Design Of Filter-Antenna For WLAN Application

With the rapid development of wireless mobile technology, people put forward higher request to communications equipment for integration, miniaturization and multifunction. It brings great opportunities and challenges to the development of wireless communication systems. It also gives a higher requirement to researchers. Filter and antenna, as important devices, are required to develop toward more integrated, multi-frequency direction. This design integrated antenna and filter, not only can effectively reduce the size of the communication device, but also improve the performance and quality of communication interference. Therefore, it is very meaningful to research them.WLAN has become one of the effective means of broadband access. An increasing number of regional and business use WLAN. Among all the standards,2.4GHz (2.40～2.48GHz) of IEEE802.11b standard and 5GHz (5.15～5.35GHz) of IEEE802.11a standard are the most common standards. Therefore, it is very meaningful to design filter-antenna at 2.4GHz and 5GHz frequency bands for WLAN system.In this paper, the design principles and implementation of filter-antenna were studied. On this basis, three filter-antennas were designed for WLAN system. The first filter-antenna, using microstrip structure, was designed for WLAN system at 5GHz band. According microstrip filter theory, a WLAN (5.15～5.35GHz) band bandpass filter was designed. Then based on this filter, the function of filtering antenna were achieved by changing the second resonator and DGS combining methods. The second antenna is a filter-antenna array for WLAN 2.4GHz band. The filter-antenna unit was designed by a combining substrate integrated cylindrical cavity filter with microstrip patch antenna. The filter-antenna array was fed by Wilkinson divider. The third filter-antenna is a dual band WLAN antenna-filter which simultaneously working in the 2.4GHz band and 5GHz, it was designed by loading stepped impedance resonator filter at the feeder portion of the "田" shape dual-band antenna to achieve the dual-band filter characteristics.In this paper, the design method of theoretical analysis combining with electromagnetic simulation software optimizing was adopted. According to the design results, all the three filter-antennas were fanbricated and measured. The measured results show that the maximum gain of the first filter-antenna is 1.85dBi;the maximum gain of the second filter-antenna array is 5dBi, the third dual filter-antenna’s maximum gains in two bands are 1.85dBi and 2.27dBi. And this three filter-antennas have a good band rejection characteristics, simple structure, small size, low cost, which meet with the design requirements basically.