INVESTIGATIONS OF MICROSTRIP PERIODIC STRUCTURES
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Periodic structures are used as microwave filters because of their inherent passband-stopband characteristics. The structure exhibits alternative passbands and stopbands. The widths and positions of the passbands and stopbands are changed with the parameters of the structure. The analysis of non-planar periodic structure filters are well documented in the literature. Recently, investigations of these structures in the microstrip configuration have also been reported. The structures under consideration in the past investigations were microstrip lines with sinusoidally varying width and triangularly width modulated microstrip lines. The work reported in this thesis is an investigation of microstrip periodic structures with rectangular and circular geometries. Closed form expressions for the ABCD parameters of a structure with N unit cells are derived. The input-output characteristics of the structures are very similar to a bandpass/bandstop filter. The design procedure for a periodic structure bandpass filter is presented. Bandpass filters are designed and fabricated. Theoretical results show agreement well with the measurement. The variations of the bandwidth and center frequency with the dimensions of the structures are studied.