MOD 11 ch 1 Flashcards Preview

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Flashcards in MOD 11 ch 1 Deck (40):
1

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

Microwave region.

2

Microwave theory is based upon what concept

. Electromagnetic field theory.

3

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

. The electromagnetic fields are completely confined.

4

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

Conductive material

5

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

Copper loss

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?

Skin effect

7

What is used as a dielectric in waveguides?

Air

8

What is the primary lower-frequency limitation of waveguides?

. Physical size

9

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

The characteristics of the dielectric of a capacitor.

10

What type of insulator works well at very high frequencies?

A shorted quarter-wave section called a metallic insulator

11

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

The "a" dimension.

12

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

The bus bar becomes wider

13

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

Energy will no longer pass through the waveguide.

14

What interaction causes energy to travel down a waveguide?

The interaction of the electric and magnetic fields.

15

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

The relative strength of the field

16

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

Magnetic lines of force must form a continuous closed loop

17

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

. The H lines cancel

18

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

The field must be perpendicular to the conductors.

19

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

Decrease to zero.

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?

The angles are equal.

21

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

Cutoff frequency

22

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

Slower.

23

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

. Group velocity.

24

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

Mode of operation

25

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

Dominant mode

26

How is the cutoff wavelength of a circular waveguide figured?

1.71 times the diameter.

27

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

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

28

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

TE.

29

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

Second.

30

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

. First

31

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

Size and shape

32

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

Slots and apertures

33

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

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

34

What is used to construct irises?

. Metal plates

35

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

Inductive.

36

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

As a shunt resistance

37

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

Horn.

38

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

Characteristic impedance

39

What is the primary purpose of a dummy load?

Absorb all energy without producing standing waves.

40

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

Heat.