[{"n": "Radio propagation", "u": "/e/radio-propagation/radio-propagation/", "s": "Radio waves travel via line-of-sight, ground wave, and skywave modes."}, {"n": "Airplane scatter", "u": "/e/radio-propagation/airplane-scatter/", "s": "Momentary radio propagation via reflection from passing aircraft."}, {"n": "Anomalous propagation", "u": "/e/radio-propagation/anomalous-propagation/", "s": "Radio propagation beyond the normal horizon due to atmospheric anomalies."}, {"n": "Artificial dielectrics", "u": "/e/radio-propagation/artificial-dielectrics/", "s": "Fabricated composites mimicking dielectrics for microwave manipulation."}, {"n": "Atmospheric duct", "u": "/e/radio-propagation/atmospheric-duct/", "s": "A horizontal atmospheric layer that guides radio waves around Earth's curvature."}, {"n": "Carrier-to-noise ratio", "u": "/e/radio-propagation/carrier-to-noise-ratio/", "s": "Ratio of modulated carrier power to noise power in a receiver."}, {"n": "Channel sounding", "u": "/e/radio-propagation/channel-sounding/", "s": "Evaluates radio environments for MIMO wireless system design."}, {"n": "Chapman function", "u": "/e/radio-propagation/chapman-function/", "s": "Chapman function models slant-path atmospheric integration on a spherical Earth."}, {"n": "Clutter (radar)", "u": "/e/radio-propagation/clutter-radar/", "s": "Unwanted radar echoes from natural and man-made sources."}, {"n": "Co-channel interference", "u": "/e/radio-propagation/co-channel-interference/", "s": "Crosstalk from two transmitters using the same channel."}, {"n": "Coherence bandwidth", "u": "/e/radio-propagation/coherence-bandwidth/", "s": "Frequency range over which channel fading is correlated."}, {"n": "Communication with submarines", "u": "/e/radio-propagation/communication-with-submarines/", "s": "Submerged submarines use VLF and ELF radio for one-way communication."}, {"n": "Communications blackout", "u": "/e/radio-propagation/communications-blackout/", "s": "A loss of communications capability due to power, ionospheric, or atmospheric causes."}, {"n": "Critical frequency", "u": "/e/radio-propagation/critical-frequency/", "s": "The frequency boundary between ionospheric reflection and penetration at vertical incidence."}, {"n": "DBm", "u": "/e/radio-propagation/dbm/", "s": "Logarithmic power unit referenced to one milliwatt, used in communications."}, {"n": "Doppler effect", "u": "/e/radio-propagation/doppler-effect/", "s": "Frequency shift due to relative motion between source and observer."}, {"n": "Earth–ionosphere waveguide", "u": "/e/radio-propagation/earth-ionosphere-waveguide/", "s": "Natural waveguide between Earth and ionosphere for ELF and VLF waves."}, {"n": "Earth–Moon–Earth communication", "u": "/e/radio-propagation/earth-moon-earth-communication/", "s": "Moon bounce enables two-way radio via lunar reflection."}, {"n": "Radio beacon", "u": "/e/radio-propagation/radio-beacon/", "s": "A fixed transmitter used for navigation, direction finding, and emergency location."}, {"n": "Epstein profile", "u": "/e/radio-propagation/epstein-profile/", "s": "Exactly solvable refractive-index profile for stratified media."}, {"n": "F region", "u": "/e/radio-propagation/f-region/", "s": "The ionospheric layer with the highest free electron concentration."}, {"n": "F2 propagation", "u": "/e/radio-propagation/f2-propagation/", "s": "Rare VHF skywave reflection off the F2 ionospheric layer."}, {"n": "Forward scatter", "u": "/e/radio-propagation/forward-scatter/", "s": "Forward scattering deflects waves by small angles, continuing near their original direction."}, {"n": "Fresnel zone", "u": "/e/radio-propagation/fresnel-zone/", "s": "Ellipsoidal zones predicting wave interference from path obstructions."}, {"n": "Fresnel zone antenna", "u": "/e/radio-propagation/fresnel-zone-antenna/", "s": "A diffractive antenna using phase control for focusing."}, {"n": "Group velocity", "u": "/e/radio-propagation/group-velocity/", "s": "Velocity of the envelope of a wave packet."}, {"n": "International Beacon Project", "u": "/e/radio-propagation/international-beacon-project/", "s": "A worldwide network of HF beacons for assessing ionospheric propagation."}, {"n": "International Reference Ionosphere", "u": "/e/radio-propagation/international-reference-ionosphere/", "s": "International standard empirical model of the terrestrial ionosphere."}, {"n": "Ionosphere", "u": "/e/radio-propagation/ionosphere/", "s": "Ionized upper atmosphere enabling long-distance radio propagation."}, {"n": "Ionospheric absorption", "u": "/e/radio-propagation/ionospheric-absorption/", "s": "Ionospheric absorption is the primary limiting factor in radio propagation."}, {"n": "Ionospheric sounding", "u": "/e/radio-propagation/ionospheric-sounding/", "s": "Real-time technique for measuring ionospheric layer altitudes via radio signals."}, {"n": "Kennelly–Heaviside layer", "u": "/e/radio-propagation/kennelly-heaviside-layer/", "s": "Ionised layer reflecting medium-frequency radio waves beyond the horizon."}, {"n": "Lateral wave", "u": "/e/radio-propagation/lateral-wave/", "s": "Interfacial waves launched at grazing incidence, distinct from conventional surface waves."}, {"n": "Line-of-sight propagation", "u": "/e/radio-propagation/line-of-sight-propagation/", "s": "Radio waves above 30 MHz travel in a direct visual path."}, {"n": "Link budget", "u": "/e/radio-propagation/link-budget/", "s": "An accounting of gains and losses in a telecommunication system."}, {"n": "Long delayed echo", "u": "/e/radio-propagation/long-delayed-echo/", "s": "Radio echoes returning seconds after transmission, with origins still debated."}, {"n": "Maximum usable frequency", "u": "/e/radio-propagation/maximum-usable-frequency/", "s": "Highest frequency for skywave communication 50% of days in a month."}, {"n": "Meteor burst communications", "u": "/e/radio-propagation/meteor-burst-communications/", "s": "Brief radio links via meteor trails, used for decades."}, {"n": "Mie scattering", "u": "/e/radio-propagation/mie-scattering/", "s": "Scattering of light by particles comparable to the wavelength."}, {"n": "Multipath propagation", "u": "/e/radio-propagation/multipath-propagation/", "s": "Multipath causes signals to arrive via multiple paths, creating interference."}, {"n": "MW DX", "u": "/e/radio-propagation/mw-dx/", "s": "Hobby of receiving distant AM radio stations via skywave propagation."}, {"n": "Non-line-of-sight propagation", "u": "/e/radio-propagation/non-line-of-sight-propagation/", "s": "NLOS propagation occurs when visual line of sight is obstructed."}, {"n": "North Atlantic Radio System", "u": "/e/radio-propagation/north-atlantic-radio-system/", "s": "Cold War troposcatter chain linking Arctic radars to NORAD."}, {"n": "Path loss", "u": "/e/radio-propagation/path-loss/", "s": "Path loss is the reduction in signal strength as it travels from transmitter to receiver."}, {"n": "Polar mesospheric summer echoes", "u": "/e/radio-propagation/polar-mesospheric-summer-echoes/", "s": "Strong radar echoes from 80–90 km in polar summer mesospheres."}, {"n": "Radar angels", "u": "/e/radio-propagation/radar-angels/", "s": "Radar angels are Bragg-scattering echoes from periodic structures like bird flocks."}, {"n": "Karl Rawer", "u": "/e/radio-propagation/karl-rawer/", "s": "German specialist in radio wave propagation and the ionosphere."}, {"n": "Rayleigh–Gans approximation", "u": "/e/radio-propagation/rayleigh-gans-approximation/", "s": "Approximate solution for light scattering by optically soft particles."}, {"n": "Sidelobes", "u": "/e/radio-propagation/sidelobes/", "s": "Unwanted lobes in an antenna's radiation pattern, distinct from the main lobe."}, {"n": "Signal-to-interference ratio", "u": "/e/radio-propagation/signal-to-interference-ratio/", "s": "Quotient of carrier power to co-channel interference power."}, {"n": "Skip zone", "u": "/e/radio-propagation/skip-zone/", "s": "A silent zone between ground-wave and sky-wave reception."}, {"n": "Skywave", "u": "/e/radio-propagation/skywave/", "s": "Skywave enables long-distance radio communication by reflecting signals off the ionosphere."}, {"n": "Space weather", "u": "/e/radio-propagation/space-weather/", "s": "Space weather studies solar wind effects on Earth's magnetosphere and ionosphere."}, {"n": "SPLAT!", "u": "/e/radio-propagation/splat/", "s": "GNU GPL-licensed tool for Longley-Rice path loss and coverage prediction."}, {"n": "Sporadic E propagation", "u": "/e/radio-propagation/sporadic-e-propagation/", "s": "Unpredictable VHF propagation via ionized patches in the lower E region."}, {"n": "Sudden ionospheric disturbance", "u": "/e/radio-propagation/sudden-ionospheric-disturbance/", "s": "A sudden ionospheric disturbance disrupts radio communications via enhanced D-region absorption."}, {"n": "Surface wave", "u": "/e/radio-propagation/surface-wave/", "s": "Electromagnetic or mechanical wave guided along an interface between two media."}, {"n": "Tropospheric scatter", "u": "/e/radio-propagation/tropospheric-scatter/", "s": "Microwave communication beyond the horizon using tropospheric scattering."}, {"n": "TV and FM DX", "u": "/e/radio-propagation/tv-and-fm-dx/", "s": "The hobby of receiving distant TV and FM signals via unusual propagation."}, {"n": "Voyager 1", "u": "/e/radio-propagation/voyager-1/", "s": "First spacecraft to enter interstellar space, launched in 1977."}, {"n": "White Alice Communications System", "u": "/e/radio-propagation/white-alice-communications-system/", "s": "Cold War tropospheric scatter network linking remote Alaskan defense sites."}, {"n": "X band", "u": "/e/radio-propagation/x-band/", "s": "A microwave band used for radar, space communications, and terrestrial broadband."}, {"n": "Antenna (radio)", "u": "/e/radio-propagation/antenna-radio/", "s": "Interface between radio waves and electric currents."}, {"n": "Scimitar antenna", "u": "/e/radio-propagation/scimitar-antenna/", "s": "A curved-plate VHF antenna used on spacecraft and aircraft."}, {"n": "Antenna equivalent radius", "u": "/e/radio-propagation/antenna-equivalent-radius/", "s": "Enables circular-cross-section analysis for non-circular antenna conductors."}, {"n": "Antenna farm", "u": "/e/radio-propagation/antenna-farm/", "s": "A dedicated area for multiple telecommunications transmitting or receiving antennas."}, {"n": "Antenna measurement", "u": "/e/radio-propagation/antenna-measurement/", "s": "Testing antennas to characterize gain, pattern, impedance, and efficiency."}, {"n": "Array gain", "u": "/e/radio-propagation/array-gain/", "s": "Array gain measures SNR improvement from coherent signal addition across elements."}, {"n": "Baseband processor", "u": "/e/radio-propagation/baseband-processor/", "s": "A chip managing all antenna-based radio functions in a device."}, {"n": "Beam diameter", "u": "/e/radio-propagation/beam-diameter/", "s": "Beam diameter defines the spatial extent of an electromagnetic beam."}, {"n": "Birkeland current", "u": "/e/radio-propagation/birkeland-current/", "s": "Field-aligned currents linking magnetosphere to ionosphere, driving auroras."}, {"n": "Geomagnetic storm", "u": "/e/radio-propagation/geomagnetic-storm/", "s": "A temporary disturbance of Earth's magnetosphere driven by solar plasma structures."}, {"n": "High-frequency Active Auroral Research Program", "u": "/e/radio-propagation/high-frequency-active-auroral-research-program/", "s": "A research facility studying the ionosphere with high-power radio waves."}, {"n": "Ionospheric storm", "u": "/e/radio-propagation/ionospheric-storm/", "s": "Ionospheric storms are geomagnetically driven disturbances in electron density."}, {"n": "Effective radiated power", "u": "/e/radio-propagation/effective-radiated-power/", "s": "ERP measures directional radio power using a half-wave dipole reference."}, {"n": "Leaky wave antenna", "u": "/e/radio-propagation/leaky-wave-antenna/", "s": "Fast-wave antenna radiating continuously along its length for directive beams."}, {"n": "Plane of polarization", "u": "/e/radio-propagation/plane-of-polarization/", "s": "A historically ambiguous term for the orientation of polarized electromagnetic waves."}, {"n": "Radiation pattern", "u": "/e/radio-propagation/radiation-pattern/", "s": "Radiation pattern describes directional dependence of an antenna's emitted field strength."}, {"n": "Radiation resistance", "u": "/e/radio-propagation/radiation-resistance/", "s": "The effective resistance representing power radiated as radio waves from an antenna."}, {"n": "Fading", "u": "/e/radio-propagation/fading/", "s": "Variation of signal attenuation over time, position, and frequency."}, {"n": "Rayleigh fading", "u": "/e/radio-propagation/rayleigh-fading/", "s": "Statistical model for signal fading in non-line-of-sight environments."}, {"n": "Free-space path loss", "u": "/e/radio-propagation/free-space-path-loss/", "s": "Signal loss between isotropic antennas in free space due to spreading."}, {"n": "Whistler (radio)", "u": "/e/radio-propagation/whistler-radio/", "s": "A VLF radio wave from lightning, heard as a descending tone."}, {"n": "Two-ray ground-reflection model", "u": "/e/radio-propagation/two-ray-ground-reflection-model/", "s": "Two-ray model predicts path loss via direct and ground-reflected waves."}, {"n": "Rain attenuation frequency scaling", "u": "/e/radio-propagation/rain-attenuation-frequency-scaling/", "s": "Scales rain attenuation measurements between frequencies for satellite link design."}, {"n": "EISCAT", "u": "/e/radio-propagation/eiscat/", "s": "European research organisation operating incoherent scatter radars in the auroral zone."}, {"n": "Radome", "u": "/e/radio-propagation/radome/", "s": "A weatherproof enclosure that protects radar antennas from the elements."}, {"n": "Two-wave with diffuse power fading", "u": "/e/radio-propagation/two-wave-with-diffuse-power-fading/", "s": "Generalized fading model for two strong signals and diffuse waves."}, {"n": "Ten-rays model", "u": "/e/radio-propagation/ten-rays-model/", "s": "Ten-ray model simulates urban radio propagation with up to three reflections."}, {"n": "Okumura model", "u": "/e/radio-propagation/okumura-model/", "s": "Empirical urban propagation model based on Tokyo measurements."}, {"n": "Equatorial electrojet", "u": "/e/radio-propagation/equatorial-electrojet/", "s": "A narrow eastward current ribbon in the daytime equatorial ionosphere."}, {"n": "Ionosonde", "u": "/e/radio-propagation/ionosonde/", "s": "A radar for examining the ionosphere using swept-frequency pulses."}, {"n": "Diversity scheme", "u": "/e/radio-propagation/diversity-scheme/", "s": "Multiple channels improve signal reliability against fading and interference."}, {"n": "Longley–Rice model", "u": "/e/radio-propagation/longley-rice-model/", "s": "A statistical model for predicting radio signal attenuation over irregular terrain."}, {"n": "Ionospheric heater", "u": "/e/radio-propagation/ionospheric-heater/", "s": "Powerful HF transmitters used to study plasma turbulence in the ionosphere."}, {"n": "Hata model", "u": "/e/radio-propagation/hata-model/", "s": "Empirical propagation model for cellular path loss prediction."}, {"n": "Electrojet", "u": "/e/radio-propagation/electrojet/", "s": "Hall currents in the ionosphere, strongest at equator and auroral zones."}, {"n": "Log-distance path loss model", "u": "/e/radio-propagation/log-distance-path-loss-model/", "s": "Predicts path loss over long distances in buildings or dense areas."}, {"n": "Single vegetative obstruction model", "u": "/e/radio-propagation/single-vegetative-obstruction-model/", "s": "Estimates attenuation from a single tree in a telecommunication link."}, {"n": "Total electron content", "u": "/e/radio-propagation/total-electron-content/", "s": "A measure of ionospheric electron column density affecting radio propagation."}, {"n": "Radiation intensity", "u": "/e/radio-propagation/radiation-intensity/", "s": "Radiant intensity is power per unit solid angle."}, {"n": "Point-to-point Lee model", "u": "/e/radio-propagation/point-to-point-lee-model/", "s": "A 900 MHz point-to-point model with adjustable regional factors."}, {"n": "Area-to-area Lee model", "u": "/e/radio-propagation/area-to-area-lee-model/", "s": "A flat-terrain path loss model with antenna and frequency corrections."}, {"n": "ITU model for indoor attenuation", "u": "/e/radio-propagation/itu-model-for-indoor-attenuation/", "s": "Estimates indoor path loss for frequencies from 900 MHz to 5.2 GHz."}, {"n": "Traveling-wave antenna", "u": "/e/radio-propagation/traveling-wave-antenna/", "s": "A non-resonant antenna using a single-pass traveling wave for radiation."}, {"n": "Rician fading", "u": "/e/radio-propagation/rician-fading/", "s": "A stochastic model for multipath fading with a dominant path."}, {"n": "Null (radio)", "u": "/e/radio-propagation/null-radio/", "s": "A direction of minimal radiation in an antenna's pattern."}, {"n": "Weissberger's model", "u": "/e/radio-propagation/weissberger-s-model/", "s": "Estimates path loss from foliage in point-to-point links."}, {"n": "ITU terrain model", "u": "/e/radio-propagation/itu-terrain-model/", "s": "Predicts median path loss using diffraction theory and terrain clearance."}, {"n": "Standard linear array", "u": "/e/radio-propagation/standard-linear-array/", "s": "A ULA with half-wavelength spacing to prevent grating lobes."}, {"n": "Egli model", "u": "/e/radio-propagation/egli-model/", "s": "Terrain model for VHF/UHF path loss prediction."}, {"n": "Squint (antenna)", "u": "/e/radio-propagation/squint-antenna/", "s": "Beam direction offset from antenna normal due to frequency or polarization."}, {"n": "Sura Ionospheric Heating Facility", "u": "/e/radio-propagation/sura-ionospheric-heating-facility/", "s": "Russian ionospheric heating facility for research and low-frequency emission studies."}, {"n": "COST Hata model", "u": "/e/radio-propagation/cost-hata-model/", "s": "Extends the Hata model to 2 GHz for urban macro cells."}, {"n": "Early ITU model", "u": "/e/radio-propagation/early-itu-model/", "s": "Estimates path loss from trees in point-to-point links."}, {"n": "Subauroral ion drift", "u": "/e/radio-propagation/subauroral-ion-drift/", "s": "A narrow, fast westward ion drift at subauroral latitudes."}, {"n": "VOACAP", "u": "/e/radio-propagation/voacap/", "s": "Empirical HF propagation model originally developed for Voice of America."}]