ISOTROPIC - antennas is the name given to any type of antenna that radiates energy out evenly in all dirrections in 3 dimensional space.
It is often said that isotropic antennas do not exist. The Sun is a perfect example of an isotropic radiator. It gives of light and radiowaves evenly in all directions.
Antenna gain is referenced to isotropic. If you put a big mirror behind the sun so that all the light on that half of the solar system was reflected back, the sun would appear to be twice as bright. It would be said have 3db gain. or 3dBi in reference to isotropic. (3dB= x 2, 6dB= x 4, 9dB= x 8, 10dB= x 10, 20dB= x 10, 30dB= x 1000)
OMNI DIRECTIONAL - antennas are similar to isotropic antennas, but they radiate evenly in a 2 dimensional plain. 1/4 wave and 5/8 wave whip and co-linear antennas are examples of omnidirectional antennas. Omni antennas may exhibit anything from 0db to 12dBi gain. 6dBi is common.
DIPOLE - antennas come in 3 types. An Open dipole which has a characteristic impedence of 75 ohms, a Folded dipole with 300 ohms impedence and a Double Folded dipole with 600 ohms impedence. Dipoles emit polaristed radiation about the axis of the element. If a dipole is mounted vertically, it emits vertical polarisation omnidirectional to the horizon.
YAGI - antennas are commonly used as Television antennas. The basic yagi has 3 elements. A Driven Element (which is usually a dipole) a Reflector (behind the driven element) and a Director (in front of the driven element). More director elements may added to the front of the antenna which increases the gain. The reflector may also be a mesh which increases front to back ratio.
CORNER REFLECTOR - A corner reflector antenna is similar to a yagi. It is basically a dipole of sorts with a larger reflector element. The element is usually bent into a 90 degree angle. These antennas have good front to back ratios, but are usually about 3-6dBi in gain.
PHASED ARRAY Double the number of existing elements will give you 3db gain.
LOOP YAGI A good broad band antenna. polarisation is horizontal for verically mounted elements.
CUBICAL QUAD Corner fed 75 ohms impedence or center feed 50 ohms.
QUAGI A Quad driven element with a quad reflector and director elements.
WAVEGUIDE - Open ended waveguide behaves much like a slot antenna. It exhibts natural 6dbi gain.
CANTENNA- Circular waveguide version of open waveguide. Exhibits 6dBi gain.
DISH Dish antennas are high gain, large bandwidth antennas. The feed type determines the bandwidth. The dish must be 2.5 wavelengths in diametre to function correctly.
PARABOLIC - Very similar to a dish or corner reflector antenna. Often exhibits high gain like a dish but uni-polarised. Usually about 20dbi
DISCONE A very broadband isotropic antenna. 0dbi gain (unity)
DOUBLE DIAMOND Dual corner fed phased cubical quad antennas on a solid reflector.
SLOT ANTENNAusually 1/2 wavelength long cut into sheet metal. Center fed with coax, but may be cut into the wall of a waveguide.
SKELETON SLOT A slot antenna reduced to 1/4 wide x 5/8 high wire, center fed. With dual parasitic yagi arrays.
ALFORD SLOT Omni directional, horizontally polarised Antenna
RHOMBIC Very high gain, physically large antenna made of wire.
HORN ANTENNA Similar to open waveguide but with a taper. The larger the opening, the higher the gain.
RANDOM LONG WIRE
CROSS FIELD A very physically small, low frequnecy antenna.