Abstract:
A grid array antenna configured to operate with millimeter wavelength signals, the grid array antenna comprising a plurality of mesh elements and at least one radiation element; each mesh element comprising at least one long side and at least one short side operatively connected to the at least one long side; at least one of: the at least one radiating element, the at least one short side, and the at least one long side having compensation for improved antenna output for improved antenna radiation.

Description:
TECHNICAL FIELD 
     This invention relates to grid array antennas and an integration structure for grid array antennas and refers particularly, though not exclusively, to grid array antennas for use with millimeter wavelength signals, and a structure for the integration of such antennas. 
     BACKGROUND 
     The grid array antenna was first proposed by Kraus in 1964. Since then, there have been some studies conducted but all were at relatively low microwave frequencies.  FIG. 1  shows the basic grid arrangement. It consists of rectangular meshes of microstrip lines on a dielectric substrate backed by a metallic ground plane and fed by a metal via through an aperture on the ground plane. Depending on the electrical length of the sides of the meshes, the grid array antenna may be resonant or non-resonant. 
     For a resonant grid array antenna, the sides of the meshes should be one wavelength by a half-wavelength in the dielectric, and the instantaneous currents would be out of phase on the long sides of the meshes and in phase on the short sides of the meshes, respectively. As a result, the long sides of the meshes behave as microstrip line elements and the short sides act as both radiating and microstrip line elements. The short sides will produce the main lobe of radiation in the boresight direction. 
     For a non-resonant grid array antenna, the length of the short side of the meshes can be slightly more than one-third wavelength and the length of the long side of the meshes should be two times longer but three times shorter than the length of the short side of the meshes in the dielectric. Assuming that it is fed from one end, the currents in the short sides of the meshes follow a phase progression producing the maximum radiation in a backward angle-fire direction. 
       FIG. 2  shows the method of amplitude control through control of microstrip line impedances (or microstrip line widths) to lower the first sidelobe. 
     The grid array antenna has caught considerable attention since the middle of 1990s.  FIG. 3(   a ) to ( c ) show the proposed miniaturized grid array antenna by: 
     (a) “meandering” the long sides of the meshes; 
     (b) dual-linearly-polarized grid array antenna by crossing the meshes; and 
     (c) a circularly-polarized grid array antenna by modifying the short sides of the meshes. 
     In addition, there has been developed a double-layer grid-array antenna. It consists of upper and lower grid array antennas, each being fed from its center terminal to radiate linearly-polarized waves. The upper and lower grid array antennas have the same configuration parameters. The orientation of the lower grid array antenna is rotated by 90° with respect to that of the upper grid array antenna. This perpendicular arrangement provides high isolation at both the center feeding terminals and results in one antenna radiating horizontally-polarized waves and the other antenna radiating vertically-polarized waves. 
     A cross-mesh array antenna is shown in  FIG. 4 . The radiation of circularly-polarized waves results from adding a layer of c-figured elements above the cross-mesh array antenna or feeding it at four terminals with signals of correct phase differences. The feeding terminals are shown in  FIG. 4(   b ). 
     In the past, grid array antennas have been excited for single-ended signals. They may also be excited for differential signals.  FIG. 5  illustrates a differential feeding scheme. One vertical (radiating) side of the center mesh is cut open with one end connected to the positive signal and the other end to the negative signal. 
     Typical antennas for millimeter wavelength signals are reflector, lens, and horn antennas. Reflector antenna technology has achieved the highest level of development for high gain applications. Lens antennas are a second high gain technology; while horn antennas limit gain to about 30 dBi due to construction limitations. Although these antennas all have a high gain, they are not suitable for commercial mm-wave radios because they are expensive, bulky, heavy and, more importantly, they cannot be integrated with solid-state devices. Printed, deposited or etched antenna arrays are used for mm-wave radio systems. 
     It has been proposed to use linearly-polarized mm-wave 60-GHz antenna arrays constructed on multilayer LTCC substrates. These antenna arrays use 4×4 microstrip patch radiating elements fed by a quarter-wavelength matched T-junction network and a Wilkinson power divider network, respectively. The measured results indicate that the antenna array fed by the matched T-junction network performs better than that fed by the Wilkinson power divider. The measured impedance bandwidths are 9.5% and 5.8% and maximum gains are 18.2 dBi and 15.7 dBi, respectively, for the antenna arrays with and without an embedded cavity. 
     Some antenna arrays have achieved wide bandwidth by three major technologies: original antenna element, laminated waveguide and design method to adjust axial ratio of circular polarization. The antenna element has laminated resonator structure formed by filled via-holes and conductive pattern, which generate wide bandwidth characteristics. Measurement results show that the array of 6×8 radiating elements has a sidelobe level less than −15 dB, gain variation less than 1 dB around 19 dBi and axial ratio less than 3 dB over a bandwidth more than 4 GHz. 
     Due to the selection of a microstrip patch and a slot as radiating elements, available antenna arrays require complex feeding networks, sophisticated process techniques, and additional embedded cavities to achieve the required performance. Also, available antenna arrays, if intended to be connected with differential radios, will require a feeding network that would become even more complex. Differential radios are more dominant than single-ended radios in highly-integrated mm-wave radios. Furthermore, the available antenna arrays provide an antenna function to the millimeter-wave radio devices. Hence, one can conclude that the available antenna arrays are yet not suitable for highly-integrated mm-wave 60-GHz radios because of their high cost and lower functionality. 
     It is known that for a resonant grid array antenna the instantaneous currents should be in phase on the short sides of the meshes. As such, the phasing of the radiating elements (short sides of the meshes) is critical.  FIG. 8  shows instantaneous current distribution on the grid array antenna at 60-GHz. It is evident from the figure that the phase synchronism is only realized for the radiating elements between the two bars of dashed lines. Hence, the conventional grid array antenna will not perform well at mm-wave frequencies. Phase compensation schemes must be devised for mm-wave grid array antennas. 
     SUMMARY 
     According to an exemplary aspect there is provided a grid array antenna configured to operate with millimeter wavelength signals, the grid array antenna comprising a plurality of mesh elements and at least one radiation element; each mesh element comprising at least one long side and at least one short side operatively connected to the at least one long side; at least one of:
         the at least one radiating element,   the at least one short side, and   the at least one long side
 
having compensation for improved antenna output for improved antenna radiation.
       

     The compensation may comprise an integrated element being at least one selected from: an inductor, a capacitor, and a resonator. The compensation may comprise a differential feeding network comprising a first terminal and a second terminal. The first terminal and the second terminal may each be operatively connected to an end of the at least one radiating element. The first terminal and the second terminal may be separated by at least a half guided wavelength. The first terminal and the second terminal may be connected at each end of the same radiating element; or the first terminal may be connected to a first radiating element&#39;s inner end, and the second terminal may be connected to a second radiating element&#39;s inner end. The first terminal and the second terminal may be separated by one and a half guided wavelengths. The compensation may comprise a patterned ground plane comprising reflective metal patches aligned with each of the at least one short sides. The at least one long side and the at least one short side may be inclined relative to each other to form mesh elements shaped as a parallelogram. A second grid array antenna may form a second layer parallel to the grid array antenna. The grid array antenna may comprise a wire grid array, and the second grid array antenna may comprise a slot grid array. The wire grid array and the slot grid array may be oriented at a relative rotation of 90° and their short sides may be relatively offset. The second grid antenna array and the grid array antenna may be parasitic of each other. The grid array antenna may further comprise a third layer as a ground plane and fences of vias to provide a cavity-back grid array. A tooth may be provided projecting perpendicularly from each of the at least one short sides and the at least one radiating element. Each of the short sides may comprise one of the at least one radiating element and each of the long sides may comprise a feeding element. 
     According to another exemplary aspect there is provided an adaptive array antenna comprising at least two grid array antennas as described above. the adaptive array antenna may further comprise a DC feeding network operatively connected to a long side of the at least one grid array antenna at an inclined angle. 
     According to a further exemplary aspect there is provided a package comprising at least one grid array antenna as described above, the package comprising four laminated layers; a first layer comprising an antenna layer; a second layer with a first opening; a third layer with a second opening; and a fourth layer with a third opening; the first, second and third opening forming a cavity for a die. 
     The second opening may be larger than the first opening, and the third opening may be larger than the second opening. The first opening, the second opening and the third opening may all be aligned. The package may further comprise an adaptive array antenna as described above. 
     According to yet a further exemplary aspect there is provided a package comprising an adaptive array antenna as described above. 
     According to a penultimate exemplary aspect there is provided a package comprising at least one grid array antenna as described above, the packing comprising three co-fired laminated layers; the three co-fired laminated layers comprising: an antenna layer; a second layer having feeding traces comprising at least one of differential antenna feeding traces, and a single-ended feeding trace; and a third layer comprising a ground of the feeding traces and signal traces. 
     The differential feeding traces may comprise two quasi-coaxial cables cascaded with two striplines, another two quasi-coaxial cables, and vias through two apertures on the ground plane. The feeding traces may be in a GSGSG arrangement. The single-ended feeding trace may comprise a quasi-coaxial cable cascaded with a via through one aperture on the ground plane. The single-ended feeding trace may comprise a GSG arrangement. The package may further comprise an adaptive array antenna as described above. 
     According to a final exemplary aspect there is provided a chip-scale package comprising a system printed circuit board drawing an open cavity in surface thereof for housing and protecting a die mounted therein, the die comprising a package as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be fully understood and readily put into practical effect there shall now be described by way of non-limitative example only exemplary embodiments, the description being with reference to the accompanying illustrative drawings. 
       In the drawings: 
         FIG. 1  is an illustration of a prior art grid array antenna with (a) top view and (b) bottom view; 
         FIG. 2  is an illustration of a prior art grid array antenna with a amplitude control; 
         FIG. 3  is three illustrations of three prior art grid array antennas; 
         FIG. 4  is an illustration of a prior art cross-mesh array antenna and its feeding terminals; 
         FIG. 5  is an illustration of a prior art grid array antenna and its differential feeding system; 
         FIG. 6  is an illustration of a prior art antenna array and its different feeding networks; 
         FIG. 7  is an illustration of a prior art antenna array with (a) its internal structure and (b) antenna element on the first feeding line; 
         FIG. 8  is an illustration of the instantaneous current distribution in a prior art grid array antenna; 
         FIG. 9  is an illustration of an exemplary embodiment with phase compensation using inductors; 
         FIG. 10  is an illustration of an exemplary embodiment using capacitors; 
         FIG. 11  is an illustration of an exemplary embodiment of a 45° linearly-polarized grid array antenna; 
         FIG. 12  is an illustration of an exemplary embodiment of a miniaturized grid array antenna using multiple-layers; 
         FIG. 13  is an illustration of an exemplary embodiment of a circularly-polarized grid array antenna; 
         FIG. 14  is an illustration of (a) a conventional meshed ground plane and (b) an exemplary embodiment of a ground plane; 
         FIG. 15  is an illustration of an exemplary embodiment of a double-layer grid array antenna with (a) wire grid array, (b) slot grid array and (c) cross-section; 
         FIG. 16  is two illustrations of two exemplary embodiments of differential feeding systems; 
         FIG. 17  is an illustration of the instantaneous current distribution in the antenna of  FIG. 16(   b ); 
         FIG. 18  is an illustration of an exemplary adaptive array antenna using exemplary embodiments of grid array antenna elements and as part of a DC feeding network; 
         FIG. 19  is an exploded perspective view of an exemplary grid array antenna with a ball grid array for wire bonding interconnects; 
         FIG. 20  is a close-up view of the antenna feed structure of  FIG. 19 ; 
         FIG. 21  is (a) top and (b) bottom views of an exemplary chip-scale package with dual grid-array antennas; 
         FIG. 22  is a close-up view of the antenna feeding structure of  FIG. 21 ; 
         FIG. 23  is a schematic side view of an exemplary embodiment of a grid-array antenna assembled with a system printed circuit board; 
         FIG. 24  shows the simulated performance of (a) S 11 , (b) gain and (c) radiation pattern for the exemplary embodiment of  FIGS. 19 and 20 ; and 
         FIG. 25  shows the simulated performance for the exemplary embodiment of  FIGS. 21 and 22 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Throughout the description common reference numerals are used for like components with a prefix number being the drawing figure number. 
     With reference to  FIG. 8 , the phase of the radiating elements can be adjusted by changing the electrical length of both long and short sides of the meshes outside the two bars. The phase of both feeding and radiating elements can also be compensated by using phase shifters or amplifiers. For example, inverting amplifiers can be used for compensating both phase and amplitude. An inductor or a capacitor or a resonator can be considered as a passive phase shifter. Except using discrete chip-type inductors, or capacitors, or resonators, it is preferred to use integral elements. The use of integral inductors is shown in  FIG. 9  for a single-layer grid-array antenna  900 . The antenna  900  has elements or meshes  902  with short sides  904  and long sides  912 . One or more of the short sides  904  are radiating elements. One or more of the radiating elements  904  has integral inductors  906  or  908 . The long sides  912  are feeding elements. One or more of the long sides/feeding elements  912  may also have integral inductors  906  or resonators  908 . Multi-layer or stacked inductors may be used. In addition, one or more of the short sides  904  may also be radiating elements. The use of integral capacitors  1010  is shown in  FIG. 10  for a single-layer grid-array antenna  1000 . Again multi-layer or stacked capacitors may be used. 
     The combination of integral inductors  906  and capacitors  1010  shown in  FIGS. 9 and 10  will yield integral resonators. 
     After using an EM simulator to understand the phase conditions of a design the phase adjusters may be added where phases need to be adjusted. 
     In addition to the above-phase compensation, the use of 45° linear polarization may be used in millimeter wavelength car radar applications as radiation with orthogonal polarization from cars coming from the opposite direction does not affect the radar operation.  FIG. 11  shows a 45° linearly-polarized grid array antenna  1100  where the angle between the long sides  1112  and the short sides  1104  of the meshes  1102  is to 45°/135° to form meshes  1102  shaped as a parallelogram. However, other angles may be used as required or desired. 
       FIG. 12  shows a miniaturized grid array antenna  1200  where the long sides  1212  are stepped and the short sides  1204  are bent in a multi-layer metal structure. The bending makes the large part of the short sides  1204  of the meshes  1202  further from the ground plane  1214 , which may improve radiation. The short sides  1204  may be in a first layer  1216 ; and the long sides  1212  may be in two different layers  1218 ,  1220 . The layers  1216 ,  1218  and  1220  may be connected by use of metal lines on the same layer created by, for example, a known printing technique. Metal lines on different layers may be connected by using metal vias. 
       FIG. 13  shows circularly-polarized grid array antenna  1300 . Each short side  1304  and radiating element  1305  of a mesh  1302  has an added tooth  1322 . Each tooth  1322  extends generally perpendicularly to the short side  1304  and radiating element  1305 . All teeth  1322  are oriented in the same direction relative to the respective short side  1304  and radiating element  1305 . The position of the tooth  1322  means that the current on the tooth has a 90° phase difference with respect to the current on the short side  1304  or radiating element  1305  to which the tooth  1322  is connected. The width of the tooth  1322  can be adjusted so that the current on the tooth has the same amplitude as that on the short side  1304  or radiating element  1305  to which the tooth  1322  is connected. Each tooth  1322  may be of a length of about a quarter guided wavelength of half length of the short side  1304 . The grid array antenna  1300  shown in  FIG. 13  gives right-hand circular polarization. Rotating the teeth  1322  180° relative to the respective short sides  1304  and radiating elements  1305  will produce left-hand circular polarization. 
     A grid array antenna usually uses a solid, flat ground-plane. It has been proposed that the ground plane may be curved or corrugated; or may be a screen or a grid with holes or perforations whose peripheral length is less than one-half wavelength. Preferably, the holes have a peripheral long that is much less than one-half wavelength. The meshed ground plane required for mechanical reliability is structurally similar to a perforated ground plane. A prior art meshed ground plane shown in  FIG. 14   a . It shifts the resonant frequency downward, expands the impedance bandwidth, and decreases the antenna gain. The exemplary patterned ground plane shown in  FIG. 14   b  shifts the resonant frequency downward and expands the impedance bandwidth with a reduced penalty in antenna gain penalty. This is because the short sides  1404  of the meshes  1402  are radiating elements. Metal patches  1424  are added to the meshed ground plane  1414  under the short sides  1404  to act as reflectors so that the backward leakage field can be reduced. As a result, the antenna gain penalty is reduced. 
     Antennas in multi-layer structures have a size advantage. However, known double-layer grid array antennas do not fully offer this advantage because the upper and lower grid array antennas have the same configuration parameters. However, the lower grid array antenna is rotated by 90° with respect to that of the upper grid array antenna.  FIG. 15  shows a two-layer grid-array antenna  1500  having an upper layer  1526  containing a wire grid array radiating element  1528 ; and a lower layer  1530  with a slot grid array radiating element  1532 . A third layer  1514  functions as the reflector. The lower layer  1530  also functions as the ground plane for the wire grid array radiating element  1528  as a wire grid array antenna. The reflector  1514  works with the lower slot grid array radiating element  1532  as a slot grid array antenna. Furthermore, a quasi-cavity is formed under the slot grid array radiating element  1532  by connecting the ground on the lower layer  1530  to the bottom reflector layer  1514  with fences of vias  1534 . This gives a cavity-back slot grid array antenna. The upper wire grid array  1528  and lower slot grid array  1532  antennas are parasitic to each other. The polarization of the double-layer grid antenna  1500  depends on the mutual orientation. For the orientation shown in  FIG. 15 , both wire  1528  and slot  1532  grid array antennas radiate the same linearly-polarized wave. However, if either wire  1528  or slot  1532  grid array rotates by 90° and if the short sides  1504  of the meshes  1502  of both wire  1528  and slot  1532  grid arrays are offset as if there was no offset, the radiation of slot grid array would be blocked by the wire grid array. Offset may also enhance the radiation of the wire grid array antenna as less radiation may be leak to the quasi-cavity. As such one radiates the linearly-horizontally-polarized waves and the other radiates linearly-vertically-polarized waves. No offset will deteriorate the radiation. Angles other than 90° may be used as required or desired. 
     As shown in  FIG. 5 , known differential feeding structures cut the center radiating element  505 . The two feeding terminals are close, so the isolation is poor. Also the excitation efficiency is not good.  FIG. 16  shows two differential feeding terminal locations. In  FIG. 16(   a ) the differential feeding terminals  1636  are connected to each end of the central radiating element  1605  and are a half guided wavelength apart. In  FIG. 16(   b ) the differential feeding terminals  1638  are connected to the wider ends of two different radiating elements  1605  and are one-and-half guided wavelengths apart. The two terminals  1636  or  1638  are separated by at least a half guided wavelength. As such, the isolation is good, and so is the excitation efficiency. 
       FIG. 17  shows the instantaneous current distribution on a grid array antenna  1700  fed for differential operation according to  FIG. 16(   b ). Differential feeding results in a better phase synchronism among more mesh elements  1702 . 
     The grid array antenna can be used as a basic element to design an adaptive array antenna or a switched beam array antenna.  FIG. 18  illustrates the use of grid array antenna elements  1800  for an adaptive array antenna for use in, for example, highly-integrated radios. The grid array antenna elements  1800  have a wider impedance bandwidth and are also suitable to be DC-coupled. For example, the DC signals can be easily supplied from the middle of the long sides  1812  of the meshes  1802  as shown in  FIG. 18 . The DC lines  1840  should have high impedance to high-frequency signals; and are preferably inclined relative to the long sides  1812  to minimize the effect on the antenna radiation. The angle of inclination should be in the range 40° to 50°. 
     A first way of integration of the grid array antenna  1900  in a ball grid array  1968  package for wire-bonding interconnect is shown in  FIGS. 19 and 20 . The package features standard wire bonding and there are four laminated layers for the package. The first layer  1950  is the antenna layer with the antenna being underneath and therefore is not shown. The ground plane  1914  is shown as is a feed via  1964  for the antenna feed. The second layer  1952  has an opening  1954  and, the third layer  1956  has a slightly larger opening  1958 . The fourth layer  1960  has the largest opening  1962 . The three openings  1954 ,  1958  and  1962  are all aligned. The traces of the second layer  1952  and the third layer  1956  are not shown. The openings  1954 ,  1958  and  1962  form a three-tier cavity that can house the radio die. 
     There are also five metallic layers for the package. A first layer provides the grid array antenna  1900 , the second layer is for the partly meshed antenna ground plane  1914 , and the next two metal layers are in the second and third layers  1952 ,  1956  with one being for the antenna feeding traces and the other for signal traces. The final metal layer is for the package ground plane  1970 , as well as being for solder ball pads  1968 . 
     Another way of integration of dual grid array antennas  2100  (one antenna  2100  for transmission and the other antenna  2100  for reception) in a chip-scale package for flip-chip bonding is shown in  FIG. 21 . There are three co-fired laminated layers for the package. The top antenna layer  2172  is a single layer and the bottom layer  2174  contains two laminated layers. There are also four metallic layers for the package. The top layer  2172  has the dual grid array antennas  2100  and the patterned ground plane  2114 . The second layer  2174  has the differential antenna feeding traces  2176 , and the single ended feeding trace  2178 ; and the third layer has the ground of the antenna feeding traces, and the signal traces (not shown). The die is flip-chip bonded to the signal traces. 
       FIG. 22  shows the feeding networks of the dual grid array antennas  2100 . For the dual-feed trace  2126 ,  FIG. 22(   a ) shows two quasi-coaxial cables cascaded first with two striplines, then another two quasi-coaxial cables, and finally vias through two apertures on the ground plane in a GSGSG arrangement. For the single-feed trace  2178 ,  FIG. 22(   b ) shows a quasi-coaxial cable cascaded with via through one aperture on the ground plane in a GSG arrangement. The GSG and GSGSG arrangements not only minimize potential electromagnetic interference but also improve the feeding performance. The GSG and GSGSG feeding networks are designed together with the grid array antenna  2100 . 
       FIG. 23  illustrates the assembling the antenna in a chip-scale package with the system printed-circuit board (PCB)  2380 . An open cavity  2382  is formed in the top surface  2384  of the PCB  2380  to house and protect the die  2386 . The lands  2388  on the chip package  2390  are soldered to the PCB  2380  to complete the interconnects from the chip package  2390  to the PCB  2380  through the package  2390 . 
     The wire-bonding technique is well established in consumer electronics. A bond wire functions as a series inductor which will drastically increase the loss as the frequency or the length are increased. Interconnection using the flip-chip technique has better performance than using the wire-bonding technique because the bump height is kept smaller than the length of the bond wire and the bump diameter is thicker than that of the bond wire. 
     Although both resonant and non-resonant grid array antennas are useful for many applications, the disclosed resonant grid array antenna is for millimeter wavelength signals. The design determines the dielectric substrate dimensions, the number of meshes, the microstrip line impedances, and the excitation location with the associated diameters of the metal via and the aperture. The grid array antennas may operate maybe, for example, 61.5 GHz with a maximum gain of ≧10 dBi. The impedance and radiation bandwidth is 7 GHz. The efficiency may be ≧80% for IEEE 802.15.3c standard applications. 
       FIGS. 24 and 25  show the simulated performance of the two examples of  FIGS. 19 and 21 . 
     Whilst there has been described in the foregoing description exemplary embodiments, it will be understood by those skilled in the technology concerned that many variations in details of design, construction and/or operation may be made without departing from the present invention.