Research On Key Techniques Of Active Frequency Selective Surfaces

Compared to traditional frequency selective surfaces (FSS), the greatest feature of activefrequency selective surfaces (Active FSS) is their ability to change their electromagneticcharacteristics so as to adapt to changes in the external environment. This thesis focuses on therealization of active frequency selective surfaces, the design of the feeder line system, and wirelesspower transmission techniques for active frequency selective surfaces.(1) Firstly, three kinds of realization for Active FSS are summarized and designed andtransmission coefficients are achieved. The working principle of each one is analysed by theequivalent circuit method and the field distribution of the FSS. The pros and cons of the three kinds ofrealization are also proposed.(2) Secondly, the influence of additional feeder line system on transmission characteristics isanalysed. Then, the aperture FSS is taken as an example. Based on the resonance principle of FSS, away of coplanar feeder line system for a single direction of polarization is presented. The adverseimpact of coplanar feeder line system on the electromagnetic characteristics of FSS is avoided.(3) Further more, a novel active FSS based on complementary structures is proposed. Thestructure is made up of square loop apertures and crossed dipoles on either side of a thin substrate.Several PIN diodes are loaded between crossed dipoles to provide different transmission states in thelow frequency band. The crossed dipoles are also used as feeding lines in the design to reduce theinfluence of additional feeder line system on transmission characteristics. Then, the coplanar feederline system proposed previously is applied in this active FSS. A double side tunableness FSS isachieved. The FSS can be switched between multiple passbands or fullband-off state. The flexibilityof FSS used in the antenna stealth applications is effectively improved.(4) Finally, a new kind of active FSS based on wireless power transmission is proposed. Thisactive FSS consists of FSS structure and its control circuit. The control circuit is supplied by theinduced voltage generated by the electromagnetic waves incident upon the FSS. The state of the PINdiodes is controlled by the circuit to provide different transmission states. The problem of theuselessness of the FSS radomes for electromagnetic waves in the working band is sloved.