Patent Publication Number: US-9899725-B2

Title: Circuitry-isolated MEMS antennas: devices and enabling technology

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase application under 35 U.S.C. § 371 of International Application No. PCT/IB2010/003487 filed 18 Dec. 2010, which claims priority to U.S. Provisional Application No. 61/287,876 filed 18 Dec. 2009. The entire contents of each of the above-referenced disclosures is specifically incorporated herein by reference without disclaimer. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to Mircroelectromecanical systems (MEMS) antennas and more particularly relates to an apparatus system and method for circuitry-isolated MEMS antennas. 
     Description of the Related Art 
     The frequency scaling law states that as frequency increases the size of the antenna and distributed microwave circuit decreases. Due to the recent advances in technology that allows for fabricating small devices, the realization of miniaturized wireless equipment operating at high frequencies becomes feasible. This explains the recent interests in the millimeter-wave (mm-wave) range that starts from 30 GHz up to 300 GHz. Several frequencies within this band are already allocated for a number of applications, as listed in Table I. 
     
       
         
           
               
             
               
                 TABLE I 
               
             
            
               
                   
               
               
                 Assigned Wireless Applications in the mm-Wave Range 
               
            
           
           
               
               
            
               
                 Frequency 
                 Assigned Applications 
               
               
                   
               
               
                 35 GHz 
                 Pavement and bridge assessment. 
               
               
                   
                 Liquid level measurement. 
               
               
                   
                 Detection and location of buried mines and unexploded  
               
               
                   
                 ordnance (UXO). 
               
               
                   
                 Detection of intrusion to structures including important  
               
               
                   
                 civil facilities. 
               
               
                   
                 Detection of slow moving objects. 
               
               
                   
                 Surveillance and monitoring of hidden activities and  
               
               
                   
                 objects. 
               
               
                   
                 Detection of intruders and moving vehicles, security,  
               
               
                   
                 obstacle detection for robotic equipment, traffic monitoring  
               
               
                   
                 and control. 
               
               
                   
                 Military seeker and sensor applications for munitions and  
               
               
                   
                 missiles. 
               
               
                 60 GHz 
                 Wireless personal area network (WPAN) applications and  
               
               
                   
                 video streaming applications. 
               
               
                   
                 Indoor ultra-high speed short-range wireless communi- 
               
               
                   
                 cation. 
               
               
                   
                 Multimedia applications. 
               
               
                   
                 Inter-satellite links. 
               
               
                   
                 Distance estimation. 
               
               
                 77 GHz 
                 Automotive Radars (car radars). 
               
               
                 71-76 GHz  
                 Outdoor 10 Gbps networks. 
               
               
                 and 
                   
               
               
                 81-86 GHz 
                   
               
               
                 94 GHz 
                 Medical and security imaging applications. 
               
               
                   
                 Cloud Radar systems. 
               
               
                   
                 Cloud profiling radar antenna system. 
               
               
                   
                 Missile guidance and collision avoidance. 
               
               
                   
                 Research radar for study of severe weather and clouds. 
               
               
                   
                 Development and instrumentation radar. 
               
               
                   
                 Military applications. 
               
               
                 140-220  
                 High-data rate wireless indoor communication systems. 
               
               
                 GHz 
                 Direct detection radiometers for remote atmospheric sensing. 
               
               
                   
                 High-resolution passive and active mm-wave imaging  
               
               
                   
                 applications. 
               
               
                   
                 Systems for detection of concealed weapons, and aircraft  
               
               
                   
                 navigation in zero visibility conditions. 
               
               
                   
                 Plasma Imaging Camera. 
               
               
                 278 GHz 
                 Radiometer systems for long-term ground-based monitoring  
               
               
                   
                 of the vertical profiles of chlorine monoxide and ozone in  
               
               
                   
                 the stratosphere over the arctic area. 
               
               
                   
               
            
           
         
       
     
     As frequency of operation increases, the antenna&#39;s dielectric losses increase significantly due to the excitation of surface waves inside the substrate carrying the antenna. This serious drawback deteriorates the performance of the conventional planar antennas, such as patches, in the mm-wave range of frequencies. An attractive solution to this problem is the use of the micromachining technology. Typically, the main idea behind the use of this technology for antennas is to etch away as much as possible dielectric volume around the radiating elements. This reduces surface wave losses significantly and allows for high radiation efficiency and gain even at high resonance frequencies. The reduction of substrate losses leads to enhancing battery life time of mobile and hand-held equipment. Moreover, MEMS antennas are still compatible with the driving circuit technology and can be monolithically integrated with the entire millimeter-wave system. Such compatibility leads to miniaturized wireless systems which obey the evolution towards compactness. 
     MEMS antennas can be classified into two main categories. The first category features one silicon wafer  102  machined such that to create a cavity  104  underneath the antenna  106 , as shown in  FIG. 1( a ) . This cavity  104  reduces the effective dielectric constant around the antenna  106  and consequently decreases substrate losses and increases radiation efficiency. Although this category enjoys low fabrication cost, it suffers from significant interference between the antenna  106  and the feeding circuit  108 . This is because of the fact that both antenna and circuit are located at one side of the ground plane  110 . The second category of MEMS antennas features two silicon wafers  102  bonded to each other with a slotted ground plane  110  in between them, as shown in  FIG. 1( b ) . One wafer  102  is micromachined and carrying the antenna  106 , while the other one is carrying the driving circuit  108 . Due to the presence of a ground plane  110  between the antenna  106  and circuit  108 , the interference between them is minimal. This comes on the expenses of increasing the fabrication cost owing to the required wafer bonding process. 
     SUMMARY OF THE INVENTION 
     Embodiments of MEMS antennas are presented. In one embodiment, only one silicon wafer is required while ground plane isolation between the MEMS antenna and circuit exists. Additional embodiments of the MEMS antenna may have diversity in polarization and radiation characteristics. In one embodiment, the frequency of operation of the MEMS antennas is 60 GHz. One of ordinary skill in the art will recognize, however, that these antennas may be tuned for operation at any other frequency within the mm-wave range. While maintaining the same geometry, increasing antenna dimensions results in reducing the frequency of operation, and vice verse. Methods of manufacturing the MEMS antenna may remain substantially the same for the entire range of dimensions along the mm-wave range. In further embodiments, the MEMS antenna may be manufactured on either high-resistivity (2,000 Ω·cm) or low-resistivity (45 Ω·cm) silicon wafers. In a particular embodiment, the wafers may have a thickness of 675 μm and dielectric constant of 11.9. 
     In one embodiment, the MEMS antenna includes a substrate, a metallic layer disposed over the substrate, the metallic layer forming a ground plane, the ground plane having a region defining a gap disposed therein, a protrusion disposed over the substrate within the region defining the gap, the protrusion extending outwardly from the ground plane, the protrusion having a length and a width, the length being greater than the width, and a first electromagnetic radiator element disposed over the protrusion, the first electromagnetic element having a length and a width, the length being greater than the width. 
     The MEMS antenna may also include a Through-Silicon Via (TSV) extending through the substrate from a first surface of the substrate to a second surface of the substrate. The TSV may have a length which extends perpendicularly to the length of the first electromagnetic radiator element. In a further embodiment, the TSV has a first end and a second end. Additionally, the first electromagnetic radiator element may include a first end and a second end, In such an embodiment, the first end of the TSV may be disposed adjacent to the first end of the first electromagnetic radiator element. In one embodiment, the first end of the TSV may be separated from the first end of the first electromagnetic radiator element by a gap. 
     In one embodiment, the length of the first electromagnetic radiator element is equal to one-half a wavelength of a standing electromagnetic wave to be radiated by the first electromagnetic radiator element. 
     In a further embodiment, the MEMS antenna may include a second protrusion disposed over the substrate within the region defining the gap, the second protrusion extending outwardly from the ground plane, the second protrusion having a length and a width, the length being greater than the width, and a second electromagnetic radiator element disposed over the second protrusion, the second electromagnetic element having a length and a width, the length being greater than the width. 
     In one embodiment, the length of the second electromagnetic radiator element may also be equal to one-half a wavelength of a standing electromagnetic wave to be radiated by the second electromagnetic radiator element. In an additional embodiment, the first electromagnetic radiator element and the second electromagnetic radiator element are arranged in a linearly polarized configuration. In certain embodiments, the first electromagnetic radiator element and the second electromagnetic radiator element each comprise a half-wavelength dipole. In one embodiment, the length of the first electromagnetic radiator element and the length of the second electromagnetic radiator element are disposed within a common plane. 
     In an embodiment, the MEMS antenna may include a second TSV extending through the substrate from a first surface of the substrate to a second surface of the substrate, wherein the second TSV comprises a first end and a second end, and the second electromagnetic radiator element comprises a first end and a second end, and wherein the first end of the second TSV is disposed adjacent to the first end of the second electromagnetic radiator element. 
     In one embodiment, the wherein the length of the first electromagnetic radiator element and the length of the second electromagnetic radiator element are disposed within separate parallel planes. In such an embodiment, the second electromagnetic radiator element may be a parasitic half-wavelength dipole. 
     In one embodiment, the MEMS antenna also includes a third protrusion disposed over the substrate within the region defining the gap, the third protrusion extending outwardly from the ground plane, the third protrusion having a length and a width, the length being greater than the width, a third electromagnetic radiator element disposed over the third protrusion, the third electromagnetic element having a length and a width, the length being greater than the width, a fourth protrusion disposed over the substrate within the region defining the gap, the fourth protrusion extending outwardly from the ground plane, the fourth protrusion having a length and a width, the length being greater than the width, and a fourth electromagnetic radiator element disposed over the fourth protrusion, the fourth electromagnetic element having a length and a width, the length being greater than the width. 
     In an embodiment, the first and second electromagnetic radiator elements are active half-wavelength dipoles, and the third and fourth electromagnetic radiator elements are parasitic halve-wavelength dipoles. The first electromagnetic radiator element may be disposed at an angle that is perpendicular to an angle of the second electromagnetic radiator element, and the third electromagnetic radiator element may be disposed at an angle that is perpendicular to an angle of the fourth electromagnetic radiator element. In a further embodiment, the first electromagnetic radiator element is disposed within a first plane, and the third electromagnetic radiator element is disposed within a second plane, and the first plane is parallel to the second plane. In particular, the first electromagnetic radiator element, the second electromagnetic radiator element, the third electromagnetic radiator element, and the fourth electromagnetic radiator element may be arranged in a circularly polarized configuration. 
     In one embodiment, the first electromagnetic radiator element and the second electromagnetic radiator element are coupled together by a ring coupler. The ring coupler may include a microstrip line disposed on a surface of the substrate that is opposite a surface of the substrate over which the first electromagnetic radiator element and the second electromagnetic radiator element are disposed. In a further embodiment, the ring coupler has a first port and a second port. In such an embodiment, power delivered through the first port is delivered equally to the first electromagnetic radiator element and the second electromagnetic radiator element, but with a one hundred and eighty degree phase shift. Power delivered through the second port may be delivered equally to the first electromagnetic radiator element and the second electromagnetic radiator element with a zero degree phase shift. In such an embodiment, the first electromagnetic radiator element and the second electromagnetic radiator element may be configured to operate as a dipole antenna when power is applied to the first port and configured to operate as a monopole antenna when power is applied to the second port. 
     In a further embodiment, the MEMS antenna may include a plurality of additional protrusions disposed over the substrate within the region defining the gap, the plurality of additional protrusions extending outwardly from the ground plane, the plurality of additional protrusions each having a length and a width, the length being greater than the width. The MEMS antenna may also include a plurality of additional electromagnetic radiator elements, each disposed over one of the plurality of additional protrusions, the plurality additional electromagnetic elements each having a length and a width, the length being greater than the width. In such an embodiment, the first electromagnetic radiator element and the plurality of additional electromagnetic radiator elements are arranged in a wire-grid array configuration. 
     A system is also presented. In one embodiment, the system includes a substrate having a first surface and a second surface, the first surface being disposed opposite the second surface. The system may also include a MEMS antenna disposed over the first surface, the MEMS antenna. The MEMS antenna may include a metallic layer disposed over the first surface of the substrate, the metallic layer forming a ground plane, the ground plane having a region defining a gap disposed therein, a protrusion disposed over the substrate within the region defining the gap, the protrusion extending outwardly from the ground plane, the protrusion having a length and a width, the length being greater than the width, and a first electromagnetic radiator element disposed over the protrusion, the first electromagnetic element having a length and a width, the length being greater than the width. Additionally, the system may include an antenna driver circuit coupled to the second surface, the antenna driver circuit being coupled to the MEMS antenna by one or more vias extending from the first surface through the substrate to the second surface. 
     The system may additionally include the various other embodiments of the MEMS antenna described above. 
     A method for manufacturing a MEMS antenna is also presented. In one embodiment, the method includes providing a substrate having a first surface and a second surface, the first surface being disposed opposite the second surface. The method may also include forming an oxide layer on at least one of the first surface and the second surface. Additionally, the method may include patterning the oxide layer in regions sufficient to form a protrusion disposed over the first surface of the substrate. An embodiment of the method may also include etching away at least a portion of the first surface of the substrate to form the protrusion disposed over the first surface of the substrate. Further, the method may include depositing a metal layer over a portion of the first surface of the substrate to form a ground plane, the ground plane having a region defining a gap disposed therein, the protrusion being disposed within the region defining a gap. Additionally, the method may include depositing a metal layer over the protrusion to form an electromagnetic radiator element. 
     A further embodiment of the method may include etching a hole through the substrate from the first surface to the second surface, and depositing a metal layer in the hole to form a via electrically coupling at least a portion of the first surface to at least a portion of the second surface. 
     The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically. 
     The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. 
     The term “substantially” and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting embodiment “substantially” refers to ranges within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5% of what is specified. 
     The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
     Other features and associated advantages will become apparent with reference to the following detailed description of specific embodiments in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. 
         FIG. 1  is a schematic block diagram illustrating one embodiment of a system for two conventional categories of MEMS antennas: (a) using single wafer, and (b) using two bonded wafers; 
         FIG. 2  is a schematic block diagram illustrating one embodiment of a system that includes MEMS antennas; 
         FIG. 3( a )-( d )  is a schematic block diagram illustrating one embodiment of a method for the process flow of the proposed MEMS antennas: (a) start-up wafer, (b) patterning of oxide on both sides, (c) deep etching of silicon from both sides, and (d) platting copper on both side; 
         FIG. 4( a )-( c )  shows a geometry of an embodiment of a linearly polarized MEMS antenna: (a) 3D zoom-out view, (b) 3D zoom-in view, and (c) top-view; 
         FIG. 5  shows the current distribution on the radiating arms of an embodiment of a linearly polarized MEMS antenna at 60 GHz; 
         FIG. 6  shows a return loss versus frequency of an embodiment of a linearly polarized MEMS antenna; 
         FIG. 7( a )-( b )  show 3D radiation patterns of an embodiment of a linearly polarized MEMS antenna at 60 GHz: (a) on high-resistivity silicon, and (b) on low-resistivity silicon; 
         FIG. 8  shows radiation patterns in two orthogonal planes of an embodiment of a linearly polarized MEMS antenna at 60 GHz; 
         FIG. 9( a )-( c )  show the geometry of an embodiment of a linearly polarized MEMS antenna with parasitic elements: (a) 3D zoom-out view, (b) 3D zoom-in view, and (c) top-view; 
         FIG. 10  shows a current distribution on an embodiment of a linearly polarized MEMS antenna with parasitic elements at 60 GHz; 
         FIG. 11  shows a return loss versus frequency of an embodiment of a linearly polarized MEMS antenna with parasitic elements; 
         FIG. 12( a )-( b )  show 3D radiation patterns of an embodiment of a linearly polarized MEMS antenna with parasitic elements at 60 GHz: (a) on high-resistivity silicon, and (b) on low-resistivity silicon; 
         FIG. 13  shows radiation patterns in two orthogonal planes of an embodiment of a linearly polarized MEMS antenna with parasitic elements at 60 GHz; 
         FIG. 14( a )-( c )  show geometry of an embodiment of a circularly polarized MEMS antenn: (a) 3D zoom-out view, (b) 3D zoom-in view, and (c) top-view; 
         FIG. 15( a )-( b )  show current distribution on the radiating arms of an embodiment of a circularly polarized MEMS antenna at 60 GHz: (a) t=0, and (b) t=T/4; 
         FIG. 16( a )-( b )  show a return loss and axial ratio versus frequency of an embodiment of a circularly polarized MEMS antenna: (a) on high-resistivity silicon, and (b) on low-resistivity silicon; 
         FIG. 17( a )-( b )  show 3D radiation patterns of an embodiment of a circularly polarized MEMS antenna at 60 GHz: (a) on high-resistivity silicon, and (b) on low-resistivity silicon; 
         FIG. 18  shows radiation patterns in two orthogonal planes of an embodiment of a circularly polarized MEMS antenna at 60 GHz; 
         FIG. 19( a )-( c )  show geometry of an embodiment of a reconfigurable MEMS dipole/monopole antenna: (a) 3D zoom-out view, (b) 3D zoom-in view, and (c) top-view; 
         FIG. 20( a )-( b )  shows photographs of a fabricated embodiment of a reconfigurable MEMS dipole/Monopole antenna: (a) top view, and (b) bottom view; 
         FIG. 21  shows a current distribution on arms of an embodiment of a reconfigurable MEMS dipole/Monopole antenna in the dipole mode at 60 GHz; 
         FIG. 22  shows S-parameters versus frequency of an embodiment of a reconfigurable MEMS dipole/Monopole antenna in the dipole mode of operation; 
         FIG. 23( a )-( b )  show 3D radiation patterns of an embodiment of a reconfigurable MEMS dipole/Monopole antenna in the dipole mode at 60 GHz: (a) on high-resistivity silicon, and (b) on low-resistivity silicon; 
         FIG. 24  shows radiation patterns in two orthogonal planes of an embodiment of a reconfigurable MEMS dipole/monopole antenna in the dipole mode at 60 GHz; 
         FIG. 25  shows a current distribution on the arms of an embodiment of a reconfigurable MEMS dipole/Monopole antenna in the monopole mode at 60 GHz; 
         FIG. 26  shows S-parameters versus frequency of an embodiment of a reconfigurable MEMS dipole/Monopole antenna in the monopole mode; 
         FIG. 27( a )-( b )  show 3D radiation patterns of an embodiment of a reconfigurable MEMS dipole/Monopole antenna in the monopole mode at 60 GHz: (a) on high-resistivity silicon, and (b) on low-resistivity silicon; 
         FIG. 28  shows radiation patterns in two orthogonal planes of an embodiment of a reconfigurable MEMS dipole/monopole antenna in the monopole mode at 60 GHz; 
         FIG. 29( a )-( b )  show geometry of an embodiment of a wire-grid MEMS antenna array: (a) 3D view, and (b) top-view; 
         FIG. 30  shows current distribution on the radiators  204  and connectors of an embodiment of a wire-grid MEMS antenna array at 60 GHz′ 
         FIG. 31  shows return loss versus frequency of an embodiment of a wire-grid MEMS antenna array; 
         FIG. 32( a )-( b )  show 3D radiation patterns of an embodiment of a wire-grid MEMS antenna array at 60 GHz: (a) on high-resistivity silicon, and (b) on low-resistivity silicon; 
         FIG. 33  shows radiation patterns in two orthogonal planes of an embodiment of a wire-grid MEMS antenna array at 60 GHz. 
     
    
    
     DETAILED DESCRIPTION 
     Various features and advantageous details are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well known starting materials, processing techniques, components, and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure. 
     One embodiment of a MEMS antennas  200  includes one or more narrow vertical silicon walls  202 . These walls  202  may carry wire-radiators  204  on top of them, as shown in  FIG. 2 . The walls  202  may be positioned on top of a silicon substrate  102  that is carrying the feeding circuit  108  from the other side. The connection between the circuit  108  and radiators  204  is performed using Through-Silicon Vias (TSVs  206 ) which are running through the entire silicon wafer  102 . The substrate&#39;s  102  side facing the walls  202  may be covered with slotted ground plane  210  through which the walls  202  are penetrating outwardly. In this way, the top side of the ground plane  210  may include the MEMS antenna  200  surrounded by air, while the back side of the ground plane  210  may include the substrate  102  carrying the driving circuit  108 . As such, isolation between the MEMS antenna  200  and circuit  108  may be maintained using single wafer  102  without the need for wafer bonding or hybrid integration. In one embodiment, the narrow slot  208  in the ground plane  210  is parallel to the wire-radiator  204 , which may reduce coupling between them and consequently negligible radiation from the narrow slot  208 . 
     The process  300  flow for fabricating the new category of MEMS antennas  200  may require as few as three processing steps. Embodiments of steps of the process  300  are illustrated in  FIG. 3 . In one embodiment, the process  300  starts with a silicon wafer  102 . The wafer  102  may be either high- or low-resistivity. In a particular embodiment, the wafer  102  thickness is 675 μm, as show in  FIG. 3( a ) . The wafer  102  may be coated with oxide  302  on both sides, which acts as an etching mask for deep silicon etching. For example, the wafer  102  may be coated with 4 μm of oxide  302 . In one embodiment, the first step in the process  200  flow is to pattern the oxide  302  on one or both sides to define holes  304  for forming the openings  308  of the TSVs  206  and holes  306  for forming the walls  202 , as shown in  FIG. 3( b ) . In one embodiment, the top silicon surface may be etched using cryogenic deep reactive ion etching for certain depth, as shown in  FIG. 3( c ) . One of ordinary skill in the art will recognize other etching processes that are suitable for forming the walls  202  and openings  308  of the TSVs  206 . Cryogenic etching may be advantageous because it may achieve smoother vertical walls that other etch methods. The TSVs  206  connecting the feeding circuit  108  at the backside to the radiators  204  on top of the walls  202  are etched also from the backside as illustrated in  FIG. 3( c ) . They may be etched using the same method. As illustrated in  FIG. 3( d ) , a metallic layer may be deposited on both sides of the wafer to cover the following: (1) the top sides of the walls to create the radiators  204 , (2) the through halls to create the vertical connectors, (3) the top side of the substrate around the walls to create the slotted ground plane, and (4) selectively the bottom side of the substrate to create the feeding microwave circuit. In one embodiment, the metallic layer may be a 1-5 μm thick copper layer. Alternatively, the layer may be gold, aluminum, or other materials suitable to form the gapped ground plane  210  and the radiators  204 . 
     In addition, as illustrated in  FIG. 3( d ) , the MEMS antenna  200  may include a gap  314  between the TSVs  206  and the radiators  204 . The gap  314  may substantially eliminate the current flow through the radiators  204 , causing the formation of a standing wave on each radiator  204  during use. The MEMS antenna  200  may also include a continuation  312  of the gapped ground plane  210  for isolation of the two radiators  204 . 
     An embodiment of a linearly polarized MEMS antenna  400  is shown in  FIG. 4 . This embodiment may include two horizontal arms  402 . In one embodiment, the two horizontal arms each comprise a thin wall  202  and a radiator  204 . For example, the radiators  204  may be copper each of which has a length of λ g /2. Each of these arms  402  may operate as a radiating half-wavelength dipole. The two dipoles  204  may be formed or placed on top of a very narrow silicon wall  202  that is formed using bulk micromachining technology. Two vertical TSVs  206  may be drilled or etched through the entire wafer  102  to create vertical arms of the antenna  400 . These arms  206  may be coupled to a 50Ω feeding coupled microstrip line  406  that may run below the substrate  102 . The upper side of the substrate may be covered with a slotted ground plane  210  through which the wall  202  is penetrating up. Two gaps  314  may be inserted between the vertical arms  206  and the horizontal arms  402 . These gaps  314  may impose current nulls at their locations and result in well-defined standing wave patterns. An open circuit stub may be connected in parallel with the antenna to enhance the impedance matching. Table II lists the optimum set of dimensions of the linearly polarized MEMS antenna  400  as fabricated on both high- and low-resistivity silicon wafers. 
     
       
         
           
               
             
               
                 TABLE II 
               
             
            
               
                   
               
               
                 GEOMETRICAL PARAMETERS OF AN  
               
               
                 EMBODIMENT OF A LINEARLY POLARIZED MEMS 
               
               
                 ANTENNA 
               
            
           
           
               
               
               
            
               
                 Antenna Geometrical 
                 On High-Resistivity 
                 On Low-Resistivity 
               
               
                 Parameters 
                 Silicon 
                 Silicon 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 H 
                 275  
                 μm 
                 275  
                 μm 
               
               
                 T 
                 400  
                 μm 
                 400  
                 μm 
               
               
                 L ant    
                 2.610  
                 mm 
                 2.438  
                 mm 
               
               
                 W ant    
                 90  
                 μm 
                 120  
                 μm 
               
               
                 G 
                 25  
                 μm 
                 25  
                 μm 
               
               
                 L tap   
                 115  
                 μm 
                 115  
                 μm 
               
               
                 L stub   
                 115  
                 μm 
                 215  
                 μm 
               
               
                 W stub    
                 80  
                 μm 
                 80  
                 μm 
               
               
                 S stub    
                 120  
                 μm 
                 120  
                 μm 
               
               
                 W line   
                 180  
                 μm 
                 180  
                 μm 
               
               
                 S line   
                 20  
                 μm 
                 20  
                 μm 
               
               
                   
               
            
           
         
       
     
     In one embodiment, the antenna may be excited with a differential mode of the feeding line, which may force the currents on the vertical arms to be opposite and hence cancel out. On the other hand, the currents on the horizontal arms may be in the same direction and they may add constructively to each other. A simulation of an embodiment of a linearly polarized MEMS antenna  400  may be performed using Ansoft/HFSS.  FIG. 5  shows a current distribution on the radiating arms at 60 GHz, which shows half-wavelength current patterns on each arm in the same direction.  FIG. 6  shows the return loss of an embodiment of the linearly polarized MEMS antenna  400  versus frequency as fabricated on both high- and low-resistivity silicon. According to these embodiments, both versions of the antenna resonate at 60 GHz as required. The 3D radiation patterns of this antenna at 60 GHz are presented in  FIG. 7 . Two orthogonal cuts in these patterns are shown in  FIG. 8 . The antenna  400  may be radiating mainly from the top side, which results in minimum interference with the driving circuit at the bottom side. The electric characteristics of an embodiment of a linearly polarized MEMS antenna  400  are listed in Table III. 
     
       
         
           
               
             
               
                 TABLE III 
               
             
            
               
                   
               
               
                 CHARACTERISTICS OF AN EMBODIMENT  
               
               
                 OF A LINEARLY POLARIZED MEMS ANTENNA 
               
            
           
           
               
               
               
            
               
                   
                 On High- 
                 On Low- 
               
               
                 Antenna 
                 Resistivity 
                 Resistivity 
               
               
                 Characteristics 
                 Silicon 
                 Silicon 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Impedance Bandwidth 
                 1.3  
                 GHz  
                 3.62  
                 GHz  
               
            
           
           
               
               
               
            
               
                 (−10 dB) 
                 (2.16%) 
                 (6%) 
               
            
           
           
               
               
               
               
               
            
               
                 Directivity 
                 7.87  
                 dBi 
                 7.81  
                 dBi 
               
            
           
           
               
               
               
            
               
                 Radiation Efficiency 
                 94.10% 
                 35.60% 
               
            
           
           
               
               
               
               
               
            
               
                 Gain 
                 7.61  
                 dBi 
                 3.33  
                 dBi 
               
               
                 Communication Range  
                 22.96  
                 m 
                 8.57  
                 m 
               
            
           
           
               
               
               
            
               
                 (P Tx  = 100 dBm and  
                   
                   
               
               
                 P Rx  = −70 dBm) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Cross-Polarization Level @ 
                 −50.20  
                 dB 
                 −39.40  
                 dB 
               
            
           
           
               
               
               
            
               
                 Broadside 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-polarization 
                 −24.00  
                 dB 
                 −22.13  
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 0 plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-Polarization 
                 −38.70  
                 dB 
                 −36.20  
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 90°plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Front-to-Back Ratio 
                 15.15  
                 dB 
                 12.44  
                 dB 
               
               
                   
               
            
           
         
       
     
     The bandwidth of an embodiment of a linearly polarized MEMS antenna  900  may be greatly enhanced by adding parasitic radiators  904 ,  906  beside the driven ones  402 ,  902 , as shown in  FIG. 9 . By making the lengths of the parasitic radiators  904 ,  906  slightly less than the driven ones  402 ,  902 , two overlapping resonances can be achieved, which enhances greatly the bandwidth of the antenna  900 . The geometrical dimensions of an embodiment of a linearly polarized MEMS antenna with parasitic elements  900  are listed in Table IV. The current distribution on the radiating arms at 60 GHz for this embodiment is shown in  FIG. 10 . The return loss of an embodiment of a linearly polarized antenna with parasitic elements is plotted versus frequency in  FIG. 11 . Comparing this figure with  FIG. 6 , shows that the addition of parasitic elements  904 ,  906  may greatly enhance the impedance bandwidth of the antenna  900 . The 3D and 2D radiation patterns of this antenna  900  are drawn in  FIGS. 12 and 13 , respectively. Table V lists the electric characteristics of an embodiment of this antenna  900  as fabricated on both high- and low-resistivity silicon. 
     
       
         
           
               
             
               
                 TABLE IV 
               
             
            
               
                   
               
               
                 GEOMETRICAL PARAMETERS OF AN 
               
               
                 EMBODIMENT OF A LINEARLY POLARIZED 
               
               
                 MEMS ANTENNA WITH PARASITIC ELEMENTS 
               
            
           
           
               
               
            
               
                 Antenna Geometrical  
                 On either High- or  
               
               
                 Parameters 
                 Low-Resistivity Silicon 
               
               
                   
               
            
           
           
               
               
               
            
               
                 H 
                 275  
                 μm 
               
               
                 T 
                 400  
                 μm 
               
               
                 L driv   
                 2.670  
                 mm 
               
               
                 W driv    
                 80  
                 μm 
               
               
                 L para   
                 2.650  
                 mm 
               
               
                 W para   
                 80 
                 μm 
               
               
                 G 
                 40  
                 μm 
               
               
                 S elem   
                 155  
                 μm 
               
               
                 L tap   
                 115  
                 μm 
               
               
                 L stub   
                 305  
                 μm 
               
               
                 W stub   
                 80  
                 μm 
               
               
                 S stub   
                 120  
                 μm 
               
               
                 W line   
                 180  
                 μm 
               
               
                 S line   
                 20  
                 μm 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE V 
               
             
            
               
                   
               
               
                 CHARACTERISTICS OF AN EMBODIMENT 
               
               
                 OF A LINEARLY POLARIZED MEMS ANTENNA 
               
               
                 WITH PARASITIC ELEMENTS 
               
            
           
           
               
               
               
            
               
                   
                 On High- 
                 On Low- 
               
               
                 Antenna 
                 Resistivity 
                 Resistivity 
               
               
                 Characteristics 
                 Silicon 
                 Silicon 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Impedance Bandwidth  
                 4.30  
                 GHz  
                 7.44  
                 GHz  
               
            
           
           
               
               
               
            
               
                 (−10 dB) 
                 (7.16%) 
                 (12.40%) 
               
            
           
           
               
               
               
               
               
            
               
                 Directivity 
                 7.49  
                 dBi 
                 7.56  
                 dBi 
               
            
           
           
               
               
               
            
               
                 Radiation Efficiency 
                 94.13% 
                 34.40% 
               
            
           
           
               
               
               
               
               
            
               
                 Gain 
                 7.23  
                 dBi 
                 2.92  
                 dBi 
               
               
                 Communication Range (P Tx  = 
                 21.03 
                 m 
                 7.80  
                 m 
               
            
           
           
               
               
               
            
               
                 100 dBm and P Rx  = −70 dBm) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Cross-Polarization Level @  
                 −46.50  
                 dB 
                 −43.90  
                 dB 
               
            
           
           
               
               
               
            
               
                 Broadside 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-polarization 
                 −19.13  
                 dB 
                 −18.10  
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 0 plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-Polarization 
                 −40.70  
                 dB 
                 −43.20  
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 90° plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Front-to-Back Ratio 
                 17.70  
                 dB 
                 17.17  
                 dB 
               
               
                   
               
            
           
         
       
     
       FIG. 14  illustrates an embodiment of a MEMS antenna  1400  that includes four λ g /2 radiating arms  402 ,  1402 ,  1404 ,  1406  mounted on top of narrow silicon walls  202  as illustrated in  FIG. 2  above. Each set of two parallel arms (e.g.,  402  and  1404 ) form one linearly polarized antenna like that described in  FIG. 4 . In one embodiment, a first linearly polarized antenna comprises arms  402  and  1404 , and a second linearly polarized antenna may comprise arms  1402  and  1406 . In one embodiment, the combination of the two linearly polarized antennas may radiate circularly polarized wave. For example, the two linearly polarized antennas may be oriented perpendicular to each other. In a particular embodiment, the phase shift between the currents on them is 90°. 
     In one embodiment, a gap may be placed between the horizontal and vertical arms of each antenna. The gap may be represented as a capacitor, whose capacitance can be controlled by the gap size. Therefore, having different gap sizes may result in different capacitances for the two antennas. For the same applied voltage difference on both antennas, the difference in capacitances may lead to phase shifts between the currents on the two antennas. By optimizing the gap sizes the required 90° phase shift may be been obtained. Table VI lists the dimensions of an embodiment of a circularly polarized antenna as fabricated on both high- and low-resistivity silicon according to the present embodiments. 
     
       
         
           
               
             
               
                 TABLE VI 
               
             
            
               
                   
               
               
                 GEOMETRICAL PARAMETERS OF AN  
               
               
                 EMBODIMENT OF A CIRCULARLY  
               
               
                 POLARIZED MEMS ANTENNA 
               
            
           
           
               
               
               
            
               
                 Antenna  
                 On High- 
                 On Low- 
               
               
                 Geometrical 
                 Resistivity 
                 Resistivity 
               
               
                 Parameters 
                 Silicon 
                 Silicon 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 H 
                 275 
                 μm 
                 275  
                 μm 
               
               
                 T 
                 400 
                 μm  
                 400 
                 μm 
               
               
                 L dip1   
                 1.175  
                 mm 
                 1.140  
                 mm 
               
               
                 W dip1   
                 90 
                 μm 
                 110 
                 μm 
               
               
                 L dip2   
                 1.215 
                 mm 
                 1.140  
                 mm 
               
               
                 W dip2   
                 90  
                 μm 
                 110 
                 μm 
               
               
                 G 1   
                 25 
                 μm 
                 23 
                 μm 
               
               
                 G 2   
                 65 
                 μm 
                 65 
                 μm 
               
               
                 L tap   
                 115  
                 μm 
                 115 
                 μm 
               
               
                 L stub   
                 61 
                 μm 
                 55 
                 μm 
               
               
                 W stub   
                 120 
                 μm 
                 120  
                 μm 
               
               
                 S stub   
                 80 
                 μm 
                 80 
                 μm 
               
               
                 W line    
                 180 
                 μm 
                 180 
                 μm 
               
               
                 S line    
                 20 
                 μm 
                 20 
                 μm 
               
               
                   
               
            
           
         
       
     
     The current distribution at 60 GHz on the radiating arms of an embodiment of a circularly polarized antenna  1400  is plotted in  FIG. 15  at two time instances that differ by quarter of a periodic time T.  FIG. 15( a )  shows that the radiating current at instant t=0 is that of the first antenna, while at t=T/4 the radiating current is that of the second antenna as shown in  FIG. 15( b ) . This may result in a Right-Hand Circularly Polarized (RHCP) wave.  FIG. 16  shows the axial ratio and return loss of an embodiment of a circularly polarized antenna  1400  fabricated on high- and low-resistivity silicon wafers. In both cases, reasonable overlapping between the axial ratio and impedance bandwidths can be observed. The 3D radiation pattern of an embodiment of a circularly polarized antenna  1400  is shown in  FIG. 17 . The radiation patterns in two orthogonal cuts are presented in  FIG. 18  for both antenna versions. The electric characteristics of an embodiment of the circularly polarized antenna  1400  are summarized in Table VII. 
     
       
         
           
               
             
               
                 TABLE VII 
               
             
            
               
                   
               
               
                 CHARACTERISTICS OF AN EMBODIMENT 
               
               
                 OF A CIRCULARLY POLARIZED MEMS ANTENNA 
               
            
           
           
               
               
               
            
               
                   
                 On High- 
                 On Low- 
               
               
                 Antenna 
                 Resistivity 
                 Resistivity 
               
               
                 Characteristics 
                 Silicon 
                 Silicon 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Impedance Bandwidth 
                 2.68  
                 GHz  
                 6.16  
                 GHz 
               
            
           
           
               
               
               
            
               
                 (−10 dB) 
                 (4.45%) 
                 (10.26%) 
               
            
           
           
               
               
               
               
               
            
               
                 Axial Ratio Bandwidth  
                 0.74  
                 GHz  
                 1.7  
                 GHz  
               
            
           
           
               
               
               
            
               
                 (3 dB) 
                 (1.22) 
                 (2.83%) 
               
            
           
           
               
               
               
               
               
            
               
                 Directivity 
                 6.38  
                 dBi 
                 7.18  
                 dBi 
               
            
           
           
               
               
               
            
               
                 Radiation Efficiency 
                 93.70% 
                 31.95% 
               
            
           
           
               
               
               
               
               
            
               
                 Gain 
                 6.10  
                 dBi 
                 2.18  
                 dBi 
               
               
                 Communication Range (P Tx  = 
                 16.21  
                 m 
                 6.57  
                 m 
               
            
           
           
               
               
               
            
               
                 100 dBm and P Rx  = −70 dBm) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Cross-Polarization Level @ 
                 −21.40  
                 dB 
                 −26.40  
                 dB 
               
            
           
           
               
               
               
            
               
                 Broadside 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-polarization 
                 −8.68  
                 dB 
                 −11.25  
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 0 plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-Polarization 
                 −10.70  
                 dB 
                 −13.60  
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 90° plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Front-to-Back Ratio 
                 11.70  
                 dB 
                 13.25  
                 dB 
               
               
                   
               
            
           
         
       
     
     An embodiment of a reconfigurable MEMS antenna  1900  is shown in  FIG. 19 . This embodiment may include two arms  1902 ,  1904 . Each arm  1902 ,  1904  may be fabricated using, for example, bulk micromachining through 675 μm thick high- or low-resistivity silicon wafers, and include narrow walls  202  as illustrated in  FIG. 2 . Two horizontal electromagnetic radiators may cover the top surfaces of the walls  202  as illustrated according to  FIG. 2 . Each arm  1902 ,  1904  may represent a half-wavelength dipole. Two vertical Through-Silicon Vias (TSVs  206 ) may be drilled or etched through the entire wafer. These TSVs  206  may represent the vertical arms of the antenna  1900 . Two gaps may be inserted between the horizontal and vertical arms. These gaps help in achieving well-defined standing wave current patterns on the antenna&#39;s arms. 
     The top surface of the substrate may be covered with slotted ground plane  210 , through which the silicon walls  202  are penetrating up. This plane  210  may isolates between the antenna  1900  and the bulk silicon substrate  102 , which may reduce surface wave losses and increases radiation efficiency. Moreover, this ground plane  210  may reduce significantly the interference between the antenna  1900  and the driving circuit  108  that may be located below the substrate  102 . In one embodiment, metallic parts of this structure are made of copper with thickness of 3 μm. One of ordinary skill in the art will recognize other thicknesses and materials suitable for use with the present embodiments. From the bottom side of the substrate  102 , the TSVs  206  may be connected to the two output ports  1910 ,  1912  of a ring coupler  1906  made of microstrip lines. Two feeding microstrip lines  1908  may be connected to the input ports of the ring coupler  1906 . The width of each line may be adjusted to have characteristic impedance of 50Ω at 60 GHz. In one embodiment, the ring may be made of a microstrip line whose width corresponds to a characteristic impedance of 70.7Ω. The radius of the ring  1906  may be adjusted such that its electric length equals 1.5λ g  at the frequency of operation. Geometrical parameters of one embodiment of this antenna  1900  are listed in Table VIII. The photographs of the fabricated prototype are presented in  FIG. 20 . 
     
       
         
           
               
             
               
                 TABLE VIII 
               
             
            
               
                   
               
               
                 GEOMETRICAL PARAMETERS OF AN  
               
               
                 EMBODIMENT OF A RECONFIGURABLE 
               
               
                 MEMS DIPOLE/MONOPOLE ANTENNA 
               
            
           
           
               
               
               
            
               
                 Antenna  
                 On High- 
                 On Low- 
               
               
                 Geometrical 
                 Resistivity 
                 Resistivity 
               
               
                 Parameters 
                 Silicon 
                 Silicon 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 H 
                 475  
                 μm 
                 475  
                 μm 
               
               
                 T 
                 200  
                 μm 
                 200 
                 μm 
               
               
                 L DIP   
                 1.210 
                 mm 
                 1.205 
                 mm 
               
               
                 W DIP   
                 70 
                 μm 
                 70 
                 μm 
               
               
                 G 
                 55 
                 μm 
                 55 
                 μm 
               
               
                 R IN   
                 384 
                 μm 
                 384 
                 μm 
               
               
                 R OUT   
                 462 
                 μm 
                 462 
                 μm 
               
               
                 L STUB   
                 200 
                 μm 
                 150 
                 μm 
               
               
                 W STUB    
                 184 
                 μm 
                 184 
                 μm 
               
               
                 W LINE   
                 184 
                 μm 
                 184  
                 μm 
               
               
                   
               
            
           
         
       
     
     If an excitation signal is applied to the first port  1910  of the ring coupler  1906 , see  FIG. 19 , the antenna vertical arms  1902 ,  1904  may be excited with the same amount of power, but with 180° phase shift. Almost no power will be transferred to the second port  1912 . The currents on the vertical arms  206  may be opposite to each other, while on the horizontal arms  1902 ,  1904  the currents will be in the same direction.  FIG. 21  shows the surface current distribution on an embodiment of antenna arms  1902 ,  1904  due to excitation from the first port  1910 , as obtained using Ansoft/HFSS simulator at 60 GHz. In this mode of operation, the vertical currents may cancel out, while the horizontal arms  1902 ,  1904  act as an array of two half-wavelength dipoles. The presence of gaps between the vertical and horizontal arms imposes current nulls around the gaps. This defines standing waves on the horizontal arms, where each wave is terminated by two nulls separated by a distance of λ g /2. 
     S-parameters of an embodiment of the antenna  1900  are plotted versus frequency in  FIG. 22 . In this mode, the antenna  1900  is excited via the first port  1910 . The coupling to other port  1912 , i.e. S 21 , is less than −18 dB over the working frequency band, which indicates good isolation between the two ports. The 3D radiation pattern of the antenna  1900  in this mode of operation at 60 GHz is drawn in  FIG. 23 . It can be seen that this embodiment of the antenna  1900  is radiating mainly from the top side in the broadside direction, while the bottom side radiation is relatively weak and results mainly from diffraction at the truncated edges of the antenna structure. The radiation patterns in two orthogonal cuts for an embodiment of the antenna  1900  in the dipole mode, are shown in  FIG. 24 . The characteristics of the antenna  1900  in this mode of operation are summarized in Table IX. 
     
       
         
           
               
             
               
                 TABLE IX 
               
             
            
               
                   
               
               
                 CHARACTERISTICS OF AN EMBODIMENT  
               
               
                 OF A RECONFIGURABLE MEMS 
               
               
                 DIPOLE/MONOPOLE ANTENNA IN A DIPOLE  
               
               
                 MODE OF OPERATION 
               
            
           
           
               
               
               
            
               
                   
                 On High- 
                 On Low- 
               
               
                 Antenna 
                 Resistivity 
                 Resistivity 
               
               
                 Characteristics 
                 Silicon 
                 Silicon 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Impedance Bandwidth  
                 2.25  
                 GHz 
                 4.30  
                 GHz  
               
            
           
           
               
               
               
            
               
                 (−10 dB) 
                 (3.75%) 
                 (7.16%) 
               
            
           
           
               
               
               
               
               
            
               
                 Directivity 
                 9.40  
                 dBi 
                 9.08  
                 dBi 
               
            
           
           
               
               
               
            
               
                 Radiation Efficiency 
                 95.15% 
                 45.7% 
               
            
           
           
               
               
               
               
               
            
               
                 Gain 
                 9.14  
                 dBi 
                 5.63  
                 dBi 
               
               
                 Communication Range (P Tx  = 
                 32.65  
                 m 
                 14.55  
                 m 
               
            
           
           
               
               
               
            
               
                 100 dBm and P Rx  = −70 dBm) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Cross-Polarization Level @ 
                 −33.90 
                 dB 
                 −27.90  
                 dB 
               
            
           
           
               
               
               
            
               
                 Broadside 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-polarization 
                 −24.90  
                 dB 
                 −21.50  
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 0 plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-Polarization 
                 −17.55  
                 dB 
                 −12.60  
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 90° Plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Front-to-Back Ratio 
                 19.60  
                 dB 
                 16.82  
                 dB 
               
               
                   
               
            
           
         
       
     
     The excitation of the monopole mode is via the second port  1912 . In this case, the ring coupler  1906  delivers half of the input power to each antenna side  1902 ,  1904  with the same phase. A negligible amount of power can couple to the first port  1910 . The surface current distribution of an embodiment of monopole mode on the antenna arms  1902 ,  1904  at 60 GHz is plotted in  FIG. 25 . It can be seen that the horizontal currents are opposite to each other, which results in relatively weak radiation from them. On the other hand, the vertical currents are in the same direction. Hence, the antenna  1900  in this mode of operation can be looked at as an array of two vertical monopoles. As in the dipole mode, the disconnection of the vertical and horizontal arms imposes current nulls at the points of disconnection. This ensures standing wave patterns terminated by these currents nulls. To enhance the matching between the antenna input impedance of the monopole mode and the feeding line, two open circuit stubs are connected in parallel with the microstrip line of port  2 , as shown in  FIG. 19 . 
       FIG. 26  shows the S-parameters that correspond to the monopole mode of operation, namely S 12  and S 22 . Good matching can be observed at 60 GHz. Again, the coupling between the two ports is very weak as indicated by S 12 =S 21 &lt;−18 dB over the working bandwidth. The 3D and 2D radiation pattern at 60 GHz of the antenna in the monopole mode of operation are shown in  FIGS. 24 and 28 , respectively. A radiation null at the broadside direction can be noticed. Unlike the radiation pattern of the dipole mode, this pattern offers better coverage around the end-fire direction. Switching between the two modes of excitation provides very good coverage for the entire half-space. Table X summarizes the characteristics of an embodiment of a reconfigurable antenna in its monopole mode of operation. 
     
       
         
           
               
             
               
                 TABLE X 
               
             
            
               
                   
               
               
                 Characteristics of an Embodiment of a  
               
               
                 Reconfigurable MEMS Dipole/Monopole 
               
               
                 Antenna in a Monopole Mode of Operation 
               
            
           
           
               
               
               
            
               
                   
                 On High- 
                 On Low- 
               
               
                 Antenna 
                 Resistivity 
                 Resistivity 
               
               
                 Characteristics 
                 Silicon 
                 Silicon 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Impedance Bandwidth  
                 1.93  
                 GHz  
                 4.94  
                 GHz  
               
            
           
           
               
               
               
            
               
                 (−10 dB) 
                 (3.21%) 
                 (8.23%) 
               
            
           
           
               
               
               
               
               
            
               
                 Directivity 
                 6.94  
                 dBi 
                 6.92  
                 dBi 
               
            
           
           
               
               
               
            
               
                 Radiation Efficiency 
                 95.40% 
                 49.50% 
               
            
           
           
               
               
               
               
               
            
               
                 Gain 
                 6.70  
                 dBi 
                 3.83  
                 dBi 
               
               
                 Communication Range (P Tx  = 
                 18.62  
                 m 
                 9.61  
                 m 
               
            
           
           
               
               
               
            
               
                 100 dBm and P Rx  = −70 dBm) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Cross-Polarization Level @ 
                 −25.90  
                 dB 
                 −31.30  
                 dB 
               
            
           
           
               
               
               
            
               
                 End-fire (φ = 0 plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Cross-Polarization Level @ 
                 −17.40  
                 dB 
                 −30.70  
                 dB 
               
            
           
           
               
               
               
            
               
                 End-fire (φ = 90° plane) 
                   
                   
               
               
                   
               
            
           
         
       
     
     An embodiment of a wire-grid array  2900  is shown in  FIG. 29 . This embodiment may include number of arms that are defined by deep reactive ion etching of silicon wafer with thickness of 675 μm. Each arm may include the structure and be formed by substantially the same process as the arms described in  FIGS. 2-4 . For example, the arms may include narrow walls  202 . The top faces of these walls  202  may be covered with metal strips, which form the radiators  204  and connectors, as shown in  FIG. 29 . The electric length of all radiators  204  may be λ g /2. Two vertical TSVs  206  with square cross-section may be drilled or etched through the entire wafer  102  and penetrate both the substrate  102  and the walls  202 . The top surface of the substrate  120  may be covered with slotted ground plane  210 , through which the silicon walls  202  project. This plane  210  may isolate between the antenna  2900  and the bulk silicon substrate  102 , which reduces surface wave losses and increases the radiation efficiency. Moreover, the presence of this plane  210  may result in reducing significantly the interference between the antenna  2900  and the feeding circuit  108  that is located below the ground plane  210 . From the bottom side of the substrate  102 , the TSVs  206  may be connected to the two strips of a coupled microstrips feeding line. This line is fed with its differential mode, whose characteristic impedance is 50Ω. An open circuit stubs is connected in parallel with the antenna array in order to enhance the impedance matching. Dimensions of one embodiment of a wire-grid array are listed in Table XI. 
     
       
         
           
               
             
               
                 TABLE XI 
               
             
            
               
                   
               
               
                 GEOMETRICAL PARAMETERS OF AN 
               
               
                 EMBODIMENT OF A WIRE-GRID MEMS 
               
               
                 ANTENNA ARRAY 
               
            
           
           
               
               
               
            
               
                   
                 Antenna  
                 On either High- or  
               
               
                   
                 Geometrical  
                 Low-Resistivity 
               
               
                   
                 Parameters 
                 Silicon 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 H  
                 275 
                 μm 
               
               
                   
                 T 
                 400 
                 μm 
               
               
                   
                 L rad1   
                 1.440 
                 mm 
               
               
                   
                 W rad1    
                 88 
                 μm 
               
               
                   
                 L rad2   
                 1.090 
                 mm 
               
               
                   
                 W rad2   
                 230 
                 μm 
               
               
                   
                 L con1   
                 3.140 
                 mm 
               
               
                   
                 W con1   
                 81 
                 μm 
               
               
                   
                 L con2   
                 1.415 
                 mm 
               
               
                   
                 W con2   
                 81 
                 μm 
               
               
                   
                 L stub    
                 275  
                 μm 
               
               
                   
                 W line   
                 180  
                 μm 
               
               
                   
                 S line   
                 20 
                 μm 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 30  shows the current distribution on the antenna&#39;s  2900  radiators  204  and connectors as obtained using Ansoft/HFSS at 60 GHz. The electrical lengths of the radiators  204  and connectors are adjusted such that the currents on the radiators  204  are in the same direction, while the currents on the connectors are opposite to each other, as shown in  FIG. 30 . Consequently, this embodiment of a wire-grid antenna  2900  structure can be considered as an array of 10 radiating dipoles. The return losses of this embodiment of the wire-grid array  2900  on both high- and low-resistivity silicon are plotted versus frequency in  FIG. 31 . Both versions are resonating at 60 GHz as required. The bandwidth of an embodiment of the wire-grid array  2900  on low-resistivity silicon is wider than that on high-resistivity due to the increased losses in the former case. The 3D radiation patterns of the wire-grid array  2900  on both high- and low-resistivity silicon are presented in  FIG. 32 . Symmetric top-side radiation patterns can be noticed. Two orthogonal cuts in these patterns are shown in  FIG. 33 . It can be seen that the cross-polarization level in both cuts is extremely low due to the perfect cancellation of the unwanted currents on the connectors. A summary of the electric characteristics of an embodiment of a wire-grid array  2900  on both high- and low-resistivity silicon is listed in Table XII. 
     
       
         
           
               
             
               
                 TABLE XII 
               
             
            
               
                   
               
               
                 CHARACTERISTICS OF AN EMBODIMENT  
               
               
                 OF A WIRE-GRID MEMS ANTENNA ARRAY 
               
            
           
           
               
               
               
            
               
                   
                 On High- 
                 On Low- 
               
               
                 Antenna 
                 Resistivity 
                 Resistivity 
               
               
                 Characteristics 
                 Silicon 
                 Silicon 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Impedance Bandwidth  
                 1  
                 GHz 
                 1.62  
                 GHz 
               
            
           
           
               
               
               
            
               
                 (−10 dB) 
                 (1.66%) 
                 (2.70%) 
               
            
           
           
               
               
               
               
               
            
               
                 Directivity 
                 13.76  
                 dBi 
                 13.92  
                 dBi 
               
            
           
           
               
               
               
            
               
                 Radiation Efficiency 
                 85.44% 
                 23.77% 
               
            
           
           
               
               
               
               
               
            
               
                 Gain 
                 13.03  
                 dBi 
                 7.63  
                 dBi 
               
               
                 Communication Range (P Tx  = 
                 79.96  
                 m 
                 23.06  
                 m 
               
            
           
           
               
               
               
            
               
                 100 dBm and P Rx  = −70 dBm) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Cross-Polarization Level @ 
                 −49.50  
                 dB 
                 −50.40  
                 dB 
               
            
           
           
               
               
               
            
               
                 Broadside 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-polarization 
                 −45.00  
                 dB 
                 −43.10 
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 0 plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Maximum Cross-Polarization 
                 −22.50  
                 dB 
                 −19.23  
                 dB 
               
            
           
           
               
               
               
            
               
                 Level (φ = 90° plane) 
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Side-Lobe Level (φ = 0 plane) 
                 −19.60  
                 dB 
                 −18.40  
                 dB 
               
               
                 Side-Lobe Level (φ = 90° plane) 
                 −17.30  
                 dB 
                 −23.80  
                 dB 
               
               
                 Front-to-Back Ratio 
                 18.90  
                 dB 
                 16.60  
                 dB 
               
               
                   
               
            
           
         
       
     
     Embodiments of MEMS antennas have been presented. These embodiments include MEMS antennas with ground plane isolation from the feeding circuitry using single silicon wafer without the need for any wafer bonding or hybrid integration. Beneficially, this reduces the fabrication cost dramatically while maintaining superior electromagnetic performance at the same time. Additionally, embodiments of a method for fabricating the proposed category of MEMS antennas has been described. In one embodiment, the method may be performed in as little as three processing steps. Embodiments of the MEMS antennas offer diversity in polarization and radiation characteristics, such as: single element for linear polarization, single element for circular polarization, reconfigurable single element for radiation pattern diversity, and a wire-grid antenna array. 
     Embodiments of the three single antenna elements appear to exhibit very high radiation efficiency (≅94%) and high gain (≅8 dBi) on high-resistivity silicon. These remarkably high figures may be achieved at high operation frequency, specifically 60 GHz. The high radiation efficiency may lead to long battery life-time, while high gain results in enlarged range of communication. On the other hand, the three single elements on low-resistivity silicon are showing significantly less radiation efficiency (≅35%) and gain (≅3.5 dBi). This gain value is suitable for short range communication such as in-door wireless systems. For such systems, the low-resistivity silicon solution is very attractive as it is much cheaper and more compatible with the driving electronics as compared to the high-resistivity silicon solution. As for embodiments of the wire-grid array, the gain is significantly higher, 13 dBi and 7.6 dBi on high- and low-resistivity silicon, owing to the increased directivity. This enlarges the communication range of the embodiments of the wire-grid array making it sufficient for several applications even if the array is fabricated on low-resistivity silicon. 
     Bandwidth of embodiments of the MEMS antennas on high- and low-resistivity silicon have been observed to be around 2 GHz and 5 GHz, respectively, which are considered sufficient for the majority of applications. However, for applications require significantly large information capacity, the bandwidth of all the proposed antennas may be enhanced by adding parasitic elements in the vicinity of the driven ones. An example of this is done for the linearly polarized antenna whose bandwidth is enhanced by about 2.5% by adding parasitic elements. Various other embodiments may also benefit from the use of parasitic elements. Embodiments of such elements show one side radiation characterized by front-to-back ratio in the order of 15 dB. This value indicates that the proposed ground-plane isolation technique is functional and minimum interference between the antenna and the driving circuit can be achieved. The polarization purity of all antennas may be as high as characterized by cross-polarization level in the range of −30 dB. 
     All of the devices and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the apparatus and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. In addition, modifications may be made to the disclosed apparatus and components may be eliminated or substituted for the components described herein where the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.