WO2005029635A2

WO2005029635A2 - Antenna with adjoining reactive surface

Info

Publication number: WO2005029635A2
Application number: PCT/IL2004/000896
Authority: WO
Inventors: Ben Zion Steinberg; Avraham Shahadi; Rafael Kastner
Original assignee: Xellant Inc.
Priority date: 2003-09-25
Filing date: 2004-09-26
Publication date: 2005-03-31
Also published as: WO2005029635A3

Abstract

An antenna assembly (20) for a communication device includes a feed structure (22), which has front and rear sides (26, 28), and which is coupled to be driven by the device so as to radiate an electromagnetic field in a given frequency band. An electrically reactive surface (24) comprising an array of reactive circuit elements (36), is positioned adjacent to the rear side of the feed structure so as to define a cavity between the feed structure and the reactive surface.

Description

ANTENNA WITH ADJOINING REACTIVE SURFACE CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of U.S.

Patent Application 10/416,436, filed May 9, 2003, in the national phase of PCT patent application PCT/IL01/01152 (published as WO 02/49147 A2) . This application claims the benefit of U.S. Provisional Patent Application

60/506,110, filed September 25, 2003. Both of these related applications are incorporated herein by reference. FIELD OF THE INVENTION The present invention relates generally to antennas, and specifically to devices and methods for controlling the Specific Absorption Rate (SAR) of radiation from the antenna of a mobile communication device in the tissues of a user of the device, and enhancement of the antenna efficiency in the presence of the user tissues (i.e., in the "talk position" of the device) . BACKGROUND OF THE INVENTION Concern has been growing over the radiation hazard involved in use of cellular telephones. In the United States and in other countries, cellular and other wireless handsets must meet regulatory requirements for maximum specific absorption rate (SAR) levels in body tissues. The above-mentioned PCT patent application PCT/IL01/01152 provides a survey of methods described in the patent literature for shielding the head against radio frequency (RF) energy emitted by cellular telephone antennas. Some attempts to reduce the health hazards of radio telephone antennas use RF-absorbing materials to shield the head. Others use electrically-conducting (grounded) surfaces . The above-mentioned PCT patent application describes an antenna for a personal communication device that comprises a feed structure, which is driven by the device to radiate an electromagnetic field in the operating frequency band of the device. A reactive surface is positioned adj cent to the rear surface of the feed structure, between the feed structure and the user's head. An electrically-asymmetrical cavity is thus defined between the rear surface of the feed structure, which is typically conductive, and the reactive surface adjacent to it. The asymmetrical cavity supports two parallel current distributions in the conductive surface and the reactive surface, running in opposite directions (i.e., out of phase) on the two surfaces. On the front side of the feed structure, only the current on the conductive surface has an effect, thereby creating a strong field on the front side of the assembly, away from the user's head. The effect of the other current, running on the reactive surface, is shielded by the conductive surface. On the rear side of the feed structure, a null field is created, since the Individual effects of the currents on the conductive and reactive surfaces cancel one another. The combination of the feed structure with the asymmetrical cavity provides strong asymmetry of the near-field distribution of the electromagnetic energy radiated by the antenna assembly. Therefore, absorption of radiation from the antenna in the user's head is reduced. In some of the embodiments described in the PCT patent application, the reactive surface comprises an array of reactive circuit elements, such as inductors and/or capacitors. In one of these embodiments, the reactive surface is made from a printed circuit board, on which inductors in the form of coils are printed in series. Each coil comprises an upper segment, printed on an upper layer or side of the printed circuit board, and a lower segment, printed on a lower layer or side of the board. The upper and lower segments are joined by feedthroughs . SUMMARY OF THE ZNVENTION Embodiments of the present invention provide an improved antenna assembly for a communication device. The assembly comprising a feed structure, which is driven by the device so as to radiate an electromagnetic field, and an electrically reactive surface comprising an array of reactive circuit elements. The reactive surface typically comprises a printed circuit board having traces printed on one or more of its faces. This surface is positioned adjacent to the rear side of the feed structure so as to define a cavity between the feed structure and the reactive surface. In a disclosed embodiment, the traces are printed so as to define inductive coils in a rectilinear configuration. The rectilinear configuration, as described further hereinbelow, is advantageous in minimizing the parasitic capacitance of the coils. The inventors have found that such printed coils can be manufactured at low cost with high precision, and thus provide an effective, economical means for designing and producing antenna assemblies with high efficiency. There is therefore provided, in accordance with an embodiment of the present invention, an antenna assembly for a communication device, the assembly including: a feed structure, which has front and rear sides, and which is coupled to be driven by the device so as to radiate an electromagnetic field, in a given frequency band; and an electrically reactive surface including an array of reactive circuit elements, which is positioned adjacent to the rear side of the feed structure so as to define a cavity between the feed structure and the reactive surface. In disclosed embodiments, the reactive surface includes a printed circuit board having a plurality of faces in one or more layers, and the reactive circuit elements include traces printed on one or more of the faces of the printed circuit board. Typically, the traces are printed so as to define inductive coils. In one embodiment, the traces defining at least some of the inductive coils are printed in a rectilinear configuration on at least two of the faces of the printed circuit board. The at least two of the faces of the printed circuit board include first and second faces, and one or more holes pass through the printed circuit board between the first and second faces. Each of the at least some of the inductive coils includes: a first linear conducting segment, aligned in a first direction on the first face of the printed circuit board; a second linear conducting segment, connected to the first linear conductor and aligned in a second direction, perpendicular to the first direction, on the first face of the printed circuit board; a third linear conducting segment, aligned in the first direction on the second face of the printed circuit board and connected to the second linear conductor through one of the holes; and a fourth linear conducting segment, connected to the third linear conductor and aligned in the second direction on the second face of the printed circuit board. In a disclosed embodiment, the feed structure and reactive surface are adapted to be mounted on the communication device so that the reactive surface intervenes between the feed structure and a head of a user of the device. Additionally or alternatively, the reactive circuit elements may include capacitors. The reactive circuit elements may be mutually connected in series and/or in parallel. Typically, the rear side of the feed structure is planar and electrically conductive, and the reactive surface is positioned parallel to the rear side of the feed structure. The reactive surface may be short- circuited to the feed structure in at least one location. In a disclosed embodiment, the feed structure includes an inverted-F feed structure. There is also provided, in accordance with an embodiment of the present invention, a method for wireless communication using a communication device operating in a given frequency band, the method including: coupling a feed structure, having a front side and a rear side, to the communication device, so that the feed structure can be driven by the device to radiate an electromagnetic field in the given frequency band; and positioning an electrically-reactive surface including an array of reactive circuit elements, adjacent to the rear side of the feed structure, so as to define a cavity between the feed structure and the reactive surface. The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic, pictorial illustration of an antenna assembly, in accordance with an embodiment of the present invention; Fig. 2A is a schematic frontal view of a rear plate of a feed structure used in an antenna assembly, in accordance with an embodiment of the present invention; Fig. 2B is a schematic frontal view of the feed structure of Fig. 2A, showing both front and rear plates; Fig. 3 is a schematic frontal view of a reactive surface used in an antenna assembly, in accordance with an embodiment of the present invention; Figs. 4A and 4B are schematic frontal views of reactive surfaces, showing details of coils printed on the surfaces, in accordance with embodiments of the present invention; Fig. 5 is a plot that schematically illustrates the SAR of an antenna assembly with and without a printed reactive surface, in accordance with an embodiment of the present invention; and Figs. 6A-6D are schematic, pictorial illustrations of antenna assemblies, in accordance with alternative embodiments of the present invention. DETAILED DESCRIPTION OF EMBODIMENTS Fig. 1 is a schematic, pictorial illustration of an antenna assembly 20 for use with a personal communication device, such as a cellular telephone, in accordance with an embodiment of the present invention. Assembly 20 comprises a feed structure 22 and an electrically- reactive shielding surface 24. Feed structure 22 comprises a front plate 26 and a rear plate 28. Here and in the description that follows, the "front" of the feed structure (or of the antenna assembly) refers to the side of the assembly that is generally pointed away from the head of the user of the communication device, while the "rear" faces toward the head. Typically, the rear surface constitutes the electrical ground of the antenna assembly. The rear surface of feed structure 22, which is typically conductive, and reactive surface 24 together define an asymmetrical cavity therebetween. Exemplary realizations of the feed structure and the asymmetrical cavity are shown in detail in the figures that follow. The combination of the asymmetrical cavity and the feed structure causes the near field of antenna assembly 20 to be strongly asymmetrical, with a sharp drop of the magnetic and/or electric field between high values at the front of the assembly and very low values at the rear. The design of the antenna assembly not only reduces absorption of radiation in the head, but also redirects the energy supplied to the feed structure into the communication channel, thereby improving the overall power budget of the communication device. Structure 22 defines an inverted-F antenna, which is shown in greater detail in Figs. 2A and 2B. Plate 28 serves as a ground plate, which is electrically connected to plate 26 by a short circuit strap 34. A pin 32 is used to connect front plate 26 to an RF feeding line driven by the device circuitry, as shown below. Surface 24 comprises an array of inductors 36. Details of this array are shown in Fig. 3. Surface 24 is held in proximity to rear plate 28 by dielectric (nonconducting) supports (not shown in this figure) and is connected by a short circuit strap 38 to the electrical ground on plate 28. Figs. 2A and 2B are schematic frontal views of feed structure 22, in accordance with an embodiment of the present invention. Fig. 2A shows rear plate 28, with front plate 26 removed, while Fig. 2B shows a view of the entire feed structure, with the front plate hiding a part of the rear plate. Reactive surface 24 is mounted behind the rear surface of rear plate 28 (and is therefore not seen in this figure.) Front plate 26, which serves as the radiating surface of the antenna assembly, is positioned parallel to the grounded rear plate 28. The two plates are mechanically connected by conductive pin 32, which serves as a feed, and by strap 34, which is positioned in a selected location to create the desired boundary conditions. Additional mechanical supports (not shown) may also be used. High-frequency power is fed to the antenna assembly through a co-planar wave guide (CPW) , in which a central conductive strip 30 is isolated from the remainder of plate 28, which is grounded, by isolating grooves 40. The rear side of plate 28 (shown in Fig. 1) is a conducting surface, which is short-circuited to the front side along the edges to provide the conditions for the CPW. The current from strip 30 is fed to plate 26 through pin 32 and flows through a patterned conductor 42, which is shaped by an isolating area 44. The pattern of the current flow on the surface of plate 26 determines the radiation pattern and electrical characteristics of the antenna . Antenna assembly 20 may be used as internal antenna in a mobile telephone. Such an antenna assembly is typically positioned inside the top of the handset and is used while the handset is held very close to the user's head. If feed structure 22 is used alone, without reactive surface 24, the radiation pattern is expected to be approximately omnidirectional. Much of the radiated energy will then be absorbed in the user's head and converted to heat. This absorption is undesirable both for the health of the user and for the efficiency of the antenna. Fig. 3 is a schematic, frontal view of reactive surface 24, in accordance with an embodiment of the present invention. If reactive surface 24 is correctly built and positioned in close proximity behind feed structure 22, the reactive surface interacts with the feed structure to significantly reduce the electromagnetic field behind the antenna, while converting most of the diverted energy into effective radiation. Surface 24 is designed to be semi-transparent to the electromagnetic energy and is tiled with discrete reactive components, typically inductive coils 50. Alternatively or additionally, surface 24 may comprise capacitors (not shown) , or a combination of inductors and capacitors. The reactive components are interconnected in series and/or parallel to form a grid whose typical period is much smaller than the antenna operating wavelength. The effective surface impedance is determined by the specific inductance and capacitance of the grid elements and by the grid structure and size. Coils 50 (or other reactive components) are typically printed on a dielectric substrate 52, which is positioned parallel to the rear surface of feed structure 22 at a distance that is derived from the average transmission wavelength. The distance is typically much smaller than the wavelength. The coils may be printed using conductive traces on one face of substrate 52 or on two or more faces, as described below. Reactive surface

24 creates a cavity together with the back surface of the feed structure, in which a specific mode of the electromagnetic field and a corresponding current distribution is supported. This cavity is bounded on one side by the metallic rear surface, or ground plane, of rear plate 28 and on the other side by the reactive surface . Short-circuit strap 38 connects the reactive surface and the rear plate. Optionally, multiple short circuits can be used in chosen locations to impose boundary conditions that support the specific modal current distribution, and thus enhance the excitation of the desired electromagnetic mode inside the cavity. Alternatively, some or all of the short circuits can be replaced by reactive circuit elements to effectively tune the electrical dimensions of the cavity to better match the desired mode. As another alternative for tuning the cavity, some or all of the short circuits can be replaced by open circuits. Yet another alternative is to use multiple reactive surfaces, as shown in Fig. 6C, so as to create multiple cavities or a single cavity with multiple walls, in close proximity to the feed structure. Theoretical analysis, computerized simulations and empirical experimentation can be used to design reactive surface 24 so that the electromagnetic cavity mode is characterized by a small and exponentially decaying field outside the cavity structure. Thus, the electromagnetic energy that is radiated in the near field behind the reactive surface is significantly reduced, while the overall efficiency of the antenna in free space conditions is only negligibly reduced by the reactive surface. In conditions of actual use, on the other hand, with the head of the user of the communication device in proximity to the reactive surface, the overall efficiency of the antenna assembly is increased due to reduced absorption of radiation in the head, and the Specific Absorption Rate (SAR) of the antenna assembly is significantly reduced. Reference is now made to Figs. 4A and 4B, which show details of coils that may be printed on substrate 52 of reactive surface 24, in accordance with embodiments of the present invention. Fig. 4A illustrates an in-line printed coil 60, of a type that is described, for example, in U.S. Patent 3,992,691, whose disclosure is incorporated herein by reference. Conductors 64, 66 are printed on both sides of dielectric substrate 52. The solid lines show conductors 64 on a first surface of the substrate, while the dotted lines show conductors 66 on the opposite surface of the substrate. Plated-through holes 68 connect the conductors on the two surfaces to create a coil whose axis is parallel to the board. Areas 70 of overlap between the top and bottom conductors creates a parasitic capacitance, which is particularly significant for thin boards and high frequencies . As a result, pure inductive reactivity cannot readily be achieved using coils of the type shown in Fig. 4A. Fig. 4B illustrates in-line printed coil 50, of the type shown above in Fig. 3. As in the embodiment of Fig.

4A, top conductors 76 and bottom conductors 74 are printed on opposite sides of substrate 52 and are interconnected through plated holes 68. Coil 50, however, is printed in a rectilinear configuration, i.e., conductors 74 and 76 comprise segments that are aligned in mutually-perpendicular directions. In this particular embodiment, each of conductors 74 and 76 comprises two mutually-perpendicular segments in an L-shape. The rectilinear configuration of coil 50 nearly eliminates the overlap between conductors 74 and 76 (except in the narrow area of hole 68, where the overlapping segments are short-circuited by the plated hole) . Thus, the parasitic capacitance of coil 50 is generally negligible. Rectilinear coils of this sort can thus be applied at very high microwave frequencies and on very thin dielectric surfaces without degradation of their inductive nature. Returning now to Fig. 3, further details of an exemplary design of reactive surface 24 will now be described. Substrate 52 typically comprises a dielectric material, such as plastic or epoxy materials available from Arlon (Rancho Cucamonga, California) , which is plated with conductors 74, 76 on both sides to form coils 50 using lithographic processes known in the art. The coils are typically arranged in straight lines in a rectangular grid. Cross conductors 78 are optionally used to allow induced current to flow in an orthogonal direction. Additional coils (not shown) may optionally be installed along the cross conductors, to increase the reactivity of the surface. The inductance of the inductors is typically uniform, but non-uniform inductance can be applied in order to create specific reactivity patterns. Short circuit strap 38 on the periphery of the inductor grid may be connected to the ground plane of plate 28, as noted above, in order to define specific modes of the cavity that is created between the reactive surface and the ground plane. In one embodiment, the dimensions of a single segment of coil 50 are about 1.5 x 0.1 mm, and the footprint of the complete coil is about 1.5 x 2 mm. The distance between two adjacent coils is 2 mm (which is less than 0.6% of the typical wavelength in typical mobile phone applications) . This coil configuration gives typical inductance values in the range of a few nH. The use of in-line printed coils, such as coils 50, to produce reactive surface 24 has the following advantages : 1. Homogeneity: As the coils are very small and can be positioned in high density compared to the wavelength, the performance of the reactive surface is approximately homogeneous . 2. Computational simplicity: The design of modern antennas leans heavily on computer simulations, such as are performed by the HFSS™ software package, distributed by Ansoft (Pittsburgh, Pennsylvania) . These simulation programs are much heavier computationally when applied to arbitrary antenna geometries, and are much more efficient when applied to discrete, lumped components. The small size of the in-line printed inductors used on reactive surface 24 enables the reactive surface to be simulated as a collection of lumped elements . 3. Reduced production cost : In embodiments such as those shown above, reactive surface 24 comprises tens of inductors. The component cost and production cost of the reactive surface when printed inductors are used are much lower than the costs of purchasing and soldering discrete components onto the surface. 4. Accuracy: The printed coils are positioned automatically and precisely on the reactive surface by the lithographic process that is used to print the conductors on substrate 52. This process is much more accurate and repeatable than the process of placing and soldering discrete components on a board. 5. Reduced losses: The printed coils are made of highly-conductive copper, without the lossy soldering materials that are generally used for soldering discrete components. 6. Reduced volume: The in-line printed coils have the advantage of very low profile , eliminating the space that would be consumed on the back side of reactive surface 24 by discrete components . Therefore, the total physical space required to accommodate antenna assembly 20 inside the mobile phone case is reduced. Fig. 5 is a plot that schematically shows the SAR computed in simulations of the performance of antenna assembly 20, in accordance with an embodiment of the present invention. The antenna assembly in this embodiment was designed to operate in the PCS band, between 1.85 and 1.91 GHz. Feed structure 22 was designed as an inverted-F antenna of the form shown above, with dimensions of approximately 20 x 40 mm. The dimensions of reactive surface 24 were approximately 15 x 12 mm, with coils 50 printed on the surface in the manner and configuration shown above in Fig. 3: twenty coils, spaced 2 mm apart, each with an inductance of approximately 4.7 nH. The reactive surface was located approximately 0.65 mm from rear plate 28 of the feed structure, in the position shown in Fig. 1. To create the curves shown in Fig. 5, the above- mentioned HFSS software was used to simulate the electromagnetic field radiated by assembly 20 as a function of frequency, with and without reactive surface 24. The energy absorbed by the user's head was calculated based on the relation of the field distribution to the position and absorbance of the head. An upper curve 80 shows the SAR calculated in this manner in the absence of surface 24, while a lower curve 82 shows the SAR with surface 24 in place. It can be seen that the use of the reactive surface reduced the SAR as a function of frequency by between 25% and 50%. Figs. 6A-6D show elements of antenna assemblies 90, 92, 94 and 96, respectively, in accordance with alternative embodiments of the present invention. The different embodiments comprise reactive surfaces 100, 102, 104, 106 and 108 in different positions relative to rear plate 28. (Front plate 26 is not shown.) Generally, the reactive surface is made much smaller than plates 28 and 26 - for example, between 10% and 25% of the area of plate 26 - in order to support the appropriate boundary conditions and enable its operation. Reducing the size of the reactive surface also reduces the volume and weight of the antenna assembly. The reactive surface is typically placed opposite the "hot spot" of the feed structure, i.e., the location at which the current flowing in the feed structure is highest, such as in the vicinity of the current feed to the radiating surface. As noted above, the characteristics of the reactive surface are chosen so as to approximately match the mode in the cavity formed by the reactive surface to the mode of the current flowing in the conductive plates of the feed structure. Each position of the reactive surface in Figs. 6A-6D creates different boundary conditions on the distribution of current in the reactive surface, and thus compensates for a different current distribution of the corresponding feed structure. Fig. 6A shows reactive surface 100, which is shorter than plate 28 and is supported on dielectric supports 110. In this configuration a short circuit 112 follows the bottom of the reactive surface. Fig. 6B shows reactive surface 102, which is shorter than plate 28 on both sides and is supported on dielectric supports 122. In this configuration short circuits 124 are at the top of the reactive surface. Fig. 6C shows multiple reactive surfaces 104, 106, which are shorter than plate 28 and are supported on dielectric supports 132. A short circuit 134 is located on the left of surface 106, while another short circuit 136 is at the top of surface 104. Fig. 6D shows reactive surface 108, which overlaps the width of plate 28 and is supported on dielectric supports 142. In this configuration, a short circuit 144 is at the top of the reactive surface. Although the embodiments described hereinabove are directed to personal communication devices, and particularly to protecting users of such devices from RF radiation emitted by device antennas, the usefulness of the present invention is by no means limited to such applications. Rather, the principles and techniques of the present invention may be applied to produce near- field directional antenna assemblies for other uses, as well. Furthermore, although the above embodiments use an inverted-F feed structure, other feed structures and associated cavity configurations will be apparent to those skilled in the art and are considered to be within the scope of the present invention. For instance, although the elements of antenna assembly 20 are shown above as being substantially planar in shape, non-planar structures may be used, as well. Various alternative feed structures and reactive surfaces are shown, for example, in the above-mentioned PCT patent application. It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art .

Claims

CLAIMS 1. An antenna assembly for a communication device, the assembly comprising: a feed structure, which has front and rear sides, and which is coupled to be driven by the device so as to radiate an electromagnetic field in a given frequency band; and an electrically reactive surface comprising an array of reactive circuit elements, which is positioned adjacent to the rear side of the feed structure so as to define a cavity between the feed structure and the reactive surface.

2. The assembly according to claim 1, wherein the reactive surface comprises a printed circuit board having a plurality of faces in one or more layers, and wherein the reactive circuit elements comprise traces printed on one or more of the faces of the printed circuit board.

3. The assembly according to claim 2, wherein the traces are printed so as to define inductive coils.

4. The assembly according to claim 3, wherein the traces defining at least some of the inductive coils are printed in a rectilinear configuration on at least two of the faces of the printed circuit board.

5. The assembly according to claim 4, wherein the at least two of the faces of the printed circuit board comprise first and second faces, and one or more holes pass through the printed circuit board between the first and second faces, and wherein each of the at least some of the inductive coils comprises: a first linear conducting segment, aligned in a first direction on the first face of the printed circuit board; a second linear conducting segment, connected to the first linear conductor and aligned in a second direction, perpendicular to the first direction, on the first face of the printed circuit board; a third linear conducting segment, aligned in the first direction on the second face of the printed circuit board and connected to the second linear conductor through one of the holes ; and a fourth linear conducting segment, connected to the third linear conductor and aligned in the second direction on the second face of the printed circuit board.

6. The assembly according to any of claims 1-5, wherein the feed structure and reactive surface are adapted to be mounted on the communication device so that the reactive surface intervenes between the feed structure and a head of a user of the device.

7. The assembly according to any of claims 1-5, wherein the reactive circuit elements comprise capacitors.

8. The assembly according to any of claims 1-5, wherein the reactive circuit elements are mutually connected in series .

9. The assembly according to any of claims 1-5, wherein the reactive circuit elements are mutually connected in parallel.

10. The assembly according to any of claims 1-5, wherein the rear side of the feed structure is planar, and wherein the reactive surface is positioned parallel to the rear side of the feed structure.

11. The assembly according to any of claims 1-5, wherein the feed structure comprises an inverted-F feed structure .

12. The assembly according to any of claims 1-5, wherein the rear side of the feed structure is electrically conductive .

13. The assembly according to any of claims 1-5, wherein the reactive surface is short-circuited to the feed structure in at least one location.

14. A method for wireless communication using a communication device operating in a given frequency band, the method comprising: coupling a feed structure, having a front side and a rear side, to the communication device, so that the feed structure can be driven by the device to radiate an electromagnetic field in the given frequency band; and positioning an electrically-reactive surface comprising an array of reactive circuit elements, adjacent to the rear side of the feed structure, so as to define a cavity between the feed structure and the reactive surface.

15. The method according to claim 14, wherein the reactive surface comprises a printed circuit board having a plurality of faces in one or more layers, and wherein positioning the array of reactive circuit elements comprises printing traces on one or more of the faces of the printed circuit board.

16. The method according to claim 15, wherein printing the traces comprises forming the traces so as to define inductive coils.

17. The method according to claim 16, wherein forming the traces comprises printing at least some of the inductive coils in a rectilinear configuration on at least two of the faces of the printed circuit board.

18. The method according to claim 17, wherein the at least two of the faces of the printed circuit board comprise first and second faces, and one or more holes pass through the printed circuit board between the first and second faces, and wherein printing the at least some of the inductive coils comprises, for each of the at least some of the inductive coils: printing a first linear conducting segment, aligned in a first direction, on the first face of the printed circuit board; printing a second linear conducting segment, connected to the first linear conductor and aligned in a second direction, perpendicular to the first direction, on the first face of the printed circuit board; printing a third linear conducting segment, aligned in the first direction and connected to the second linear conductor through one of the holes, on the second face of the printed circuit board; and printing a fourth linear conducting segment, connected to the third linear conductor and aligned in the second direction, on the second face of the printed circuit board.

19. The method according to any of claims 14-18, wherein positioning the reactive surface comprises mounting the reactive surface on the communication device so that the reactive surface intervenes between the feed structure and a head of a user of the device .

20. The method according to any of claims 14-18, wherein the reactive circuit elements comprise capacitors.

21. The method according to any of claims 14-18, wherein the rear side of the feed structure is planar, and wherein positioning the reactive surface comprises positioning the reactive surfaces parallel to the rear side of the feed structure.

22. The method according to any of claims 14-18, wherein coupling the feed structure comprises coupling an inverted-F feed structure to the device.

23. The method according to any of claims 14-18, wherein the rear side of the feed structure is electrically conductive .

24. The method according to any of claims 14-18, and comprising short-circuiting the reactive surface to the feed structure in at least one location.