| With the emormous development of wireless communications, lots of technologies are emerging to make wireless devices with better performance. Generally, the performance of a wireless communication systen is dependent on antenna, transmitter power and spectrum, receiver sensitivity, and signal processing, etc. Antenna is one of the most important components, which can transmit and receive electromagnetic waves. The large communication capacity of antenna system is widely required to meet the stringent demand in morden communications. To solve data capacity problem, multiband/wideband antennas are the candidates to make antenna operate on multiple communication standards simultaneously. Besides, multiple-input multiple-output(MIMO) technology can employ multiple antennas at both the transmitter and receiver sides for multiple parallel independent signals. It can also improve the system communication capacity and quality in multipath fading environment without additional bandwidth and power. The analysis on antenna porlarization modes(especially linear circular polarization, circular polarization and polarization diversity) have been made. The different porlarization modes are applied to various communication systems. The author’s main contributions are outlined as follows:1. The practical background and introduction of multiband/wideband antennas and MIMO antenna system are focused on in the first part. Then the concept and classification of antenna polarization(especially linear polarization, circular polarization and polarization diversity) are also exhibited in detail, which are very valuable to the latter work in this paper.2. Based on the introductions above, multipile band multiple polarized antennas with small size have been proposed, whose impedance matching, radiation and polarization characteristics have also been studied and discussed. For multiple band multiple linear polarization, a novel compact UWB antenna design integrated with three extra controllable bands(GSM 1800/WCDMA/WLAN) is proposed. Good linear polarization is achieved in the multiple operations. The equivalent circuit model of the proposed antenna is carried out to comprehend the design mechanism. For multiple band multiple circular polarization, a dual-band circularly polarized(CP) antenna is presented based on the design of stacked-layer, corner-cut and complementary split ring resonator(CSRR). Besides, two ultra broadband monopole antennas with multiple CP radiation property are also presented in this paper. The axial ratio(AR) parameter has been analyzed in quantitative, which successfully describes the flexible CP property.3. Along with wideband wireless communication requirements, it is becoming important to improve the impedance and AR bandwidths of typical CP antennas greatly. Therefore, several broadband coplanar waveguide(CPW)-fed CP antennas have been proposed. Firstly, a printed S-shaped slot antenna fed by CPW is proposed for broadband CP radiation. The proposed antenna has broad impedance and AR bandwidths. The surface current analysis and a parametric study of the design are also carried out to explain the mechanism of wideband circular polarization. Secondly, a CPW-fed nesting-L slot CP antenna with enhanced bandwidth and radiation is proposed. By placing a reflector underneath the antenna, one can obtain unidirectional radiation patterns with greatly improved gains compared with single antenna. Thirdly, a compact ultra-broadband CP slot-linked antenna is proposed. The series feedline and linked-slot-structure have folded the surface current path on the antenna, therefore increasing the ratio of electric length to resonant wavelength, and realizing antenna miniaturization at the premises of not reducing impedance and AR bandwidths.4. Utilizing polarization diversity principle, dual-band MIMO antenna arrays for mobile terminal applications are proposed with high isolations. To improve the system isolation further, several other methods are also introduced in the mobile MIMO arrays. In this paper, two kinds of small-size dual-band MIMO antenna arrays consisting of six planar inverse-F antenna(PIFA) elements and eight PIFA elements are presented, respectively. The above two MIMO arrays have the limited overall MIMO sizes while maintaining excellent isolations in both the dual bands finally.5. For base station MIMO array, a design of sixteen-channel artificial magnetic conductor(AMC) loaded wideband array antennas is proposed for MIMO system. The MIMO system is constructed by sixteen dipole elements. Also applying polarization diversity between different elements, the MIMO antennas demonstrate good isolation performance within compact MIMO array volume. The equivalent circuit and operation principle of the presented AMC unit cell are analyzed in this paper. Periodical AMC surfaces are introduced underneath the dipole elements to achieve low profile, antenna miniaturization and impedance bandwidth enhancement.
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