Dual band antenna

[0002] This application is a U.S. patent application entitled “DUAL BAND ANTENNA”, invented by Tai Lung-Sheng, Lin Hsien-Chu and Kuo Chia-Ming, contemporaneously filed and assigned to the same assignee of the present invention.

[0003] 1. Field of the Invention

[0004] The present invention relates to an antenna, and in particular to an antenna which is capable of operating in two distinct frequency bands.

[0005] 2. Description of the Prior Art

[0006] In recent years, planar inverted-F antennas (PIFA) have become increasingly popular. U.S. Pat. No. 5,926,139 issued to Korich on Jul. 20, 1999 discloses a conventional antenna. The conventional antenna comprises a planar dielectric substrate having opposite upper and lower major surfaces. A ground plane and a radiating element are respectively disposed on opposite major surfaces of the substrate. The radiating element comprises a first radiating portion and a second radiating portion. The first radiating portion is sized to function as a first PIFA operating in a first frequency band. The second radiating portion is sized to function as a second PIFA operating in a second frequency band. Therefore, the conventional antenna is capable of operating in two frequency bands. However, because the radiating element and the ground plane are respectively disposed on the opposite major surfaces of the substrate, the antenna has to form a grounding pin extending through the dielectric substrate to interconnect the ground plane and the radiating element, and a feed pin extending through the ground plane and the substrate to couple the radiating element to a transceiver circuitry. The conventional antenna has, therefore, a complex structure. Furthermore, the conventional antenna has a narrow bandwidth.

[0007] Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of existing antennas.

[0008] A main object of the present invention is to provide a dual band antenna having a simple structure and having a wide bandwidth.

[0009] A dual band antenna in accordance with the present invention is mounted in an electronic device for transmitting or receiving signals. The dual band antenna comprises a planar conductive element and a feeder cable electrically connecting to the conductive element. The conductive element includes a first radiating strip, a second radiating strip, a ground portion, and a connection strip. The connection strip interconnects the first and the second radiating strips with the ground portion. The first radiating strip and the connection strip are configured and sized to function as a first planar inverted-F antenna (PIFA) operating in a higher frequency band. The second radiating strip and the connection strip are configured and sized to function as a second PIFA operating in a lower frequency band. Because the first and the second radiating strips, the ground portion and the connection strip are all disposed in the same plane, the dual band antenna has a simple structure and has a wide bandwidth in the higher frequency band.

[0010] 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.

[0011] FIG. 1 is a top view of a dual band antenna in accordance with the present invention;

[0012] FIG. 2 is a top view of the dual band antenna of FIG. 1 with a feeder cable thereof removed for clarity, showing detailed dimensions thereof,

[0013] FIG. 3 is a horizontally polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 2.45 GHz;

[0014] FIG. 4 is a vertically polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 2.45 GHz;

[0015] FIG. 5 is a horizontally polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 5.35 GHz;

[0016] FIG. 6 is a vertically polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 5.35 GHz;

[0017] FIG. 7 is a horizontally polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 5.725 GHz;

[0018] FIG. 8 is a vertically polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 5.725 GHz; and

[0019] FIG. 9 is a test chart recording for the dual band antenna of FIG. 1, showing Voltage Standing Wave Ratio (VSWR) as a function of frequency.

[0020] Reference will now be made in detail to a preferred embodiment of the present invention.

[0021] Referring to FIG. 1, a dual band antenna 1 in accordance with a preferred embodiment of the present invention is mounted in an electrical device (not shown), such as laptop computer, desktop computer or mobile phone, for transmitting or receiving signals. The dual band antenna 1 comprises a planar conductive element (not labeled) and a coaxial feeder cable 6.

[0022] The planar conductive element of the dual band antenna 1 can be formed of a planar metal sheet or can be formed on a same major surface of a planar insulative substrate (such as a printed circuit board, not shown). The conductive element comprises a horizontal first radiating strip 2, a horizontal second radiating strip 3 extending from the first radiating strip 2, a ground portion 5, and a connection strip 4. The connection strip 4 interconnects the first and the second radiating strips 2, 3 with the ground portion 5. The connection strip 4 comprises an upright first segment 41, a middle second segment 42 and an upright third segment 43. The first segment 41 extends downwardly from a joint of the first and the second radiating strips 2, 3. The second segment 42 horizontally extends from a lower end of the first segment 41. The third segment 43 extends downwardly from the second segment 42. The ground portion 5 is rectangular and connects with a lower end of the third segment 43.

[0023] The coaxial feeder cable 6 has an inner core conductor 61 and an outer shield conductor 62 surrounding the inner core conductor 61. The inner core conductor 61 is soldered to the lower end of the first segment 41 of the connection strip 4 for transmitting signals between the dual band antenna 1 and a signal unit of an electrical device (not shown). The outer shield conductor 62 is soldered on the ground portion 5 for grounding the dual band antenna 1. The distance between the solder point of the outer shield conductor 62 on the ground portion 5 and the third segment 43 is predetermined to achieve a desired matching impedance for two distinct frequency bands.

[0024] Detailed dimensions of the dual band antenna 1 are shown in FIG. 2. The dimensions are in millimeters and are such that the dual band antenna 1 is configured to resonate within the two frequency bands. The first radiating strip 2 and the connection strip 4 are configured and sized to function as a first planar inverted-F antenna (PIFA), resonating in a higher frequency band between 4.84 GHz and 5.80 GHz (i.e., the 5 GHz frequency band). The second radiating strip 3 and the connection strip 4 are configured and sized to function as a second PIFA, resonating in a lower frequency band between 2.39 GHz and 2.53 GHz (i.e., the 2.45 GHz frequency band). The first and the second PIFAs constitute nearly independent regions having different resonant frequencies.

[0025] FIGS. 3-8 respectively show horizontally and vertically polarized principle plane radiation patterns of the dual band antenna 1 operating at frequencies of 2.45 GHz, 5.35 GHz and 5.725 GHz (the principle plane is the X-Y plane shown in FIG. 1). Note that each radiation pattern is close to a corresponding optimal radiation pattern.

[0026] FIG. 9 shows a test chart recording of Voltage Standing Wave Ratio (VSWR) of the dual band antenna 1 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 GHz frequency band, indicating acceptably efficient operation in these two frequency bands and a wide bandwidth in the 5 GHz frequency band.

[0027] 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.