Transmission Line Equivalent Circuit / Input Impedance, Standing Wave Ration, and Power

Question 1

Three (3) Important Requirements of Transmission Line

Answer 1

1. There must be minimum loss
2. Reflection of signal on the line must be avoided
3. There should be no stray radiation or pick-up of signal by the line itself

Question 2

Transmission line analysis is used when

Answer 2

1. The frequency of operation is high
2. The length of the transmission line is long
3. The length of the line is an appreciable fraction of the signal wavelength

Question 3

What are the transmission line parameters? (It has 4)

Answer 3

1. resistance per unit length (R)
2. inductance per unit length (L)
3. conductance per unit length (G)
4. capacitance per unit
   length (C)

Question 4

A two-conductor transmission line supports a TEM wave; that is, the electric and magnetic fields on the line are ______ to each other and ______ to the direction of wave propagation.

Answer 4

perpendicular; transverse

Question 5

An important property of TEM waves is that the fields E and H are uniquely related to ______ and ______, respectively:

Answer 5

voltage (V) and current (I)

Question 6

It is the ratio of the positively traveling voltage wave to the current wave at any point on the line. It is also defined as the impedance seen looking into an infinite long line or the impedance seen looking into a finite length of line that is terminated in a purely resistive load with resistance equal to the characteristic impedance of the line.

Answer 6

Characteristic Impedance (Zo)

Question 7

A transmission line is said to be ____ if the conductors of the line are perfect and the dielectric medium separating them is ____

Answer 7

lossless

Question 8

A _______ is one in which the attenuation constant 𝜶 is frequency independent while the phase constant 𝜷 is linearly dependent on frequency.

Answer 8

distortionless line

Question 9

_______ is defined as the ratio of the actual velocity of propagation of an electromagnetic wave through a given medium to the velocity of propagation through a vacuum (free space).

Answer 9

Velocity factor

Question 10

The velocity at which an electromagnetic wave travels through a transmission line depends on the ______ of the insulating material separating the two conductors

Answer 10

dielectric constant

Question 11

The velocity at which an electromagnetic wave travels through a transmission line varies also with the _____ and _____ of the cable

Answer 11

inductance and capacitance

Question 12

Because wavelength is directly proportional to velocity and the velocity of propagation of a TEM wave varies with _____, the wavelength of a TEM wave also varies with _____.

Answer 12

dielectric constant

Question 13

The quantity 𝜷𝒍 is usually referred to as the ________ of the line and can be expressed in degrees or radians.

Answer 13

electrical length

Question 14

A transmission line is defined as long if its length exceeds ____ of a wavelength; otherwise, it is considered short.

Answer 14

𝟏/𝟏𝟔𝒕𝒉

Question 15

If a transmission line is ideal, there is (an/no) attenuation to the signal amplitudes and the propagation constant turns out to be purely imaginary

Answer 15

no

Question 16

When the transmission line length is ______, the input impedance is _____ to the characteristic impedance.

Answer 16

infinite; equal

Question 17

The input impedance for a lossless line seen looking into a transmission line that is terminated in short or an open can be ____, depending on the distance from the termination.

a. resistive
b. inductive
c. capacitive
d. all of the above

Answer 17

d. all of the above

Question 18

OPEN LINE

In an Open Line, a _______ transmission line terminated in an open circuit is equivalent to a series resonant LC circuit.

Answer 18

quarter-wavelength

Question 19

OPEN LINE

Any transmission line that is ______ wavelength and terminated in an open circuit is equivalent to ______. The amount of capacitance depends on the exact electrical length of the line.

Answer 19

less than one-quarter; capacitor

Question 20

OPEN LINE

A transmission line between _______ and ______ that is terminated in an open circuit is equivalent to an _______. The amount of inductance depends on the exact electrical length of the line.

Answer 20

one-quarter and one-half wavelength; inductor

Question 21

SHORTED LINE

In a Shorted Line, a quarter-wavelength transmission line terminated in a ____ is equivalent to a parallel LC circuit.

Answer 21

short circuit

Question 22

SHORTED LINE

Any transmission line that is _______ wavelength and terminated in an short circuit is equivalent to _____. The amount of inductance depends on the exact electrical length of the line.

Answer 22

less than one-quarter; inductor

Question 23

SHORTED LINE

Any transmission line that is _______ wavelength and terminated in an short circuit is equivalent to ______. The amount of capacitance depends on the exact electrical length of the line.

Answer 23

more than one-quarter; capacitor

Question 24

An ordinary transmission line is _______; the power propagates equally well in both directions.

Answer 24

bidirectional

Question 25

The wave that propagates from source toward the load is called ______

Answer 25

incident wave

Question 26

The wave that propagates from load to source is called ______

Answer 26

reflected wave

Question 27

The incident power propagates toward the ______, and reflected power propagates toward the ______. Similarly for the voltage and current

Answer 27

load; source

Question 28

Incident voltage and current are always ______ for a resistive characteristic impedance.

Answer 28

in phase

Question 29

For an infinitely long line, all incident power is _____ in the line, and there is no reflected power.

Answer 29

stored

Question 30

If the line is terminated in a purely resistive load equal to the characteristic impedance of the line, the load ______ all the incident power (this assumes lossless line)

Answer 30

absorbs

Question 31

________ is the portion of the incident power that was not absorbed by the load and reflected back to the source. Therefore, it can never exceed the incident power.

Answer 31

Reflected power

Question 32

A transmission line with no reflected power is called _____ or _____.

Answer 32

flat or nonresonant line

Question 33

If the load is either a short or an open circuit, all the incident power is ______ toward the source.

Answer 33

reflected

Question 34

If the source were replaced with an open or a short and the line is lossless, energy present on the line would
____________ between the source and load ends similar to the way energy is transferred back and forth between inductor and capacitor in an LC tank circuit. This is called resonant line.

Answer 34

reflect back and forth (oscillate)

Question 35

It is the ratio of the voltage reflection wave to the incident wave at the load

Answer 35

reflection coefficient

Question 36

It is the ratio of the reflected voltage wave to that of the incident wave

Answer 36

voltage reflection coefficient

Question 37

The ______________ at any point on the line is the negative of the voltage reflection coefficient at that point.

Answer 37

current reflection coefficient

Question 38

When ZL = ZO, all incident power is absorbed by the load. This is called _________

Answer 38

matched line

Question 39

When ZL ≠ ZO, some of the incident power are absorbed by the load and some is reflected (returned) back to source. This is called ______ or ______. With this, two waves travelling in opposite direction present on the line at the same time.

Answer 39

unmatched or mismatched line

Question 40

The two travelling waves set up an interference pattern known _________

Answer 40

standing wave

Question 41

As the incident and reflected wave pass each other, stationary pattern of voltage and current are produced on the line. This stationary pattern are called __________ because they appear to remain in a fixed position on the line, varying only in amplitude.

Answer 41

standing waves

Question 42

It is defined as the ratio of the maximum voltage to the minimum voltage or the maximum current to the minimum current of a standing wave on a transmission line. Essentially, it is a measure of the mismatch between the load impedance and the characteristic impedance of the transmission line.

Answer 42

Standing Wave Ratio (SWR)

Question 43

When the incident and reflected waves are equal in amplitude (a total mismatch), 𝑺𝑾𝑹 = ∞. This is the ________.

Answer 43

worst-case condition

Question 44

When there is no reflected wave
(𝐸𝑟 = 0), 𝑺𝑾𝑹 = 𝟏. This is the _______.

Answer 44

ideal situation

Question 45

One hundred percent of the source incident power is (absorbed/not absorbed) by the load.

Answer 45

not absorbed

Question 46

The disadvantage/s of NOT having a matched (flat) transmission line:

a. Reflections and re-reflections cause more power loss
b. Reflections cause ghost images
c. Mismatches cause noise interference
d. all of the above

Answer 46

d. all of the above

Question 47

When the incident waves of voltage and current reach an open termination none of the power is absorbed; it is all ______ back toward the source.

Answer 47

reflected

Question 48

The characteristics of a transmission line terminated in a OPEN LINE.

a. The voltage incident wave is reflected back just as if is it were to continue (no phase reversal)
b. The current incident wave is reflected back 180° from how it would have continued
c. The sum of the incident and reflected current waveforms is minimum at the open
d. The sum of the incident and reflected voltage waveforms is maximum at the open
e. all of the above

Answer 48

e. all of the above

Question 49

When the incident waves of voltage and current reach an short termination none of the power is absorbed; it is all _____ back toward the source.

Answer 49

reflected

Question 50

The characteristics of a transmission line terminated in a SHORTED LINE.

a. The voltage incident wave is reflected back 180° from how it would have continued
b. The current incident wave is reflected back the same as if it had continued
c. The sum of the incident and reflected current waveforms is maximum at the short
d. The sum of the incident and reflected voltage waveforms is minimum at the short
e. all of the above

Answer 50

e. all of the above