With the repaid development of wireless communication systems, the radiating antennas with low cost and dual-band operation are in demand for various applications, such as wireless local area network (WLAN). The WLAN systems unitize the unlicensed bands, the ISM band at 2.4 GHz and 5.2 GHz only for the industrial, scientific and medical applications, to reduce the cost of the network building. The slot antenna has been investigated since the 1940s and many research studies have discussed the feeding structure, the bandwidth characteristics and the radiation phenomenon. The slot is etched on the ground plane of the substrate and radiation from both sides of the substrate is achieved by a microstrip or CPW-fed in a resonator cavity. In order to derive the maximum beam at the broadside direction, the length of the slot antenna should be limited to one wavelength. The technology of applying two different slot loops in the aperture was proposed to create dual bands. FIG. 12 shows a conventional slot antenna comprising a plurality of etched slots 62 in the ground plate 61 of the substrate 60 and a sub-antenna 64 extends from the ground plate 61 and to the opening 63 of the slot 62 so as to be the signal feedline. Another conventional slot antenna is disclosed in FIG. 13 and the slot 72 is etched as a T-shaped slot in the ground plate 71 of the substrate 70. A T-shaped feedline 73 is located in the inner periphery of the slot 72. Nevertheless, none of the conventional slot antennas is satisfied.
The present invention intends to provide the CPW-fed slot antenna to perform the dual-band characteristic and miniaturize the slot size utilizing the E-like feeding structure and adding the matching stub at the slot edge and four floating patches on the backside of the substrate. According to the measured results, the bandwidth of the lower resonant frequency distributes from 2.38 GHz to 2.60 GHz and one of higher resonant frequency ranges from 5.13 GHz to 5.73 GHz. The above techniques are effective and realizable for the design of the CPW-fed slot antenna.