Compact Multiband Antennas with Polarization Diversity and Wideband Characteristics using Artificial Electromagnetic Structures

Abstract

With the rapid changes in the technological advancements of wireless communication, the design and development of advanced diverse antennas that are smaller in size but higher in performance with enhanced bandwidth and independently controllable multiple bands of operation has become a challenging need. In addition, the features of circular polarization (CP) at the multiple resonant frequencies and provision for control in sense of polarization at each of the CP bands of the antenna are desired. The different performance parameters and radiation characteristics of these antenna designs play a significant role in the optimum realization of the concerned wireless devices. Hence, this thesis presents novel antenna designs that offer radiating bands at frequencies pertaining to various applications related to wireless technology, radar systems, satellite communication devices among many other applications. In order to obtain the desired characteristics, artificially synthesized metamaterials (MTMs) have been used whose properties can be easily tuned and controlled so as to obtain superior performance in MTM based antennas. The thesis presents MTM based slot antennas that are designed to operate at multiband frequencies and offer easy opportunity for independent tuning of the frequency bands. The different types of MTM unit cells used include the split ring resonators (SRRs) and copper strip arrays whose properties have helped design slot antennas that operate with triband, quadband and pentaband frequencies with compact antenna geometries. The other designs presented in the thesis include compact slot antenna geometries that operate at multiple frequency bands having at least one band of operating bandwidth greater than 50%. A fictitious short circuit is excited in a quarter wavelength slot using a suitably designed microstrip feed line to obtain the wideband compact design. Multiple bands are obtained by introducing SRR and modified SRR structures. The concept of transmission line is also briefly introduced in the thesis and a novel compact UWB slot antenna design is discussed where rows of artificially dispersed transmission lines are used to obtain the various vresonance modes that combine with the fundamental slot modes to give the UWB resonance. The remaining designs included in the thesis involve slot antennas that offer the feature of circular polarization at multiple frequency bands. This is obtained by altering the slot structure and by introducing different MTM-based structures, inclined copper strip strips, U-strips and meandered slots. The different frequency bands can be tuned according to the application by changing the sizes of the structures and also the sense of polarization at the different bands can be altered. All the designs are fabricated and the different parameters are compared based on simulated and fabricated results. The last chapter presents a brief comparison of the proposed designs with the previous works and gives a brief idea on the scope for future works. The compactness, radiation efficiencies, peak gain values, operating bandwidths, axial ratio values are the various parameters looked into and compared with previous designs in literature.