Patent Publication Number: US-2022216603-A1

Title: High gain stripline antenna assemblies

Description:
RELATED APPLICATIONS 
     This application relates to and claims priority benefits from U.S. States Provisional Patent Application No. 63/133,306, entitled “High Gain Stripline Antenna Assemblies,” filed Jan. 2, 2021, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF EMBODIMENTS OF THE DISCLOSURE 
     Embodiments of the present disclosure generally relate to antenna assemblies, and more particularly, to stripline-based antenna assemblies. 
     BACKGROUND OF THE DISCLOSURE 
     An antenna typically includes an array of conductors electrically connected to an electronic receiver or a transmitter. An electronic transmitter provides a time-varying voltage to terminals of the antenna, which, in response, radiates electromagnetic radio waves at a frequency corresponding to the time-varying voltage. Alternatively, as radio waves are received by the antenna, a time-varying voltage corresponding to the frequency of the radio wave is generated at the terminals, which, in turn is provided to the electronic receiver. Various types of known passive antennas are configured to transmit and receive radio waves equivalently with such a reciprocal behavior. 
     In some aerospace applications, there is a need for antennas that are capable of being positioned on conformal or non-planar surfaces, such as wings and fuselages of aircraft. Small aircraft, such as unmanned aerial vehicles (UAVs) or drones, in particular, have surfaces with low radii of curvature. Such aircraft typically need light weight antennas with low aerodynamic drag and low visibility. Further, various surfaces of aircraft may be formed from conductive or carbon fiber materials, which are known to change the electrical behavior of antennas, such as monopole and dipole antennas and derivatives (for example, whip, blade, Yagi, and other such antennas). 
     Various known planar antennas that include microstrip feeds and pin feeds exhibit low bandwidth, due to their narrowband impedance matching. However, the bandwidth can be increased by using a proximity-coupled feed line. Still, planar antennas generally have low gain and bandwidth due to their thin nature. 
     SUMMARY OF THE DISCLOSURE 
     A need exists for a stripline-based antenna that exhibits increased or otherwise improved gain and bandwidth. 
     With that need in mind, certain embodiments of the present disclosure provide an antenna assembly including one or more dielectrics having a first surface and a second surface opposite from the first surface. An antenna layer includes one or more antenna elements disposed on the first surface of the one or more dielectrics. A stripline feed network is disposed on or within the one or more dielectrics. One or more cavities are formed in the one or more dielectrics. The one or more cavities are disposed below the one more antenna elements. 
     In at least one embodiment, the antenna layer further includes one or more coplanar ground elements separated from the one or more antenna elements. As a further example, one or more vias connect the one or more coplanar ground elements to a ground plane disposed below the one or more dielectrics. 
     In at least one embodiment, a ground plane is disposed below the one or more dielectrics. As a further example, at least one additional dielectric is disposed below the ground plane. 
     The one or more antenna elements may include an inclusive slot. 
     In at least one embodiment, the one or more cavities are between the first surface and the second surface. 
     In at least one embodiment, the one or more antenna elements are above the one or more cavities. 
     In at least one example, at least a portion of the stripline feed network is disposed between the one or more antenna elements and the one or more cavities. 
     As an example, the one or more dielectrics include a first dielectric having the first surface. A second dielectric is secured to the first dielectric. The second dielectric is disposed between the first dielectric and at least a portion of the stripline feed network. A third dielectric includes the one or more cavities and the second surface. The at least a portion of the stripline feed network is disposed between the second dielectric and the third dielectric. 
     In at least one embodiment, a first diameter or axial envelope of the one or more antenna elements is within a second diameter or axial envelope of the one or more cavities. 
     As an example, the one or more antenna elements include at least two antenna elements. The one or more cavities include at least two cavities. 
     Certain embodiments of the present disclosure provide a method of forming an antenna assembly. The method includes providing one or more dielectrics having a first surface and a second surface opposite from the first surface; disposing an antenna layer including one or more antenna elements on the first surface of the one or more dielectrics; disposing a stripline feed network on or within the one or more dielectrics; and forming one or more cavities in the one or more dielectrics below the one more antenna elements. 
     In at least one embodiment, the method also includes providing the antenna layer with one or more coplanar ground elements separated from the one or more antenna elements. The method may further include connecting the one or more coplanar ground elements to a ground plane disposed below the one or more dielectrics with one or more vias. 
     In at least one embodiment, the method includes disposing a ground plane below the one or more dielectrics. The method may further include disposing at least one additional dielectric below the ground plane. 
     In at least one embodiment, said forming includes forming the one or more cavities between the first surface and the second surface. 
     In at least one embodiment, the method further includes disposing at least a portion of the stripline feed network between the one or more antenna elements and the one or more cavities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic block diagram of an antenna assembly, according to an embodiment of the present disclosure. 
         FIG. 2  illustrates a schematic block diagram of the antenna assembly secured to a structure, according to an embodiment of the present disclosure. 
         FIG. 3  illustrates a perspective top view of the antenna assembly, according to an embodiment of the present disclosure. 
         FIG. 4  illustrates a top view of the antenna assembly of  FIG. 3 . 
         FIG. 5  illustrates a cross-sectional view of an antenna layer disposed on a first dielectric through line  5 - 5  of  FIG. 4 , according to an embodiment of the present disclosure. 
         FIG. 6  illustrates a cross-sectional view of a stripline feed network disposed underneath a second dielectric through line  5 - 5  of  FIG. 4 , according to an embodiment of the present disclosure. 
         FIG. 7  illustrates a cross-sectional view of cavities formed within a third dielectric through line  5 - 5  of  FIG. 4 , according to an embodiment of the present disclosure. 
         FIG. 8  illustrates a cross-sectional view of a ground plane disposed over a fourth dielectric through line  5 - 5  of  FIG. 4 , according to an embodiment of the present disclosure. 
         FIG. 9  illustrates a cross-sectional view of the antenna assembly through line  5 - 5  of  FIG. 4 . 
         FIG. 10  illustrates a flow chart of a method of forming an antenna assembly, according to an embodiment of the present disclosure. 
         FIG. 11  illustrates a graph of predicted gain in relation to elevation angle for an antenna assembly having cavities, as described herein, compared to an antenna assembly without cavities. 
         FIG. 12  illustrates a graph of predicted return loss in relation to frequency for an antenna assembly having cavities, as described herein, compared to an antenna assembly without cavities. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The foregoing summary, as well as the following detailed description of certain embodiments, will be better understood when read in conjunction with the appended drawings. As used herein, an element or step recited in the singular and preceded by the word “a” or “an” should be understood as not necessarily excluding the plural of the elements or steps. Further, references to “one embodiment” are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional elements not having that property. 
     Certain embodiments of the present disclosure provide a stripline-based antenna assembly that exhibits improved gain as compared to known stripline antennas. The antenna assembly includes at least one proximity-coupled antenna element with an inclusive slot and a coplanar ground plane on a first surface of one or more dielectrics, such as a radio frequency (RF) board. An embedded stripline feed is below the stripline feed antenna element, a ground plane below the stripline feed, and a cavity between the stripline feed antenna element and ground plane. The slot and coplanar ground improve the cross polarization of the antenna. The stripline feed minimizes or otherwise reduces power loss in the feed network (in comparison to microstrip and grounded coplanar waveguide feeds). Further, the ground plane minimizes or otherwise reduces any change in electrical behavior when the antenna assembly is placed on conductive surfaces (for example, wings, fuselage, tail fin, and/or the like). 
     The antenna assemblies according to embodiments of the present disclosure includes one or more antenna elements and coplanar ground elements electrically coupled to a stripline feed. A stripline feed minimizes or otherwise reduces power loss through the feed network. A cavity between the antenna element(s) and backside ground plane improves gain of the antenna assembly. The backside ground plane minimizes or otherwise reduces change in electrical behavior due to conductive surfaces. The antenna assemblies can be manufactured using subtractive (for example, laser etching, milling, wet etching, or the like) or additive (for example, printing, film deposition, or the like) methods. 
       FIG. 1  illustrates a schematic block diagram of an antenna assembly  100 , according to an embodiment of the present disclosure. The antenna assembly includes an antenna layer  102  disposed on one or more dielectrics  104 , such as one or more dielectric layers. The antenna layer  102  includes one or more antenna elements  106  separated from coplanar ground elements  108 . That is, the antenna element(s)  106  are coplanar with the ground elements  108  within the antenna layer  102 . 
     In at least one embodiment, the antenna element(s) is proximity coupled (or electrically coupled), and includes an inclusive slot. The inclusive slot and coplanar ground elements  108  improve cross polarization of the antenna assembly  100 . The one or more dielectrics  104  may form at least part of an RF board. 
     A stripline feed network  116  is disposed under or within the one or more dielectrics  104 . For example, the stripline feed network  116  is disposed underneath the one or more dielectrics  104 . As another example, the stripline feed network  116  is sandwiched between two different dielectrics  104 . The stripline feed network  116  minimizes or otherwise reduces power loss (as compared to microstrip and grounded coplanar waveguide feeds). 
     One or more dielectrics  118  can be disposed underneath the stripline feed network  116 . For example, the stripline feed network  116  can be sandwiched between the one or more dielectrics  104  and the one or more dielectrics  118 . 
     In at least one embodiment, one or more cavities  110  (for example, air gaps) are formed in the one or more dielectrics  104 . The one or more cavities  110  are aligned with the one or more antenna elements  106 . For example, the one or more antenna elements  106  are disposed on a first surface  112 , such as an upper surface, of the one or more dielectrics  104  that is opposite a second surface  114 , such as a lower surface. The one or more cavities  110  are between the first surface  112  and the second surface  114 . In at least one embodiment, the antenna element(s)  106  are above the one or more cavities  110 . The antenna element(s)  106  are not within the one or more cavities  110 . Instead, the antenna element(s)  106  are aligned over, above, or the like from the one or more cavities  110 . In at least one embodiment, the antenna element(s)  106  are secured on the first surface  112  and axially aligned over the one or more cavities  110 . 
     In at least one embodiment, the one or more cavities  110  are disposed between the stripline feed network and the one or more antenna elements  106 . In at least one embodiment, the one or more cavities  110  are above the stripline feed network  116 . In at least one embodiment, a first cavity  110  is above the stripline feed network  116 , and a second cavity  110  is below the stripline feed network  116 . 
     A ground plane  120  is disposed below the one or more dielectrics  118 . Optionally, the ground plane  120  can be secured to the one or more dielectrics  104 , and the one or more dielectrics  118  can be secured underneath the ground plane  120 . For example, the ground plane  120  can be sandwiched between the one or more dielectrics  104  and the one or more dielectrics  118 . Optionally, the antenna assembly  100  may not include the one or more dielectrics  118 . Instead, the ground plane  120  may be secured to the stripline feed network  116  and/or the second surface  114  of the one or more dielectrics  104  (such as when the stripline feed network  116  is disposed within the one or more dielectrics  104 ). The ground plane  120  minimizes or otherwise reduces any change in electrical behavior when the antenna assembly  100  is placed on conductive surfaces (for example, wings, fuselage, tail fin, and/or the like). 
     In at least one embodiment, one or more vias connect the coplanar ground elements  108  to the ground plane  120 . For example, each coplanar ground elements  108  connects to the ground plane  120  through a separate via. 
     The one or more cavities  110  between the antenna element(s)  106  and ground plane  120  improve gain of the antenna assembly  100 . It has been found that the antenna assembly  100  exhibits improved gain as compared to known stripline antennas. 
     As described herein, the antenna assembly  100  includes one or more dielectrics  104  having the first surface  112  and the second surface  114  opposite from the first surface  112 . The antenna layers  102  includes one or more antenna elements  106  disposed on the first surface  112  of the one or more dielectrics  104 . The stripline feed network  116  is secured on, within, or below the one or more dielectrics  104 . In at least one embodiment, the stripline feed network  116  is below the one or more antenna elements  106 . One or more dielectrics  118  are secured below the stripline feed network  116 . The one or more cavities  110  are formed in the one or more dielectrics  118 . The one or more cavities  110  are disposed below the one more antenna elements  106 . 
       FIG. 2  illustrates a schematic block diagram of the antenna assembly  100  secured to a structure  122 , according to an embodiment of the present disclosure. For example, the structure  122  is a portion of a body of an aircraft. In at least one embodiment, the structure  122  is a wing, fuselage, tail fine, or the like of an aircraft. The structure  122  includes communication equipment or electronics  124  that connect to the stripline feed network  116 , such as through a microstrip. 
     As shown, the antenna layer  102  is disposed on the first surface  112  of a first dielectric  104   a.  A second dielectric  104   b  separates the first dielectric  104   a  from the stripline feed network  116 . The stripline feed network  116  is disposed between the second dielectric  104   b  and a third dielectric  104   c.  A cavity  110  is formed within the third dielectric  104   c.  The cavity  110  is underneath the antenna element  106 . In at least one embodiment, the cavity  110  is directly underneath the antenna element  106 . The cavity  110  may have a diameter or width  125  that exceeds the diameter or width  127  of the antenna element  106 . Accordingly, the axial envelope  129  of the cavity  110  is greater than the axial envelope  131  of the antenna element  106 . In at least one embodiment, the axial envelope  131  of the antenna element  106  does not extend past the axial envelope  129  of the cavity  110 . Accordingly, the axial envelope  131  of the antenna element  106  is within the axial envelope  129  of the cavity  110 . 
     The ground plane  120  is disposed underneath the third dielectric  104   c.  For example, the ground plane  120  is secured to the second surface  114  of the third dielectric  104   c.    
     As shown in  FIG. 2 , the first dielectric  104   a  has the first surface  112 . The second dielectric  104   b  is secured to the first dielectric  104   a.  The second dielectric  104   b  is disposed between the first dielectric  104   a  and at least a portion of the stripline feed network  116 . The third dielectric  104   c  includes the cavity  110 , and the second surface  114 . The at least a portion of the stripline feed network  116  is disposed between the second dielectric  104   b  and the third dielectric  104   c.    
     In at least one embodiment, a fourth dielectric  126  is disposed between the structure  122  and the ground plane  120 . The fourth dielectric  126  can be mounted directly to the structure  122 . Alternatively, the antenna assembly  100  does not include the fourth dielectric  126 . 
     The antenna assembly  100  can include more or less dielectrics than shown. For example, the antenna assembly  100  may not include the second dielectric  104   b.    
     Further, the antenna assembly  100  can include more antenna elements  106  than shown. As an example, antenna assembly  100  can include two, three, four, or more antenna elements  106  above one or more cavities  110 . In at least one embodiment, a single cavity  110  is disposed underneath multiple antenna elements  106 . In at least one other embodiment, each antenna element  106  is disposed above a separate and distinct cavity  110 . For example, the antenna assembly  100  can include two or more antenna elements  106  disposed above two or more cavities  110 , with each antenna element  106  disposed over a separate cavity  110 . 
     It is to be understood that the terms first, second, third, fourth, and the like are merely for labeling purposes. A “first,” may be a “second,” “third,” “fourth,” or vice versa. 
       FIG. 3  illustrates a perspective top view of the antenna assembly  100 , according to an embodiment of the present disclosure.  FIG. 4  illustrates a top view of the antenna assembly  100  of  FIG. 3 . Referring to  FIGS. 3 and 4 , for the sake of clarity, portions of the antenna assembly  100  are shown transparent. 
     As shown, the antenna assembly  100  includes four antenna elements  106  disposed above four cavities  110 , respectively. Optionally, the antenna assembly  100  can include more or less antenna elements  106  disposed above more or less cavities  110 . The antenna elements  106  are not within the cavities  110 . Rather, the antenna elements  106  are disposed above the cavities  110 , as described above. 
     The antenna elements  106  can include inclusive slots  140 , which improve cross polarization of the antenna assembly  100 . Optionally, less than all of the antenna elements  106  include inclusive slots  140 . Alternatively, none of the antenna elements  106  include inclusive slots  140 . 
     A microstrip  142  (such as a conductor and ground plane) connects a power divider  144 , such as in an edge-to-edge fashion. The power divider  144  in turn connects to, or optionally forms part of, the stripline feed network  116 , which couples to the antenna elements  106 , such as via proximity coupling. Electrical vias  150  connect the coplanar ground elements  108  of the antenna layer  102  to the ground plane  120  (shown in  FIGS. 1 and 2 ). In at least one embodiment, the cavities  110  (or additional cavities) can extend below and/or above portions of the stripline feed network  116  outside of the diameters or axial envelopes of the antenna elements  106 . For example, cavities  110  may extend below and/or above an entirety of the stripline feed network  116 . 
       FIG. 5  illustrates a cross-sectional view of the antenna layer  102  disposed on the first dielectric  104   a  through line  5 - 5  of  FIG. 4 , according to an embodiment of the present disclosure. The coplanar ground elements  108  are separated from the antenna elements  106  by gaps  160 , thereby electrically isolating the coplanar ground elements  108  from the antenna elements  106 . In at least one embodiment, a metal, such as copper, can be deposited or printed onto the first dielectric  104   a  (such as the first or upper surface  112 ) to form the antenna elements  106  and the coplanar ground elements  108 . 
       FIG. 6  illustrates a cross-sectional view of the stripline feed network  116  disposed underneath the second dielectric  104   b  through line  5 - 5  of  FIG. 4 , according to an embodiment of the present disclosure. In at least one embodiment, a metal, such as copper, can be deposited or printed onto a lower or bottom surface  162  of the second dielectric  104   b  to form the stripline feed network  116 . 
       FIG. 7  illustrates a cross-sectional view of the cavities  110  formed within the third dielectric  104   c  through line  5 - 5  of  FIG. 4 , according to an embodiment of the present disclosure. In at least one embodiment, the cavities  110  may be etched into the third dielectric  104   c.  The cavities  110  may extend between and through upper and lower surfaces of the third dielectric  104   c.    
       FIG. 8  illustrates a cross-sectional view of the ground plane  120  disposed over the fourth dielectric  126  through line  5 - 5  of  FIG. 4 , according to an embodiment of the present disclosure. In at least one embodiment, a metal, such as copper, can be deposited or printed onto an upper surface  164  of the fourth dielectric  126  to form the ground plane  120 . 
       FIG. 9  illustrates a cross-sectional view of the antenna assembly  100  through line  5 - 5  of  FIG. 4 . Laminate layers  170 ,  172 , and  174  may be used to secure the various layers of the antenna assembly  100  together. The vias  150  can be formed by etching and filling with conductive ink or electroplating. The vias  150  electrically connect the coplanar ground elements  108  with the ground plane  120 . As shown in  FIG. 9 , at least a portion of the stripline feed network  116  is disposed between the antenna elements  106  and the cavities  110 . 
       FIG. 10  illustrates a flow chart of a method of forming an antenna assembly, according to an embodiment of the present disclosure. Referring to  FIGS. 2-10 , at  200 , the antenna elements  106  are disposed on a top surface (such as the first surface  112 ) of the first dielectric  104   a.  At  202 , the coplanar ground elements  108  are disposed on the top surface of the first dielectric  104   a.  At  204 , a conductor forming the stripline feed network  116  is disposed on the bottom surface  162  of the second dielectric  104   b.  At  206 , the cavities  110  are etched into the third dielectric  104   c.  At  208 , the ground plane  120  is disposed on the upper or top surface  164  of the fourth dielectric  126 . At  210 , the first dielectric  104   a,  the second dielectric  104   b,  the third dielectric  104   c,  and the fourth dielectric  104   c  are laminated together. At  212 , the vias  150  are etched and filled with conductive epoxy. 
       FIG. 11  illustrates a graph of predicted gain in relation to elevation angle for an antenna assembly having cavities, as described herein, compared to an antenna assembly without cavities.  FIG. 12  illustrates a graph of predicted return loss in relation to frequency for an antenna assembly having cavities, as described herein, compared to an antenna assembly without cavities. 
     Referring to  FIGS. 11 and 12 , a numerical model of a high gain stripline antenna assembly in a 2×2 array designed to operate near 10 GHz was developed using a finite element method (FEM) solver to predict the performance. The antenna array with no cavities has a nominal gain of ˜8.8 dBi and a 2:1 VSWR bandwidth of ˜580 MHz. The antenna assembly with cavities has a nominal gain of ˜9.9 dBi and a 2:1 VSWR bandwidth of ˜1170 MHz. It has been found that the gain-bandwidth product of the antenna assembly is improved by a factor of more than 2.5 by using cavities. 
     As described herein, embodiments of the present disclosure provide stripline-based antenna assemblies that exhibit increased or otherwise improved gain and bandwidth. 
     While various spatial and directional terms, such as top, bottom, lower, mid, lateral, horizontal, vertical, front and the like may be used to describe embodiments of the present disclosure, it is understood that such terms are merely used with respect to the orientations shown in the drawings. The orientations may be inverted, rotated, or otherwise changed, such that an upper portion is a lower portion, and vice versa, horizontal becomes vertical, and the like. 
     As used herein, a structure, limitation, or element that is “configured to” perform a task or operation is particularly structurally formed, constructed, or adapted in a manner corresponding to the task or operation. For purposes of clarity and the avoidance of doubt, an object that is merely capable of being modified to perform the task or operation is not “configured to” perform the task or operation as used herein. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments of the disclosure without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments of the disclosure, the embodiments are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments of the disclosure should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112(f), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 
     This written description uses examples to disclose the various embodiments of the disclosure, including the best mode, and also to enable any person skilled in the art to practice the various embodiments of the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the various embodiments of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if the examples have structural elements that do not differ from the literal language of the claims, or if the examples include equivalent structural elements with insubstantial differences from the literal language of the claims.