Compact antenna

An antenna, including a planar dielectric substrate and a conductive ground plane formed on the substrate. A conductive monopole is formed on the substrate and has an end point located in proximity to a feed region of the ground plane. A conductive coupling element is formed on the substrate and is coupled to the ground plane at a coupling region of the ground plane. The coupling element is folded around the monopole.

FIELD OF THE INVENTION

The present invention relates generally to antennas, and specifically to antennas that may be used in multiple bands.

BACKGROUND OF THE INVENTION

As the size of communication devices, such as cellular telephones, is reduced, typically the size of the antenna is required to be reduced as well. However, basic properties of the antenna may limit the freedom that a designer has to reduce the size of the antenna without adversely affecting the overall antenna performance. A paper titled “Introduction to Ultra-Wideband Antennas,” by Schantz, presented at the IEEE Conference on Ultra Wideband Systems and Technologies, November, 2003, describes some of the limitations that the author believes may hold for antennas. The paper is incorporated herein by reference.

The effect of a chassis to which the antenna is coupled is evaluated in a paper titled “Resonator-Based Analysis of the Combination of Mobile Handset Antenna and Chassis,” by Vainikainen et al., published in IEEE Transactions on Antennas and Propagation, Vol. 50, No. 10, October, 2002. The paper is incorporated herein by reference.

Finnish Patent Fl 114260 B, to Vainikainen et al., which is incorporated herein by reference, describes a coupling device for sending or receiving RF signals. The patent describes an antenna using radiation from a ground plane.

In a paper titled “Thin dual-resonant stacked shorted patch antenna for mobile communications,” by Ollikainen et al., published in Electronic Letters Volume 35, number 6, in March, 1999, the authors describe an antenna constructed from two stacked patches. The paper is incorporated herein by reference. One of the patches is a driven element, while the other acts as a parasitic element. The driven patch is formed on one side of a 1.6 mm substrate, on the other side of which is formed a ground plane. The parasitic patch is stacked above the driven patch, making the total height of the antenna 4 mm.

U.S. Patent Application 2003/0201942 A1, to Poilasne et al., which is incorporated herein by reference, describes a multi-band antenna. The antenna comprises one or more first plates and one or more second plates. The plates are mounted over a ground plate.

In a paper titled “A Low-Profile Antenna Solution for Mobile Phones with GSM, UMTS and WLAN Operation,” by Rennings et al., presented at the European Microwave Conference, Paris, France in October, 2005, the authors describe an antenna formed by printing dual-layers on a substrate. The paper is incorporated herein by reference.

In a paper titled “Low-Profile Planar Monopole Antenna for GSM/DCS/PCS Triple-Band Mobile Phone,” by Lee et al., and published in the IEEE Antennas and Propagation Society International Symposium 2002, Volume 3, pages 26-29, the authors describe an antenna printed on a substrate. The paper is incorporated herein by reference. The antenna has a single feed point with a microstrip feed line.

PCT Patent Application WO 2004/027922, to Kadambi et al., which is incorporated herein by reference, describes an antenna which may be printed on a substrate. The antenna is connected to one region of a ground plane on the substrate.

SUMMARY OF THE INVENTION

In an embodiment of the present invention, an antenna comprising at least two elements is formed on a planar dielectric substrate, and a conductive ground plane is also formed on the same substrate. A first element of the antenna comprises a monopole, which is located on the substrate so as to have one of its end points, herein termed the feed end point, in proximity to a feed region of the ground plane. The feed end point and feed region form a feed zone for the antenna. Typically, the monopole is in the form of a linear or folded or meandering conductive flat strip, and the length of the strip is arranged so that the impedance of the monopole is substantially capacitive. The monopole may be a single-band monopole or a multi-band monopole.

A second element of the antenna, herein termed a coupling element, comprises a conductive strip, which is formed on the substrate and which is folded around the monopole. The coupling element may be formed so as to have a length that is at least 1.5 times the length of the monopole. Typically, the length of the coupling element is twice or more the length of the monopole. The coupling element is connected galvanically or capacitively to a coupling region of the ground plane, which is typically a different region from the feed region of the ground plane.

The monopole, in conjunction with the coupling element and the ground plane, radiates efficiently in a high-frequency band. In addition, the monopole couples a low-frequency band electric field, via the coupling element, to the ground plane, which radiates efficiently at the low-frequency band. The coupling by the coupling element occurs mainly via the electric field, which is strong at edge regions of the ground plane. The coupling element, by virtue of folding around the monopole and being coplanar with the monopole and the ground plane, does not radiate. Typically, the widest possible overall bandwidth of the combined structure of monopole, coupling element, and ground plane is determined mainly by the size of the ground plane, and a center frequency of the combined structure is determined mainly by the length of the coupling element in conjunction with the resonance frequency of the ground plane. A narrow bandwidth of the coupling element does not prevent wide band operation, if the center frequencies of the coupling element and the ground plane are relatively close together. The combined structure may thus be conveniently configured to form a very good antenna for both the low and the high-frequency bands. Furthermore, the monopole and the coupling element may be laid out extremely compactly in a planar form and may be produced at very low cost, simply by removal of conductive material from one or both outer surfaces of the substrate.

In one embodiment one or more reactive devices may be connected to the monopole and/or the coupling element, so as to alter the electrical length of the elements.

In an alternative embodiment the monopole and the coupling element may be on opposite surfaces of the substrate.

In some embodiments, the monopole, the coupling element, and the ground plane, are on one common surface of the substrate.

Both the feed region and the coupling region are typically close to a common edge of the ground plane. Alternatively, one or both of the regions may be indented from the edge, in which case the monopole and/or the coupling element may be correspondingly extended. In a disclosed embodiment, a length of an indentation, and of a corresponding section of the coupling element within the indentation, is adjusted to improve performance of the antenna by reducing the antennas reflection coefficient. In some disclosed embodiments, the indentation is configured to have more than one direction, for example by being formed in the shape of an “L,” the different directions providing control for directions of polarization of radiation from the antenna. The polarization may be further controlled by selecting whether the section of the coupling element galvanically or capacitively couples to the ground plane. Alternatively or additionally, polarization may be controlled by locating the coupling region along an edge of the ground plane different from the edge close to the feed region.

In an alternative disclosed embodiment, the antenna comprises one or more further coupling elements in addition to the coupling element described above. Each of the further elements is coupled to a respective region of the ground plane. In these alternative embodiments, the length of the monopole is arranged to be too short to radiate efficiently, and acts mainly to couple electric or magnetic fields via the coupling elements to the ground plane, which has dimensions chosen to enable it to radiate efficiently. For example, in the case of one further coupling element, the length of the original coupling element may be selected so that it enables efficient radiation from the ground plane at a high-frequency band, and the length of the further coupling element may be selected so that it enables efficient radiation from the ground plane at a low-frequency band.

There is therefore provided, according to an embodiment of the present invention, an antenna, including:

a planar dielectric substrate;

a conductive ground plane formed on the substrate;

a conductive monopole formed on the substrate and having an end point located in proximity to a feed region of the ground plane; and

a conductive coupling element formed on the substrate and coupled to the ground plane at a coupling region of the ground plane, the coupling element being folded around the monopole.

Typically, the conductive monopole has a monopole length, and the conductive coupling element has a coupling element length equal to at least 1.5 times the monopole length. In an embodiment the coupling element length is equal to at least two times the monopole length.

The monopole and the coupling element may be configured so that the monopole together with the ground plane radiate with an efficiency of 30% or more in a first frequency band having a first center frequency and in a second frequency band having a second center frequency. The first and second frequency bands may be disjoint. In one embodiment the first frequency band includes frequencies between 820 MHz and 960 MHz, and the second frequency band includes frequencies between 1.7 GHz and 2.2 GHz.

The monopole and the coupling element may be configured so that the monopole together with the ground plane radiate with an efficiency of at least 30%.

The monopole and the coupling element may be configured so that the monopole together with the ground plane radiate with an efficiency of at least 30% at a frequency less than or equal to 6 GHz.

Typically, at least one of the conductive monopole and the conductive coupling element includes a flat strip.

In some embodiments, the antenna includes one or more reactive elements electrically connected to at least one of the conductive monopole and the conductive coupling element. The one or more reactive elements may be electrically connected between the conductive coupling element and the ground plane.

In a disclosed embodiment, the monopole and the coupling element are formed on opposite surfaces of the substrate.

The ground plane may include a first ground plane section formed on a first surface of the substrate and a second ground plane section formed on a second surface of the substrate.

The ground plane may include an indentation, and the feed region may be located in proximity to the indentation.

In one embodiment the ground plane includes an indentation, and a section of the coupling element is disposed within the indentation so as to couple electrically to an end point of the indentation. The indentation and the section of the coupling element may be linear. A length of the indentation and of the section may be selected so as to optimize at least one of a reflection coefficient and a radiation efficiency of the antenna at a selected frequency. Alternatively, the indentation and the section of the coupling element may be non-linear. The indentation may include a first indentation section having a first direction and a second indentation section having a second direction different from the first direction, and the section of the coupling element may include a first coupling element section disposed within the first indentation section and a second coupling element section disposed within the second indentation section. One of the first indentation section and the first coupling element section may have a first dimension, and one of the second indentation section and the second coupling element section may have a second dimension, and the first and the second dimensions may be selected so as to determine a polarization characteristic of radiation from the antenna.

Typically, the coupling element is coupled capacitively to the ground plane.

Alternatively, the coupling element is coupled galvanically to the ground plane.

The antenna may include a further conductive coupling element formed on the substrate and connected to the ground plane at a further coupling region. The conductive coupling element may have a coupling element length, and the further conductive coupling element may have a further coupling element length, and the coupling element length and the further coupling element length may be selected so that the coupling element and the further coupling element radiate respectively in a first radiation frequency band and in a second radiation frequency band different from the first radiation frequency band. The conductive monopole may have a monopole length selected so that the folded monopole acts primarily to couple an electric field to the conductive coupling element and the further conductive coupling element.

In an alternative embodiment, the conductive ground plane, the conductive monopole, and the conductive coupling element are formed on one common surface of the substrate.

The coupling region and the feed region may be in different locations. The coupling region and the feed region may partly overlap.

The ground plane typically includes a ground plane edge, and at least one of the coupling region and the feed region may be in proximity to the ground plane edge. At least one of the coupling region and the feed region may be at least 3 mm from an end of the edge.

The ground plane may have a ground plane length and the monopole may have a monopole length, and a ratio between the monopole length and the ground plane length is in a range between 0.25 and 0.6.

The monopole may include a folded monopole, a meander monopole or a linear monopole.

The ground plane may include a first edge and a second edge different from the first edge, the feed region may be formed in proximity to the first edge and the coupling region may be formed in proximity to the second edge. The coupling element may include a linear element having a dimension selected so as to determine a polarization characteristic of radiation from the antenna.

In a disclosed embodiment the dielectric substrate includes a plurality of dielectric layers, and at least two of the ground plane, the monopole, and the coupling element are formed on different layers included in the dielectric layers.

The monopole may include a single-band monopole or a multi-band monopole.

The coupling element may include a further coupling element galvanically connected to the coupling element and capacitively coupling to a further coupling region of the ground plane.

Typically, the monopole as viewed from the feed region and the coupling element as viewed from the coupling region are configured to turn in opposite directions. Alternatively, the monopole as viewed from the feed region and the coupling element as viewed from the coupling region are configured to turn in like directions.

The end point may be configured to couple to a live side of a feed to the antenna.

The antenna may include a matching circuit coupled to the conductive monopole and located in proximity to the end point.

There is further provided, according to an embodiment of the present invention a method for producing an antenna, including:

providing a planar dielectric substrate;

forming a conductive ground plane on the substrate;

forming a conductive monopole on the substrate, the monopole having an end point located in proximity to a feed region of the ground plane;

forming a conductive coupling element on the substrate;

coupling the conductive coupling element to the ground plane at a coupling region of the ground plane; and

folding the coupling element around the monopole.

There is further provided, according to an embodiment of the present invention an antenna, including:

a dielectric substrate;

a conductive ground plane formed on the substrate and having a first edge and a second edge;

a first conductive monopole formed on the substrate and having a first end point located in proximity to the first edge;

a first conductive coupling element formed on the substrate and coupled to the ground plane at a first coupling region of the ground plane, the first coupling element being folded around the first monopole;

a second conductive monopole formed on the substrate and having a second end point located in proximity to the second edge; and

a second conductive coupling element formed on the substrate and coupled to the ground plane at a second coupling region of the ground plane, the second coupling element being folded around the second monopole.

Typically, the ground plane, the first monopole, and the first coupling element are configured to operate at a first frequency, and the ground plane, the second monopole, and the second coupling element are configured to operate at a second frequency different from the first frequency.

In one embodiment the ground plane, the first monopole, and the first coupling element, are configured to operate at a given frequency, and the ground plane, the second monopole, and the second coupling element are configured to operate at the given frequency.

There is further provided, according to an embodiment of the present invention a method for producing an antenna, including:

providing a dielectric substrate;

forming a conductive ground plane having a first edge and a second edge on the substrate;

forming a first conductive monopole on the substrate, the first monopole having a first end point located in proximity to the first edge;

forming a first conductive coupling element on the substrate;

coupling the first conductive coupling element to the ground plane at a first coupling region of the ground plane;

folding the first coupling element around the first monopole;

forming a second conductive monopole on the substrate, the monopole having a second end point located in proximity to the second edge;

forming a second conductive coupling element on the substrate;

coupling the second conductive coupling element to the ground plane at a second coupling region of the ground plane; and

folding the second coupling element around the second monopole.

There is further provided, according to an embodiment of the present invention an antenna, including:

a planar dielectric substrate;

a conductive ground plane formed on the substrate and having a ground plane edge;

a conductive monopole formed on the substrate in proximity to the ground plane edge and having an end point located in proximity to a feed region of the ground plane; and

a conductive coupling element formed on the substrate in proximity to the ground plane edge and coupled to the ground plane at a coupling region of the ground plane, the coupling element being configured so that a portion of the conductive monopole lies between a section of the element and the ground plane edge.

Typically, the feed region and the coupling region include respective sections of the ground plane edge.

In an embodiment at least one of the sections is at least 3 mm from an end of the edge.

There is further provided, according to an embodiment of the present invention a communication device, including:

a transceiver; and

an antenna coupled to the transceiver, the antenna including:

a planar dielectric substrate;

a conductive ground plane formed on the substrate;

a conductive monopole formed on the substrate and having an end point located in proximity to a feed region of the ground plane; and

a conductive coupling element formed on the substrate and coupled to the ground plane at a coupling region of the ground plane, the coupling element being folded around the monopole.

There is further provided, according to an embodiment of the present invention a method for producing a communication device, including:

providing a transceiver; and

coupling an antenna to the transceiver, the antenna including:

a planar dielectric substrate,

a conductive ground plane formed on the substrate,

a conductive monopole formed on the substrate and having an end point located in proximity to a feed region of the ground plane, and

a conductive coupling element formed on the substrate and coupled to the ground plane at a coupling region of the ground plane, the coupling element being folded around the monopole.

There is further provided, according to an embodiment of the present invention an antenna, including:

a planar dielectric substrate;

a conductive ground plane formed on the substrate;

a conductive loop formed on the substrate and having an end point located in proximity to a feed region of the ground plane; and

a conductive coupling element formed on the substrate and coupled to the ground plane at a coupling region of the ground plane, the coupling element being folded around the loop.

There is further provided, according to an embodiment of the present invention a method for producing an antenna, including:

providing a planar dielectric substrate;

forming a conductive ground plane on the substrate;

forming a conductive loop on the substrate, the loop having an end point located in proximity to a feed region of the ground plane; and

forming a conductive coupling element on the substrate and coupling the coupling element to the ground plane at a coupling region of the ground plane so that the coupling element folds around the loop.

There is further provided, according to an embodiment of the present invention an antenna, including:

a planar dielectric substrate;

a conductive ground plane formed on the substrate;

a conductive monopole having an end point located in proximity to a feed region of the ground plane; and

a conductive coupling element coupled to the ground plane at a coupling region of the ground plane, at least one of the conductive monopole and the conductive coupling element having a section external to a plane of the substrate, a projection of the coupling element onto the plane being folded around a projection of the monopole onto the plane.

There is further provided, according to an embodiment of the present invention, a method for producing an antenna, including:

providing a planar dielectric substrate;

forming a conductive ground plane on the substrate;

forming a conductive monopole having an end point located in proximity to a feed region of the ground plane; and

coupling a conductive coupling element to the ground plane at a coupling region of the ground plane, at least one of the conductive monopole and the conductive coupling element having a section external to a plane of the substrate, a projection of the coupling element onto the plane being folded around a projection of the monopole onto the plane.

There is further provided, according to an embodiment of the present invention, an antenna, including:

a planar dielectric substrate;

a conductive ground plane formed on the substrate and operative as a parallel resonant circuit having a first resonance frequency;

a conductive coupling element, operative as a series resonant circuit having the first resonance frequency, and located in proximity to the conductive ground plane so as to be coupled thereto by a first field chosen from at least one of a first electric field and a first magnetic field; and

a conductive monopole, operative as a series resonant circuit having a second resonance frequency, and located in proximity to the conductive coupling element so as to be coupled thereto by a second field chosen from at least one of a second electric field and a second magnetic field.

Typically, a first electric coupling generated by the first electric field is greater than a first magnetic coupling generated by the first magnetic field, and a second electric coupling generated by the second electric field is greater than a second magnetic coupling generated by the second magnetic field.

In one embodiment the conductive monopole and the conductive ground plane are coupled by a third field chosen from at least one of a third electric field and a third magnetic field.

There is further provided, according to an embodiment of the present invention, a method for producing an antenna, including:

providing a planar dielectric substrate;

forming a conductive ground plane on the substrate, the conductive ground plane being operative as a parallel resonant circuit having a first resonance frequency;

locating a conductive coupling element, operative as a series resonant circuit having the first resonance frequency, in proximity to the conductive ground plane so as to be coupled thereto by a first field chosen from at least one of a first electric field and a first magnetic field; and

locating a conductive monopole, operative as a series resonant circuit having a second resonance frequency, in proximity to the conductive coupling element so as to be coupled thereto by a second field chosen from at least one of a second electric field and a second magnetic field.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made toFIG. 1, which is a schematic diagram of a communication device10, according to an embodiment of the present invention. Device10is typically a cellular phone or a personal digital assistant (PDA), and the device is hereinbelow assumed to comprise a cellular phone. Phone10has an enclosure11, within which operational elements of the phone are mounted. Phone10comprises a transceiver14which is mounted on a dielectric substrate22. Typically, substrate22is a planar dielectric substrate for a multilayer printed circuit board (PCB)12, and components of transceiver14are mounted on the substrate. In some embodiments of the present invention, substrate22may comprise one or more dielectric layers of multilayer PCB12, and other dielectric layers of the multi-layer PCB may be located above and/or below substrate22. For clarity, such other layers are not shown inFIG. 1. It will be understood that substrate22may comprise dielectrics other than those used for a PCB. For example, the scope of the present invention includes substrates such as are formed from flexible dielectrics, and/or dielectrics that may be coated and/or deposited and/or painted onto a surface.

Substrate22is typically one layer of PCB12, which comprises a conductive ground plane21as another layer. An antenna20, herein by way of example assumed to comprise a multi-band antenna, is formed on substrate22, and the antenna is coupled to transceiver14by a feed15. Feed15may be any convenient system that efficiently transfers radiation between the transceiver and the antenna, and is herein by way of example assumed to comprise a coaxial cable. Antenna20is described in more detail below.

FIGS. 2A and 2Bare schematic diagrams of multi-band antenna20, according to an embodiment of the present invention.FIGS. 2A and 2Bshow two views of antenna20and substrate22: a front view of a front surface24of the substrate, and a back view of a rear surface26of the substrate. The views are shown relative to a set of x, y, z orthogonal axes. Substrate22is assumed by way of example to be approximately rectangular with dimensions of the order of 115 mm long×40 mm wide. Also by way of example, the substrate is assumed to be approximately 1 mm in depth.

In the following description a section28of ground plane21, having a ground plane edge39parallel to the x axis, is assumed to be formed to cover approximately the lower 100 mm of rear surface26. A section29of the ground plane is galvanically connected to section28, typically by vias not shown inFIGS. 2A and 2B. Section29has a ground plane edge35parallel to the x axis, and is assumed to cover approximately the lower 100 mm of front surface24. Thus ground plane edges35and39, respectively defining a top region32of the front surface of the substrate and a top region41of the rear surface, are approximately 15 mm from a top edge37of substrate22. Except as described below, regions32and41do not have conductive material.

A conductive folded single-band monopole30is formed in top region32, typically as a strip of conductive material having a constant width along the strip of approximately 1 mm. However, embodiments of the present invention may use different widths of conductive material, typically within a range of approximately 0.5 mm to approximately 4 mm. Furthermore, in some embodiments of the present invention, the width of the conductive material may be varied along the length of monopole30. Monopole30is arranged to have two connected orthogonal linear sections31and33, respectively parallel to the y and x axes, having a total length of approximately 3 cm. Typically, for example for cellular applications, the total length of monopole30is within a range between approximately 2.5 cm and approximately 4 cm, so that the ratio of monopole length to ground plane length is in a range between approximately 0.25 and 0.6. At these lengths, in a high-frequency radiation band between approximately 1.7 GHz and approximately 2.2 GHz and having a center frequency of approximately 1.9 GHz, the monopole acts as a single-band monopole which is an approximately quarter-wavelength radiator, thus radiating efficiently in the high-frequency band.

The monopole is arranged so that an end36is close to, but does not touch, edge35, at a region38of the ground plane. Feed15(FIG. 1) has a “live” side and a ground side which are respectively connected to end36and region38. Thus, if feed15comprises a coaxial cable, the central conductor of the cable is connected to end36, and the shield of the cable is connected to region38. Alternatively, other systems known in the art may be used to feed the antenna, such as a microstrip. Region38is herein termed the ground plane feed region, and is assumed to be a region bordering edge35and within a distance of the order of 5 mm from end36. End36and region38act as a feed zone40for antenna20.

A second element34, herein also termed a coupling element, is also formed in top region32. Element34is formed from a conductive strip which typically has the same width as the strip forming monopole30. The coupling element is typically arranged to have a length that is approximately 1.5 times the length of monopole30, or longer. Typically, the length of coupling element34is approximately twice or more the length of monopole30.

Element34is configured in top region32to be folded around monopole30so as to at least partially enclose the monopole. The folding may be accomplished by arranging different linear sections of element34to be parallel to the x or y axes, as shown in the figure. In the case of monopole30, element34, and ground plane edge35lying on a common surface of substrate22, the element is considered to be folded around the monopole if some section of the element may be chosen so that a portion of the monopole lies between the chosen section and ground plane edge35, as measured in the surface and orthogonally to the edge.

Alternatively, monopole30, element34, and ground plane edge35may lie on two or more different surfaces of substrate22, the surface wherein the monopole lies being termed the monopole surface. In this case, the element is considered to be folded around the monopole if some section of a projection of the element onto the monopole surface may be chosen so that a portion of the monopole lies between the chosen section and ground plane edge35, or a projection of ground plane edge35onto the monopole surface, as measured in the monopole surface and orthogonally to the edge.

Regarding the term “projection,” in the specification and in the claims, if an element is in a plane, a projection of the element onto the plane is assumed to be congruent with the element.

Element34has a first end42and a second end44. End42is located so that typically it galvanically connects to edge35of ground plane21at a region46, which has a different, separate, location from feed region38. Region46is herein termed the ground plane coupling region, and is assumed to be a region of the ground plane bordering edge35and within of the order of 5 mm from end42. Advantageously, element34and section29comprise one continuous piece of conductive material. The separation of coupling region46and feed region38is typically at least 5 mm, and both regions are typically located at least 3 mm from the ends of edge35.

A terminating linear section48of element34is parallel to the y axis, and is arranged so that the distance between end44and edge35is in a range between approximately 1 mm and approximately 10 mm. In a disclosed embodiment, the distance is approximately 7 mm.

A low-frequency band is assumed herein to be in a range between approximately 820 MHz and approximately 960 MHz. The low-frequency band has a center frequency of approximately 880 MHz, which is approximately 55% less than the center frequency of the high-frequency band referred to above. In the low-frequency band monopole30couples electric fields via coupling element34to ground plane21, which radiates efficiently in the low-frequency band, since it is of the order of half a wavelength in length for these frequencies. Coupling element34acts as a resonant coupling element which does not radiate. Element34differs from a parasitic element by virtue of the fact that resonance frequencies of the element and monopole30are in different ranges. Typically, the difference between the two resonance frequencies is greater than 33% of the center frequency of the high-frequency band. Thus antenna20acts as an efficient radiator in both the low-frequency and high-frequency bands. Inspection ofFIG. 2Ashows that, in addition, antenna20is extremely compact, occupying a surface area of the order of 5 cm2or less, with the depth of a single printed circuit board. The lengths of sections of monopole30and/or coupling element34may be adjusted easily so that antenna20radiates efficiently at multi-band frequencies, other than those listed above, typically of the order of 900 MHz and of the order of 2 GHz. It will be understood that the extremely compact characteristic of the antenna may be maintained given such adjustment. Advantageously, the adjustments in lengths may be initially verified using antenna simulation software which typically involves a Method of Moments analysis. For example Agilent Technologies, of Santa Clara, Calif., provide a software package GENESYS™ that may be used for simulating the antenna.

The inventors have found that in embodiments of the present invention, typically the size of the ground plane mainly determines the widest possible bandwidth of the combined structure comprising monopole, coupling element, and ground plane, and that the length of the coupling element in conjunction with the resonance frequency of the ground plane mainly determines the center frequency of the bandwidth. In the case of a communication device such as a cell phone, the size of the ground plane may be constrained by the dimensions of the cell phone. However, within these constraints, by adjusting the sizes of the coupling element and/or the ground plane, an antenna with a wide or a narrow bandwidth, and having an efficiency of approximately 30% or more, may be configured for a wide range of frequencies.

FIG. 2Cis a schematic equivalent circuit49of antenna20, according to an embodiment of the present invention. Monopole30typically acts as a first series resonant circuit43, comprising an inductor L1and a capacitor C1. Coupling element34typically acts as a second series resonant circuit45, comprising an inductor L2and a capacitor C2. Ground plane21typically acts as a parallel resonant circuit47, comprising an inductor L3and a capacitor C3. Circuit43has a resonance frequency within the high-frequency band, and circuits45and47have approximately equal resonance frequencies within the low-frequency band.

Circuit43is shown as being coupled to circuit45by a field coupling FC1. Circuit45is shown as being coupled to circuit47by a field coupling FC2. Field couplings FC1and FC2are by electric or magnetic fields. Typically, because the couplings occur in proximity to the edge of ground plane21, where the electric field is high, field couplings FC1and FC2substantially comprise only electric fields, and the couplings are mainly capacitive.

In addition to the two couplings described above, there may also be a field coupling FC3between circuit43and circuit47. This coupling, represented by a double headed arrow, is substantially similar to the couplings described above, i.e., the coupling may be by electric or magnetic fields, and is typically mainly by electric fields. The inventors are not aware of any good symbol to represent capacitive coupling, so it will be appreciated that the representations of field couplings FC1, FC2, and FC3inFIG. 2Care purely illustrative. For the three couplings, the electric coupling of the electric field is greater than, and is typically significantly greater than, the magnetic coupling of the magnetic field.

The amount of coupling between the three different circuits is a function of the dimensions of monopole30, coupling element34, and ground plane21, as well as of the relative positions of the monopole, the coupling element, and the ground plane with respect to each other. In addition, the amount of coupling is a function of the frequency at which the coupling occurs.

Equivalent circuits generally similar to equivalent circuit49apply, mutatis mutandis, to other embodiments of the present invention described herein. Changes to equivalent circuit49for such embodiments will be apparent to a person having ordinary skill in the art.

FIG. 3Ais a schematic diagram of a multi-band antenna50, according to an embodiment of the present invention. Apart from the differences described below, the operation of antenna50is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation. Antenna50has a rear view substantially similar to the rear view of antenna20(FIG. 2B).

Antenna50comprises a coupling element54, which performs substantially the same functions as coupling element34(FIG. 2A). An end52of coupling element54connects to section29at a coupling region56of the ground plane. Coupling region56has generally the same dimensions as coupling region46. In contrast to antenna20, coupling region56is relatively close to feed region38and the two regions typically partially overlap. As for antenna20, the coupling and feed regions for antenna50are both adjacent to a common edge35.

FIG. 3Bis a schematic diagram of a multi-band antenna57, according to an embodiment of the present invention. Apart from the differences described below, the operation of antenna57is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation. Antenna57has a rear view substantially similar to the rear view of antenna20(FIG. 2B).

In antenna57one or more further monopoles are galvanically connected to monopole30to form a multi-band monopole59. By way of example, in antenna57a second monopole58is galvanically connected to monopole30. The lengths of the monopoles in multi-band monopole59are typically set to be different, so that the multi-band monopole radiates in a plurality of frequency bands corresponding to the number of monopoles. The one or more further monopoles, such as monopole58, typically have widths that are generally similar to the width of monopole30.

FIG. 3Cis a schematic diagram of a multi-band antenna70, according to an embodiment of the present invention. Apart from the differences described below, the operation of antenna70is generally similar to that of antenna50(FIG. 3A), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation. Antenna70has a rear view substantially similar to the rear view of antenna20(FIG. 2B).

In antenna70a further coupling element72is galvanically connected to coupling element54. Element72is in the form of an inverted “L” having a total length of the order of 1 cm. There is a gap78between an end74of element72and edge35, the gap typically being of the order of 0.5 mm or less. Thus element72capacitively couples to a second coupling region76of ground plane21. Region76comprises a region which borders edge35and is within of the order of 5 mm from end74. The inventors have found that element72increases the coupling of monopole30to ground plane section29, so that the ground plane radiates at the high-frequency band of the monopole, and so that the efficiency of radiation of antenna70improves. Dimensions of element72, the x position of end74, and the width of gap78, may be altered to optimize the efficiency of radiation of the antenna.

FIGS. 4 and 5are schematic diagrams of front views of multi-band antennas90and100, according to alternative embodiments of the present invention. Apart from the differences described below, the operation of antennas90and100is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in antennas20,90, and100are generally similar in construction and in operation. Antennas90and100have rear views substantially similar to the rear view of antenna20.

In antenna90, a substantially linear monopole92, having approximately the same length as folded monopole30, replaces the folded monopole. In antenna100, a meander monopole102, having approximately the same length as folded monopole30, replaces the folded monopole. Linear monopole92and meander monopole102are typically formed as conductive strips approximately 1 mm wide, and function in substantially the same manner as monopole30.

FIG. 6is a schematic diagram of a multi-band antenna120, according to an embodiment of the present invention.FIG. 6is a front view of antenna120. Antenna120has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna120is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation. In antenna120one or more reactive devices122connect sections of a coupling element134, which functions substantially as does element34. In one embodiment, the one or more reactive devices comprise a capacitor and inductor in parallel, having values which cause the devices to act as a stop-band filter. In another embodiment, devices122comprise one inductive element124connecting a section126and a section128of coupling element134.

Except for being broken into two sections, element134is generally similar in layout to coupling element34. However, the presence of reactive devices122allows the physical lengths of sections126and/or128to be reduced so that the overall size of antenna120may be less than that of antenna20. The change in physical length may be made substantially without affecting the overall performance of antenna120. In the case of inductive element124, a value may be chosen so that although the physical length of coupling element134is reduced, the presence of the inductive element allows the electrical length of the coupling element, i.e., the number of wavelengths at which the element resonates, to be substantially the same as the electrical length of coupling element34. A typical value for the inductance of element124is of the order of 5 nH.

Alternatively or additionally, the one or more reactive devices122may be located on monopole30, typically by breaking section33of the monopole at a location129. For clarity, devices122on monopole30are shown inFIG. 6with broken lines. Devices122located on the monopole perform generally the same functions, as described above, as devices122located on element134.

FIG. 7is a schematic diagram of a multi-band antenna170, according to another embodiment of the present invention.FIG. 7is a front view of antenna170. Antenna170has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna170is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation. In place of coupling element34, antenna170comprises a coupling element174, which is generally similar to element134(FIG. 6), except that element174is configured as one continuous conductive strip. Coupling element174functions substantially as does element34. An end172of element174is galvanically connected to ground plane21at a coupling region176, which has generally the same dimensions as coupling region46. In addition, one or more reactive devices178are connected between a region182, in proximity to edge35of ground plane21, and a portion180of element174.

In one embodiment reactive devices178comprise a capacitor and inductor in series, or alternatively in parallel. Devices178may be positioned, i.e., locations of region182and/or the connection to portion180, may be adjusted to effectively alter the position and/or size of coupling region176, as shown by a broken line184, as well as to alter the effective length of coupling element174.

FIGS. 8A and 8Bare schematic diagrams of a multi-band antenna220, according to an embodiment of the present invention.FIG. 8Ais a front view andFIG. 8Bis a rear view of the antenna. Apart from the differences described below, the operation of antenna220is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation. In antenna220, a coupling element234and folded monopole30are on opposite surfaces of substrate22, so that element234is in region41.

Elements234and34are generally similar in operation as well as in layout, so that, as shown by broken lines236, element234folds around monopole30. Elements244,248, and242of element234respectively correspond to elements44,48, and42of element34. The overall length of element234is substantially similar to the overall length of element34, and coupling element234connects to a coupling region246of section28of the ground plane, the coupling region having generally the same dimensions as coupling region46. In contrast to antenna20, the feed and the coupling regions of antenna220are adjacent to different edges, i.e., edges35and39, of ground plane21.

In configuring coupling element234on rear surface26, the coupling element and section28of the ground plane are advantageously made from one continuous piece of conductive material.

FIG. 9Ais a schematic diagram of a multi-band antenna320, according to an embodiment of the present invention.FIG. 9Ais a front view of antenna320. Antenna320has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna320is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation. In antenna320, a folded monopole330performs substantially the same functions as monopole30. Monopole330is generally similar to monopole30in shape, dimensions, and location. However, an end336of monopole330is aligned with edge35, and a first indentation335is made in edge35so that the alignment does not cause monopole330to galvanically contact section29. A feed region338, which has generally the same dimensions as feed region38, is in proximity to the lower edge of indentation335. Feed region338and end336act as a feed zone340for antenna320.

A coupling element334is generally similar in function and in dimensions to element34. However, a second indentation339, which typically is linear and orthogonal to edge35, is made in section29, and element334comprises a section337which extends within indentation339. Section337extends so that an end342of the section galvanically contacts to ground plane section29, forming a coupling region346in proximity to the end. Coupling region346is a region within of the order of 5 mm from end342. A length Lindentof section337, and of the indentation, may be set so as to take advantage of the different current and potential characteristics of section29as antenna320operates, so as to improve impedance matching of frequencies radiated by the antenna.

Thus, at edge35there is generally high potential but low current providing a high impedance, whereas at a central line344of section29there is generally high current but low potential providing a low impedance. Using these criteria, a value of Lindentmay be selected so as to optimize the voltage standing wave ratio (VSWR), i.e., to optimize the reflection coefficient and/or the radiation efficiency of antenna320. Advantageously, the determination of an optimal value of Lindentmay be made using a Method of Moments software package, such as that referenced above. In one embodiment, a value of Lindentis approximately 20 mm, for radiation in the high and low-frequency bands referred to above. In some embodiments, the value of Lindentmay be selected to set a polarization characteristic of antenna320, typically the polarization in a high-frequency band of the antenna, since the polarization of radiation from the antenna is a function of the directions and magnitudes of currents flowing in ground plane section29.

In contrast to element34, a terminating linear section341of coupling element334is configured to be parallel to the x axis. In one embodiment, section341is approximately 5 mm long, and there is a gap of approximately 2 mm between the edge of section341and edge35.

FIG. 9Bis a schematic diagram of a multi-band antenna360, according to an embodiment of the present invention.FIG. 9Bis a front view of antenna360. Antenna360has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna360is generally similar to that of antenna320(FIG. 9A), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation.

In contrast to antenna320, end342is not galvanically connected to ground plane section29. Rather, there is a space362between end342and the ground plane, so that coupling element334only capacitively couples to the ground plane. By altering the dimensions of the space between indentation339and section337, as well as of space362, the directions of currents flowing in the ground plane adjacent to section337, and the magnitudes of the currents, may be adjusted, so that the polarization of the radiation from antenna360may be correspondingly adjusted.

FIG. 9Cis a schematic graph of antenna efficiency vs. frequency, for an embodiment of the present invention. The graph shows values that the inventors have measured for a disclosed embodiment generally similar to that illustrated inFIG. 9A. As is shown in the graph, the efficiency for both the low-frequency band and the high-frequency band referred to above is typically 50% or better across both of the bands. For the whole frequency range from approximately 850 MHz to 2.2 GHz, which covers the five common cellular bands GSM850/900/1800/1900 and WCDMA2100, the efficiency is approximately 40% or greater, and is typically 50% or greater. Other embodiments of the present invention, described herein, have efficiency vs. frequency graphs which are generally similar to the graph ofFIG. 9C.

As stated above, typically the size of the ground plane mainly determines the widest possible overall bandwidth of the combined structure of monopole, coupling element, and ground plane, and the length of the coupling element in conjunction with the resonance frequency of the ground plane mainly determines the center frequency. Thus, by adjusting the sizes of the coupling element and the ground plane, antennas having typical efficiencies of 30% or more for frequencies as low as approximately 400 MHz and as high as approximately 6 GHz may be formed, including the wireless local area network bands of 2.4 GHz and 5.6 GHz.

FIG. 10Ais a schematic diagram of a multi-band antenna420, according to an embodiment of the present invention.FIG. 10Ais a front view of antenna420. Antenna420has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna420is generally similar to that of antenna320(FIG. 9A), and elements indicated by the same reference numerals in both antennas320and420are generally similar in construction and in operation.

In antenna420an indentation422in section29is not linear, but, by way of example, is formed as an “L” shape, so that a first element424of the L is parallel to the y axis, and a second element426of the L is parallel to the x axis. A coupling element434is generally similar to coupling element334. However, a terminating section436of element434is arranged to follow and lie within indentation422, so that, in the example illustrated herein, section436is also L-shaped, having a first section438parallel to the y axis and a second section440parallel to the x axis. Section440terminates at an end442which galvanically connects to ground section29. There is a coupling region444for end442, which is a region within of the order of 5 mm from the end. The length of section438is Lindenty, and the length of section440is Lindentx.

Since indentation422and enclosed section436are non-linear, the electric fields between the different parts of the indentation and their respective enclosed sections are non-parallel. Thus, the electric field in element424due to section438is generally parallel to the x axis, whereas the electric field in element426due to section440is generally parallel to the y axis. The direction of the electric field between terminating section436and ground plane29affects the current flowing in the ground plane, which in turn affects the polarization of the radiation transmitted by antenna420. Thus, by selecting different values of Lindentyand Lindentxfor sections438and440, the direction and/or the ellipticity of the polarization of radiation transmitted by antenna420may be adjusted. In one embodiment, the value of Lindentyis approximately 15 mm, and the value of Lindentxis approximately 10 mm, to give radiation in the high and low-frequency bands referred to above.

Alternatively or additionally, the direction and/or the ellipticity of the polarization of radiation transmitted by antenna420may be adjusted by altering other dimensions of indentation422and enclosed section436. For example, a width Windentyof section438, and/or a width Windentxof section440may be varied. Furthermore, the widths of the separations between section438and the edges of element424, and the widths of the separations between section440and the edges of element426may also be varied. Altering dimensions of indentation422and enclosed section436alters the directions and magnitudes of currents flowing in the ground plane, which in turn alters the polarization of radiation. The dimensions may be adjusted so that, given the electric field restrictions that apply because of boundary conditions on the ground plane, the directions and magnitudes of currents flowing in the ground plane alter the polarization of radiation in a desired manner.

FIG. 10Bis a schematic diagram of a multi-band antenna450, according to an embodiment of the present invention.FIG. 10Bis a front view of antenna450. Antenna450has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna450is generally similar to that of antenna420(FIG. 10A), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation.

In contrast to antenna420, end442is not galvanically connected to ground plane section29. Rather, there is a space452between end442and the ground plane, so that coupling element434only capacitively couples to the ground plane. By altering the dimensions of space452the directions of currents flowing in the ground plane adjacent to section436, and the magnitudes of the currents, may be adjusted, so that the polarization of the radiation from antenna450may be correspondingly adjusted.

FIG. 11is a schematic diagram of a multi-band antenna470, according to another embodiment of the present invention.FIG. 11is a front view of antenna470. Antenna470has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna470is generally similar to that of antenna320(FIG. 9A), and elements indicated by the same reference numerals in both antennas470and320are generally similar in construction and in operation.

In place of coupling element334, antenna470comprises a coupling element472, which is generally similar to, and which performs substantially the same functions as, element334. Coupling element472has a terminating section471similar to terminating linear section341. However, in place of section337, coupling element472comprises a linear section474, which is located at an edge473of substrate22, in an indentation480of section29of the ground plane. Thus, section474and section29have a common edge473. Linear section474connects galvanically at an end476of the section to ground plane section29, at a coupling region478. Coupling region478is a region within of the order of 5 mm from end476.

By adjusting the length of linear section474, the impedance of coupling element372may be adjusted, substantially as described above for coupling element334. In addition, as explained above, adjusting the dimensions of linear section474may allow for adjustment of the polarization of radiation radiated by antenna470.

FIG. 12is a schematic diagram of a multi-band antenna520, according to an embodiment of the present invention.FIG. 12is a front view of antenna520. Antenna520has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna520is generally similar to that of antenna320(FIG. 9A), and elements indicated by the same reference numerals in both antennas520and320are generally similar in construction and in operation. Antenna520comprises a coupling element534, which has generally similar dimensions, and performs generally the same functions, as element334. However, in contrast to element334, coupling element534is not connected galvanically to ground plane section29.

Rather, element534comprises a section536which parallels edge35and which capacitively couples element534to a coupling region538of section29. Coupling region538is a region within of the order of 5 mm from a lower edge542of section536. A gap540between section536and edge35is approximately 1 mm or less, and typically is approximately 0.5 mm. The length of section536and the size of gap540may be adjusted to change the capacitive coupling between element534and ground plane section29. Typically, a width of section536is larger than that of other sections of element534. In one embodiment, the length of section536is approximately 7 mm, and the width of the section is approximately 2 mm.

FIG. 13is a schematic diagram of a multi-band antenna620, according to an embodiment of the present invention.FIG. 13is a front view of antenna620. Antenna620has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna620is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas20and620are generally similar in construction and in operation. Antenna620comprises coupling element34and coupling region46in section29. In addition, antenna620comprises one or more further coupling elements formed on substrate22and connected galvanically or coupled capacitively to ground plane21.

By way of example, antenna620is shown to comprise a second coupling element632having an end641connected galvanically to a second coupling region642. Second coupling region642is a region within of the order of 5 mm from end641. Antenna620also comprises a folded monopole630. However, in contrast to antenna20, monopole630is configured to be shorter in length than monopole30, so that instead of acting generally as a radiating element, monopole630acts to couple high-frequency and low-frequency band electric or magnetic fields via elements632and34, respectively, to ground plane21.

Monopole630is fed at a feed zone640which comprises a feed region638in section29and an end636of the monopole. Feed region638has generally the same dimensions as feed region38.

Second coupling element632is configured to radiate in the high-frequency band, so is approximately 3 cm in total length. Regions46,638, and642are separate regions, and coupling elements34and632are folded around monopole630.

FIG. 14is a schematic diagram of a multi-band antenna720, according to an embodiment of the present invention.FIG. 14is a front view of antenna720. Antenna720has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna720is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas20and720are generally similar in construction and in operation.

In place of monopole30, antenna720comprises a loop722, configured from a conductive strip generally as described above for monopole30. Loop722has a length of approximately 3 cm for the cellular bands referenced above, and performs substantially the same functions as monopole30, although the loop is not a member of the monopole family. Loop722has a ground plane feed region728which is in proximity to a first end724of the loop. Region728is a region within of the order of 5 mm from end724. First end724and region728act as a feed zone730for antenna720. End724, region728, and zone730are respectively similar in construction and operation to end36, region38and feed zone40of antenna20. Loop722has a second end726which galvanically connects to ground plane section29.

FIGS. 15A and 15Bare schematic diagrams of a multi-band antenna820, according to an embodiment of the present invention.FIG. 15Ais a front view andFIG. 15Bis a rear view of antenna820. Apart from the differences described below, the operation of antenna820is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas20and820are generally similar in construction and in operation.

A region822of section29, and a corresponding region824of section28, are removed from those sections, forming lower edges826and828of the shortened sections. Regions822and824are substantially equal in length, the length typically being of the order of 10 mm. An element830is formed in region822, element830being galvanically connected to section29at edge826. Element830is configured to improve the specific absorption ratio (SAR) of antenna820. If necessary dimensions of monopole30and coupling element34may be adjusted from those of antenna20, so that element830does not significantly affect the efficiency of antenna820compared with the efficiency of antenna20. Such adjustments may advantageously be made using antenna simulation software, such as that exemplified above.

FIG. 16AandFIG. 16Bare schematic diagrams of a multi-band antenna920, according to an embodiment of the present invention.FIG. 16Ais a front view andFIG. 16Bis a rear view of antenna920. Apart from the differences described below, the operation of antenna920is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas20and920are generally similar in construction and in operation.

In contrast to ground plane21of antenna20, which extends across the width of substrate22, in antenna920a rectangular area922of section29, and a corresponding area924of section28, are removed from the sections. Removal of areas922and924leaves respective edges926and928that are parallel to the y-axis. The width of the two areas is equal, typically having a value of approximately 7 mm.

A second folded monopole930and a second coupling element934are formed in area922. A combination935of monopole930and coupling element934is typically geometrically similar to a combination937of monopole30and coupling element34. However, combination935is typically reduced by a factor greater than 1 compared with the size of combination937. Herein, by way of example, combination935is assumed to be reduced by a factor of 2. Combination935is rotated by 90° with respect to combination937.

As for monopole30, an end936of monopole930is close to, but does not touch, edge926at a second ground plane feed region938, the region and the end forming a feed zone940. Region938is assumed to be a region bordering edge926and within a distance of the order of 3 mm from end936.

An end942of element934is galvanically connected to edge926of ground plane section29at a second ground plane coupling region946. Region946is assumed to be a region within a distance of the order of 3 mm from end942.

Combination935forms, together with ground plane21, an antenna947which operates in two frequency bands, according to substantially similar principles as those described above for antenna20. However, in contrast to antenna20wherein the low-frequency band is approximately determined by the length of ground plane21, the low-frequency band of antenna947, herein also termed the second low-frequency band, is approximately determined by the width of ground plane21. The high-frequency band of antenna947, herein also termed the second high-frequency band, is approximately determined by the length of monopole930. Thus antenna920may operate in four different frequency bands.

In some embodiments of the present invention transceiver14(FIG. 1) comprises a single transceiver and feed15is a single feed which is coupled to monopole30and to monopole930at zones40and940, so that the single transceiver operates in four frequency bands.

Alternatively, transceiver14comprises two sub-transceivers, and feed15comprises a respective feed to each sub-transceiver. One of the sub-transceivers is connected to monopole30at zone40, and the second sub-transceiver is connected to monopole930at zone940. The second low-frequency band of combination935may be configured to be approximately the same as the high-frequency band of combination937. In this configuration, the different physical locations and/or orientations of combination937and935enable the two sub-transceivers to be operated in a diversity mode, wherein one of the sub-transceivers is configured as a main transceiver, and the second sub-transceiver is configured as a diversity transceiver. Operation in a diversity mode improves the overall quality of signals received by phone10.

The scope of the present invention includes elements of antennas which are linear and/or curved, as is exemplified by an antenna1020, described with reference toFIG. 17below.

FIG. 17is a schematic diagram of a multi-band antenna1020, according to an embodiment of the present invention.FIG. 17is a front view of antenna1020. Antenna1020has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna1020is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation.

In contrast to antenna20, antenna1020comprises one or more elements having non-linear sections. By way of example, a monopole1022is generally similar in properties to monopole30. However, rather than being formed of two orthogonal sections, monopole1022is formed as a curved element, resonating at generally the same high-frequency band as monopole30. Also by way of example, a coupling element1034is generally similar in properties to coupling element34. However, coupling element1034comprises a first curved element1024which connects two linear elements of the coupling element. Coupling element1034also comprises a second curved element1026which terminates the coupling element, as well as a third curved element1028. As shown inFIG. 17, substrate22may advantageously be curved at corners of the substrate to conform with curved elements1024and1026.

FIGS. 18A and 18Bare schematic diagrams of a multi-band antenna1120, according to an embodiment of the present invention.FIG. 18Ais a front view of antenna1120.FIG. 18Bis a side view of the antenna. Antenna1120has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna1120is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation.

In contrast to antenna20, wherein coupling element34is substantially coplanar with monopole30and ground plane section29, antenna1120comprises a coupling element1134which is not planar and is not coplanar with the monopole and the ground plane section, although coupling element1134performs substantially the same functions as element34. Coupling element1134comprises a first section1136which is generally orthogonal to a plane1138wherein the monopole and the ground plane section lie. Section1136, typically having a length of the order of 5 mm, is galvanically connected to ground plane section29at region46, and is galvanically connected to a second section1140of the coupling element. Second section1140is typically supported by a dielectric element1142, having a plane generally parallel to plane1138, and coupling element1134is configured so that a projection of the element onto plane1138folds around monopole30, and is generally similar in dimensions to coupling element34.

FIGS. 19A and 19Bare schematic diagrams of a multi-band antenna1160, according to an embodiment of the present invention.FIG. 19Ais a front view of antenna1160.FIG. 19Bis a side view of the antenna. Antenna1160has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna1160is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation.

In contrast to antenna20, wherein monopole30is substantially coplanar with coupling element34and ground plane section29, antenna1160comprises a monopole1162which is not planar and is not coplanar with the coupling element and the ground plane section, although monopole1162, having sections1164and1166generally similar to sections33and31, performs substantially the same functions as monopole30. Monopole1162comprises a section1168which is generally orthogonal to a plane1170wherein the coupling element and the ground plane section lie. Section1168, typically having a length of the order of 4 mm, has a first end which is galvanically connected to section1166of the monopole, and a second end which is close to, but does not touch, edge35, at region38of the ground plane, and which couples to the live side of feed15. There is thus a gap1172between the second end of section1168and region38of ground plane section29. Monopole1162is typically supported by a dielectric element1174, having a plane generally parallel to plane1178, and the monopole is configured so that coupling element34folds around a projection of the monopole onto plane1170. The projection is generally similar in dimensions to monopole30.

FIG. 20is a schematic diagram of a multi-band antenna1220, according to an embodiment of the present invention.FIG. 20is a front view of antenna1220. Antenna1220has a rear view substantially similar to the rear view of antenna20. Apart from the differences described below, the operation of antenna1220is generally similar to that of antenna20(FIGS. 2A and 2B), and elements indicated by the same reference numerals in both antennas are generally similar in construction and in operation.

Antenna1220comprises a coupling element1226, which is generally similar in dimensions to coupling element34. Thus, element1226terminates in a linear section1230parallel to the y axis, section1230corresponding to section48of element34. Element1226has a first end1222and a second end1228, which respectively correspond to ends42and44, and which have generally the same spatial relationship with edge35as ends42and44. End1222typically galvanically connects to a ground plane coupling region1224of edge35. Region1224corresponds to region46of antenna20.

However, in antenna1220coupling element1226and monopole30turn in the same, like, directions as viewed from feed region38(for the monopole), and coupling region1224(for the coupling element). Thus, taking the feed region and the coupling region as starting points, and viewing from above the x-y plane of antenna1220, both the monopole and the coupling element turn, or bend, in a clockwise direction.

This is in contrast to the directions of turning of coupling element34and monopole30in antenna20. As shown inFIG. 2A, element34and monopole30turn in opposite directions as viewed from their coupling region and feed region. Thus, taking coupling region46and feed region38as starting points, and viewing from above the x-y plane, element34turns, or bends, in a counter-clockwise direction, but monopole30turns in a clockwise direction.

In an alternative embodiment of antenna1220, a matching circuit1232may be added to monopole30, at a location close to end point36, so as to alter the effective reactance of the antenna in the low-frequency bands.

It will be understood that combinations of aspects of antennas other than those exemplified above are included in the scope of the present invention. As a first example, one or more inductive elements, generally similar to that described with reference to antenna120(FIG. 6), may be incorporated in monopole330and/or coupling element334of antenna320(FIG. 9A), and the dimensions of the monopole or the element may be adjusted correspondingly. As a second example, one or both of coupling elements34and632of antenna620(FIG. 13) may be connected to ground plane29via a linear and/or a non-linear indentation, such as those exemplified in antenna320(FIG. 9A) and antenna420(FIG. 10A). As a third example, one or both of coupling elements34and632of antenna620(FIG. 13) may be positioned on rear surface26, and ground section28removed appropriately, generally as described with regard to antenna220(FIGS. 8A and 8B).

As a fourth example, one or both of coupling elements34and632of antenna620may have a section formed along an edge of substrate22, generally as described with respect to antenna470(FIG. 11). As a fifth example, if substrate22comprises a multi-layer substrate, each of the separate components of a specific antenna, i.e., the monopole, the one or more coupling elements, and sections of the ground plane, may be formed on different surfaces of the same or different layers. As a sixth example, antennas1120and1160(FIGS. 18A,18,19A,19B) may be combined, so that both the coupling element and the monopole are in planes which are different from a plane containing the ground plane. Furthermore, the coupling element, the monopole, and the ground plane may comprise three distinct planes. As a seventh example, a matching circuit generally similar to matching circuit1232(FIG. 20) may be added to monopole30of antenna20(FIG. 2A). Other examples of element combinations will be apparent to those skilled in the art. The dimensions in the above embodiments are given solely by way of example and may be adjusted according to the desired operating frequencies of the antenna and other constraints.