Investigation And Realization Of Amplitude Based Beam Steering System Of Antenna Arrays

Abstract

The wireless world we live in has been made possible due to the design and development of antenna systems. These play a critical role in the transmission and reception of electromagnetic signals over large distances. For efficient signal transmission, multiple antennas are arranged in a specific 1D or a 2D system called an Antenna Array. One of the key applications of antenna arrays is to focus the energy of the entire antenna array at a user defined point in space; this gives the user the ability to change the focusing of the energy to move from one specific point to another. This has been conventionally achieved using phase shifters in front of each antenna element thus ensuring there is a path difference in the signals [1] [2] emanating from each antenna. These signals combine in the far field giving rise to a specific antenna pattern. The goal of this dissertation is to present an alternative system that uses amplitude as the main variable instead of phase in order to achieve beam steering. With the work of Costas [3] [4] as a starting point, a fully functional beam steering system using amplitude has been designed and built and the design of each block in the functional system is elucidated in this thesis. The amplitude beam steering system consists of interleaved arrays that are fed with alternating phases of 0° and 90° (with a further option to flip the sign if needed) and with proper weights in order to steer the beam. The design of the antenna arrays is outlined with specific focus on the unit element which is the microstrip dipole and the optimization of its parameters. The simulated results of the individual dipole are then compared to the fabricated dipole antenna. Following this, a detailed discussion on the ground plane with slots is presented that makes the patterns unidirectional. Simulations showing the performance of the arrays are presented which confirm the idea of the amplitude based beam steering system. The designed ground plane is fabricated and the behavior of the antennas in the ground plane is characterized and is very similar to the simulation results. This is then followed by the design of the feed networks that are used to power the amplitude based arrays. Wilkinson Power divider is used as the main fundamental splitter to equally split the powers. The proper weights that are calculated are implemented using attenuators and the design of the attenuators is dealt with in detail as well. For the comparison of performance, a normal array along with its feed networks using meandered lines is designed and fabricated. Simulations show the performance behavior of the normal and amplitude arrays and the overall testing of both of the arrays is performed in the antenna chamber and the results are outlined. The normalized radiation patterns of the measured amplitude array validate the idea of amplitude based steering. Performance metrics in terms of gain and input power ratios are discussed in detail. This is followed by an analysis of mutual coupling and design of decoupling circuit and its optimization. The final chapter in this dissertation deals with the conclusion and the future work which is extension of this idea to 2D beam scanning.