Dual band antenna with bending structure

The present invention relates to an antenna, and in particular to a dual band antenna having a bending structure which is adapted for a wireless communication device.

There is a growing need for dual band antennas for use in wireless communication devices to adapt the devices for dual band operation. For example, the transition of application frequency from 2.45 GHz (IEEE802.11b) to 5.25 GHz (IEEE802.11a) requires an antenna which operates at both frequencies, rather than two single band antennas. Referring to FIG. 7, Finnish patent application FI-982366 discloses a planar inverted-F antenna (PIFA) radiating element 600 defining a non-conductive slot 601 - 602 - 603 which divides the planar radiating element into a first branch located within a second branch. A feed point 604 and a ground contact 605 are located close to the inner end of the slot. The first branch and the second branch constitute two adjacent PIFA radiating elements on one and the same planar surface and in the vicinity of one and the same ground plane 606 . The patent application also discloses that the first branch is the higher frequency element, and the second branch is the lower frequency element.

However, this substantially planar structure make the dual band antenna unsuitable for installation in a space having an irregular shape, such as is found in a laptop computer.

Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of existing antennas.

A primary object, therefore, of the present invention is to provide an improved dual band antenna with a bending structure and reduced dimensions which is adapted to fit in a space having an irregular shape.

A dual band antenna in accordance with the present invention comprises a ground patch having a connecting portion and a bending portion, a first radiating branch transversely extending from the connecting portion, and a second radiating branch partly surrounding the first radiating branch and including a connecting patch extending from the connecting portion and a radiating patch extending from the connecting patch. The connecting portion, the first radiating branch and the connecting patch are located in a same first plane. The bending portion and the radiating patch are respectively in separate planes making predetermined angles with the first plane to form a bending structure adapted for an irregular installation space in an electronic device.

Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of a preferred embodiment when taken in conjunction with the accompanying drawings.

FIG. 1 is a frontal view of a preferred embodiment of a dual band antenna in accordance with the present invention without a coaxial cable;

FIG. 2 is a side view FIG. 1, illustrating dimensions of the dual band antenna of FIG. 1;

FIG. 3 is a perspective view of the dual band antenna of FIG. 1 assembled with a coaxial cable and installed in an electronic device;

FIG. 4 is a test chart recording for the dual band antenna of FIG. 1, showing Voltage Standing Wave Ratios (VSWR) as a function of frequency;

FIG. 5 is an illustration of horizontally polarized principle plane radiation patterns of the dual band slot antenna of FIG. 1 operating at frequency of 2.45 GHz;

FIG. 6 is an illustration of horizontally polarized principle plane radiation patterns of the dual band slot antenna of FIG. 1 operating at frequency of 5.25 GHz; and

FIG. 7 is a plane view of a conventional antenna.

Reference will now be made in detail to a preferred embodiment of the present invention.

Referring to FIGS. 1, 2 and 3 , a dual band antenna in accordance with the present invention comprises an antenna body 1 and a coaxial feeder cable 14 electrically connected to the antenna body 1 .

The antenna body 1 is made from a metal foil and includes a first radiating branch 11 , a second radiating branch 12 and a ground patch 10 . The ground patch 10 has a connecting portion 101 and a bending portion 102 . The first radiating branch 11 operates at a predetermined first frequency and is a planar inverted-F antenna (PIFA). The first radiating branch 11 extends transversely from the connecting portion 101 and bends longitudinally to extend parallel to the connecting portion 101 with a slot 110 therebetween. The second radiating branch 12 operates at a predetermined second frequency and includes a connecting patch 121 extending transversely from the connecting portion 101 and a radiating patch 120 extending longitudinally from the connecting patch 121 . The radiating patch 120 is also parallel to the connecting portion 101 and the first radiating branch 11 with a slot 111 therebetween, but is in a different plane. The first radiating branch 11 is partly surrounded by the second radiating branch 12 , with a transverse L-shape slot 15 defined between the first radiating branch 11 and the second radiating branch 12 . A solder tab 13 connects to the connecting portion 101 at a lower end of the slot 15 and is perpendicular to the connecting portion 101 . A hole 130 is defined in the solder tab 13 . The connecting portion 101 , the first radiating branch 11 and the connecting patch 121 are located in a same first plane. The radiating patch 120 and the bending portion 102 are located in separate second and third planes, the second plane of the radiating patch 120 making an angle of θ 1 with the first plane, and the third plane of the bending portion 102 making an angle of θ 2 with a line normal to the first plane.

The coaxial feeder cable 14 comprises a conductive inner core 140 , a dielectric layer (not labeled) and a conductive braiding layer 141 over the dielectric layer.

A thickness of the metal foil is 2 mm. Other detailed dimensions of the dual band antenna are shown in FIGS. 1 and 2.

In assembly, particularly referring to FIG. 3, the coaxial cable 14 is held by the solder tab 13 , and passes through the hole 130 . The inner core 140 is soldered to the radiating patch 120 and the braiding layer 141 is soldered to the solder tab 13 . The dual band antenna as shown in FIG. 3 is assembled in a speaker box of a laptop computer (not labeled), with the bending structure of the dual band antenna fitted into the contours of an irregular space in the speaker box.

In use, RF signals are fed to the dual band antenna by the conductive inner core 140 of the coaxial cable 14 and the conductive braiding layer 141 . The conductive braiding layer 141 is connected to ground via its soldered connection to the solder tab 13 , which electrically connects to the ground patch 10 which is grounded. The first radiating branch 11 constitutes a high-frequency resonant structure, operating around 5.25 GHz. The second radiating branch 12 constitutes a low-frequency resonant structure, operating around 2.45 GHz. The first and second radiating branches 11 , 12 constitute nearly independent regions having different resonant frequencies. This is an advantage where the antenna must operate in different environments.

The angles θ 1 and θ 2 and dimensions of the antenna can be changed to fit the contours and size of the space available for installation. Changes in dimensions and angles θ 1 and θ 2 change the radiation patterns of the antenna, allowing a designer to choose dimensions and angles θ 1 and θ 2 to fit a given requirement.

In particular, a width W of the first radiating branch 11 affects the bandwidth of the high-frequency band. A wider first radiating branch will yield a wider bandwidth. A gap distance between the radiating patch 120 and the bending portion 102 affects the bandwidth of the low-frequency band. A longer gap provides a broader bandwidth.

FIG. 4 shows a test chart recording of Voltage Standing Wave Ratios (VSWR) of the dual band antenna as a function of frequency. Note that VSWR drops below the desirable maximum value “2” in the 2.45 GHz frequency band and in the 5.25 GHz frequency band, indicating acceptably efficient operation in these two frequency bands. The location of the solder point of the inner core 140 on the radiating patch 120 can be varied between a side and central areas to achieve the optimal VSWR for both bands.

FIGS. 5 and 6 respectively show horizontally polarized principle plane radiation patterns of the dual band slot antenna operating at frequencies of 2.45 GHz and 5.25 GHz.

It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.