Physics & RF
B16 Polarization, Gain & Direction — Study Guide
This guide covers Polarization, Gain & Direction as part of Physics & RF. Start with the vocabulary, then try to answer each question before revealing the answer. Connect these facts to a real radio link or electrical circuit and practice the subject in the arcade when you are ready.
Acronyms first
| Term | Meaning |
|---|---|
| RHCP | Right-Hand Circular Polarization |
| LHCP | Left-Hand Circular Polarization |
| dBi | Decibels relative to an isotropic antenna |
| GNSS | Global Navigation Satellite System |
| LPI | Low Probability of Intercept |
| LPD | Low Probability of Detection |
| MIMO | Multiple Input Multiple Output |
| LMR | Land Mobile Radio |
| FOB | Forward Operating Base |
Key facts
Polarization is defined by the orientation of the…
E-field only
Why focus on the E-field for polarization?
It interacts most strongly with matter (electrons)
Reciprocity means an antenna's pattern and impedance are…
the same whether transmitting or receiving
A vertical whip antenna produces…
vertically polarized waves
For maximum signal transfer, the receive antenna must…
match the transmit antenna's polarization
At lower frequencies, which polarization travels better along Earth's surface?
Vertical
Why does horizontal polarization lose more over the ground?
It induces stronger ground currents that sap the wave's energy
Scenario: AM broadcast picked up by vehicle whip antennas uses…
vertical polarization
Scenario: police patrol cars and handhelds (LMR) usually use…
vertical polarization
Scenario: a traditional rooftop TV antenna lying flat uses…
horizontal polarization
Man-made electrical noise is mostly ____ polarized, so ____ polarization gives some immunity.
vertically; horizontal
Which polarization is less prone to multipath from ground reflections and works best when both ends are stationary and aligned?
Horizontal
Which polarization is best for mobile users (cars, handhelds) thanks to an omni pattern?
Vertical
Circular polarization is made by combining two perpendicular waves of equal amplitude…
90° out of phase
Circular polarization's E-field traces a…
helix / corkscrew
GPS satellites transmit with…
RHCP
Scenario: a tumbling satellite's signal angle keeps changing. Best polarization for steady reception?
Circular
How does military radar use circular polarization to cut rain clutter?
Raindrops reverse the handedness; the receiver ignores the reversed return
An idealized point-source antenna radiating equally in ALL directions:
Isotropic
A real antenna radiating equally in all HORIZONTAL directions with a doughnut pattern:
Omnidirectional
An antenna concentrating energy in one specific direction:
Directional
An isotropic antenna is a real antenna you can buy.
False
Antenna gain compares power in a direction to…
an ideal isotropic antenna
Higher gain antennas…
focus energy in one direction, raising effective radiated power
Scenario: cell towers covering pie-shaped areas use…
sectorized antennas
Scenario: tactical radios that must talk without aiming use…
omnidirectional antennas
Scenario: long-distance secure SATCOM links use…
high-gain parabolic antennas
Scenario: EW teams locating, intercepting or jamming enemy signals use…
directional antennas
Beamwidth is…
the angular width of the main lobe
Narrow beamwidth gives…
higher gain and longer range
Wide beamwidth gives…
lower gain and broader coverage
Directional antenna used for radar and EW at UHF and microwave frequencies:
Horn antenna
Scenario: a FOB needs an encrypted link to HQ. Best antenna?
High-gain dish pointed at HQ
Scenario: a moving convoy needs constant 360° coverage. Best antenna?
Omnidirectional
Scenario: you need to jam an enemy drone's control signal. Best antenna?
Directional beam
A tactical advantage of directional antennas:
LPI/LPD — harder for the adversary to detect
A limitation of directional antennas:
Must be aimed precisely; hard to use moving without auto-tracking
Practice this module
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