Study On The Performance And Miniaturization Of Microwave Filter In Wireless Communication Systems

In recent years with the fast development of mobile communications, personal communications and the high integration of integrated circuits, microwave filter as one of the necessarily equipments in wireless communications systems, are becoming smaller and smaller. At the same time, with the fast development of computers, finite-difference time-domain (FDTD) method is becoming a powerful tool of analyzing these electromagnetic problems. In this dissertation, several novel miniaturized or high performance microwave filters are presented and FDTD analysis of some filters is studied. The dissertation is classified into four parts stated as follows.Firstly, introduces FDTD and presents a novel FDTD method. The FDTD formulation, based on wave equation, employs approximation techniques. The proposed algorithm uses much shorter time than the standard FDTD method. This method has much higher efficiency.Secondly, g / 4, g / 2 and g type transmission-line stepped impedance resonators (SIR's) have been introduced, standardizes these three types of SIR's and systematically summarizes their fundamental characteristics, such as resonance conditions, resonator length, spurious (higher order) responses, and equivalent circuits.Thirdly, a tapped bandpass filter composed of two coupled stepped-impedance resonators (SIR) is proposed . A coupling capacitor located at the end of resonators is introduced, by which strong coupling between them can be achieved, thus, a wider passband and lower insert loss can be realized. The performance is improved while the volume keeps no changes; A novel laminated bandpass filter composed of two SIR is proposed. The volume of proposed filter is about 60% of conventional filter while the performance is better than the former, describes the design of a compact stripline ceramic filter. Using short-circuit SIRs, this structure can restrain parasitical passband availably with decreasing volume and inserted losses of filter; A new compact SIR filter is proposed, in which impedance ratio has no impact on the volume. By reversing one of two resonators, the size of the filter is much smaller.Lastly, presents a new compact and simple microstrip patch bandpass filter structure using only one resonator. This filter has two transmission zeros on the both sides of the passband. The volume of this filter is about 1/3 or 1/2 of conventional filter. Without coupling gaps, the new filter can reduce uncertainty in fabrication; A class of new planar dual-mode filters using one square single patch without coupling gaps are proposed. Transmission zeros can be implemented on the either side of the passband by changing the locations of two feed lines. A novel dual-mode elliptic-function bandpass filter structure without coupling gaps is also proposed.