Abstract:
Disclosed is a wideband antenna comprising a dielectric-loaded cavity-backed patch antenna driven with a stripline. The antenna includes a dielectric resonator. The stripline feeds a probe disposed within the dielectric resonator. The probe emits EM radiation, which is coupled to the patch antenna for transmission.

Description:
BACKGROUND 
       [0001]    Unless otherwise indicated, the foregoing is not admitted to be prior art to the claims recited herein and should not be construed as such. 
         [0002]    Conventionally, millimeter wave applications use a wide-band patch antenna configured with a stripline. Wide-band patch antennas are typically made from a low dielectric (∈ r =2.2) material and provided over a relatively thick substrate. This thickness tends to set up surface waves at mm frequencies, resulting in poor radiating performance. Also, when the patch antenna and stripline are made separately and then combined together, the overall substrate is too thick to include any other types of antennas, for example dipoles, in the same stack-up. Alternate antenna structures can be integrated with a stripline, but do not perform well due to non-ideal parallel plate modes. 
       SUMMARY 
       [0003]    An antenna in accordance with embodiments of the present disclosure include a stripline that feeds a patch antenna. The stripline may include a ceramic substrate that defines a dielectric resonator cavity within it. A perimeter of the dielectric resonator cavity may be defined by a substrate integrated waveguide (SIW) and an electromagnetic (EM) probe disposed within the SIW. First and second ground planes disposed above and below the SIW further define the perimeter of the dielectric resonator. A signal line feeds the EM probe, which emits EM radiation (radio waves) that are coupled to the patch antenna for transmission by the patch antenna. 
         [0004]    In embodiments, the antenna further includes a patch substrate spaced apart from the ceramic substrate of the stripline by the first ground plane. The patch substrate may support the patch antenna. 
         [0005]    In embodiments, the first ground plane may include a cut-out portion to provide a radio transparent path between the EM probe and the patch antenna. 
         [0006]    In some embodiments, the patch antenna comprises several conductive strips. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    With respect to the discussion to follow and in particular to the drawings, it is stressed that the particulars shown represent examples for purposes of illustrative discussion, and are presented in the cause of providing a description of principles and conceptual aspects of the present disclosure. In this regard, no attempt is made to show implementation details beyond what is needed for a fundamental understanding of the present disclosure. The discussion to follow, in conjunction with the drawings, make apparent to those of skill in the art how embodiments in accordance with the present disclosure may be practiced. In the accompanying drawings: 
           [0008]      FIG. 1  shows a top view of an illustrative antenna in accordance with the present disclosure. 
           [0009]      FIGS. 1A ,  1 A- 1 ,  1 B and  1 C illustrate side views of the antenna shown in  FIG. 1 . 
           [0010]      FIGS. 2A-2D  illustrate various dimensions in accordance with a particular embodiment of an antenna in accordance with the present disclosure. 
           [0011]      FIG. 3  shows a perspective view of an antenna of the present disclosure. 
           [0012]      FIG. 4  illustrates an antenna array. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    In the following description, for purposes of explanation, numerous examples and specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be evident, however, to one skilled in the art that the present disclosure as expressed in the claims may include some or all of the features in these examples, alone or in combination with other features described below, and may further include modifications and equivalents of the features and concepts described herein. 
         [0014]      FIG. 1  shows a top view of an antenna  100  in accordance with embodiments of the present disclosure. A coordinate system illustrates the X, Y, and Z directions for discussion purposes. The Z-axis is the axis perpendicular to the drawing sheet. 
         [0015]    The antenna  100  may include a suitable connection interface  102  for connecting to a feedline  14  to receive an externally generated signal  12 . The signal  12 , which may be generated by electronics  10 , can be provided to the feedline  14  for transmission by the antenna  100 . Merely as an example, the electronics  10  may be the transmitting electronics in a cellular telephone, a laptop computer, etc. 
         [0016]    The antenna  100  may be a multilayered structure. Various structures may be formed or otherwise embedded in the several layers of the multilayered structure of antenna  100 . A substrate integrated waveguide (SIW) cavity  104  may be defined within one of the layers of the antenna. In some embodiments, for example, the SIW cavity  104  may be defined by an array of vias  104   a  formed in the layer. 
         [0017]    The antenna  100  may include a signal line  106  that is connected to the connection interface  102 . An electromagnetic (EM) probe  108  may be connected to the other end of signal line  106 . The EM probe  108  may be exposed through an open region (cut out)  142  in one of the layers of the antenna  100 . 
         [0018]    In accordance with the present disclosure, the antenna  100  may include a patch antenna  110  disposed atop the multilayered structure of the antenna. In some embodiments, the patch antenna  110  may comprise several conductive strips, such as illustrated in the figure. The conductive strips may be separate, or they may be connected. In other embodiments, the patch antenna  110  may comprise a single piece of conductive material. 
         [0019]      FIG. 1  shows some view lines  2 - 2  and  3 - 3 . The view line  2 - 2  is used to show a cutaway view of antenna  100 , looking in the Y direction. Likewise, the view line  3 - 3  is used to show a cutaway view of antenna  100  looking in the X direction. The cutaway views show additional details of the structure of the antenna  100 , which will now be described. 
         [0020]      FIG. 1A  illustrates a cutaway view of antenna  100  along view line  2 - 2 , showing additional details of the antenna&#39;s multilayered structure and the various structures disposed on the several layers. In some embodiments, the multilayered structure may comprise a first substrate  122  and a second substrate  124 . A first ground plane (metal layer, conductive layer)  126  may be disposed between the first and second substrates  122 ,  124 . A second ground plane  128  may be disposed on the first substrate  122  opposite the first ground plane  126 . 
         [0021]    The first ground plane  126  may include an opening or cut-out  142  where portions of the first and second substrates  122 ,  124  contact each other. In some embodiments, the first and second substrates  122 ,  124  may both include recessed portions to accommodate the first ground plane  126 , such as illustrated in  FIG. 1A . In some embodiments, the first ground plane  126  may be received in a recessed portion of the first substrate  122 , such as illustrated in  FIG. 1A-1  for example. In other embodiments, the first ground plane  126  may be received in a recessed portion of the second substrate  124  (not shown). 
         [0022]    The first substrate  122  may have embedded within it the signal line  16 , the SIW cavity  104 , the EM probe  108 . The vias  140   a  comprising the SIW cavity  104  may be formed through the first substrate  122 . In some embodiments, the vias  104   a  may extend from the first ground plane  126  to the second ground plane  128 . 
         [0023]    The EM probe  108  may comprise a pad  132  and a via  134 . The pad  132  may be disposed on or near a major surface of the first substrate  122 .  FIG. 1A , for example, shows the pad  132  extends slightly beyond a major surface of the first substrate  122 . In another embodiment, the pad  132  may be disposed substantially flush with a major surface of the first substrate  122 , such a illustrated in  FIG. 1A-1  for example. 
         [0024]    The via  134  may be formed in the first substrate  122 , extending from the pad  132  to the signal line  16 . The via  134  may contain a conductive material to provide an electrical connection between the pad  132  and the signal line  16 . In some embodiments, the structures encompassed by the boxed region shown in dashed lines in  FIG. 1A  may be referred to as a “stripline.” 
         [0025]    The second substrate  124  may support or otherwise carry the patch antenna  110  on a major surface of the second substrate, and thus may be referred to as the “patch substrate.” In accordance with the present disclosure, the patch antenna  110  may be spaced apart from the EM probe  108  by the patch substrate  124 . Accordingly, the patch antenna  110  is not electrically connected to the signal line  16  or to the pad  132  of EM probe  108 . 
         [0026]      FIG. 1B  illustrates a cutaway view of antenna  100  showing additional details of the antenna&#39;s multilayered structure and the various structures along view line  3 - 3 . As shown in  FIG. 1B , in some embodiments, the connection interface  102  may be located on a side of the antenna  100 . In other embodiments, the connection interface  102  may be located elsewhere.  FIG. 1C , for example, shows a connection interface  102   a  disposed on a bottom of the antenna. The second ground plane  128 ′ may include an opening to accommodate the connection interface  102   a . An insulative layer  114  may electrically insulate the connection interface  102   a  from the second ground plane  128 ′. A via  112  may provide an electrical connection from the connection interface  102   a  to signal line  16   a.    
         [0027]      FIGS. 2A and 2B  show a typical illustrative embodiment of the antenna  100  of the present disclosure, viewed along view line  2 - 2  ( FIG. 2A ) and along view line  3 - 3  ( FIG. 2B ). The relative dimensions between the structures have been exaggerated to facilitate the illustration. The specific dimensions may depend on factors such as intended environment that the antenna  100  may be exposed to, operating frequency range, materials used, specific designs (e.g., the patch antenna  110 , EM probe  108 , etc.). 
         [0028]    In a particular embodiment, for example, the first substrate  122  may be a ceramic material having a thickness of about 0.33 mm as illustrated in  FIG. 2A . The second substrate  124  may be ceramic having a thickness of about 0.1 mm. The ceramic material may have a dielectric constant ∈ r =6.7 and a dielectric loss tangent of 0.005. It will be appreciated of course that these parameters may vary depending on design, choice of material, and so on. 
         [0029]    In some embodiments, the first substrate  122  and the second substrate  124  may be the same ceramic. In other embodiments, the first and second substrates  122 ,  124 , may be of different ceramic materials. In still other embodiments, materials other than ceramics may be used. In a particular embodiment, however, it may be desirable to use ceramic. The use of ceramics allows for a well known process called low temperature co-fired ceramics (LTCC), which allows for the structures of the antenna  100  to formed in the same process. 
         [0030]    The SIW cavity  104  may be measured according to its inside cavity measurements as illustrated in  FIG. 2A . In a particular embodiment, for example, the SIW cavity  104  may have inside measurements of 1.3 mm×1.6 mm. Alternatively, the SIW cavity  104  may be measured according to its outside cavity measurements, also illustrated in  FIG. 2A . In a particular embodiment, for example, the outside measurement may be 1.65 mm×1.95 mm. It will be appreciated of course that in other embodiments, the SIW cavity  104  can be any suitable size to accommodate other designs. In some embodiments, the vias  104   a  that define the SIW cavity  104  may be arranged to form other shapes such a square, circle, etc. 
         [0031]    In some embodiments, the SIW cavity  104  may be centered within the bulk of the first substrate  124 . Referring to  FIGS. 2A and 2B , the bulk separation between the outer periphery of the SIW cavity  104  and the outer periphery of the first substrate  122  can be on the order of many millimeters. 
         [0032]    In some embodiments, the signal line  16  may be disposed within the first substrate  122  substantially equidistant from the first ground plane  126  and the second ground plane  128 .  FIG. 2A , for example, shows separation distances d 1  and d 2 , where d 1  is substantially equal to d 2 . In addition, the signal line  16 , as well as the EM probe  108 , may be positioned along the X-axis substantially in the middle of the SIW cavity  104 ; e.g., distance d 3  is substantially equal to d 4 . 
         [0033]    Referring to  FIGS. 2A and 2B , the pad  132  may be substantially as wide (width, W) as the signal line  16 , and may have a length dimension L. In a particular implementation, for example, the pad  132  was designed with 0.1 mm (W)×0.45 mm (L). It will be appreciated that, in general, the dimensions for pad  132  are a design factor; for example, to optimize performance. 
         [0034]    In various embodiments, the EM probe  108  may be positioned along the Y-axis as shown in  FIG. 2B . However, for practical design purposes, the EM probe  108  may be offset in the X-axis direction; for example, to accommodate for an asymmetrical feed. Similarly, in various embodiments, the position of pad  132  may likewise be along the Y-axis, and may include an X-axis offset. 
         [0035]    Referring to  FIGS. 2C and 2D , in some embodiments, the dimensions of the patch antenna  110  and the dimensions of the cut-out  142  may be determined by the desired operating frequency of the antenna  100 . The operating frequency defines the working wavelength. This, in turn, controls the dimensions of the patch antenna  110  (W P ×L P ) and the dimensions of the cut-out  142  (W C ×L C ). 
         [0036]      FIG. 3  shows a perspective view of an embodiment of antenna  100  in accordance with the present disclosure. The figure illustrates relative positions of the various structures described above. 
         [0037]    In operation, the SIW cavity  104  embedded within the ceramic material of the first substrate  122  and bounded by the first and second ground planes  126 ,  128  define a dielectric resonator cavity ( FIG. 2C ). The symmetrical arrangement of the signal line  16  and the EM probe  108  described above can facilitate resonance of radio waves within the dielectric resonator cavity. 
         [0038]    Radio waves may be introduced into the cavity from the EM probe  108 . When the dimensions of the SIW cavity  104  are designed to the frequency range of the radio waves, the radio waves will bounce back and forth (resonate) between the walls of the resonator cavity, namely the vias  104   a  of the SIW cavity  104  and the first and second ground planes  126 ,  128 , to form standing waves. The opening  142  in the first ground plane  126  is transparent to the radio waves (radio transparent), allowing radio power to radiate from the resonator cavity and couple to the patch antenna  110 . 
         [0039]    An advantageous aspect of the antenna  100  is that the dielectric loaded SIW cavity  104  formed beneath the patch antenna  110  supports wide-band and unidirectional radiation, while at the same time suppressing surface wave modes that would degrade overall performance. By incorporating the SIW cavity  104  within the structure of the antenna  100 , an antenna array can be configured with low mutual coupling between antennas. Antennas according to the present disclosure are therefore very suitable for wide-angle scanning array applications. 
         [0040]      FIG. 4 , for example, shows an antenna array  400  comprising an array of antennas  100 ′ ( FIG. 1C ). The antenna array  400  may use the antenna embodiment of  FIG. 1C , where the connection interface  102 ′ is provided on the bottom surface of each antenna  100 ′ to facilitate connecting feedlines to the antennas. As can be seen in  FIG. 4 , dimensions of the first and second substrates  122 ,  124  of the antennas  100 ′ can be selected to ensure that the dielectric resonator cavities (represented by the cut-out regions  142 ) of the antennas  100 ′ are sufficiently spaced apart (d S1 , d S2 ) from each other so as to reduce mutual coupling between the dielectric resonator cavities. In some embodiments, the dimensions of each antenna  100 ′ may be designed so that d S1  is substantially equal to d S2 . In other embodiments, d S1  may be different from d S2 . In still other embodiments, the separations d S1 , d S2  between dielectric resonator cavities may vary across the array  400 . 
         [0041]    In a particular implementation of the antenna  100 , using ceramic material having a dielectric constant of ∈ r =6.7, the following observations were noted:
       wide impedance bandwidth: 15% fractional bandwidth (FBW) for S 11 &lt;10 dB   flat gain bandwidth: &lt;2 dB variation within 57-66 GHz   substantially constant radiation patterns       
 
         [0045]    Antennas in accordance with the present disclosure are compact and have a planar geometry that is suitable for conventional printed circuit board (PCB) and LTCC processes. Antennas in accordance with the present disclosure can be designed for mm wave applications (e.g., 60 GHz), but can be easily scaled for other frequencies. 
         [0046]    The above description illustrates various embodiments of the present disclosure along with examples of how aspects of the particular embodiments may be implemented. The above examples should not be deemed to be the only embodiments, and are presented to illustrate the flexibility and advantages of the particular embodiments as defined by the following claims. Based on the above disclosure and the following claims, other arrangements, embodiments, implementations and equivalents may be employed without departing from the scope of the present disclosure as defined by the claims.