Patent Publication Number: US-7907091-B2

Title: Antennas

Description:
TECHNICAL FIELD 
     This invention relates to antennas and refers particularly, though not exclusively, to patch and microstrip antennas suitable for in-package use and having an improved bandwidth. 
     BACKGROUND 
     Driven by growing pressure to lower cost and to shrink physical volume, various microstrip antennas for antenna-in-package designs (“AiP”) have been developed in the past few years for portable wireless radio transceivers. These include AiP designs:
         (a) suitable for multi-chip solutions for wireless radio transceivers;   (b) with both active and parasite microstrip patch antennas suitable for multi-chip solutions for wireless radio transceivers;   (c) with a microstrip patch antenna suitable for multi-chip solutions for wireless radio transceivers;   (d) with a microstrip patch antenna suitable for single-chip solutions for wireless radio transceivers;   (e) using an inverted-F antenna suitable for multi-chip solutions for wireless radio transceivers; and   (f) using an inverted-F antenna for multi-chip solutions for wireless radio transceivers.       

     The existing AiP designs have serious drawbacks:
         (1) AiP designs using microstrip patch antennas can have fractures and warping if they are implemented in low temperature, co-fired ceramic (“LTCC”) technology;   (2) AiP designs using inverted-F antennas have to two-dimensionally integrate with multi-chip radios. As such they need a larger footprint on printed circuit boards (“PCB”); and   (3) they are designed for single-ended signal operation requiring complex conversion circuits to link to highly-integrated radios where differential signal operation is preferred.       

     SUMMARY 
     An antenna on a substrate, the antenna being symetrical about a central longitudinal axis of symmetry, the antenna comprising a first portion that is substantially rectangular, a second portion that is substantially rectangular, the first portion and the second portion being spaced from each other and being operatively connected by an intermediate portion. 
     The first portion may comprise a first sub-portion and a second sub-portion, the first sub-portion and the second sub-portion being spaced apart and being aligned on an axis perpendicular to the axis of symmetry. The first sub-portion and the second sub-portion may be separated by a capacitive portion of the antenna. The intermediate portion may be operatively connected to both the first sub-portion and the second sub-portion. The capacitive portion may extend into the first portion from an outer edge of the first portion to form the first sub-portion and the second sub-portion. 
     The intermediate portion may be substantially parallel to the axis of symmetry, and substantially perpendicular to both the first portion and the second portion. The first portion and the second portion may be substantially identical. 
     The antenna may be a stripline antenna; and the first portion, the second portion and the intermediate portion may comprise a ribbon radiating element. The capacitive portion may comprise two first elements, the two first elements being parallel, spaced apart, and both being parallel to the axis of symmetry. A first feed line for the antenna may be operatively connected to one of the two first elements. A second feed line may be operatively connected to a second of the two first elements. 
     The intermediate portion may comprise two intermediate elements being spaced apart from each other, parallel to each other, and parallel to the axis of symmetry. 
     The first portion and the second portion may each comprise:
         an outer edge element,   end elements at and operatively connected to each end of the outer edge elements,   each end element extending substantially perpendicularly to the outer edge element; and   inner edge elements operatively connected to the end elements and extending substantially perpendicularly to the end elements.       

     The two intermediate elements may intersect and may be operatively connected to each inner edge element; and each inner edge element may have a gap therein extending between the two intermediate elements. A spacing of the two intermediate elements may be less than a spacing of the end elements of the first portion and the end elements of the second portion. The outer edge element of the first portion may have an opening therein aligned with and of the same transverse length as the spacing of the two first elements. 
     The antenna may further comprise a projection element extending into the second portion from the outer edge element of the second portion. The projection element may have a void therethrough, the void being centered on the axis of symmetry. The projection element may extend inwardly from the outer edge element of the second portion such that an inner end of the projection elements is substantially aligned with an inner edge of the inner edge element of the second portion. 
     The second portion may comprise a third sub-portion and a fourth sub-portion, the third sub-portion and the fourth sub-portion being spaced apart and being aligned on an axis perpendicular to the axis of symmetry. The third sub-portion and the fourth sub-portion may be separated by the projection element. The intermediate portion may be operatively connected to both the third sub-portion and the fourth sub-portion. The projection element may extend into the second portion from the outer edge element of the second portion to form the third sub-portion and the fourth sub-portion. 
     The ribbon radiating element may be of substantially constant width along its length. 
     The first elements may extend inwardly from the outer edge element of the first portion such that an inner end of each of the first elements is substantially aligned with an outer edge of the inner edge element of the first portion. 
     The antenna may further comprise a ground plane having two holes for the first feed line and the second feed line, the first and second feed lines passing through the substrate from the first elements to the ground plane. Alternatively, the antenna may further comprise a ground plane having a hole for the first feed line, the first feed line passing through the substrate from the first element to the ground plane. 
     The antenna may further comprise a dielectric material on the substrate, the antenna being formed in a manner selected from: on the dielectric material, and in the dielectric material. 
     The first portion, second portion and intermediate portion may comprise a driven element. The driven element may be outside a ribbon of exposed dielectric material. The antenna may further comprise parasitic elements within the ribbon of exposed dielectric material, the parasitic elements being operatively connected to the driven elements by capacitive coupling. 
     According to a second aspect there is provided an antenna-in-package comprising the antenna described above. The antenna-in-package may further comprise a semiconductor chip mounted beneath the ground plane; the semiconductor chip having connects that are operatively connected to at least one of: the first feed line, and the first and second feed lines. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be clearly 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 a top view of an exemplary embodiment; 
         FIG. 2  is a vertical cross section along the lines and in the direction of arrows  2 - 2  on  FIG. 1 ; 
         FIG. 3  is a top view of another exemplary embodiment; 
         FIG. 4  is a vertical cross section along the lines and in the direction of arrows  4 - 4  on  FIG. 3 ; 
         FIG. 5  is a top view of a further exemplary embodiment; 
         FIG. 6  is a vertical cross section along the lines and in the direction of arrows  6 - 6  on  FIG. 5 ; 
         FIG. 7  is a top view of an exemplary ground plane; 
         FIG. 8  is a top view of another exemplary ground plane; 
         FIG. 9  is a top view of an exemplary integration of the antenna of  FIGS. 3 and 4  in an AiP; 
         FIG. 10  is a bottom view of the exemplary integration of the antenna of  FIG. 9 ; 
         FIG. 11  is an exploded bottom view of the exemplary integration of the antenna of  FIGS. 9 and 10 ; 
         FIG. 12  is an exploded bottom view of the exemplary integration of the antenna of  FIGS. 9 and 10  but for dual feed; 
         FIG. 13  is a side view of the exemplary integration of the antenna of  FIG. 12 ; 
         FIG. 14  is an illustration of the antenna feeding network for the embodiment of  FIG. 12 ; 
         FIG. 15  is a graph of the S 11  of the embodiment of  FIGS. 1 and 2 ; 
         FIG. 16  is a top view of a penultimate exemplary embodiment; 
         FIG. 17  is a vertical cross-section along the lines and in the direction of arrows  17 - 17  on  FIG. 16 ; and 
         FIG. 18  is a vertical cross-sectional view corresponding to  FIG. 1  but of a final exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     The exemplary embodiments have new radiating elements and new ground-plane structures, and new integration with AiP designs in LTCC technology. The antennas described and illustrated may be used as stand-alone antennas and/or may be integrated into AiP designs in a two or three dimensional manner. They may be used for single and multi-band applications. 
     In the market, there are several LTCC material systems. For example, there are those of E. I. DuPont Nemours and Co of Wilmington, Del., USA as shown in Table 1: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 PROPERTY 
                 VALUE 
               
               
                   
                   
               
             
            
               
                   
                 Thickness 1) 
                   
               
               
                   
                 951-AX 
                 205 μm 
               
               
                   
                 951-A2 
                 130 μm 
               
               
                   
                 951-AT 
                  90 μm 
               
               
                   
                 951-C2 
                  40 μm 
               
               
                   
                 Dielectric constant 
                 7.8 (10 MHz) 
               
               
                   
                 Dissipation factor 
                 0.15% (10 MHz) 
               
               
                   
                 Insulation resistance 
                 &gt;10 12 Ω(100 VDC) 
               
               
                   
                 Breakdown voltage 
                 &gt;1000 V/25 μm 
               
               
                   
                 Colour 
                 blue 
               
               
                   
                 Thermal conductivity 
                 3 W/mK 
               
               
                   
                 Thermal expansion 
                 5.8 ppm/K (25 . . . 300° C.) 
               
               
                   
                 Fired density 
                 3.1 g/cm 3   
               
               
                   
                 Flexural strength 
                 320 Mpa 
               
               
                   
                   
               
            
           
         
       
     
       FIGS. 1 and 2  show an exemplary embodiment of a stripline antenna  8  that has a ribbon radiating element  10  mounted on or in a dielectric material  11 , all on a substrate  12 . The dielectric material  11  may be an LTCC material, liquid crystal polymer, or any other suitable dielectric material. The substrate  12  may be of any suitable material. The ribbon radiating element  10  is a conductive metal such as, for example, copper. 
     The ribbon radiating element  10  is symmetrical about a central, longitudinal axis of symmetry  14 . On each side of, and parallel to, the axis of symmetry  14  are two first elements  16  that are parallel to each other and spaced apart. The two first elements  16  form the capacitive portion of the antenna  8 , the remainder of the ribbon radiating element  10  forming the inductive portion of the antenna  8 . Feed to the radiating element  10  is at a feed connection  18  in one of the first elements  16 . 
     The ribbon radiating element  10  is generally formed by first and second portions  20 ,  22  respectively that are spaced-apart and substantially rectangular, and an intermediate portion  24 . The first and second portions  20 ,  22  are joined by the intermediate portion  24 . The intermediate portion  24  is substantially parallel to the axis of symmetry  14 , and perpendicular to both the first and second portions  20 ,  22 . 
     By substantially rectangular is meant that the shape approximates a rectangle, and may have curved corners rather than square corners. The four sides do not have to be exactly straight and may be slightly curved. 
     The first portion  20  has an outer edge element  25  from which the two first elements  16  extend. The two first elements  16  are operatively connected to and are generally perpendicular to the outer edge element  25 , with the outer edge element  25  having an opening  26  aligned with and of the same extent in the transverse direction (i.e. perpendicular to the axis of symmetry  14 ) as the spacing of the two first elements  16 . At each end of the outer edge element  25  and being operatively connected to the outer edge element  25  are two end elements  28  that are also generally perpendicular to the outer edge element  25 . 
     Extending transversely of the end elements  28  is an inner edge element  30  that is operatively connected to the end elements  28  and generally perpendicular to the end elements  28 . 
     The two first elements  16  extend into the first portion  20  such that their inner ends  44  are somewhat aligned with the outer edge  46  of inner edge element  30 , but are spaced from the corners  48  of the inner edge element  30  and the intermediate elements  32 . The two first elements  16  divide the first portion  20  into two sub-portions  51 ,  52  that are spaced apart by the two first elements  16  and are transversely aligned—aligned on an axis transverse to the axis of symmetry  14 . In this way the two intermediate elements  32  are operatively connected to and perpendicular to the respective sub-portions  51 ,  52 . 
     The intermediate portion  24  has two intermediate elements  32  that are operatively connected to and generally perpendicular to the inner edge element  30 . The intermediate elements  32  are parallel to and equally spaced from the axis of symmetry  14 . The inner edge element  30  has a gap  34  that extends between the two intermediate elements  32 . 
     The second portion  22  is substantially identical to the first portion  20  (on the basis that the two first elements  16  do not form part of the first portion  20 ) and also has an outer edge element  36 . At each end of the outer edge element  36  and being operatively connected to the outer edge element  36  are two end elements  38  that are also generally perpendicular to the outer edge element  36 . 
     Extending transversely of the end elements  38  is an inner edge element  40  that is operatively connected to the end elements  38  and generally perpendicular to the end elements  38 . The two intermediate elements  32  are operatively connected to and generally perpendicular to the inner edge element  40 . The inner edge element  40  has a gap  42  extending between the two intermediate elements  32 . 
     The ribbon radiating element  10  is preferably of constant width throughout its length. It is preferably formed on the dielectric  11  by any suitable technique such as, for example, printing. 
     The feed connection  18  is for a feed line  50  that passes through the substrate  12  and dielectric  11  as well as a hole  47  in a ground plane  54  ( FIG. 7 ). The ground plane  54  is a preferably a rectangular or square grid structure, as shown. 
     In one particular form of the exemplary embodiment of  FIGS. 1 and 2 , the resonant frequency is at 5.78 GHz; S 1 , is about −11.29 dB; bandwidth is 50 MHz (5.76 GHz-5.81 GHz); gain is 4.8 dBi; efficiency is 80%, the pattern is quasi omni-directional. 
       FIGS. 3 and 4  show another exemplary embodiment. The same reference numerals are used as for the embodiment of  FIGS. 1 and 2  but with a prefix number 2. Here, the difference over the exemplary embodiment of  FIGS. 1 and 2  is the addition of a projection element  256  that extends into the second portion from the outer edge element  236 . The projection element  256  is operatively connected to and is generally perpendicular to the outer edge element  236 . The projection element  256  has an elongate and centrally-located void  258  therethrough that is centered on the axis of symmetry  214 . The projection element  256  extends into the second portion  222  such that its inner end  260  is somewhat aligned with the inner edge  262  of inner edge element  230 , but the projection element  256  is spaced from the intermediate elements  232 . The projection element  256  divides the second portion  222  into two sub-portions  264 ,  266  that are spaced apart by the projection element  256  and are transversely aligned—aligned on an axis transverse to the axis of symmetry  214 . In this way the two intermediate elements  232  are operatively connected to and perpendicular to the respective sub-portions  264 ,  266 . 
     By the addition of the projection element  256  the bandwidth of the antenna  208  is increased as it creates a longer and U-shaped current flow path of a width that is preferably substantially the same as the ribbon radiating element  210 . 
     A particular exemplary form of the exemplary embodiment of  FIGS. 3 and 4  has a resonant frequency at 5.775 GHz; S 11  is around −12.3 dB; a bandwidth of 70 MHz (bandwidth 5.74 GHz to 5.81 GHz); gain is 4.75 dBi; efficiency is 83%; and the pattern is quasi omni-directional. 
     The exemplary embodiments of  FIGS. 1 and 2 , and  FIGS. 3 and 4 , are suitable for single-ended signal operation. By the addition of a second feed line and connection they become suitable for differential signal operation.  FIGS. 5 and 6  show the embodiment of  FIGS. 3 and 4  with dual-feed for differential signal operation. Again the same reference numerals are used for like components but with the addition of a prefix number 3. A second feed to the radiating element  310  is at a second feed connection  368  in the second of the first elements  316 . The second feed connection  368  is for a second feed line  370  that passes through the substrate  312 , dielectric  311  and a second hole  372  in the ground plane  374  ( FIG. 8 ). The second feed connection  368  and second feed line  370  may also be used with the embodiment of  FIGS. 1 and 2  in a similar manner. 
     By using the ribbon radiating element  210  of exemplary embodiment of  FIGS. 3 and 4  with the ground-plane  54  of  FIG. 7  in a particular form of the exemplary embodiments it is possible to obtain a single-ended antenna with a resonant frequency at 5.77 GHz; S 11  of about −16.5 dB; bandwidth of 110 MHz (5.72 GHz to 5.83 GHz); gain of 4.4 dBi; efficiency of 83%; and a pattern that is quasi omni-directional. 
     Similarly, using the ribbon radiating element of  FIGS. 5 and 6  with the ground-plane  374  of  FIG. 8  in a particular form of the exemplary embodiments it is possible to obtain a differential LTCC chip antenna. 
       FIGS. 9 to 11  show integration of the antenna of the exemplary embodiment of  FIGS. 3 and 4  into an AiP design. The design as shown is for single-ended operation and has two deep resonances seen from S 11 : one is about −12.3 dB at 5.64 GHz and the other is −12.4 dB at around 5.82 GHz. Between the two deep resonances, the S 11  is below −10 dB and the bandwidth is more than 240 MHz (5.60 GHz to 5.84 GHz). The gain is 4.7 dBi, efficiency is 80%, and the pattern is quasi omni-directional.  FIG. 12  shows an AiP design with dual feed for differential operation. 
       FIGS. 13 and 14  show the feeding network used in integration. The antenna  308 , substrate  312  and ground  374  are for the exemplary embodiment of  FIGS. 5 and 6 . They are mounted on and integrated with a semiconductor chip  376  with the semiconductor chip  376  being beneath the ground plane  374 . The feed lines  350 ,  370  connect with connects  378  of the chip  376 . The feeding network of  FIG. 14  has connection balls  380  for connection with a PCB, feed via  381  to the antenna  308 , and short (that is, connecting one ground to another ground) vias  382 . The ends  384  are for connection to the chip  376 . 
     The measured results shown in  FIG. 15  shows the performance of AiP designs incorporating for single-ended signal operation. 
     As shown in  FIGS. 16 and 17 , complementary designs may also be used where the antenna  408  is formed as a slot antenna so that the “ribbon”  486  is actually a gap in the metal to expose the dielectric  411 . The metal is formed outside the “ribbon”  486  as well as within the “ribbon”  486 . The region outside the “ribbon”  486  is a driven element  488  of the antenna  408  as the feed connection  418  is in metal formed in the metalized “gap”  426 . The driven element  488  is a radiating element and is generally formed by first and second portions  420 ,  422  respectively that are spaced-apart and substantially rectangular, and an intermediate portion  424 . The first and second portions  420 ,  422  are joined by the intermediate portion  424 . The intermediate portion  424  is substantially parallel to the axis of symmetry  414 , and perpendicular to both the first and second portions  420 ,  422 . 
     Within the “ribbon”  486  are three parasitic elements  490 ,  492  and  494  all of which are driven by the driven element  488  by capacitive coupling. 
     In  FIG. 18 , the ribbon  510  and the dielectric  511  are co-planar and the ribbon  510  is formed in the dielectric  511  rather than on the dielectric  511 , as is shown in  FIGS. 2 ,  4  and  6 . This form may also be used for the exemplary embodiment of  FIGS. 16 and 17 . 
     Whilst there has been described in the foregoing description preferred embodiments of the present invention, 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.