With increasing demand for modern technology in the communication systems, antenna arrays have attracted much interest in the areas of radio broadcasting, space communication, weather forecasting, radar and imaging. Antenna array with controlled low or ultralow sidelobes is of particular importance and it has been an on-going challenge for the antenna design engineers in the past few decades, as it requires a high dynamic range of excitations. Another desired feature provided by an antenna array is the ability to perform electronic beam steering and adaptive interference suppression.
These benefits can be achieved with the use of complicated feed network and expensive phase shifters and it can only found in the specialised military systems. Therefore this has motivated the research into the development of a simple and low cost system for the commercial applications.
The idea of time modulation was proposed to produce an antenna pattern with controlled low or ultralow sidelobe level, as well as achieving real time electronic beam scanning without the use of phase shifter. However, a fundamental problem of this concept is the generation of undesired harmonics or sidebands as they waste power.
This dissertation mainly focuses on the two important characteristics - pattern synthesis and multiple beams scanning of the time modulated antenna array and evaluates its potential application in the communication system.
The first main chapter of this research proposes two novel approaches to successfully suppress the sideband radiation and hence improve radiation efficiency. The following part of the study introduces a way of combining the electronic beam scanning with the controlled low or ultralow sidelobes and applies the null steering technique in the time modulated linear array. The final but most important attribute of this thesis is to propose the concept of time redundancy and evaluate the potential feasibility of employing smart antenna technology into the time modulated antenna array for a two-channel communication system, where individual adaptive beamforming can be performed to extract desired signal while suppressing interference from separate sources independently.
