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The optic concept of holography can been extended to the microwave frequencies offering new potential for antenna applications. The attention to these applications has been renewed by the possibility to realize modulated surface impedances on the basis of artificial magnetic surfaces, as suggested by Sievenpiper (D. Sievenpiper et al.). The holographic surface (M. ElSherbiny et al., 2004) that provides a given direction of the maximum radiated power density, can be obtained by interference of the incident wave from a feeder and a plane wave coming from the direction of maximum radiation. The range of operation of holographic antennas is such as the incident wave is dominated by a surface wave (SW) contribution. The same phenomenon can be also seen as local angular transformation from a SW in a leaky wave (LW) (M. Nannetti et al., 2007). This paper has the objective to give guideline for the design of a particular class of holographic antennas based on an curvilinear strips printed on a grounded slab.

This paper analyses the problem of the radiation from a structure composed by a curvilinear strip grating printed on a grounded dielectric slab and excited by a cylindrical surface wave. Such a structure is interesting for millimeter wave antenna applications. Some examples are shown to validate the design oriented formulation provided here.

This paper shows that a holographic pattern arising from the interference between a plane wave and a cylindrical surface wave is the same as that obtained by locally applying the dispersion condition in the small perturbation regime to a locally tangent periodic strip grating. This result seems not to add more to the holographic process to design actual antennas; however, other equations suggests a more general guidline to the design of such antennas when the perturbation regime is no longer valid, or for different excitations. Some prototypes of elliptical strip grating antennas have been designed, realized and successfully measured. This additional results are presented during the oral session.

A numerical moment-method for treating the dipole-FSS loaded hard rectangular waveguide has been presented. The results obtained from it agree with CST simulations. An unusual upper modal cutoff-frequency, not present in the conventional bare-slab loaded waveguide, was found in the dipole-loaded one. Modes of such waveguides thus possess band-pass properties. If appropriately designed, a stopband is possible. This suggests that when these waveguides are used as the lower frequency elements of a multi-band interlaced array, the operation of the higher frequency elements within the stopband allows the two functions to be performed simultaneously without interference. Measurements on a manufactured dipole-loaded waveguide were also made. The experimentally-obtained dispersion diagrams concur well with CST simulations and with a third independent approach based on network theory (Maci, S. et al., IEEE Trans. Antennas Propag., vol.53, no.1, 2005).

In recent years, a great interest has been devoted to the study of the dispersion properties of planar structures realized by frequency selective surfaces (FSS) on grounded dielectric slab. In this paper, the method is generalized in order to deal with a wide class of FSS-based artificial surfaces. A new derivation of the FSS admittance matrix is proposed and some general properties of this kind of structures are pointed out

The generalization of the method presented in Maci et al. allows an efficient dispersion analysis for printed periodic FSS-type surfaces. The method, which has been tested here for a dipole-FSS backed by a ground plane, consists of a pre-processing performed on the broadband reflection-coefficient data obtained from a full-wave analysis. After that, the FSS is characterized via its resonances for a few values of the incident angles. This determines in a straightforward way poles and zeros of an equivalent impedance, simply synthesized by an L-C dispersive circuit. Due to the weak dispersion features of poles and zeros, the L-C circuit can be identified in a simple analytical form which, after analytical continuation, is applied to formulate the transverse resonance equation. The process is much simpler and faster than a full-wave solution for dispersion, while being sufficiently general.

The physico-chemical stability of SiC/SiC fiber ceramic composite (SiC/SiC/sub f/) in contact with Li/sub 2/O in fusion-relevant conditions has been experimentally studied at 800/spl deg/C in flowing helium (0.1 L/min) containing either 0.1% H/sub 2/ or 100 ppm H/sub 2/O and for exposure times of up to 4032 h. The exposed SiC/SiC specimens have been characterized. The results obtained demonstrate that although the surface coating of the specimens is strongly attacked through chemical corrosion processes, the main physico-chemical characteristics of SiC/SiCf are affected to a limited extent only in the case of He+0.1% H/sub 2/ flowing gas, the bulk material not being attacked.