LOW PROFILE ANTENNA

There is provided a low profile antenna comprising a line source, a corporate feed network, and a plurality of radiating elements. The radiating elements are arranged in a linear array so as to be discrete in a first direction and each continuous in a second direction substantially perpendicular to the first direction. The corporate feed network is integrated with the linear array of radiating elements to provide for a compact design.

DETAILED DESCRIPTION

Referring now toFIG. 1, an antenna aperture100having a low profile will now be described. The antenna aperture100illustratively comprises a line source102and a linear radiator array104comprising a number N of horizontal radiators1061, . . . ,106Neach extending along the X axis and a number M of vertical radiators (not shown) each extending along the Y axis. It should be understood that the number of radiators as in1061, . . . ,106Nin the array104may vary according to system requirements. Each radiator as in1061, . . . , or106Nmay be a tapered slot antenna that is adapted to radiate at a given directionality the energy of an electromagnetic wave received thereat. It should be understood that other configurations of the radiator may apply.

Referring toFIG. 2aandFIG. 2bin addition toFIG. 1, the antenna aperture100further comprises a corporate feed network108supplying electromagnetic energy to the radiators1061, . . . ,106N. In one embodiment, the radiators1061, . . . ,106Nare integrated with the feed network108as a single component. For this purpose, both the radiators1061, . . . ,106Nand the feed network108may be manufactured from the same waveguide piece110having an air-filled or other appropriate structure, such as a dielectric-filled or partially-filled waveguide structure. For example, each radiator as in1061, . . . , or106Nmay be etched on the waveguide piece110and excited using the corporate feed network108also etched on the waveguide piece110. High speed machining, extrusion, casting, molding, e.g. injection molding, or any other suitable manufacturing process known to those skilled in the art may also be used. The radiator array104may for instance be manufactured using solid metal extrusions, hollow extrusions, plastic extrusions, or composite extrusions with application of a metal coating or foil. The line source102may then be provided separately from the integrated radiators1061, . . . ,106Nand feed network108. In particular, when in use, the line source102may be coupled to feed network108to become part thereof. In this manner, a low weight and compact size antenna aperture100may be provided.

The line source102may further be coupled to a source of electromagnetic signals (not shown), from which an input signal may be received. The line source102may then transform the input into an output having an expanded dimension, e.g. width, along the X axis. In one embodiment discussed further below, a single mode input is provided by the source to the line source102and the latter outputs a single linear beam that is continuous along the X axis. The signal output by the line source102may then be transmitted to the feed network108and replicated thereby to feed each one of the N horizontal radiators1061, . . . ,106Nfor transmittal. Although the antenna aperture100is described herein in the context where it is used as a transmitter, it should be understood that the antenna aperture100may, by reciprocity, be used as a receiver and route receive signals to single outputs.

The feed network108may comprise a plurality of transmission or feed lines as in1121, . . . ,112nand power dividers (not shown) provided over a number n of successive feed levels. The first feed level, i.e. level1, is illustratively the level closest to the line source102while the last feed level, i.e. level n, is the level closest to the radiator array104. Each one of the transmission lines provided at the last feed level n, e.g. transmission line112ninFIG. 2aandFIG. 2b, may then be coupled to a corresponding radiator, e.g. radiator1061, of the radiator array104. In this manner, the output of each one of the transmission lines found at the last feed level may be provided to the corresponding radiator as in1061, . . . , or106Nfor feeding thereof. In particular, the feed network108illustratively receives at an input port114thereof the expanded signal output by the line source102. The feed network108may then split the energy of the received signal among the transmission lines1121, . . . ,112nof the multiple feed levels. This may be achieved using power dividers that implement binary power splits, i.e. power splits of 2n−1, with n=1, 2, 3, 4 . . . being the number of feed levels of the corporate feed architecture. As known to those skilled in the art, the power splits may be accomplished by using tapered lines or impedance transformers. It should also be understood that, instead of binary power splits, the feed network108may achieve triple or quadruple power splits. Still, binary power splits may be preferable as they gave a simple design.

For this purpose, each one of the transmission lines1121, . . . ,112n−1is split into two (2) transmission lines provided at the next feed level. For instance, a transmission line at a level n, e.g. transmission line1122at the second feed level, is illustratively terminated by a junction116, which branches out into a first and a second transmission line provided at the following level n+1, e.g. transmission lines1123at the third feed level. It should be understood that depending on the type of power splits accomplished, each transmission line at a given level may be split into more than two (2) transmission lines at the next level. The junction116may be a tee junction where the first and second transmission lines, e.g. transmission lines1123, meet at an angle of substantially ninety (90) degrees and are collinear to one another. It should be understood that, although other configurations, e.g. y-junction geometries, may apply, the tee junction geometry may be preferable as it ensures a low profile for the feed network108. Also, the energy of the signal routed through the transmission line of level n, e.g. transmission line1122, is illustratively divided at the junction116among the first and second transmission lines of level n+1, e.g. transmission lines1123.

Although even power distribution may be desirable, the power split provided at each junction116of the feed network108may be an equal or unequal power split. Thus, the amplitudes of the signals provided at the first and the second transmission lines of level n+1 may be equal or unequal. As will be discussed further below, non-uniform power distribution may be used to lower sidelobe levels of the gain pattern of the antenna aperture100. The phases of the signals provided at the first and the second transmission lines of level n+1 may also be uniform or non-uniform, e.g. equal or unequal. For instance, non-uniform phases may be used when it is desired to squint a beam or otherwise shape the far-field gain pattern of the antenna aperture100. InFIG. 2aandFIG. 2b, the feed network108feeds N=16 radiators1061, . . . ,106Nusing equal binary power splits and uniform phase over n=5 levels.

In one embodiment, the combination of the line source102and the feed network108may be used to feed N horizontal radiators1061, . . . ,106Nand M=1 vertical radiators (not shown), i.e. a single vertical radiator as in1181. As such, the linear radiator array104illustratively comprises N horizontal radiators1061, . . . ,106Narranged in a single column along the Y axis so that the radiator array104comprises a radiator arrangement, which is discrete along the vertical Y axis and continuous along the horizontal X axis. The line source102may then provide the horizontal excitation to the radiator array104while the corporate feed network108provides the vertical excitation.

Referring toFIG. 3aandFIG. 3bin addition toFIG. 1, although the embodiment ofFIG. 1illustrates a radiator array104where each horizontal radiator as in1061, . . . ,106Nis continuous along the X axis, it should be understood that each horizontal radiator as in1061, . . . ,106Nmay also be discretized along the X axis. In particular, to arrive at the embodiment ofFIG. 1, the line source102may comprise a folded reflective line source architecture200, as shown inFIG. 3a. Still, it should be understood that other configurations may apply. The folded reflective line source200may be used to transform a single mode input202into a single line source204that is continuous along the X axis, i.e. the horizontal direction. The line source204illustratively has a dimension along the X axis, e.g. a width, that is expanded compared to the dimension of the single mode input202along the same X axis.

For this purpose, the folded reflective line source200may comprise a plurality of taper regions as in206adapted to expand a beam propagating therethrough. The taper regions206may be provided in a stacked relationship and connected by 180 degree reflectors as in208. Each reflector208may be used to fold the direction of propagation of a beam traveling down each one of the taper regions206, thereby ensuring compactness of the structure. The folded reflective line source200may also comprise a reflective phase compensator210for compensating for the phase error introduced during travel of the beam down the successive taper regions206. Using such a folded reflective line source200to build the antenna aperture100may result in a circuit largely comprised of slab waveguides. Such a slab waveguide geometry illustratively has low loss and allows most of the antenna design to be constructed from low cost extrusions. For example, aluminum metal extrusions or metal coated plastic extrusions or molded parts may be used.

Alternatively and as shown inFIG. 3b, the line source102may comprise a corporate feed line source architecture300, which produces an output that is discretized along the X axis. The energy radiated by each one of the horizontal radiators as in1061, . . . ,106Nmay in turn be discretized. In particular, the corporate feed line source300may be used to transform a single mode input302into a plurality of discrete outputs304distributed along the direction of the X axis. The discrete outputs304may together form a discretized output306having an overall dimension along the X axis, e.g. a width, that is expanded compared to the dimension of the single mode input302along the same X axis. For this purpose, the corporate feed line source300may comprise multiple feed lines as in308providing binary power splits over a plurality of levels (not shown). In the embodiment ofFIG. 3b, the corporate feed line source300transforms the single mode input302into sixty-four (64) discretized outputs304over seven (7) levels.

Referring now toFIG. 4in addition toFIG. 1, the antenna aperture100may be incorporated into a computer-controlled elevation over azimuth rotary antenna positioner400. As known to those skilled in the art, such an antenna positioner400may be used to position the antenna100for tracking a moving object (not shown). In the embodiment ofFIG. 4, an antenna aperture having a dimension along the X axis, i.e. a length, of 594.06 mm, a dimension along the Y axis, i.e. a height of 152.50 mm, and a dimension along the Z axis, i.e. a width of 56.31 mm is used. Elevation and azimuth gain patterns may then be measured, as shown inFIG. 5aandFIG. 5b.

FIG. 5ashows a simulated azimuth gain pattern500at a frequency of 30 GHz for the antenna aperture100ofFIG. 4. It can be seen that the first sidelobe502in the azimuth gain pattern500is approximately 23 dB below the peak504, as desired in aeronautical applications and the like. Indeed, it is desirable, when communicating with a geostationary satellite, for the azimuth pattern as in500to provide low side lobe levels in order to comply with regulatory requirements to limit interference with adjacent satellites.

FIG. 5bshows a simulated elevation gain pattern600at a frequency of 30 GHz for the antenna aperture100ofFIG. 4. As discussed above, since the elevation feed shown inFIG. 5billustratively uses equal output binary power splitters (not shown) for splitting the power of the signal received from the line source102, a uniform excitation may be achieved along the Y axis, i.e. the vertical direction, of the radiator array104. This results in higher sidelobes being obtained for the elevation gain pattern600than for the azimuth gain pattern500. In particular, the uniform excitation leads to the first sidelobe604being at approximately 13 dB below the peak602. As discussed above with reference toFIG. 2aandFIG. 2b, it should be understood that feed designs using unequal splits may be used in some applications. In this case, one could achieve an antenna aperture where each radiator of the radiator array104provides a non uniform illumination, e.g. more energy is output towards the center of the radiator than at the edges thereof. The gain pattern of such an antenna aperture would thus comprise a wider main beam and lower sidelobe levels. However, this would lower the gain of the overall antenna structure. As gain is the principal limiting factor for aeronautical satellite communications antennas, sidelobe control in the elevation plane is of limited utility. The reduction in antenna gain would therefore not provide any additional net benefit for the intended applications.

Referring back toFIG. 1, the antenna aperture100illustratively has low loss and high gain over a large frequency bandwidth. In particular, broadband response over 50% of the bandwidth may be achieved and the design may be scalable from 5 GHz to 75 GHz operating frequency. This is particularly desirable for satellite communications applications where a wideband signal is to be radiated in a single direction regardless of the input frequency. The antenna aperture100may further allow for a minimal number of radiator elements to be used in the radiator array104, thus achieving a low profile and low weight structure having a flat plate, i.e. compact, design. The impact of an installed system on the operating costs of a device, such as an aircraft, may therefore minimized while achieving high performance.