Study On Radial Line Array And Miniature Element Antennas

With the vigorous development of the small synthetic aperture radars (SAR), the small satellite and the millimeter-wave systems, antenna has to meet all kinds of requirements. Not only the antenna gain and bandwidth criterions, but also the antenna cost, efficiency, size and weight are needed to be taken into account when we design an antenna. The radial line array antenna is a kind of antenna with high efficiency, compact structure, easy feeding, small size and low cost. Since the 90s of the 20th century, the radial line arrays have been developing rapidly and attracting extensive attentions. According to practical research subjects, this dissertation is mainly concerned with the fast analysis and design on radial line array, inexpensive radial line array with high efficiency and miniature element antennas design. The author's major contributions on this subject can be summarized as follows:1. Based on the principle of the method of moment (MoM) and the equivalent network modal for radial line slot array, the physical meanings of array elements during the solution procedure of problem are discussed, and an improved equivalent network analysis method is proposed by combining with the full-wave approach. In practice, the Ansoft HFSS full-wave software is used to create the extracting modals for different kinds of equivalent parameters, including the self-impedance of feeding probe, the self-admittance of slots, the mutual admittance of slots and the current transfer coefficients. Furthermore, the inaccuracy of the radiation function of the single slot is improved by calculating and curve fitting. Finally, a Matlab program is designed and written. Through an example, the obtained results show that the improvement of accuracy is evident and this method is capable of solving some complicated configurations.2. The printed substrate technique is introduced in the radial line slot antenna (RLSA) design to improve the fabrication tolerance, reduce the cost of production and increase the configuration flexibility. On the other hand, in order to eliminate the dielectric loss and further simplify the configuration, a non-dielectric-filled RLSA is proposed based on the investigations on the radiation patterns of the concentric annular array. A linearly-polarized RLSA then is designed for X-band Mini-SAR application, by using this new structure and the matching slot design, and two simple methods are proposed to decrease the reflection coefficient on the feeding port. Finally, an antenna prototype is fabricated. The good agreements between the simulated and measured results indicate that the proposed antenna design is correct and effective.3. For accelerating the solving process, the approach by analyzing the element antenna and feeding network independently is applied and an equivalent partial analysis modal is introduced based on the symmetry of feeding network structure. In addition, since the full consideration is given to the inner coupling between the probes, the accuracy of the computation can be guaranteed under given conditions. By using this analysis modal, power distribution is investigated on the probes lied in different circles and optimized uniform excitation is obtained. This designed network, combined with low-profile circularly polarized helix elements, realizes pencil-beam radiation. An antenna prototype is then fabricated. The simulated and measured results agree well which validates our design.4. Based on the in-deep study on the resonance and radiation characteristics of monopole and inverted-L antenna (ILA), a double-folded inverted-L antenna (DFILA) is proposed for the radial line array antenna elements design. Since the antenna operates on the third resonant mode and characterized by symmetry space current distribution, low profile and forward radiation are both achieved. Using this structure, linearly polarized (LP) and circularly polarized (CP) element antenna are designed and implemented. The concept of orthogonal impedance is introduced into the CP antenna design so that the antenna size is very small. In order to enhance mechanical intensity of this antenna, a structure using printed technique is then proposed. An integrated DFILA printed antenna for handheld RFID reader is designed and fabricated in combination with actual application. Finally, a method is proposed for size reduction and improvement of radiation of printed monopole by loading a pair of resonators. The simulated and measured results agree well which prove the validity of the design.