This invention 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 200MHz

Dielectrically-loaded antennas are disclosed in, for instance, U.S. Patents 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.

In the above-mentioned U.S. 7,439,934 and related U.S. Patent Application Nos. 12/661,296 filed 15 March 2010, and 13/317,097 filed 7 October 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.

U.S. Published Application No. 2011/0221650 (Application No. 13/014,962, filed 27 January 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.

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 No. 11/998,471 filed 28 November 2007).

UK patent application GB1118159.1, filed on 20 October 2011, discloses a radiofrequency assembly comprising the combination of a dielectrically loaded antenna and a printed circuit board mounting the antenna. The printed circuit board has a cut-out dimensioned to accommodate the antenna.

The disclosure of each of the above patent applications and patents is incorporated in the present application by reference.

It is an object of the invention to provide an improved antenna and printed circuit board combination.

According to a first aspect of the invention, 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 and occupying the major part of the inner volume defined by the core outer surface, 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 mounting projections bearing conductors for connecting the antenna to associated circuitry; the printed circuit board mounting the antenna has an aperture dimensioned to accommodate the antenna core with the passage extending substantially parallel to the plane of the board; wherein the aperture has inner edge portions surrounding the antenna core such that at least one of the inner edge portions and the core outer surface are substantially in close proximity or in contact; the antenna mounting projections at both ends of the passage engage respective inner edge portions of aperture 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. The aperture is preferably rectangular, and its side inner edge portions extend parallel to the side surface portion of the core, wherein the side inner edge portions are substantially in close proximity or in contact with the side surface portion of the core. Effectively, this prevents excessive movement of the antenna, and thereby providing a robust mounting structure.

The spacing between the side edges and the side surface portion of the core may be less than 0.5mm.

The printed circuit board comprises an electrically conductive layer which extends to a distance from at least one of the side inner edge portions of the aperture. The distance between the electrically conductive layer and the at least one of the said side inner edge portions is set such that the performance of antenna is not materially affected by the electrically conductive layer. Preferably the distance is between 1mm to 3mm.

The conductive layer lies in a plane generally parallel to the antenna axis and the conductive layer is a ground plane.

In the preferred embodiment of the invention, 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.

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.

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.

In the preferred embodiment, the antenna mounting projections comprise mounting tabs which 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.

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 projection 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 tab 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.

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.

According to a second aspect of the invention, a dielectrically-loaded antenna has an operating frequency in excess of 200MHz 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.

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. The invention will now be described by way of example with reference to the drawings in which:

Figure 1 is a perspective view of a radiofrequency circuit assembly in accordance with the invention, showing an antenna mounted in an aperture in a printed circuit board, the antenna being viewed from below and to one side;

Figure 2 is a plane view of the assembly of Figure 1, the antenna being viewed from above; Figure 3 is an exploded perspective view of the assembly, the antenna being viewed from below and to one side;

Figure 4 is an exploded perspective view of the antenna forming part of the assembly shown in Figures 1 to 3, viewed from below and to one side;

Figure 5 is a plane view of the assembly of Figure 1, the assembly being viewed from one side; and

Figure 6 is a perspective view of a radiofrequency circuit assembly in accordance with another embodiment of the invention, showing an antenna mounted in an aperture in a printed circuit board and equipment circuitry, the antenna being viewed from below and to one side.

Referring to Figures 1 to 3, a radiofrequency circuit assembly in accordance with the invention 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 14S of the core, four axially coextensive plated helical antenna elements 10A - 10D. This preferred antenna is a backfire helical antenna, in that it has a shielded feed housed in an axial bore 14B that passes through the core from a distal end outer surface portion 14D to an oppositely directed proximal end outer surface portion 14P of the core. Both end surface portions 14D, 14P 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 US2011/0221650.

As best seen in Figure 1, the longitudinal laminate board 16 has a proximal extension 16P extending beyond the proximal end surface portion 14P of the core. This extension 16P itself extends laterally beyond the diameter of the bore 14B and is received in grooves 11 opening out in the proximal end surface portion 14P. An antenna having grooves opening out in the proximal end surface portion is disclosed in GB 1120466.6 filed on 25 November 2011. At the other end of the bore 14B, the longitudinal laminate board 16 has a distal end portion 16D (see Figure 3) which projects beyond the distal outer surface portion 14D of the core.

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 14D 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 18S dimensioned to receive the distal end portion 16D of the longitudinal laminate board 16, as shown in Figure 2.

Referring to Figure 4, the slot 18S in the lateral laminate board 18 has elongate side walls 18SW which are each plated (only one such plated wall 18SW is visible in Figure 4), each plated side wall 18SW being connected to a respective segment- shaped inner plated area 181 on the proximal face 18PF of the laminate board 18. On each side of the slot, the lateral laminate board 18 has arcuate peripheral conductor areas 18P 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 18SW and the peripheral conductor areas 18P. These circuit elements may constitute an impedance matching network of the kind disclosed in the above-mentioned US7,439,934. Referring again to Figure 2, the distal end surface portion 14D of the core carries four radial connection portions formed as radial tracks 10AR - 10DR each associated with one of the helical elements 10A - 10D. These radial connection tracks 10AR - 10DR are connected in pairs 10AR, 10BR; 10CR, 10DR to arcuate conductors (not shown) plated on the core distal surface portion 14D adjacent the end of the bore 14B.

The orientation of the longitudinal laminate board 16 with respect to the conductive pattern on the core end face 14D, 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 16D of the latter housed in the slot 18S, the peripheral plated conductor areas 18P of the lateral laminate board 18 are in face-to- face contact with the arcuate conductors on the core distal end face 14D.

The distal end portion 16D of the longitudinal laminate board 16 carries conductive connecting pads 16DP, only one of which is visible in Figure 4, for contacting the plated side walls 18SW of the slot 18S.

Since, during manufacture of the antenna 10, solder paste is screen-printed on the proximally facing conductive areas 181, 18P 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 16DP on the distal end portion 16D of the longitudinal laminate board, as well as the arcuate conductors on the core end face 14D, on the one hand, with the correspondingly located plated areas of the slot side walls 18SW and peripheral conductors 18P of the lateral laminate board 18 on the other hand. As a result, the antenna elements 10A - 10D 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.

At their proximal ends, the antenna elements 10A - 10D 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 14P of the core. Conductive pads 16PP on the lateral extensions of the longitudinal laminate board part 16 (see Figures 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. The combination of the sleeve 20, the plating of the core proximal surface portion 14P and the shield conductors of the transmission line form a balun at the operating frequency of the antenna, the rim 20U of the conductive sleeve 20 acting as a resonant annular conductive path interconnecting the helical antenna elements 10A - 10D. 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 of the present invention 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.

In accordance with the present invention, 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 an aperture 12C of the printed circuit board. As shown in Figures 1 and 3, the aperture 12C is dimensioned to accommodate the antenna with the axial bore 14B of the core lying generally in the plane of the printed circuit board 12. The aperture 12C has inner edges 12CS1, 12CS2, 12CD, 12CP surrounding the antenna, as shown in Figure 3. The aperture 12C is rectangular, and its side edges 12CS1, 12CS2 running parallel to the side surface portion 14S of the core such that the side edges 12CS1, 12CS2 and the side surface portion 14S are in close proximity when the antenna 10 is mounted in the aperture 12C, as shown in Figure 5. This prevents excessive movement of the antenna and thereby providing a robust mounting structure. In another configuration, one (or both) of the side edges of the aperture 12C and the side surface portion 14S of the core is in contact to further eliminate any movement of the antenna. In one example, the spacing, between the side edges 12CS1, 12CS2 and the side surface portion 14S is less than 0.5mm.

At least one side of the printed circuit board 12 is plated over the majority of its area to form a ground plane 21. In this instance, the ground plane 21 extends to a distance from one of the aperture side edges 12CS2 and the distance of the aperture side edge 12CS2 from the ground plane is chosen such that the performance (such as the circular polarisation performance and the gain) of the antenna is not affected by the presence of the ground plane. However, it would be appreciated that this distance varies according to the application. In one example, the distance, d, of the aperture side edge 12CS2 from the ground plane is between 1 mm to 3 mm.

In the region of the conductive sleeve 20 and the proximal end surface portion 14P of the antenna core, the ground plane may be much closer to the antenna core since they are substantially non-radiating. In this embodiment, the distance between the ground plane 21 and the aperture side edge 12CS2 near the distal end of the antenna 10 is much smaller. This is acceptable because the voltage in each of the antenna elements 10A - 10D is at a minimum at the distal end of the antenna; and therefore the performance of the antenna is not affected by the presence of the ground plane 21 near the distal end of the antenna 10.

In this embodiment, 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. As shown in Figure 3, a plated conductive pad 12PP is formed a distance from one of the side edges 12CS1 of the aperture 12CS, above the distal end surface portion 14D of the core. On the same face of the printed circuit board 12, there are plated conductive pads 12D adjacent the base edge 12CP of the aperture 12C, as seen in Figure 3.

Referring to Figure 4 in conjunction with Figures 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 18F which project laterally on opposite sides of the discshaped portion so as to project beyond the side surface portion 14S of the antenna core and one of the radially extending integral fingers 18F overlaps the plated conductor pad 12PP of the printed circuit board 12 and the other radially extending integral finger overlaps a portion of the ground plane 21. Each projecting finger 18F carries a conductive area 18FP at its end, plated on the laminate board surface which faces the distal end surface portion 14D of the core. During manufacture of the assembly, solder paste is applied to the conductive pad and the portion of the ground plane so that when the assembly is passed through a reflow oven with the lateral laminate board fingers 18F abutting the conductive pad and the portion of the ground plane, a solder fillet is formed in the angle between the respective conductive pads at each mounting location formed by the juxtaposition of the board fingers 18F and the printed circuit board. In GB 1118159.1, the integral fingers overlap inwardly projecting tongues of the printed circuit board such that the integral fingers abut the printed circuit tongues when the antenna is mounted onto the printed circuit board. Conversely, in the present invention, the close proximity between the side edges 12CS1, 12CS2 and the side surface portion 14S eliminates the requirement of these projecting tongues. Effectively, this provides more material around the area of the printed circuit board on which the fingers abut, thereby providing a stronger assembly. On the underside of the proximal extension 16P 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 12BP on the printed circuit board 12. During manufacture of the assembly, solder paste is applied to a pad 12BP and a portion of the ground plane 21 adjacent the conductive pads 12BP so that when the assembly is passed through the reflow oven with the longitudinal laminate board proximal extension 16P overlying the printed circuit board 12 adjacent the base edge 12B of the aperture 12C, solder joints are formed between the pad 12BP and the portion of the ground plane 21 on the board 12 and the conductive areas on the underside of the feed structure longitudinal laminate board extension 16P.

As a consequence of the projection of the proximal extension 16P of the feed structure longitudinal laminate board 16 and the laterally extending fingers 18F of the feeder structure lateral laminate board 18, and of their juxtaposition with portions of the printed circuit board 12 adjacent the aperture 12C, they provide antenna mounting tabs at opposite respective ends of the core passage or bore 14B 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 16P and the laterally projecting laminate board fingers 18F 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 16P and the conductive pad 12BP 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.

It is not necessary for the antenna mounting tabs formed by the proximal extension 16P and the lateral extensions 18F to be secured to the printed circuit board 12 by solder joints. Other fastening techniques may be used, including non-conductive bonding.

While, in the preferred embodiment, the surface portions of the mounting tabs formed by the proximal extension 16P and the lateral fingers 18F 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. 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 invention 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 30 (as shown in Figure 6) and other circuitry thereby maximising the integration of equipment circuitry with the antenna.