Transmission Line Equivalent Circuit / Input Impedance, Standing Wave Ration, and Power Flashcards
Three (3) Important Requirements of Transmission Line
- There must be minimum loss
- Reflection of signal on the line must be avoided
- There should be no stray radiation or pick-up of signal by the line itself
Transmission line analysis is used when
- The frequency of operation is high
- The length of the transmission line is long
- The length of the line is an appreciable fraction of the signal wavelength
What are the transmission line parameters? (It has 4)
- resistance per unit length (R)
- inductance per unit length (L)
- conductance per unit length (G)
- capacitance per unit
length (C)
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.
perpendicular; transverse
An important property of TEM waves is that the fields E and H are uniquely related to ______ and ______, respectively:
voltage (V) and current (I)
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.
Characteristic Impedance (Zo)
A transmission line is said to be ____ if the conductors of the line are perfect and the dielectric medium separating them is ____
lossless
A _______ is one in which the attenuation constant πΆ is frequency independent while the phase constant π· is linearly dependent on frequency.
distortionless line
_______ 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).
Velocity factor
The velocity at which an electromagnetic wave travels through a transmission line depends on the ______ of the insulating material separating the two conductors
dielectric constant
The velocity at which an electromagnetic wave travels through a transmission line varies also with the _____ and _____ of the cable
inductance and capacitance
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 _____.
dielectric constant
The quantity π·π is usually referred to as the ________ of the line and can be expressed in degrees or radians.
electrical length
A transmission line is defined as long if its length exceeds ____ of a wavelength; otherwise, it is considered short.
π/ππππ
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
no
When the transmission line length is ______, the input impedance is _____ to the characteristic impedance.
infinite; equal
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
d. all of the above
OPEN LINE
In an Open Line, a _______ transmission line terminated in an open circuit is equivalent to a series resonant LC circuit.
quarter-wavelength
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.
less than one-quarter; capacitor
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.
one-quarter and one-half wavelength; inductor
SHORTED LINE
In a Shorted Line, a quarter-wavelength transmission line terminated in a ____ is equivalent to a parallel LC circuit.
short circuit
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.
less than one-quarter; inductor
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.
more than one-quarter; capacitor
An ordinary transmission line is _______; the power propagates equally well in both directions.
bidirectional
The wave that propagates from source toward the load is called ______
incident wave
The wave that propagates from load to source is called ______
reflected wave
The incident power propagates toward the ______, and reflected power propagates toward the ______. Similarly for the voltage and current
load; source
Incident voltage and current are always ______ for a resistive characteristic impedance.
in phase
For an infinitely long line, all incident power is _____ in the line, and there is no reflected power.
stored
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)
absorbs
________ 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.
Reflected power
A transmission line with no reflected power is called _____ or _____.
flat or nonresonant line
If the load is either a short or an open circuit, all the incident power is ______ toward the source.
reflected
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.
reflect back and forth (oscillate)
It is the ratio of the voltage reflection wave to the incident wave at the load
reflection coefficient
It is the ratio of the reflected voltage wave to that of the incident wave
voltage reflection coefficient
The ______________ at any point on the line is the negative of the voltage reflection coefficient at that point.
current reflection coefficient
When ZL = ZO, all incident power is absorbed by the load. This is called _________
matched line
When ZL β 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.
unmatched or mismatched line
The two travelling waves set up an interference pattern known _________
standing wave
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.
standing waves
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.
Standing Wave Ratio (SWR)
When the incident and reflected waves are equal in amplitude (a total mismatch), πΊπΎπΉ = β. This is the ________.
worst-case condition
When there is no reflected wave
(πΈπ = 0), πΊπΎπΉ = π. This is the _______.
ideal situation
One hundred percent of the source incident power is (absorbed/not absorbed) by the load.
not absorbed
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
d. all of the above
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.
reflected
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 180Β° 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
e. all of the above
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.
reflected
The characteristics of a transmission line terminated in a SHORTED LINE.
a. The voltage incident wave is reflected back 180Β° 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
e. all of the above
