Advanced Techniques for Microwave Systems

Preface The wide area of Microwave Systems is a rapidly-growing one, it is therefore rapidly becoming a very extended and complex sector of human scientific and technical knowledge. The idea to write a book on Advanced Microwave Systems has been therefore a very challenging one for me and the people who helped me in the effort for building the book itself. The first thing I thought was that we could treat only a few arguments with good deepness, therefore I reduced my attention to some advanced sectors of the subject. The Reader will find in this book four Parts: one devoted to transmission lines and periodic structures, the second one to filters, the third to the more and more important area of microsystems, the last one is devoted to antennas. The first Part on transmission lines and periodic structures begins with a Chapter on Electromagnetic Band-Gap (EBG) waveguide structures, that presents a rigorous semi-analytical approach for analyzing vertical full-height posts in a rectangular waveguide. When the posts are stacked along the waveguide, the reflection and transmission matrices are concatenated over the entire system using the recurrence relations. This leads to the generalized reflection and transmission matrices characterizing the frequency response of an EBG formed by an array of circular posts in the rectangular waveguide. Numerical examples for the frequency responses of a pair of two identical dielectric posts and their 9-stacked structure are presented for the excitation by the fundamental TE10 mode. In the second Chapter fractional transmission lines and waveguides are treated. Fractional curl operator is an intermediate step operator between the vector identity operator and the ordinary curl operator used in vector calculus. It yields solutions which are intermediate between the original solution of the Maxwell equations and the solution dual to the original one. Using fractional curl operator, the fractional dual transmission lines and fractional dual waveguides are discussed. Behaviors of field lines and impedances of the fractional dual guides are discussed. Then two-dimensional metallic periodic structures are studied. In this third Chapter, the rigorous mode-matching method incorporating Floquet-Bloch theory was employed to systematically investigate eigen-waves propagating in a two-dimensional periodic medium made up of a metallic cylinders array arranged in a square lattice. The dispersion characteristics and phase relation of the eigen-waves are demonstrated to explain the physical insight of wave process involved in 2D metallic periodic structures. Significantly, the extraordinary refraction occurring at the interface between the two-dimensional metallic periodic structures (or wired-based metamaterial) and a dielectric medium was confirmed by the Snell’s law and phase-relation diagram developed in this work. The following work is on three-dimensional EBG structures. In this fourth Chapter, a Fourier Modal Method (FMM) for accurate and efficient characterization of three-dimensional Electromagnetic Band-Gap materials is presented. The EBG has a finite thickness and it is considered as a superposition of doubly-periodic gratings, infinitely extending only in two dimensions. The potentiality of the approach in the analysis of electromagnetic crystals is discussed. Some applications are presented: an EBG with a complete 3D band-gap; a spatial, frequency and polarization filtering cavity; a woodpile superstrate to be employed for directivity-enhancing of planar antennas. The last contribution of the first Part (fifth Chapter) is devoted to three-dimensional gratings. A novel numerical method in the frequency domain is presented for analyzing three-dimensional gratings using a model of doubly-periodic magneto-dielectric layer. The method is based on the three-dimensional volume integral equations for the equivalent electric and magnetic polarization currents of the assumed periodic medium. The arbitrary profiles of three-dimensional dielectric or metallic gratings can be flexibly modeled by adjusting the material parameters and sizes or locations of the parallelepiped segments in the unit cell. The numerical examples for various grating geometries and their comparisons with those presented in the literature demonstrate the usefulness of the proposed method. The second Part of the book is completely devoted to RF waveguide filters. This Part, which may be a volume in itself, was built in extended form in order to write a very useful design path for the Engineer who needs to design and realize a key component as an RF filter. It is due to the wide experience of the filters group of a major European research center (ESA-ESTEC). The Chapter provides guidelines on the design process of RF waveguide bandpass filters. As an example, the design of a simple filter is used to illustrate the process in detail starting from the technical specifications to the measurement results. In particular, attention is given to the steps that are critical in the design process of filters used for space applications when the environmental and RF power constraints become design drivers. The steps in the process are described, and the necessary formulas and calculations are given using the data for the example filter. In the third Part the arguments treated belong to the area of materials and Microsystems. The aim of the first Chapter is to overview the technology, modeling and measurement techniques devoted to RF Micro-Electro-Mechanical Systems (MEMS) and related architectures based on micro-switches. In particular, the main aspects in optimizing the manufacturing yield are stressed, together with the modeling issues. Experimental results obtained for a binary distributed phase shifter based on RF MEMS coplanar shunt switches are also presented. The scope of the second Chapter is to outline the Compound Semiconductor (CS) Microwave Monolithic Integrated Circuit (MMIC) technology, by systematically reviewing state of the art devices, fabrication technologies, circuits design methods and their related performances, in view for their application in advanced microwave systems. For this purpose, the specific advantages and limitations of each technological approach, also compared to alternative solutions based on vacuum tubes or other solid state devices, is outlined. The third and fourth Chapters are dedicated to SiGe components, by stressing technologies and design techniques, respectively. The dynamism of modern life mandates support tools and electronic equipments, more and more powerful, handy and aligned with changing needs. The engine of this challenge is a wide set of technologies whose success is based on the optimum trade-off among performance, level of integration, and cost. While compound semiconductors are generally exploited for very high performance applications, their inherent high production cost and low compatibility with high integration levels for base-band functional blocks limit the adoption to niche markets. Recently, SiGe HBT technologies have demonstrated competitive performance with respect to compound semiconductors. Moreover, they entail much lower production costs and guarantee full compatibility with CMOS devices (BiCMOS processes). Therefore, SiGe technologies can be considered a powerful alternative to compound semiconductors. The fifth and conclusive Chapter of the third Part is on the use of diamond in electronic devices. Diamond is an astonishing material. Used mainly for jewelry, it is today studied for electronic devices to be operated in harsh environment or as the base material for high power, high frequency applications due to the unique electrical, physical, chemical and mechanical properties. Diamond can be classified as a wide band gap semiconductor, its suitability for performance in the microwave range is today demonstrated through an affordable deposition technology and rather simple device structures. The fourth and last Part is devoted to some advanced antenna systems. The first Chapter focuses on the general properties of planar periodic leaky-wave antennas, and presents an accurate and versatile method for analyzing this class of structures using the method of moments together with a mixed-potential form of the electric field integral equation. This type of antenna structure consists of a planar periodic metallization on a grounded substrate, and is thus low in profile and simple to fabricate. Depending on the frequency, radiation may occur in either the backward or the forward directions. In the second Chapter design strategies are reviewed and presented for harmonic-tuned active integrated antennas based on the use of microstrip patches and compact photonic bandgap filters. The synthesis of optimal values for the antenna input impedance at the fundamental, second, and third harmonic frequencies can be achieved by perturbing either the geometry of the antenna or the geometry of the filter. Numerical simulations of input impedance and radiation properties are provided on specific examples of antennas to validate the proposed approaches. The third Chapter describes frequency-scanning leaky-wave antennas based on stub-loaded ridge-rectangular waveguides. First of all, the modified mode-matching method is introduced to accurately analyze such a guide because it includes many conductor edges at which the fields diverge. Then leakage properties of the guide to design an antenna are given in the form of parametrical studies. Next, an example of a designed antenna is shown numerically and experimentally. Finally, the problems on the excitation by the coax feed, arraying the antenna and so on are discussed. The fourth Chapter is relevant to multibeam antennas. These radiators constitute a key enabling technique for advanced satellite communication missions. To match the ever growing demand in terms of link performances, frequency reuse and traffic reconfigurability, satellite multibeam antennas are of fundamental importance. Their increased available gain results in a reduction of the on-board required RF power and a simplification of the user terminal. Some recent developments in multi-beam antennas for broadband communications missions are presented here. In the fifth and last Chapter an overview of the issues involved in the design of phased array antennas for high data rate mobile-to-satellite communications is presented. Dielectric Resonator Antennas (DRAs) are here selected as radiators since they are suitable to be used in active integrated antennas. The tuning of the antenna input impedance at the fundamental frequency as well as at higher harmonics is a key point in the design process: therefore, flexible harmonic tuning techniques are devised and implemented. In this Volume the contributions of several Specialists working in Industries, Universities and Research Institutions, coming from America, Asia, and Europe is presented. Different approaches to the subject are present and theoretical, experimental, practical, and innovative realizations are, in turn, reported. The Reader can, in this way, have a quite complete idea of the different aspects of the subject. I would like to thank the Authors for their excellent contributions. Moreover, I would like to acknowledge Professor Kiyotoshi Yasumoto, of Kyushu University of Fukuoka, Japan, Professor Fabrizio Frezza, of Sapienza University of Rome, Italy, for their help and suggestions in preparing the scientific content, Dr. Lara Pajewski, of “Roma Tre” University of Rome, Italy, for her precious contribution for the Book cover, and Drs. Pandalai and Gayathri, of the Research Signpost, for their care in the general managing of the Book. Finally special thanks to my daughter Valentina, for her “bright and dark suns” contribution. Rome, Italy, December 2011 Giuseppe Schettini