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NEETS 11 : MICROWAVE PRINCIPLES Flashcards

1
Q

What is the region of the frequency spectrum from 1000

MHz to 100,000 MHz called?

A

Microwave region

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2
Q

Microwave theory is based upon what concept

A

Electromagnetic field theory

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3
Q

Why are coaxial lines more efficient at microwave

frequencies than two-wire transmission lines?

A

The electromagnetic fields are completely confined

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4
Q

What kind of material must be used in the construction

of waveguides?

A

Conductive material

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5
Q

The large surface area of a waveguide greatly reduces
what type of loss that is common in two-wire and coaxial
lines?

A

Copper loss

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6
Q

What causes the current-carrying area at the center
conductor of a coaxial line to be restricted to a small layer
at the surface?

A

Skin effect

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7
Q

What is used as a dielectric in waveguides?

A

Air

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8
Q

What is the primary lower-frequency limitation of

waveguides?

A

Physical size

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9
Q

At very high frequencies, what characteristics are

displayed by ordinary insulators?

A

The characteristics of the dielectric of a capacitor

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10
Q

What type of insulator works well at very high

frequencies?

A

A shorted quarter-wave section called a metallic insulator

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11
Q

The frequency range of a waveguide is determined by what

dimensison?

A

The “a” dimension

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12
Q

What happens to the bus bar dimensions of the waveguide

when the frequency is increased?

A

The bus bar becomes wider

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13
Q

When the frequency is decreased so that two
quarter-wavelengths are longer than the “a” (wide)
dimension of the waveguide, what will happen?

A

Energy will no longer pass through the waveguide.

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14
Q

What interaction causes energy to travel down a

waveguide?

A

The interaction of the electric and magnetic fields

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15
Q

What is indicated by the number of arrows (closeness

of spacing) used to represent an electric field?

A

The relative strength of the field

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16
Q

What primary condition must magnetic lines of force meet

in order to exist?

A

Magnetic lines of force must form a continuous closed loop

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17
Q

What happens to the H lines between the conductors of

a coil when the conductors are close together?

A

The H lines cancel

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18
Q

For an electric field to exist at the surface of a
conductor, the field must have what angular relationship
to the conductor?

A

The field must be perpendicular to the conductors

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19
Q

When a wavefront is radiated into a waveguide, what
happens to the portions of the wavefront that do not satisfy
the boundary conditions?

A

Decrease to zero

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20
Q

Assuming the wall of a waveguide is perfectly flat, what
is the angular relationship between the angle of incidence
and the angle of reflection?

A

The angles are equal

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21
Q

What is the frequency called that produces angles of
incidence and reflection that are perpendicular to the
waveguide walls?

A

Cutoff frequency

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22
Q

Compared to the velocity of propagation of waves in air,

what is the velocity of propagation of waves in waveguides?

A

Slower

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23
Q

What term is used to identify the forward progress

velocity of wavefronts in a waveguide?

A

Group velocity

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24
Q

What term is used to identify each of the many field

configurations that can exist in waveguides?

A

Mode of operation

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25
Q

What field configuration is easiest to produce in a

given waveguide?

A

Mode of operation

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26
Q

How is the cutoff wavelength of a circular waveguide

figured?

A

1.71 times the diameter

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27
Q

The field arrangements in waveguides are divided into
what two categories to describe the various modes of
operation?

A

Transverse electric (TE) and transverse magnetic (TM)

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28
Q

The electric field is perpendicular to the “a” dimension

of a waveguide in what mode?

A

TE

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29
Q

The number of half-wave patterns in the “b” dimension
of rectangular waveguides is indicated by which of the two
descriptive subscripts?

A

Second

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30
Q

Which subscript, in circular waveguide classification,
indicates the number of full-wave patterns around the
circumference?

A

First

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31
Q

What determines the frequency, bandwidth, and

power-handling capability of a waveguide probe?

A

Size and shape

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32
Q

Loose or inefficient coupling of energy into or out of

a waveguide can be accomplished by the use of what method?

A

Slots and apertures

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33
Q

What is the result of an impedance mismatch in a

waveguide?

A

Standing waves that cause power losses, a reduction in
power-handling capability, and an increase in frequency and
sensitivity

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34
Q

What is used to construct irises?

A

Metal plates

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35
Q

An iris placed along the “b” dimension wall produces

what kind of reactance?

A

Inductive

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36
Q

How will an iris that has portions along both the “a”

and “b” dimension walls act at the resonant frequency?

A

As a shunt resistance

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37
Q

What device is used to produce a gradual change in

impedance at the end of a waveguide?

A

Horn

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38
Q

When a waveguide is terminated in a resistive load, the

load must be matched to what property of the waveguide?

A

Characteristic impedance

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39
Q

What is the primary purpose of a dummy load?

A

Absorb all energy without producing standing waves

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40
Q

The energy dissipated by a resistive load is most often

in what form?

A

Heat

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41
Q

What is the result of an abrupt change in the size,

shape, or dielectric of a waveguide?

A

Reflections

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42
Q

A waveguide bend must have what minimum radius?

A

Greater than 2 wavelengths

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43
Q

What is the most common type of waveguide join?

A

Choke joint

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44
Q

What is the most likely cause of losses in waveguide

systems?

A

Improperly connected joints or damaged inner surface

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45
Q

What is the primary purpose of a directional coupler?

A

Sampling energy within a waveguide

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46
Q

How far apart are the two holes in a simple directional

coupler?

A

1/4 wavelength

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47
Q

What is the purpose of the absorbent material in a directional coupler?

A

Absorb the energy not directed at the pick-up probe and a

portion of the overall energy

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48
Q

In a directional coupler that is designed to sample the
incident energy, what happens to the two portions of the
wavefront when they arrive at the pickup probe?

A

The wavefront portions add

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49
Q

What happens to reflected energy that enters a
directional coupler that is designed to sample incident
energy?

A

The reflected energy adds at the absorbent material and is

absorbed

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50
Q

What two variables determine the primary frequency of

a resonant cavity?

A

Size and shape of the cavity

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51
Q

Energy can be inserted or removed from a cavity by what

three methods?

A

Probes, loops, and slots

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52
Q

Inductive tuning of a resonant cavity is accomplished

by placing a nonmagnetic slug in what area?

A

The area of maximum H lines

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53
Q

What are the two basic types of T junctions?

A

E-type and H-type

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54
Q

Why is the H-type T junction so named?

A

The junction arm extends in a direction parallel to the H

lines in the main waveguide

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55
Q

The magic-T is composed of what two basic types of T

junctions?

A

E-type and H-type

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56
Q

What are the primary disadvantages of the magic-T?

A

Low power-handling capability and power losses

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57
Q

What type of junctions are formed where the arms of a

hybrid ring meet the main ring?

A

Basic E-type junctions

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58
Q

Hybrid rings are used primarily for what purpose?

A

High-power duplexes

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59
Q

Ferrite devices are useful in microwave applications

because they possess what properties?

A

Magnetic properties and high resistance

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60
Q

Which of the two types of electron motion (orbital
movement and electron spin) is more important in the
explanation of magnetism?

A

Electron spin

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61
Q

The interaction between an external field and the

binding force of an atom causes electrons to do what?

A

Wobble at a natural resonant frequency.

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62
Q

The resonant frequency of electron wobble can be changed

by variation of what force?

A

The applied magnetic field

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63
Q

Rotating the plane of polarization of a wavefront by

passing it through a ferrite device is called what?

A

Faraday rotation

64
Q

What happens to the impedance of interelectrode

capacitance as frequency increases?

A

Impedance decreases

65
Q

What undesirable effect is caused by the inductance of

the cathode lead?

A

Degenerative feedback

66
Q

How does transit time affect the relationship of the grid

voltage and the plate current at high frequencies?

A

Transit time causes the grid voltage and plate current to

be out of phase

67
Q

Moving tube electrodes apart to decrease interelectrode
capacitance causes an increase in the effect of what
property?

A

Transit time

68
Q

The kinetic energy of an electron is directly

proportional to what property?

A

Velocity

69
Q

What will be the effect upon an electron traveling in
the opposite direction to the lines of force in an
electrostatic field?

A

The electron will be accelerated

70
Q

How is a beam of electrons velocity-modulated?

A

By alternately speeding up or slowing down the electrons

71
Q

What portion of an electron gun causes the electrons to

accelerate or decelerate?

A

The buncher grids

72
Q

What is the effect upon an electron that enters the
buncher gap when the potential across the grids is at 0
volts?

A

There is no effect

73
Q

What determines the placement of the catcher cavity?

A

The frequency period of the buncher grid signal

74
Q

What is the basic principle of operation of a klystron?

A

Velocity modulation

75
Q

The electrons in the beam of a klystron are speeded up

by a high dc potential applied to what elements?

A

The accelerator grid and the buncher grids

76
Q

The two-cavity klystron uses what cavity as an output

cavity?

A

The catcher cavity

77
Q

A two-cavity klystron without a feedback path will

operate as what type of circuit?

A

Amplifier

78
Q

What can be added to the basic two-cavity klystron to
increase the amount of velocity modulation and the power
output?

A

Intermediate cavities between the input and output

cavities

79
Q

How is the electron beam of a three-cavity klystron

accelerated toward the drift tube?

A

A large negative pulse ?is applied to the cathode

80
Q

Which cavity of a three-cavity klystron causes most of

the velocity modulation

A

The middle cavity

81
Q

In a multicavity klystron, tuning all the cavities to
the same frequency has what effect on the bandwidth of the
tube?

A

The bandwidth decreases

82
Q

The cavities of a multicavity klystron are tuned to

slightly different frequencies in what method of tuning?

A

Stagger tuning

83
Q

What element of the reflex klystron replaces the output

cavity of a normal klystron?

A

The reflector or repeller

84
Q

When the repealer potential is constant, what property
of the electron determines how long it will remain in the
drift space of the reflex klystron?

A

Velocity

85
Q

The constant-speed electrons of an electron bunch in
a reflex klystron must remain in the repeller field for what
minimum time?

A

Three-quarter cycle

86
Q

If the constant-speed electrons in a reflex klystron
remain in the repeller field for 1 3/4 cycles, what is the
mode of operation?

A

Mode 2

87
Q

Debunching of the electron bunches in the higher modes
of a reflex klystron has what effect on
output power?

A

Power is reduced

88
Q

What limits the tuning range around the center frequency

of a reflex klystron in a particular mode of operation?

A

The half-power points of the mode

89
Q

What is the primary use of the twt?

A

Voltage amplification

90
Q

The magnet surrounding the body of a twt serves what

purpose?

A

Used to focus the electrons into a tight beam

91
Q

How are the input and output directional couplers in

a twt connected to the helix?

A

The directional couplers are not physically connected to

the helix

92
Q

What relationship must exist between the electron beam
and the traveling wave for bunching to occur in the electron
beam of a twt?

A

The traveling wave must have a forward velocity equal to

or less than the speed of the electrons in the beam.

93
Q

What structure in the twt delays the forward progress

of the traveling wave?

A

The helix

94
Q

The folded waveguide in a bwo serves the same purpose

as what component in a twt?

A

Helix

95
Q

What serves as a grid in a magnetron?

A

A magnetic field

96
Q

A cylindrical copper block with resonant cavities
around the circumference is used as what component of a
magnetron?

A

Anode or plate

97
Q

What controls the output frequency of a magnetron?

A

The resonant cavities

98
Q

What element in the magnetron causes the curved path

of electron flow?

A

The permanent magnet

99
Q

What is the term used to identify the amount of field
strength required to cause the electrons to just miss the
plate and return to the filament in a circular orbit?

A

The critical value of field strength

100
Q

A magnetron will produce oscillations when the

electrons follow what type of path?

A

Circular

101
Q

What is the primary difference in construction between

the basic magnetron and the negativeresistance magnetron?

A

The negative-resistance magnetron has a split plate

102
Q

What starts the oscillations in a negative-resistance

magnetron?

A

The application of the proper magnetic field

103
Q

Why is the negative-resistance magnetron often operated

with reduced filament voltage?

A

To reduce the effects of filament bombardment

104
Q

What type of electron-resonance anode block does not

require strapping?

A

Rising-sun block

105
Q

Without strapping, the resonant cavities of a

hole-and-slot anode are connected in what manner?

A

Series

106
Q

What are the electrons called that give up energy to

the ac field in a magnetron?

A

Working electrons

107
Q

Why is the pi mode the most commonly used magnetron mode

of operation?

A

Greater power output

108
Q

What two methods are used to couple energy into and out

of magnetrons?

A

Loops and slots

109
Q

Magnetron tuning by altering the surface-to-volume
ratio of the hole portion of a hole-and-slot cavity is what
type of tuning?

A

Inductive

110
Q

Capacitive tuning by inserting a ring into the cavity
slot of a magnetron is accomplished by what type of tuning
mechanism?

A

A cookie-cutter tuner

111
Q

Name the procedure used to reduce excessive arcing in

a magnetron?

A

Baking in

112
Q

What causes the negative-resistance property of tunnel

diodes?

A

The tunneling action

113
Q

What determines the frequency of a tunnel-diode

oscillator?

A

The tuned circuit or cavity frequency

114
Q

Why is the tunnel diode loosely coupled to the cavity

in a tunnel-diode oscillator?

A

To increase the stability

115
Q

What is the purpose of the circulator in a tunnel-diode

amplifier?

A

Prevent feedback to the tuned input circuit

116
Q

What limits the usefulness of high-gain, tunnel-diode

frequency converters?

A

Stability problems

117
Q

The varactor is a pn junction that acts as what type

of electronic device?

A

Variable capacitor

118
Q

The underlying principle of operation of the parametric

amplifier is based on what property?

A

Reactance

119
Q

What is the most important feature of the parametric

amplifier?

A

The low-noise characteristic

120
Q

How is amplification achieved in the circuit shown in

figure 2-43?

A

By varying the amount of capacitance in the circuit

121
Q

What is the purpose of the pump in a parametric

amplifier?

A

Supplies the electrical energy required to vary the

capacitance

122
Q

The pump signal frequency must be of what value when
compared to the input signal of a simple parametric
amplifier?

A

Exactly double the input frequency

123
Q

What is the primary difference between the pump signal
of a simple parametric amplifier and the pump signal of a
nondegenerative parametric amplifier?

A

The pump signal of a nondegenerative parametric amplifier

is higher than twice the input signal.

124
Q

In a nondegenerative parametric amplifier the
difference between the input frequency and the pump
frequency is called what?

A

Idler- or lower-sideband frequency

125
Q

What is the output frequency of an upper-sideband

parametric-frequency converter?

A

The sum of the input frequency and the pump frequency

126
Q

What is the primary advantage of bulk-effect devices

over normal pn-junction semiconductors?

A

Larger microwave power outputs

127
Q

What happens to the electrons of a gallium-arsenide
semiconductor when they move from the normal low-energy
conduction band to the high-energy conduction band?

A

The electrons become immobile

128
Q

The point on the current curve of a gallium-arsenide
semiconductor at which it begins to exhibit negative
resistance is called what?

A

Threshold

129
Q

The domain in a gallium-arsenide semiconductor has what
type of electrical field when compared to the other regions
across the body of a semiconductor?

A

A field of much greater intensity

130
Q

What characteristic of a gunn oscillator is inversely
proportional to the transit time of the domain
across the semiconductor?

A

The frequency

131
Q

What is the junction arrangement of the original

avalanche transit-time diode?

A

Pnin

132
Q

What causes dc bias energy to be absorbed by avalanche
electrons and given up to the microwave field applied to
an avalanche transit-time diode?

A

The negative-resistance property

133
Q

During the manufacture of a point-contact diode, what
is the purpose of passing a relatively large current from
the catwhisker to the silicon crystal?

A

To form a small region of p-type material

134
Q

What is the capacitive reactance across a point-contact

diode as compared to a normal junction diode?

A

Lower

135
Q

What are the most important advantages of the Schottky

barrier diode?

A

Lower forward resistance and low noise

136
Q

At frequencies above 100 megahertz, the intrinsic (i)

region causes a pin diode to act as what?

A

Variable resistance

137
Q

The pin diode is primarily used for what purpose?

A

A switching device

138
Q

Microwave antennas and low-frequency antennas are

similar in what ways?

A

Operating principles and electrical characteristics

139
Q

What term is used to express the efficiency of an antenna?

A

Power gain or power ratio

140
Q

What term is used to express the measurement of the degree

of mismatch between a line and its load?

A

Standing-wave ratio (swr)

141
Q

What type of antenna radiates in and receives energy from

all directions at once?

A

Omnidirectional

142
Q

What is the term that is used to describe narrowness in

the radiated beam of an antenna?

A

Antenna directivity

143
Q

What characteristic allows the same antenna to both

transmit and receive?

A

Reciprocity

144
Q

What type of reflector is most often used in directive

antennas?

A

Parabolic

145
Q

Microwaves can be focused and reflected in the same way

as what other type of waves?

A

Light waves

146
Q

How many major lobes are radiated by a parabolic

reflector?

A

One

147
Q

A horizontally truncated paraboloid antenna is used for

what purpose?

A

Determine elevation

148
Q

The beam from a horizontally positioned cylindrical

paraboloid is narrow in what plane?

A

Vertical

149
Q

What is the purpose of a collimating lens?

A

Forces the radial segments of a wavefront into parallel

paths.

150
Q

How does a waveguide-type lens focus spherical

wavefront microwave energy?

A

Some wavefronts are accelerated so that all wavefronts exit

the lens at the same time.

151
Q

What type of lens decelerates a portion of a spherical

wavefront?

A

Delay lens

152
Q

What is a set of antenna elements called?

A

Antenna Array

153
Q

What type of antenna has all elements connected to the

same energy source?

A

Driven Array

154
Q

What determines the beam elevation angle of an antenna

that is electronically scanned in elevation?

A

Frequency or phase of radiated energy

155
Q

What is the polarization of the energy radiated by a

vertical slot?

A

Horizontal

LOOKS FAM (6 decks)

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