GNSS antenna systems, elements and methods
The design of a Global Navigation Satellite System (GNSS) antenna requires consideration of a range of characteristics including, for example, the ability for tracking satellites at low elevation, phase centre variation (PCV), antenna efficiency and impedance, axial ratio and up-down ratio (UDR), antenna bandwidth, etc. whilst also providing a light weight, compact and robust form factor. For rover applications this becomes particularly important when the satellites being accessed may be at low elevations where prior art GNSS antenna exhibit poor performance. To address this a GNSS antenna is provided comprising a domed array of opposed metallized antenna elements which are indirectly coupled via a pair of dipoles to the feed network thereby avoiding the difficulties associated with direct electrical connections of feed circuits to antenna elements.
1 . A wideband circularly polarized antenna comprising:
a ground plane substrate with at least two metal layers, with the upper metal layer continuously metallised to comprise a ground plane surface, and with a first central mounting slot and a second central mounting slot disposed co-centric with and orthogonal to said first central mounting slot, and a plurality of peripheral mounting slots,
a first and a second dipole substrate of equal outer dimensions, equally patterned with a balun and a narrowband dipole imprinted in metal layers on the dipole substrate, said balun connected to metallized terminals on projecting tabs at the center of the lower edge of said dipole substrates, said first and second dipoles including interlocking slots to provide for assembly of a three dimensional crossed dipole structure,
an assembly comprised of an orthogonal dipole structure mounted on said ground plane substrate by insertion of the respective ones of the projecting tabs, into said first and second central mounting slots with first and second balun feeds connected a first and a second output of feed circuit comprised of an RF 90 degree coupler
a first and a second opposed petal pair each comprised of a first petal and a distal second petal etched in metal with a non-conductive margin, on a semi-flexible substrate each of identical dimensions, each petal with a wider end and a distal narrower end, with a central axis longer than the wider end, with progressively decreasing width between said wider end and said narrower end, said first and second petals co-linear, with the proximate ends of said first and second petals being the narrower ends, said first and second opposed petal pairs disposed with the axis of each orthogonal to the other, with the common mid-point between first and second petals on each extended axis defined as the geometric antenna center,
each of said metallized petals having a plurality of metallized attachment tabs at the wider end, electrically isolated from said metallized petals, said semi-flexible substrate of sufficient length to form a domed structure by insertion of said attachment tabs into said peripheral mounting slots in said ground plane with said petal pairs aligned along the axes of the crossed dipoles,
the upper edge of said first and second dipole substrates is sculpted identically to provide a precise space between the opposed petal pairs and said crossed narrowband dipoles whereby said dipoles are effective through electromagnetic coupling to comprise a wideband distributed feed network for a circularly polarized antenna, wherein none of said opposed petal pairs is directly connected.
2 . The wideband circularly polarized antenna according to claim 1 , wherein
said plurality of metallized attachment tabs associated with a single one of each of said metallized petals is electrically connected by thin conducting metallized links, each immediately adjacent to the attachment tabs, and parallel with the wider edge of the metallized petal;
said metallized links being electrically isolated from said metallized petals by means of a narrow, unmetallized opening between the metallized link and the metallized petal; and
the metallized link is electrical connected to ground and presents a predetermined capacitance to its associated metallized petal.
3 . The wideband circularly polarized antenna according to claim 1 , wherein
each petal of said first and said second opposed petal pairs has a plurality of unmetallized slots etched into the petal metallization, parallel to the petal axis, of a pre-determined number, length and width, on the continuous semi-flexible substrate, terminated at the edge of the wider end of the metallized patch and the unmetallized opening.
4 . A wideband circularly polarized antenna comprising:
a ground plane substrate with at least two metal layers, with the upper metal layer continuously metallised to comprise a ground plane surface, and with a first central mounting slot and a second central mounting slot disposed co-centric with and orthogonal to said first central mounting slot, and a plurality of peripheral mounting slots,
a first and a second dipole substrate of equal outer dimensions, equally patterned with a balun and a narrowband dipole imprinted in metal layers on the dipole substrate, said balun connected to metallized terminals on projecting tabs at the center of the lower edge of said dipole substrates, said first and second dipoles including interlocking slots to provide for assembly of a 3 dimensional crossed dipole structure,
an assembly comprised of an orthogonal dipole structure mounted on said ground plane substrate by insertion of the respective ones of said projecting tabs into said first and second central mounting slots, and four interstitial support substrates mounted orthogonal to the ground plane, each rotated 45 degrees relative to an arbitrary one of said crossed dipole axes, so as to be similarly disposed in each quadrant of said crossed dipole structure, each interstitial support substrate having an upper profile identical to said crossed dipoles,
with first and second balun feeds connected a first and a second output of feed circuit comprised of an RF 90 degree coupler
a first, a second, a third and a fourth opposed petal pairs each comprised of a first petal and a distal second petal etched in metal with a non-conductive margin, on a semi-flexible substrate each of identical dimensions, each petal with a wider end and a distal narrower end, with a central axis longer than the wider end, with progressively decreasing width between said wider end and said narrower end, said first and second petals co-linear, with the proximate ends of said first and second petals being the narrower ends,
the axis of an arbitrary second petal pair is rotated by 45 degrees relative to the axis of said first petal pair, with equal rotation between said third and said second petal pairs and said fourth and said third petal pairs, each with a common mid-point between first and second petals on each extended axis of each petal pair defined as the geometric antenna center,
each of said metallized petals having a plurality of metallized attachment tabs at the wider end, electrically isolated from said metallized petals, said semi-flexible substrate of sufficient length to form a domed structure by insertion of said attachment tabs into said peripheral mounting slots in said ground plane with at least one of said petal pairs aligned along the axes of the one of said crossed dipoles,
the upper edge of said first and second dipole substrates sculpted identically to provide a precise space between the opposed petal pairs associated with each of said crossed narrowband dipoles, the upper edges of said interstitial support substrates further sculpted identically to said dipole substrates whereby said dipoles are effective through electromagnetic coupling to comprise a wideband distributed feed network for a circularly polarized antenna, wherein none of said opposed petal pairs is directly connected.
5 . The wideband circularly polarized antenna of claim 4 , wherein
said plurality of metallized attachment tabs associated with a single one of each of said metallized petals are electrically connected by thin conducting metallized links, each immediately adjacent to the attachment tabs, and parallel with the wider edge of the metallized petal;
said metallized links being electrically isolated from each of said metallized petals by means of a narrow, unmetallized opening between the metallized link and the metallized petal; and
the metallized link is electrical connected to ground and presents a predetermined capacitance to its associated metallized petal.
6 . The wideband circularly polarized antenna of claim 5 , wherein
each petal of said first and said second opposed petal pairs has a plurality of unmetallized slots etched into the petal metallization, parallel to the petal axis, of a pre-determined number, length and width, on the continuous semi-flexible substrate, terminated at the edge of the wider end of the metallized patch and the unmetallized opening.
7 . A method of providing a wideband circularly polarized antenna, the method comprising
providing a ground plane substrate ( 120 ) with at least two metal layers, with the upper metal layer continuously metallized to comprise a ground plane surface, and with a first central mounting slot and a second central mounting slot disposed co-centric with and orthogonal to said first central mounting slot, and a plurality of peripheral mounting slots;
providing a first dipole substrate ( 220 ) and a second dipole substrate ( 230 ) of equal outer dimensions, equally patterned with a balun and a narrowband dipole imprinted in metal layers on the dipole substrate, said balun connected to metallized terminals on projecting tabs ( 130 ) at the center of the lower edge of said dipole substrates, said first dipole substrate ( 220 ) and a second dipole substrate ( 230 ) including interlocking slots to provide for assembly of a three-dimensional orthogonal crossed dipole structure;
forming an assembly by forming the three-dimensional orthogonal crossed dipole structure comprising the first dipole substrate ( 220 ) and second dipole substrate ( 230 ) mounted on the ground plane substrate ( 120 ) by insertion of the respective ones of the projecting tabs ( 130 ) into said first and second central mounting slots where the projecting tabs when assembled into said first and second central mounting slots are electrically connected to first and second balun feeds which connect with a first output and a second output of a feed circuit comprising an RF 90 degree coupler; wherein
the wideband circularly polarized antenna has one of a first configuration and a second configuration;
the wideband circularly polarized antenna further comprises a first opposed petal pair and a second opposed petal pair where each is comprised of a first petal ( 110 ) and a distal second petal ( 110 ) etched in metal with a non-conductive margin, on a semi-flexible substrate each of identical dimensions, each petal ( 110 ) with a wider end and a distal narrower end, with a central axis longer than the wider end, with progressively decreasing width between said wider end and said narrower end, said first and second petals ( 110 ) co-linear, with the proximate ends of said first and second petals ( 110 ) being the narrower ends, said first and second opposed petal pairs disposed with the axis of each orthogonal to the other, with the common mid-point between first and second petals ( 110 ) on each extended axis defined as the geometric antenna center;
each of said metallized petals ( 110 ) having a plurality of metallized attachment tabs ( 1010 ) at the wider end, electrically isolated from said metallized petals, said semi-flexible substrate of sufficient length to form a domed structure by insertion of said attachment tabs ( 1010 ) into said peripheral mounting slots in said ground plane with said petal pairs aligned along the axes of the crossed dipoles; and
the upper edge of said first and second dipole substrates ( 220 , 230 ) is sculpted identically to provide a precise space between the opposed petal pairs and said crossed narrowband dipoles whereby said dipoles are effective through electromagnetic coupling to comprise a wideband distributed feed network for a circularly polarized antenna, wherein none of said opposed petal pairs is directly connected.
8 . The method according to claim 7 , wherein
said plurality of metallized attachment tabs ( 1010 ) associated with a single one of each of said metallized petals is electrically connected by thin conducting metallized links ( 1320 ), each immediately adjacent to the attachment tabs, and parallel with the wider edge of the metallized petal;
said metallized links ( 1320 ) being electrically isolated from said metallized petals by means of a narrow, unmetallized opening between the metallized link ( 1320 ) and the metallized petal; and
the metallized link ( 1320 ) is electrical connected to ground and presents a predetermined capacitance to its associated metallized petal.
9 . The method according of claim 7 , wherein
each petal of said first and said second opposed petal pairs has a plurality of unmetallized slots etched into the petal metallization, parallel to the petal axis, of a pre-determined number, length and width, on the continuous semi-flexible substrate, terminated at the edge of the wider end of the metallized patch and the unmetallized opening.
10 . The method according to claim 7 , wherein
providing a metallic element disposed between the second distal ends of each petal of the first opposed pair of metallized petals and the second distal ends of petal of the second opposed pair of metallized petals; wherein
the metallic element is capacitively coupled to the centre ends of the plurality of petal pairs; and
a linear dimension of the metallic element is determined in dependence upon a tuning to be applied to the first opposed pair of metallized petals and the second opposed pair of metallized petals.
11 . The method according to claim 7 , wherein
local current maxima in each of the antenna metallized petals are offset from the dipole center; and
an inflexion in the magnitude of a current in the combined radiating elements comprising the narrow band dipole and symmetrical arrangement of metallized petals occurs at the center of the dipole.
12 . A method of providing a wideband circularly polarized antenna, the method comprising
providing a ground plane substrate ( 120 ) with at least two metal layers, with the upper metal layer continuously metallized to comprise a ground plane surface, and with a first central mounting slot and a second central mounting slot disposed co-centric with and orthogonal to said first central mounting slot, and a plurality of peripheral mounting slots;
providing a first dipole substrate ( 220 ) and a second dipole substrate ( 230 ) of equal outer dimensions, equally patterned with a balun and a narrowband dipole imprinted in metal layers on the dipole substrate, said balun connected to metallized terminals on projecting tabs ( 130 ) at the center of the lower edge of said dipole substrates, said first dipole substrate ( 220 ) and a second dipole substrate ( 230 ) including interlocking slots to provide for assembly of a three-dimensional orthogonal crossed dipole structure;
forming an assembly by forming the three-dimensional orthogonal crossed dipole structure comprising the first dipole substrate ( 220 ) and second dipole substrate ( 230 ) mounted on the ground plane substrate ( 120 ) by insertion of the respective ones of the projecting tabs ( 130 ) into said first and second central mounting slots where the projecting tabs when assembled into said first and second central mounting slots are electrically connected to first and second balun feeds which connect with a first output and a second output of a feed circuit comprising an RF 90 degree coupler; wherein
the wideband circularly polarized antenna has one of a first configuration and a second configuration;
the wideband circularly polarized antenna further comprises four interstitial support substrates ( 210 A, 210 B, 21 C, 210 D) mounted orthogonal to the ground plane, each rotated 45 degrees relative to an arbitrary one of said crossed dipole axes, so as to be similarly disposed in each quadrant of said crossed dipole structure, each interstitial support substrate having an upper profile identical to said crossed dipoles;
a first opposed petal pair, a second opposed petal pair, a third opposed petal pair and a fourth opposed petal pair where each is comprised of a first petal ( 110 ) and a distal second petal ( 110 ) etched in metal with a non-conductive margin, on a semi-flexible substrate each of identical dimensions, each petal ( 110 ) with a wider end and a distal narrower end, with a central axis longer than the wider end, with progressively decreasing width between said wider end and said narrower end, said first and second petals ( 110 ) co-linear, with the proximate ends of said first and second petals being the narrower ends;
the axis of an arbitrary second petal pair is rotated by 45 degrees relative to the axis of said first petal pair, with equal rotation between said third and said second petal pairs and said fourth and said third petal pairs, each with a common mid-point between first and second petals ( 110 ) on each extended axis of each petal pair defined as the geometric antenna center;
each of said metallized petals having a plurality of metallized attachment tabs ( 1010 ) at the wider end, electrically isolated from said metallized petals, said semi-flexible substrate of sufficient length to form a domed structure by insertion of said attachment tabs ( 1010 ) into said peripheral mounting slots in said ground plane with at least one of said petal pairs aligned along the axes of the one of said crossed dipoles; and
the upper edge of said first and second dipole substrates ( 220 , 230 ) sculpted identically to provide a precise space between the opposed petal pairs associated with each of said crossed narrowband dipoles, the upper edges of said interstitial support substrates ( 210 A, 210 B, 21 C, 210 D) further sculpted identically to said dipole substrates whereby said dipoles are effective through electromagnetic coupling to comprise a wideband distributed feed network for a circularly polarized antenna, wherein none of said opposed petal pairs is directly connected.
13 . The method according to claim 12 , wherein
said plurality of metallized attachment tabs ( 1010 ) associated with a single one of each of said metallized petals is electrically connected by thin conducting metallized links ( 1320 ), each immediately adjacent to the attachment tabs, and parallel with the wider edge of the metallized petal;
said metallized links ( 1320 ) being electrically isolated from said metallized petals by means of a narrow, unmetallized opening between the metallized link ( 1320 ) and the metallized petal; and
the metallized link ( 1320 ) is electrical connected to ground and presents a predetermined capacitance to its associated metallized petal.
14 . The method according of claim 12 , wherein
each petal of said first opposed petal pair, the second opposed petal pair, the third opposed petal pair and the fourth opposed petal pair has a plurality of unmetallized slots etched into the petal metallization, parallel to the petal axis, of a pre-determined number, length and width, on the continuous semi-flexible substrate, terminated at the edge of the wider end of the metallized patch and the unmetallized opening.
15 . The method according to claim 12 , wherein
providing a metallic element disposed between the second distal ends of each petal of the first opposed pair of metallized petals, the second distal ends of petal of the second opposed pair of metallized petals; the second distal ends of petal of the third opposed pair of metallized petals and the second distal ends of petal of the fourth opposed pair of metallized petals; wherein
metallic element is capacitively coupled to the centre ends of each of the first opposed petal pair, the second opposed petal pair, the third opposed petal pair and the fourth opposed petal pair; and
a linear dimension of the metallic element is determined in dependence upon a tuning to be applied to the first opposed petal pair, the second opposed petal pair, the third opposed petal pair and the fourth opposed petal pair.
16 . The method according to claim 12 , wherein
local current maxima in each of the antenna metallized petals are offset from the dipole center; and
an inflexion in the magnitude of a current in the combined radiating elements comprising the narrow band dipole and symmetrical arrangement of metallized petals occurs at the center of the dipole.