Reference is hereby made to U.S. Provisional Patent Application 61/352,995, entitled SINGLE-BRANCH MULTI-BAND ANTENNA, filed June 9, 2011, the disclosure of which is hereby incorporated by reference and priority of which is hereby claimed pursuant to 37 CFR 1.78(a)(4) and (5)(i).

FIELD OF THE INVENTION

The present invention relates generally to antennas and more particularly to compact antennas capable of operating in multiple bands.

BACKGROUND OF THE INVENTION

The following Patent documents are believed to represent the current state of the art:

U.S. Patents: 7,053,844; 7,835,707 and 6,975,278.

SUMMARY OF THE INVENTION

The present invention seeks to provide a compact single-branch multiband antenna, for use in wireless communication devices.

There is thus provided in accordance with a preferred embodiment of the present invention a multiband antenna, including a ground plane, an open-ended radiating element offset from the ground plane and fed at a feed point, the open-ended radiating element radiating in a first frequency band and a conductive ground leg extending between the feed point and the ground plane, the conductive ground leg galvanically connecting the open ended-radiating element to the ground plane, the conductive ground leg radiating in a second frequency band and having an electrical length at least equal to about a quarter of a wavelength corresponding to the second frequency band.

Preferably, the open-ended radiating element and the conductive ground leg are located in close proximity to the ground plane and the ground leg is folded.

In accordance with a preferred embodiment of the present invention, the open-ended radiating element is supported by a non-conductive carrier.

Preferably, the open-ended radiating element includes an initial section, located on an upper surface of the carrier and an open-ended terminal section, located on a lower surface of the carrier.

Preferably, the initial section and the terminal section are galvanically connected by a via or plated through-hole component.

Preferably, the ground leg is located on the upper surface of the carrier.

Preferably, the ground leg extends parallel to the initial section of the open-ended radiating element and to an edge of the ground plane and is separated from the edge by a gap.

Preferably, the first frequency band includes a low-frequency band.

Preferably, the second frequency band includes a high-frequency band.

Preferably, a bandwidth of the high-frequency band is greater than a bandwidth of the low-frequency band.

In accordance with another preferred embodiment of the present invention, the open-ended radiating element and the ground leg are deployed over the ground plane. Preferably, the open-ended radiating element and the ground leg are supported by a conductive support structure.

Preferably, the first frequency band includes a high-frequency band.

Preferably, the second frequency band includes a low-frequency band.

In accordance with a further preferred embodiment of the present invention, the ground leg transforms an impedance of the open-ended radiating element.

Preferably, the open-ended radiating element includes the only open- ended radiating element of the multiband antenna.

Preferably, the open-ended radiating element and the ground leg include a monolithic structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

Figs. 1A and IB and 1C are simplified respective top, underside and perspective views of an antenna constructed and operative in accordance with a preferred embodiment of the present invention;

Fig. 2 is a graph showing the return loss of an antenna of the type shown in Figs. 1A - 1C,

Fig. 3 is a simplified perspective view of an antenna constructed and operative in accordance with another preferred embodiment of the present invention; and

Fig. 4 is a graph showing the return loss of an antenna of the type shown in Fig. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to Figs. 1A, IB and 1C, which are simplified respective top, underside and perspective views of an antenna constructed and operative in accordance with a preferred embodiment of the present invention.

As seen in Figs. 1A - 1C, there is provided an antenna 100 including a ground plane 102 preferably abutted by a non-conductive carrier 104. An open-ended radiating element 106 is located in close proximity to the ground plane 102 and is preferably supported by the carrier 104. Open-ended radiating element 106 preferably radiates in a first frequency band. As is readily appreciated from consideration of Figs. 1A - 1C, open-ended radiating element 106 is the sole open-ended radiating branch of antenna 100. This notwithstanding, antenna 100 operates as a multiband antenna, capable of radiating in at least two frequency bands, as will be explained in greater detail below.

As seen most clearly in Fig. 1A, open-ended radiating element 106 preferably includes an initial section 108 located on an upper surface 110 of carrier 104. As seen most clearly in Fig. 1C, initial section 108 of open-ended radiating element 106 preferably tunnels through carrier 104 at a region 112. The section 108 then wraps around carrier 104 to form a terminal open-ended section 114, preferably located on a lower surface 116 of carrier 104, as seen most clearly in Fig. IB.

In the embodiment illustrated in Figs. 1A - 1C, segment 108 is shown as descending through carrier 104 in region 112. Region 112 may comprise a via or plated through-hole component, by way of which galvanic contact between initial section 108 and terminal section 114 of open-ended radiating element 106 is established.

Open-ended radiating element 106 is preferably fed at a feed point 118, which feed point 118 is preferably located adjacent to and spaced from an upper edge 120 of the ground plane 102. Feed point 118 is preferably connected to a feedline 122, which feedline 122 may optionally include a number of matching circuit components and preferably terminates at a radio-frequency input point 124.

Extending between feed point 118 and the ground plane 102, and preferably located in close proximity to ground plane 102, there is provided an electrically and physically elongate, preferably folded conductive ground leg 126. Ground leg 126 serves to galvanically connect the open-ended radiating element 106 to the ground plane 102. Ground leg 126 is preferably located on the upper surface 110 of carrier 104. Ground leg 126 preferably extends parallel to the first segment 108 of open- ended radiating element 106 and to the edge 120 of the ground plane and is separated therefrom by a small gap 128. It is appreciated, however, that other orientations of the ground leg 126 and/or the open-ended radiating element 106 are also possible.

It is further appreciated that although open-ended radiating element 106 and ground leg 126 are distinguished between herein for the purposes of differentiation between their different functions, open-ended radiating element 106 and ground leg 126 are preferably formed as a monolithic structure. This monolithic structure may comprise a three-dimensional conductive trace, as in the embodiment illustrated in Figs. 1A - 1C. Alternatively, open-ended radiating element 106 and ground leg 126 may be formed as planar printed features directly on a surface of the ground plane 102, whereby carrier 104 may be obviated.

Non-conductive carrier 104 preferably comprises a dielectric material having a relative dielectric permittivity greater than one and ground plane 102 preferably comprises a PCB ground plane. It is appreciated, however, that ground plane 102 may comprise any suitable conductive structure, including a portion of a casing of a wireless device into which antenna 100 may be incorporated.

In operation, antenna 100 operates as a multiband antenna, radiating in at least two frequency bands. The ability of antenna 100 to radiate in more than one frequency band despite including only a single open-ended radiating element 106 arises from the unique electrically and physically elongate structure of the ground leg 126. This structure allows ground leg 126 to operate as a radiating element in its own right, radiating in a second frequency band. Ground leg 126 has an electrical length at least equal to about a quarter of a wavelength corresponding to the second frequency band.

Thus, antenna 100 is capable of radiating in two frequency bands respectively provided by open-ended radiating element 106 and ground leg 126. Antenna 100 thus differs from conventional multiband antennas, which typically require multiple open-ended radiating elements in order to radiate in more than one frequency band. As a result of antenna 100 including only a single open-ended radiating element, antenna 100 is more compact and may be located in closer proximity to the ground plane than conventional multiband antennas. It is appreciated, however, that antenna 100 may be easily modified by one skilled in the art to radiate in additional frequency bands, beyond those provided by open-ended radiating element 106 and ground leg 126, by the inclusion of additional appropriately located open-ended radiating branches.

In addition to its operation as a radiating element, ground leg 126 has a second function in antenna 100 as an impedance matching element. Near field coupling between the ground plane 102, the ground leg 126 and the open-ended radiating element 106 serves to control the impedance match of the open-ended radiating element 106 to the input impedance of antenna 100, which input impedance is preferably approximately 50 Ohms. In the absence of ground leg 126, the natural impedance of the open-ended radiating element 106 would tend to be significantly lower than 50 Ohms due to its particular topology and close proximity to ground plane 102.

Ground leg 126 is distinguished from conventional, electrically short, ground connections employed for purposes of impedance matching by its electrically and physically elongate, folded structure. Conventional ground connections generally do not also function as radiating elements, as does ground leg 126, due to their small electrical size.

In operation of antenna 100, open-ended radiating element 106 preferably radiates in a low-frequency band and ground leg 126 preferably radiates in a high-frequency band. Ground leg 126 preferably has an electrical length at least equal to about a quarter of a wavelength corresponding to the high-frequency band. It is appreciated that the high-frequency band of multiband antenna 100 differs fundamentally in its nature from higher-order resonant modes typically associated with low-frequency monopole or PIFA antennas. The latter higher-order resonant modes are typically observed at frequencies two or three times greater than the fundamental operating frequency of the antenna and change in accordance with changes to that fundamental operating frequency.

In contrast, the high- and low-frequency bands of antenna 100 are not significantly interdependent and may be separately adjusted by means of modifications to the design of open-ended radiating element 106 and ground leg 126. It is noted, however, that changes to the ground leg 126 are likely to somewhat influence the operating characteristics of the open-ended radiating element 106 due to the resultant change in the ground leg's function as an impedance transformer for the open-ended radiating element 106.

Reference is now made to Fig. 2, which is a graph showing the return loss of an antenna of the type shown in Figs. 1A - 1C.

First local minima A of the graph generally corresponds to the low- frequency band, preferably provided by open-ended radiating element 106 and second local minima B generally corresponds to the high-frequency band, preferably provided by ground leg 126.

As is evident from consideration of regions A and B, the bandwidth of the high-frequency band is wider than the bandwidth of the low-frequency band. The is due to the presence of the gap 128 between the ground leg 126 and the edge 120 of the ground plane 102, shown in Fig. 1A, which gap 128 forms a resonant structure which enhances the high-frequency bandwidth.

As shown in Fig. 2, by way of example, the operating frequencies of antenna 100 may lie in the 700 - 2100 MHz range. However, it is appreciated that antenna 100 may be adapted to operate over a wide range of operating frequencies, including cellular communication frequencies, WiFi, WiMax, and LTE bands. Operating frequencies of antenna 100 may be adjusted by way of modifications to various geometric parameters of antenna 100, including, but not limited to, the length of the open-ended radiating element 106, the length of the ground leg 126 and the size of gap 128.

Reference is now made to Fig. 3, which is a simplified perspective view of an antenna constructed and operative in accordance with another preferred embodiment of the present invention.

As seen in Fig. 3, there is provided an antenna 300, including a ground plane 302 abutted by a perpendicularly extruding conductive support structure 304. An open-ended radiating element 306 is offset from the ground plane 302. Open-ended radiating element 306 is preferably located in close proximity to the ground plane 302 and is particularly preferably deployed over it. Open-ended radiating element 306 preferably radiates in a first frequency band.

As seen most clearly in view A, open-ended radiating element 306 is preferably fed at a feed point 308 by a feedline 310. In the embodiment illustrated in Fig. 3, feedline 310 is shown, by way of example, to be a coaxial cable. It is appreciated, however, that feedline 310 may alternatively be any other suitable feeding structure.

Extending between feed point 308 and the support structure 304 there is provided an electrically and physically elongate, preferably folded ground leg 312, which ground leg 312 serves to galvanically connect open-ended radiating element 306 to the ground plane 302 by way of the support structure 304. Ground leg 312 radiates in a second frequency band and has an electrical length at least equal to about a quarter of a wavelength corresponding to the second frequency band.

Ground leg 312 is preferably deployed over and in close proximity to ground plane 302. Support structure 304 thus functions both to support ground leg 312 and open-ended radiating element 306 at a predetermined height above the ground plane 302 and also to galvanically connect them to the ground plane 302 at two connections points 314 and 316. It is appreciated that the perpendicularly extruding design of support structure 304 is shown in Fig. 3 by way of example only and that a wide variety of other shapes, sizes and orientations of support structure 304, including a greater or fewer number of connection points to the ground plane 302, are also possible.

It is appreciated from consideration of Fig. 3 that antenna 300 includes only a single open-ended radiating element, namely open-ended radiating element 306. This notwithstanding, antenna 300 operates as a multiband antenna, capable of radiating in at least first and second frequency bands. The ability of antenna 300 to operate in multiple bands is due to the unique electrically and physically elongate structure of ground leg 312, which allows ground leg 312 to act both as a radiating element and an impedance matching element as described above in reference to ground leg 126 of antenna 100. The structure of ground leg 312 thus allows antenna 300 to operate as a multiband antenna, radiating in at least two frequency bands, respectively provided by open-ended radiating element 306 and ground leg 312. In operation of antenna 300, open-ended radiating element 306 preferably radiates in a high-frequency band and ground leg 312 preferably radiates in a low- frequency band. Ground leg 312 preferably has an electrical length at least equal to about a quarter of a wavelength corresponding to the low-frequency band. It is appreciated that the operation of antenna 300 thus may generally resemble the operation of antenna 100, with the difference that in antenna 300 the open-ended radiating element 306 radiates in a high-frequency band and the ground leg 312 radiates in a low- frequency band, whereas in antenna 100 the open-ended radiating element 106 radiates in a low-frequency band and the ground leg 126 radiates in a high-frequency band.

Antenna 300 generally shares the advantages described above in reference to antenna 100, including its compactness and low interdependency of its low- and high- frequency bands.

Open-ended radiating element 306 and ground leg 312 may be adapted for attachment to a wireless device in which antenna 300 is to be incorporated, for example by means of heat stake inserted into a multiplicity of holes 318 in the body of antenna 300.

Reference is now made to Fig. 4, which is a graph showing the return loss of an antenna of the type shown in Fig. 3.

First local minima A of the graph generally corresponds the low- frequency band, preferably provided by ground leg 312 and second local minima B generally corresponds to the high-frequency band, preferably provided by open-ended radiating element 306.

As shown in Fig. 4, by way of example, the operating frequencies of antenna 300 may lie in the 2360 - 2660 and/or 4900 - 6000 MHz range. However, it is appreciated that antenna 300 may be adapted to operate over a wide range of operating frequencies, including WiFi, WiMax, BlueTooth, ZigBee, 6-LoWPAN, cellular communications and LTE operating bands. Operating frequencies of antenna 300 may be adjusted by way of modifications to various geometric parameters of antenna 300, including, but not limited to, the length of the open-ended radiating element 306, the length of the ground leg 312 and the separation of the open-ended radiating element 306 and ground leg 312 from the ground plane 302. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly claimed hereinbelow. Rather, the scope of the invention includes various combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof as would occur to persons skilled in the art upon reading the forgoing description with reference to the drawings and which are not in the prior art.