IEEE Antennas and Propagation Soclety Newsletter. April 1987

laboratories. Adeauacv between local needs and locallv I I available technology has been the guideline of the program, although state-of-the-art products have resulted in some cases, As a result of such Drograms. activities in the microwave area Feature Article Author I I Introducing Antonio Roberto Panieali

have considerably grown in. the past years and SBMO was created in 1982 to gather al l experts on the area. In conclusion, SBMO is more than happy to invite Y O U to BSc in e l ec t ron ic s f rom the Institute Tecnologico da

Antonio Roberto Panicali was born in 1940. He earned his

participate on its second international symposium, "Gathering Aeronautics sp ~ ~ ~ ~ i l in 1964, and his mC and PhD at the the World through Microwaves". University of Illinois a t Champaign-Urbana, USA, in 1968 and

1970, respectively. He is Associate Professor in the EE Department of the University of Sao Paulo, and Senior Engineer of TELEBRAS R&D Center a t Campinas-SP-Brazil.

Introducing ,Feature Article Authors

He served on the AP-S chairman of followinn

Ad Com during 1979-1981 and was . Committees;Meetings,Constitution -

and Bylaws, and I n s t i t u t i o n a l L i s t i n g s . He also served a s AP-S l iason to the Geoscience and Remote Sensing Society during this t ime period. Since 1979, he has been Associate Editor for the AP-S Transactions and the Journal of Oceanic Engineering.

Gory S. Brown

Gary S. Brown was born in Jackson, MS on 13 Apr i l 1940. He received the B.S., H.S. , and Ph.D. degrees from the University of I l l i n o i s .

From 1963 t o 1967, he was a Research Assistant in the Old Antenna Laboratory of the University of I l l i n o i s where he was involved with direction finding, shaped beam antennas, and millimeter waveguides. While in t he U.S. Army Signal Corps (1968-1969) he served in an engineering capacity dealing with the Integrated Wide- band Communication System (IWCS) in the Republic of Vietnam. During 1970, he w a s employed by TRV Systems Group where h i s work involved monopulse, ECM, and multiple-beam antenna analysis and development. From 1971-1973, he was with the Research Triangle Insti tute where his pr imary area of i n t e r e s t was radar a l t imetry. From 1973 t o 1985 he was employed by Applied Science Associates, Inc. of Apex, NC where he was involvedwith microwave remote sensing, rough surface scattering, and propagation through random media. In 1985 he joined the facul ty of the Virginia Polytechnic Inst i tute and State Univeristy in Blacksburg, VA. He is a member of Commissions Band F of URSI and he received the 1978 R.W.P. King Award from AP-S.

He served on the Technical Committee of the 1972 IEEE/G-AP Symposium and assis ted the Special Events Chairman during the 1978 IEEE/AP-S Symposium. He is Publ ic i ty Chairman f o r t h e 1987 IEEE/AP-S Symposium.

Warren 1. Stutzman

Warren L. Stutzman was born in Elgin, IL , on October 22, 1941. He received the B.S. degree i n e l e c t r i c a l e n g i n - eer ing and the A.B. degree i n mathematics from the Univ- e r s i t y of I l l i n o i s , Urbana, i n 1964. In 1965 and 1969 he received the M.S. and Ph.D. degrees , respect ively, i n e lec t r ica l engineer ing from the Ohio State University, Columbus.

I n 1969 he jo ined the facul ty of Virginia Polytechnic I n s t i t u t e and State University, Blacksburg, where he is currently a Professor of Electr ical Engineer ing. H i s r e sea rch i n t e re s t s are millimeter wave propagation, communication systems, and antenna synthes is .

D r . Stutzman is a member of Sigma X i and Eta Kappa Nu.

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Electromagnetics at Virginia Tech W. L. Stutzman and G. S. Brown

Background

hlany of the members of AP-S and URSI will be visiting Virginia Tech this June to attend the 1987 Symposium. It is therefore appropriate to introduce the efforts which are on going a t Virginia Tech in theoretical and applied slectromagnetics. There is a saying in Virginia that Virginia Tech is the best kept secret in the state; with this article, we hope to let the secret out - at least in electromagnetics!

Virginia Tech is a contraction for Virginia Polytechnic Institute and State University but it is probably better known as VPI. Founded in 1872 as the state's land grant university, it has very strong programs in engineering and agriculture. Until the mid 1960s, the school's main emphasis was on undergraduate education, and the student body primarily comprised male military cadets. During the period from the mid 1960s to the present, the school has undergone a significant expansion in scope and size. Today thcre are 22,000 students enrolled including some 5,000 graduate students. Nearly all fields of study are available. The Engineering College is among the nation's largest with some 6,000 students; Bachelors, \lasters, and PhDs are offered in ten engineering departments. Through the efforts of the faculty, the college now ranks in the top ten percent of engineering institutions reporting their research expenditures. A s the college gains national prominance, it has attracted additional support from the greater university and the government of Virginia.

The Cascades - A scenic waterfall area in the nearby Jefferson National Forest

The Virginia Tech campus is located in the New River Valley between the Blue Ridge and Alleghany Mountains in southwest Virginia, The military tradition of the school is reflected in the classical architecture of the campus which is largely situated around a tree-bordered oval called the Drill Field. hlany of the buildings are constructed with locally quarried stone.

Burruss Hall - the main administration building for the university

The Electrical Engineering Department limited its undergraduate enrollment several years ago to 1200 students. The graduate program is continuing to grow and presently stands at 250 students. The research involvement of the faculty has increased steadily over the past 20 years to an annual dollar level of over $2,000,000 for the 55 faculty members in the department. The remainder of this article will focus on the electromagnetic activities within the EE Department.

Academic Propram in Electromagnetics

The undergraduate academic program at Virginia Tech has always maintained strong course requirements in traditional basic areas. For example, one full year of electromagnetics is required at the junior level (three quarters or two semesters). All senior level EE course work is elective, and to accommodate this there are 45 quarter courses offered. Of these courses, there are four in traditional electromagnetics topics (microwaves, antennas, and propagation), five in electrooptics, three in radio engineering, and one in satellite comnlunications. All of these courses are generally survey in nature. Emphasis is placed on fundamental physical concepts as well as a significant design content. The solid background provided by the one year of required elechomagnetics at the junior level allows each of these courses to be taken without any other

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IEEE Antennas and Propugation Society Newsletter, April 1987

as a prerequisite. The popularity of these senior level electromagnetics courses is at an all time high at Virginia Tech. For example, the microwaves, antennas, and fiber optics courses currently have total enrollments of 120, 90, and 290, respectively.

The graduate academic program comprises one year of electromagnetics, one year of electrooptics, and one year of microwave systems oriented courses. There are approximately 35 graduate students in electromagnetics with a faculty complement of 14. Clearly, this is one of the larger electromagnetics oriented faculty in the country. Members of the Virginia Tech faculty actively involved in electromagnetics teaching and research are listed below by their primary area of specialty.

ProDapatioq ODtiCS

I. M. Besieris R. 0. Claus C. W. Bostian R. J. Pieper G. S. Brown T. C. Poon D. A. de Wolf A. Safaai-Jazi D. B. Hodge R. C. Robertson hficrowaves Antennas

T. Pratt W. A. Davis S. M. Riad W. L. Stutzman

Needless to say, many of these individuals have expertise in more than one specialty. Another point to note here is the inclusion of the optics oriented program and facdty under the electromagnetics banner. This is not a classical approach but one that has so far been beneficial to both programs primariIy because of the emphasis upon coherent optics within the optics program. The electromagnetics faculty is also quite proud of the fact that our Department Head, D. B. Hodge, has an extensive background in electromagnetics; so much so that he literally has Maxwell’s equations cast in concrete in his home. Now that is real dedication to the cause!

where Virginia Tech faculty and graduate students have a demonstrated capability,

In the general area of very low frequency EM, there is a continuing interest in the application of EM techniques to the problem of subsurface feature detection and identification. Current work includes the analysis of models of the earth containing both two and three dimensional heterogeneities, as well as the allied problem of assessing the effects of two and three dimensional anomalies on the interpretation of magnetotelluric data.

The Satellite Group at Virginia Tech has been conducting experimental and modeling research for a number of years with the primary purpose of understanding earth-to-space communications links above 1 GHz. Experiments have been conducted to measure rain and ice crystal propagation effects (primarily attenuation and depolarization) with the ATS-6, CTS, COMSTAR, SIRIO, and INTELSAT V spacecraft. This experimental work has been accompanied by programs in propagation theory and modeling which have generated prediction techniques for attenuation, depolarization, and dispersion in the 10-30 GHz band. Virginia Tech was the first site to conduct dual-polarized site diversity measurements and the only university group to make simultaneous CTS (11.7 GHz) and COMSTAR (19.04 and 28.56 GHz) measurements. Virginia Tech also has the only U. S. multiple-polarization meteorological radar dedicated to propagation measurements. This S-band radar forms the core instrument in a program of simultaneous measurements using the radar and the 11.6 GHz downlink from INTELSAT-V to two (diversity) earth terminals for the purpose of evaluating the utility of the S-band radar in estimating the degree of propagation impairment at 11.6 GHz. Propagation studies are also being carried out for the Land Mobile Satellite System (LMSS) where models for the primary statistics of vegetatively shadowed paths and for the fade durations and interfade intervals of all paths are being developed.

Memorial Chapel - A non-denominational place of worship for students and faculty

Research h e r a m s in Electromavnetics

Research at Virginia Tech is also a relatively good indication of the interest areas of the electromagnetics faculty. Like other schools maintaining strong programs in EM, Virginia Tech has fostered a very broad based EM research effort. The following material is a very brief discussion of the major research areas

A View of the antenna farm used for propagation studies

There is a great deal of work at Virginia Tech that falls under the general category of theoretical research on propagation and scattering by random, inhomogeneous, or nonlinear media. In attempting to describe the propagation of EM waves in inhomogeneous media, one often finds that simple theories such as ray tracing give rise to spurious field singularities. However, by expanding the concept of a field as a function of spatial coordinates to that of a

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IEEE Antennas and Propagation Society Newsletter, April 1987

iistribution function depending on spatial wavenumber coordinates, the infinities can be overcome at an acceptable cost. This is a very succinct description of the wave kinetic approach to wave propagation which has been studied extensively at Virginia Tech. One particular application of this approach is the numerical simulation of an optical beam propagating through a random medium; the phase space methodology is expressly used to overcome the problem of ray singularities. In another program, several efforts are underway to clarify the effects of electromagnetic scattering from particulate media that can attain appreciable densities and that may consist of non-tenuous scatterers. A somewhat allied area of research is the development of the radiative transport equations for wave propagation through a particulate medium directly from Maxwell's equations. Along more practical lines, Virginia Tech is involved in a program to estimate the effects of a vegetative or a snow layer on the scattering from a rough surface in the microwave to millimeter wavelength bands. Closely coupled to this research is an ongoing effort to analyze, understand and predict the effects of multiple scattering in the process of scattering from a randomly rough surface. This work has led to the development of a number of new methods which show promise of yielding insight into the complexities of this problem. Applications of rough surface scattering theory abound and Virginia Tech is involved in a particular xeanographic remote sensing program employing B multiple beam radar system to provide increased coverage over a single beam system. Virginia Tech has a similar research effort aimed toward the development of a range-Doppler clutter map for near airport environments. Finally, the field of nonlinear wave propagation has undergone a resurgence of interest and Virginia Tech is involved in this general area through the pursuit of new types of pulsed-wave solutions of hfaxwell's equations.

Current antenna research topics center sround computer code development for the design 3f reflectors, phased arrays, wire antennas, and deep apertures. The reflector code permits analysis of an arbitrarily shaped reflector coupled with an arbitrarily positioned feed array assembly. The reflector code, called the reflector antenna program (RAP), has been used in optimization studies for offset and axisymmetric VSAT reflectors, for studies of improved numerical evaluation of radiation fields, and for accurate evaluation of patterns of reflector systems with feed arrays of complex configuration.

Phased array research has focused on the development of a computer-aided-design code which includes both array mutual coupling (via its scattering matrix) and the coupling associated with the feed network. This code is being used to study ways of designing arrays with known trimming devices which compensate for total system coupling to produce the design excitation set.

Extensive revisions to the MiniNEC wire antenna code have been made over the last year and a half. These include a conversion to the Pascal language, correction of the numerical integration procedure to enable the analysis of extremely thin wires, a full revision of the kernel evaluation to permit the analysis of structures such as closely spaced Yagis and folded dipoles, and the addition of screen plots of currents an? patterns. Work is presently progressing toward

the inclusion of the effects of a lossy ground. The problem of deep apertures or apertures in thick screens is of interest because of the difficulties associated with resonances in both surface dimensions depth. The deep depth requires some unique development in order to solve the problem numerically.

At Virginia Tech, we have one of the few time domain research programs in the U. S . Some of this program's research activities include the development of a computer package for transient analysis of transmission networks, the modeling and characterization of the state-of-the-art (DC-18 GHz) 20 ps sampling oscilloscope used by NBS as the national standard for pulse measurement. The program's activities also include signal processing of time domain waveforms which led to the development of the automated optimal compensation deconvolution in the presence of noise and the development of the complete FFT of step-like waveforms. Research in hybrid microwave integrated circuits has been carried out in conjunction with the department's hybrid thick-film microelectronics laboratory. Examples of this work include the design, construction, and characterization of a variety of wideband coplanar waveguide structures and components using thick-film technology.

In the broad area of microwave applications, Virginia Tech developed and is continuing to refine a means for estimating foliage biomass based on the net reduction in the power radiated through a foliage sample. Another program entails devising new techniques for determining the dielectric and conductive properties of thick film materials. There is an on-going effort to develop calibration techniques for use with network analyzers. In one phase of this program, techniques have been developed which circumvent the phase problems associated with an imperfect open circuit reference.

Under the general heading of fiber optics, Virginia Tech has very strong research efforts in the areas of optical fiber communication, sensing via fiber methods, and waveguide fabrication. Fiber communication research includes the design of high speed local area network and point-to-point physical devices, e . g . asymmetrical couplers, systems, and analysis and optimization of wideband single-mode fibers. Fiber sensing research has centered around the development of intrinsic dielectric waveguide sensors for the measurement of distributed strain, temperature, and other physical fields in a wide range of environments. Acoustic wave propagation in optical fiber waveguides, with application to sensor devices, is also being studied. Research in fiber fabrication has mainly been directed toward the analysis and construction of novel waveguide structures with refractive index geometries, coatings, and packings which optimize sensing and communication system performance. Acousto-optic diffraction research is concentrating on the application of a strong interaction plane wave theory for light and sound to problems such as the design of wide bandwidth acousto-optic modulators and high resolution laser beam deflectors. Digital image processing is being studied as a means for extending the depth of focus of conventional optical systems, and an optical scanning heterodyne technique for performing real time spatial filtering on diffusely reflecting objects is presently under investigation. Finally, the distortion of surfaces modulated by surface acoustic waves is being studied by optical means.

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