Antennas
Every common antenna, how each works, and the feed lines and hardware that connect them.
Antenna fundamentals
The ideas that apply to every antenna.
How antennas workTurning current into radio waves and back again.Gain and directivitydBi, dBd and where the energy goes.Radiation patternsReading azimuth and elevation plots, beamwidth and front-to-back.Antenna impedance and radiation resistanceWhat the feed line sees at the feed point.Bandwidth and efficiencyHow wide an antenna works and how much power is actually radiated.Ground effects and heightHow earth and height shape the pattern.Near field and far fieldWhy distance from the antenna changes the physics.Antenna modelingUsing NEC-based software to predict performance.
Wire antennas
Dipoles, loops and long wires: the antennas most operators start with.
The half-wave dipoleThe reference antenna: pattern, impedance and length.The inverted VA dipole with one support and a lower impedance.Fan and trap dipolesCovering several bands with one antenna.Off-center-fed dipolesMultiband operation with a 4:1 balun.End-fed half-wave antennasA half-wave fed through a high-impedance transformer.Long wires and random wiresSimple wire with a tuner: benefits and traps.The folded dipoleWider bandwidth and four times the impedance.Doublets and the G5RVOpen-wire-fed multiband antennas.Full-wave loopsA wire loop with gain and low noise.Slopers and the inverted LWire antennas for one support and the low bands.
Vertical and mobile antennas
Omnidirectional antennas for base, vehicle and low bands.
The quarter-wave verticalA monopole over ground: the workhorse omnidirectional antenna.Radials and ground planesWhy a vertical needs a counterpoise and how many radials.5/8-wave and colinear antennasSqueezing gain out of a vertical.J-poles and Slim JimsEasy VHF/UHF verticals built from wire or ladder line.Mobile whips and loading coilsShort antennas that work on a vehicle.Multiband HF verticalsTrap, tuned and autotuned vertical designs.
Beam and directional antennas
Concentrating power in one direction.
The Yagi-Uda beamDriven element, reflector and directors.Quad and delta-loop beamsLoop elements for gain and low noise.Log-periodic antennasWide bandwidth with moderate gain.Moxon and hex beamsCompact wire beams with good front-to-back.Phased arraysSteering a pattern with phase and spacing.Dish and parabolic antennasMicrowave gain with a reflector.Helical and satellite antennasCircular polarization for space work.
Compact, portable and stealth
Antennas for small spaces, backpacks and restricted lots.
Small magnetic loopsTiny, high-Q antennas with a narrow bandwidth.Loaded and short antennasTrading size against efficiency.Portable and field antennasLight, quick designs for SOTA, POTA and camping.Stealth antennasWorking within HOA or apartment restrictions.Handheld radio antennasRubber ducks, whips and getting more from an HT.
Receiving and direction-finding antennas
Antennas chosen for hearing rather than transmitting.
Feed lines and matching
Getting power to the antenna and keeping it there.
Coaxial cableConstruction, types and choosing a coax.Open-wire and ladder lineLow-loss balanced feed lines.Characteristic impedanceWhat Z0 means and why it must match.Feed line loss and velocity factorAttenuation by frequency and electrical length.SWR and reflectionsStanding waves, reflection coefficient and return loss.Antenna tunersWhat they match and what they don't fix.Baluns and ununsBalanced-unbalanced and impedance transformers.Common-mode chokesKeeping RF off the outside of the coax.Stubs, quarter-wave sections and the gamma matchMatching with pieces of transmission line.The Smith chartA map of impedance and reflection.RF connectorsPL-259, N, BNC, SMA and when to use each.
Installation and protection
Getting an antenna up and keeping it safe.