Dual frequency band inverted-F antenna

A dual frequency band inverted-F antenna used for communicating a low frequency signal and a high frequency signal includes a substrate, a ground metal, a vortical metal structure, a short circuit leg, a feeding leg, and a terminal micro strip. The ground metal and the terminal micro strip are formed on the lower surface of the substrate. The vortical metal structure, formed on the upper surface of the substrate, further has a short circuit end and an open circuit end. The short circuit leg connects electrically the short circuit end of the vortical metal structure with the ground metal. The feeding leg extends along a predetermined direction of the vortical metal structure to couple with a feeding circuit on the substrate. The terminal micro strip connects electrically to the open circuit end through a first conductive aperture. By increasing the encircling number of the vortical metal structure, the coupling effect is generated so that the equivalent wavelength of the high frequency signal can be longer, thus the resonance frequency thereof can be reduced, and so a first frequency can be still kept communicating at a lower frequency band and a second frequency can also be added for communicating at a higher frequency band.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to a design of printed inverted-F antenna, and more particularly to a printed inverted-F antenna for communicating in dual frequency band and having a function of adjusting coupled impedance.

(2) Description of the Prior Art

Rapid innovation and development upon wireless communication technology have made mobile communication products as one of mainstream products nowadays. These mobile communication products include mobile phones, PDAs, notebooks, etc. They can couple with proper communication modules to link a Wireless Local Area Network (WLAN) for transmitting or/and receiving e-mail and instant information such as news, stocks quotations, and so on. In the art, the WLAN is an on-site wireless communication means that utilizes a WLAN card to transmit wirelessly vast data between computer systems. Apparently, in the WLAN, conventional complicated wiring webs have been replaced by wireless communication facilities. One of those wireless communication facilities is the antenna; in particular, a flat inverted-F antenna. The flat inverted-F antenna, characterized on its slim size and light weight, has been widely adopted as a built-in antenna in most of the mobile communication products.

Referring now toFIG. 1for a conventional compact printed antenna, the antenna includes a substrate10, a ground metal12, a strip metal20, a short circuit leg14and a feeding leg16; in which the ground metal12, the strip metal20, the short circuit leg14and the feeding leg16are all printed circuits located on the substrate10.

The ground metal12is shaped to form a coplanar wave guide (CPW) feeding structure24as shown in FIG.1. The feeding leg16grows perpendicularly from the metal strip20and extends through the feeding structure24to further connect to a matching circuit (not shown in the drawing). The feeding leg16and the ground metal12are not connected with each other so as to avoid a short circuit problem. The strip metal20is parallel with the ground metal12. The short circuit leg14is provided to bridge a short circuit end18of the strip metal20and the ground metal12. On other hand, opposing to the short circuit end18, an open circuit end22of the strip metal20is formed. The distance between the open circuit end22and the short circuit end18is preferably one quarter of a concerned wavelength. Alternatively in the art, one of another solutions of the inverted-F antenna is shown inFIG. 2, in which the ground metal30and the compact printed antenna including a conductive aperture32, an open circuit end34, a feeding leg36, a metal strip40, a short circuit end42are fabricated respectively on opposing surfaces of the substrate38.

As the surface size of the compact printed antenna has a restriction that limits the length of the strip metal20to one quarter of the wavelength, the size of the antenna is thereby limited to a constant range of one quarter of the wavelength and thus cannot be shrunk effectively. Through the development of passive elements in the contemporary integrated circuits has been targeting at the miniaturization of elements, yet the antenna size of the communication products is still restricted by the unbreakable limitation of one-quarter signal wavelength

Besides, the operating frequency of the aforementioned compact printed antenna is limited to a single frequency band. For example, in a wireless local area network (WLAN), the operating frequency is usually located around ISM (Industrial Scientific Medical)2.4 GHz. Recently, noble wireless devices such as blue tooth apparatus are wildly adopted in wireless communication equipments. Hence, the interference problems such as co-channel interference and next-channel interference become much more serious. Also, it must be pointed out that the resonance frequency of the compact printed antenna between 8 GHz and 9 GHz is usually beyond the contemporary communication protocol. Therefore, the present invention is introduced not only to provide a shrunk size to the printed antenna but also to make the antenna operable under a dual-frequency band.

SUMMARY OF THE INVENTION

Accordingly, it is one object of the present invention to provide a dual frequency band inverted-F antenna.

It is another object of the present invention to provide a shrunk size printed inverted-F antenna by using a vortical metal structure.

It is one more object of the present invention to provide a printed inverted-F antenna having the function of adjusting the coupled impedance.

In one embodiment of the present invention, the dual frequency band inverted-F antenna can include a substrate, a ground metal, a vortical metal structure, a short circuit leg, and a feeding leg. The ground metal is formed on a lower surface of the substrate. The vortical metal structure, formed on an upper surface of the substrate, further has a short circuit end and an open circuit end, in which the open circuit end is located within the center of the vortical metal structure. The short circuit leg connects electrically the short circuit end of the vortical metal structure with the ground metal. The feeding leg extends along a predetermined direction of the vortical metal structure to couple with a feeding circuit on the substrate. By increasing the encircling number of the vortical metal structure, the induced coupling effect is then generated so that the equivalent wavelength of the high frequency signal becomes longer and thereby the resonance frequency thereof can be reduced, and hence a first frequency for the antenna to transmit/receive signals can be kept communicating at a lower frequency band while a second frequency can be still added for communicating at a higher frequency band.

In one embodiment of the present invention, the dual frequency band inverted-F antenna can include a substrate, a ground metal, a vortical metal structure, a short circuit leg, a feeding leg, and a terminal micro strip. The ground metal and the terminal micro strip are both formed but separated on a lower surface of the substrate. The vortical metal structure formed on an upper surface of the substrate further has a short circuit end and an open circuit end. The short circuit leg connects electrically the short circuit end of the vortical metal structure with the ground metal. The feeding leg extends along a predetermined direction of the vortical metal structure to couple with a feeding circuit on the substrate. The terminal micro strip connects electrically to the open circuit end through a first conductive aperture and has the function of adjusting the coupled impedance with the feeding circuit. By increasing the encircling number of the vortical metal structure, the induced coupling effect is then generated so that the equivalent wavelength of the high frequency signal becomes longer and thereby the resonance frequency thereof can be reduced. Hence, a first frequency can be introduced to communicate at a lower frequency band, and a second frequency can be also added to communicate at a higher frequency band.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention disclosed herein is a printed inverted-F antenna for communication products to transmit and receive signals in dual frequency band (a lower frequency signal and a higher frequency signal) and having the function of adjusting the coupled impedance. In the following description, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by one skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. In other instance, well-known components are not described in detail in order not to unnecessarily obscure the present invention.

Referring toFIG. 3for a first embodiment of the present invention, the dual frequency band inverted-F antenna includes a substrate80, a ground metal60, a feeding leg66, a short circuit leg68and a vortical metal structure71. The substrate80is a dielectric material where the ground metal60, the feeding leg66, the short circuit leg68and the vortical metal structure71are formed thereon as printed circuits. Besides, the ground metal60shown in a dotted line in the drawing is formed on a lower surface of the substrate80, and, on the other hand, the other parts of the antenna shown in dark color in the drawing are formed on an upper surface of the substrate80. The vortical metal structure71is formed by an elongated metal strip bending into a vortical structure or made of a sheet of metal by punching into a vortical structure. The vortical metal structure71can further have an open circuit end64and a short circuit end70to form an open circuit-short circuit structure, in which the open circuit end70is located within the center of the vortical metal structure71.

Additionally, the shape of vortical metal structure71can be a circular type, an angular type, a square, or the like. The short circuit end70connects electrically the ground metal60on the other side via the short circuit leg68which extends through a penetrating conductive aperture62. The feeding leg66extends along a predetermined direction of the vortical metal structure71to couple with a feeding circuit on the substrate80(not shown in the drawing).

In foregoing description, the ground metal60is located at an opposing surface to that constructing the rest circuits of the printed inverted-F antenna. Yet, in another embodiment of the present invention not shown here, the ground metal60and other circuits of printed inverted-F antenna can be still fabricated on the same surface of the substrate80with a proper arrangement to avoid any short-circuiting problem .

The distance between the open circuit end64and the short circuit end70of the antenna is preferable one quarter of the wavelength for the lower operating frequency (i.e., the first frequency) that is the equivalent current path length of the open circuit-short circuit oscillation signal. Upon such an arrangement, the linear distance between the open circuit end64and the short circuit end70can be shortened and thus the size of the dual frequency band inverted-F antenna can be effectively reduced.

Besides, the vortical metal structure71will generate inductance and internal impedance that may be changed and adjusted by altering the number of vortex of the vortical metal structure71. That is, the dual frequency band inverted-F antenna can be appropriately adjusted so as to meet an individual applicable spectrum, a grounding metal format and an antenna input impedance and so as to increase the freedom for adjusting the input impedance. Furthermore, as shown inFIG. 4, by increasing the encircling number of the vortical metal structure72, the induced coupling effect can then be generated so that the equivalent wavelength of the operated high frequency signal can become longer and thereby the resonance frequency can be reduced.

FIG. 5shows the computer-simulation results illustrating the input return loss versus frequency for the antennas as shown inFIG. 2(solid line100) andFIG. 3(dotted line200), respectively.FIG. 6also shows the computer-simulation results illustrating the input return loss versus frequency for the antenna as shown inFIG. 4(solid line300) Line100and Line200are results obtained respectively from simulating the embodiments shown in FIG.3andFIG. 4, in which different numbers of vortex of the vortical metal structure are provided but the linear distance between the open circuit end and the short circuit end in both embodiments is set equal to one quarter of the wavelength for the lower operating frequency (the first frequency). As observed from line200and line300, a higher operating frequency (the second frequency ) in appropriate frequency band for used in communication can be achieved by increasing the encircling number of the vortical metal structure. As shown inFIG. 6, the first operating frequency segment310is approximately located at 2.45 GHz and the second operating frequency segment320is approximately located between 5 to 6 GHz. In the field of operating in a WLAN, the lower frequency band can be used under the standard of IEEE 802.11b and the higher frequency band can be located at the standard of IEEE 802.11a, HiperLAN1, and HiperLAN2 so that the antenna of the present invention can be operated in dual frequency band.

Referring now toFIG. 7for a third embodiment of the present invention, the dual frequency band inverted-F antenna can include a substrate90, a ground metal84, a feeding leg86, a short circuit leg88, a vortical metal structure94, and a terminal micro strip76. The substrate90is a dielectric material, and the ground metal84, the feeding leg86, the short circuit leg88, the vortical metal structure94, and the terminal micro strip76are formed as printed circuits located on the substrate90. Besides, the ground metal84and the terminal micro strip76shown in dotted lines are formed on the back side of the substrate90, while the other parts of the antenna shown all in solid lines are formed on the front side of the substrate90. The vortical metal structure94is formed by bending an elongated metal strip into a vortical structure or made of a sheet of metal by punching into a vortical structure. The vortical metal structure94further provides an open circuit end78and a short circuit end92to form a open circuit-short circuit structure, wherein the open circuit end78is located within the center of the vortical metal structure94.

Additionally, the shape of vortical metal structure94can be a circular type, an angular type, a square, or the like. The terminal micro strip76formed on the back side of the substrate90can utilize a through first conductive aperture82to connects electrically with the open circuit end78on the front side. It is also noted that both the terminal micro strip76and the ground metal84are formed on the same side of the substrate90but without any connection in between. The short circuit end92connects electrically the ground metal84through the short circuit leg88and a through second conductive aperture74. The feeding leg86extends along a predetermined direction of the vortical metal structure94to couple with a feeding circuit on the substrate90(not shown in the drawing).

Nevertheless, in another embodiment not shown here, the ground metal84and other circuits of the printed inverted-F antenna (the terminal micro strip76is not included) can still be fabricated on the same surface of the substrate90. Yet, attention upon layouts is still needed to prevent any possible short-circuiting.

The distance between the open circuit end78and the short circuit end92of the antenna is preferably one quarter of the wavelength for the lower operating frequency (the first frequency) that is the equivalent current path length of the open circuit-short circuit oscillation signal. Therefore, under the arrangement that the equivalent current path length equals to one quarter of the wavelength, the linear distance between the open circuit end78and the short circuit end92can be shortened and the size of the dual frequency band inverted-F antenna can be effectively reduced.

Accordingly, in one aspect of the present invention typically shown inFIG. 3orFIG. 4, a higher operating frequency can be achieved through altering the number of vortex of the vortical metal structure94. However, in another aspect of the present invention typically shown inFIG. 7, the inverted-F antenna can be appropriately adjusted to meet the individual applicable spectrum, the grounding metal format and the antenna input impedance so as to increase the freedom of adjusting the input impedance by adjusting the width, length or direction of the terminal micro strip76.

Please refer toFIG. 8, which illustrates the input return loss versus frequency for the third embodiment of the present invention as shown in FIG.7. As shown, the first operating frequency segment410is approximately located at 2.45 GHz and the second operating frequency segment420is approximately located between 5 to 6 GHz so that the antenna of the present invention can be operated in dual frequency band.

In summary, the dual frequency band inverted-F antenna of the present invention can not only hold the same advantages with the conventional techniques such as compactness, well transmission efficiency, cost-saving toward manufacturing, omni-directional pattern, mixed polarization, and easy tuning to a function equally in most wireless application, but also provides several advantages as follows over the conventional techniques:(1) By increasing the encircling number of the vortical metal structure in accordance with the present invention, the original lower operating frequency can not only be maintained but also the other higher frequency that enables the inverted-F antenna to be operated in dual frequency band communication can be achieved.(2) The vortical metal structure of the present invention can maintain the equivalent current path length to one quarter of the wavelength for the lower operating frequency and thereby the size of the antenna can be effectively shrunk.(3) The vortical metal structure and the terminal micro strip according to the present invention can generate sufficient inductance to adjust the antenna input impedance so that the increasing upon the freedom of the inverted-F antenna coupling impedance is possible.