The Design And Realization Of The Wide Stopband Low-Pass Filters And Dual-Band Antennas

Wireless local area network (WLAN) is one of the fastest communication technologies in the 21st century. More and more compact"dual-band"products following the standards of IEEE 802.11 a/b/g are needed. And the new challenges have been faced to the relevant components. So the low-pass filters which have some special advantages are deeply needed, such as the compact structure, convenient manufacture and perfect stopband which can suppress harmonics and spurious signals effectively. For antenna, the small size dual-band antennas which can work both in 2.4-2.484GHz and 5.15-5.825GHz are also favored. The goals of this thesis are the design and realization one or two new wide stopband low-pass filters and compact dual-band antennas.In the first part, a new compact low-pass filter prototype is proposed, which is composed of a pair of parallel coupled-line and two linked open-stubs. Using the theory of transmission line and equivalent circuit, the equivalent circuit model of this new prototype is obtained. Then, using the proposed equivalent circuit model, the influences on the characteristics of the passband and stopband by the key parameters are discussed in detail. In order to improve the stopband characteristics of the low-pass filters, two different improvements for the prototype are put forward. The first method is cascading two prototypes, it can sharper the cutoff frequency response and deeper stopband, but extend the size. The second method is using defected ground structure (DGS) to improve the band characteristics while keep the size small. The design and analysis procedures of these two structures are given in detail. The optimal structural parameters are obtained using simulation software. Three low-pass filters are manufactured and tested. The test results show that LPF with DGS not only can increase the return loss in passband, but also provides wide stopband, sharp cutoff frequency response and keep the small size.In the second part, we proposed two different structures of dual-band antennas which are used for WLAN. One antenna is a printed monopole dual-band antenna which is composed of a rectangular plane and a two-element uniform array. The affections on antenna performances from structural parameters are investigated carefully. According to simulation optimizing, the best parameters of the antenna structure are achieved. The another antenna is a stair-shaped dual-band antenna which the slot on ground is defected as"工". We use the software to analyze and optimize the important parameters of this antenna. Two optimal dual-band antennas are manufactured and tested in microwave chamber. The test results show that the two new type compact antennas can both satisfy the WALN standards of IEEE 802.11 a/b/g which can cover the operation frequency of 2.4-2.484GHz and 5.15-5.825GHz. The antennas have omni-directional radiation pattern and can be integrated with other circuits easily. These provide new approaches in design the printed dual-band antennas for WLAN systems.In the last part, some useful conclusions and discussions are given. These provide a useful guide for further research.