Abstract:
A reflectarray is disclosed. The reflectarray includes a first array of conductive patches supported by a substrate, wherein each conductive patch in the first array has a first center line along a Y-direction and a second centerline along an X-direction, a plurality of first variable capacitors, wherein each first variable capacitor is electrically coupled to one of the conductive patches in the first array along the first centerline, and a plurality of second variable capacitors, wherein each second variable capacitor is electrically coupled to one of the conductive patches in the first array along the second centerline.

Description:
FIELD 
     The present invention relates to the field of antennas. More particularly, the present invention relates to a reflectarray. 
     BACKGROUND 
     Referring to  FIG. 1 , a microstrip reflectarray  10  is a low profile reflector, consisting of an array of microstrip patch antenna elements  20  disposed on a surface  15  capable of reflecting energy to or from feed  25 . Reflectarrays are flat, inexpensive, easy to install and easy to manufacture. By loading each microstrip patch antenna element  20  with a single varactor diode  30 , as depicted in  FIG. 2 , a progressive phase distribution can be achieved in the microstrip reflectarray  10 , see the paper by Luigi Boccia, et al., entitled “Experimental Investigation of a Varactor Loaded Reflectarray Antenna,” 2002 IEEE MTT-S Digest, pages 69-71. Although the microstrip reflectarray  10  containing microstrip patch antenna elements  20  with varactor diodes  30  allows beam steering, the microstrip reflectarray  10  operates at a single frequency band and in a single polarization. 
     Unlike prior art, it is possible to operate a reflectarray according to the present disclosure at dual frequencies and it is possible to operate a reflectarray according to the present disclosure at dual frequencies and in dual polarization. 
     SUMMARY 
     According to a first aspect, a reflectarray is disclosed, the reflectarray comprising: a first array of conductive patches supported by a substrate, wherein each conductive patch in the first array has a first center line along a Y-direction and a second centerline along an X-direction; a plurality of first variable capacitors, wherein each first variable capacitor is electrically coupled to one of the conductive patches in the first array along the first centerline; and a plurality of second variable capacitors, wherein each second variable capacitor is electrically coupled to one of the conductive patches in the first array along the second centerline. 
     According to a second aspect, a method for manufacturing a reflectarray is disclosed, the method comprising: forming a first array of conductive patches on a substrate, wherein each conductive patch in the first array has a first center line along a Y-direction and a second centerline along an X-direction; coupling each first variable capacitor of a plurality of first variable capacitors to one of the conductive patches in the first array along the first centerline; and coupling each second variable capacitor of a plurality of second variable capacitors to one of the conductive patches in the first array along the second centerline. 
     According to a third aspect, a reflectarray is disclosed, the reflectarray comprising: an array of conductive patches supported by a substrate, wherein each conductive patch in the first array has a first center line along a Y-direction and a second centerline along an X-direction; a plurality of first variable capacitors, wherein each first variable capacitor is electrically coupled to one of the conductive patches in the array along the first centerline; a plurality of parasitic elements wherein each parasitic element is disposed adjacent to each of the conductive patches in the array of conductive patches; and a plurality of second variable capacitors, wherein each second variable capacitor is electrically coupled to one of the adjacent parasitic elements the second centerline. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts a microstrip reflectarray, associated with PRIOR ART; 
         FIG. 2  depicts a microstrip patch antenna element of  FIG. 1 , associated with PRIOR ART; 
         FIG. 3  depicts a reflectarray according to the present disclosure; 
         FIG. 4  depicts a rectangular patch of  FIG. 3 ; 
         FIG. 5  depicts another reflectarray according to the present disclosure; 
         FIG. 6  depicts a unit cell of  FIG. 5 ; 
         FIG. 7  depicts an exemplary cross section of the unit cell of  FIG. 5 ; 
         FIG. 8  depicts another exemplary cross section of the unit cell of  FIG. 5 ; and 
         FIGS. 9   a - 9   i  depict exemplary top views of the unit cell of  FIG. 6 . 
     
    
    
     In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of every implementation nor relative dimensions of the depicted elements, and are not drawn to scale. 
     DETAILED DESCRIPTION 
     A phase of a reflection from each patch antenna in a reflectarray may be dictated by the frequency of the resonance for the mode excited in the patch antenna structure. The reflected phase may vary with frequency by 360 degrees around the mode&#39;s resonant frequency, and the modes resonance frequency may be varied with a variable capacitor. Thus by using a varactor to vary the resonance frequency of each patch antenna independently, the phase of the energy scattered from each patch antenna may be varied across the surface of the reflectarray. A steerable antenna pattern according to the present disclosure may be used to control the spatial location of the peak in the reflected radiation by controlling the phase of the scattered energy. 
     Referring to  FIG. 3 , a reflectarray  30  operable to reflect energy at two different frequencies according to the present disclosure is shown. The reflectarray  30  contains a substrate  31  supporting rectangular patches  35  having a centerline along a Y-direction and another centerline along an X-direction. The patches  35  may be separated by a distance of about ½λ to about 1λ wavelength of the energy to be reflected. Referring to  FIG. 4 , each rectangular patch  35  has a length L, a width W and contains a varactor diode  45  on the centerline along the Y-direction and a varactor diode  40  on the centerline along the X-direction. In one exemplary embodiment, variable capacitors, Microelectromechanical systems (MEMS) capacitors and/or diodes are used instead of varactor diodes. 
     The length L of the patches  35  can be used to determine a frequency f 1  of the energy polarized along the Y-direction that is going to be reflected off of the patches  35 . Specifically, 
               f   1     =         (     speed   ⁢           ⁢   of   ⁢           ⁢   light     )       2   ⁢   L       .           
Similarly, the width W of the patches  35  can be used to determine a frequency f 2  of the energy polarized along the X-direction that is going to be reflected off the patches  35 . Specifically,
 
     
       
         
           
             
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     By varying the voltage applied to the varactor diode  45 , the phase of the reflected energy polarized along the Y-direction can be varied. Similarly, by varying the voltage applied to the varactor diode  40 , the phase of the reflected energy polarized along the X-direction can also be varied independently of the energy polarized along the Y-direction. 
     Referring to  FIG. 5 , a reflectarray  50  operable to reflect energy at two different frequencies in both polarizations according to the present disclosure is shown. The reflectarray  50  contains a substrate  51  supporting a plurality of unit cells  52  containing two rectangular patches  55   a  and  55   b  each having a centerline along the Y-direction and another centerline along the X-direction. The unit cells  52  may be separated by a distance of about ½λ to about 1λ wavelength of the energy to be reflected. Referring to  FIG. 6 , each rectangular patch  55   a  and  55   b  has a length L, a width W and contains varactor diodes  65   a  and  65   b  on the centerline along the Y-direction and varactor diodes  60   a  and  60   b  on the centerline along the X-direction. In one exemplary embodiment, the length L of the rectangular patch  55   a  is not necessarily equal to the length L of the rectangular patch  55   b . In another exemplary embodiment, the width W of the rectangular patch  55   a  is not necessarily equal to the width W of the rectangular patch  55   b.    
     The length L of the patches  55   a  can be used to determine a frequency f 1  of the energy polarized along the Y-direction that is going to be reflected off the patches  55   a . Specifically, 
               f   1     =         (     speed   ⁢           ⁢   of   ⁢           ⁢   light     )       2   ⁢   L       .           
Similarly, the width W of the patches  55   a  can be used to determine a frequency f 2  of the energy polarized along the X-direction that is going to be reflected off the patches  55   a . Specifically,
 
     
       
         
           
             
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     The length L of the patches  55   b  can be used to determine a frequency f 1  of the energy polarized along the X-direction that is going to be reflected off the patches  55   b , specifically, 
               f   1     =         (     speed   ⁢           ⁢   of   ⁢           ⁢   light     )       2   ⁢   L       .           
Similarly, the width W of the patches  55   b  can be used to determine a frequency f 2  of the energy polarized along the Y-direction that is going to be reflected off the patches  55   b , specifically,
 
     
       
         
           
             
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     By varying the voltages applied to the varactor diodes  60   a ,  60   b ,  65   a  and  65   b , the phase of the reflected energy for f 1  and f 2  polarized along the X-direction and Y-direction can be varied. 
     In one exemplary embodiment, the patches  55   a  and  55   b  may be located on the same dielectric layer  80  as shown in  FIG. 7 . In another exemplary embodiment, the patches  55   a  and  55   b  may be separated by a dielectric layer  85  as shown in  FIG. 8 . 
     Although  FIGS. 3-6  show patches  35 ,  55   a  and  55   b  as being rectangularly shaped, one skilled in the art can appreciate that other shapes can be used without departing from the scope of the present invention. For example, 1) oval shaped patches  90 - 91  with varactors  92 - 95  may be used as shown in  FIG. 9   a ; 2) square patches  96 - 97  with asymmetrically positioned varactors  98 - 101  may be used as shown in  FIG. 9   b , the asymmetric location of the varactors  98 - 101  causing two different orthogonal modes to have different resonant frequencies; 3) square patches  105 - 106  with slots  107 - 114  and varactors  115 - 118  may be used as shown in  FIG. 9   c , the mode with the current flow parallel to the side with one of the slots  107 - 114  will have at a lower resonance frequency than the other perpendicular mode due to the longer effective current path for that mode; 4) square patches  120 - 121  with parasitic elements  122 - 123  and varactors  124 - 127  may be used as shown in  FIGS. 9   d ,  9   e  and  9   f , the parasitic elements  122 - 123  will decrease the frequency of the mode polarized perpendicular to the edges to which the parasitic elements were introduced; 5) square patches  130 - 131  with different sized parasitic elements  132 - 135  with varactors  136 - 139  may be used as shown in  FIG. 9   g ; 6) square patches  140 - 141  with parasitic elements  142 - 145  may be used where varactors  146  and  148  are located on the parasitic elements  142  and  148  and varactors  147  and  149  are located on the square patches  140 - 141  as shown in  FIG. 9   g ; and 7) square patches  150 - 151  with parasitic elements  152 - 155  may be used where varactors  156  and  158  are located between the patch elements  150 - 151  and the parasitic elements  152 ,  158  and where varactors  157 ,  159  are located on the patch elements  150 - 151  as shown in  FIG. 9   i.    
     The foregoing detailed description of exemplary and preferred embodiments is presented for purposes of illustration and disclosure in accordance with the requirements of the law. It is not intended to be exhaustive nor to limit the invention to the precise form(s) described, but only to enable others skilled in the art to understand how the invention may be suited for a particular use or implementation. The possibility of modifications and variations will be apparent to practitioners skilled in the art. No limitation is intended by the description of exemplary embodiments which may have included tolerances, feature dimensions, specific operating conditions, engineering specifications, or the like, and which may vary between implementations or with changes to the state of the art, and no limitation should be implied therefrom. Applicant has made this disclosure with respect to the current state of the art, but also contemplates advancements and that adaptations in the future may take into consideration of those advancements, namely in accordance with the then current state of the art. It is intended that the scope of the invention be defined by the Claims as written and equivalents as applicable. Reference to a claim element in the singular is not intended to mean “one and only one” unless explicitly so stated. Moreover, no element, component, nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element, component, or step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for . . . ” and no method or process step herein is to be construed under those provisions unless the step, or steps, are expressly recited using the phrase “step(s) for . . . .”