| In the designing process of an FSS, certain features stand out as being desirable for most applications. First, a quality element must have a stable resonant frequency with the angle of incidence. Second, the FSS's bandwidth must be large enough to allow flat reflection or transmission characteristics. If an FSS is being used as reflector, its reflection coefficient curve must be flat within the bandwidth, and if it is being used as a bandpass, its transmission coefficient curve must be flat within the bandwidth. The present Dissertation discusses two new techniques for frequency stabilization and design of broadband elements. The shape of each FSS element plays a big role in its fundamental characteristics. Some FSS elements have poor resonant frequency stability and smaller bandwidth, others have good resonant frequency stability and larger bandwidth. The choice of a given element depends mostly on the specific application of the FSS.; One type of element that has a particularly poor resonant frequency stability is the center connected FSS elements. The present dissertation shows a new technique of frequency stabilization for two center connected elements: tripoles and cross dipoles. Conventional methods of frequency stabilization include increasing the supporting dielectric layer, decreasing inter-element spacing, and use of skewed arrays. This dissertation uses a varying surface impedance approach to achieve frequency stabilization for rectangular arrays.; In the present dissertation two new broadband FSS elements are created. Methods of creating broadband FSS's include multilayer Screens, dielectric loading, decreasing the inter-element spacing, and element shape. Here the shape of the FSS element is used to create the broadband FSS. The technique starts with the analysis of inset dual band fractal structures. The fractal structures are then modified to create a dual band FSS with their resonant frequencies close to each other, but not in the same reflection band. With the appropriate combination of elements, a new element with broadband characteristics is formed. Numerical and measured results are discussed. |
