Abstract:
This disclosure relates to a radiofrequency circuit assembly and a dielectrically-loaded antenna for use in the assembly. The antenna comprises a solid electrically insulative core having a passage therethrough extending from a first core surface portion to a second, oppositely facing core surface portion, and a printed circuit feeder structure secured in the core passage and having exposed antenna mounting projections at opposite respective ends of the passage. The printed circuit board mounting the antenna has a cut-out dimensioned to accommodate the antenna core with the passage extending substantially parallel to the plane of the board. The antenna mounting projections at both ends of the passage engage respective edge portions of the said printed circuit board adjacent the cut-out so that the antenna core is supported by the printed circuit board between spaced-apart mounting locations adjacent the oppositely facing core surface portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/551,387, filed on Oct. 25, 2011, and entitled “RADIOFREQUENCY CIRCUIT ASSEMBLY”, and also claims priority to United Kingdom Patent Application 1118159.1, filed on Oct. 20, 2011, and entitled “RADIOFREQUENCY CIRCUIT ASSEMBLY”, both of which are hereby incorporated herein by reference. 
     
    
     FIELD 
       [0002]    This disclosure relates to a radiofrequency circuit assembly and a dielectrically-loaded antenna for use in the assembly, the assembly and the antenna being for operation at a frequency in excess of 200 MHz 
       BACKGROUND 
       [0003]    Dielectrically-loaded antennas are disclosed in, for instance, U.S. Pat. Nos. 5,854,608, 5,945,963, 5,859,621, 6,690,336, 7,439,934 and 7,903,044. Each of these antennas has at least one pair of diametrically opposed helical antenna elements which are plated on a substantially cylindrical electrically insulative core made of a high relative dielectric constant material such as barium titanate. The material of the core occupies the major part of the volume defined by the core outer surface. Extending through the core from one end face to an opposite end face is an axial bore or passage containing a feed. At one end of the bore conductors of the feed are coupled to respective antenna elements which have associated connection conductors plated on the respective end face adjacent the end of the passage. At the other end of the passage, one of the feed conductors is connected to a conductor which links the antenna elements and, in each of these examples, is in the form of a conductive sleeve encircling part of the core to form a balun. Each of the antenna elements terminates on a rim of the sleeve and each follows a respective helical path from its connection to the feed. 
         [0004]    In the above-mentioned U.S. Pat. No. 7,439,934 and related U.S. patent application Ser. Nos. 12/661,296 filed 15 Mar. 2010, and U.S. Ser. No. 13/317,097 filed 7 Oct. 2011, the feed structure incorporates a laminate board oriented perpendicularly to a feed line in the passage so as to lie face-to-face on the end face of the core. This laminate board incorporates an impedance matching network to provide an impedance match between the characteristic impedance of the feed line and the radiation resistance presented by the antenna elements. 
         [0005]    U.S. Published Application No. 2011/0221650 (application Ser. No. 13/014,962, filed 27 Jan. 2011) discloses dielectrically-loaded antennas with quasi-coaxial laminate board feed structures in the core passage, the perpendicular laminate board overlying the end face of the core having a slot which receives an end portion of the laminate board in the core passage. This U.S. patent application also discloses methods for connecting the antenna to a printed circuit board bearing associated radiofrequency circuitry, e.g. a radiofrequency front-end amplifier. 
         [0006]    Another prior patent application involving the combination of a dielectrically-loaded antenna and printed circuit board is U.S. Published Application No. 2008/0136738 (application Ser. No. 11/998,471 filed 28 Nov. 2007). 
         [0007]    The disclosure of each of the above patent applications and patents is incorporated in the present application by reference. 
       SUMMARY 
       [0008]    It is an object of embodiments of the disclosed technology to provide an improved antenna and printed circuit board combination. 
         [0009]    According to a first aspect of the disclosed technology, a radiofrequency circuit assembly comprises the combination of a dielectrically-loaded antenna and a printed circuit board mounting the antenna, wherein: the antenna comprises a solid electrically insulative core of a material having a relative dielectric constant greater than 5, the core having a passage therethrough extending from a first core surface portion to a second, oppositely facing core surface portion, and a printed circuit feeder structure secured in the core passage and having exposed antenna mounting projections at opposite respective ends of the passage, at least one of the tabs bearing conductors for connecting the antenna to associated circuitry; the printed circuit board mounting the antenna has a cut-out dimensioned to accommodate the antenna core with the passage extending substantially parallel to the plane of the board; the antenna mounting projections at both ends of the passage engage respective edge portions of the said printed circuit board adjacent the cut-out so that the antenna core is supported by the printed circuit board between spaced-apart mounting locations adjacent the oppositely facing core surface portions, the board further comprising conductive areas at at least one of the mounting locations, electrically connecting the conductors of the feeder structure to circuitry on the board. 
         [0010]    In one embodiment of the disclosed technology, the antenna is a backfire multifilar helical antenna for receiving and/or transmitting circularly polarised waves. In this case the core is cylindrical, having first and second oppositely directed core surface portions oriented perpendicularly to the axis of the cylinder, and a cylindrical side surface portion bearing radiating elements as plated helical conductors. The feeder structure comprises a printed circuit transmission line in the core passage coupled, at end of the passage, to the radiating elements and, at the opposite end of the passage, to conductive areas on the printed circuit board mounting the antenna. A matching network may be included as part of the feeder structure, typically located on a laminate board overlying the transverse core surface portion where the feeder structure is coupled to the helical antenna elements. 
         [0011]    In the preferred embodiment, the feeder structure comprises two laminate board parts: a longitudinal laminate board part forming a transmission line which is housed in the core passage, and a lateral laminate board part extending laterally from the distal end of the core passage over the adjacent transversely oriented core surface portion. Conductors on the lateral laminate board part are electrically connected to conductors on this adjacent core surface portion so as to couple the antenna elements to the transmission line via, if present, the matching network. 
         [0012]    In the case where the lateral laminate board part lies in a plane perpendicular to the core axis and is a laminate board component which is separately formed from that of the longitudinal laminate board part, the lateral laminate board part has a slot receiving a distal end portion of the longitudinal laminate board part. At least one conductor on the lateral laminate board part is electrically connected to a conductor on the longitudinal laminate board part at an edge of the slot. 
         [0013]    In the preferred embodiment, the antenna mounting tabs include lateral outer extensions of the lateral laminate board part, which extensions project beyond the side surface portion of the antenna. At the other end of the passage, the longitudinal laminate board part projects beyond the respective end of the passage to form another mounting tab. Accordingly, with the longitudinal laminate board part fixed in the core passage, the core is effectively suspended between two spaced-apart mounting locations where the mounting tabs are secured to the printed circuit board mounting the antenna. 
         [0014]    It is preferred that each of the antenna mounting tabs has a surface portion which is bonded to a major face of the printed circuit board mounting the antenna, these mounting tab surface portions being coplanar so that the connections to the printed circuit board are all made on one side of the latter. The connections between the mounting tabs and the printed circuit board are preferably solder joints, both mounting tabs and printed circuit board having plated conductive areas in registry with each other. 
         [0015]    In the case of the lateral laminate board part comprising a laminate board oriented perpendicularly to the longitudinal laminate board part and to the axis of the core, the mounting tabs of the lateral laminate board part may comprise integral oppositely projecting fingers which have coplanar surface portions secured to the printed circuit board major face. 
         [0016]    According to a second aspect of the disclosed technology, a dielectrically-loaded antenna has an operating frequency in excess of 200 MHz and comprises: an electrically insulative core of a solid material which has a relative dielectric greater than 5 and occupies the major part of the interior volume defined by the core outer surface, the core outer surface comprising oppositely directed distal and proximal outer surface portions, a side surface portion extending between the distal and proximal surface portions, and a passage extending through the core from the distal surface portion to the proximal surface portion; a three-dimensional antenna element structure disposed on or adjacent the side surface portion of the core; and a feeder structure comprising a longitudinal laminate board part housed in the core passage and a lateral laminate board part extending laterally from one end of the core passage over the distal surface portion of the core; wherein the feeder structure has exposed antenna mounting projections at opposite respective ends of the core passage, at least one of the projections having a conductive surface for connecting the antenna to associated circuitry; and wherein the mounting projections include distal mounting projections forming extensions of the lateral laminate board, which extensions project laterally in opposite directions beyond the said side surface portion of the core. 
         [0017]    The printed circuit board mounting the antenna typically carries a receiver front end, which may include a low-noise amplifier or a complete receiver, for instance, a GPS receiver chip. In this way, the combination of the antenna and the printed circuit board mounting the antenna may constitute a rugged self-contained receiver module for mounting in a variety of devices. The printed circuit board may also include a transmitter for generating RF power signals to be fed to the antenna. 
         [0018]    The disclosed technology will be described below by way of example with reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In the drawings: 
           [0020]      FIG. 1  is a perspective view of a radiofrequency circuit assembly in accordance with embodiments of the disclosed technology showing an antenna mounted in a cut-out in a printed circuit board, the antenna being viewed from below and to one side; 
           [0021]      FIG. 2  is a perspective view of the assembly of  FIG. 1 , the antenna being viewed from above; 
           [0022]      FIG. 3  is an exploded perspective view of the assembly, the antenna being viewed from above and to one side; 
           [0023]      FIG. 4  is an exploded perspective view of the antenna forming part of the assembly shown in  FIGS. 1 to 3 , viewed from below and to one side; and 
           [0024]      FIG. 5  is an exploded perspective view of a second assembly in accordance with embodiments of the disclosed technology, the antenna being viewed from above and to one side. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Referring to  FIGS. 1 to 3 , a radiofrequency circuit assembly in accordance with embodiments of the disclosed technology comprises a dielectrically-loaded antenna  10  and a printed circuit board  12  mounting the antenna. The antenna is a quadrifilar helical antenna having a cylindrical dielectric core and, plated on a cylindrical side surface portion  14 S of the core, four axially coextensive plated helical antenna elements  10 A- 10 D. This preferred antenna is a backfire helical antenna, in that it has a shielded feed housed in an axial bore  14 B that passes through the core from a distal end outer surface portion  14 D to an oppositely directed proximal end outer surface portion  14 P of the core. Both end surface portions  14 D,  14 P are planar and perpendicular to the central axis of the cylindrical core. The feed is a multiple-layer longitudinally oriented laminate board  16  having an embedded inner conductor and, on opposite sides of the inner conductor, shield conductors formed by plated outer conductive layers which are connected to each other by a series of vias running along the edges of the longitudinal board so that the outer layers and the inner, embedded layer together form a quasi-coaxial transmission line. These features of the laminate board are not shown in the drawings, but are disclosed in the above-referenced US 2011/0221650. As also disclosed in US2011/0221650, the longitudinal laminate board has nibs projecting from each longitudinal edge to an extent such that the laminate board  16  is an interference fit in the bore  14 B. 
         [0026]    As best seen in  FIG. 1 , the longitudinal laminate board  16  has a proximal extension  16 P extending beyond the proximal end surface portion  14 P of the core. This extension  16 P itself extends laterally beyond the diameter of the bore  14 B and has an edge abutting the core proximal end surface portion  14 P substantially along a diameter of the core. 
         [0027]    At the other end of the bore  14 B, the longitudinal laminate board  16  has a distal end portion  16 D (see  FIG. 3 ) which projects beyond the distal outer surface portion  14 D of the core. 
         [0028]    The longitudinal laminate board  16  forms part of a composite feed structure which also includes a lateral laminate board  18  which, in this embodiment, comprises a plated disc lying in face-to-face contact on the distal end surface portion  14 D of the core, the plane of the board lying perpendicular to the core axis. As disclosed in US2011/0221650, the lateral laminate board  18  has a central slot  18 S dimensioned to receive the distal end portion  16 D of the longitudinal laminate board  16 , as shown in  FIG. 2 . 
         [0029]    Referring to  FIG. 4 , the slot  18 S in the lateral laminate board  18  has elongate side walls  18 SW which are each plated (only one such plated wall  18 SW is visible in  FIG. 4 ), each plated side wall  18 SW being connected to a respective segment-shaped inner plated area  181  on the proximal face  18 PF of the laminate board  18 . On each side of the slot, the lateral laminate board  18  has arcuate peripheral conductor areas  18 P extending over the side edges of the board  18 . Embodied in and/or carried by the lateral laminate board are circuit elements (not shown) interconnecting the conductors associated with the slot side walls  18 SW and the peripheral conductor areas  18 P. These circuit elements may constitute an impedance matching network of the kind disclosed in the above-mentioned U.S. Pat. No. 7,439,934. 
         [0030]    Referring again to  FIG. 3 , the distal end surface portion  14 D of the core carries four radial connection portions formed as radial tracks  10 AR- 10 DR each associated with one of the helical elements  10 A- 10 D. These radial connection tracks  10 AR- 10 DR are connected in pairs  10 AR,  10 BR;  10 CR,  10 DR to arcuate conductors  10 AB,  10 CD plated on the core distal surface portion  14 D adjacent the end of the bore  14 B. 
         [0031]    The orientation of the longitudinal laminate board  16  with respect to the conductive pattern on the core end face  14 D, together with the dimensions of the lateral laminate board  18 , are such that when the lateral laminate board  18  is fitted to the longitudinal laminate board  16  with the distal portion  16 D of the latter housed in the slot  18 S, the peripheral plated conductor areas  18 P of the lateral laminate board  18  are in face-to-face contact with the arcuate conductors  10 AB,  10 CD on the core distal end face  14 D. 
         [0032]    The distal end portion  16 D of the longitudinal laminate board  16  carries conductive connecting pads  16 DP, only one of which is visible in  FIG. 3 , for contacting the plated side walls  18 SW of the slot  18 S. 
         [0033]    Since, during manufacture of the antenna  10 , solder paste is screen-printed on the proximally facing conductive areas  181 ,  18 P of the lateral laminate board  18 , subsequent heating of the assembled antenna components in a reflow oven causes the solder interconnection of the connecting pads  16 DP on the distal end portion  16 D of the longitudinal laminate board, as well as the arcuate conductors  10 AB,  10 CD on the core end face  14 D, on the one hand, with the correspondingly located plated areas of the slot side walls  18 SW and peripheral conductors  18 P of the lateral laminate board  18  on the other hand. As a result, the antenna elements  10 A- 10 D are coupled in pairs to the inner and outer conductors of the feed line and the lateral laminate board  18  is rigidly secured to the longitudinal laminate board  16  to form a unitary feed structure, and to the core. 
         [0034]    At their proximal ends, the antenna elements  10 A- 10 D are connected to a common virtual ground conductor  20  which is annular and in the form of a plated sleeve  20 . The sleeve  20  is conductively continuous with a plated conductive covering of the proximal end surface portion  14 P of the core. Conductive pads  16 PP on the lateral extensions of the longitudinal laminate board part  16  (see  FIGS. 1 and 4 ) extend to the distal edges of the latter and are connected to the outer shield conductors (not shown) of the transmission line formed by the longitudinal laminate board  16 . During manufacture of the antenna, solder paste is applied to the conductive pads  16 PP so that during reflow heating, the pads are electrically connected by solder fillet joints to the plates proximal end surface portion  14 P of the core. The combination of the sleeve  20 , the plating of the core proximal surface portion  14 P and the shield conductors of the transmission line form a balun at the operating frequency of the antenna, the rim  20 U of the conductive sleeve  20  acting as a resonant annular conductive path interconnecting the helical antenna elements  10 A- 10 D. Further details of the antenna  10  and its operation are disclosed in the above-mentioned prior art publications. The quadrifilar helical antenna of the preferred embodiment has a cardioid-shaped, distally directed radiation pattern for circularly polarised waves and is, therefore, suited to reception and transmission of satellite communication signals, including the reception of global positioning system signals. 
         [0035]    In accordance with embodiments of the disclosed technology, the above-described antenna  10  is mounted to a printed circuit board to form a radiofrequency circuit assembly. More particularly, the antenna  10  is mounted in a cut-out  12 C of the printed circuit board, as shown in  FIGS. 1 to 3 , the cut-out  12 C being dimensioned to accommodate the antenna with the axial bore  14 B of the core lying generally in the plane of the printed circuit board  12 . The cut-out or aperture  12 C is rectangular, its side edges  12 CS running parallel to the side surface portion  14 S of the core. At least one side (the underside in  FIG. 1 ) of the printed circuit board  12  is plated over the majority of its area to form a ground plane. In this instance, the ground plane extends to the cut-out side edges  12 CS and the spacing of the aperture side edges  12 CS from the radiating elements  10 A- 10 D of the antenna is about 2.5 mm. In other embodiments, depending on the nature of the antenna and the intended function of the circuit assembly, the spacing may be less than or more than 2.5 mm, e.g. down to 1 mm, or, typically, up to 5 mm. It is not necessary for the ground plane of the printed circuit board  12  to extend fully to the edges  12 CS of the aperture in the region of the antenna elements  10 A- 10 D. Indeed, the ground plane may be spaced from the aperture edges  12 CS, the restrictions on spacing from the antenna elements  10 A- 10 D applying with respect to the edges of the ground plane rather than to the aperture edges in that case. 
         [0036]    In the region of the conductive sleeve  20  and the proximal end surface portion  14 P of the antenna core, the aperture periphery may be much closer to the antenna core since they are substantially non-radiating. 
         [0037]    In this embodiment, the aperture  12 C is open-ended in that it is open in the region of the distal end surface portion  14 D of the core, although the aperture sides extend beyond the core distal end surface portion  14 D. It follows that the ground plane of the printed circuit board  12  does not extend over the distal end of the antenna  10 , i.e. leaving the part of the outer surface of the antenna facing the maximum of the radiation pattern clear of adjacent conductive material. Put another way, the conductive parts of the printed circuit board  12  do not extend over the distal face of the antenna. 
         [0038]    As seen in  FIGS. 2 and 3 , each side wall  12 CS of the cut-out or aperture  12 C in the printed circuit board  12  is shaped so as to be closer to the antenna, i.e. closer to the antenna axis, where it is in registry with the distal end surface portion  14 D of the core. Accordingly, the printed circuit board  12  has two tongues  12 T adjacent the antenna distal end surface portion  14 D. As shown in  FIG. 3 , each tongue  12 T has a plated conductive pad  12 TP. On the same face of the printed circuit board  12 , there are plated conductive pads  12 BP adjacent the base edge  12 CB of the cut-out  12 C, as seen in  FIG. 1 . 
         [0039]    Referring to  FIG. 4  in conjunction with  FIGS. 1 to 3 , on the antenna the lateral laminate board  18  of the feeder structure has mounting tabs in the form of radially extending integral fingers  18 F which project laterally on opposite sides of the disc-shaped portion so as to project beyond the side surface portion  14 S of the antenna core and so as to overlap the inwardly projecting tongues  12 T of the printed circuit board  12 . Each projecting finger carries a conductive area  18 FP at its end, plated on the laminate board surface which faces the distal end surface portion  14 D of the core. During manufacture of the assembly, solder paste is applied to the conductive pads  12 TP on the printed circuit board tongues  12 T so that when the assembly is passed through a reflow oven with the lateral laminate board fingers  18 F abutting the printed circuit board tongues  12 T, a solder fillet  24  ( FIG. 1 ) is formed in the angle between the respective conductive pads at each mounting location formed by the juxtaposition of the board fingers  18 F and the printed circuit tongues  12 T. 
         [0040]    On the underside of the proximal extension  16 P of the antenna feed structure longitudinal laminate board  16  there are conductive areas (not shown in the drawings) located so as to be in registry with the conductive pads  12 BP on the printed circuit board  12  adjacent the cut-out edge  12 B. During manufacture of the assembly, solder paste is applied to the pads  12 BP so that when the assembly is passed through the reflow oven with the longitudinal laminate board proximal extension  16 P overlying the printed circuit board  12  adjacent the base edge  12 B of the cut-out  12 C, solder joints are formed between the pads  12 BP on the board  12  and the conductive areas on the underside of the feed structure longitudinal laminate board extension  16 P. 
         [0041]    As a consequence of the projection of the proximal extension  16 P of the feed structure longitudinal laminate board  16  and the laterally extending fingers  18 F of the feeder structure lateral laminate board  18 , and of their juxtaposition with portions of the printed circuit board  12  adjacent the cut-out  12 C, they provide antenna mounting tabs at opposite respective ends of the core passage or bore  14 B so that the antenna has longitudinally or axially spaced-apart mountings. The antenna core is, therefore, effectively suspended between spaced-apart mounting locations on the printed circuit board  12 , providing mechanical robustness. The mounting tabs formed by the proximal laminate board extension  16 P and the laterally projecting laminate board fingers  18 F are, in this preferred embodiment, bonded to a major face of the printed circuit board  12  by conductive, i.e. solder, joints. The conductive joints between the longitudinal laminate board proximal extension  16 P and the conductive pads  12 BP on the upper face of the printed circuit board  12  constitute electrical connections between the antenna feed structure and circuitry (not shown) on the printed circuit board  12 . 
         [0042]    It is not necessary for the antenna mounting tabs formed by the proximal extension  16 P and the lateral extensions  18 F to be secured to the printed circuit board  12  by solder joints. Other fastening techniques may be used, including non-conductive bonding. 
         [0043]    While, in the preferred embodiment, the surface portions of the mounting tabs formed by the proximal extension  16 P and the lateral fingers  18 F overlying the printed circuit board  12  are co-planar and bonded to a single planar surface of the board  12 , alternative configurations are possible, including attachment to opposite sides of the printed circuit board mounting the antenna, or seating of the tabs or other projecting elements in recesses or notches in the board, to give just two examples. 
         [0044]    In a particular alternative embodiment, the cut-out  12 C in the printed circuit board  12  mounting the antenna is a cut-out having only two sides, as shown in  FIG. 5 , being, effectively, a cut-out  12 C taken from a corner of the board  12 . The cut-out  12 C has a single side edge  12 CS and a base edge  12 B. The periphery  12 P of the printed circuit board  12  preferably extends laterally of the antenna axis at least as far as the outer cylindrical surface  14 S of the antenna core, but the lateral extent of the board may be less than this, providing it is of sufficient lateral extent to receive the proximal mounting tab  16 P in an overlapping relationship. In this embodiment, the lateral laminate board  18  of the antenna feed structure has a single laterally projecting finger  18 F which, in the finished assembly, is secured to a single tongue  12 T adjacent the antenna distal end surface portion  14 D. The single finger  18 F of the lateral laminate board  18  forms a distal mounting tab for the antenna  10 , the core of the antenna being effectively suspended between the spaced-apart mounting locations of the projecting finger  18 F and the proximal mounting tab  16 P mounted on portions of the printed circuit board  12  adjacent the cut-out  12 C. 
         [0045]    The above-described assembly constitutes a robust self-contained module for incorporation in portable communication equipment in particular, such equipment including handheld devices with global positioning system receivers, in devices for two-way satellite communication, in tracking devices, and so on. Falling within the scope of the disclosed technology are assemblies including antennas other than quadrifilar helical antennas. For instance, antennas with cubiod-shaped dielectric cores may be used, as well as helical antennas with less than or more than four helical elements. Examples of such antennas for receiving and/or transmitting linearly polarised or circularly polarised waves for terrestrial or satellite systems are disclosed in the above-mentioned prior patent publications. The printed circuit board  12  may simply carry a low noise amplifier, a transmitter output stage, or filters but, advantageously, may include a complete integrated circuit receiver and other circuitry thereby maximising the integration of equipment circuitry with the antenna.