FRENZEL SUMMARY

CHAPTER10MicrowaveT echniques1. Microwaves are radio signals in the frequencyrange from I to 300 GHz.

2. The RF spectrum below UHF is mostly already fully occupied leaving little or no room for the growth of new radio services.

3. At microwave frequencies, tremendous bandwidth is available for new radio services as well as for wide-bandwidth signalssuch as TV, multiplexedsignals, or computer data.

4. The microwave frequencies are used primarily for telephone communications, radar, and satellite communications.

5. Other microwave applications include cable TV, space communications, radioastronomy, and heating.

6. The primary benefit of microwaves is wide bandwidth availability .

7. Themain disadvantagesofmicrowaves arethattheyare limitedtoline-of-sighttransmissiondistances, conventional components are not usable, and circuits are more difficult toanalyze and design.

8. The allocation of the RF spectrum is handled by the Federal Communications Commission (FCC) in the UnitedStates.

9. Balanced transmission line is not used for microwaves because of radiation losses. Coaxial cable is not usedbecause of its high attenuation.

10. The preferredtransmission line for microwaves is waveguides.

11. Because of the short physical length of transmission lines at microwave frequencies, quarter- and halfwave lines are commonly used for tuned circuits andfilters.

12. T wo printed circuit board implementations of transmission lines, called stripline and microstrip, are widely usedto create resonant circuitsandfilters.

13. A waveguide is a hollow metal pipe with a circular or rectangular cross section used for carrying microwave signalsfrom one place to another .

14. Awaveguide actslik eahigh-passfilter,passingall frequenciesabove itscut-offrequencyandrejecting those below it.

15. The cutofffrequency fco of awaveguide depends upon itsphysicalsize. For a rectangular waveguide, it is 300/2a. Whereas the wide dimension of the waveguide in meters.

16. The microwave signal carried by a waveguide is made up of electric (E) and magnetic (H) fields that bounce off the walls of the waveguide as they propagate along its length.

17. The modes of a waveguide describe the various patterns of electric and magnetic fields that are possible.

18. A transverse electric (TE) mode is one where the electric field is transverse or perpendicular to the direction of propagation.

19. A transverse magnetic (TM) mode is one where the magnetic field is perpendicular to the direction ofpropagation. 20. Waveguides are available in standard lengths and sizes, and special pieces are used for right-angle bends and 90° twists.21. Half-wavelength sections of waveguides with shorted or closed ends are known as resonant cavities since they "ring" or oscillate at the frequency determinedby their dimensions.

22. Cavity resonators are metallic chambers of various shapes and sizes that are used as parallel-tunedcircuits and filters. They have a Q of upto 30,000.

23. Point-contact and Schottky or hot-carrier diodes are widely uses as mixers in microwave equipment as they have low capacitance andinductance.

24. Varactor diodes are widely used as microwave frequency multipliers. Multiplication factors of 2 and 3are common with power levels up to 20Wand efficiencies up to80 percent.

25. Step-recovery or snap-off diodes are also widely used as frequency multipliers with multiplication factors upto 10, power ratings up to 50W.and efficiencies approaching80 percent.

26. A Gunn diode is a microwave semiconductor device used to generate microwave energy . When combined with a microstrip, stripline or resonant cavity, simple low power oscillators with frequencies up to 50GHz are easily implemented.

27. Both I MPAT T and T RA PAT T diodes are GaAs devices operated with high reverse bias to produceavalanche breakdown. Bothare used in microwave oscillators.

28. A klystron is a vacuum tube usedfor microwave amplificationand oscillation.

29. Klystrons use a cavity resonat or to velocity modulate an electron beam which imparts energy toanother cavity, producing power amplification. Klystrons are available which produce from a few to many thousandsof watts.

30. A single-cavity reflex klystron is used as a microwave oscillator .

31. Klystrons are being gradually replaced by Gunn diodes and traveling-wave tubes.

32. A magnetron is a diode vacuum tube used as a microwave oscillator in radar and microwave ovens toproduce powers upto the megawattrange.

33. In a magnetron, a strong magnetic field creates circular paths of electron flow to excite cavities into oscillation.

34. A traveling-wave tube (T WT ) is a microwave power amplifier with very wide bandwidth.

35. Amicrowave signal applied toahelix around the T WT produces velocityanddensity modulation of the electronbeam over a long distance which induces a higher -power signal in the helix.

36. The most commonly used microwave antenna is the horn,which is essentiallyarectangularwaveguidewith a flared end. 37. A pyramidal horn flares in both waveguide dimensions. A sectoral horn flares in only one dimension.

38. Horn antennas are directional and produce a beam width in the 10° to 60° range with a gain in the 10-to 20-dB range, depending upon dimensions.

39. A parabolic or dish-shaped reflector is used with most microwave antennas to focus the RF energy intoa narrow beam and increase gain.40. The parabolic reflector usually has a diameter that is no less than 10 wavelengths at the operatingfrequency .

41. The gainanddirectivity of a parabolic reflectorantenna is directly proportional to its diameter .

42. Parabolic reflector antennas are fed by placing a horn antenna at the focal point or by placing the horn at the center

of the reflector and placing a small reflector at the focal point. The latter is known as Cassegrain feed.

43. Ahelical antennais madeup of sixto eight turnsofheavywireortubing to form a coilorhelix.It isfed with coaxand is backed upwith a reflector .

44. Helical antennasare used at UHF and microwave frequencies and have a gain in the 12- to 20-dB range and a beamwidth in the 12° to 45° range.

45. Helical antennas produce circular polarization where the electric and magnetic fields rotate. The polarization may be right-handor left-hand depending uponthe direction in which the helix is wound. 46. Helical antennas can receive either vertically or horizontally polarized signals but can only receive a circularly polarized signal of the same direction.

47. A popular omnidirectional microwave antennais the bicone.

SELF- TESTSupplythe missing word(s) in each statement.Choose the letter that best answers each question.1. Microwaves are frequencies above _____ GHz,

1. 12. The mainadvantage ofmicrowaves is that more of the _____ is available for signals.

2. bandwidth or spectrum3. List seven reasons whymicrowaves are more difficult to work withthan lower frequency signals.

3. more difficultto analyze; different measurement techniques; resistors, capacitors, andinductors actlik e LCR circuits; conventional semiconductors do not work owing tointernal capacitances and longtransit time; special, expensive vacuum tubes are used for power amplification; line-of-sighttransmission differences; excessive signal reflection and absorption

4. The applications most commonly found in the microwave region are _____ and _____.

4. telephone, radar5. List four popular uses for microwaves.

5. television signal relay, space communications, radiotelescopes, microwave heating

6. The government agency that regulates radio communicationsin the United States is the _____.

6. Federal CommunicationsCommission7. Name fourtechniques that have helped squeeze more signals intothe givenspectrum.

7. improved receiver selectivity, SSB, multiplexing, reduced FM deviation

8. T wo reasonswhy conventional transistors won't work atmicrowave frequencies are _____ and _____.

8. internal capacitance, long transit time9. At microwave frequencies, conventional components like resistors, capacitors, and inductors act like_____ circuits.

9. LCR10. The TV channels 2 to 13 occupy a total bandwidth of about 72 MHz. At a frequency of 200 MHz, this representsa bandwidth of _____ percent ofthe spectrum space. At 2 GHz, it represents _____ percent.

10. 36, 3.611. T rue or false. T win leadis not used at microwave frequencies.

11. true

12. The maindisadvantage of using coax for microwave signalsis its high _____.

12. attenuation13. Coax is notused beyond frequencies of about _____ GHz.

13. 614. A hollow metal pipe used tocarry microwaves is called a(n) _____.14. waveguide15. T wo types of transmission line made of PCB material used to produce tuned circuits and filters are_____.15. microstrip, stripline16. The two ways to couple or extractenergy from a waveguide are by using a _____ or a _____.

16. probe, loop

17. A waveguide acts as a(n) _____ filter .17. high-pass

18. A rectangular waveguide has a width of 1.2 in. and a height of 0.7 in. The waveguide will pass allsignals above _____ GHz.

18. 4.92119. A waveguide has a cutoff frequency of 5 GHz.

a. T rue or false. It will passa signal of 8 GHz. b. T rue or false. It will passa signal of 3 GHz.19. (a) true, (b) false

20. The magnetic and electric fields in a waveguide are designated by the letters _____ and _____,respectively .

20. H, E21. The basic operatingmode of mostwaveguides is designated _____.

21.TEO,122. If the H field in the waveguide is perpendicular to the direction of signal travel, the mode is said to be _____.

22. transverse magnetic23. A one-half wavelength section of waveguide shorted at both endscreates a(n) _____.

23. cavityresonator24. A cavity resonator actsas a(n) _____ circuit.

24. parallel resonant25. Resonant cavities are used as _____.

25. tuned circuits, filters26. Mechanically varyingthe cavity's dimensions allows its _____.

26. resonant frequency27. List three reasons why conventional diodes andtransistors do not work in the microwave region. 27. high capacitance, highinductance, long transit time28. A point-contactdiode has a(n) _____ anode and a(n) _____ cathode.

28. P-type silicon, tungsten whisker29. A microwave diode with an N-type silicon cathode and a metal anode forming a junction is called a(n)_____ diode.

29. Schottky barrier, or hotcarrier30. The mostcommon application of microwave signal diodes is in _____ circuits.

30. mixer31. A diode thatacts lik e a V V C is a(n) _____ diode.

31. varactor32. T wo types of diodes widely used asfrequency multipliers are the _____ and _____ diodes.

32. varactor, snap-off or step-recovery diode33. A diode with no junction that is widely used with a cavity resonator to form an oscillator is the_____diode.

33. Gunn34. The _____, _____, and _____ diodes are also usedas oscillators.

34. IMP A TT, TRAPATT, tunnel35. Microwave diodes that cause a current decrease for a voltage increase have what is known as a(n)_____ characteristic.

35. negative resistance36. An IMPA TT diode operates with_____ (forward, reverse) bias.

36. reverse37. A tunnel diode operates with _____ (forward, reverse) bias.

37. forward38. T rue or false. Klystrons can be used as amplifiers or oscillators.

38. true39. T rue or false. A magnetron operates as an amplifier .

39. false40. A T WT is an _____ (amplifier, oscillator).

40. amplifier41. The operating frequencyof klystrons and magnetronsis determinedby _____.

41. cavityresonators42. The cavities in a klystron produce _____ modulation of the electron beam.

42. velocity43. In a klystron amplifier, the input is applied to the _____ cavity and the output taken from the _____cavity .

43. buncher, catcher44. A one-cavity klystron that oscillates is knownas a(n) _____ klystron.

44. reflex45. Low-power klystronsare being replaced by _____, and high-power klystrons are being replaced by _____.

45. Gunn diodes, TWT s46. A(n) _____ causes the electrons in a magnetron totravel in circular paths.

46. permanentmagnet47. T wo major applications of magnetrons are in _____.

47. radar, microwave ovens48. The T WT is a microwave _____.

48. amplifier49. Density modulation of the electron beamin a T WT is produced by a(n) _____.

49. helix50. The major benefit of a T WT is its wide _____.

50. bandwidth51. The mostcommonly used microwave antenna is the _____ antenna.

51. horn52. Increasing the length of a horn antenna causes its gain to _____ andits beam width to_____.

52. increase, decrease53. A hornantenna is six wavelengths long at 8 GHz. That lengthis _____ in.

53. 11.854. The beam width of a horn antenna is usually in the _____ to degree _____ range. ,

54. 10, 6055. The width of a horn antenna is 8 cm. The height is 6 cm. The operating frequency is 8 GHz. The beamangle is _____ degrees. The gain is _____ dB. Assume k = 0.5.

55. 37.5, 13.356. Horn antennas have _____ (narrow, wide) bandwidth.

56. wide57. The geometric shape ofa microwave reflector is a(n) _____.

57. parabola58. In order for a dish, reflector to work, the antennamust be located atthe _____ of the dish.

58. focal point59. The antenna usedwith a dish reflector is usually a(n)_____.

59. horn60. A parabolic reflector antenna has a diameter of 9 m. The frequency of operation is 8 GHz. The gain is_____ dB. The beam width is _____ °.

60. 55.39, 0.24261. The effect of a parabolic reflectoron an antennais to _____ gainand_____ beam width.

61. increase, decrease62. A dish with a horn at its center and a small reflectorat the focal pointis saidto use _____ feed.

62. Cassegrain63. The benefits of a helical antenna are its _____ and _____.

63. simplicity, low cost64. The gainof a helical antenna is typically in the _____ to _____ –dB range.

64. 12, 2065. The beam width of a helical antenna is in the _____ to _____ degree range.

65. 12, 4566. The helical antenna radiates a(n) _____ polarized wave.

66. circularly67. The acronym R H C P means _____.

67. right-handcircularpolarization68. A popular omni directional microwave antenna is the _____.

68. bicone69. T rue or false. A helical antenna will receive either vertical or horizontally polarized signals.

69. true70. T rue or false. An R H C P antenna canreceive a signal froman L H C P antenna.

70. false

FRENZELChapter 10: Microwave Techniques 1. The main benefit of using microwaves is

Ans: More spectrum space2. Radio communications are regulated in the United States by the

Ans: Federal Communications Commission 3. Which of the following is not a disadvantage of microwaves?

Ans: higher-cost equipment 4. Which of the following is a microwave frequency

Ans: 22 GHz 5. Which of the following is not a common microwave application?

Ans: mobile radio 6. Coaxial cable is not widely used for long microwave transmission lines because of its

Ans: high loss 7. Stripline and microstrip transmission lines are usually made with

Ans: PCBs 8. The most common cross section of a wave guide is a

Ans: rectangular 9. A rectangular waveguide has a width of 1 in. and a height of 0.6 in. Its cutoff frequency is

Solution: 1 in = 0.0254 m

10. A waveguide has a cutoff frequency of 17 GHz. Which of the signals will not be passed by the waveguide?

Ans: 15 GHz 11. Signal propagation in a waveguide is by

Ans: Electric and magnetic fields 12. When the electric field in a waveguide is perpendicular to the direction of wave propagation, the mode is said to be Ans: Transverse electric 13. The dominant mode in most waveguides is

Ans: TE0,114. A magnetic field is introduced into a waveguide by a

Ans: Probe 15. A half-wavelength, closed section of a waveguide that acts as a parallel resonant circuit is known as a(n)

Ans: Cavity resonator 16. Decreasing the volume of a cavity causes its resonant frequency to

Ans: Increase 17. A popular microwave mixer diode is the

Ans: Gunn 18. Varactor and step-recovery diodes are widely used in what type of circuit

Ans: Frequency multiplier 19. Which diode is a popular microwave oscillator

Ans: Gunn 20. Which type of diode does not ordinarily operate with reverse bias

Ans: Tunnel 21. Low-power Gunn diodes are replacing

Ans: Reflex klystrons 22. Which of the following is not a microwave tube?

Ans: Cathode-ray tube 23. In a klystron amplifier, velocity modulation of the electron beam is produced by the

Ans: Buncher cavity 24. A reflex klystron is used as a(n)

Ans: Oscillator 25. For proper operation, a magnetron must be accompanied by a

Ans: Permanent magnet 26. The operating frequency of klystrons and magnetrons is set by the

Ans: Cavity resonator 27. A magnetron is used only as a(n)

Ans: oscillator 28. A common application for magnetrons is in

Ans: Radar29. In a TWT, the electron beam is densitymodulated by a

Ans: Helix 30. The main advantage of a TWT over a klystron for microwave amplification is

Ans: Wider bandwidth 31. High-power TWTs are replacing what in microwave amplifiers?

Ans: klystrons 32. The most widely used microwave antenna is a

Ans: horn antenna 33. What happens when a horn antenna is made longer?

Ans: Gain increases 34. A pyramidal horn used at 5 GHz has an aperture that is 7 by 9 cm. The gain is about

35. Given the frequency and dimensions in Question 34 above the beamwidth is about

36. The diameter of a parabolic reflector should be at least how many wavelengths at the operating frequency?

Ans: 10 37. The point where the antenna is mounted with respect to the parabolic reflector is called

Ans: Focal point 38. Using a small reflector to beam waves to the larger parabolic reflector is known as

Ans: Cassegrain feed 39. Increasing the diameter of a parabolic reflector causes which of the following

Ans: Decreasing beamwidth and increasing gain 40. A helical antenna is made up of a coil and a

Ans: Reflector 41. The output of a helical antenna is

Ans: Circularly polarized 42. A common omnidirectional microwave antenna is the

Ans: Bicone

MILLERChapter 15 Microwaves & Lasers 1 Which is not a type of horn antenna design for microwave frequencies?

a. Parabolic horn b. Circular horn c. Pyramidal horn d. Sectoral horn

2 Cassegrain feed to a paraboloid antenna involves a a. Dipole antenna b. Point-source antenna c. Secondary reflector d. Any of the above

3 Calculate the beamwidth of a microwave dish antenna with a 6-m mouth diameter when used at 5 Ghz.

a. 0.49° b. 4.9° c. 7° d. 0.7°

4 Zoning refers to a. A method of producing a radome b. Changing a spherical wavefront into a plane wave c. Creating a polar radiation pattern d. Fading into nonreality

5 Which microwave oscillator has high gain, low-noise characteristics, and wide bandwidth?

a. Traveling wave tube oscillator b. Gunn Oscillator

c.Klystron oscillator d. Magnetron oscillator

6 Which is not an advantage of the Gunn gallium arsenide oscillator?

a. Ease of removing heat from the chip b. Small size c. Ruggedness d. Lack of filaments e. Low cost of manufacture

7 The i in P-I-N diode refers to a. Indium b. Impact c. Integrated d. Intrinsic

8 Which is not a typical application of a ferrite in a microwave system?

a. attenuator b. amplifier c. isolator d. circulator

9 A low noise microwave amplifier that provides amplification via the variation of a reactance is known as a

a. Maser b. Laser c. Yig d. Parametric amplifier

10 The major difference between a laser and a maser isthe a. Frequency of the signal being amplified b. Amplitude of the signal being amplified c. Bandwidth of the signal being amplified d. Phase of the signal being amplified

11 Lasers are useful in a. Industrial welding b. Surgical procedures c. Distance measuring d. Compact disc players e. All the above

12 The following semiconductor is not used as a microwave device:

a. PIN diode b. Baritt diode c. Zener diode d. Tunnel diode

13 Which of the following represent typical failure mode(s) for a TWT amplifier?

a. Low gain b. Spurious modulation c. Poor frequency response d. Low RF output e. All the above

14 Which of the following is not used as a microwave antenna? a. Patch antenna b. Marconi antenna c. Lens antenna d. Horn antenna

15 Compared to linear power supplies, switching power supplies are

a. Less efficient b. More efficient c. Simpler d. Heavier

BLAKEChapter 17: Microwave DevicesMULTIPLE CHOICE1. The microwave frequency range is considered to start at:

a. 100 MHz c. 10 GHzb. 1 GHz d. 100 GHz

2. The UHF range is: a. below the microwave range c. above the microwave range b. inside the microwave range d. same as the microwave range3. The dominant mode of a waveguide depends on: a. the shape of the waveguide c. the point of signal injection b. the power level of the signal d. none of the above4. The dominant mode of a rectangular waveguide is: a. TE 01 c. TE 10 b. TM 01 d. TM105. The dominant mode of a circular waveguide is: a. TE 01 c. TE 11 b. TM 01 d. TM116. Circular waveguides use TM 01 mode because: a. it is dominant c. it is the only mode possible b. of its circular symmetry d. it is more efficient7. The characteristic impedance of a waveguide: a. is fixed b. depends on the frequency it carries c. depends on the longer dimension of its cross section d. both b and c8. Power can be coupled into or out of a waveguide: a. with a magnetic field probe c. through a hole in the waveguide b. with an electric field probe d. all of the above

9. Directional couplers for waveguides are characterized by: a. their insertion loss c. their directivity b. their coupling specification d. all of the above10. Striplines and microstrips are used to: a. couple sections of waveguide c. couple components on a circuit board b. couple waveguides to antennas d. none of the above11. A resonant cavity is a type of: a. tuned circuit c. antenna b. defect in a waveguide d. none of the above12. A TEE connector used with waveguides is: a. an H-plane TEE c. a "magic" TEE b. an E-plane TEE d. all of the above13. TWT stands for: a. Transverse Wave Transmission c. Traveling-Wave Tube b. Transverse-Wave Tube d. Traveling-Wave Transmission14. An "isolator" is a device that: a. isolates frequencies in a waveguide b. allows a signal to pass in one direction only c. separates signals among various ports d. prevents microwaves from leaking out of a waveguide15. A "circulator" is a device that: a. rotates signal polarity in a waveguide b. allows a signal to pass in one direction only c. separates signals among various ports d. prevents microwaves from being "trapped" in a waveguide16. GaAs stands for: a. gallium arsenide c. gallium astenite b. gallium assembly d. none of the above17. IMPATT stands for: a. impact avalanche and transit time c. implied power at transmission terminal b. induced mobility at transmission time d. none of the above18. YIG stands for: a. Yttrium-Iron-Gallium c. Yttrium-Iron-Garnet b. Yttrium-Iron-Germanium d. none of the above19. A YIG can be tuned by applying: a. an electric field c. mechanical pressure b. a magnetic field d. an "exciter" signal20. The device commonly used in microwave ovens is the: a. TWT c. magnetron b. klystron d. YIG21. The device commonly used in satellite communications is the: a. TWT c. magnetron b. klystron d. YIG22. The device commonly used in UHF transmitters is the: a. TWT c. magnetron b. klystron d. YIG23. A microwave phased array is often made using: a. slots c. Fresnel lenses b. Yagis d. all of the above24. RADAR stands for: a. radio ranging c. radio detection and ranging b. radio depth and ranging d. remote detection and ranging25. RADAR uses: a. pulsed transmission c. the Doppler effect b. continuous transmission d. all of the above26. The maximum effective range for pulsed radar: a. increases with increasing repetition rate c. decreases with increasing pulse period b. decreases with increasing repetition rate d. none of the above27. The minimum effective range for pulsed radar: a. increases with increasing pulse duration c. is always a tenth of the maximum range b. decreases with increasing pulse duration d. none of the above

COMPLETION1. ____________________ is the effect of a pulse "spreading out" as it travels through a waveguide.

ANS: Dispersion2. The electric field is ____________________ along the walls of a rectangular waveguide.

ANS: zero3. The waveguide mode with the lowest cutoff frequency is the ____________________ mode.

ANS: dominant

4. In TE10 mode, the ____________________ field peaks in the middle of the waveguide cross section.

ANS: electric5. In TE20 mode, the electric field has ____________________ peaks in the waveguide cross section.

ANS: two6. In a circular waveguide, ____________________ mode is used because of its circular symmetry.

ANS: TM017. A waveguide acts as a ____________________-pass filter.

ANS: high8. In a waveguide, group velocity is always ____________________ than the speed of light.

ANS: slower9. In a waveguide, phase velocity is always ____________________ than the speed of light.

ANS: faster10. In a waveguide, impedance ____________________ as frequency increases.

ANS: decreases11. A ____________________ TEE is a combination of E-plane and H-plane TEES.

ANS: hybrid12. The Q of a resonant cavity is very ____________________ compared to lumped LC circuits.

ANS: high13. A wavemeter is a resonant ____________________ with an adjustable plunger.

ANS: cavity14. A Gunn device oscillates because of its negative ____________________.

ANS: resistance15. Both magnetrons and TWTs are slow ____________________ tubes.

ANS: wave16. Both klystrons and TWTs are ____________________-beam tubes.

ANS: linear17. A ____________________ antenna is just a waveguide with a hole in it.

ANS: slot18. A ____________________ antenna is a flat piece of copper on an insulating substrate with a groundplane on the other side.

ANS: patch19. The radar cross section of a target is typically ____________________ than its actual size.

ANS: smaller20. The frequency of the returned signal will be ____________________ than the transmitted signal if thetarget is moving toward the radar antenna.

ANS: higher

SHORT ANSWER1. Calculate the TE10 cutoff frequency for a rectangular waveguide if the longer dimension of its cross section is 5 cm.

ANS: 3 GHz2. Calculate the group velocity in a waveguide carrying a signal that is twice its cutoff frequency.

ANS: 260 x 106 meters per second3. Calculate the phase velocity in a waveguide carrying a signal that is twice its cutoff frequency.

ANS: 346 x 106 meters per second4. Calculate the wavelength of a 2-GHz signal in a waveguide with a 1-GHz cutoff frequency.

ANS: 173 millimeters5. Find the gain in dBi of a 10-GHz horn antenna with dE= dH= 60 mm.

ANS: 14.86. Find the maximum unambiguous range for a pulsed radar sending 10k pulses per second.

ANS: 15 km7. Find the minimum unambiguous range for a pulsed radar sending 2-msec duration pulses.

ANS: 300 meters