antenna 103. The first antenna 103 and the spacer element 137 may be supported by the second antenna only (for example if the spacer element is free to slide up and down relative to the antenna housing), by only the antenna housing 127 (for example if the spacer element 137 is not free to move up and down relative to the housing), or by a combination of both the antenna element 123 and the housing.
The first RF port 111 is connected to one of (e.g. the upper) conical elements 119, 121, of the bicone antenna via a suitable RF lead 145, which may conveniently pass through the inner conduit 124 of the second antenna element 123, as shown in
An example of the embodiment of the antenna assembly illustrated in
The antenna assembly further comprises a housing 239 which at least partially encloses the first, second and third antennas 203, 205, 207 and which, in this embodiment, comprises an outwardly extending cylindrical wall 241 defining an internal space 243 for accommodating the antennas and an optional top or cover 245 positioned adjacent the upper end 247 of the housing. The housing assembly includes a support section 215 extending upwardly from the base 213 which supports the lower antenna 207. A spacer element 249 separates the first and second dipole elements of the lower antenna 207 and optionally extends between opposed wall sections 251, 253 of the housing. A spacer element 253 separates the second and third antennas and spaces the antennas apart in the vertical direction. Similarly, a spacer 255 is positioned between the first and second antennas 203, 205 to separate the antennas from one another and which also spaces the antennas apart in the vertical direction. An additional spacer element 257, 259 is provided between respective dipole elements of the first and second antennas to separate the dipole elements of the same antenna, and which may optionally extend between opposed wall sections 251, 253 of the housing. Each of the spacer elements 253, 255 between the antennas may have any of the features described above in connection with the spacer element 137 of the antenna assembly 101 shown in
The first RF port 217 is connected to the first antenna 203 via a suitable RF lead 261, the second RF port 219 is connected to the second antenna 205 via a suitable RF lead 263 and the third RF port 221 is connected to the third antenna 203 via a suitable RF lead 265. One or more of the RF leads may conveniently pass through the internal conduit defined through the tubular dipole elements of the antennas, for example as shown in
As mentioned above, each transceiver module may be adapted to operate over a specific frequency band. Two or more modules connectable to the same antenna may be configured to operate over the same frequency band. One or more frequency bands may be divided into two or more sub bands and two or more modules connectable to the same antenna may be configured to operate within the same frequency band but different sub-bands thereof. In a specific, non-limiting example, each of transceiver modules 307, 309 and 311 are configured to operate within a mid-frequency band and each module is adapted to operate within a different sub-frequency band of the mid-band. Transceiver module 305 of the first group 303 may be configured to operate within a high frequency band, for example, and transceiver module 313 may be adapted to operate over a low frequency band, and possibly over a sub band within a low frequency band. Each of the transceiver modules 319, 321, 323 of the second group 317 may be configured to operate within a low frequency band and each may operate within a different sub-band of the low frequency band. Each low frequency sub-band of the second group of transceiver modules may be different from the low frequency sub-band of the transceiver module 313 of the first group. In other embodiments, any other configuration of receiver modules is possible. Although the switching/multiplexer module in the embodiment of
In some embodiments, two or more different operating frequency bands of two or more modules may be substantially adjacent one another so that the transceiver modules together cover a continuous spectrum of frequencies between the lower frequency band and the upper frequency of the upper frequency band.
Although in some embodiments, one or more antennas of the antenna assembly may comprise a broadband antenna, each antenna may beneficially comprise a relatively narrow band antenna tuned to operate over a specific limited frequency band to provide increased antenna gain and coverage performance.
In other embodiments, the RF system connected to an antenna assembly may comprise one or more transmitter modules adapted only for transmitting RF signals, or one or more receiver modules configured only for receiving RF signals from the antenna assembly or one or more transceiver modules capable of both transmitting and receiving RF signals to and from an antenna assembly. In some embodiments, two or more modules may be switchably coupled to a single antenna of an antenna assembly or a single module may be switchably coupled between different antennas of the same antenna assembly or between different antennas of different antenna assemblies.
According to another aspect of the present invention, an antenna assembly is provided having at least one antenna in which the direction of radiation emitted from the antenna is biased in a downward direction so that there is a higher concentration of electromagnetic radiation below the horizon than above the horizon. In some embodiments, means may be provided for concentrating the electromagnetic radiation in a narrower elevational band. Examples of embodiments of this aspect of the invention are described below with reference to
In this embodiment, each of the predetermined reduced intensity lines 417, 421, 425 above the respective line of maximum intensity and reduced intensity lines 419, 423, 427 below the respective line of maximum intensity are at the same elevational angle, α, relative to the respective line of maximum intensity. Thus, with respect to the arrangement of
As can be seen in
Each antenna may radiate over a full range of azimuthal angles or at least a range which includes one or both sides of the support structure and the distribution of radiation emitted from the antenna is directed downwardly over either the full range of azimuthal angles or a partial range which includes one or both sides of the vehicle. It can be appreciated that, with this arrangement, the intensity of radiation emitted from the antenna assembly near one or both sides of the vehicle can be considerably increased.
The combination of both tilting the angular distribution of electromagnetic radiation downwardly and concentrating the angular distribution within a narrower range of angles increases the intensity of radiation at locations at or near the surface on which the antenna assembly is placed. Depending on the tilt angle, this arrangement may also increase the intensity of radiation at positions closer to the antenna assembly support structure. For example, referring to
In some embodiments, the angle subtending the upper and lower lines of reduced intensity is about 45°, with the elevational angle γ1 between the horizontal and upper reduced intensity line being about 15° and the angle γ2 between the horizontal 411 and the lower reduced intensity line 419 being about −30°.
In the arrangement of
The upper element of the second antenna 407 couples to the first antenna and the lower element couples to the third antenna 409. However, due to the longer length of the third antenna relative to the first, the lower element of the second antenna couples more strongly to the third antenna than the upper element does to the first antenna. In some embodiments, this may effectively increase the electrical length of the lower element relative to the upper element, thereby biasing the radiation from the second antenna downwardly.
In any of the embodiments described herein, the direction of radiation from an antenna can be controlled by controlling the relative phase of RF signals between the antenna and another adjacent antenna, for example in an arrangement where the antennas are positioned one above the other. The elevational distribution of electromagnetic radiation from an antenna may be controlled in a similar manner. Some embodiments may include a phase controller for controlling the relative phase of signals passed to two or more antennas. For example, one or more phase controllers may be included in the RF transmitter/receiver of the embodiment of
Referring to
The combination of the first and second antenna assemblies 503, 505 of the antenna system 501 shown in
Another aspect of the present invention provides an antenna which is capable of biasing the spread of emitted electromagnetic radiation either downwardly or upwardly, i.e. in a direction other than 90° relative to the antenna axis. Examples of embodiments of the antenna will now be described with reference to
In the above antenna configurations shown in
In other embodiments, the features of the embodiments of
In any embodiment, one or more antennas may be vertically or cross-polarized. Cross-polarization has the benefit of mitigating spatial nulls caused by multi-path cancellation. Although fading will typically provide some gain for situations involving unmatched polarization, polarization diversity may enhance the performance irrespective of whether the vehicle or other support structure is stationary or moving.
In any embodiments, any antenna which is designed to operate at a frequency of greater than or equal to about 200 MHz or another frequency which is substantially reflected or scattered by the support structure may be arranged so that a direct path or line of sight exists between at least a portion of the antenna and one or more critical positions spaced a predetermined distance from either the center of or a peripheral edge of the support structure. In any embodiments, the antenna assembly may include a housing for accommodating the antennas and which is adapted to substantially prevent the ingress of moisture and/or particulate matter from the ambient.
Other aspects and embodiments of the present invention comprise any one or more features disclosed herein in combination with any one or more other features disclosed herein.
In any aspect or embodiment of the invention, any one or more features may be omitted altogether or substituted by another feature which may or may not be an equivalent or variant thereof.
Modifications to the embodiments described above will be apparent to those skilled in the art.
This U.S. non-provisional patent application claims priority from U.S. Provisional Patent Application No. 60/969,305 filed on 31 Aug., 2007, the entire contents of which is incorporated herein by reference.
Number | Name | Date | Kind |
---|---|---|---|
4186403 | Dorne | Jan 1980 | A |
5364049 | Long | Nov 1994 | A |
5600335 | Abramo | Feb 1997 | A |
6057804 | Kaegebein | May 2000 | A |
6225954 | Edvardsson et al. | May 2001 | B1 |
6366237 | Charles | Apr 2002 | B1 |
7183992 | Hung | Feb 2007 | B2 |
7202826 | Grant et al. | Apr 2007 | B2 |
Number | Date | Country |
---|---|---|
2462721 | Apr 2004 | CA |
2560382 | Mar 2007 | CA |
2001119217 | Apr 2001 | JP |
9613075 | May 1996 | WO |
2004091106 | Oct 2004 | WO |
Number | Date | Country | |
---|---|---|---|
20090140939 A1 | Jun 2009 | US |
Number | Date | Country | |
---|---|---|---|
60969305 | Aug 2007 | US |