Research And Design Of Highly Selective And Miniaturized Bandpass Filter In Wireless Communication Systems

The characteristics of compact size, high selectivity, and low insertion loss for modern microwave filters are highly required in the modern mobile and satellite communication systems. So miniaturized and highly selective filter is currently a research hotpoint. Based on the real demand, the new technology and new structure of miniaturized and highly selective filter are analyzed thoroughly in this thesis. The dissertation is classified into five parts stated as follows.Firstly, novel and exact methods are presented for maximizing the band-edge selectivity of the quasi-elliptic function and general Chebyshev function filters. The technology satisfactorily resolves maximizing the BES with the least order n .Secondly, A general method is presented for synthesizing microwave filter with source-load cross coupling. The equivalent circuit of the low-pass prototype of a general lossless coupled resonator filter is proposed, and the corresponding transfer function t(s) is derived. The expressions of M SL, M Siand M iLin the coupling matrix M are obtained based on two-port admittance matrix [ Y N]. Then, two novel hexagonal open-loop quasi-elliptic resonator microstrip filters are designed, one symmetric and the other asymmetric, are designed.Thirdly,transmission zero conditions of three types of different coupled lines are analyzed, which areλ/2 serial microstrip lines using skew-symmetric and symmetric feed structure,λ/2 parallel coupled microstrip lines using skew-symmetric and symmetric feed structure, andλ/2 hairpin resonators using skew-symmetric feed structure. the number and Principles, location of transmission zeros are discussed, and then these structures are applied to the design of microstrip filters with multiple transmission zeroes.Fourthly, ultra wideband characteristics of three types of coupled line filters with different defected ground structure are studied, and lowpass characteristics of three types of transmission line filters with different defected ground structure are analyzed, and then these structures are applied to the design of ultra wideband filters with transmission zeroes.Finally, Through analysis of bianisotropic split ring resonator (SRR) metamaterials, the uniform physical explanation for SRR resonance band gaps is gained by revealing the fact that imaginary wave number does lead to the SRR resonance. The magnetic resonance of SRRs has been explained particularly and comprehensively. Meanwhile, a novel compact multilayer filter, which is based upon the small size of SRR, the skew-symmetric feed scheme and the multilayer technology, is proposed.