| With the advancing of the industry plans on Compass Navigation Satellite System (CNSS) and Internet of Things (IOT), the relevant electronic systems have put out higher requirement of the antenna. However, present technologies of the bandwidth enhancement, dual-band, and array for circularly polarised (CP) directional microstrip antennas are difficult to meet these requirements. In the dissertation, these technologies are researched for CNSS and RFID applications. First of all, the configuration and design methodology of a novel90degree phase shifter using the weak coupled-line loaded with stub is proposed. Then, based on the wideband power distribution and phase shift feed network, the compact wideband CP directional microstrip antennas with multiple-feed structure and the dual-band CP directional RFID reader antennas are proposed and implemented. At last, an asymmetric coupled-line power divider and an uneven rotated feed network are employed for the design of a CP directional microstrip antenna array. The detailed contents and innovational work are summarized as followings:1. A novel90degree phase shifter using a weak coupled-line loaded with stub is proposed.The wideband90degree phase shifter is the key component in microwave area, and a high-performance multi-feed CP antenna requires the designs achieving wider band, simple design, good portability, easy implement, low-cost, convenient installation, and so on. The technology of current phase shifter is unable to fulfill these tasks simultaneously. In the dissertation, three types of novel90degree phase shifters using a weak coupled-line separately loaded with a stub, a stepped impedance resonator, and a radial stub are proposed. The circuit theory is analyzed by the even-and odd-mode equivalent circuit method and the design methodology is presented. The single-layer microstrip phase shifters are simulated, fabricated, and measured. Result shows that the proposed phase shifters are competent for the design of CP antennas, and achieve the bandwidths of70.8%,105%, and118%, respectively. This section provides support for the research of the wideband and dual-band CP directional microstrip antennas.2. The wideband CP directional microstrip antennas are investigated for the dual-mode CNSS terminal applications.The dual-mode CNSS terminal with the functions of GPS compatibility and interoperability requires the antenna support the frequency range from1.227to2.492 GHz. In other words, the fractional bandwidth must larger than68%. Moreover, the antenna should possess the advantages of compact size and light-weight for portable terminals. In the dissertation, multi-feed networks based on the wideband90degree phase shifter and power divider are designed, and the feed structure of rotated quadruple semi-fan-annulus patches is proposed. Then, compact wideband CP directional microstrip antennas employ the dual-feed network and the quad-feed network are proposed and investigated, respectively. At last, the antennas are simulated, implemented, and measured for verification. Result shows that the proposed antenna achieves the CP bandwidth of72%and makes a break-through on the research of bandwidth enhancement. The design is about one-fourth the size of the smallest existing antenna. It is a good candidate for the dual-mode CNSS terminal applications.3. The dual-band CP directional microstrip antennas are researched for dual-band RFID reader applications.In order to improve competitiveness of the dual-band readers, the dual-band CP antenna is a good choice because of its ability to achieve low-cost, small-size and light-weight. The existing dual-band CP directional antennas are hard to realize the dual-band operation with larger frequency ratio of2.45/0.92GHz. Therefore, only few of studies have been done, and the existing structures have disadvantages for practical applications. In the dissertation, the novel design of0.92/2.45GHz dual-band CP directional RFID reader antennas are proposed by using the wideband feed network with dual-band radiation structures. The antennas have single port and same CP direction at two bands, and this configuration is beneficial to cost reduction and design of the monomer dual-band front end. The proposed antennas are verified by simulation and experimentation, and it achieves acceptable bandwidth, gain, axial ratio, and radiation pattern at two bands.4. The CP microstrip antenna array using an asymmetric coupled-line power divider and an uneven rotated feed network is proposed.In order to ensuring the high accuracy identification with less interference to adjacent and rear domains, the CP microstrip antenna array must not only exhibits higher gain but also features lower sidelobe level and larger front-to-back ratio. In the dissertation, a rotated CP directional16-element microstrip antenna array at2.45GHz is proposed by using an asymmetric coupled-line power divider and an uneven rotated feed network. The design method and performance improvement are proved by comparing it with the array antenna, which is based on a T-shape power divider and an even rotated feed network. Comparison shows that the CP bandwidth increases from8.2%to11.9%, the enhancement of the return loss larger than6dB, and the reduction of the axial ratio greater than0.9dB in the band. Moreover, the performances of sidelobe level and front-to-back ratio are improved effectively. |
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