Y.T. Lo

Bio: Y.T. Lo is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Microstrip antenna & Patch antenna. The author has an hindex of 22, co-authored 36 publications receiving 3712 citations.

Theory and experiment on microstrip antennas

Abstract: A simple theory based on the cavity model is developed to analyze microstrip antennas. Formulas for numerous canonical shapes are given. In general the theoretically predicted radiation patterns and impedance loci closely agree with those measured for many antennas of various shapes and dimensions investigated thus far. In fact, this theory enables the computation of both patterns and impedance loci with little effort. The input admittance locus generally follows a circle of nearly constant conductance, but its center is shifted to the inductive region in the Smith chart plot. Peculiar properties for the case with degenerate or slightly degenerate eigenvalues are discussed. An accurate formula for determining the resonant frequency of a rectangular microstrip antenna is also given.

An improved theory for microstrip antennas and applications

Abstract: An improvement to a recently reported theory for the analysis of the pattern and impedance loci of microstrip antennas is developed. It yields a theory which is simple and inexpensive to apply. The fields in the interior of the antennas are characterized in terms of a discrete set of modes. The poles corresponding to these modes are complex and depend on the losses in the antenna. The representation of the fields in terms of these modes is rigorous only for a bona fide cavity with no copper loss. The proper shift in the complex poles due to the addition of copper and radiative losses is approximated by lumping the latter two together with the dielectric loss to form an effective loss tangent. By so doing, it is found that the resulting expressions for impedance of the microstrip antenna are in good agreement with measured results for all modes and feed locations. The theory is applied to the evaluation of impedance variation with feed location, to multiport analysis, and to the design of circularly polarized microstrip antennas.

An Improved Theory for Microstrip Antennas and Applications. Part I.

Abstract: : An improvement to a recently reported theory for the analysis of the pattern and impedance loci of microstrip antennas is developed. It yields a theory which is simple and inexpensive to apply. The fields in the interior of the antennnas are characterized in terms of a discrete set of modes. The poles corresponding to these modes are complex and depend on the losses in the antenna. The representation of the fields in terms of these modes in rigorous only for a bona fide cavity with no copper loss. The proper shift in the complex poles due to the addition of copper and radiative losses is approximated by lumping the latter two together with the dielectric loss to form an effective loss tangent. By so doing, it is found that the resulting expressions for impedance of the microstrip antenna is in good agreement with measured results for all modes and feed locations. The theory is applied to the evaluation of impedance variation with feed location, multiport analysis, and to design of circularly polarized microstrip antennas. (Author)

A mathematical theory of antenna arrays with randomly spaced elements

Abstract: Various probabilistic properties of a large antenna array with randomly spaced elements have been studied. It is found that for almost all cases of practical interest the required number of elements is closely related to the desired sidelobe level and is almost independent of the aperture dimension, the resolution (or the beamwidth) depends mainly on the aperture dimension, and the directive gain is proportional to the number of elements used if the average spacing is large. As a consequence the number of elements required is considerably less than that with uniform spacings. Starting with a given number of elements and a given aperture size, it is possible to improve the resolution by a factor of ten, a hundred, or more by spreading these elements over a larger aperture with little risk in obtaining a much higher sidelobe level and a lower directive gain. In fact, this method offers a solution which is optimum in a certain statistical sense, i.e., all sidelobes are of equal level with equal probability. In addition, this analysis also gives a simple estimate of the sidelobe level of most nonuniformly spaced antenna arrays. In a number of such arrays studied by various investigators with high speed computers, the agreement found is remarkable.

Multiple scattering of EM waves by spheres part I--Multipole expansion and ray-optical solutions

Abstract: Solution to the multiple scattering of electromagnetic (EM) waves by two arbitrary spheres has been pursued first by the multipole expansion method. Previous attempts at numerical solution have been thwarted by the complexity of the translational addition theorem. A new recursion relation is derived which reduces the computation effort by several orders of magnitude so that a quantitative analysis for spheres as large as 10\lambda in radius at a spacing as small as two spheres in contact becomes feasible. Simplification and approximation for various cases are also given. With the availability of exact solution, the usefulness of various approximate solutions can be determined quantitatively. For high frequencies, the ray-optical solution is given for two conducting spheres. In addition to the geometric and creeping wave rays pertaining to each sphere alone, there are rays that undergo multiple reflections, multiple creeps, and combinations of both, called the hybrid rays. Numerical results show that the ray-optical solution can be accurate for spheres as small as \lambda/4 in radius is some cases. Despite some shortcomings, this approach provides much physical insight into the multiple scattering phenomena.

Tabu Search

Abstract: From the Publisher: This book explores the meta-heuristics approach called tabu search, which is dramatically changing our ability to solve a hostof problems that stretch over the realms of resource planning,telecommunications, VLSI design, financial analysis, scheduling, spaceplanning, energy distribution, molecular engineering, logistics,pattern classification, flexible manufacturing, waste management,mineral exploration, biomedical analysis, environmental conservationand scores of other problems. The major ideas of tabu search arepresented with examples that show their relevance to multipleapplications. Numerous illustrations and diagrams are used to clarifyprinciples that deserve emphasis, and that have not always been wellunderstood or applied. The book's goal is to provide ''hands-on' knowledge and insight alike, rather than to focus exclusively eitheron computational recipes or on abstract themes. This book is designedto be useful and accessible to researchers and practitioners inmanagement science, industrial engineering, economics, and computerscience. It can appropriately be used as a textbook in a masterscourse or in a doctoral seminar. Because of its emphasis on presentingideas through illustrations and diagrams, and on identifyingassociated practical applications, it can also be used as asupplementary text in upper division undergraduate courses. Finally, there are many more applications of tabu search than canpossibly be covered in a single book, and new ones are emerging everyday. The book's goal is to provide a grounding in the essential ideasof tabu search that will allow readers to create successfulapplications of their own. Along with the essentialideas,understanding of advanced issues is provided, enabling researchers togo beyond today's developments and create the methods of tomorrow.

Beamforming: a versatile approach to spatial filtering

Abstract: An overview of beamforming from a signal-processing perspective is provided, with an emphasis on recent research. Data-independent, statistically optimum, adaptive, and partially adaptive beamforming are discussed. Basic notation, terminology, and concepts are included. Several beamformer implementations are briefly described. >

Phased Array Antenna Handbook

Abstract: Phased Arrays in Radar and Communication Systems. Pattern Characteristics and Synthesis of Linear and Planar Arrays. Patterns of Nonplanar Arrays. Elements, Transmission Lines, and Feed Architectures for Phased Arrays. Summary of Element Pattern and Mutual Impedance Effects. Array Error Effects. Special Array Feeds for Limited Field of View and Wideband Arrays.

Theory of Reflectance and Emittance Spectroscopy

Abstract: Acknowledgements 1. Introduction 2. Electromagnetic wave propagation 3. The absorption of light 4. Specular reflection 5. Single particle scattering: perfect spheres 6. Single particle scattering: irregular particles 7. Propagation in a nonuniform medium: the equation of radiative transfer 8. The bidirectional reflectance of a semi-infinite medium 9. The opposition effect 10. A miscellany of bidirectional reflectances and related quantities 11. Integrated reflectances and planetary photometry 12. Photometric effects of large scale roughness 13. Polarization 14. Reflectance spectroscopy 15. Thermal emission and emittance spectroscopy 16. Simultaneous transport of energy by radiation and conduction Appendix A. A brief review of vector calculus Appendix B. Functions of a complex variable Appendix C. The wave equation in spherical coordinates Appendix D. Fraunhoffer diffraction by a circular hole Appendix E. Table of symbols Bibliography Index.

Compact and Broadband Microstrip Antennas

Abstract: Preface. 1. Introduction and Overview. 1.1 Introduction. 1.2 Compact Microstrip Antennas. 1.3 Compact Broadband Microstrip Antennas. 1.4 Compact Dual-Frequency Microstrip Antennas. 1.5 Compact Dual-Polarized Microstrip Antennas. 1.6 Compact Circularly Polarized Microstrip Antennas. 1.7 Compact Microstrip Antennas with Enhanced Gain. 1.8 Broadband Microstrip Antennas. 1.9 Broadband Dual-Frequency and Dual-Polarized Microstrip Antennas. 1.10 Broadband and Dual-Band Circularly Polarized Microstrip Antennas. 2. Compact Microstrip Antennas. 2.1 Introduction. 2.2 Use of a Shorted Patch with a Thin Dielectric Substrate. 2.3 Use of a Meandered Patch. 2.4 Use of a Meandered Ground Plane. 2.5 Use of a Planar Inverted-L Patch. 2.6 Use of an Inverted U-Shaped or Folded Patch. 3. Compact Broadband Microstrip Antennas. 3.1 Introduction. 3.2 Use of a Shorted Patch with a Thick Air Substrate. 3.3 Use of Stacked Shorted Patches. 3.4 Use of Chip-Resistor and Chip-Capacitor Loading Technique. 3.5 Use of a Slot-Loading Technique. 3.6 Use of a Slotted Ground Plane. 4. Compact Dual-Frequency and Dual-Polarized Microstrip Antennas. 4.1 Introduction. 4.2 Some Recent Advances in Regular-Size Dual-Frequency Designs. 4.3 Compact Dual-Frequency Operation with Same Polarization Planes. 4.4 Compact Dual-Frequency Operation. 4.5 Dual-Band or Triple-Band PIFA. 4.6 Compact Dual-Polarized Designs. 5. Compact Circularly Polarized Microstrip Antennas. 5.1 Introduction. 5.2 Designs with a Cross-Slot of Unequal Arm Lengths. 5.3 Designs with a Y-Shaped Slot of Unequal Arm Lengths. 5.4 Designs with Slits. 5.5 Designs with Spur Lines. 5.6 Designs with Truncated Corners. 5.7 Designs with Peripheral Cuts. 5.8 Designs with a Tuning Stub. 5.9 Designs with a Bent Tuning Stub. 5.10 Compact CP Designs with an Inset Microstrip-Line Feed. 6. Compact Microstrip Antennas with Enhanced Gain. 6.1 Introduction. 6.2 Compact Microstrip Antennas with High-Permittivity Superstrate. 6.3 Compact Microstrip Antennas with Active Circuitry. 7. Broadband Microstrip Antennas. 7.1 Introduction. 7.2 Use of Additional Microstrip Resonators. 7.3 Microstrip Antennas with an Air Substrate. 7.4 Broadband Slot-Loaded Microstrip Antennas. 7.5 Broadband Microstrip Antennas with an Integrated Reactive Loading. 7.6 Broadband Microstrip Antennas with Reduced Cross-Polarization Radiation. 8. Broadband Dual-Frequency and Dual-Polarized Microstrip Antennas. 8.1 Introduction. 8.2 Broadband Dual-Frequency Microstrip Antennas. 8.3 Broadband Dual-Polarized Microstrip Antennas. 9. Broadband and Dual-Band Circularly Polarized Microstrip Antennas. 9.1 Introduction. 9.2 Broadband Single-Feed Circularly Polarized Microstrip Antennas. 9.3 Broadband Two-Feed Circularly Polarized Microstrip Antennas. 9.4 Broadband Four-Feed Circularly Polarized Microstrip Antennas. 9.5 Dual-Band Circularly Polarized Microstrip Antennas. Index.