The increasing demand for high data rate transmissions in wireless communications and low power consumption, has led to a growing scientific interest concerning wideband and ultrawideband antennas. Besides, the need to integrate more than one service in only one device has made wideband technology very attractive among the scientific community. To this purpose, several kind of techniques have been introduced in literature for increasing the operative bandwidth of well-known radiating structures such as microstrip patch antennas, monopole antennas, printed monopole/dipole antennas, etc. However, all these antenna configurations, which typically are made of metals and dielectric materials, are prone to low antenna radiation efficiencies. Indeed, high efficiency is essential in satellite applications where good link margins are required or in mm-wave communications where the power losses in the system components may be relevant. Besides, high-efficiency antennas are essential for providing a long-range coverage in WLAN access points and base stations, especially in indoor environments where circular polarization is employed to limit multipath effects. For these reasons, an extensive research activity concerning high-efficiency dielectric resonator antennas has been carried out during the past decades. The main goal of this research work, carried out during these three years of Ph.D. studies, is to introduce novel wideband high-efficiency and high-gain dielectric resonator antennas working in both linear and circular polarization and suitable for terrestrial and satellite communications. Besides, an extensive time-domain analysis of the proposed radiating structures, aimed to investigate their suitability to work with UWB pulse signals, has been also carried out. The thesis is organized in five chapters. In the first chapter, after a short description concerning several wireless communication standards and UWB systems, the state-of-art of some of the most important wideband and ultrawideband antennas proposed in literature, is briefly illustrated. A special emphasis is given to dielectric resonator antennas exhibiting broad impedance bandwidths, high gains, pattern stability and good circular polarization performances. In the second chapter, the Singularity Expansion Method (SEM) and the Matrix Pencil Method (MPM), aimed to the extraction of residues and poles of an antenna impulsive response, useful for a better comprehension of the resonating processes taking place into the considered radiating structures, and for computing the antenna time domain response to arbitrary excitation signals, are described. In the third chapter, the main features of the full-wave commercial software CST Microwave Studio™, based on the Finite Integration Technique (FIT), and employed for the analysis and design of the proposed dielectric resonator antennas, are briefly described. In the fourth chapter, a novel wideband multi-level multi-permittivity dielectric resonator antenna working in both linear and circular polarization is introduced. The radiating structure, equipped with a suitable metal reflector, exhibits a maximum gain of about 10 dBi, a high front-to back ratio and a broad impedance bandwidth (between 79% and 82%), resulting suitable for several wireless communications standards (e.g. WLAN and WiMAX) and C-band satellite applications. Besides, a time-domain analysis of the antenna based on FIT and SEM techniques, aimed to the investigation of its relative group delay and fidelity factor, has been also presented. In the fifth chapter, a wideband high-gain mushroom-shaped dielectric resonator antenna, equipped with a suitable metal reflector and a dielectric lens, has been proposed for wireless, C-band radar and UWB applications. Thanks to the dielectric lens the gain of the cylindrical dielectric resonator along the boresight direction is significantly enhanced, while the presence of the metal reflector strongly improve the antenna front-to-back ratio, making the antenna characteristics independent from those of the installation site. The antenna is fed with two/four probes, opportunely disposed around the DR, with the aim of exciting a circular/linear polarization. An antenna prototype was realized to verify the performances predicted by the numerical computations. Measured and numerical results show an antenna radiation efficiency higher than 90% along the antenna operative bandwidth, a fractional bandwidth of about 65% and a maximum achieved gain higher than 15 dBi. Finally, a time domain analysis of the antenna performed by means of the Finite Integration Technique and the SEM procedure showed that the antenna can also operate with UWB pulse signals.
HIGH-GAIN ULTRAWIDEBAND DIELECTRIC RESONATOR ANTENNAS FOR WIRELESS APPLICATIONS / Miozzi, Emanuela. - (2017 Feb 27).
HIGH-GAIN ULTRAWIDEBAND DIELECTRIC RESONATOR ANTENNAS FOR WIRELESS APPLICATIONS
MIOZZI, EMANUELA
27/02/2017
Abstract
The increasing demand for high data rate transmissions in wireless communications and low power consumption, has led to a growing scientific interest concerning wideband and ultrawideband antennas. Besides, the need to integrate more than one service in only one device has made wideband technology very attractive among the scientific community. To this purpose, several kind of techniques have been introduced in literature for increasing the operative bandwidth of well-known radiating structures such as microstrip patch antennas, monopole antennas, printed monopole/dipole antennas, etc. However, all these antenna configurations, which typically are made of metals and dielectric materials, are prone to low antenna radiation efficiencies. Indeed, high efficiency is essential in satellite applications where good link margins are required or in mm-wave communications where the power losses in the system components may be relevant. Besides, high-efficiency antennas are essential for providing a long-range coverage in WLAN access points and base stations, especially in indoor environments where circular polarization is employed to limit multipath effects. For these reasons, an extensive research activity concerning high-efficiency dielectric resonator antennas has been carried out during the past decades. The main goal of this research work, carried out during these three years of Ph.D. studies, is to introduce novel wideband high-efficiency and high-gain dielectric resonator antennas working in both linear and circular polarization and suitable for terrestrial and satellite communications. Besides, an extensive time-domain analysis of the proposed radiating structures, aimed to investigate their suitability to work with UWB pulse signals, has been also carried out. The thesis is organized in five chapters. In the first chapter, after a short description concerning several wireless communication standards and UWB systems, the state-of-art of some of the most important wideband and ultrawideband antennas proposed in literature, is briefly illustrated. A special emphasis is given to dielectric resonator antennas exhibiting broad impedance bandwidths, high gains, pattern stability and good circular polarization performances. In the second chapter, the Singularity Expansion Method (SEM) and the Matrix Pencil Method (MPM), aimed to the extraction of residues and poles of an antenna impulsive response, useful for a better comprehension of the resonating processes taking place into the considered radiating structures, and for computing the antenna time domain response to arbitrary excitation signals, are described. In the third chapter, the main features of the full-wave commercial software CST Microwave Studio™, based on the Finite Integration Technique (FIT), and employed for the analysis and design of the proposed dielectric resonator antennas, are briefly described. In the fourth chapter, a novel wideband multi-level multi-permittivity dielectric resonator antenna working in both linear and circular polarization is introduced. The radiating structure, equipped with a suitable metal reflector, exhibits a maximum gain of about 10 dBi, a high front-to back ratio and a broad impedance bandwidth (between 79% and 82%), resulting suitable for several wireless communications standards (e.g. WLAN and WiMAX) and C-band satellite applications. Besides, a time-domain analysis of the antenna based on FIT and SEM techniques, aimed to the investigation of its relative group delay and fidelity factor, has been also presented. In the fifth chapter, a wideband high-gain mushroom-shaped dielectric resonator antenna, equipped with a suitable metal reflector and a dielectric lens, has been proposed for wireless, C-band radar and UWB applications. Thanks to the dielectric lens the gain of the cylindrical dielectric resonator along the boresight direction is significantly enhanced, while the presence of the metal reflector strongly improve the antenna front-to-back ratio, making the antenna characteristics independent from those of the installation site. The antenna is fed with two/four probes, opportunely disposed around the DR, with the aim of exciting a circular/linear polarization. An antenna prototype was realized to verify the performances predicted by the numerical computations. Measured and numerical results show an antenna radiation efficiency higher than 90% along the antenna operative bandwidth, a fractional bandwidth of about 65% and a maximum achieved gain higher than 15 dBi. Finally, a time domain analysis of the antenna performed by means of the Finite Integration Technique and the SEM procedure showed that the antenna can also operate with UWB pulse signals.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
