CHAPTER

1INTRODUCTION

The purpose of this introductory chapter is to provide a short, and admit-tedly incomplete, survey of what the microwave engineering field encom-passes. Section 1.2 presents a brief discussion of many of the varied andsometimes unique applications of microwaves. This is followed by a thirdsection in which an attempt is made to show in what ways microwaveengineering differs from the engineering of communication systems at lowerfrequencies. In addition, a number of microwave devices are introduced toprovide examples of the types of devices and circuit elements that areexamined in greater detail later on in the text.

1.1 MICROWAVE FREQUENCIES

The descriptive term microwaves is used to describe electromagnetic waveswith wavelengths ranging from 1 cm to 1 m. The corresponding frequencyrange is 300 MHz up to 30 GHz for 1-cm-wavelength waves. Electromag-netic waves with wavelengths ranging from 1 to 10 mm are called millime-ter waves. The infrared radiation spectrum comprises electromagnetic waveswith wavelengths in the range 1 ^m (10~6 m) up to 1 mm. Beyond theinfrared range is the visible optical spectrum, the ultraviolet spectrum, andfinally x-rays. Several different classification schemes are in use to designatefrequency bands in the electromagnetic spectrum. These classificationschemes are summarized in Tables 1.1 and 1.2. The radar band classifica-tion came into use during World War II and is still in common use todayeven though the new military band classification is the recommended one.

In the UHF band up to around a frequency of 1 GHz, most communi-cations circuits are constructed using lumped-parameter circuit compo-

1

FOUNDATIONS FOR MICROWAVE ENGINEERING

TABLE 1.1Frequency band designation

Frequencyband

3-30 kHz

30-300 kHz

300-3,000 kHz

3-30 MHz

30-300 MHz

300-3,000 MHz

3-30 GHz

30-300 GHz

Designation

Very low frequency(VLF)

Low frequency(LF)

Medium frequency(MF)

High frequency(HF)

Very high frequency(VHF)

Ultrahigh frequency(UHF)

Superhigh frequency(SHF)

Extreme high fre-quency (EHF)

Typical service

Navigation, sonar

Radio beacons, navigationalaids

AM broadcasting, maritimeradio, Coast Guard commun-ication, direction finding

Telephone, telegraph, andfacsimile; shortwaveinternational broadcasting;amateur radio; citizen'sband; ship-to-coast and ship-to-aircraft communication

Television, FM broadcast,air-traffic control, police,taxicab mobile radio,navigational aids

Television, satellite com-munication, radiosonde,surveillance radar,navigational aids

Airborne radar, microwavelinks, common-carrier landmobile communication, satellitecommunication

Radar, experimental

TABLE 1.2Microwave frequency band designation

Frequency

500-1,000 MHz1-2 GHz2-3 GHz3-4 GHz4-6 GHz6-8 GHz8-10 GHz

10-12.4 GHz12.4-18 GHz18-20 GHz20-26.5 GHz26.5-40 GHz

Microwave band designationOld

VHFLSS

ccXXKuKKKa

New

CDEFGHIJJJKK

2

INTRODUCTION 3

nents. In the frequency range from 1 up to 100 GHz, lumped circuitelements are usually replaced by transmission-line and waveguide compo-nents. Thus by the term microwave engineering we shall mean generallythe engineering and design of information-handling systems in the fre-quency range from 1 to 100 GHz corresponding to wavelengths as long as 30cm and as short as 3 mm. At shorter wavelengths we have what can becalled optical engineering since many of the techniques used are derivedfrom classical optical techniques. The characteristic feature of microwaveengineering is the short wavelengths involved, these being of the same orderof magnitude as the circuit elements and devices employed.

The short wavelengths involved in turn mean that the propagationtime for electrical effects from one point in a circuit to another point iscomparable with the period of the oscillating currents and charges in thesystem. As a result, conventional low-frequency circuit analysis based onKirchhoff s laws and voltage-current concepts no longer suffices for anadequate description of the electrical phenomena taking place. It is neces-sary instead to carry out the analysis in terms of a description of the electricand magnetic fields associated with the device. In essence, it might be said,microwave engineering is applied electromagnetic fields engineering. Forthis reason the successful engineer in this area must have a good workingknowledge of electromagnetic field theory.

There is no distinct frequency boundary at which lumped-parametercircuit elements must be replaced by distributed circuit elements. Withmodern technological processes it is possible to construct printed-circuitinductors that are so small that they retain their lumped-parameter charac-teristics at frequencies as high as 10 GHz or even higher. Likewise, opticalcomponents, such as parabolic reflectors and lenses, are used to focusmicrowaves with wavelengths as long as 1 m or more. Consequently, themicrowave engineer will frequently employ low-frequency lumped-parame-ter circuit elements, such as miniaturized inductors and capacitors, as wellas optical devices in the design of a microwave system.

1.2 MICROWAVE APPLICATIONSThe great interest in microwave frequencies arises for a variety of reasons.Basic among these is the ever-increasing need for more radio-frequency-spectrum space and the rather unique uses to which microwave frequenciescan be applied. When it is noted that the frequency range 109 to 1012 Hzcontains a thousand sections like the frequency spectrum from 0 to 109 Hz,the value of developing the microwave band as a means of increasing theavailable usable frequency spectrum may be readily appreciated.

At one time (during World War II and shortly afterward), microwaveengineering was almost synonymous with radar (RAdio Detection AndRanging) engineering because of the great stimulus given to the develop-ment of microwave systems by the need for high-resolution radar capable of

4 FOUNDATIONS FOR MICROWAVE ENGINEERING

detecting and locating enemy planes and ships. Even today radar, in itsmany varied forms, such as missile-tracking radar, fire-control radar,weather-detecting radar, missile-guidance radar, airport traffic-control radar,etc., represents a major use of microwave frequencies. This use arisespredominantly from the need to have antennas that will radiate essentiallyall the transmitter power into a narrow pencil-like beam similar to thatproduced by an optical searchlight. The ability of an antenna to concentrateradiation into a narrow beam is limited by diffraction effects, which in turnare governed by the relative size of the radiating aperture in terms ofwavelengths. For example, a parabolic reflector-type antenna produces apencil beam of radiated energy having an angular beam width of140°/(D/A0), where D is the diameter of the parabola and Ao is thewavelength. A 90-cm (about 3 ft) parabola can thus produce a 4.7° beam ata frequency of 1010 Hz, i.e., at a wavelength of 3 cm. A beam of this type cangive reasonably accurate position data for a target being observed by theradar. To achieve comparable performance at a frequency of 100 MHz wouldrequire a 300-ft parabola, a size much too large to be carried aboard anairplane.

In more recent years microwave frequencies have also come intowidespread use in communication links, generally referred to as microwavelinks. Since the propagation of microwaves is effectively along line-of-sightpaths, these links employ high towers with reflector or lens-type antennasas repeater stations spaced along the communication path. Such links are afamiliar sight to the motorist traveling across the country because of theirfrequent use by highway authorities, utility companies, and television net-works. A further interesting means of communication by microwaves is theuse of satellites as microwave relay stations. The first of these, the Telstar,launched in July 1962, provided the first transmission of live televisionprograms from the United States to Europe.

Since that time a large number of satellites have been deployed forcommunication purposes, as well as for surveillance and collecting data onatmospheric and weather conditions. For direct television broadcasting themost heavily used band is the C band. The up-link frequency used is in the5.9- to 6.4-GHz band and the receive or down-link frequency band isbetween 3.7 and 4.2 GHz. For home reception an 8-ft-diameter parabolicreflector antenna is commonly used. A second frequency band has also beenallocated for direct television broadcasting. For this second band the up-linkfrequency is in the 14- to 14.5-GHz range and the down-link frequencies arebetween 10.95 and 11.2 GHz and 11.45 and 11.7 GHz. In this band areceiving parabolic antenna with a 3-ft diameter is adequate. At the presenttime this frequency band is not being used to any great extent in the UnitedStates. It is more widely used in Europe and Japan.

Terrestrial microwave links have been used for many years. The TD-2system was put into service in 1948 as part of the Bell Network. It operatedin the 3.7- to 4.2-GHZ band and had 480 voice circuits, each occupying a

INTRODUCTION

3.1-kHz bandwidth. In 1974, the TN-1 system operating in the 10.7- to11.7-GHz band was put into operation. This system had a capacity of 1,800voice circuits or one video channel with a 4.5-MHz bandwidth. Since thattime the use of terrestrial microwave links has grown rapidly.

At the present time most communication systems are shifting to theuse of digital transmission, i.e., analog signals are digitized before transmis-sion. Microwave digital communication system development is progressingrapidly. In the early systems simple modulation schemes were used andresulted in inefficient use of the available frequency spectrum. The develop-ment of 64-state quadrature amplitude modulation (64-QAM) has made itpossible to transmit 2,016 voice channels within a single 30-MHz RFchannel. This is competitive with FM analog modulation schemes for voice.The next step up is the 256-QAM system which is under development.

For the ready processing and handling of a modulated carrier, modula-tion sidebands can be only a few percent of the carrier frequency. It is thusseen that the carrier frequency must be in the microwave range for efficienttransmission of many television programs over one link. Without the devel-opment of microwave systems, our communications facilities would havebeen severely overloaded and totally inadequate for present operations.

Even though such uses of microwaves are of great importance, theapplications of microwaves and microwave technology extend much further,into a variety of areas of basic and applied research, and including a numberof diverse practical devices, such as microwave ovens that can cook a smallroast in just a few minutes. Some of these specific applications are brieflydiscussed below.

Waveguides periodically loaded with shunt susceptance elements sup-port slow waves having velocities much less than the velocity of light, andare used in linear accelerators. These produce high-energy beams of chargedparticles for use in atomic and nuclear research. The slow-traveling electro-magnetic waves interact very efficiently with charged-particle beams havingthe same velocity, and thereby give up energy to the beam. Anotherpossibility is for the energy in an electron beam to be given up to theelectromagnetic wave, with resultant amplification. This latter device is thetraveling-wave tube, and is examined in detail in a later chapter.

Sensitive microwave receivers are used in radio astronomy to detectand study the electromagnetic radiation from the sun and a number of radiostars that emit radiation in this band. Such receivers are also used to detectthe noise radiated from plasmas (an approximately neutral collection ofelectrons and ions, e.g., a gas discharge). The information obtained enablesscientists to analyze and predict the various mechanisms responsible forplasma radiation. Microwave radiometers are also used to map atmospherictemperature profiles, moisture conditions in soils and crops, and for otherremote-sensing applications as well.

Molecular, atomic, and nuclear systems exhibit various resonancephenomena under the action of periodic forces arising from an applied

6 FOUNDATIONS FOR MICROWAVE ENGINEERING

electromagnetic field. Many of these resonances occur in the microwaverange; hence microwaves have provided a very powerful experimental probefor the study of basic properties of materials. Out of this research onmaterials have come many useful devices, such as some of the nonreciprocaldevices employing ferrites, several solid-state microwave amplifiers andoscillators, e.g., masers, and even the coherent-light generator and amplifier(laser).

The development of the laser, a generator of essentially monochro-matic (single-frequency) coherent-light waves, has stimulated a great inter-est in the possibilities of developing communication systems at opticalwavelengths. This frequency band is sometimes referred to as the ultrami-crowave band. With some modification, a good deal of the present mi-crowave technology can be exploited in the development of optical systems.For this reason, familiarity with conventional microwave theory and devicesprovides a good background for work in the new frontiers of the electromag-netic spectrum.

The domestic microwave oven operates at 2,450 MHz and uses amagnetron tube with a power output of 500 to 1000 W. For industrialheating applications, such as drying grain, manufacturing wood and paperproducts, and material curing, the frequencies of 915 and 2,450 MHz havebeen assigned. Microwave radiation has also found some application formedical hyperthermia or localized heating of tumors.

It is not possible here to give a complete account of all the applicationsof microwaves that are being made. The brief look at some of these, as givenabove, should convince the reader that this portion of the radio spectrumoffers many unusual and unique features. Although the microwave engi-neering field may now be considered a mature and well-developed one, theopportunities for further development of devices, techniques, and applica-tions to communications, industry, and basic research are still excellent.

1.3 MICROWAVE CIRCUIT ELEMENTSAND ANALYSIS

At frequencies where the wavelength is several orders of magnitude largerthan the greatest dimensions of the circuit or system being examined,conventional circuit elements such as capacitors, inductors, resistors, elec-tron tubes, and transistors are the basic building blocks for the informationtransmitting, receiving, and processing circuits used. The description oranalysis of such circuits may be adequately carried out in terms of loopcurrents and node voltages without consideration of propagation effects.The time delay between cause and effect at different points in these circuitsis so small compared with the period of the applied signal as to be negligible.It might be noted here that an electromagnetic wave propagates a distanceof one wavelength in a time interval equal to one period of a sinusoidally

INTRODUCTION

time-varying applied signal. As a consequence, when the distances involvedare short compared with a wavelength Ao (Ao = velocity of light/frequency),the time delay is not significant. As the frequency is raised to a point wherethe wavelength is no longer large compared with the circuit dimensions,propagation effects can no longer be ignored. A further effect is the greatrelative increase in the impedance of connecting leads, terminals, etc., andthe effect of distributed (stray) capacitance and inductance. In addition,currents circulating in unshielded circuits comparable in size with a wave-length are very effective in radiating electromagnetic waves. The net effectof all this is to make most conventional low-frequency circuit elements andcircuits hopelessly inadequate at microwave frequencies.

If a rather general viewpoint is adopted, one may classify resistors,inductors, and capacitors as elements that dissipate electric energy, storemagnetic energy, and store electric energy, respectively. The fact that suchelements have the form encountered in practice, e.g., a coil of wire for aninductor, is incidental to the function they perform. The construction usedin practical elements may be considered just a convenient way to build thesedevices so that they will exhibit the desired electrical properties. As is wellknown, many of these circuit elements do not behave in the desired mannerat high frequencies. For example, a coil of wire may be an excellent inductorat 1 MHz, but at 50 MHz it may be an equally good capacitor because of thepredominating effect of interturn capacitance. Even though practical low-frequency resistors, inductors, and capacitors do not function in the desiredmanner at microwave frequencies, this does not mean that such energy-dis-sipating and storage elements cannot be constructed at microv/ave frequen-cies. On the contrary, there are many equivalent inductive and capacitivedevices for use at microwave frequencies. Their geometrical form is quitedifferent, but they can be and are used for much the same purposes, such asimpedance matching, resonant circuits, etc. Perhaps the most significantelectrical difference is the generally much more involved frequency depen-dence of these equivalent inductors and capacitors at microwave frequen-cies.

Low-frequency electron tubes are also limited to a maximum usefulfrequency range bordering on the lower edge of the microwave band. Thelimitation arises mainly from the finite transit time of the electron beamfrom the cathode to the control grid. When this transit time becomescomparable with the period of the signal being amplified, the tube ceases toperform in the desired manner. Decreasing the electrode spacing permitsthese tubes to be used up to frequencies of a few thousand megahertz, butthe power output is limited and the noise characteristics are poor. Thedevelopment of new types of tubes for generation of microwave frequencieswas essential to the exploitation of this frequency band. Fortunately, severalnew principles of operation, such as velocity modulation of the electronbeam and beam interaction with slow electromagnetic waves, were discov-ered that enabled the necessary generation of microwaves to be carried out.

8 FOUNDATIONS FOR MICROWAVE ENGINEERING

Dielectricsupport

(a) id) (c)

FIGURE 1.1Some common transmission lines, (a) Two-conductor line; (6) coaxial line; (c) shielded stripline.

These fundamental principles with applications are discussed in a laterchapter.

For low-power applications microwave tubes have been largely re-placed by solid-state devices, such as transistors and negative resistancediodes. However, for high-power applications microwave tubes are stillnecessary.

One of the essential requirements in a microwave circuit is the abilityto transfer signal power from one point to another without radiation loss.This requires the transport of electomagnetic energy in the form of apropagating wave. A variety of such structures have been developed that canguide electromagnetic waves from one point to another without radiationloss. The simplest guiding structure, from an analysis point of view, is thetransmission line. Several of these, such as the open two-conductor line,coaxial line, and shielded strip line, illustrated in Fig. 1.1, are in commonuse at the lower microwave frequencies.

At the higher microwave frequencies, notably at wavelengths below10 cm, hollow-pipe waveguides, as illustrated in Fig. 1.2, are often preferredto transmission lines because of better electrical and mechanical properties.The waveguide with rectangular cross section is by far the most commontype. The circular guide is not nearly as widely used.

(a) (d)

FIGURE 1.2Some common hollow-pipe waveguides, (a) Rectangular guide; (6) circular guide; (c) ridgeguide.

(c)

INTRODUCTION

The ridge-loaded rectangular guide illustrated in Fig. 1.2c is some-times used in place of the standard rectangular guide because of betterimpedance properties and a greater bandwidth of operation, In addition tothese standard-type guides, a variety of other cross sections, e.g., elliptical,may also be used.

Another class of waveguides, of more recent origin, is surface wave-guides. An example of this type is a conducting wire coated with a thin layerof dielectric. The wire diameter is small compared with the wavelength.Along a structure of this type it is possible to guide an electromagneticwave. The wave is bound to the surface of the guide, exhibiting an ampli-tude decay that is exponential in the radial direction away from the surface,and hence is called a surface wave. Applications are mainly in the millime-ter-wavelength range since the field does extend a distance of a wavelengthor so beyond the wire, and this makes the effective guide diameter some-what large in the centimeter-wavelength range. A disadvantage of surfacewaveguides and open-conductor transmission lines is that radiation lossoccurs whenever other obstacles are brought into the vicinity of the guide.

The development of solid-state active devices, such as bipolar transis-tors and, more notably, field-effect transistors (FET), has had a dramaticimpact on the microwave engineering field. With the availability of mi-crowave transistors, the focus on waveguides and waveguide componentschanged to a focus on planar transmission-line structures, such as mi-crostrip lines and coplanar transmission lines. These structures, shown inFig. 1.3, can be manufactured using printed-circuit techniques. They arecompatible with solid-state devices in that it is easy to connect a transistorto a microstrip circuit but difficult to incorporate it as part of a waveguidecircuit. By using gallium-arsenide material it has been possible to designfield-effect transistors that provide low noise and useful amplification atmillimeter wavelengths. At the lower microwave frequencies hybrid inte-grated microwave circuits are used. In hybrid circuit construction thetransmission lines and transmission-line components, such as matchingelements, are manufactured first and then the solid-state devices, such asdiodes and transistors, are soldered into place. The current trend is towardthe use of monolithic microwave integrated circuits (MMIC) in which boththe transmission-line circuits and active devices are fabricated on a singlechip. A variety of broadband MMIC amplifiers have been designed. Thedevelopment of MMIC circuits for operation at frequencies up to 100 GHz iswell under way.

A unique property of the transmission line is that a satisfactoryanalysis of its properties may be carried out by treating it as a network withdistributed parameters and solving for the voltage and current waves thatmay propagate along the line. Other waveguides, although they have severalproperties similar to transmission lines, must be treated as electromagneticboundary-value problems, and a solution for the electromagnetic fields mustbe determined. Fortunately, this is readily accomplished for the common

1 0 FOUNDATIONS FOR MICROWAVE ENGINEERING

Ground plane

(a)

(b)

FIGURE 1.3(a) microstrip transmission line; (6) coplanar transmission line.

waveguides used in practice. For waveguides it is not possible to defineunique voltage and current that have the same significance as for a trans-mission line. This is one of the reasons why the field point of view isemphasized at microwave frequencies.

Associated with waveguides are a number of interesting problemsrelated to methods of exciting fields in guides and methods of couplingenergy out. Three basic coupling methods are used: (1) probe coupling, (2)loop coupling, and (3) aperture coupling between adjacent guides. They areillustrated in Fig. 1.4, and some of them are analyzed later. These coupling

[a) (c)

FIGURE 1.4Basic methods of coupling energy into and out of waveguides, (a) Probe coupling; (6) loopcoupling; (c) aperture coupling.

INTRODUCTION 1 1

FIGURE 1.5Waveguide-to-coaxial-line transitions that use probe coupling as shown in Fig. 1.4a. (Photo-graph courtesy of Ray Moskaluk, Hewlett Packard Company.)

devices are actually small antennas that radiate into the waveguide. Aphotograph of a waveguide-to-coaxial-line transition is shown in Fig. 1.5.

Inductive and capacitive elements take a variety of forms at microwavefrequencies. Perhaps the simplest are short-circuited sections of transmis-sion line and waveguide. These exhibit a range of susceptance values fromminus to plus infinity, depending on the length of the line, and hence mayact as either inductive or capactive elements. They may be connected aseither series or shunt elements, as illustrated in Fig. 1.6. They are com-monly referred to as stubs and are widely used as impedance-matchingelements. In a rectangular guide thin conducting windows, or diaphragms,as illustrated in Fig. 1.7, also act as shunt susceptive elements. Their

ia) [b) Ic)

FIGURE 1.6Stub-type reactive elements, (a) Series element; (b) shunt element; (c) waveguide stub.

1 2 FOUNDATIONS FOR MICROWAVE ENGINEERING

(a) U>)

FIGURE 1.7Shunt susceptive elements in a waveguide,(a) Inductive window; (6) capacitive win-dow.

FIGURE 1.8Cylindrical cavity aperture coupled to arectangular waveguide.

inductive or capacitive nature depends on whether there is more magneticenergy or electric energy stored in local fringing fields.

Resonant circuits are used both at low frequencies and at microwavefrequencies to control the frequency of an oscillator and for frequencyfiltering. At low frequencies this function is performed by an inductor andcapacitor in a series or parallel combination. Resonance occurs when thereare equal average amounts of electric and magnetic energy stored. Thisenergy oscillates back and forth between the magnetic field around theinductor and the electric field between the capacitor plates. At microwavefrequencies the LC circuit may be replaced by a closed conducting enclo-sure, or cavity. The electric and magnetic energy is stored in the field withinthe cavity. At an infinite number of specific frequencies, the resonantfrequencies, there are equal average amounts of electric and magneticenergy stored in the cavity volume. In the vicinity of any one resonantfrequency, the input impedance to the cavity has the same properties as fora conventional LC resonant circuit. One significant feature worth noting isthe very much larger Q values that may be obtained, these being often inexcess of 104, as compared with those obtainable from low-frequency LCcircuits. Figure 1.8 illustrates a cylindrical cavity that is aperture coupled toa rectangular waveguide. Figure 1.9 is a photograph of a family of wave-guide low-pass filters. The theory and design of microwave filters is given inChap. 8. A photograph of a family of waveguide directional couplers isshown in Fig. 1.10. The design of directional couplers is covered in Chap. 6.The photograph in Fig. 1.11 shows a family of coaxial-line GaAs diodedetectors.

When a number of microwave devices are connected by means ofsections of transmission lines or waveguides, we obtain a microwave circuit.The analysis of the behavior of such circuits is carried out either in terms ofequivalent transmission-line voltage and current waves or in terms of theamplitudes of the propagating waves. The first approach leads to an equiva-lent-impedance description, and the second emphasizes the wave nature ofthe fields and results in a scattering-matrix formulation. Both approachesare used in this book. Since transmission-line circuit analysis forms thebasis, either directly or by analogy, for the analysis of all microwave circuits,

FIGURE 1.9A family of waveguide low-pass filters for various microwave frequency bands. (Photographscourtesy of Ray Moskaluk, Hewlett Packard Company.)

FIGURE 1.10A family of waveguide directional couplers for various microwave frequency bands. (Photo-graphs courtesy of Ray Moskaluk, Hewlett Packard Company.)

13

1 4 FOUNDATIONS FOR MICROWAVE ENGINEERING

FIGURE 1.11Coaxial-line GaAs diode detectors for variousmicrowave frequency bands. (Photographscourtesy of Ray Moskaluk, Hewlett PoxkardCompany.)

a considerable amount of attention is devoted to a fairly complete treatmentof this subject early in the text. This material, together with the fieldanalysis of the waves that may propagate along waveguides and that mayexist in cavities, represents a major portion of the theory with which themicrowave engineer must be familiar.

The microwave systems engineer must also have some understandingof the principles of operation of various microwave tubes, such as klystrons,magnetrons, and traveling-wave tubes, and of the newer solid-state devices,such as masers, parametric amplifiers, and microwave transistors. This isrequired in order to make intelligent selection and proper use of thesedevices. In the text sufficient work is done to provide for this minimum levelof knowledge of the principles involved. A treatment that is fully adequatefor the device designer is very much outside the scope of this book.

Solid-state oscillators for use as local oscillators in receiver front endshave largely replaced the klystron. Solid-state oscillators for low-powertransmitters are also finding widespread use. Thus the future for microwaveengineering is clearly in the direction of integrated solid-state circuits andthe development of the necessary passive components needed in thesecircuits, which are also compatible with the fabrication methods that areused.

In the light of the foregoing discussion, it should now be apparent thatthe study of microwave engineering should include, among other things, atleast the following:

1. Electromagnetic theory2. Wave solutions for transmission lines and waveguides3. Transmission-line and waveguide circuit analysis4. Resonators and slow-wave structures5. Microwave oscillators and amplifiers6. Antennas7. Microwave propagation8. Systems considerations

INTRODUCTION 15

FIGURE 1.12A microwave network analyzerused to measure scattering ma-trix parameters. (Photographscourtesy of Ray Moskaluk,Hewlett Packard Company.)

Apart from the last three, these are the major topics covered in the text. Itis not possible to discuss in any great detail more than a few of the manymicrowave devices available and in current use. Therefore only a selectednumber of them are analyzed, to provide illustrative examples for the basictheory being developed. The available technical literature may be, andshould be, consulted for information on devices not included here. Appropri-ate references are given throughout the text.

The number of topics treated in this text represents a good deal morethan can be covered in a one-semester course. However, rather than limitthe depth of treatment, it was decided to separate some of the morespecialized analytical treatments of particular topics from the less analyticaldiscussion. These specialized sections are marked with a star, and can beeliminated in a first reading without significantly interrupting the continu-ity of the text.f The student or engineer interested in the design ofmicrowave devices, or in a fuller understanding of various aspects of mi-crowave theory, is advised to read these special sections.

As in any engineering field, measurements are of great importance inproviding the link between theory and practice at microwave frequencies.

tProblems based on material in these sections are also marked by a star.

REFERENCES

1 6 FOUNDATIONS FOR MICROWAVE ENGINEERING

Space does not permit inclusion of the subject of microwave measurementsin this text. A number of excellent texts devoted entirely to microwavemeasurements are available, and the reader is referred to them.

There are a variety of commercially available instruments that enablemicrowave measurements to be carried out automatically with computercontrol. The photograph in Fig. 1.12 shows a network analyzer equipped tomeasure the scattering-matrix parameters of a microwave device. The scat-tering-matrix parameters, as a function of frequency, can be displayed on aSmith chart. The scattering-matrix parameters are commonly used in placeof the usual impedance and admittance parameters to characterize a mi-crowave device and are described in Chap. 4.

1. Historical Perspectives of Microwave Technology, IEEE Trans., vol. MTT-32, September,1984, Special Centennial Issue.

2. Kraus, J. D.: "Antennas," 2nd ed., McGraw-Hill Book Company, New York, 1988.3. Collin, R. E.: "Antennas and Radiowave Propagation," McGraw-Hill Book Company, New

York, 1985.4. Stutzman, W. L., and G. A. Thiele: "Antenna Theory and Design," John Wiley & Sons,

Inc., New York, 1981.5. Elliott, R. S.: "Antenna Theory and Design," Prentice-Hall, Inc., Englewood Cliffs, N.J.,

1981.6. Balanis, C. A.: "Antenna Theory, Analysis, and Design," Harper & Row Publishers, Inc.,

New York, 1982.7. Pratt, T., and C. W. Bostian: "Satellite Communications," John Wiley & Sons, New York,

1986.8. Ivanek, F. (ed.): "Terrestrial Digital Microwave Communications," Artech House Books,

Norwood, Mass., 1989.9. Skolnik, M. I.: "Introduction to Radar Systems," McGraw-Hill Book Company, New York,

1962.10. Montgomery, C. G.: "Technique of Microwave Measurements," McGraw-Hill Book Com-

pany, New York, 1947.11. Ginzton, E. L.: "Microwave Measurements," McGraw-Hill Book Company, New York,

1957.12. Bailey, A. E. (ed.): "Microwave Measurement," Peter Peregrinus, London, 1985.13. Okress, E. C: "Microwave Power Engineering," Academic Press, New York, 1968.14. Ulaby, F. T., R. K. Moore, and A. K. Fung: "Microwave Remote Sensing: Active and

Passive. Microwave Remote Sensing, Fundamentals and Radiometry," vol. 1, Addison-Wesley, Reading, Mass., 1981.