| With fast development and wide applications of wireless communication, the communication equipments and their electronic devices are required to be compact and to achieve multifunctional operations. As a transmitting and receiving part, antenna plays vital role in communication systems and it is always the principal obstacle to the miniaturization of the communication system. Consequently, the design of compact antennas which is compatible to modern information communication , with good performance, broadband, high efficiency, simplicity in fixing and multifunctional operations, is becoming one of the most advanced subjects in the field.Microstrip antennas (MSA) have been widely used in many moden applications such as radar, satellite communications, mobile communications and other communication systems due to their intrinsic advantages as conformability, light weight, simplicity in design and being easily integrated in circuits. However, some shortcomings of MSA such as high quality factor, low gain, narrow bandwidth, etc, make them unfit for many practical applications. In this dissertation, some researches on miniaturization and broadband techniques of MSA and printed antennas have been done based on the investigation existing technologies. By exploiting the antenna diversity scheme, advantage of millimeter-wave communication, electromagnetic bandgap (EBG) structure application in reduction of radar cross section (RCS) and technique of reconfigurable antenna, the miniaturization, broadband and circular polarization antennas which are compatible to modern information communicating are fabricated. The thesis mainly consists of following parts:1. The theories of the finite integration methods (FIM), finite difference time domain method (FDTD), method of moments (MOM) and particle swarm optimization (PSO) and their applications in antenna designs are introduced briefly.The method of the PSO combination of CST Microwave Studio is presented emphatically in antenna design.2. To abtain performance of miniaturization, multi-band, good efficiency and zero blind spot for WLAN applications, in this paper, by exploiting the antenna diversity scheme controlled by switches supported by current wireless LAN (WLAN) chip sets, the systems of spiral patch, planar inverted–F antenna (PIFA) are designed. These antenna systems are capable of multi-band operation at about 2.45GHz 5.25GHz and 5.8GHz bands. During modeling of these antenna systems, by exploiting the chipset internal switching diversity scheme, the antenna elements are fabricated perpendicularly on one substrate board to obtain diversity or conversion of polarization. In addition, these antenna systems not only meet the requirement for triple-band but also well abtain performance of miniaturization.3. In order to design broadband millimeter-wave antenna and to achieve antenna with high gains and circular polarization required in millimeter-wave communications system, in this paper, spiral patch, E-shape patch and elliptical ring patch operating at millimeter broadbands are proposed. During the design of the antennas, PSO is used to pick up and to optimize the parameters of antennas from CST Microwave Studio. In addition, the techniques of diagonal feeding of square patch, air gap and slots are introduced to design a millimeter-wave array antenna with high gains and circular polarization, which is also optimized by the PSO combination of CST Microwave Studio. The modeling of this antenna, with simplicity in designing and feeding,4. To meet the demand of electromagnetic stealth in airborne vehicles, in this paper, performance of the surrounding periodic 2nd-uniplanar compact electromagnetic bandgap (2nd-UC-EBG) ground plane and its application in the RCS reduction of MSA which operating at X band has been studied. According to the unique feature of the band gap of EBG structure, using the surrounding periodic 2nd-UC-EBG ground to replace the solid ground can effectively reduce the RCS of MSA outside operating band while having little RCS rising inside the operating band during 2-18GHz. In addition, its gain, bandwidth and back lobes control of radiation patterns are all improved..5. To achieve the performance of broadband and polarization diversity for millimeter-wave wireless communication, the technique of reconfigurable antenna and its application for miniaturization of antennas are discussed. By exploiting techniques of air gap, vertical slots and diagonal feeding of square patch, a broadband and circularly polarized reconfigurable antenna with characteristic of micro-electromechanical system (MEMS) switches is presented. This polarization diversity antenna can work in left hand circular polarization (LHCP) or in right hand circular polarization (RHCP) mode by changing the states of MEMS switches.
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