Ž . A comparison with the case of a dielectric nondispersive  cluster 8 when the shift of the value of the plasma cluster velocity corresponding to the maximum reflectivity of the electromagnetic wave in the waveguide  is lacking shows 1 that the shift of the reflectivity maximum to smaller values of the cluster velocity is due to the existence of a double- dispersion mechanism: a plasma dispersion and a waveguide dispersion. ACKNOWLEDGMENTS The authors would like to thank Prof. V. A. Buts for useful and stimulating discussions, and Prof. A. I. Nosich for editing the manuscript. Financial support by the Science and Tech- nology Center in the Ukraine is gratefully acknowledged. REFERENCES 1. K. Landecker, ‘‘Possibility of Frequency Multiplication and Wave Amplification by Means of Some Relativistic Effects,’’ Phys. Re  ., Vol. 86, No. 6, 1952, pp. 852855. 2. M. A. Lampert, ‘‘Reflection of Electromagnetic Waves by Cerenkov Electron Gas,’’ Phys. 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Application ( ) aux Couches Minces,’’ Ann. Phys. France , Vol. 5, No. 1112, 1950. 15. M. Born and E. Wolf, Principles of Optics, Pergamon Press, Oxford, 1964.  1998 John Wiley & Sons, Inc. CCC 0895-247798 CYLINDRICAL DIELECTRIC RESONATOR ANTENNA FOR MATERIAL CHARACTERIZATION S. Fargeot, 1 A. Vergonjanne, 2 M. Aubourg, 1 and P. Guillon 1 1 I.R.C.O.M  U.M.R  CNRS 87000 Limoges, France 2 ENSIL Ester Technopole 87000 Limoges, France Recei  ed 23 September 1997 ABSTRACT: The radiation characteristics of a cylindrical dielectric resonator antenna on the top of a ground plane are in estigated both theoretically and experimentally. A finite-element method with absorbing boundary conditions is used to describe the system. A material character- ization method is described using these radiation characteristics.  1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 273275, 1998. Key words: cylindrical dielectric resonator antenna; radiation pattern; finite-element method; material characterization method I. INTRODUCTION The actual expansion of telecommunication implies knowl- edge of the electromagnetic characteristics of a propagation medium in order to use communication simulation tools. For example, recent developments in radio communication need the characteristic materials around the emission and recep- tion stations to improve the electromagnetic propagation analysis. In this paper, a nondestructive material characterization method is presented. This method is based on the use of a Ž . cylindrical dielectric resonator antenna CDRA operating on its fundamental HEM mode. It permits a material charac- 11 terization in situ around 3.6 GHz. A dielectric resonator placed on the top of a ground plane in an open environment offers attractive features for antenna applications. These include small size, no ohmic losses, and different radiation characteristics depending on the operating mode. Most publications use approximative methods to predict resonant frequency and quality factors like the perfect mag-  netic wall method 1 or by replacing the DRA by a polariza-  tion electric current source 2 . In this paper, a rigorous theoretical analysis of a CDRA operating on the HEM fundamental mode is presented 11 and compared with experimental results. In the second part, the material characterization method is presented. The main advantage of this method is the small dimen- Ž sions of the system used at this frequency CDRA diameter: . 12 mm versus 6 mm height . Around 3 GHz, most of the available characterization methods require the use of systems of great dimensions; for example, the free-space method requires horn antennas of important dimensions and a sam- ple of 300  300 mm to focalize the field. II. THEORETICAL AND EXPERIMENTAL ANALYSIS OF THE STRUCTURE A rigorous analysis method is used to describe all of the electromagnetic phenomena: the finite-element method Ž . FEM in three dimensions. The open environment is simu- Ž . lated by absorbing boundary conditions ABCs developed by   Enquyst and Majda 4 introduced in the FEM 5 . MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 17, No. 4, March 1998 273