Abstract:
A method of manufacturing an antenna comprising: providing a millimeter wave (MMW) antenna attached to a signal pad on an integrated circuit mounted on a substrate, and adjusting one or more parameters of the antenna to conform to predetermined desired thresholds, levels or ranges, wherein the adjustment is selected from the group consisting of: locating a conducting or dielectric object at a desired tuner location in proximity to the antenna to tune the central signal frequency, locating a conducting reflector at a desired reflector location in proximity to the antenna to tune the radiation direction or pattern, and selecting a conducting patch or object as a radiator/detector element to modify the bandwidth. Also a millimeter wave (MMW) antenna.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Singapore Patent Application 200907908-8 filed in the Singapore Patent Office on Nov. 25, 2009, the entire contents of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a millimeter wave (MMW) antenna and a method of manufacturing an antenna, particularly though not solely to tuning the central signal frequency, radiation direction/pattern and/or the bandwidth of a directional bond wire antenna, patch antenna or box/polygon antenna. 
     BACKGROUND 
     In most communications system the antenna is a very important part of the design. In MMW communications systems, the antenna may be very small due to the short wavelength. For such a small size antenna, high radiation efficiency and high coupling efficiency may be important considerations. 
     A MMW antenna is often made on a printed circuit board (PCB) or other solid substrate. Prior art PCB substrates may have a high loss factor for MMW and hence the radiation efficiency of an antenna built on this kind of substrate may be less than optimal. 
     One possible improvement is to use special processing on low loss material such as MicroElectroMechanical Systems (MEMS) processing on glass (alumina). However this may involve complex processing and high cost. 
     The coupler from the IC die to the substrate where the antenna is, may also cause loss. Although the antenna may be located on the IC die (on-chip antenna) to avoid some coupling loss and reduce the size, the radiation efficiency of an on-chip antenna may very low due to the high loss tangent of the IC die. 
     Another approach is using a bond wire on the signal port on the IC die and design the wire&#39;s length and shape so that the bond-wire works as an antenna. Because the bond wire is over air, the loss of the IC die and PCB substrate has little effect to the antenna. Such an antenna is called bond-wire antenna (BWA). 
     SUMMARY OF THE INVENTION 
     In general terms the invention proposes to tune a MMW antenna by 
     locating a conducting or dielectric object at a desired tuner location in proximity to the antenna to tune the central signal frequency, 
     locating a conducting reflector at a desired reflector location in proximity to the antenna to tune the radiation direction or pattern and/or to increase the bandwidth, and/or 
     selecting a conducting patch or object as a radiator/detector element to modify the bandwidth. 
     This may have the advantage(s) that:
         the antenna structure may be simple,   the cost of the antenna may be low,   the system implementation may be easy,   frequency and radiation pattern tuning mechanism may be more practical and flexible for the real system and application,   both differential feeding and single ended feeding may be used,   bandwidth may be &gt;15 GHz in case of 60 GHz central signal frequency,   bandwidth may be further widened to 30 GHz by adding a reflector,   bandwidth for the patch antenna with reflector may be 40 GHz in case of 60 GHz central signal frequency,   central signal frequency of the antenna may be tunable by a frequency tuner, and/or   radiation direction/pattern may be tunable by a reflector.       

     In a first particular expression of the invention there is provided a method of manufacturing an antenna as claimed in claim  1 . 
     In a second particular expression of the invention there is provided a MMW antenna as claimed in claim  21 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more example embodiments of the invention will now be described, with reference to the following figures, in which: 
         FIG. 1(   a ), is a schematic diagram of a single fed BWA according to a first example embodiment; 
         FIG. 1(   b ), is a schematic diagram of a differential fed BWA according to a second example embodiment; 
         FIG. 2 , is a schematic diagram of a differential fed BWA with cylindrical frequency turner according to a third and a forth example embodiment, 
         FIG. 3(   a ), is a graph of return loss (S 11 ) for the third example embodiment of  FIG. 2 , 
         FIG. 3(   b ), is a graph of return loss (S 11 ) for the forth example embodiment of  FIG. 2 , 
         FIG. 4 , is a schematic diagram of a single-end fed BWA with triangular dielectric tuner according to a fifth example embodiment, 
         FIG. 5 , is a graph of return loss (S 11 ) for the fifth example embodiment in  FIG. 4 , 
         FIG. 6(   a ), is a graph of the radiation pattern for the first example embodiment of  FIG. 1(   a ), 
         FIG. 6(   b ), is a graph of the return loss for the first example embodiment of  FIG. 1(   a ), 
         FIG. 6(   c ), is a graph of the radiation pattern for the second example embodiment of  FIG. 1(   b ), 
         FIG. 6(   d ), is a graph of the return loss for the second example embodiment of  FIG. 1(   b ), 
         FIG. 7 , is a schematic diagram of a single-end fed BWA according to a sixth example embodiment with a reflector pasted in a first location, 
         FIG. 8(   a ), is a graph of the radiation pattern for the sixth example embodiment of  FIG. 7 , 
         FIG. 8(   b ), is a graph of the return loss for the sixth example embodiment of  FIG. 7 , 
         FIG. 9 , is a schematic diagram of a single-end fed BWA according to a seventh example embodiment with a reflector pasted in a second location, 
         FIG. 10(   a ), is a graph of the radiation pattern for the seventh example embodiment of  FIG. 9 , 
         FIG. 10(   b ), is a graph of the return loss for the seventh example embodiment of  FIG. 9 , 
         FIG. 11(   a ), is a schematic diagram of a single-end fed triangle patch antenna (metal box) according to an eight example embodiment, 
         FIG. 11(   b ), is a graph of the return loss for the eighth example embodiment of  FIG. 11(   b ), 
         FIG. 12(   a ), is a schematic diagram of a single-end fed triangular patch antenna (2-layer ceramic PCB box) according to a ninth example embodiment, 
         FIG. 12(   b ), is a graph of the return loss for the ninth example embodiment of  FIG. 12(   b ), 
         FIG. 13(   a ), is a schematic diagram of a differential fed triangular patch antenna (2-layer ceramic PCB box) according to an tenth example embodiment, 
         FIG. 13(   b ), is a graph of the return loss for the tenth example embodiment of  FIG. 13(   b ), 
         FIG. 14(   a ), is a schematic diagram of a differential fed triangular patch antenna (metal box) according to an eleventh example embodiment, 
         FIG. 14(   b ), is a graph of the return loss for the eleventh example embodiment of  FIG. 14(   b ), 
         FIG. 15(   a ), is a schematic diagram of a single-end fed triangle patch antenna (metal box) with reflector according to an twelfth example embodiment, 
         FIG. 15(   b ), is a graph of the return loss for the twelfth example embodiment of  FIG. 15(   b ), 
         FIG. 15(   c ), is a graph of the radiation pattern for the twelfth example embodiment of  FIG. 15(   b ), 
         FIG. 16(   a ), is a schematic diagram of 6-side metal polygon antenna according to an thirteenth example embodiment, 
         FIG. 16(   b ), is a graph of the return loss for the thirteenth example embodiment of  FIG. 16(   b ), 
         FIG. 16(   c ), is a graph of the radiation pattern for the thirteenth example embodiment of  FIG. 16(   b ), 
         FIG. 17  is a photo of a prototype of the seventh embodiment, 
         FIG. 18  is a graph of the measured performance of the prototype in  FIG. 17 , and 
         FIG. 19  is a photo of a prototype of the eighth example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description a number of embodiments are described for tuning or adjusting a MMW antenna. These adjustments would normally occur during manufacturing but might also occur during installation, maintenance or retrofitting to improve performance of an existing antenna. Once the adjustments have been made the antenna may either be left as adjusted or encapsulated in dielectric or resin to prohibit further movement of the components (in this case the components would be sized according to the wavelength in that dielectric and a compensation made in the tuning process). The adjustments may be categorised into: 
     a. tuning of the central signal frequency, 
     b. tuning of the radiation direction/pattern, and 
     c. modifying the bandwidth. 
       FIGS. 1(   a ) and  1 ( b ) show a MMW antenna according to the first and second example embodiments. In the first and second example embodiments the antenna is a BWA surrounded by air. In  FIG. 1(   a ) the antenna  100  according to the first example embodiment is a single-end feed BWA. There are two bond wires  102 , 104  attached to two small bond pads (0.1 mm×0.1 mm)  106 ,  108  on a PCB substrate  110 . An integrated circuit  112  is mounted on a ground plane  114  which in turn is mounted on the substrate  110 . The ground plane  114  only extends to the edges of the integrated circuit  112 , although the size of the ground plane may be bigger eg: greater than two wavelengths wide and greater than one wavelength long. The ground plane is grounded via bond wires attached to a ground pad on the integrated circuit  112 . The other ends of the bond wires  102 , 104  are commoned together and connected to a signal pad  116  on the integrated circuit  112 . The bond wires are arranged orthogonally (although anywhere from an angle of 60 to 120 degrees is possible), and are approximately a quarter wavelength at the central signal frequency. The single-end fed BWA  100  works as a monopole antenna with two arms. The wires are generally oriented in a straight line. 
     In  FIG. 1(   b ) the antenna  120  according to the second example embodiment is a differential fed BWA. There are two longer bond wires  122 , 124  attached to two small distant bond pads  126 , 128  mounted on a PCB substrate  130 , and two shorter bond wires  132 , 134  attached to two small closer bond pads  136 , 138 . The two longer bond wires  122 , 124  are about three quarter wavelength and the two shorter bond wires  132 , 134  are about quarter wavelength. Again an integrated circuit  142  is mounted on a ground plane  144  which in turn is mounted on the substrate  130 . The ground plane ground plane  144  only extends to the edges of the integrated circuit  142 . The other ends of the longer bond wires  122 , 124  are commoned together and connected to a first signal pad  146  on the integrated circuit  142 . The other ends of the shorter bond wires  132 , 134  are commoned together and connected to a second signal pad  148  on the integrated circuit  142 . The differential fed BWA  120  works as a J-pole antenna with two arms in positive and negative ports, respectively. 
     Because the two-wire design, the BWAs&#39;  100 ,  120  bandwidth may be enlarged. For example, the differential fed BWA  120  according to the second example embodiment may have a bandwidth of 15 GHz at a central signal frequency of 60 GHz (relative bandwidth &gt;25%). 
     A possible problem for the BWA  100 ,  120  of the first and second example embodiments may be that the wire bond geometry may make it difficult to consistently manufacture an antenna with parameters within a small tolerance, especially when bonding wires are manually bonded. In certain applications it may be useful for the central signal frequency and/or radiation beam pattern to be within a predetermined tolerance. 
     Tuning of the Central Signal Frequency 
     Depending on the application it may be desirable to modify the central signal frequency. Accordingly,  FIG. 2  shows a differential feeding BWA  200  with frequency tuner  218  according to the third and forth example embodiments. The central signal frequency can be tuned by approaching a dielectric cylinder  218 ( b ) between the two wires  202 , 204  from far to the feeding point  216  according to the third example embodiment. In this case, the resonant frequency or central signal frequency of the antenna becomes lower. The cylinder may have a diameter of 0.3 mm and height of 0.3 mm, with dielectric constant  10  and loss tangent 0.001. 
     Alternatively, a metal cylinder  218 ( a ) according to the forth example embodiment approaches to the feeding point can make the antenna resonant frequency higher. The cylinder may be a hollow copper cylinder, with the same size as the dielectric cylinder. 
       FIG. 3  shows the return loss of the BWA with cylinder tuner according to the third and forth example embodiments. In  FIG. 3(   a ) the central signal frequency  300  becomes lower with the distance between a dielectric cylinder  218 ( b ) and feeding point  216  reducing. In  FIG. 3(   b ) the BWA central signal frequency  302  increases with the distance between a metal cylinder  218 ( a ) and the feeding point  216  reducing. 
     In order to tune the antenna  200  according to the third or forth example embodiments, the cylinder  218  is located in various positions and the central signal frequency is tested until it is within the desired range. The cylinder  218  is then fixed in place by pasting it on the substrate  230 . 
       FIG. 4  shows a single-ended BWA  400  with frequency tuner  418  according to a fifth example embodiment. The central signal frequency may be more significantly changed by using a triangular dielectric tuner  418 . 
       FIG. 5  shows the return loss of the BWA  400  with triangular tuner  418  according to the fifth example embodiment. The central signal frequency  500  becomes lower when the triangular dielectric tuner  418  approaches to the feeding point  416 . 
     Again in order to tune the antenna  400  according to the fifth example embodiment, the triangular dielectric tuner  418  is located in various positions and the central signal frequency is tested until it is within the desired range. The cylinder  418  is then fixed in place by pasting it on the substrate  430 . 
     Alternatively if the wires are encapsulated in resin the central frequency may be tuned after encapsulation. One method of doing this would be to drill a hole in the resin, where the significance of the hole would be used in tuning, eg: the deeper or wider the hole, the higher the central signal frequency. 
     Tuning of the Radiation Direction/Pattern 
       FIG. 6(   a ) to  FIG. 6(   d ) show the radiation pattern and return loss of the first and second example embodiments. The maximum gain directions  600 , 602  and  604 , 606  are two diagonal directions (approximately about x=y and x=−y or 45 and 135 degrees from the x axis) in the PCB substrate plane (x,y plane, z=0). 
     Depending on the application it may be desirable to modify the radiation direction or pattern. According to the sixth example embodiment  700  shown in  FIG. 7 , a reflector  718  is positioned at a first location  720  on the back side of a PCB substrate  710 . The reflector is floating and may be copper. The reflector  718  may be greater than two wavelengths wide and greater than one wavelength long. The first location  720  is about in line with the back side of the integrated circuit distant from the signal pad. The substrate may for example be 0.625 mm thick. If the reflector is designed within the near field of the antenna, it may be used to effect the radiation pattern and the bandwidth. 
       FIG. 8(   a ) shows the radiation pattern  800  change by introducing the reflector  718  in this first location  720 . The maximum radiation directions are still two diagonal directions (approximately about x=y and x=−y or 45 and 135 degrees from the x axis) however the radiation is much more uniform becoming more omnidirectional in the positive y direction. 
       FIG. 9  shows another reflector  918  located at second location  920  approximately around the bond pads  906 , 908  underneath the substrate  910 . to change the radiation direction according to the seventh example embodiment  900 . The second location  920  is adjacent a front side of the integrated circuit proximate from the signal pad. 
       FIG. 10(   a ) shows that the maximum radiation direction may be modified to the vertical direction (z-axis)  1000  and forward direction (y-axis)  1002  if the reflector  918  is at the second location  920 . Also as shown in  FIG. 10(   b ) the reflector  918  underneath under the BWA  900 , the BWA signal bandwidth  1004  can be enlarged to as much as 30 GHz at a 60 GHz central signal frequency (relative bandwidth &gt;50%). 
     Modifying the Bandwidth 
     Depending on the application it may be desirable to modify the bandwidth. For example metal patches as the radiation element may be used to increase the bandwidth. 
       FIG. 11(   a ) shows an antenna  1100  according to the eighth example embodiment with a single-end fed  1116  triangle patch/metal box  1118  as the radiator/detector element.  FIG. 11(   b ) shows the bandwidth  1130  achieved is 20 GHz. 
     The box  1118  is a hollow metal box made from copper. The box  1118  is 1.1 mm wide and 0.6 mm long with a height of 0.3 mm. In plan view it may be an isosceles triangle, with the two equal angles being less than 60 degrees, for example 30 degrees. The feed  1116  is attached to the adjacent apex of the two equal short sides and the long unequal side is distant from the feed  1116 . The apex is spaced approximately 50 microns from the integrated circuit. The box  1118  is attached to the substrate and the integrated circuit is attached to a ground plane on the substrate. 
       FIG. 12(   a ) shows an antenna  1200  according to the ninth embodiment with a single-end fed  1216  triangular patches  1218 , 1219  as the radiator/detector element separated by a 2-layer ceramic box  1220 .  FIG. 12(   b ) shows the bandwidth  1230  achieved is 20 GHz. 
     The patches  1218 , 1219  are 0.7 mm wide and 0.38 mm long. In plan view they may be an isosceles triangle, with the two equal angles being less than 60 degrees, for example 30 degrees. The feed  1216  is attached to the adjacent apex of the two equal short sides of the top patch  1218  and the long unequal side is distant from the feed  1216 . The apex is spaced approximately 50 microns from the integrated circuit. The bottom patch  1219  is attached to the substrate and the integrated circuit is attached to a ground plane on the substrate. The ceramic box  1220  is 1 mm long, 3 mm wide and 0.254 mm high. The ceramic box may be made from quart with a dielectric constant of 9.1 and a loss factor of 0. 
       FIG. 13(   a ) shows an antenna  1300  according to the tenth embodiment with a differential fed  1316  triangular patches  1318 ,  1319 ,  1320 ,  1321  as the radiator/detector element separated by a 2-layer ceramic PCB box  1322 .  FIG. 13(   b ) shows the bandwidth  1330  achieved is 10 GHz. 
     The patches  1318 ,  1319 ,  1320 ,  1321  are 1.475 mm wide and 0.95 mm long. The are spaced 50 micron from each other and from the integrated circuit. In plan view they may be an isosceles triangle, with the two equal angles being less than 60 degrees, for example 30 degrees. The feed  1316  is attached to the adjacent corner of the two the top patches  1318 , 1320  and the apex of all of the patches  1318 ,  1319 ,  1320 ,  1321  is distant from the integrated circuit. The ceramic box  1322  may be the same as in the ninth embodiment. 
       FIG. 14(   a ) shows an antenna  1400  according to the eleventh embodiment with a differential fed  1416  double triangular patch antenna (metal box)  1418 , 1419  as the radiator/detector element. The geometry and orientation of the boxes  1418 , 1419  may similar to the patches  1318 ,  1319 ,  1320 ,  1321  in the tenth embodiment except with a height of  FIG. 14(   b ) shows the bandwidth  1430  achieved is 15 GHz with another band of 20 GHz at a higher frequency. 
       FIG. 15(   a ) shows an antenna  1500  according to the twelfth embodiment with a single-end fed  1516  triangle patch (metal box)  1518  as the radiator/detector element with a reflector  1520  in the second location  1522 .  FIG. 15(   b ) shows the bandwidth  1530  achieved is 40 GHz. The box is similar to that in the eighth embodiment and the reflector is similar to that the seventh embodiment. 
       FIG. 16  shows an antenna  1600  according to the thirteenth embodiment with a single-end fed  1616  6-side metal polygon  1618  as the radiator/detector element.  FIG. 16(   b ) shows the bandwidth  1630  achieved is 40 GHz. The 6-side metal polygon  1618  may be designed such that each pair of symmetrical sides contributes one of resonant frequencies. Thus the lengths of the sides of each pair may be adjusted, so that the 3 resonant frequencies can be aligned to be close but still different from each other so that the bandwidths overlap. In this way a desired central frequency can be achieved concurrently with an enlarged bandwidth. 
       FIG. 17  shows a prototype  1700  of the seventh example embodiment and 
       FIG. 18  shows the performance  1800  of the prototype  1700 . 
       FIG. 19  shows a prototype  1900  of the eighth example embodiment. 
     While example embodiments of the invention have been described in detail, many variations are possible within the scope of the invention as will be clear to a skilled reader.