Sharif Digital Repository

In the communication systems, there are two types of blockers: in-band and out-of-band. High frequency pre-filters and band-pass filters can be used to suppress the out-of band blockers. However, using these methods does not affect the in-band interferers. Spatial filtering by means of phased array antennas and using frequency filtering can suppress both types of interferers. In a typical phased array receiver, all of the received signals pass through active blocks (such as LNAs, active phase shifters, driver amplifiers, etc.) that amplify the interferers before canceling them. Therefore, because of the high strength of the interferers, the dynamic range of the front-end blocks preceding... 

The most important feature of the fifth generation of mobile telecommunications is the increase of information transfer rate and together with it the increase of the capacity of telecommunication channels in comparison with the previous generation. One solution is to increase the frequency toward millimeter-wave frequencies. Currently, the most suitable option for the millimeter-wave frequency band is the 28 GHz band, which has received a lot of attention due to its availability and the possibility of implementing cheap integrated circuits using CMOS technology in this band. In addition to the features that this frequency band has; This band has limitations such as high emission losses and... 

A phase shifter is a microwave element that changes the phase of the input signal at a specific center frequency and bandwidth and, ideally, produces a signal with the same amplitude and a modified phase at the output. In practice, this phase change in the passive phase shifter is accompanied by a decrease in amplitude due to different factors. Various use cases can be described for phase shifters in telecommunication circuits, but its most important application is in regulating the relative phase of each antenna in a phased array system, which is the most common method of beam steering and forming. A phased array system is one of the leading solutions to achieve beamforming and high... 

Sonic and ultrasonic measurements are used for checking status of wells. Well logging is used to estimate well specifications like borehole diameter, casing thickness, cement bond quality and cement sheath thickness. In this thesis, some reported works in field of sonic/ultrasonic measurement of oil wells are reviewed and results of software implementation of ultrasonic measurement with pitch-catch arrangement, pulse-echo arrangement and phased array arrangement are presented. ultrasonic measurement with pitch-catch arrangement uses one transducer for transmitting ultrasonic waves and two transducers (in different distances) for receiving ultrasonic waves. Ultrasonic measurement with... 

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... 

Mutually coupled oscillator arrays have been considered. Detuning of free running frequencies of perimeter elements has been used in these arrays in order to steer the beam without phase shifters. Characteristic equations of transient and steady-state conditions of amplitude and phase of the elements of coupled oscillator arrays has been derived. Literature review is done in coupled oscillator arrays. Sensitivity analysis of beam pointing angle due to free running frequencies of elements in coupled oscillator arrays has been done and the various planar arrays has been compared. Sensitivity analysis of beam pointing angle due to phase error of elements in conventional phased array antennas... 

Phase shifters are commonly used in the implementation of phased-array antenna systems.The function of these systems is highly dependent on the performance of phase shifters. In addition, phase shifter circuits are used in some applications such as antenna test and regulation, power amplifier linearization, and QAM modulator implementation, to name but a handful. In this project, design of phase shifter blocks, as well as limitations of fabrication on silicon substrate, is studied and these blocks are designed for maximum bandwidth and minimum sensitivity based on fabrication characteristics and environmental conditions. Design of a 6-bit phase shifter based on vector-sum method is the... 

In synthetic aperture radar (SAR) satellites, the nadir echo is defined as the backscattered signal from the point directly below the satellite on the earth surface. If the timing of the radar is such that the nadir echo arrives at the receiver while the receiver is turned on for receiving the desired signal, it could damage the receiver or disrupt the resulting SAR image, unless it is suppressed enough by proper design of antenna radiation pattern. In current SAR satellites, ”avoiding” this phenomenon is associated with two problems: 1) limiting the swath width, 2) imposing stringent restrictions on the selection of pulse repeatition frequency (PRF). Therefore, ”suppressing” the nadir echo,... 

On the demand of higher directivity, higher throughput and less interference, phased array systems and MIMO have become attractive to reach these goals. The advantages of phased array systems include the ability to perform electronic beam steering and arbitrary pattern synthesis. Phase shifters and variable gain amplifiers are used to reach these advantages. In this thesis, a ‘’ C‘’ band (4.8 GHz-6.2 GHz) vector-sum phase shifter using HMIC technology for realizing a phased array receiver is designed. This phase shifter can change the signal phase and amplitude. The main blocks of this phase shifter are low-insertion phase and low-noise variable gain amplifier, which consists of current... 

Next-generation wireless communication requires phased-array systems to ensure Gb/s data communication. This work demonstrates a four-element phased array receiver based on N-path filters for the 5G-FR1 frequency band. The behaviour of the circuit including non-idealities and effects due to mismatch in the paths is modeled and verified via simulations. As the time-variant nature of the N-path filter introduces multiple frequency translations, third harmonic selection of the switching frequency rather than the fundamental helps to reduce the input frequency of the multiphase clock generator by a factor of three. Therefore, the proposed structure is capable of third harmonic reception as well... 

The purpose of Direction-of-arrival(DOA) estimation in MIMO communication networks is to find the direction of signals that are mixed together and mixed with noise by using an array of multiple receiving antennas. DOA estimation is an important issue in array signal processing. The traditional methods for DOA estimation try to solve this problem with mathematical algorithms. For example, some of these methods are based on parameter estimation; such as DOA estimation methods using maximum likelihood estimation methods. Some of other traditional methods are based on subspace decomposition; Like the famous MUSIC method. The traditional methods of DOA estimation usually have a drawback, and that... 

The significant growth in wireless data traffic over the past few years has necessitated the use of new frequency bands for wireless communications. With the advent of the fifth-generation mobile network (5G), millimeter wave band will be widely employed for the purpose of wireless data transmission, increasing in channel bandwidth and data rate. Due to high propagation loss, severe vulnerability to blockage and poor reflection in millimeter wave frequencies, beamforming for antenna arrays is being considered a key enabler for millimeter wave applications in 5G. Beamforming contributes significantly to maintaining channel stability and capacity through enhancing Signal-to-Noise-Ratio (SNR)...