Guest Editorial Special Issue On Wireless Communications - Antennas ...

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 46, NO. 6, JUNE 1998

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Guest Editorial Special Issue on Wireless Communications

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HIS issue is devoted to the topic of wireless communications. The importance of this topic is widely appreciated by the technical community as well as by the general population. The public’s demand for ubiquitous personal and mobile communications is responsible for an explosive growth in terrestrial and satellite wireless communications that will continue well into the next millennium. We are now getting closer and closer to one of the most inspiring dreams of mankind, namely, “to create global connectivity anywhere, anytime, and with anyone.” Fig. 1 depicts an artist’s rendition of this global connectivity. One of the current key challenges in wireless communications is the application of reduced size antennas with improved performance and lower cost. Small antennas are required because of the demand for shirt pocket personal radios as well as unobtrusive base stations. In addition, the consumer’s desire for personal communications within buildings increases the challenges in the fields of antennas and propagation. The upcoming direct user-to-satellite communications systems have further necessitated the development of novel antenna designs for acceptable circular polarization performance in the presence of the user’s head. The frequency spectrum is a finite resource that can be extended through frequency reuse, which is strongly influenced by antenna and propagation issues. In fact, overall system performance, as measured by coverage and capacity, is determined by antennas and propagation. Diversity techniques at both the base station and terminal can be exploited for performance improvement. Diversity involves antennas and is intended to overcome propagation impairments. All of the forgoing have tremendous cost implications. For example, frequency reuse by increasing the number of base stations and reducing individual base-station coverage is extremely expensive and should be minimized. Antennas and propagation play the central role in the deployment of wireless communication systems. This special issue addresses most of the associated critical topics. There was tremendous response to our call for papers. Because submissions were of high quality and the page budget of this issue was limited, the decision was made not to include any invited review papers. After careful evaluations of the submitted papers, the following 24 papers and four letters were selected to represent diversified areas of interests in modern wireless communications. The discussion of the contributions that follow is organized by technical topics. Base-Station Antennas: The wide availability and low cost of digital signal processing and computing hardware in recent years is causing a dramatic change in base-station antenna Publisher Item Identifier S 0018-926X(98)05035-2.

systems. Intelligence is being added to base-station antennas forming the new field of smart base-station antennas, which is a large part of the first topic in this issue. Jeng et al. present results from a smart-array base-station experiment at 900 MHz. It is demonstrated that fading reduction and signal-tointerference ratio can be improved for a variety of array configurations and processing algorithms. Lindmark et al. performed an in-depth performance evaluation of a 12-element smart array for spatial division multiple access (SDMA) applications. The experimental model is in the personal communication system (PCS) band and includes polarization diversity through dual-slant 45 channels. Experiments showed that direction of arrival angle errors are acceptably small for mobile communications. Perini and Holloway conducted experiments at 850 MHz in urban and rural environments to compare two forms of diversity at the base station, spatial, and angle diversity. Angle diversity was demonstrated to perform as well as conventional spatial diversity in dense urban locations. Cho et al. examined microcell base-station diversity configurations in urban areas at 2.2 GHz for handheld terminals. Experimental results are presented that quantify the diversity gain achievable with two vertically separated, vertically polarized spatial-diversity base-station antennas as well as two collocated vertical and horizontal linear antennas used for polarization diversity. In addition, four-branch diversity, which combines both spatial and polarization diversity, is examined. Base-station antenna designs for implementing these diversity configurations are also presented. Demmerle and Wiesbeck describe a compact low-cost biconical multibeam antenna for use with SDMA base stations. Measured data for the antenna are presented along with implementation suggestions. Handset Antennas: The introduction of personal communication technology has resulted in a widespread awareness of the critical role wireless services play in today’s communications centered marketplace. Antennas play a paramount role in an optimal design of these services. Nakano et al. present a novel dual-frequency and wide-band voltage standing wave ratio (VSWR) handset antenna by combining normalmode helical and inverted F antennas. Both the results of numerical simulations and measurements are summarized. Ando et al. discuss the development of a microstrip antenna with rotatable patch. One of the key features of their design is that due to the rotation feature of the antenna mount, the antenna patch is always vertically oriented. To improve the radiation efficiency of antennas positioned near the user’s head, Tay et al. describe the application of a dipole antenna configuration with enhanced performance. Both the details of the antenna development and representative measured data are presented in the paper. Herscovici shows an interesting

0018–926X/98$10.00  1998 IEEE

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Fig. 1. An artist’s rendition of the global connectivity.

concept for the construction of microstrip antennas which could have applications as integrated antennas in mobile communications. In a letter, Montiel et al. summarize the design and construction of an active notch antenna for wireless applications. These are only a sample of efforts being pursued in the field of designing novel antennas. As market needs evolve, newer concepts will be considered and efforts will be focused on antennas that could be effectively integrated with the rest of the hand-held unit electronics. Human Interactions with Handset Antennas: Clearly, the electromagnetic interactions among the antenna, the handheld unit and the human operator is one of the key factors to be considered in designing the antennas. This area of research has received tremendous attention in recent years. The importance of this interaction issue is from both the viewpoint of understanding what the close presence of the human does to the antenna performance and also from the health consideration. Colburn and Rahmat-Samii demonstrate how the presence of the human head can significantly affect the circular polarization of a candidate helical antenna for direct user-to-satellite applications. This is a very important consideration when one evaluates the overall link budget of such a system. Interesting comparisons between the finitedifference time-domain (FDTD) and method of moments (MoM) techniques are presented in this paper. For pager-type antennas, Chen and Chuang present detailed numerical studies based on the volume MoM for superquadric loop antennas in the presence of the human body. Radiation patterns are shown to demonstrate how the close proximity of the antenna to the human body alters the radiation performance. Tinniswood et al. provide many useful comparative results for the evaluation of specific absorption rate (SAR) using FDTD. These authors

employ anatomically detailed model of the head and realistic model of handset units. The tabulated results should establish a good reference basis for assessing the performance of various handset designs. Lazzi et al. show a comparison between measurements and numerical data computed with FDTD methods for handset antennas near a human head model. Kim and Rahmat-Samii demonstrate the importance of including the effects of thin biological tissues such as skin in the evaluation of the human and antenna interactions at Kaband frequencies. These authors also show how the application of directional antennas will reduce the interaction effects. Antennas in a Mobile Environment: The complexity of the mobile environment necessitates application of unique antennas and the assessment of their performance in this environment. Norklit and Anderson present a detailed study of modeling the diffuse channel and the role of array antennas in this environment. These authors also incorporate the results of various measurements in their paper. The concept of using a switched parasitic antenna array in base-station tracking is discussed in a paper by Preston et al. Abou-Jaoude and Walton summarize the modeling techniques for characterizing on-glass conformal automobile antennas. In particular, they demonstrate the effectiveness of using geometric theory of diffraction (GTD) methods to determine antenna vehicular interaction. Propagation: This area is experiencing renewed interest because it usually is the limiting influence for terrestrial wireless links. Unfortunately, the worst propagation environments are where the demand for coverage and capacity is the greatest. Inner cities introduce blockage and multipath conditions that limit useful link distances and reduce reliability. This section of the issue addresses several important propagation topics


in wireless. Liang and Bertoni introduce a new method for propagation prediction in cities. It is less complex than full three-dimensional methods, yet is accurate as demonstrated with measured results at 900 and 1900 MHz in an urban environment with mixed building heights. Mazar and Bronshtein develop a field-based waveguide model to treat the urban propagation problem. Model predictions agree with previous measured results. Torrico et al. use a theoretical model to predict propagation loss between a base station and a mobile in the presence of trees and buildings in residential areas. Calculated results are presented for 800 MHz to 2 GHz. Brennan and Cullen present a theoretical method for predicting UHF propagation in open terrain. Surface scattering effects are included. Comparisons are made to published measured data. Bianchi and Sivaprasad propose a method for modeling atmospheric anomalies that lead to signal distortions on long terrestrial microwave links. The model can be integrated into a digital radio system model. Su et al. examine slow fading for urban mobile wireless links at 1900 MHz. Both measured campaign results as well as model predictions are detailed. Indoor Antennas and Propagation: The demand for personal wireless communications has extended to inside buildings. This presents unique challenges for antenna design and propagation analysis. Kuga et al. introduce an antenna for use in an indoor base station. The ceiling mounted notch-wire antenna has horizontal and vertical polarizations to provide polarization diversity. Both numerical and measured results are presented at -band. Yang et al. present a ray-tracing method for modeling indoor propagation and penetration into buildings. Moment-method simulations and measured data from 900 to 1800 MHz are compared to the ray-tracing model results. Obayashi and Zander examined the effects of people on indoor radio links at 900 MHz and 60 GHz. A ray-based model as well as measurements were used. Marinier et al.

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address the same problem. They present statistical results from indoor propagation measurements at 30 GHz. Satellite Systems: The final topic is the important one of satellite systems. Dietrich et al. describe the GLOBALSTAR cellular satellite system, which is near deployment. The paper emphasizes the several spacecraft antennas.

The future of wireless communications will continue to involve antennas and propagation. In fact, these topics will become more closely related. For example, the total performance of a hand-held terminal is a complicated interplay involving the antenna, the physical structure of the radio, the human operator, and the propagation environment. Future analysis and design will consider all of these together.

The Guest Editors would like to thank the authors and the reviewers for their efforts in making this issue a timely one and hope that it will serve as a well-referenced publication in the rapidly evolving field of wireless communications. We would also like to thank the Transactions Editor, Professor P. L. E. Uslenghi, for his support during the completion of this issue. YAHYA RAHMAT-SAMII, Guest Editor University of California, Los Angeles Los Angeles, CA 90095 USA [email protected] WARREN L. STUTZMAN, Guest Editor Virginia Polytechnic Institute & State University Blacksburg, VA 24061 USA [email protected]

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Yahya Rahmat-Samii (S’73–M’75–SM’79–F’85) received the M.S. and Ph.D. degrees in electrical engineering from the University of Illinois, Urbana-Champaign. He is currently a Professor of Electrical Engineering at the University of California, Los Angeles (UCLA). He was a Senior Research Scientist at NASA’s Jet Propulsion Laboratory/California Institute of Technology before joining UCLA. He was a Guest Professor at the Technical University of Denmark (TUD) in the summer of 1986. He has also been a consultant to many aerospace companies. He has authored and coauthored over 400 technical journal articles and conference papers and has written 14 book chapters. He is the coauthor of Impedance Boundary Conditions in Electromagentics (Washington, DC: Taylor and Francis, 1995). He is also the holder of several patents. He has had pioneering research contributions in diverse areas including electromagnetics, antennas, measurement and diagnostics techniques, numerical and asymptotic methods, satellite and personal communications, and human/antenna interactions. Dr. Rahmat-Samii was the 1995 President of IEEE Antennas and Propagation Society. He was appointed an IEEE Antennas and Propagation Society Distinguished Lecturer and presented lectures internationally. He was elected as a Fellow of IAE in 1986. Currently he is a member of the Strategic Planning and Review Committee (SPARC) of IEEE. He has been the guest and plenary session speaker at many national and international symposia. He was one of the Directors and Vice President of the Antennas Measurement Techniques Association (AMTA) for three years. He was also a member of UCLA’s Graduate council. For his contributions, he has received numerous NASA and JPL Certificates of Recognition. In 1984 he was the recipient of the prestigious Henry Booker Award of URSI. In 1992 and 1995, he was the recipient of the Best Application Paper Award (Wheeler Award) for papers published in the 1991 and 1993 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION. He is a member of Commissions A, B, and J of USNC/URSI, AMTA, Sigma Xi, Eta Kappa Nu, and the Electromagnetics Academy. He is listed in Who’s Who in America, Who’s Who in Frontiers of Science and Technology, and Who’s Who in Engineering.

Warren L. Stutzman (F’89) received the B.S. (electrical engineering) and B.A. (mathematics) degrees from the University of Illinois, Urbana-Champaign, in 1964, and the M.S. and Ph.D. degrees (electrical engineering) from The Ohio State University, Columbus, in 1965 and 1969, respectively. In 1969, Dr. Stutzman joined the electrical engineering faculty of Virginia Polytechnic Institute and State University, Blacksburg, where he is currently the Thomas Phillips Professor of Engineering. He is Director of the Satellite Communications Group and the Antenna Laboratory at Virginia Tech, which are part of the Center for Wireless Telecommunications. In 1983 he was a Visiting Professor at the Physical Science Laboratory, New Mexico State University, Las Cruces. He works in several areas of antennas and propagation. His research activities include antennas for wireless, wide-band elements and arrays, phased-array antennas, reflector antennas, personal communication systems, and atmospheric effects on earth-space communication links. He is coauthor of Antenna Theory and Design (New York: Wiley, 1981, 1998) and is the author of Polarization in Electromagnetic Systems (Norwood, MA: Artech House, 1993). Dr. Stutzman has held the following offices in the Antennas and Propagation Society: Administrative Committee from 1984 to 1986; Chairman of the AP-S Meetings Committee from 1988 to 1991; Vice President in 1991; and President in 1992. He received the Wheeler Prize for the Best Applications Paper for IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION in 1992 and 1995.