Patent Publication Number: US-9893430-B2

Title: Short coincident phased slot-fed dual polarized aperture

Description:
BACKGROUND 
     1. Field 
     Embodiments of the present invention relate to antenna arrays. 
     2. Related art 
     Dual polarity flared notch antennas arrays are commonly used, for example, in radar systems. For some applications, it is desirable for the two polarities of the dual polarity flared notch antenna array to have coincident phase centers. 
       FIG. 1A  is a cross sectional view of a conventional flared notch antenna  100  having two flares  110 , a feed  120  crossing a notch  130  located between the two flares  110  and backed by a cavity  140 . Due to the location of the feed  120  across the notch  130 , a conventional flared notch antenna  100  cannot be operated in a dual polarity arrangement with coincident phase centers because the flares  110  and the feed  120  of the second polarity would interfere (e.g., intersect or cross) with those of the first polarity. 
       FIG. 1B  is a cross sectional view illustrating a conventional flared notch antenna  100 ′ having an alternative feed scheme including an alternative feed  120 ′. 
       FIGS. 2A and 2B  are cross sectional views of alternative flared notch antennas which can be used to provide a coincident phased dual polarity flared notch antenna array.  FIG. 2A  is reproduced from FIG. 2 of W. R. Pickles, et al. “Coincident Phase Center Ultra Wideband Array of Dual Polarized Flared Notch Elements” Antennas and Propagation Society International Symposium, IEEE 2007. In the antenna arrays shown in  FIGS. 2A and 2B , the feed  220  is split into a first and a second feed  222  and  224 . Similarly, the notch  230  is split into first and second slots  232  and  234  which are backed by their respective cavities  242  and  244 . The first and second feeds  222  and  224  extend across their respective slots  232  and  234 . Because the feed  220  no longer crosses the center of the structure (e.g., in the middle of the space between the flares  210 ), this structure makes it possible to arrange flares and feeds for both the first and second polarities without the use of an offset in the z-direction. 
     In addition to a balun, an impedance transformer is generally used as part of a radiating element in order to provide impedance matching between the source impedance (generally, 50Ω) and the free space impedance (approximately 377Ω). In the conventional flared notch radiator  100  illustrated in  FIG. 1A , the flares  110  are used as the impedance transformer to provide this impedance matching. However, because the flares  110  are directly connected to the feed  120 , the flares must provide all of the matching from 50Ω to 377Ω and therefore are relatively long. 
     SUMMARY 
     Embodiments of the present invention are directed to a short coincident phased slot-fed dual polarized aperture phased antenna array. 
     According to one embodiment of the present invention, a coincident phased dual-polarized antenna array configured to emit electromagnetic radiation includes: a plurality of electromagnetic radiators arranged in a grid, the plurality of electromagnetic radiators defining a plurality of notches; a ground plane spaced from the electromagnetic radiators; a conductive layer disposed between the electromagnetic radiators and the ground plane, the conductive layer having a plurality of slots laterally offset, from the notches and being spaced apart from and electrically insulated from the electromagnetic radiators; and a plurality of feeds, each of the feeds spanning a corresponding slot of the slots and electrically connected to a portion of the conductive layer at one side of the corresponding slot. 
     The ground plane may be spaced from the conductive layer. 
     A spacer layer may be between the plurality of slots and the ground plane. 
     The spacer layer may be filled with a dielectric material. 
     A plurality of cavities may be between the plurality of slots and the ground plane. 
     The cavities may be filled with a dielectric material. 
     The conductive layer may be spaced apart from the electromagnetic radiators by an electrically insulating parallel plate layer. 
     The electrically insulating parallel plate layer may be filled with a dielectric material. 
     One of the slots may be located between adjacent ones of the notches. 
     Two of the slots may be located between adjacent ones of the notches. 
     A first of the feeds spanning a first slot of the slots may be electrically coupled in parallel to a second of the feeds spanning a second slot of the slots, wherein the first slot may be adjacent to the second slot, and wherein the first slot and the second slot may be on opposite sides of a notch of the notches. 
     The electromagnetic radiators may include metalized molded plastic flares. 
     The feeds may be microstrip feeds. 
     The feeds may be stripline feeds. 
     According to another embodiment of the present invention, a method of emitting electromagnetic radiation along a plurality of radiating paths includes: providing a plurality of electromagnetic radiators arranged in a grid, the plurality of electromagnetic radiators defining a plurality of notches; providing a ground plane spaced from the electromagnetic radiators; providing a conductive layer between the electromagnetic radiators and the ground plane, the conductive layer having a plurality of slots laterally offset from the notches and being spaced apart from and electrically insulated from the electromagnetic radiators; providing a plurality of feeds, each of the feeds spanning a corresponding slot of the slots and electrically connected to a portion of the conductive layer at one side of the corresponding slot; and supplying a plurality of electromagnetic signals to the feeds. 
     Two of the slots may be located between adjacent ones of the notches. 
     A first of the feeds spanning a first slot of the slots may be electrically coupled in parallel with a second of the feeds spanning a second slot of the slots, wherein the first slot may be adjacent to the second slot, wherein the first slot and the second slot may be on opposite sides of a radiating path of the radiating paths, and wherein a same electromagnetic signal of the electromagnetic signals may be supplied to the first micro strip line or strip line feed and the second micro strip line or strip line feed. 
     The feeds may be microstrip feeds. 
     The feeds are stripline feeds. 
     The method may further include providing a spacer layer or a plurality of cavities between the plurality of slots and the ground plane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention. 
         FIG. 1A  is a cross-sectional view of a conventional flared notch antenna which may be used in a dual polarized arrangement. 
         FIG. 1B  is a cross sectional view illustrating a conventional flared notch antenna having an alternative feed scheme. 
         FIG. 2A  is a cross-sectional view of a prior coincident phased radiator having a balanced feed and having feed lines running along two orthogonal planes. 
         FIG. 2B  is a cross-sectional view of a prior coincident phased radiator similar to that of  FIG. 2A  having an alternative feed scheme. 
         FIG. 3A  is a cross sectional view a coincident phased slot fed antenna array according to one embodiment of the present invention. 
         FIG. 3B  is a cross sectional view of an embodiment of the present invention similar to the embodiment of  FIG. 3A , but having an alternative feed scheme. 
         FIG. 3C  is a cross sectional view of an embodiment of the present invention similar to the embodiment of  FIG. 3A , in which the resonators of  FIG. 3A  are replaced by a spacer layer backed by a ground plane. 
         FIG. 3D  is a cross sectional view of an embodiment of the present invention similar to the embodiment of  FIG. 3B , in which the resonators of  FIG. 3B  are replaced by a spacer layer backed by a ground plane. 
         FIG. 3E  is a cross sectional plans view of the embodiment illustrated in  FIG. 3A , as taken along line E-E of  FIG. 3A . 
         FIG. 4A  is a cross sectional view a coincident phased slot fed antenna array according to one embodiment of the present invention. 
         FIG. 4B  is a cross sectional view of an embodiment of the present invention similar to the embodiment of  FIG. 4A , but having an alternative feed scheme. 
         FIG. 4C  is a cross sectional view of an embodiment of the present invention similar to the embodiment of  FIG. 4A , in which the resonators of  FIG. 4A  are replaced by a spacer layer backed by a ground plane. 
         FIG. 4D  is a cross sectional view of an embodiment of the present invention similar to the embodiment of  FIG. 4B , in which the resonators of  FIG. 4B  are replaced by a spacer layer backed by a ground plane. 
         FIGS. 5A, 5B, and 5C  illustrate calculated co-polarization insertion loss from 0.25 GHz to 2.50 GHz for H-Plane, E-Plane, and D-Plane scans, respectively in one embodiment of the present invention. 
         FIGS. 6A, 6B, and 6C  illustrate calculated Cx-polarization insertion loss, not including aperture projection loss from 0.25 GHz to 2.50 GHz for H-Plane, E-Plane, and D-Plane scans, respectively, according to one embodiment of the present invention. 
         FIGS. 7A and 7B  illustrated calculated co-polarization insertion loss along the E-Plane and the H-Plane according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, only certain exemplary embodiments of the present invention are shown and described, by way of illustration. As those skilled in the art would recognize, the invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Also, in the context of the present application, when an element is referred to as being “on” another element, it can be directly on another element or be indirectly on another element with one or more intervening elements interposed there between. Like reference numerals designate like elements throughout the specification. 
     Many of today&#39;s sensors require coincident-phased dual polarization apertures with a wide scan capability and very wide bandwidth (e.g., &gt;2:1 bandwidth). In addition, in lower frequency applications, an antenna array having a low profile and small volume is desirable due to weight and packaging constraints. Low loss is also a desirable characteristic for such applications. In addition, an antenna array having a simplified construction can reduce manufacturing costs. 
     However, as described in the Background section above, a conventional flared notch antenna is not well suited to applications requiring coincident-phased dual polarization apertures because the feed lines in any adaptation of the conventional design would interfere (e.g., intersect or cross). 
     Adapting a conventional flared notch antenna to provide a coincident-phased dual polarization aperture would require offsetting the feeds in the z-direction (e.g., in the antenna boresight direction) in order to provide space such that the feed lines  120  of each polarity do not interfere. However, such a configuration would be difficult to manufacture (due to, for example, the multiple layers required for the feed lines) and would likely exhibit higher cross-polarization coupling. 
     Embodiments of the present invention are directed to a flared notch antenna in which the feed lines are spaced apart from the radiating notch of the flares along a direction perpendicular to antenna boresight direction, thereby providing a coincident phased dual polarity element that is suited for both low-frequency and high-frequency applications. In embodiments of the present invention, a slot-fed balun is configured to drive radiating elements in a push-pull manner, where slot resonators are fed with a parallel plate structure. 
     In general, embodiments of the present invention are capable of wideband operation, have low loss, and have a simple construction. For the low-frequency applications, embodiments of the present invention are capable of wideband performance (simulated up to 3.5:1 bandwidth) in a very low profile and lightweight structure, and having low cross-polarization coupling. 
       FIG. 3A  is a cross sectional view of a coincident phased slot-fed dual polarized antenna array with a single slot resonator according to one embodiment of the present invention. Embodiments making use of a single slot resonator may be used in higher-frequency applications where the height of a radiating portion  302  is not a major concern but physical packaging may be a limitation. In this embodiment, the overall height of the radiating portion  302  may be ˜1 wavelength tall at the highest operating frequency. The flared slot sections transform from approximately 300 ohms down to a drive point impedance, usually approximately 100 ohms, that is selected based on physical feature size (e.g., a 50 ohms slot line would be too narrow to accommodate two orthogonal slots because they would physically interfere). A 100 ohm slot may be coupled to an 80 ohm stripline feed, which is in turn transformed down to 50 ohms in the stripline board. This single slot-fed balun configuration offers a coincident phase center yet has separate resonators for the two polarizations, each offset by half a unit cell from the common throat section. 
     Referring to  FIG. 3A , according to one embodiment of the present invention the antenna array  300  includes a radiating portion  302  and a feed portion  304  separated from the radiating portion  302  by a parallel plate layer  306 . The radiating portion  302  includes a plurality of flares  310  which are spaced from one another by a unit cell size. The flares  310  are arranged to form notches  380  between the flares. The feed portion  304  includes microstrip feeds (including corresponding excitations)  320  spanning slots  330  which are backed by cavities  340 . The feed portion  304  is coupled to the radiating portion  302  through the parallel plate layer  306  such that signals applied to the microstrip feeds (via the corresponding excitations)  320  from a driving circuit are coupled to the radiating portion  302  via the parallel plate section  306  to radiate electromagnetic energy. In addition, electromagnetic waves received by radiating portion  302  are coupled to the microstrip feed lines  320  across the parallel plate layer  306  to be processed by a receiving circuit connected to the microstrip feed lines (via the corresponding excitations)  320 . 
     In the embodiment illustrated in  FIG. 3A , the slots  330  are aligned with the center lines of the flares  310  (e.g., along the dotted lines shown in  FIG. 3A ). Therefore, the slots  330  and the feeds  320  spanning the slots are spaced apart from the notches  380  (and the radiating paths  350 ) located between the flares  310  and therefore no offset in the z-direction is needed between the radiating elements aligned with the first polarity and the radiating elements aligned with the second polarity, thereby simplifying construction of the apparatus. 
     The antenna  300  includes two separate assemblies: the radiating portion (also commonly referred to as the radiators)  302  and the feed portion or feeds  304 . The radiating portion  302  can be constructed a multiple ways, including: molded (e.g., injection molded) or machined 3-D structures that are attached to a planar surface or sheet with similar footprint (facesheet); or an eggcrate structure formed by interlocking radiator printed circuit cards. The feed portion can be manufactured using standard multilayer printed wiring boards (PWB or printed circuit board) processes. The radiating  302  and feed  304  portions can be physically separated by a parallel plate spacer layer which may include low-dielectric foam layers or by using spacers located at various points between the radiating portion  302  and the feed portion  304  (thereby leaving air or vacuum between the radiator and feed assemblies). The physical space between the radiating portion  302  and the feed portion  304  forms the parallel plate layer  306 . 
       FIG. 3B  is a cross-sectional view of a coincident phased slot-fed dual polarized antenna array constructed according to an alternative embodiment of the present invention in which the microstrip feeds  320  of the embodiment of  FIG. 3A  are replaced with stripline feeds (including corresponding excitations)  320 ′ between conducting plates  342  and  344 . The use of a stripline feed between conducting plates simplifies construction when compared to the embodiment shown in  FIG. 3A , thereby reducing costs. 
       FIG. 3C  is a cross-sectional view of another embodiment of the present invention. In the embodiment shown in  FIG. 3C , the cavities  340  of the embodiment of  FIG. 3A  are replaced by a spacer layer  340 ′ backed by a ground plane  370  and therefore does not include a separate cavity for each of the radiating elements. The spacer layer  340 ′ may be filled with an insulating dielectric material or air or vacuum (e.g., when used in outer space). Eliminating separate cavities also simplifies and reduces the cost of manufacturing. At higher operating frequencies, separate cavities also become more difficult to implement due to their small feature sizes. 
       FIG. 3D  is a cross-sectional view of another embodiment of the present invention which is a combination of features of the embodiments shown in  FIGS. 3B and 3C . In the embodiment shown in  FIG. 3D , the cavities  340  of the embodiment of  FIG. 3B  are replaced by a spacer layer  340 ′ backed by a ground plane  370  and the microstrip feed is replaced with a stripline feed  320 ′ between conducting plates  342  and  344 . 
       FIG. 3E  is a cross sectional plan view of the embodiment of the present invention shown in  FIG. 3A , as taken along line E-E of  FIG. 3A . As seen in the plan view, the feeds  320  extend across slots  330  located beneath the flares  310  and not beneath the notches  380  between the flares  310 . As such, the feeds  320  drive the radiators, which include flares  310 , which intersect with one another and that are spaced apart from one another. As seen in  FIG. 3E , micro strip line  320   x  is arranged to drive a first radiator arranged along the x axis, the first radiator including a first portion  310   x ′ and a second portion  310   x ″. Feed  320   y  is spaced apart from feed  320   x  in the x and y directions and therefore, in some embodiments of the present invention, may be located in the same plane as the feed  320   x  (e.g., feed  320   y  may have the same z coordinate as the feed  320   x ). 
     The embodiments of  FIGS. 3A, 3B, 3C, 3D, and 3E  are well suited to higher frequency applications in which the antenna height, light weight, and small volume are not critical considerations. 
       FIG. 4A  is a cross-sectional view of an antenna array according to another embodiment of the present invention which is substantially similar to the embodiment illustrated in  FIG. 3A . The embodiment shown in  FIG. 4A  differs from the embodiment shown in  FIG. 3A  in that two slots  430  are located beneath each flare  410 . Embodiments of the present invention making use of a two slot resonator may be particularly suitable for applications where low profile and weight are most important. The height of the radiating portion  402  can be made significantly shorter by including a power combiner to quickly lower the impedance from free space to component impedance (usually 50 ohms). For example, the height of the flares  410  can be made much shorter by designing the flare impedance transformation to transform from 300 to 200 ohms. The 200 ohms drive points are, in turn, divided down via a parallel plate section to two push-pull resonator sections within the unit cell, each at 100 ohms. The two 100 ohm stripline feeds section are later combined with a reactive power divider to provide the final 50 ohm aperture port. This two-resonator configuration greatly reduces aperture height. In addition, the shorter radiator height also reduces cross-polarization coupling. 
     Referring to  FIG. 4A , a two slot radiator includes a radiating portion  402  and a feed portion  404  separated from the radiating portion  402  by a parallel plate layer  406  and is configured to emit electromagnetic radiation along radiating paths  450 . The radiating portion includes a plurality of flares  410  arranged to define a plurality of notches  480  between the flares, where the radiating paths  450  extend along the notches  480 . The feed portion  404  includes excitations  420  and each of the excitations  420  is coupled to corresponding feeds including a first feed  422  and a second feed  424 . As shown in  FIG. 4A , the feed portion also includes a plurality of slots  430  backed by cavities  440 , each of the slots  430  being located between a notch  480  and a center line (e.g., the dotted line) of a flare  410 . Therefore, the slots  430  are spaced apart from both the center line and the notch  480 . In addition, as shown in  FIG. 4A , each of the unit cells includes two cavity backed slots  430  (e.g., the cavity backed slots  430  to the immediate left and right of the notch  480 ) and both of the slots  430  are driven by the same excitation  420 . The feed portion  404  is coupled to the radiating portion  402  through the parallel plate layer  406  such that signals applied to the microstrip feeds  422  and  424  from a driving circuit are coupled to the radiating portion  402  via the parallel plate section  406  to radiate electromagnetic energy. In addition, electromagnetic waves received by radiating portion  402  are coupled to the microstrip feeds  422  and  424  across the parallel plate layer  406  to be processed by a receiving circuit connected to the excitation  420 . 
     In addition, in this arrangement, a single radiating element or unit cell (e.g., between two adjacent dotted lines as shown in  FIG. 4A ) is coupled to two feeds  422  and  424 , which are combined to become excitation  420 . Assuming each of the feeds  420  has a source impedance of 50Ω, then, the impedance would be 1000 at feeds  422  and  424 . At the lower portion of the flares  410  (e.g., the portion adjacent to the layer  406 ) is 200Ω. As such, the height of the flares  410  may be reduced because the flares are designed to transform the impedance from 200Ω to the free space impedance of 377Ω rather than from 100Ω to 377Ω, or even 50Ω to 377Ω. 
     In another embodiment of the present invention, in a manner similar to that of the embodiment describe with respect to  FIG. 3C  above,  FIG. 4C  illustrates an embodiment in which the cavities  440  of the embodiment of  FIG. 4A  are replaced by a spacer layer  440 ′ backed by a ground plane  470 . 
     In another embodiment of the present invention similar to that shown in  FIG. 3D , as shown in  FIG. 4D , the cavities  440  of the embodiment of  FIG. 4B  are replaced by a spacer layer  440 ′ backed by a ground plane  470  and the microstrip feeds are replaced by stripline feeds between ground plates. 
     The embodiments of  FIGS. 4A, 4B, 4C, and 4D  are suited to lower frequency applications in which space and weight constraints do not allow antennas having high profiles. 
     Similar to the embodiment described above in reference to  FIG. 3A , the antenna  400  includes two separate assemblies: the radiating portion (also commonly referred to as the radiators)  402  and the feed portion or feeds  404 . The radiating portion  304  can be constructed a multiple ways, including: molded or machined 3-D structures that are attached to a planar surface or sheet with similar footprint (facesheet); or an eggcrate structure formed by interlocking radiator printed circuit cards. The feed portion can be manufactured using standard multilayer printed wiring boards (PWB or printed circuit board) processes. The radiating  402  and feed  404  portions can be physically separated by a parallel plate spacer layer which may include low-dielectric foam layers or by using spacers located at various points between the radiating portion  402  and the feed portion  304  (thereby leaving air or vacuum between the radiator and feed assemblies). The physical space between the radiating portion  402  and the feed portion  404  forms the parallel plate layer  406 . 
     In one embodiment, a 0.5-2 GHz design has been modeled with 4″ (about 10 cm) total height, using 2.2″ (about 5.6 cm) lattice spacing. According to another embodiment, a 0.5 to 3.3 GHz design is 5.2″ (about 13 cm) tall, using 1.5″ (about 3.8 cm) lattice spacing. 
       FIGS. 5A, 5B, and 5C  illustrate calculated co-polarization insertion loss from 0.25 GHz to 2.50 GHz for H-Plane, E-Plane, and D-Plane scans, respectively, in the dual-slot embodiments of the present invention as illustrated in  FIGS. 4A, 4B, 4C, and 4D . E (or H)-cut is for the case that the radiation is scanned along the E (or H)—field plane. In other words, for a vertically polarized element, the vertical plane is the E-plane, and horizontal plane would be its H-plane. As shown in  FIGS. 5A, 5B, and 5C , excellent scan performance in provided at up to 45 degrees. 
       FIGS. 6A, 6B, and 6C  illustrate calculated Cx-polarization insertion loss, not including aperture projection loss from 0.25 GHz to 2.50 GHz for H-Plane, E-Plane, and D-Plane scans, respectively, in the dual-slot embodiments of the present invention as illustrated in  FIGS. 4A, 4B, 4C, and 4D . As shown in  FIGS. 6A, 6B, and 6C , Cx-polarization levels are low, even at 60 degrees. 
       FIGS. 7A and 7B  illustrate calculated co-polarization insertion loss (just like  FIGS. 5A, 5B ) for one embodiment of the present invention, in the 0.5-3.3 GHz embodiment described above, which has a different and longer radiating aperture. 
     In one embodiment of the present invention, the flares and radiators are made of a metalized molded (e.g., injection molded) plastic. Flares and radiators according to these embodiments can be made according to a plastic molding process. In such an embodiment, discrete metalized molded flared tops (e.g., corresponding to the flares) are bonded to a facesheet to form the radiating apertures, and the facesheet is then bonded over the separately-formed feed portion. The facesheet would be a thin dielectric layer with the same pattern (the footprint of the radiating elements) on both sides. Multiple plated thru vias would connect the top and bottom metal patterns. These metalized molded flared tops would get bonded conductively over these patterns. 
     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.