The dual-band antenna of the present invention includes a substrate having a first edge, an emitting unit, a transmission line, and a ground pad. The emitting unit disposed on the first surface of the substrate has a first wire and a second wire, which are crossed at a feeding point. The transmission line coupled to the feeding point is used to transmit the RF signals. The ground pad disposed on the second surface of the substrate has a base and an extension. The base is extended from the substrate toward feeding point. The extension is adjacent to the emitting unit and is extended from the base toward the first edge. The combination of the base and the extension forms an “L” shape.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a dual-band antenna, and more particularly, to a dual-band antenna distributed on the printed circuit board.

2. Description of the Prior Art

As communication technology is increasingly improved, the weight, volume, cost, performance, and complexity of a communication system also become more important, so antennas that transmit and receive signals in a wireless communication system especially “draw designers” attention. In a wireless local area network (WLAN), because the space for setting up an antenna is limited and the antenna should transmit a large amount of data, the antenna should be carefully designed. The ordinary antennas used in a WLAN are flat printed antennas, which have the following characteristics: 1. a small volume, weight, and thickness due to being one single device; 2. low cost and simple to be manufactured by using a printed circuit; 3. easy adjustment of the resonant frequency, pattern, impedance, and polarization of the antenna by changing the structure and size and of the circuit. The flat printed antennas also have the following disadvantages: 1. low radiation efficiency and low gain; 2. narrow bandwidth (the bandwidth is about 5% of the center frequency). Because the signals of WLAN bands, 802.11b(2.4 GHz) and 802.11a(5.2 GHz), are easily influenced by surface features in the area. Since the printed antennas have the above disadvantages, how to improve the gain and bandwidth of the antenna at high frequency (5.2 GH) needs to be overcome by designers.

Please refer to theFIG. 1andFIG. 2. Because WLANs operate in the bands 802.11b and 802.11a for receiving the dual bands by the antenna, a dual-band antenna2is disclosed by Taiwan patent 557603, which has a first horizontal wire21, a second horizontal wire22, and a vertical radiation wire23disposed on the top surface26of an interface substrate24. A ground28is disposed on the bottom surface26of the interface substrate24. The first horizontal wire21and the second horizontal wire22cooperate with the vertical radiation wire23to produce the high operation frequency and low operation frequency of the dual-band monopole antenna2. A micro-strip25transmits the RF signals generated by the antenna. Therefore, when designers adjust the length or the width of the wire21or the wire22to change the behavior of one band of the antenna, the behavior of the other band will also be changed, making it difficult to design this kind of antenna.

SUMMARY OF INVENTION

Therefore, the purpose of the present invention is to provide a dual-band antenna, which has larger gain and bandwidth and is easier to design.

The dual-band antenna of the present invention includes a substrate, an emitting unit, a transmission line, and a ground pad. The emitting unit and the ground pad are on the opposite sides of the substrate. The transmission line coupled to the emitting unit is used to transmit the received or emitted RF signals.

The substrate has a first edge, and a first surface and a second surface that is on the opposite side of the substrate from the first surface. The emitting unit has a first wire and a second wire and is disposed on the first surface substantially between the first edge and a feeding point. The first wire and the second wire are crossed at the feeding point and the transmission line is coupled to the feeding point transmitting RF signals. The ground pad disposed on the second surface of the substrate includes a base and an extension. The base is extended from the substrate toward feeding point. The extension is adjacent to the emitting unit and extends from the base toward the first edge. The combination of the base and the extension forms an “L” shape.

DETAILED DESCRIPTION

The content, the characteristics, and the advantages of the present invention are clearly described in the following preferred embodiment and the figures.

Please refer toFIG. 3andFIG. 4. The dual-band antenna of the present invention comprises a substrate11, an emitting unit12, a transmission line13, and a ground pad14.

The emitting unit12and the ground pad14are on opposite sides of the substrate. The transmission line13coupled to the emitting unit is used to transfer the RF signals received or emitted by emitting unit12. In the present invention, the transmission line13is a microstrip line. In other embodiment, it can be coaxial cable or a coplanar waveguide, and not to be limited by this disclosure.

The substrate11is a printed circuit board made of fiberglass reinforced epoxy resin and has a first surface111and a second surface112that is on the opposite side of the printed circuit board from the first surface111. The printed circuit board also has a first edge shown at the top ofFIG. 3. The emitting unit12and the transmission line13are printed on the first surface111of the substrate11. The emitting unit12has a first wire121and a second wire122. The first wire121, the second wire122, and the transmission line13are crossed at a feeding point123used to emit the RF signals from the transmission line13or receive the RF signals from the air. The first wire121and the second wire122are extended away from the feeding point123and bent at some angle, resulting in the emitting unit12being substantially between the feeding point123and the first edge of the substrate11. The end portions of the wire121and the wire122are substantially parallel and form a mouth124. The first wire121is longer than the second wire122and is used to decide the low operating frequency of the dual-band antenna1. The second wire122is used to decide the high operating frequency of the dual-band antenna1. Because the wire121and the wire122do not have a common part, designers can adjust two bands of the dual-band antenna1respectively without affecting each other. It is help for shortening the lag-time.

Transmission line13extending from the feeding point123to the downside of the substrate11is combined with the emitting unit12to form a similar “F” shape.

The ground pad14disposed on the second surface112of thee substrate11comprises a base141and an extension142. The base141extends toward the feeding point123from the first edge of the substrate11. The extension is adjacent to the emitting unit and extends from the base141toward the first edge of the substrate11. The combination of the base and the extension makes an “L” shape, which generates electromagnetic coupling effects with the emitting unit12on the first surface111so that the first wire121and the second wire122can shorten the length corresponding to the operation frequency (one fourth wavelength of the electromagnetic signal, λ/4) as well as improve gain and bandwidth.

Please refer toFIGS. 5–23, which are the measurement results of the dual-band antenna.FIG. 5andFIG. 6illustrate the reflection coefficient under −10 dB. The low frequency bandwidth in the dual-band antenna1is 560 MHz (2410 MHz˜2970 MHz), and the high frequency bandwidth in the dual-band antenna1is 730 MHz (5100 MHz˜5845 MHz).FIGS. 5–23also disclose the corresponding VSWR(voltage standing wave ratio). From the results, it is found that the operation frequency of the dual-band antenna1covers 2.4 GHz (2.4 GHz˜2.484 GHz) and 5.2 GHz (5.15 GHz˜5.35 GHz), which meet the specification of dual-band WLAN.FIGS. 7–23illustrate the radiation pattern and gain of the experimental results in the preferred embodiment of the present invention operating at the frequencies of 2.4, 2.45, 2.5 GHz and 5.15, 5.25, 5.35, 5.75, 5.85 GHz. From the preferred embodiment of the present invention, it demonstrates that besides the characteristic of the dual-band operation, it have a characteristic of higher gain when operating at high frequency (5.2 GHz).

In summary, the dual-band antenna1of the present invention utilizes the ground pad14similar to an “L” shape and the electromagnetic coupling effect generated by the emitting unit12to effectively reduce the length of the first wire121and the second wire122corresponding to the operation frequency. Moreover, because of the special shapes of the first wire121and the second wire122of the emitting unit12and no common part between the first wire121and the second wire122, the first wire121and the second wire122have a better degree of isolation. It is easier for the designers to adjust each wire independently to change the properties of the antenna, shortening the product lag-time and improving the high frequency gain as well as the bandwidth of the dual-band antenna.