Practice Quiz Flashcards
Sketch a Log Periodic Dipole Antenna
Identify which end is the feed and which is the direction of radiation.
Describe the element sizing and spacing
Why is AM radio wave propagation better at night?
During the day, the ionosphere is ionized by solar radation, causing radio waves to be absorbed and reflected off the lower ionospheric D layer, limiting their propagation range.
At night, these layers of the ionosphere dissipate and radio waves penetrate higher into the ionosphere into the F layer, allowing for longer-range transmission via inospheric reflection.
What two factors determine the maximum Usable Frequency between any two points?
Ionospheric Density: Higher electron densities result in greater abosption of high frequency radio waves higher inospheric density -> lower MUF
Angle of Incidence: Higher angle of incidence (less verticle) means higher frequencies are absorbed more and refracted less. Lower angle of incidence -> lower MUF
Why does the angular field distribution still depend on distance within the Radiating Near Field?
The Radiating Near Field consists of both reactive and radiative components.
The reactive components are where the field distribution to be out of phase and is closer to the antenna.
The radiative components are where the field distribution is in phase and is further from the antenna.
Closer to the antenna, near field effects such as reactive power storage and release and Proximity Effect become more dominant, increasing the Reactive Component.
What do ridged horn antennas do to bandwidth?
Ridges reduce reflections and standing wave effects, improving impedence matching, increasing bandwidth.
What are the units for Radiation Intensity?
Watts per Steradian (W/sr) which represents the power radiated per unit solid angle.
What type of polarization is most commonly used in satellite communications?
Circular.
Less Cross-Polarization, improved multipath rejection.
What are the driven element configuration in an End Fire Array?
A series of equally spaced driven elements, progressively phase shifted 90 degrees.
What type of antenna is best to produce a pencil beam?
Parabolic Antennas
Do Horn Antennas have high or low Beamwidth typically?
High
Draw a Yagi-Uda array and label the parasitic elements and driven elements.
Draw the current and voltage distribution for a Half-Wave Dipole
What is an advantage of a cosec^2 pattern offer over a fan pattern?
Less wasted energy on higher elevation coverage where threates are less likely.
Identify the formula for the path length of a signal.
List three factors that affect the fficiency of a Parabolic Reflector antenna
Aperature Taper Efficiency
Spillover Efficiency
Surface Error
Cross Polarization
Aperature Blockage
Non-Single Point Feed
What are advantages of slotted waveguide antennas?
Cheaper and more durable.
What will the radiation pattern look like?
Explain an Archimedean Spiral Antenna
Spiral shaped windings in a planar structure. Fed from the center and EM waves propagate outward along the spiral arms, giving circular polarization.
Wideband response due to continuous variation in the antenna dimentions.
What is the difference between an Archimedean Spiral Antenna and a Conical Antenna?
Conical is directional, with a narrower beamwidth and high directivity.
Conical has lower bandwidth.
Why would we use a quarterwave vs a halfwave? (Advantage / disadvantage)
Quarterwave -> Physically smaller
Halfwave -> Higher directivity
How can you cancel out an inductive antenna?
Make it shorter.
Longer antennas have a higher path length which causes higher inductance.
How can you cancel out a capactive antenna?
Make it longer.
What happens to the received power if the receiving antenna is horizontally polarized?
It will not be recieved due to cross polarization.
Identify the free space path loss equation.
Identify the efficiency of an antenna equation
How do you know if an antenna is inductive or capacitive based on the wavelength and the physical length?
