Abstract:
An antenna array structure is disclosed for use in receiving, transmitting, or transceiving electromagnetic radiation. The antenna array structure includes a first planar substrate with one or more grooves formed therein with at least one secondary planar substrate having an antenna formed thereon placed in one of the grooves in the first substrate. The use of this three-dimensional structure takes advantage of the inherent directionality due to the guidance of electromagnetic radiation by the secondary planar substrate. This antenna array structure provides the advantages of reduced cross talk between adjacent antennae and can readily be produced using standard silicon fabrication techniques.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an integrated circuit antenna structure for use in receiving, transmitting, and/or transceiving millimeter waves. In particular, the present invention relates to a three-dimensional integrated circuit antenna structure. 
     BACKGROUND 
     Arrays of millimeter- (mm-) wave antennas have application to a number of imaging systems including security, robotic vision, and imaging through smoke or weather related obscurants. More recently, monolithic arrays of mm-wave antennas have been explored for use in these applications due to the simplicity of their fabrication on a single substrate. 
     However, monolithic mm-wave antenna arrays developed to date suffer from the problem of strong coupling of the mm-wave antennae to the dielectric substrate upon which they are formed as well as a closely spaced groundplane. This substrate coupling leads to poor efficiency in the mm-wave antennae. Poor efficiency of the mm-wave antennae results in poor imaging when the mm-wave antenna array is used in a passive mode. To improve imaging, a mm-wave illumination source can be used to increase the quantity of received mm-wave radiation. The use of a mm-wave illumination source is either not feasible or is undesirable in many applications, especially military applications. 
     The substrate coupling also leads to significant cross talk problems between mm-wave antennae within an array. This cross talk reduces image fidelity, thereby requiring improved signal processing of the resultant antenna signals. Alternatively, the spacing between adjacent mm-wave antennae within an array must be increased. However, increasing the spacing between adjacent mm-wave antennae reduces image resolution, which is undesirable. 
     SUMMARY 
     It is an object of the present invention to provide an integrated circuit antenna array with significantly reduced substrate coupling. It is a further object of the present invention to provide an integrated circuit antenna array that can be produced at low cost using standard silicon fabrication techniques. 
     In a first embodiment, the present invention includes a single integrated circuit antenna for receiving, transmitting, or transceiving electromagnetic radiation. The first embodiment includes a first substrate having at least one first electrical lead formed on a surface thereof. The first embodiment also includes a second substrate having an antenna for receiving, transmitting, or transceiving electromagnetic radiation formed on a surface thereof and at least one second electrical lead. One end of the at least one second electrical lead is electrically connected to the antenna, while a second end of the at least one second electrical lead is positioned adjacent to an edge of the second substrate. The second substrate is disposed with respect to the first surface of the first substrate such that the at least one first electrical lead is electrically connected to a corresponding one of the second electrical lead. 
     In a second embodiment, the present invention includes a plurality of integrated circuit antennae for receiving, transmitting, or transceiving electromagnetic radiation. The second embodiment includes a first substrate having a plurality of first electrical leads formed on a surface thereof. The second embodiment also includes at least one secondary substrate having at least one antenna for receiving, transmitting, or transceiving electromagnetic radiation formed on a surface thereof and a corresponding at least one second electrical lead for each antenna formed thereon. One end of each of the at least one second electrical lead is electrically connected to a corresponding antenna, while a second end of the at least one second electrical lead is positioned adjacent to an edge of a corresponding second substrate. Each of the at least one secondary substrate is disposed with respect to the first surface of the first substrate such that each of the ends of the plurality of first electrical leads is electrically connected to a corresponding one of the second electrical leads. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a perspective view of an integrated circuit antenna structure according to a first embodiment of the present invention. 
     FIG. 2 is a top view of a first planar substrate according to a first embodiment of the present invention. 
     FIG. 3 a  is a side view of a second planar substrate showing an integrated circuit antenna according to a first embodiment of the present invention and  3   b  is a side view of a second planar substrate showing an integrated circuit antenna and a director according to a first embodiment of the present invention. 
     FIGS. 4 a-c  illustrate possible alternative fabrication techniques for use with the present invention. 
     FIGS. 5 a-d  illustrate possible antenna configurations for use with the present invention. 
     FIG. 6 is a perspective view of an alternative integrated circuit antenna structure configuration according to the first embodiment of the present invention. 
     FIGS. 7 a-f  are perspective views of integrated circuit antenna array structure configurations according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a perspective view of a first embodiment of an integrated circuit antenna structure  100 . The first embodiment includes a first substrate  102 , preferably a silicon wafer. A first electrical lead  104  is formed on a top major surface of the first substrate  102 . A ground plane  106  is optionally formed on the bottom major surface of the first substrate  102 . The first electrical lead  104  and the ground plane  106  are preferably layers of aluminum or an aluminum alloy and formed by standard silicon integrated circuit fabrication techniques. 
     Various electronic circuitry  108  is optionally formed on the surface of the first substrate  102  as seen in FIG.  2 . This electronic circuitry  108  serves one of three functions depending upon the particular application for the integrated circuit antenna structure  100 . If the integrated circuit antenna structure  100  is to be used for receiving mm-wave electromagnetic radiation, the electronic circuitry  108  will be used for detecting a change in resistance, voltage, or current imposed on the first electrical lead  104  by an antenna  110 , or an antenna load  112 . 
     In some applications, the integrated circuit antenna structure  100  can be used for transmitting mm-wave electromagnetic radiation. In these cases, the electronic circuitry  108  will be used to generate an appropriate drive current or voltage to be conducted to the antenna  110  via the first electrical lead  104 . If the integrated circuit antenna structure  100  is to be used for transceiving mm-wave electromagnetic radiation, the electronic circuitry will be used to both detect the change in resistance, current, or voltage in the first electrical lead  104 , as well as to generate an appropriate drive current or voltage in the first electrical lead  104 . Depending upon the application and the frequency of the electromagnetic radiation, stripline, microstrip, or twin leads may be required for the first electrical lead  104 . 
     The integrated circuit antenna structure  100  further includes a second substrate  114  as seen in FIG. 3 a,  preferably a silicon wafer. The second substrate  114  has the antenna  110  formed on the major surface thereof. In the gap between the antenna  110  halves, the antenna load  112  may be optionally formed. This antenna load  112  absorbs the mm-wave electromagnetic radiation energy absorbed by the antenna  110 . The temperature of the antenna load  112  may increase due to the absorbed energy, thereby causing the impedance of the antenna load  112  to change. Alternatively, the absorbed energy may cause a change in the voltage or current across the antenna load  112 . A second electrical lead  116  is formed on a surface of the second substrate  114 . A first end of the second electrical lead  116  is electrically connected to a corresponding end of the antenna  110  or antenna load  112 . A second end of the second electrical lead  116  is adjacent to an edge of the second substrate  114 . The second electrical lead  116  is used to sense a change in the resistance, voltage, or current in the antenna  110  or antenna load  112  when the antenna is used to receive mm-wave electromagnetic radiation. A director  118  is optionally formed on a surface of the second substrate  114  as seen in FIG. 3 b.  The director  118  provides additional directivity to any mm-wave electromagnetic radiation transmitted or received by the antenna  110 . The antenna  110 , the second electrical lead  116 , and the director  118  are preferably aluminum and formed by standard silicon integrated circuit fabrication techniques. The optional antenna load  112  is preferably a bolometer formed of a material having a high temperature coefficient of resistance, such as vanadium oxide. The antenna load  112  is also preferably formed by standard silicon integrated circuit fabrication techniques. 
     Fabrication of the integrated circuit antenna structure  100  is complete when the second substrate  114  is disposed with respect to the first surface of the first substrate  102  such that the first electrical lead  104  is electrically connected to the second end of the second electrical lead  116 . Preferably, an angle θ formed between the first substrate  102  and the second substrate  114  is 90 degrees. In any case, the angle θ formed between the first substrate  102  and the second substrate  114  is non-zero, i.e. the first substrate  102  and the second substrate  114  are not parallel. A non-electrically conducting epoxy, not illustrated, can be used to secure the second substrate  114  to the surface of the first substrate  102 . 
     Alternative methods for fabricating the integrated circuit antenna structure  100  are shown in FIGS. 4 a - 4   c.  FIG. 4 a  illustrates the use of a channel  120  formed in the surface of the first substrate  102 . The edge of the second substrate  114  is then placed in the channel  120  such that the first electrical lead  104  is aligned and in electrical contact with the second electrical lead  116 . FIG. 4 b  illustrates the use of two slots  122 ,  124  formed through the first substrate  102 . The edge of the second substrate  114  is then processed to form corresponding tabs  126 ,  128 . The tabs  126 ,  128  are then placed in the slots  122 ,  124  such that the first electrical lead  104  is aligned and in electrical contact with the second electrical lead  116 . An alternative method for fabricating the first electrical lead  104  is shown in FIG. 4 c.  With this alternative method, the first electrical lead  104  is formed with a portion on the edge of the channel  120  in the first substrate  102 . By placing a portion of the first electrical lead  104  on the edge of the channel  120 , a larger conducting surface can be provided thereby improving the electrical contact between the first electrical lead  104  and second electrical lead  116 . In each of these fabrication methods a first electrical lead  104  is in direct electrical and physical contact with a corresponding second electrical lead  116 . 
     As shown in FIGS. 5 a - 5   d,  a variety of integrated circuit antenna configurations is possible. In the simplest case, as illustrated in FIG. 5 a,  the antenna can be a dipole antenna  130 . The dipole antenna provides the narrowest bandwidth of mm-wave electromagnetic radiation. In applications with low received mm-wave electromagnetic radiation power, a broad bandwidth integrated circuit antenna configuration is preferable to increase received signal strength. A first example of a broad bandwidth integrated circuit antenna configuration is a bow tie antenna  132  illustrated in FIG. 5 b.  A broader bandwidth integrated circuit antenna configuration is achieved by using a spiral antenna  134  illustrated in FIG. 5 c.  A third broadband antenna configuration is illustrated in FIG. 5 d.  The third broadband antenna is a log periodic antenna  136  having antenna legs of differing lengths. Further, the antenna legs may be fabricated on both sides of the second substrate providing greater flexibility in design of the antenna. When the antenna is fabricated on both sides of the substrate, the material used for the second substrate must be carefully selected for both dielectric constant and thickness. Broad bandwidth integrated circuit antenna configurations using the bow tie antenna  132 , the spiral antenna  134 , or the log periodic antenna  136  can be used in various transmission or transceiver applications. As examples, a system requiring the transmission of modulated mm-wave signals or a spread spectrum application that requires very broad bandwidth would each benefit from the use of the bow tie antenna  132 , the spiral antenna  134 , or the log periodic antenna  136 . 
     In the integrated circuit antenna structure  100 , where a longitudinal axis of the antenna  110  is parallel with the surface of the first substrate  102 , a transmitted mm-wave would propagate very strongly in a direction normal to the surface of the first substrate  102  and centered with respect to the antenna  110 . This directionality is due to the transmitted mm-wave preferentially propagating down the length of the second substrate  114  and the ground plane  106  on the bottom surface of the first substrate  102 . An alternative configuration, illustrated in FIG. 6, includes the antenna  110  oriented with its longitudinal axis normal to the surface of the first substrate  102  and does not include the ground plane  106  on the bottom of the first substrate  102 . In this case, a transmitted mm-wave again preferentially propagates down the length of the second substrate  114  resulting in the mm-wave propagating in a direction parallel to the surface of the first substrate  102  and parallel to the surface of the second substrate  114 . 
     In a second embodiment of the present invention, a plurality of integrated circuit antennae are incorporated. FIGS. 7 a-f  illustrate the second embodiment of the present invention incorporating from 2 to 16 antennae. 
     FIG. 7 a  illustrates a simple integrated circuit multi-antenna array structure  140  that incorporates only two antennae  142 ,  144  such that an angle φ between the two antennae  142 ,  144  is 90 degrees. With the axis of the two antennae  142 ,  144  parallel to the surface of the first substrate  102 , the response to received mm-wave electromagnetic radiation can be approximately doubled as the antennae  142 ,  144  can absorb both orthogonal polarizations of the incident mm-wave electromagnetic radiation. When the axis of the two antennae  148 ,  150  is normal to the surface of the first substrate  102 , as shown in FIG. 7 b,  the directionality of the integrated circuit multi-antenna array structure  146  is dramatically increased. When the integrated circuit multi-antenna array structure  146  is used for transmitting mm-wave electromagnetic radiation, the introduction of an appropriate phase difference between the currents or voltages used to drive the two antennae  148 ,  150  can result in directional transmission of the mm-wave electromagnetic radiation in any angular direction about an axis formed by the intersection of the planes of the two antennae  148 ,  150 , thereby forming a phased array. 
     FIGS. 7 c  and  7   d  illustrate integrated circuit multi-antenna array structures  152 ,  154  that include 4 and 8 antennae respectively with an axis of each antenna normal to the surface of the first substrate  102 . The advantage of the 4 and 8 integrated circuit multi-antenna array structures  152 ,  154  is their enhanced angular direction control relative to the two antenna integrated circuit multi-antenna array structure  146 . The integrated circuit multi-antenna array structures  152 ,  154  also provide for an easier method of transmitting higher mm-wave electromagnetic radiation power. 
     The enhanced angular direction control of the integrated circuit multi-antenna array structures  152 ,  154  is also advantageous when used for receiving mm-wave electromagnetic radiation. By measuring a phase difference in the signals received by each of the plurality of antennae, the direction from which the radiation emanated can be ascertained. This has potential use in remote sensing applications where the integrated circuit multi-antenna array structure  152 ,  154  can be used to sense objects moving in a given area, for example animals by a water hole or military personnel or equipment in a battle field. 
     FIGS. 7 e  and  7   f  illustrate small mm-wave electromagnetic radiation sensing integrated circuit multi-antenna array structures  156 ,  158  for use in producing mm-wave electromagnetic radiation images. FIG. 7 e  illustrates an integrated circuit multi-antenna array structure  156  of 16 antennae that have the axis of each antenna parallel to the surface of the first substrate  102  and parallel to each other. FIG. 7 f  illustrates an integrated circuit multi-antenna array structure  158  of 16 antennae that have the axis of each antenna parallel to the surface of the first substrate  102 , but alternate with respect to each other such that both polarizations of the incident mm-wave electromagnetic radiation can be absorbed. In either integrated circuit multi-antenna array structure  156 ,  158 , the optional antenna load  112  would preferably be formed for each antenna. The optional electronic circuitry  108  would preferably be formed on the surface of the first substrate  102  such that the change in resistance, voltage, or current in the antenna  110  or its corresponding antenna load  112  would be sensed. This change in resistance, voltage, or current could then be used to form an image based upon mm-wave electromagnetic radiation, much like an optical focal plane array uses photodetectors and appropriate readout electronics to produce an image based upon visible or infrared electromagnetic radiation. 
     While the present invention has been described by way of example, a number of variations will be apparent to one skilled in the art. Such variations include, but are not limited to, the use of planar substrates other than silicon. The first planar substrate could be formed of GaAs to take advantage of GaAs electronics for certain transmitter or transceiver applications. The second planar substrate could be formed of suitable dielectric material that may provide better mm-wave electromagnetic radiation guiding properties, lower absorption of the mm-wave electromagnetic radiation, or better thermal properties. The prior art discloses a large number of antenna configurations of which only the dipole antenna, the bow tie antenna, and the spiral antenna have been illustrated. Alternative antenna configurations may provide various advantages for certain receiver, transmitter, or transceiver applications. A number of alternative antenna loads for the antennae can also be found in the prior art. These alternative antenna loads include materials other than vanadium oxide for use in a bolometer-type load such as bismuth. Antenna loads other than bolometers can also be used as long as the mm-wave electromagnetic radiation is absorbed and a suitable measurable indicia is produced. 
     While this Detailed Description elaborates upon embodiments of the invention as it relates specifically to small arrays of mm-wave integrated circuit antennae, this is not meant to limit application of the invention. Alternative embodiments may incorporate different configurations, substitutions, and modifications without departing from the scope of the invention.