Patent Description:
<CIT> discloses a two-dimensional periodic pattern of capacitive and inductive elements defined in the surface of a metal sheet that are provided by a plurality of conductive patches each connected to a conductive back plane sheet between which an insulating dielectric is disposed. The elements acts to suppress surface currents in the surface defined by them. In particular, the array forms a ground plane mesh for use in combination with an antenna. The performance of a ground plane mesh is characterized by a frequency band within which no substantial surface currents are able to propagate along the ground plane mesh. Use of such a ground plane in aircraft or other metallic vehicles thereby prevents radiation from the antenna from propagating along the metallic skin of the aircraft or vehicle. This eliminates surface currents between the antenna and the ground plane thereby reducing power loss and unwanted coupling between neighboring antennae. The surface also reflects electromagnetic waves without the phase shift that occurs on a normal metal surface. This allows antennas to be constructed that were previously impractical.

Further prior art is in <NPL> and in <NPL>.

Micropatch antennas are well suited for navigation receivers in global navigation satellite systems. These antennas have the desirable features of compact size and wide bandwidth. Wide bandwidth is of particular importance for navigation receivers that receive and process signals from more than one GNSS. Currently deployed GNSSs are the US Global Positioning System (GPS), the Russian GLONASS system, the Chinese BeiDou system and the European Galileo system. Other Global and regional Satellite Navigation Systems such as Japan QZSS and Indian IRNSS systems are planned. Multi-system navigation receivers provide higher reliability due to system redundancy and better coverage due to a line-of sight to more satellites.

There is a current focus in the industry directed to miniaturization in designing antenna systems delivering broadband operations with a directional pattern (DP) of a defined shape being ensured. For GNSS applications, it is typically required to provide operation in a bandwidth ranging from <NUM> to <NUM> and <NUM> to <NUM>. In addition, there is a desire that DP in the backward hemisphere be as low as possible to suppress signals reflected from the underlying ground surface. As such, the DP back-lobe needs to have a low level, i.e., providing a high front-to-back ratio.

Compact antennas often include resonant antennas with one or more defined resonances where the resonant elements have a simple geometry. For example, patch antennas are widely used given such antennas have a low height but operate in comparatively narrow frequency band. Also, stacked patch antennas are utilized for operations involving several frequency bands. To provide a low level of the back-lobe and a small lateral dimension, an additional parasitic stacked patch antenna can be designed. For example, <CIT> describes one such antenna system having a top antenna assembly and bottom antenna assembly. The bottom antenna assembly is adjusted such that the fields of the top and bottom antenna assemblies are subtracted in the lower hemisphere. Although such an antenna system has a small lateral size, the presence of the two antenna assemblies result in overall height increases, and increased production costs in view of the complicated overall antenna design.

Numerical optimization methods allow for designing antennas with complicated structures that are more streamlined but carry a considerable computational load in view of the optimization methodologies. To address the excessive computation requirement, it is desirable to use a structure as a set of elementary cells with simple geometric shapes. For example, one broadband low-profile structure without explicit resonances is described in <CIT>. In this broadband design, the currents have many different flowing ways. However, such an antenna has a larger-sized lateral diameter (i.e., <NUM>), and the operational design includes an absorber thereby causing a reduction in antenna efficiency. Further, conducting strips of such an antenna structure are complicated in their geometric shape thereby making numerical optimization more difficult than designs with more streamlined geometries.

In another antenna design, <CIT> describes an antenna with a patch in the central area with the patch being excited by a coaxial pin. Around the coaxial pin is a set of metamaterial structure units with each metamaterial structure unit comprising an upper metal patch, a metalized shorting pin, a metal grounding plate and a dielectric substrate. This antenna structure employs simpler shaped elements which contributes to a lower numerical optimization overhead and makes it possible to obtain fewer resonances. However, it appears that these resonances are quite narrow-banded, and the structure has a more limited parameter variability thereby restricting numerical optimization capabilities.

Therefore, a need exists for an improved GNSS compact antenna system having a low back-lobe level, higher degree of parameter adjustability and less complex geometric shapes to increase numerical optimization efficiency.

In accordance with partial aspects of various embodiments, an improved GNSS compact antenna is provided comprising a conducting ground plane and a driven element for exciting right hand circularly polarized waves.

In accordance with partial aspects of an embodiment, the antenna has a multi-segment structure such that the area around the driven element is divided into elementary cells with conductors and circuit elements arranged therein. The antenna also includes a set of circuit elements connecting the neighboring elementary cells and the driven element. Each elementary cell has a first conductor located above and parallel with the ground plane (i.e., a horizontal conductor over the ground plane). In addition, each elementary cell can have a second conductor connected and orthogonal to the ground plane (i.e., a vertical conductor) and a circuit element connecting the horizontal and vertical conductors. The horizontal conductor comprises a plurality of characteristic points to which circuit elements, connecting neighboring elementary cells or any elementary cell and the driven element, are connected. Both the impedance of each circuit elements and the design of each elementary cell can be different, but the antenna has <NUM>-fold rotational symmetry (i.e., <NUM>° rotational symmetry) relative to the vertical axis. Impedance of the circuit elements can be selected by any number of numerical optimization methods.

In an embodiment, the antenna includes a vertical wall at an external perimeter of the antenna (i.e., a conducting vertical coupling element located along a peripheral region of the antenna and having a first edge and a second edge). A portion of the elementary cells are connected to a top edge of the vertical wall via the circuit elements, and the bottom edge of the vertical wall forms a galvanic couple with the ground plane. In a further embodiment, a slot is formed between the bottom edge of the vertical wall and the ground plane in which circuit elements are connected. The arrangement and nominal values of impedance of these circuit elements can differ, but the four-fold rotational symmetry of the antenna is maintained. The vertical wall also maintains the <NUM>-fold rotational symmetry and can take any number of different geometries (e.g., a square, circular or any other geometry).

These and other advantages of the embodiments will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings.

In accordance with various embodiments, an improved GNSS compact antenna is provided comprising a conducting ground plane and a driven element for exciting right hand circularly polarized waves.

<FIG> show an antenna configured in accordance with an embodiment. Antenna <NUM> comprises conducting ground plane <NUM>, driven element <NUM>, a plurality of elementary cells <NUM> arranged around driven element <NUM>, a first plurality of circuit elements <NUM> connecting neighboring elementary cells <NUM> and a second plurality of circuit elements <NUM> connecting the plurality of elementary cells <NUM> and driven element <NUM>. Each one of elementary cells <NUM> has a certain volume and, as shown in <FIG>, the conditional limits of each one of elementary cells <NUM> are marked by dotted lines.

As will be readily appreciated, driven element <NUM> generates right hand circularly polarized waves in a well-known fashion. Driven element <NUM> is not resonant, cannot operate as a separate antenna and may be constructed using a metal plate and a dividing circuit. Driven element <NUM> is excited by a plurality of slots or pins in a well-known fashion. Driven element <NUM>, illustratively, has four (<NUM>) slots <NUM>-<NUM>, and the dividing circuit (not shown) providing equally-amplitude excitation of electromagnetic field in slots with a phase shift of ninety degrees (<NUM>°) such that right hand circularly polarized wave is excited in the direction of axis <NUM>. In slots <NUM>-<NUM> there is a third plurality of circuit elements <NUM>-<NUM> ensuring antenna's match. Each output of the dividing circuit is connected to a wire which crosses a corresponding slot <NUM>-<NUM> and thus excites an electromagnetic field in the slot. In an embodiment, excitation can be implemented using a well-known method used in the patch antenna design, namely by excitation pins arranged vertically between ground plane <NUM> and a plate of the driven element <NUM>.

<FIG> show various alterative configurations of elementary cells <NUM> shown in <FIG>. Common to all of these embodiments is that each elementary cell <NUM> comprises a horizontal conductor <NUM> located over conducting ground plane <NUM> (i.e., a horizontal conductor over the ground plane), a vertical conductor <NUM> (i.e., a second conductor connected and orthogonal to the ground plane) and circuit element <NUM>. Vertical conductor <NUM> is connected to ground plane <NUM>. A first end of circuit element <NUM> is connected to horizontal conductor <NUM>, and the other second end of circuit element <NUM> is connected to the top end of vertical conductor <NUM>. In order to facilitate the foregoing connections, the top end of the vertical conductor incorporates contact pad <NUM>. At the first and second ends (i.e., opposing ends) of horizontal conductor <NUM> there are contact pads <NUM>, which can be connected to circuit elements <NUM> and <NUM>. The number of contact pads in elementary cell <NUM> can vary as shown in the various configurations set forth in <FIG>.

In the embodiment of <FIG>, horizontal conductor <NUM> is cross-shaped with the each respective end of the cross-shape having a respective contact pad (i.e., contact pad <NUM>-<NUM>, contact pad <NUM>-<NUM>, contact pad <NUM>-<NUM> and contact pad <NUM>-<NUM>). Correspondingly, four circuit elements <NUM> and/or <NUM> (see, <FIG>) can be connected to individual elementary cell <NUM>. In the embodiment of <FIG>, horizontal conductor <NUM> is T-shaped, with the ends comprising three (<NUM>) contact pads (i.e., pad <NUM>-<NUM>, pad <NUM>-<NUM>, pad <NUM>-<NUM>). In the embodiment of <FIG>, horizontal conductor <NUM> is L-shaped with two contact pads <NUM>-<NUM> and <NUM>-<NUM>, respectively. In the configuration of <FIG>, horizontal conductor <NUM> is square ringed with vertical conductor <NUM> in the center. The sides of horizontal conductor <NUM> comprise four (<NUM>) contact pads (not shown) to connect circuit elements <NUM> and <NUM> in a similar fashion as previously described with respect to <FIG>.

In accordance with the embodiment shown in <FIG>, vertical conductor <NUM> is connected to ground plane <NUM> via circuit element <NUM> with the horizontal conductor <NUM> illustratively shaped similar to that as detailed above and shown in <FIG>. In ground plane <NUM> there is an opening in the center of which there is the bottom end of vertical conductor <NUM>. The bottom end of conductor <NUM> has no galvanic contact with ground plane <NUM> and is connected to a first end of circuit element <NUM>. The other second end of circuit element <NUM> is connected to ground plane <NUM>. In accordance with the embodiment shown in <FIG>, circuit element <NUM> is eliminated and horizontal conductor <NUM> is galvanic coupled with vertical conductor <NUM>. In accordance with the embodiment shown in <FIG>, the connection of vertical conductor with elementary cell <NUM> is eliminated.

As detailed previously, in accordance with an embodiment, antenna <NUM> may comprise different elementary cells <NUM> while maintaining <NUM>-fold rotational symmetry (<NUM>°) relative to vertical axis <NUM>. To that end, <FIG> shows the <NUM>-fold rotation symmetry of antenna <NUM> (shown in <FIG>) in accordance with an embodiment. As shown in <FIG>, elementary cells <NUM>-1A, <NUM>-1B, <NUM>-1C and <NUM>-1D have the same design and are arranged with <NUM>-fold rotational symmetry (<NUM>°) relative to vertical axis <NUM>. Elementary cells <NUM>-2A, <NUM>-2B, <NUM>-2C and <NUM>-2D also have the same design and are arranged with <NUM>-fold rotational symmetry (<NUM>°) relative to vertical axis <NUM>. However, the design of elementary cell <NUM>-1A is different from that of elementary cell <NUM>-2A. In particular, a horizontal conductor of elementary cell <NUM>-1A is L-shaped, and a horizontal conductor of elementary cell <NUM>-2A is T-shaped. As noted previously, vertical conductor <NUM> may be present in certain ones of elementary cells <NUM>, and absent in other ones of the elementary cells (e.g., absent from elementary cells <NUM>). The antenna embodiment shown in <FIG> comprises different circuit elements <NUM> while still maintaining <NUM>-fold rotational symmetry (<NUM>°).

For example, circuit elements <NUM>-1A, <NUM>-1B, <NUM>-1C and <NUM>-1D have the same impedance and are arranged to achieve <NUM>° symmetry relative to vertical axis <NUM> in accordance with the embodiment. Circuit elements <NUM>-2A, <NUM>-2B, <NUM>-2C and <NUM>-2D have equal impedance as well and are arranged symmetrically about vertical axis <NUM>. The impedance of circuit element <NUM>-1A can differ from impedance of circuit element <NUM>-4A. In particular, the impedance of circuit element <NUM>-1A can correspond to an idle run condition (i.e., the element is missing), and the impedance of circuit element <NUM>-2A can correspond to a short circuit condition. Similarly, the impedance of circuit elements can be different in circuit elements <NUM>-1A, <NUM>-1B, <NUM>-1C and <NUM>-1D, and <NUM>-2A, <NUM>-2B, <NUM>-2C and <NUM>-2D.

<FIG> shows antenna <NUM> having lumped circuit elements configured in accordance with an embodiment. As shown, horizontal conductors <NUM> are illustratively manufactured in the form of a metallization layer in PCB <NUM>. Driven element <NUM> and the dividing circuit can be also placed on PCB <NUM>. In the embodiment, each circuit element <NUM> is made as a lumped circuit element soldered to horizontal conductors <NUM> of elementary cells <NUM>. As shown, horizontal conductors <NUM>-<NUM> and <NUM>-<NUM> belong to neighboring elementary cells <NUM> (see, <FIG>), and circuit element <NUM> is connected to such neighboring cells and soldered out to PCB <NUM>. In a well-known fashion, circuit element <NUM> can be made as a lumped capacitor, inductor or resistor. <FIG> gives a side view of antenna <NUM> having the lumped circuit elements configured as detailed above.

If capacitive impedance is required, circuit element <NUM> can be made as a distributed element. In this case, circuit element <NUM> is a plurality of conductors in PCB <NUM>. <FIG> shows an embodiment wherein circuit element <NUM> is in the form of conductor <NUM> located in a first (e.g., top) layer of PCB <NUM>, and conductor <NUM> in second (e.g., bottom) layer of PCB <NUM>. Conductor <NUM> is connected to conductor <NUM>-<NUM> with the aid of metallized hole <NUM> in a conventional manner. Circuit element <NUM> can be also made as interdigital structure <NUM>, as shown in <FIG>, in which the length of the region between two electrodes is increased by an interlocking-finger design for metallization of the electrodes. Circuit elements <NUM>, <NUM>, and <NUM> can be made in the same way, and ground plane <NUM> can be manufactured as a PCB.

<FIG> shows antenna <NUM> configured in accordance with an embodiment using a conducting vertical wall (i.e., a conducting vertical coupling element). In particular, conducting vertical wall <NUM> is maintained along the entire external perimeter of the antenna. Illustratively, vertical wall <NUM> comprises four (<NUM>) rectangular conductors. In other embodiments, vertical wall <NUM> can be shaped as a cylinder or a polygon. In this case, there is an additional plurality of circuit elements <NUM>. Each circuit element of the plurality of circuit elements <NUM> is connected with the a first edge (i.e., top edge) of vertical wall <NUM> via one end and connected with the corresponding horizontal conductor <NUM> via the other end. The plurality of circuit elements <NUM> can comprise elements with different impedance, however <NUM>-fold rotational symmetry is maintained for elements <NUM>, as detailed previously. Also, the second edge (i.e., bottom edge) of vertical wall <NUM> along the entire perimeter is connected with ground plane <NUM>. In a further embodiment, the top end of vertical wall <NUM> can be connected with flat metal surface <NUM>, as shown in <FIG>. Illustratively, surface <NUM> can be an integrated part of the housing to where the antenna is fixed, for example, an aircraft body. In this case, the antenna is flush with the body rather than protruding therefrom in order to achieve better aerodynamic characteristics of the aircraft.

<FIG> show exemplary antenna <NUM> using a connection of a vertical wall (i.e., a conducting vertical coupling element) to a ground plane via circuit elements in accordance with an embodiment. Here, as shown in <FIG>, vertical wall <NUM> has no galvanic contact with ground plane <NUM>, and the slot being between vertical wall <NUM> and ground plane <NUM>. In this slot there can be a plurality of circuit elements <NUM>, one end of each of such circuit elements is connected to vertical wall <NUM>, and the other end is connected with ground plane <NUM>. In practice, such a structure can be implemented by manufacturing ground plane <NUM> in the form of a metallization layer in PCB <NUM>, as shown in <FIG>. Each circuit element of the plurality of circuit elements <NUM> is located on the bottom side of PCB <NUM>. One end of circuit element <NUM> is connected with vertical wall <NUM> using vertical pin <NUM>, and the other end of circuit element <NUM> is connected with ground plane <NUM> using metallized hole <NUM> in a conventional manner. The plurality of circuit elements <NUM> comprise elements with different impedance and maintaining the <NUM>-fold rotational symmetry, as detailed above for elements <NUM>. Availability of the slot between vertical wall <NUM> and ground plane <NUM> excites an additional electromagnetic field thereby reducing DP back-lobe level after subtraction from the field of driven element <NUM>.

The nominal impedance values of the individual circuit elements in pluralities of circuit elements <NUM>, <NUM>, <NUM> and <NUM>, respectively, are selected by an optimization procedure. More particularly, since the impedance of circuit elements in the pluralities of circuit elements <NUM>, <NUM>, <NUM> and <NUM> is the only variable parameter, and the geometric parameters do not change in optimization, the electrodynamic problem can be reduced to calculating a scattering matrix and partial DP, which considerably decreases computation time and allows for a consideration of structures with sufficient complexity and with a greater number of optimized parameters. The use of the optimization procedure with a preliminary calculation of scattering matrix is described, for example, in "<NPL>.

In view of dividing the whole structure into elementary cells having only horizontal and vertical conductors, as detailed above, the calculation of the scattering matrix is considerably simplified as well. The synthesis of antenna <NUM>, for example, will now be discussed. At a first iteration all elementary cells <NUM> are the same with an extremely sophisticated design, i.e., in addition to horizontal conductor <NUM> there is vertical conductor <NUM> and circuit element <NUM>, as shown, for example, in <FIG>. Circuit elements <NUM> are connected to all possible ends of each elementary cell <NUM>. Further, the electrodynamic problem is solved and the impedance of circuit elements are determined according to the obtained scattering matrix with the assistance of the optimizer in a conventional manner. After that, if any circuit element <NUM> in operation of the optimizer needs idle run impedance, the corresponding circuit element <NUM> and possibly vertical conductor <NUM> are removed from the structure. Thus, elementary cells shown in <FIG> are obtained from elementary cells shown in <FIG>. Similarly, circuit elements <NUM> and <NUM> are removed from the structure, if they require impedance close to idle run in the process of optimization. The circuit elements, impedance of which are near to a short circuit condition, are replaced by metal conductors. During optimization, a structure with a smaller number of optimized parameters but with more diverse elementary cells <NUM> is achieved. Further, the scattering matrix is calculated anew, and the optimization procedure must be executed again.

<FIG> show plots <NUM> and <NUM>, respectively, of experimental results produced using the antenna embodiment shown in <FIG> and <FIG>, respectively. The specific antenna structure utilized to generate these results comprised sixty (<NUM>) elementary cells according to the configurations shown in <FIG> and <FIG>, one hundred (<NUM>) circuit elements <NUM>, and twelve (<NUM>) circuit elements <NUM>. The antenna structure maintains <NUM>-fold rotational symmetry with the nominal values of fifteen (<NUM>) circuit elements <NUM>, twenty-five (<NUM>) circuit elements <NUM> and three (<NUM>) circuit elements <NUM> were determined using the optimization procedure, as detailed above. The height of PCB <NUM> over ground plane <NUM> was <NUM> millimeters, and ground plane <NUM> is a receiver housing with horizontal dimensions of <NUM> millimeters x <NUM> millimeters, and a height of <NUM> millimeters. Based on the results shown in <FIG>, the antenna obtained in optimization had a VSWR level no greater than two (<NUM>) in the entire GNSS band (i.e., <NUM>-<NUM> and <NUM>-<NUM>), and the back-lobe level of no more than -<NUM> dB with all circuit elements <NUM>, <NUM> and <NUM> having capacitive impedance.

<FIG> shows plot <NUM> of VSWR results produced using the antenna embodiment shown in <FIG>. In this case, the antenna structure had four vertical walls <NUM><NUM> millimeters high x <NUM> millimeters long, and <NUM> independent parameters were optimized. As can be seen from plot <NUM>, VSWR results do not exceed level two (<NUM>) in practically all GNSS bands.

Claim 1:
An antenna (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
a ground plane (<NUM>);
a driven element (<NUM>) disposed in a first layer and configured to excite a right hand circularly polarized wave;
a plurality of elementary cells (<NUM>) arranged in the first layer around the driven element (<NUM>), wherein at least one elementary cell (<NUM>) of the plurality of elementary cells (<NUM>) is different from each of the remaining elementary cells (<NUM>) in the plurality of elementary cells (<NUM>), and each elementary cell (<NUM>) of the plurality of elementary cells (<NUM>) comprises a first conductor located in the first layer above and parallel with the ground plane (<NUM>); and
a first plurality of circuit elements (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), each circuit element (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) of the first plurality of circuit elements (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) connecting a particular pair of elementary cells (<NUM>) in the plurality of elementary cells (<NUM>) such that the antenna (<NUM>, <NUM>, <NUM>, <NUM>) maintains a <NUM>-fold rotational symmetry relative to a vertical axis orthogonal to the ground plane (<NUM>).