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 the FIG. 1 and FIG. 2. Because WLANs operate in the bands 802.11b and 802.11a for receiving the dual bands by the antenna, a dual-band antenna 2 is disclosed by Taiwan patent 557603, which has a first horizontal wire 21, a second horizontal wire 22, and a vertical radiation wire 23 disposed on the top surface 26 of an interface substrate 24. A ground 28 is disposed on the bottom surface 26 of the interface substrate 24. The first horizontal wire 21 and the second horizontal wire 22 cooperate with the vertical radiation wire 23 to produce the high operation frequency and low operation frequency of the dual-band monopole antenna 2. A micro-strip 25 transmits the RF signals generated by the antenna. Therefore, when designers adjust the length or the width of the wire 21 or the wire 22 to 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.