Sharif Digital Repository

In the year 2004 when the first instance of graphen was built in laboratory, entice the attraction of many research groups. Because in spite of absence of graphen to that time, physicists given the unique properties for it. So it was the time to use that marvel properties which only theoretically available, to design and built one atom thick circuits. In this dissertation for the first time, we want by using method of moment and multilayer green functions in spectral domain, analyze graphene-based ribbon and stepped electrical conductivity distribution waveguides and calculate their characteristics such as propagation constant, surface currents and characteristics impedance with external... 

Today’s technological trend towards higher performance microwave and digital circuits at increasingly smaller sizes poses new challenges to both the microwave and high-speed VLSI designers. One aspect of these challenges lies in the fact that nonuniform transmission structures must often be used to reduce circuit sizes, to increase circuit bandwidth, to reduce discontinuity effects, and to optimize the overall circuit performance. Coupled microwave transmition lines are one of most common microwave circuits, that are use to design couplers, power dividers, hybrids, baluns, filters, phase shifters, matching circuts and so on. The broadband tight couplers are one of interesting devices that... 

tIncreasing the bandwidth of a receiver is limited to the bandwidth of the system's internal components such as amplifiers, power dividers / combiners, and directional couplers, which are widely used in array antenna systems. Wilkinson splitters are often used for balanced power dividers and hybrid branch line couplers are used for directional couplers because their macrostrip structure makes them lighter and cheaper, and ultimately increases their use. Unfortunately, these elements provide up to 20% fractional bandwidth, which is not enough in our intended use. Also, the design of the power divider at millimeter wave frequencies has challenges such as matching impedance across all bands and...