MOD 11 ch 1

Question 1

What is the region of the frequency spectrum from 1000 MHz to 100,000 MHz called?

Answer 1

Microwave region.

Question 2

Microwave theory is based upon what concept

Answer 2

. Electromagnetic field theory.

Question 3

Why are coaxial lines more efficient at microwave frequencies than two-wire transmission lines?

Answer 3

. The electromagnetic fields are completely confined.

Question 4

What kind of material must be used in the construction of waveguides?

Answer 4

Conductive material

Question 5

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

Answer 5

Copper loss

Question 6

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

Answer 6

Skin effect

Question 7

What is used as a dielectric in waveguides?

Answer 7

Air

Question 8

What is the primary lower-frequency limitation of waveguides?

Answer 8

. Physical size

Question 9

At very high frequencies, what characteristics are displayed by ordinary insulators?

Answer 9

The characteristics of the dielectric of a capacitor.

Question 10

What type of insulator works well at very high frequencies?

Answer 10

A shorted quarter-wave section called a metallic insulator

Question 11

The frequency range of a waveguide is determined by what dimensison?

Answer 11

The “a” dimension.

Question 12

What happens to the bus bar dimensions of the waveguide when the frequency is increased?

Answer 12

The bus bar becomes wider

Question 13

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

Answer 13

Energy will no longer pass through the waveguide.

Question 14

What interaction causes energy to travel down a waveguide?

Answer 14

The interaction of the electric and magnetic fields.

Question 15

What is indicated by the number of arrows (closeness of spacing) used to represent an electric field?

Answer 15

The relative strength of the field

Question 16

What primary condition must magnetic lines of force meet in order to exist?

Answer 16

Magnetic lines of force must form a continuous closed loop

Question 17

What happens to the H lines between the conductors of a coil when the conductors are close together?

Answer 17

. The H lines cancel

Question 18

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

Answer 18

The field must be perpendicular to the conductors.

Question 19

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

Answer 19

Decrease to zero.

Question 20

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

Answer 20

The angles are equal.

Question 21

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

Answer 21

Cutoff frequency

Question 22

Compared to the velocity of propagation of waves in air, what is the velocity of propagation of waves in waveguides?

Answer 22

Slower.

Question 23

What term is used to identify the forward progress velocity of wavefronts in a waveguide?

Answer 23

. Group velocity.

Question 24

What term is used to identify each of the many field configurations that can exist in waveguides?

Answer 24

Mode of operation

Question 25

What field configuration is easiest to produce in a given waveguide?

Answer 25

Dominant mode

Question 26

How is the cutoff wavelength of a circular waveguide figured?

Answer 26

1.71 times the diameter.

Question 27

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

Answer 27

Transverse electric (TE) and transverse magnetic (TM).

Question 28

The electric field is perpendicular to the “a” dimension of a waveguide in what mode?

Answer 28

TE.

Question 29

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

Answer 29

Second.

Question 30

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

Answer 30

. First

Question 31

What determines the frequency, bandwidth, and power-handling capability of a waveguide probe?

Answer 31

Size and shape

Question 32

Loose or inefficient coupling of energy into or out of a waveguide can be accomplished by the use of what method?

Answer 32

Slots and apertures

Question 33

What is the result of an impedance mismatch in a waveguide?

Answer 33

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

Question 34

What is used to construct irises?

Answer 34

. Metal plates

Question 35

An iris placed along the “b” dimension wall produces what kind of reactance?

Answer 35

Inductive.

Question 36

How will an iris that has portions along both the “a” and “b” dimension walls act at the resonant frequency?

Answer 36

As a shunt resistance

Question 37

What device is used to produce a gradual change in impedance at the end of a waveguide?

Answer 37

Horn.

Question 38

When a waveguide is terminated in a resistive load, the load must be matched to what property of the waveguide?

Answer 38

Characteristic impedance

Question 39

What is the primary purpose of a dummy load?

Answer 39

Absorb all energy without producing standing waves.

Question 40

The energy dissipated by a resistive load is most often in what form?

Answer 40

Heat.