Reflectarray

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. 9a-9i 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'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 f₁ 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 f₂ of the energy polarized along the X-direction that is going to be reflected off the patches 35. Specifically,

f 2 = ( speed ⁢ ⁢ of ⁢ ⁢ light ) 2 ⁢ W .

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 55a and 55b 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 55a and 55b has a length L, a width W and contains varactor diodes 65a and 65b on the centerline along the Y-direction and varactor diodes 60a and 60b on the centerline along the X-direction. In one exemplary embodiment, the length L of the rectangular patch 55a is not necessarily equal to the length L of the rectangular patch 55b. In another exemplary embodiment, the width W of the rectangular patch 55a is not necessarily equal to the width W of the rectangular patch 55b.

The length L of the patches 55a can be used to determine a frequency f₁ of the energy polarized along the Y-direction that is going to be reflected off the patches 55a. Specifically,

f 1 = ( speed ⁢ ⁢ of ⁢ ⁢ light ) 2 ⁢ L .
Similarly, the width W of the patches 55a can be used to determine a frequency f₂ of the energy polarized along the X-direction that is going to be reflected off the patches 55a. Specifically,

f 2 = ( speed ⁢ ⁢ of ⁢ ⁢ light ) 2 ⁢ W .

The length L of the patches 55b can be used to determine a frequency f₁ of the energy polarized along the X-direction that is going to be reflected off the patches 55b, specifically,

f 1 = ( speed ⁢ ⁢ of ⁢ ⁢ light ) 2 ⁢ L .
Similarly, the width W of the patches 55b can be used to determine a frequency f₂ of the energy polarized along the Y-direction that is going to be reflected off the patches 55b, specifically,

f 2 = ( speed ⁢ ⁢ of ⁢ ⁢ light ) 2 ⁢ W .

By varying the voltages applied to the varactor diodes 60a, 60b, 65a and 65b, the phase of the reflected energy for f₁ and f₂ polarized along the X-direction and Y-direction can be varied.

In one exemplary embodiment, the patches 55a and 55b may be located on the same dielectric layer 80 as shown in FIG. 7. In another exemplary embodiment, the patches 55a and 55b may be separated by a dielectric layer 85 as shown in FIG. 8.

Although FIGS. 3-6 show patches 35, 55a and 55b 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. 9a; 2) square patches 96-97 with asymmetrically positioned varactors 98-101 may be used as shown in FIG. 9b, 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. 9c, 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. 9d, 9e and 9f, 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. 9g; 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. 9g; 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. 9i.

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 . . . .”