Module 2 Flashcards
yb The complex impedance value of a(n) ______ and ______ is purely imaginary, having a real part equal to 0. Select all that apply.
capacitor and inductor
Ohm’s Law can be represented by the equation ________.
V = IR
At microwave frequencies used in radar applications, characteristic impedance can be found by dividing _______ by ________.
inductance, capacitance
According to Ohm’s Law, ZL is equal to VL/_______.
IL
Alternating current values are written in ______ letters.
lowercase
Impedance in ac circuits is analogous to ______ in DC circuits
resistance
A circuit branch consisting of a resistor in series with an inductor would have a total ZT consisting of the ________ of the two impedances
Sum
In a load matched system, Zin is ________ ZT.
equal to
Transmission lines are similar to waveguides at _______ frequencies.
microwave
Z0 at radar frequencies maintains a ______ value over the length of the line.
constant
Using a λ/4 stub is one method for keeping the inner and outer conductors separated in a _____ transmission line.
rigid coaxial
Transmission lines may propagate in _____ mode(s).
2 modes
_____ mode is not usable at lower frequencies. Select all that apply
Transverse electric and Transverse magnetic
Coaxial cables use _____ mode
TEM (Transverse Electromagnetic)
For an ac current at high frequencies, the magnitude of the current _____ as it gets further from the conductor surface.
decreases exponentially
In a flexible transmission line, the outer conductor is covered with _____ to protect it against moisture.
Plastic
H/m is the unit of _____ in a transmission line
inductance
When a dielectric is present, it determines the _____ per unit length in a transmission line.
capacitance
A(n) ___ load has zero load resistance.
short-circuit
_____ can be used to find a point of damage in a transmission line.
Reflections
The _____ is used to calculate the amplitude of a reflected signal.
reflection coefficient
A standing wave occurs when the _____ of the power source does not match the load impedance.
characteristic impedance
Coaxial cables propagate signals in the _______ mode
transverse electromagnetic
Magnetic fields form circles around the center conductor in the _____ mode.
transverse electromagnetic
The skin depth of a material _____ as frequency increases.
decreases
For an AC current at high frequencies, _____ is at its maximum value at the surface of the conducting material
current density
What are disadvantages of using a rigid coaxial transmission line? (3 answers)
Susceptible to moisture
Limited line length at extremely high frequencies
Prevents unwanted noise
What are the functions of a waveguide
Keeps the transmitted power out of the receiver.
Routes the received pulse to the receiver.
Routes transmitted pulse energy to the antenna.
Waveguides have lower transmission losses than coaxial cables because they contain a(n) _______ dielectric.
air
Readings from the ________ are used to calculate VSWR.
directional coupler
In a two wire transmission line, a /4 stub appears as a(n) _______on the line at microwave frequencies
open
On a two-wire transmission line, an attached stub will be seen as a ______ below the cutoff frequency.
short
The _____ prevents the transmitter from emitting unwanted frequencies
spurious radiation filter
The _____ allows the transmitter to radiate without sending RF waves through the antenna.
dummy load
The ______ takes the received energy collected by the reflector and sends it down the waveguide to the receiver.
feed horn
Connecting a shorted λ/4 stub to a two-wire transmission line makes it appear as ______ above the cutoff frequency
an open
Transmission lines and ______ work in transverse electric mode.
waveguides
The E-field and the ______ lines are always perpendicular to each other.
H-Field
H-field lines are measured in _______ per meter.
amperes
A _____ uses the magnetic properties of iron oxide to manipulate the magnetic fields in a waveguide.
ferrite device
The _____ is a solid-state device located just before the receiver in the waveguide run
T/R limiter
The duplexer used by the FAA is also called a ________.
circulator
A frequency-steering device that allows two radar channels to connect to the same antenna simultaneously is called a _____.
diplexer
Diplexers consist of _____ that route each channel’s frequency from the antenna to the correct receiver
frequency filters
Radar systems differentiate between aircraft and weather targets through the use of a
Polarizer
The direction of a reflection’s rotation changes when a target is illuminated by a linearly polarized wave.
False
A waveguide component that gradually expands the dimensions of a waveguide so that its impedance matches that of free space is called a _____.
Feedhorn
A _____ reduces a specific microwave frequency while allowing others to pass through the waveguide.
ferrite attenuator
The waveguide component that absorbs energy in a waveguide and dissipates it as heat is called a __________.
dummy load
When using a diplexer, channel frequencies should be separated by at least _____ MHz in order to prevent transmitter outputs from interfering with the other channel’s receiver.
60
If reflected power increases at a particular azimuth, it normally indicates _____ malfunction
rotatory joint
When a _____ object is illuminated by a circularly polarized wave, the reflected wave will rotate in the same direction
round
The final component of a waveguide system traveling towards the antenna is the _____.
feedhorn
Radar signals are transverse electromagnetic waves, just like infrared and ultraviolet light except for _____.
frequency
Electromagnetic fields comprise two __________ oscillating fields which travel together __________.
perpendicular, in-phaseper
Microwave antennas communicate at __________ frequencies. (2 Answers)
radar and radio
Gain in a parabolic antenna depends on ________. (3 answers)
dish diameter
distance to target
feed illumination
In receive mode, solid state array antennas permit a better determination of a target’s ________ than would be possible from antenna position alone.
azimuth
The passive element method shifts the phase of a microwave signal with a binary signal that varies the _________ around the _________.
magnetic field . ferrite
What standard point of measurement is most often used to determine horizontal beamwidth?
The point of maximum power in the main lobe
What determines vertical beam patterns? (2 answers)
The angle a feed assembly uses to illuminate the reflector
The antenna angle itself
The difference between RF propagation and light propagation is partially due to ______ and ______ factors being more impactful for microwave frequencies
Water vapor
Atmospheric Pressure
The number of oscillations or cycles per unit of time is a wave’s __________.
frequency
The distance between similar features of a waveform, such as two successive peaks, is a wave’s __________.
wavelength
What is radio wave attenuation?
a reduction in apparent power
Microwave systems use ________ and ______ reflectors.
dipoles and parabolic reflectors
When an antenna is fed by a transmission line, __________ acts as an impedance matcher between the line and free space.
the feedhorn
What is antenna gain?
The concentration of power into a single direction
Electromagnetic field polarity is always in the direction of the __________ field vector.
magnetic
feedhorn provides impedance transformation between a __________ and free space
waveguide
What is the function of phase shifters in a solid state array antenna? (2 answers).
Detect targets off the boresite
Ensure all signals reach a target in phase
In a solid state array antenna, the active element method uses ______ to select the path RF signals are directed to.
TR Switches
With regard to antennas, the azimuth gating circuit _____ coverage while ______ ground reflections
improves . minimizing
Vertical lobing depends on _______. (3 answers)
antenna tilt and height
terrain surface
vertical lobing is caused by _______ from the target combining with the _______ ______
Reflections . direct wave
We can create circularly polarized waves by first splitting the linearly polarized wave into a horizontal component and a vertical component, and then delaying one component by ________.
90°
Which of the following does the Inductosyn use to generate improved azimuth change pulses (IACP) and azimuth change pulses (ARP) (2 answers)
Rotor with one winding
Stator with two windings
The number of hits per scan on a target depends on the _________. (3 answers)
antenna Pulse Repetition Frequency (PRF)
antenna beamwidth
antenna RPM
We can minimize the negative impact of misplaced echoes by changing the __________ between two or more values each time the transmitter fires.
Pulse Repetition Frequency (PRF)
An antenna’s pedestal and reflector are designed to withstand ________ within tolerance.
wind
The __________ couples RF energy between the stationary waveguide from equipment and the rotating portion of the antenna.
Rotary Joint
An azimuth-sensitive VSWR increase is a classic indication of __________ problems
Rotary Joint
We can determine the wave polarization by looking at the direction of ___________.
the E-field vector
An E-field vector perpendicular to the line of propagation indicates the wave is
linearly polarized
The amount of time a target is within beamwidth decreases as _______ increases
rotational speed
What can cause holes in radar coverage? (3 answers)
PRF too low
RPM too fast
Beamwidth too narrow
A second-time around echo will cause a target’s _____________ to be processed incorrectly
range
