Finals Part 2

Question 1

hollow, conductive tubes—rectangular, elliptical, or
circular in shape—that confine the waves and minimize losses.

Answer 1

Waveguides

Question 2

Waveguides act as _______, only allowing frequencies above a certain cutoff to
propagate.

Answer 2

high-pass filters

Question 3

Types of Waveguides

Answer 3

Rectangular
Circular
Elliptical

Question 4

number of ways in which electrical energy can propagate along a
waveguide.

Answer 4

Modes

Question 5

Modes requires a certain boundary condition, for instance: there cannot be any ________________ in ideal conductors for the waveguide

Answer 5

electric field along the wall

Question 6

Modes requires a certain boundary condition, for instance: _________ would have to be needed but is impossible since
there cannot be any voltage across a short circuit.

Answer 6

Voltage gradient along the wall

Question 7

Modes in a waveguide can be understood by imagining waves __________ reflecting inside the guide

Answer 7

as rays of
light

Question 8

Each mode corresponds to a different
reflection angle. As the angle increases, the ray travels ___________, which slows down the effective velocity along the guide, even though the wave still moves at the speed of light

Answer 8

the ray travels a longer path

Question 9

Each mode in a waveguide has a cutoff frequency below which it won’t propagate. _________, known as the ________, which uses the lowest cutoff frequency.

Answer 9

Single-mode operation known as the Dominant mode

Question 10

Waveguides operate between the

Answer 10

cutoff of the dominant mode and the next higher mode

Question 11

Modes are classified
as ________ or ________ based on the field
patterns inside the guide.

Answer 11

transverse electric (TE) or transverse
magnetic (TM)

Question 12

occurs when multiple modes propagate through a waveguide at
the same time

Answer 12

Dispersion

Question 13

If a short pulse of microwave energy is sent into the
waveguide, each mode travels at a ___________, causing the pulse
to arrive at the other end spread out over time.

Answer 13

slightly different speed

Question 14

This spreading—dispersion—
can lead to _______, especially if another pulse follows closely behind, as the overlapping pulses may interfere with each other

Answer 14

signal distortion

Question 15

To avoid this, it’s best
to operate the waveguide in __________, allowing only one mode to propagate and preserving the integrity of the signal.

Answer 15

single-mode operation

Question 16

Formula for the longer dimension of the waveguide

Answer 16

a = λc / 2

where:
a = the longer dimension of the waveguide (m)
λc = cutoff wavelength (m)

Question 17

Formula for cutoff frequency

Answer 17

fc = c / 2a

where:
a = the longer dimension of the waveguide (m)
fc = cutoff wavelength (Hz)
c = speed of light (3x10^8 m/s)

Question 18

Formula for cutoff wavelength

Answer 18

λc = c / fc

where:
fc = cutoff wavelength (Hz)
c = speed of light (3x10^8 m/s)

Question 19

In an air-filled rectangular waveguide, electromagnetic waves
reflect off the walls rather than traveling straight, causing the signal
to move at a slower pace than the speed of light. This slower speed
is called __________

Answer 19

group velocity

Question 20

Group velocity is significantly __________ due to the zigzag path the wave takes

Answer 20

less than the speed of light

Question 21

Formula for group velocity

Answer 21

Vg = c * sqrt[ 1 - (fc/f)^2 ]

where:
Vg = group velocity (m/s)
c = speed of light (3x10^8 m/s)
fc = cutoff frequency (Hz)
f = operating frequency (Hz)

Question 22

The variation in group velocity can be physically explained by the angle at which the wave _______, which changes with frequency

Answer 22

reflects off the waveguide walls

Question 23

Near the cutoff frequency, the wave
bounces ___________ while covering the same
distance along its length compared to higher frequencies

Answer 23

more frequently across the guide

Question 24

formula for time

Answer 24

t = d / s

where
d: length of the guide
s: group velocity

Question 25

formula for the difference in arrival for the two frequencies

Answer 25

Δt = | t1 - t2 |

Question 26

refers to the rate at which the phase of a wave appears to move along a waveguide

Answer 26

Phase velocity

Question 27

Phase velocity can exceed the speed of light because it doesn't represent the ________

Answer 27

movement of any physical object or energy.

Question 28

Formula for Phase Velocity

Answer 28

Vp = c / (sqrt[ 1 - (fc/f)^2 ]) where: Vp = phase velocity (m/s) c = speed of light (3x10^8 m/s) fc = cutoff frequency (Hz) f = operating frequency (Hz)

Question 29

The relationship between phase velocity and group (formula)

Answer 29

VgVp = c^2

Question 30

Formula for waveguide impedance

Answer 30

Zo = 377 / (sqrt[ 1 - (fc/f)^2 ]) where: Zo = waveguide impedance (ohms) fc = cutoff frequency (Hz) f = operating frequency (Hz)

Question 31

Formula for wavelength in the guide

Answer 31

λg = Vp / f where: λg = wavelength in the guide (m) Vp = phase velocity (m/s) f = operating frequency (Hz)

Question 32

Another formula for wavelength in the guide

Answer 32

λg = λ / (sqrt[ 1 - (fc/f)^2 ]) where: λg = wavelength in the guide (m) λ = free-space wavelength (m/s) Vp = phase velocity (m/s) f = operating frequency (Hz)

Question 33

Shorted stubs of adjustable length can be used, but a simpler method is to add capacitance or inductance by _____________. As the screw is inserted farther into the guide, the effect is _____________

Answer 33

inserting a tuning screw into the guide. first capacitive, then series-resonant, and finally inductive.

Question 34

Three basic ways to launch a wave down a guide

Answer 34

Probe Loop Hole

Question 35

To launch a wave in one direction within a waveguide, a ______ is placed at an ___________ typically at the center of the wide dimension for the TE₁₀ mode—and positioned a ________ from the shorted end. This setup ensures that the reflected wave, after two 180° phase shifts, adds constructively to the __________

Answer 35

probe electric-field maximum quarter guide-wavelength forward wave.

Question 36

A _______ couples to the magnetic field in a waveguide and is placed where the magnetic field is strongest—near the end wall for the TE₁₀ mode. This is similar to how current ___________ of a conventional transmission line, with magnetic and electric fields in the guide _________, respectively.

Answer 36

loop peaks at the shorted end analogous to current and voltage

Question 37

A _________ can be made in the waveguide to allow electromagnetic energy to ______ from the surrounding space. Since waveguides are reciprocal devices—like transmission lines—the same methods used to _________ into a waveguide can also be used to _______

Answer 37

hole enter or exit couple power extract it

Question 38

_________ use variations like two holes spaced a quarter-wavelength apart to ensure wave propagation in only one direction.

Answer 38

Directional couplers

Question 39

Directional couplers causes signals in the undesired direction to ____________, while allowing constructive interference in the desired direction.

Answer 39

to cancel due to a 180° phase difference

Question 40

In directional couplers, additional holes can be used to enhance ______, and resistive material absorbs _______ at the end of the secondary guide.

Answer 40

coupling unwanted signals

Question 41

Directional couplers are characterized by their ___________. All three are normally specified in decibels

Answer 41

insertion loss, coupling, and directivity

Question 42

the amount by which a signal in the main guide will be attenuated.

Answer 42

insertion loss

Question 43

gives the amount by which the signal in the main guide is greater than that coupled to the secondary waveguide.

Answer 43

coupling specification

Question 44

ratio between the power coupled to the secondary guide, for signals travelling in the two possible directions along the main guide

Answer 44

directivity

Question 45

Changes in a waveguide ’ s shape or size affect its internal electric and magnetic fields, potentially altering its characteristic impedance if the change is significant

Answer 45

BENDS

Question 46

Bends are classified as __________, depending on whether they affect the direction of the electric or magnetic field, respectively, with reference to the TE₁₀ mode.

Answer 46

E-plane or H-plane

Question 47

with its carefully designed gradual bends, resembles plumbing and is just as tricky to install.

Answer 47

Rigid waveguide

Question 48

like their transmission line counterparts, split a signal into two paths and come in E-plane and H-plane types

Answer 48

Waveguide tees

Question 49

A type of waveguide tees that produces in-phase outputs

Answer 49

H-plane tee (shunt tee)

Question 50

A type of waveguide tee that gives out-of-phase signals

Answer 50

E-plane tee (series tee)

Question 51

A type of waveguide tee that combines both types, offering features like signal isolation—e.g., an input at one port results in outputs at two ports but none at a fourth, depending on the input configuration.

Answer 51

hybrid or "magic" tee

Question 52

short section where waves reflect back and forth. If its length is exactly half a wavelength, the reflections reinforce each other, creating resonance and a buildup of energy

Answer 52

waveguide cavity

Question 53

type of cavity resonators

Answer 53

cylindrical coaxial re-entrant radial re-entrant

Question 54

At lower frequencies, loads and attenuators use

Answer 54

resistors

Question 55

At microwave frequencies, resistors become impractical due to

Answer 55

unwanted inductance and capacitance

Question 56

use resistive materials like carbon to absorb energy.

Answer 56

waveguide attenuators

Question 57

Types of waveguide attenuators

Answer 57

flap and rotating vane

Question 58

A type of waveguide attenuator that inserts a carbon vane into the guide

Answer 58

flap attenuator

Question 59

a type of waveguide attenuator that varies loss based on the vane’s orientation to the electric field.

Answer 59

rotating vane

Question 60

Terminating loads use _________ to absorb energy without reflections.

Answer 60

carbon inserts

Question 61

a component used in waveguide systems to absorb RF energy and prevent reflections

Answer 61

waveguide termination, also known as a dummy load

Question 62

waveguide termination is a resistive load matched to the _____, ensuring the waveguide operates effectively and prevents standing waves. This is crucial for maintaining signal integrity and overall system performance.

Answer 62

waveguide's characteristic impedance,

Question 63

useful microwave components that generally use ferrites in their operation.

Answer 63

Isolators and circulators

Question 64

is a device that allows a signal to pass in only one direction. In the other direction, it is greatly attenuated.

Answer 64

An isolator

Question 65

An isolator can be used to shield a source from a

Answer 65

mismatched load

Question 66

Energy will still be reflected from the load, but instead of reaching the source, the ________ is dissipated in the isolator.

Answer 66

reflected power

Question 67

multi-port device that directs signals from one port to the next in a counterclockwise direction, allowing signal separation.

Answer 67

circulator

Question 68

A typical use of a circulator is as a ______, where it routes the transmitter output to the antenna and the received signal to the receiver, while preventing the strong transmit signal from damaging the receiver.

Answer 68

transmit-receive switch

Question 69

Applications of Waveguides

Answer 69

Photonic Integrated Circuits Optical interferometers Optical Fiber Waveguide Components for Medical Linear Accelerators