Sharif Digital Repository

Switched Parasitic Antennas, as a kind of Smart Antennas, have several applications in Telecommunications and Radar systems. In the realm of wireless applications, these antennas provide the system with higher capacity owning to the fact that they are able to direct the main beam toward the desirable user. Moreover, they can be used to degrade the adverse effects of Multi-path. Multi-path reduction not only benefits mobile communication but applies to many applications of radar systems. These antennas, in addition, can be utilized in Direction Finding. In the case of other types of Smart Antennas, the above mentioned benefits can be achieved with high costs due to the fact that there are a... 

Mars rover Curiosity is a mobile scientific laboratory which it’s mission is to assess the biological potential of the landing site and characterize the geology of the landing region. This rover communicate to a Mars orbiter named MRO satellite in the UHF band which relies the signals to the Earth stations. Also this rover communicate to the Earth stations directly in the X band. In this thesis, we determine the technical characteristics of stations and simulate Earth-Mars radio links. So we calculate :
1. determine the technical characteristics of Earth stations
2. determine the technical characteristics of satellite and Curiosity
3. Earth-Mars orbital position in the... 

In recent years due to the advances in semiconductor technology and the ability to implement small-scale manufacturing, communication at 60 GHz band receive more attention than ever has been. The use of this frequency band is not only about 7-9 GHz unlicensed broadband access provided, but getting smaller devices make it possible to use multiple antennas at the transmitter and receiver, and thus taking advantage of multiple input – multiple output systems. Antennas used in these systems should have features such as small size , low weight, high gain and bandwidth and also they should keep their high efficiency and gainat high frequency range (about a few GHz ). To achieve these features... 

Over the past few years , demand for wireless communication services have grown at a formidable rate. As such we need to find new ways to support more and more wireless users in a confined space. this means that the capacity of networks should be significantly increased to overcome formidable rate of subscribers growth. That is why the smart antennas have become very popular in communication systems. Smart antennas are a kind of adaptive antenna arrays with smart signal processing algorithms used to find direction of arrival(DOA) of the signal, and use it to calculate suitable weights to direct the antenna beam on the desired user and nulling interferences. In this thesis, DOA estimation... 

In this thesis, some of the well-known DOA algorithms namely Bartlett, Capon, Linear prediction, Maximum Entropy, Pisarenko harmonic decomposition, Minimum norm and MUSIC are analyzed and compared with each other in the identical situations using a uniform linear array. Then based on these comparisons, the appropriate algorithm is selected. In the next step since the linear arrays can't estimate both angles of arrival (Azimuth and Elevation) simultaneously, two dimensional (2D) geometries are introduced and are also compared to each other. Then one of them (circular array) is selected for dipole antenna arrays. The performance of the selected array is evaluated using isotropic elements for... 

In the new generations of mobile communication systems, smart antennas are used to achieve higher capacities. Since these systems have the ability to form a radiation pattern where the desired signal is received with minimum distortion and inteferers are received with a significant attenuation therefore their application makes it possible to have a large signal to inteference ratio. In addition by setting the main beam direction towards the desired signal, it is conceivable to realize the the communication with a lower power. The optimal methods for angle-of-arrival estimation and beamforming in one and two dimensional structures has been studied in the literature, but the three dimensional... 

Multiple-Input Multiple-Output (MIMO) communications at millimeter-wave (mm-wave) frequencies (e.g., in the 60 GHz band) is a modern technology recently considered for various applications, such as emerging 5G services for multi-user MIMO (MU-MIMO) and high-resolution frequency-modulated continuous wave (FMCW) MIMO radars to support multi-gigabit throughputs in short-range environments via spatial multiplexing-diversity. Nevertheless, the impairments of communication channels in this frequency band, including significant propagation loss and severe blockage effect, are quite challenging to allow an efficient communication link. Hence, beamforming/beam steering can play a crucial role in 60... 

The interferometer method, as one of the most accurate schemes for wideband direction finding (DF), is used. The interferometer method has various algorithms which can be implemented depending on the required specifications. The advantages and disadvantages of these algorithms have been evaluated and the appropriate algorithm for a general practical case in view of the ambiguity resolution is proposed. The receivers’ channel phase tracking error is of significant concern in practice, in interferometric DF systems. The induced error due to channels phase tracking error is estimated. Furthermore the use of physically realizable antennas, achievement of high accuracy, minimum number of antennas... 

Novel two dimensional and three dimensional antenna array geometries for smart antenna application are introduced. MMSE beamforming algorithm, using these arrays, in presence of signal, noise and interferences is implemented. Beamforming approach is used for every type of array assuming uniform and log-normal distributions for the interference amplitudes. Equal volume cylindrical or prism type arrays with circular, hexagonal, triangular, square and star cross sections with equal number of elements are considered for comparison. Novel geometries consisting of rotated cross sections are studied as well. In each case the relative SIR’s are compared in these geometries, showing that the... 

The main objective of this project is to discuss a DOA estimation system performance in a multipath environment. For this goal, first the basics of the DOA Estimation systems are discussed. Evaluation of different types of algorithms and choosing an appropriate one is an important step in this regard. Moreover the comparison of different array structures is necessary to choose the appropriate one. The major part of the project has been dedicated to discussion of multipath phenomenon as a major source of error in DOA estimation and studying the multipath mitigation algorithms to eliminate the aforementioned error. A model based on the concept of Bistatic Radar Cross Section is proposed to... 

The main objective of this project is to analysis and design of ultra ultra wideband dual polarization vivaldi antenna array for electronic support measure system. In modern satellite communication and radar systems, antenna are required to have the characteristics of both ultra wide band and dual-polarization so as to satisfy various needs such as expanding the information volume, improving the quality of receiving information and increasing the ratio of bandwidth utilization. For this reason we first design a single element of vivaldi antenna for 6-18GHz range and then with design of SMA connector shown that result with and without SMA is same. In the next step we design(under... 

With the advancement of automotive technology, the use of automotive radar for collision avoidance and pedestrian detection has been increasingly become universal. In this thesis, our goal is to design a dual-band radar antenna for obstacle detection and a 5G omnidirectional antenna for communication purposes in self-driving cars. We will first introduce the automotive radar and its operation. Next, the FMCW radar, which is simultaneously effective for speed, distance and direction estimation is introduced. Then we introduce the leaky wave antenna as the frequency scanning antenna. This is realized in an SIW waveguide technology. The main issue in this part is the achievement of high... 

Due to the widespread use of satellite communications including live TV broadcast, DVB-S and satellite Internet, it is necessary to accurately assess the level of signal received and the EIRP of the satellite. Nilesat21(7°W), Eutelsat3B(3°E), Badr(26°E), Express AM6(53°E) and Intelsat20(68.5°E) have been chosen to be meticulously assessed and analyzed.The chosen satellites contain the westernmost for Tehran to the easternmost, which has been listed above from west to east, respectively.In addition, the signal attenuation is closely monitored in the city of Tehran during rainfall for the above-mentioned satellites. In the meantime, the rain rate is also recorded.Another major factor that... 

Transferred Electron Device is a semiconductor device being capable of generating oscillation in microwave frequencies. Applying a bias voltage to the device and putting it in a resonant circuit, a periodic waveform in the output current is observed. The cause of the generation of oscillation in the device is related to the characteristics of velocity-field in the device. In some part of the characteristics, it is observed that increasing the field inside the device causes the velocity of electrons to be reduced. This causes the generation of the negative conductance and the oscillation of the output current under some conditions. The purpose of this thesis is to represent an equivalent... 

Due to the short wavelengths in millimeter waves and the specific characteristics of wave propagation in this frequency band, the methods used for modeling channel response in lower frequency bands are not applicable without appropriate modifications. Considering the fact that many obstacles in the channel have sizes comparable to the wavelength (eg branches and tree leaves, brick spacing and roughness height of many surfaces), statistical-empirical methods can be an efficient way of modeling propagation in the presence of such components.
Here an attempt has been made to obtain an appropriate model for the propagation channel using propagation models proposed in the literature. Surface... 

Nonlinear transmission line (NLTL) a guiding structure contains nonlinear elements. For discrete NLTLs, this structure is periodically loaded with nonlinear elements. In the structure of this line nonlinear elements such as ceramic capacitors, nonlinear magnetic elements, vector diodes, Mos transistors, etc can be used. With the rapid development of semiconductor devices and microwave band systems, the demand for implementation of NLTLs has increased. These lines provide wide band-width, cut-off frequencies over the hundreds of GHz and picosecond rise time for various systems.Among the applications of NLTL, the generation of high power RF pulses has attracted the most attention. In this... 

A microwave transceiver system requires an array of amplifiers. Low-noise amplifiers (LNAs) are integral parts of receivers while transmitters are based on several stages of power amplifiers (PAs). In modern communication standards, power amplifiers have to achieve high efficiencies over increasingly larger dynamic ranges and banwidths, while maintaining tight linearity requirements. In these systems, PAs must be highly efficient to simplify the thermal management and to reduce dc power requirements. Recently, the use of monolithic microwave integrated circuit (MMIC) for commercial and military applications have been paid more attention to, given the fact that the possibility of building... 

Nowadays dielectric substrates are widely used in Microwave Integrated Circuits. These substrates are made layer by layer in order to have favorable mechanical and thermal properties. The materials of the layers are usually different from each other and often each layer is a combination of different materials. This difference in material type and manufacturing method causes the substrate to have a different permitivity coefficient in two major directions, namely parallel and perpendicular direction. In fact, the electric field observes a different permitivity coefficient in each direction. This causes a problem in circuits that have both perpendicular and parallel electric field... 

The fifth generation of mobile communication has a significant development in comparison to the last generations. However, the available frequency bands in sub-6 GHz frequencies are insufficient to fulfill this development. So the mm-waves bands play an essential role in 5G. The 5G applications demand antennas with low dimensions, wide beam, high gain, and wide bandwidth. In this thesis, a mm-wave antenna is designed and optimized by machine learning to meet 5G requirements. In addition, two arrays of this antenna are proposed with 4 and 8 elements. The analog beamforming is achieved by means of these arrays. The 4-element array is simulated in an IPhone package model. Finally, an antenna... 

Microwave oscillators play a pivotal role in microwave circuitry today. Being inherently nonlinear, having a simple circuit model of a complex nonlinear circuit can greatly aid in elucidating oscillator behavior. A significant aspect in this realm is the precise understanding of the nonlinear behavior of active elements, such as transistors, which significantly impact oscillator performance. For oscillator design, having a comprehensive circuit model that encompasses the nonlinear behavior affecting frequency and output power can prove highly beneficial. Additionally, in networks comprising numerous coupled oscillators, the direct approach to analyze these networks using harmonic balance...