Synthesis And Application Of Asymmetric Coplanar Waveguide And Microstrip Antenna

In resent years, broadband or dual-band wireless communication technologies are widely adopted due to the need of wireless communications. The improvement of the passive components and the emergence of the new devices promote the continuous development of wireless communication technology. Coplanar waveguide (CPW) is an important microwave transmission line. It offers several advantages over microstrip line, such as low radiation losses, high circuit density, and ease of making series and shunt connections. The emergence of CPW arouses a landmark revolution of monolithic microwave integrated circuits (MMIC) and related fields. As an extension of CPW, asymmetric coplanar waveguide (ACPW) has got more and more attention. The synthesis of ACPW is the basis of ACPW component research and design, which is very important.Antennas are the essential components of wireless communication systems. The performance of antenna has a significant effect on the performance of the whole system. Microstrip antennas are widely used due to the merits of small volume, light weight, low cost. The specifications of microstrip antennas for each wireless communication system are different, so it is necessary to design corresponding microstrip antennas.Under the supports of the National Natural Science Foundation of China, the Traffic Applied Basic Research Project of the Ministry of Transport of China, and the Fundamental Research Funds for the Central Universities, this dissertation is devoted to the researches on synthesis models for ACPW and single-feed truncated-corner circularly polarized microstrip antennas (CPMA), ACPW-based dual-band bandpass filters and broadband directional couplers, and novel microstrip antennas suitable for engineering application. Details are as follows:(1) The quasi-static analysis formulae for ACPWFDT (ACPW with finite dielectric thickness) and ACPWCBSO (ACPW with conductor backing and substrate overlaying) are deduced with the conformal mapping theory (CMT). Using the CMT analysis data sets and artificial neural networks (ANNs), synthesis models for ACPWFDT and ACPWCBSO are constructed. The synthesis models are validated by the comparison with the CMT analysis, electromagnetic simulation, and measurement. To improve the calculation accuracy of synthesis models for ACPWCBSO, a novel hybrid algorithm combining genetic algorithm (GA) and Levenberg-Marquardt (LM) algorithm (hybrid GA-LM algorithm) is proposed. Using the hybrid GA-LM algorithm to train the synthesis models, the maximal relative error is less than 8.1%, which is smaller compared with that using the existing algorithms (greater than 15%).(2) Dual-band bandpass filters with asymmetric stepped-impedance ACPW resonators are proposed. Compared to traditional stepped-impedance dual-band bandpass filters, the proposed filters have two additional transmission zeros near the first passband, which improves frequency selectivity of the filter. Furthermore, an open-circuit resonator embedded into CPW is proposed and inserted into the input/output port of filter to achieve one or two independent controllable transmission zeros as a result of significantly improving the performance of the filter.(3) The conditions of the realization of a parallel coupled line directional coupler with ideal match and isolation are deduced. To meet the condition, a capacitive phase velocities compensation technique based on ACPW is proposed. Using the technique, a broadside-coupled CPW directional coupler is designed. The bandwidth (isolation more than 20 dB) of the designed coupler is improved from 25% to 61.8%. To further enhance the isolation of the coupler, an improved scheme combining defected ground structure (DGS) and ACPW compensation technique is proposed. Using the improved scheme, the bandwidth (isolation more than 20 dB) is enhanced to be 81.1% with a best isolation of 57.2 dB.(4) Two ANN-based synthesis models for microstrip antenna are proposed, one is applied to the traditional single-feed truncated-corner CPMA, and another is used to the tunable single-feed corner-truncated CPMA. Two key design parameters of the corner-truncated patch can be directly obtained with the proposed synthesis models, which significantly improve the antenna design efficiency. The models are validated by the comparison with electromagnetic simulation and measurement.(5) A broadband linearly-polarized microstrip antenna with low cross-polarization and low voltage standing wave ratio (VSWR) is proposed. By means of the stacked patch configuration and two-dimensional meander strip feed technique, the VSWR<1.2 bandwidth of the microstrip antenna is enhanced to be 22% from 804 to 1002 MHz. Furthermore, the antenna has a cross-polarization level of less than -20 dB in both E-and H-planes. In addition, a parametric study and a design guideline of the proposed antenna are presented.(6) A horizontally meandered strip (HMS) feed technique is proposed to achieve good impedance match and symmetrical broadside radiation patterns. Based on the feed technique, two single-feed broadband circularly polarized (CP) stacked microstrip antennas are designed for ultrahigh frequency (UHF) radio frequency identification (RFID) applications. The 3-dB axial ratio (AR) bandwidths of the proposed antennas are 10.8% (838-934 MHz) and 13.5%(838-959 MHz). In CP operation bandwidths, the VSWR is less than 1.5, and antenna gain is larger than 8.5 dBi, which meet engineering applications.(7) A novel 2×2 sequentially rotated microstrip antenna array with unequal input impedance elements and a conductor-backed ACPW series-feed network is proposed. The corner truncated patch element is fed by a three-dimensional meander strip, which can easily control the input impedance and has slight effects on the radiation performance. Compared to micro strip-line feed networks, the radiation loss of the proposed feed network is lower. The measured results show that the proposed antenna array has an impedance bandwidth (VSWR<1.5) of about 40.5%, a 3-dB AR bandwidth of about 25.6%, and a gain-level larger than 11.6 dBi across the broadband global area network (BGAN) operating bands. Therefore, the proposed antenna array can be a good candidate for Inmarsat BGAN portable terminal applications.