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NEETS > NEETS 11 CH 1,2 > Flashcards

NEETS 11 CH 1,2 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

Dominant mode

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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 joint?

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

-type and H-type. 1-68

56
Q

What are the primary disadvantages of the magic-T?

A

Low power-handling capability and power losses

57
Q

What type of junctions are formed where the arms of a hybrid ring meet the main ring?

A

Basic E-type junctions.

58
Q

Hybrid rings are used primarily for what purpose?

A

High-power duplexes.

59
Q

Ferrite devices are useful in microwave applications because they possess what properties?

A

Magnetic properties and high resistance

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

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.

62
Q

The resonant frequency of electron wobble can be changed by variation of what force?

A

The applied magnetic field

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 effec

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.2-64

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 heli

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.2-66

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.

NEETS (11 decks)

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