ISBN-10:
0780334868
ISBN-13:
9780780334861
Pub. Date:
09/28/1998
Publisher:
Wiley
Active Antennas and Quasi-Optical Arrays / Edition 1

Active Antennas and Quasi-Optical Arrays / Edition 1

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Product Details

ISBN-13: 9780780334861
Publisher: Wiley
Publication date: 09/28/1998
Pages: 350
Product dimensions: 8.78(w) x 11.18(h) x 0.97(d)

About the Author

Amir Mortazawi is an associate professor in the Electrical Engineering Department at the University of Central Florida, Orlando. His research interests include millimeter-wave power combining oscillators and amplifiers; quasi-optical techniques; and nonlinear analysis of microwave circuits.

Tatsuo Itoh is director of Joint Services Electronics Program (JSEP) and is also director of Multidisciplinary University Research Initiative (MURI) program at the University of California, Los Angeles. He was an honorary visiting professor at both the Nanjin Institute of Technology, China, and the Japan Defense Academy. In 1994, Dr. Itoh was appointed as adjunct research officer for Communications Research Laboratory, Ministry of Post and Telecommunication, Japan. He currently holds a visiting professorship at the University of Leeds, UK, and is an external examiner of the graduate program of the City University of Hong Kong Dr. Itoh is a fellow of the IEEE, a member of the Institute of Electronics and Communication Engineers of Japan, and Commissions B and D of USNC/URSI. In 1994 he was elected as an honorary life member of the MTT Society.

James Harvey is a research program manager at the US Army Research Office with primary responsibilities in the fields of electromagnetics, antennas and antenna structures, millimeter-wave circuit integration, low power/minimum power system design, and mine detection. His programs include a focus on small, multifrequency, multifunctional antennas for US Army vehicles, radio propagation over complex terrain affecting data communications, and new millimeter-wave circuit integration techniques, such as spatial power combining and micromachining.

Read an Excerpt

Active Antennas and Quasi-Optical Arrays


By Amir Mortazwi Tatsuo Itoh James Harvey

John Wiley & Sons

ISBN: 0-7803-3486-8


Chapter One

Historical and Review Papers

This chapter contains a collection of review and historical papers on quasi-optical and active antenna techniques for power combining and beam control. In addition to their archival value, the papers in this chapter have been selected to provide a general tutorial introduction to the subject, a theoretical background, an explanation of basic concepts, and a summary of recent trends. This chapter was intended to serve as a useful stand-alone overview of the topical area, without the technical detail provided in the chapters to follow.

The first paper in this chapter, "Quasi-optical power combining: A perspective," has been written specifically for this book by Mink, Steer, and Wiltse. It summarizes recent trends in the field, which have occurred since the publication of Mink's seminal paper in 1986. In addition to specific references, an extensive general bibliography has also been included. It is written in a style to be useful to the general reader and the engineer entering the new field. This paper is followed by Mink's 1986 paper, in which the concept of quasi-optical power combining was successfully quantified for the first time.

Several different architectural structures have been utilized for the design of quasi-optical power combining circuits. Quasi-optical techniques have been used to interface arrays of oscillators with a modal electromagnetic field and arrays of amplifiers with a traveling electromagnetic field. The near-term industrial and military emphasis is on amplifier arrays, because good low-power tunable sources of high-purity signals are available that can be amplified quasi-optically to high-power levels. The architecture introduced by Mink in his 1986 paper combined an array of oscillators in an open resonant cavity. The third paper in this chapter describes the quasi-optical power combining in oscillator and amplifier grid arrays. In grid array architecture, devices are spaced much closer than a wavelength, with the metallic connectors acting collectively as a large antenna structure. An alternative structure uses an array of unit cells, each containing an amplifier or oscillator circuit and a separate resonant antenna element. This type of architecture is described in later chapters. A third alternative architecture is a relatively recent, emerging development, a two-dimensional combining structure, which is described in detail in Chapter 8.

One potential advantage of quasi-optical power combining over other combining techniques is the ease with which higher order functionality, such as beam control, external injection locking, frequency multiplication, and frequency mixing can be introduced. An excellent review paper by York discusses injection locking and beam steering of oscillator arrays by control of oscillator phase and frequency but could not be included in this volume. An alternative beam control technique is a beam steering quasi-optical grid, discussed in Chapter 5. The fourth paper in this chapter is a review of quasi-optical mixer approaches and also describes some frequency multiplication applications.

Most quasi-optical arrays based on semiconductor technology utilize active antennas or active antenna elements in the unit cell. The active antenna element is usually a printed planar antenna incorporating an active semiconductor device directly integrated with the antenna structure. As a result this antenna element minimizes transmission line losses and provides quasi-optical arrays with the potential for very high efficiency power combining. In addition to its application in arrays, individual active antennas can provide functionality not available from conventional passive antennas. Paper 5 is a review of active integrated antennas.

Quasi-Optical Power Combining: A Perspective

James W. Mink, Michael B. Steer, and James C. Wiltse North Carolina State University, Raleigh, NC 27695-7911 Georgia Tech Research Institute, Atlanta, GA 30332

Abstract-This section summarizes recent progess in power-combining of solid-state sources at microwave and millimeter wavelengths.

Introduction

For many years, there has been a need to obtain more power from solid-state devices, both sources and amplifiers in the upper microwave, millimeter, and submillimeter wavelength regions of the electromagnetic spectrum. There exist many system applications in common use today and their range of application is expanding, It is safe to predict that these systems will be utilized in the future across the spectrum of endeavors from communications to radar, transportation, industrial, and scientific applications (such as radio astronomy and spectroscopy). Satisfying this expanding demand mandates the utilization of previously unused, or little used, millimeter and submillimeter wave bands. In accordance with a long-term trend, systems will migrate toward higher and higher frequencies; the necessary technology, however, is not very well developed at the present time. A fundamental limitation has been and continues to be the lack of convenient power sources and amplifiers. Component costs have been driven by the small size and tight tolerance associated for millimeter sources and in the case of waveguide components, by the need for hand assembly. This is more urgent at millimeter-wave frequencies than at microwave-wave frequencies because microwave sources generally give better performance in terms of parameters such as power output, efficiency, and/or spectral purity. Solid-state devices are highly reliable; however, their output power tends to be very low due to the small physical size of the active region, resulting in the well-known 1/[f.sup.2] falloff of available power. Hence, a need exists to combine the outputs of many individual elements to satisfy the system power requirement.

Many of the problems stated above may be resolved through the use of quasi-optical techniques. The term "quasi-optical" is used to denote the utilization of a short-wavelength electromagnetic technique (approaching optical) in a relatively long wavelength (microwave) region. Quasi-optical devices typically have cross-sectional dimensions in the order of 10-100 wavelengths and are relatively easy to fabricate. Tolerance requirements are greatly relaxed since boundary surfaces along the propagating directions of the guiding structure are not critical for mode selection and maintenance of mode purity. Rather, easily manufactured lenses or reflectors, and the spacing between them, establish the mode parameters. In addition, the rather large transverse dimensions of quasi-optical structures allow one the freedom to include numerous solid state sources to achieve the desired output power.

Architectures

All quasi-optical systems have several features in common: at least one transverse dimension is large compared to the wavelength; the longitudinal dimension is also large and may be large compared to the transverse dimension; hence, many individual solid-state sources may be integrated into the structure. While dimensions are large compared to the wavelength, the mode supported by the structure is only a single mode, or at most a small number of modes may exist in the structure. The concept employs a wavebeam resonator (Fabry-Perot resonator) as the power combining concept and is similar to an optical laser as shown in Figure 1. The resonator enforces the collective emission of otherwise independent oscillators with a resonator geometry practical for short-wavelength emission, which makes it possible for all oscillators to operate in a coherent manner. In the case of the laser, a very large number of oscillators, in the form of individually excited molecules, populate the volume of the resonator. Individual molecular oscillators are stimulated in a coherent fashion by the standing wave or by the mode that is characteristic of the quasi-optical geometry. This basic concept has been extended to the developing of coherent emission of a collection of individual solid-state devices in the millimeter and submillimeter wave combiners. The departure for analogy to the laser is due to the fact that individual oscillators are macroscopic devices which include coupling elements (antennas), rather than individual molecules.

In recent years, research emphasis has been placed upon three principal classes of quasi-optical systems. One of the first structures to be investigated was that of an open resonator, commonly referred to as the Fabry-Perot resonator, with solid-state sources located in a plane transverse to the direction of propagation. The electromagnetic mode structure of open resonators is well known and characterized. Since the physical size of each solid-state source is much smaller than the wavelength, a coupling device must be employed to extract energy from the active element and transfer it to the wavebeam. Many coupling devices have been investigated, including small dipoles, loop elements, microstrip elements, and one-dimensional waveguide structures. In each case, the goal of such coupling elements is to impedance match between the active device and the electromagnetic wavebeam. An example of an open resonator structure is shown in Figure 2. Feedback required for oscillation is obtained primarily through the electromagnetic wavebeam, with a small but measurable contribution due to direct mutual interaction between the coupling devices.

The second structure is that of the grid oscillator and amplifier, which is the most highly developed quasi-optical structure at this point in time. The investigation of this structure is primarily due to the efforts of Professor Rutledge and his associates. In this case an array of active elements is placed in a uniform grid, which intercepts the electromagnetic wave, with each element connected to its nearest neighbors via a printed transmission line/antenna structure. When one considers the grid structures, feedback to obtain oscillation is principally via the transmission line located between the active elements, also with significant coupling via the electromagnetic wave beam. Since the adequate feedback for oscillation requires both components of feedback, grid structures are well suited for both amplifiers as well as oscillators. In the oscillator case, the electromagnetic beam coupling is relatively small, and it becomes essential to ensure that all active elements oscillate coherently and in phase, as opposed to antiphase oscillation. An example of the typical grid amplfier of the type pioneered by Professor Rutledge and his associates is shown in Figure 3a. Also shown in Figure 3b is a detailed depiction of one active element cell. Grid amplifiers have shown gain of about 5 dB operating at about 40 Ghz with maximum power output of 670 mW. Grid oscillators are very similar to grid amplifiers, except that the feedback element, in this case a reflector, is added to the system. To date grid oscillators have produced the highest power level of about 10 W in the X-band.

The third class of quasi-optical systems are based upon the hybrid dielectric slab-beam waveguide. The hybrid slab-beam waveguide consists of a thin dielectric slab, usually grounded on one side, into which phase correcting elements are inserted. The phase correction element for an oscillator is usually a partially transparent curved reflector; energy is extracted through that reflector. The hybrid dielectric slab-beam wave-guide confines the beam in one dimension through wavebeam techniques as discussed above and in the second transverse direction (normal to the dielectric slab surface) through the technique of total internal reflection as normally employed by slab dielectric waveguides. For this structure, one obtains a large area suitable for the integration of active elements along the direction of propagation and across the wavebeam. The advantage of this technique is that the active elements may be integrated as a component of the ground plane and coupled to the wavebeam through apertures in the ground plane. This technique provides adequate coupling to the wavebeam, while providing a mechanism for efficient cooling of the active elements. The hybrid dielectric slab-beam waveguide techniques continue to show promise; however, they are the least developed of the three techniques discussed here. An amplifier based upon these techniques has shown input to output gain of about 10 dB in the X-band. An example of a hybrid dielectric slab / wave-beam amplifier system is shown in Figure 4. Also shown in Figure 4 are details of the active device to wavebeam coupling element and phase correcting elements.

Current status and Recent Results

The early experiments with grid array power-combiners mainly employed two-terminal devices such as Gunn or impact avalanche transit time (IMPATT) diodes at X-band or below. Later, similar investigations were conducted at millimeter wavelengths. However, two-terminal devices have low efficiencies, as well as less flexibility than three-terminal devices. Thus, recent experiments have been conducted utilizing transistors such as field effect transistors (FETs), pseudo-morphic HEMT (PHEMT), or heterojunction bipolar transistors (HBTs). An excellent summary of this work through 1994 was given in a survey by R. A. York. The three-terminal devices give an extra degree of control (albeit at the cost of added complexity), but, more important, offer higher efficiencies, particularly PHEMTs at [K.sub.[a]] - band. (This is important from the point of view of heat removal from the small grid array structure.) Monolithic grid structures have also been investigated.

Conclusion

Table 1 lists the specification of selected results reported for quasi-optical spatial combiners. While the intention of quasi-optical techniques is to develop high-power sources at millimeter wavelengths, most research to date has been conducted in the microwave region of the spectrum. In addition to the references, a biblography of relevant, key papers which indicates the magnitude of research effort addressing quasi-optical power combining techniques is provided. It should be pointed out that the results shown in Table 1 have been primarily proof-of-concept demonstrations and additional development effort is required. However, several academic, government, and industrial institutions currently have programs focused upon the millimeter spectrum.

Quasi-Optical Power Combining of Solid-State Millimeter-Wave Sources

JAMES W. MINK, SENIOR MEMBER, IEEE

Abstract-Very efficient power combining of solid-state millimeter-wave sources may be obtained through the application of quasi-optical resonators and monolithic source arrays. Through the theory of reiterative wavebeams (beam modes) with application of the Lorentz reciprocity theorem, it is shown that planar source arrays containing 25 individual elements or more result in very efficient power transfer of energy from the source arrays to the fundamental wave-beam mode. It is further shown that for identical sources within a properly designed quasi-optical power combiner, the output power tends to increase much faster that number of source elements.

I. Introduction

Conventional waveguide power combiners are limited in power output, efficiency, and number of sources that may be combined in the millimeter-wave region. This limitation is a consequence of the requirement that linear dimensions of conventional waveguide resonators be of the order of one wavelength to achieve acceptable mode separation and to avoid multimode operation. On the other hand, quasi-optical resonators have linear dimensions large compared to wavelength and they offer an attractive approach to overcome these limitations. Fundamental limitations of power combining utilizing quasi-optic resonator techniques is discussed in this paper, and it is shown that very high combining efficiency may be obtained. The approach utilizes an array of source elements placed within a transverse plane near one reflecting surface of the resonator. Energy is extracted from the system through one reflector which is partially transparent.

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Table of Contents

Introduction.

Historical and Review Papers.

Transmitting and Receiving Active Antennas.

Spatial Power Combining Oscillators.

Spatial Power Combining Amplifiers.

Beam Control.

Active Integrated Antennas and Quasi Optical Systems.

Analysis and CAD.

Emerging Technologies-Two Dimensional Quasi Optics.

Author Index.

Subject Index.

About the Editors.

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