The Design And Study On Microwave Filters In Short-range Wireless Communication

With the development of short-range wireless communications, microwave filters in wireless communications are given more stringent requirements. Microwave filter is one of the most important components, and its performance will directly influence the communication system. Many scholars have made a lot of research in the theory, design methods and configuration forms of microwave filters.The paper mainly researches microwave filters in short-range wireless communications, and analyzes the design methods of Ultra-wideband bandpass filters and dual-band bandpass filters. Then the designs, analysis and executions of the microwave filters are given. The contents of this paper are as follows:First, the standards and applications of short-range wireless communications are introduced, and the microwave filters in the communication system are also presented. Especially, the author introduces the current research of Ultra-wideband filters and dual-band filters.Secondly, based on the characteristics of coplanar waveguide (CPW), a novel miniature ultra-wideband bandpass filter with coplanar CPW-fed is proposed, realized and measured. The UWB performance of the filter is achieved by combining wideband couple gap and parallel-coupled CPW line not cascading multiple resonator. Thus the size of filter is reduced largely, and the length of this filter is only 0.42λ_g0(λ_g0 is the guided wavelength of central frequency). Measured results indicate that the insertion loss is less than 2.0dB; the return loss is higher than 10dB, and the group delay variation is less than 0.29ns within the whole passband. Furthermore, Using the dielectric with high constant, the size of the former design is reduced. The size is 10mm×10mm, which can be used in the compact circuits. Meanwhile, the parameters of the structures are analyzed by using EM simulation software.Finally, the author designs two kinds of dual-band filters that are used in the devices and systems of WLAN (wireless local area network). One of the designs is the microstrip structure using hairpin impedance resonators. There are two uniform impedance resonators with 1/2 wavelength, which respectively control the central frequency of each passband. Measured results indicate that the design of this filter can achieve the dual-band at 2.4GHz/5.2GHz or 2.4GHz/5.8GHz. The insertion losses are respectively 1.7dB and 2.3dB, and the return losses are higher than 10dB. The other design is the square patch structure with two arc slots. The arc slots change the distribution of the surface currents, and the dual-band filter with 2.45GHz/5.2GHz can be achieved. Measured insertion losses are respectively 2.7dB and 2.4dB, and the return losses are higher than 10dB. The influences of the parameters in the two designs are analyzed, and the measured results have good agreements with the EM simulated results.