الفهرس 
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Abstract
Microwave band pass filters are essential components in communication systems. The rapid growth of wireless and mobile communications require high performance and compact filtering structure.For filter using microstrip, reducing size is the main challenge of the filter design.
This thesis presents the analysis and design of defected ground structure (DGS) filters. Firstly, different shapes of DGS resonator are used and the effect of these shapes on the resonance frequency are studied .The DGS resonator gives us high performance and compact filtering structure.
In order to reduce the resonance frequency the resonator length must be increased ,but the size of the filter is increased.
Secondly, we study another way to reduce the resonance frequency by inserting lumped capacitor in the slot that increases the effective capacitance of the resonator, reduces the resonant frequency, so the dimensions of the filter will be reduced and its performance will be improved. Different lumped capacitors are added with different capacitances. Therefore, the dimensions of the filter are reduced by 60% by increasing the lumped capacitor from 0 to 1pF.