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... 

Millimeter-wave imaging is used in a vast applications like security, medical and non-destrcutive testings. Frequency scanning antenna is one of the optimum solution in mm-wave imaging systems, because of its accuracy, agility and low cost. In this method, changing the frequency plays the main role and leads the main beam to scan the space. In this thesis, by observing different frequency scanning structures, like microstrip antenna, slotted waveguide antenna array, substrate integrated waveguide leaky-wave antenna, different structures are designed and simulated. The antenna, which results in the best performance for an imaging system is selected for fabrication and measurement. The... 

The aim of doing this project is design and fabrication of a X band low phase noise oscillator Using oversized cavity resonator and transposed gain amplifier.One of the most important factors in reducing oscillators phase noise is the quality factor of its resonator and by increasing the quality factor, we can reduce the phase noise. So by doing this , in this project we want to increase the quality factor of the resonator part of the oscillator and design an oscillator in the X frequency band ( approximately 8 GHz ) .As we know the Q factor for waveguide cavity resonator is increased when we use them in the higher order modes and there is a great improvement in Q factor T when we use them... 

Millimeter wave technology may prove to be one of the key technologies of the 21st century, covering a broad range of applications including high-speed telecommunication, wireless sensing, and ultra-fast digital computing. The ultimate (commercial) success of these technologies depends on the ability to integrate mm-wave circuitry on a chip, bringing about significant size and cost reduction. Traditionally, mm-wave systems have made extensive use of waveguides based on hollow- or dielectric-filled metallic cavities for the transfer and processing of signals. Cavity waveguides exhibit very low loss, but are not well-suited to high volume manufacturing or on-chip integration due to their... 

An important issue in High-Frequency circuits is the transmission of electrical signals in Integrated Circuits and Printed Circuit Boards (PCBs). At high frequencies, however, the often used transmission lines suffer from high conductor and substrate loss as well as unwanted electromagnetic coupling to other circuit elements caused by parasitic substrate surface. One method through which both of the above problems may be solved is utilizing waveguide structures on PCBs and ICs. In this way, due to the reduction of conductor loss, a large proportion of signal passes easily. Moreover, and because of closed nature of cavity waveguides, neighboring circuits are protected against electromagnetic... 

In this project, we were intended to study the ultra-strong coupling in optical waveguides. Hence, we analyze the interaction of an electromagnetic wave with a quantum well embedded in a dielectric slab waveguide. First, we designed a QW with and alloys, which the energy of its electron-heavy holes transition is . By exploiting the envelope function approximation, we derived the wavefunction of electrons and holes, their eigen-energies, and the dipole moment of electon-holes. For finding the wavefunction of holes and their eigen-energies, we used the Luttinger Hamiltonian. Next, we calculated the electrical susceptibility of a three level quantum system (as a model for QW), by using... 

Nowadays, wireless communication plays a key role in everyday lives and has many different applications. Today’s communication systems require high bandwidths in order to transfer data with higher bitrates. Among these, modeling a wireless channel is one of the most important challenges in wireless communications. Modeling an indoor Ultra-Wide-Band (UWB) wireless channel has been involved in a great number of researches. In order to model a UWB channel, we need to correctly investigate electromagnetic waves inside the buildings. Amongst different methods that are used for this aim, ray tracing method is one of the most accurate and fast ones. In this thesis, time-domain reflection and... 

The objective of this thesis is to design an electrically tunable array of rectangular waveguide slot antennas. Because of its simplicity in design and fan shaped radiation pattern, for many decades, this kind of antennas were used in many systems like radars. Conventionally, beam steering of these types of antennas is done by a frequency sweep of waveguide in vicinity of the center frequency. Because each element is a resonant slot, its low bandwidth puts limitations in the frequency sweep. In this project, instead of frequency sweep in slot array antennas, we will consider adjusting these antennas using varactor diodes. Apart from varactor’s adjusting capability and its effect on radiated... 

Ridge gap waveguide is a new technology with low loss and high power handling capability in millimeter wave(mm-wave) frequencies. In this technology there is no need for electrical connection between the constitutive parts and using dielectric material as a substrate. This thesis focuses on the capabilities of this technology in realization of devices used in communication systems at the mm-wave frequency. Novel devices based on this technology have been designed, fabricated and tested. The main goal of the thesis is realization of the whole RF front end of a communication system in Ka band based on this technology. So at first step, a ridge gap waveguide transmission line is evaluated and a... 

Phase noise is one of the most important parameters in communication systems especially in receivers. Implementation of low phase noise oscillators has always been important.One of the most important parameters in reducing the phase noise of the oscillator is the quality factor of the cavity used in its structure. As a result, increasing the quality factor of the cavity can reduce the oscillation phase noise. Cylindrical waveguides in higher order modes have a higher quality factor than the main modes of excitement. As a result, this property can be used to increase the quality factor of the cavity and reduce the phase noise of the oscillator. This will increase the size of the cavity. The... 

Today, the internal connections of the CPUs with a few billion wired transistors in 14 copper layers on the silicon wafer are possible. Recently, power dissipation has slowed the growth rate of clock growth in CPUs, and nowadays sometimes more than 60% power is lost in connections. In this situation, the increase in efficiency has been achieved in accordance with Moore's law with multi-core chips. This theme has made the connections between the cores much more important than before. Usually the information in the network structure on chip (NOC) is transmitted on these connections. Therefore, all three aspects of delay, power dissipation and bit rate are important for communication channels.... 

Lorentz reciprocity theorem is one of the most fundamental concepts in electromagnetism. Although, in specific conditions, for example in nonlinear systems or systems with broken time-reversal symmetry it can be violated. In recent years, many interests have been attracted towards such systems. With a proper design, they can support nonreciprocal or at specific conditions unidirectional propagation behavior. For example, despite ordinary dielectrics, in ferrite layers, the propagation constant of surface waves on ferrite edge, depends on the direction of propagation with respect to magnetization direction. Furthermore, in the specific interval of frequencies, ferrite structures allow... 

In this study, we simulated and analyzed a plasmonic waveguide modulator based on single layer graphene. It includes a graphene sheet, which sandwiches between two layers of silicon dioxide. Then, some gates are arranged on either side of the waveguide on a periodic structure. When an electric field is applied perpendicular to the waveguide plate, the Fermi level of graphene under the gates, changes. Detailed analysis is performed by the method of lines based on Maxwell's equations along the propagation direction of the waveguide. Computation of the multi-gate device starts by examining the effect of Fermi level. Transmission coefficient of the magnetic-field norms of the modulator is... 

E-plane waveguide filters are good choices due to highly manfacturing accuracy in Q-band microwave devices.To increase the attenuation slop or selectivity of such filters one need to synthesis transmission zeros with cross coupled resonators.With this method for constanst degree and return loss, attenuation slop increases in comparison to direct coupled resonators.
In this thesis we designed and fabricated a Q-band 4th degree filter,with center frequency at 42.1746 GHz and bandwidth of 350 MHz with two transmission zeros. Results of simulations and measurments are given in chapters 3 and 5.
Microwave filters using coupled resonators are important components in microwave systems.... 

Structural health monitoring (SHM) has been motivated in aircraft and civil industries over the two last decades. Ultrasonic guided wave propagation technique is one of the best damage detection methods in airplane thin wall structures because of their large distance traveling and low attenuation.
In fact by efficient design of sensors pattern one can effectively pick up the changes that happen in propagated signals due to presence of any kind of structural damage. This could be effectively achieved by numerical simulation techniques like finite element modeling. To obtain a damage detection algorithm based on instantaneous baseline data, here, finite element technique is employed for... 

In recent years, a strong interplay between quantum mechanics and the physics of waveguide arrays was established based on a formal analogy between atomic and photonic lattices. The study of light evolution in photonic lattices has provided deep insights into the physics of wave function dynamics and, hence, peculiar quantum mechanical features. Arrays of evanescently coupled waveguides is a very versatile model system for discrete physics. Anderson localization and Bloch oscillations are two examples of coherent quantum transport phenomena, which have been investigated in this thesis. In the first part of this thesis, we investigate numerically the effect of long-range interaction on the... 

In this thesis a substrate integrated waveguide (SIW) filter is designed and constructed using the contour integral method. A substrate integrated waveguide can overcome the drawbacks of regular waveguides, namely bulkiness, high costs and the difficulty to be integrated with other elements in high frequencies. In planar structures with arbitrary shapes where green’s functions aren’t available, we can use the contour integral method to construct the impedance matrix. Because the SIW structure supports TEn0¬ modes, we can consider SIW as a planar structure and thus use the contour integral method. Regular filter structures are usually analyzed using the FEM method (with HFSS) or the FIT... 

Mode extraction in photonic and quantum-well structures requires solving transcendental equations and applying complex root searching methods, which incurs a diversity of numerical obstacles. In this thesis, the most effective methods for derivation of complex roots in such equations are investigated and analyzed. Thus the complex modes of an arbitrary one-dimensional photonic structure are extracted with highly adjustable precision and accuracy. The improper modes, i.e. solutions of the improper dispersion equation, are also studied and extracted by exploiting numerical methods. After this step, the migration of modes caused by changing the physical parameters of the structure is... 

Potential of plasmonic waveguide structures to confine light in sub-wavelength scales attracted many attentions in recent years. Among these structures planar metal-insulator-metal waveguide and plasmonic slot waveguide are more promising. That is because of their easy fabrication process along with their various reported applications. However, there are some obstacles in the path of developing plasmonic integrated circuits, among whichhigh propagation loss can be named as the most important. To solve this issue, photonic waveguides can be used as the lossless interconnections between small footprint plasmonic components on optical chips. Therefore, application of plasmonic slot waveguide...