Patent Grant
10505279
Embodiments described herein relate generally to slot antennas, and more particularly, to circularly polarized connected-slot antennas.
Conventional slot antennas include a slot or aperture formed in a conductive plate or surface. The slot forms an opening to a cavity, and the shape and size of the slot and cavity, as well as the driving frequency, contribute to a radiation pattern. The length of the slot depends on the operating frequency and is typically about λ/2 and inherently narrowband. Conventional slot antennas are linearly polarized and can have an almost omnidirectional radiation pattern. More complex slot antennas may include multiple slots, multiple elements per slot, and increased slot length and/or width.
Slot antennas are commonly used in applications such as navigational radar and cell phone base stations. They are popular because of their simple design, small size, and low cost. Improved designs are constantly sought to improve performance of slot antennas, increase their operational bandwidth, and extend their use into other applications.
Embodiments described herein provide improved designs for slot antennas. In an embodiment, the slot is formed in a circular shape and includes one or more feed elements that can be phased to provide circular polarization. The slot is connected in the sense that it is formed by a dielectric extending between conductors. The connected-slot antennas described herein can be configured for specific frequencies, wider bandwidth, and different applications such as receiving satellite signals at global navigation satellite system (GNSS) frequencies (e.g., approximately 1.1-2.5 GHz).
In accordance with an embodiment, a circularly polarized connected-slot antenna configured to receive radiation at GNSS frequencies includes a dielectric substrate, a circular patch overlying the dielectric substrate, one or more impedance transformers, and a metamaterial ground plane. Each of the one or more impedance transformers include a microstrip overlying the dielectric substrate and a ground pad that is separated from the microstrip by a dielectric. Each microstrip is coupled to a first antenna feed at an input and coupled to the circular patch at an output. Each ground pad is coupled to ground. The metamaterial ground plane includes a plurality of conductive patches, a ground plane, and a conductive fence. The plurality of conductive patches are arranged along a first plane below the circular patch and are separated from the circular patch by at least the dielectric substrate. Each conductive patch is separated from others of the conductive patches. The plurality of conductive patches are arranged in a pattern that provides circular symmetry with respect to a center of the circularly polarized antenna. The ground plane is arranged along a second plane and is electrically coupled to at least a first portion of the plurality of conductive patches. The conductive fence extends around a perimeter of the plurality of conductive patches and around a perimeter of the ground plane. The ground plane and the conductive fence are coupled to ground.
In embodiments that include more than one impedance transformer, the output associated with each microstrip is spaced from adjacent outputs associated with other microstrips by approximately equal angular intervals.
In an embodiment, the plurality of conductive patches are arranged in a pattern that provides circular symmetry with respect to a phase center of the circularly polarized antenna.
In another embodiment, the plurality of conductive patches include a center conductive patch surrounded in a radial direction by a plurality of intermediate conductive patches. In some embodiments, the plurality of intermediate conductive patches may extend radially to an outer edge of the dielectric substrate. In other embodiments, the plurality of intermediate conductive patches may be surrounded in a radial direction by a plurality of outer conductive patches. The plurality of outer conductive patches may extend radially to an outer edge of the dielectric substrate.
In another embodiment, the circularly polarized antenna includes a conductive ring surrounding the circular patch and overlying the dielectric substrate. The conductive ring may be coupled to ground and isolated from the circular patch.
In another embodiment, the circularly polarized antenna includes a discontinuous ring comprising discrete conductive elements surrounding the circular patch.
In some embodiments, the dielectric separating each microstrip and ground pad is the dielectric substrate. In other embodiments, the dielectric separating each microstrip and ground pad is separate from the dielectric substrate.
In another embodiment, each microstrip includes at least two conductive traces. A first one of the at least two conductive traces has one end connected to the first antenna feed and another end connected to the output. A second one of the at least two conductive traces has one end connected to the first antenna feed and another end free from connection with a conductor. The first conductive trace and the second conductive trace extend substantially parallel to but separate from each other along multiple sections of the microstrip. Each section of the microstrip extends substantially perpendicular to an adjacent section of the microstrip. In some embodiments, a width of the first one of the at least two conductive traces decreases between the first antenna feed and the output.
In another embodiment, the circular patch comprises an inner conductive ring.
In another embodiment, the circular patch is disposed on a top side of the dielectric substrate and the plurality of conductive patches are disposed on a backside of the dielectric substrate.
In yet another embodiment, the circular patch includes one or more elongated sections extending radially outward from the circular patch. Each of the one or more elongated sections is coupled to the output of a corresponding microstrip, and each microstrip is disposed radially outward beyond an end of an associated one of the one or more elongated sections.
In accordance with another embodiment, a circularly polarized antenna includes a dielectric substrate, a circular patch overlying the dielectric substrate, a first conductive ring surrounding the circular patch and overlying the dielectric substrate, one or more antenna feeds coupled to the circular patch, and a metamaterial ground plane. The first conductive ring is coupled to ground and isolated from the circular patch. The metamaterial ground plane includes a plurality of conductive patches arranged along a first plane below the circular patch and separated from the circular patch by at least the dielectric substrate. The plurality of conductive patches are arranged in a pattern that provides circular symmetry with respect to a center of the circularly polarized antenna. The metamaterial ground plane also includes a ground plane arranged along a second plane, the ground plane electrically coupled to at least a first portion of the plurality of conductive patches. The first portion of the plurality of conductive patches and the ground plane are coupled to ground.
In accordance with yet another embodiment, an antenna configured to receive radiation at GNSS frequencies includes a dielectric substrate, a circular patch overlying the dielectric substrate, a first conductive ring surrounding the circular patch and overlying the dielectric substrate, one or more impedance transformers, and a metamaterial ground plane. Each of the one or more impedance transformers are coupled to a first input feed and coupled to the circular patch at an output. The metamaterial ground plane includes a plurality of conductive patches and a ground plane. The plurality of conductive patches are arranged along a first plane below the circular patch and are separated from the circular patch and the first conductive ring by at least the dielectric substrate. The plurality of conductive patches are arranged in a pattern that provides circular symmetry with respect to a center of the circularly polarized antenna. The ground plane is arranged along a second plane and is electrically coupled to at least a first portion of the plurality of conductive patches. The first portion of the plurality of conductive patches and the ground plane are coupled to ground.
Numerous benefits are achieved using embodiments described herein over conventional techniques. By having a connected-slot structure with multiple feeds and phasing, a broadband circularly polarized antenna may be obtained. This enables the reception of all GNSS signals, available worldwide, with a single antenna, resulting in significant cost and size savings. For example, some embodiments include connected-slot antennas that have a simple design and a relatively small size so that they can be produced economically. Also, in some embodiments, the connected-slot antennas include a metamaterial ground plane with a plurality of conductive patches that are arranged in a pattern that provides circular symmetry with respect to a center of the antenna. This arrangement of conductive patches can reduce gain variation with azimuth angle, especially at low elevation angles, and improve phase center stability. Additionally, some embodiments may include impedance transformers with microstrips formed on the same plane as the circular patch. This can improve alignment of the antenna features, contribute to phase center stability, and reduce fabrication costs. Also, some embodiments may include a discontinuous ring comprising discrete conductive elements surrounding a circular patch. This can increase antenna gain in GNSS frequency bands and increase antenna bandwidth. Depending on the embodiment, one or more of these features and/or benefits may exist. These and other features and benefits are described throughout the specification with reference to the appended drawings.
a-5b are simplified views along line B-B of the connected-slot antenna shown in
Embodiments described herein provide circularly polarized connected-slot antennas. In some embodiments, the connected-slot antennas include a metamaterial ground plane that includes conductive patches arranged in a pattern that provides circular symmetry with respect to a center of the connected-slot antennas. In some embodiments, the connected-slot antennas may be configured to operate over a wide bandwidth so that they can receive radiation at different GNSS frequencies.
The dielectric substrate 102 may comprise a non-conductive material such as a plastic or ceramic. The circular patch 106 and the conductive ring 104 may comprise a conductive material such as a metal or alloy. In some embodiments, the dielectric material may include a non-conductive laminate or pre-preg, such as those commonly used for printed circuit board (PCB) substrates, and the circular patch 106 and the conductive ring 104 may be etched from a metal foil in accordance with known PCB processing techniques.
In some embodiments, the circular patch 106 and the conductive ring 104 each have a substantially circular shape, and diameters of the circular patch 106 and the conductive ring 104, as well as a distance between the circular patch 106 and the conductive ring 104, may be determined based on a desired radiation pattern and operating frequency. In an embodiment, the dielectric substrate 102 is substantially the same shape as the conductive ring 104 and has a diameter that is the same as or greater than an outside diameter of the conductive ring 104. The circular patch 106 and/or dielectric substrate 102 may be substantially planar in some embodiments or have a slight curvature in other embodiments. The slight curvature can improve low elevation angle sensitivity.
The connected-slot antenna in this example also includes four feeds 108 that are disposed in the connected slot and coupled to the circular patch 106. Other embodiments may include a different number of feeds (more or less). The feeds 108 provide an electrical connection between the circular patch 106 and a transmitter and/or receiver. The feeds 108 are disposed around a circumference of the circular patch 106 so that each feed 108 is spaced from adjacent feeds 108 by approximately equal angular intervals. The example shown in
The placement of the feeds 108 around the circular patch 106 allows the feeds 108 to be phased to provide circular polarization. For example, signals associated with the four feeds 108 shown in
This cross section also shows that the connected-slot antenna in this example includes conductive patches 110 disposed on a backside of the dielectric substrate 102. The conductive patches 110 are arranged along a first plane below the circular patch 106 and separated from the circular patch 106 by the dielectric substrate 102. The conductive patches 110 may be separated from adjacent conductive patches 110 by a dielectric (e.g., air or another dielectric).
In some embodiments, the conductive patches 110 may be separated from the circular patch 106 and the conductive ring 104 by one or more additional dielectrics as well. As an example, the conductive patches 110 may be disposed on a top surface of dielectric 114 (as shown in
The conductive patches 110, the first vias 112, the second via 117, and the ground plane 116 form a metamaterial ground plane. The metamaterial ground plane can provide an artificial magnetic conductor (AMC) with electromagnetic band-gap (EBG) behavior. This allows the metamaterial ground plane to be disposed at a distance of less than λ/4 from the circular patch 106 and the conductive ring 104 while still providing a constructive addition of the direct and reflected waves over the desired frequencies (e.g., 1.1-2.5 GHz). In some embodiments, the metamaterial ground plane also provides surface wave suppression and reduces left hand circular polarized (LHCP) signal reception to improve the multipath performance over a wide bandwidth. With the metamaterial ground plane, antenna gain can be on the order of 7-8 dBi, with strong radiation in the upper hemisphere including low elevation angles, and negligible radiation in the lower hemisphere for enhanced multipath resilience.
The conductive patches 110, the first vias 112, the second via 117, and the ground plane 116 may comprise a conductive material such as a metal or alloy. In an embodiment, the conductive patches 110 and the ground plane 116 may be etched from a metal foil in accordance with known PCB processing techniques. The first vias 112 and the second via 117 may comprise a metal pin (solid or hollow) or may be formed using a via etch process that forms via holes through the dielectrics and then deposits a conductive material in the via holes.
The dielectric 114 may comprise an electrically non-conductive material such as a plastic or ceramic. In some embodiments, the dielectric 114 may include a non-conductive laminate or pre-preg, such as those commonly used as for PCB substrates.
In some embodiments, the second via 117 may extend only from the ground plane 116 to one of the conductive patches 110 in a manner similar to the first vias 112 in this example (rather than also extending through the dielectric substrate 102 to the circular patch 106). Examples of the center via extending only from the ground plane to one of the conductive patches are shown in
These different configurations are provided merely as examples, and each of the examples shown in
Also, in some embodiments, each of the conductive patches 110 may be coupled to the ground plane 116 using additional vias (instead of only some of the conductive patches 110 being coupled to the ground plane 116 as shown in the figures). Further, in some embodiments, the first vias 112 may extend through the dielectric substrate 102 like the second via 117. In these embodiments, the first vias 112 may either be coupled to the conductive ring 104 or may be isolated from the conductive ring 104.
a-5b are simplified bottom views along line B-B of the connected-slot antenna shown in
This arrangement provides conductive patches arranged in a pattern that provides circular symmetry with respect to a center (or phase center) of the antenna. The conductive patches 110c1, 110c2, 110c3 provide circular symmetry by having equal distances between a center of the conductive patch 110c1 and any point along curved inner edges of the intermediate conductive patches 110c2, between the center and any point along curved outer edges of the intermediate conductive patches 110c2, between the center and any point along curved inner edges of the outer conductive patches 110c3, and between the center and any point along curved outer edges of the outer conductive patches 110c3. Thus, all paths are the same that pass radially outward from a center of the center conductive patch 110c1 and through the intermediate and outer conductive patches 110c2, 110c3. The circular symmetry can reduce variation in gain and improve phase center stability, particularly for low angle signals.
Any number of intermediate conductive patches 110c2 and outer conductive patches 110c3 can be used. The number may be based on a number of feeds in some embodiments. For example, there may be a corresponding intermediate conductive patch 110c2 for each feed. The number of intermediate conductive patches 110c2 may be equal to the number of feeds in some embodiments. In other embodiments, the number of intermediate conductive patches 110c2 may be greater than the number of feeds. For example, the embodiments shown in
Like the example shown in
The feeds 118 in this example may comprise a conductive material such as a metal or alloy. In an embodiment, the feeds 118 may be etched from a metal foil in accordance with known PCB processing techniques. The circular patch 106, conductive ring 104, and dielectric substrate 102 may be arranged in a manner similar to that described above with regard to
In the example shown in
In an embodiment, the impedance transformers 120 each include a microstrip and ground pad that are separated by a dielectric. These features can be illustrated with reference to
The ground pads 126 and microstrips 121 may comprise a conductive material such as a metal or alloy. In an embodiment, the ground pads 126 and microstrips 121 may be etched from a metal foil in accordance with known PCB processing techniques.
The circular patch 106, conductive ring 104, and dielectric substrate 102 may be arranged in a manner similar to that described above with regard to
The different shapes of the traces in
The example shown in
The example shown in
Portions of the conductive ring extending along the backside of the dielectric substrate 102 may not exist separate from the ground pad 126 and/or the conductive patches (the ground pad 126 and/or the conductive patches may provide electrical continuity with the portions of the conductive ring 104 on the frontside of the dielectric substrate 102). Examples are shown in
Some embodiments may replace the conductive ring with a discontinuous ring. The discontinuous ring is formed by discrete conductive elements on a surface of a dielectric substrate that are connected to ground. The ground connection may be provided by a shield (or ground) of a transmission line or by an electrical connection to a ground plane. Using a discontinuous ring may reduce bandwidth, but it can increase gain in GNSS frequency bands of 1.164-1.30 GHz and 1.525-1.614 GHz.
An example of a discontinuous ring is shown in
The conductive fence may be considered to be part of a metamaterial ground plane (along with conductive patches and a ground plane). The conductive fence can eliminate discontinuities at the edges of the conductive patches and the ground plane and form a cavity with the ground plane. This can reduce residual surface waves by shorting them to ground. The conductive fence can improve LHCP isolation, low elevation angle sensitivity, antenna bandwidth, and multipath resilience.
The conductive fence 146 may comprise a conductive material such as a metal or alloy and may be electrically grounded. In an embodiment, the conductive fence 146 is shaped like a band that surrounds the conductive patches 110 and the ground plane. The conductive fence 146 may abut a portion of the conductive patches 110 (those conductive patches 110 that are disposed along a perimeter) and the ground plane 116. In some embodiments, the conductive fence 146 and the ground plane 116 may be combined to form a single conductive element (e.g., a cavity or shield). In some embodiments, the dielectric 114 in this example may be air and the first and second vias 112, 117 may extend to the ground plane 116.
In this example, conductive patches 110 are arranged along a first plane, and the ground plane 116 is arranged along a second plane. The conductive fence 148 extends from the first plane to the second plane and around a perimeter of the conductive patches 110 and a perimeter of the ground plane 116. A major surface of the conductive fence 148 extends substantially perpendicular to the first plane and the second plane. In some embodiments, the conductive fence 148 and the ground plane 116 may be combined to form a single conductive element (e.g., a cavity or shield). In some embodiments, the dielectric 114 in this example may be air and the first vias 112 may extend to the ground plane 116.
In this example, the circular patch 106 and the first conductive ring 104 are separated by a first connected slot, and the first conductive ring 104 and the second conductive ring 111 are separated by a second connected slot. Like the first feeds 108, the second feeds 109 are spaced from adjacent second feeds 109 by approximately equal angular intervals.
This embodiment is provided as an example of a connected-slot antenna that includes multiple conductive rings. Other embodiments may include additional conductive rings with additional feeds. The number of conductive rings and the number of feeds may be determined based on desired operating frequency bands.
While the present invention has been described in terms of specific embodiments, it should be apparent to those skilled in the art that the scope of the present invention is not limited to the embodiments described herein. For example, features of one or more embodiments of the invention may be combined with one or more features of other embodiments without departing from the scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Thus, the scope of the present invention should be determined not with reference to the above description, but should be determined with reference to the appended claims along with their full scope of equivalents.
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