9 TYPES OF ANTENNAS

TYPES ANTENNAS

4 arm conical spiral
alford loop
aperture synthesis
array
axial mode helix
biconical w/polarizer
biconical
cavity backed circuit fed slot
cavity backed spiral
circular loop
conical spiral
corner reflector
dipole array, linear
dipole
discone
dual polarized sinuous
guide fed slot
helix, normal mode
helix, axial mode
horn
linear dipole array
log periodic
loop, circular
loop, alfred
loop, square
luneberg lens
microstrip patch
monopole
normal mode helix
parabolic
patch
reflector
rhombic
sinuous, dual polarized
slot, guide fed
slot, cavity backed
spiral, 4 arm conical
spiral, conical
spiral, cavity backed
square loop
vee
yagi
The Yagi antenna is narrow band, designed to work on only one channel or FM. It has the best gain for its size, and a correspondingly narrow main lobe (beam). If you need the highest gain, or to discriminate against an interfering signal 20-40 degrees azimuth off the desired signal, use a Yagi.

Omni. This antenna, sold for FM radio, is a bent folded dipole. It is advertised a an Omni, but only approximates omnidirectional reception.

A helical wire can have axial or broadside to axis radiation. Helix antennas are used for every VHF, UHF and microwave purpose from point to point to TV broadcast.
The supersturnstile. Take the turnstile used for omnidirectional reception, stretch the wires into vertical sheets, and nick the middle of the sheet into a sort of vertical bow tie, and you get the broad band antenna common to VHF TV broadcasting. O, yes, you can think of these things as slot type antenas also, since they have a vertical slot between the two batwings.

Rohmbic;Wire in the shape of a rhomboid makes a long wire into a high gain precision antenna.
RADIATION PATTERNS
The radiation pattern is a graphical depiction of the relative field strength transmitted from or received by the antenna. Antenna radiation patterns are taken at one frequency, one polarization, and one plane cut. The patterns are usually presented in polar or rectilinear form with a dB strength scale. Patterns are normalized to the maximum graph value, 0 dB, and a directivity is given for the antenna. This means that if the side lobe level from the radiation pattern were down -13 dB, and the directivity of the antenna was 4 dB, then the sidelobe gain would be -9 dB.
FREQUENCY / PHASE EFFECTS OF ANTENNAS
The radiation patterns of the antennas presented in the previous section are for antenna geometries most commonly used. The antenna should be viewed as a matching network that takes the power from a transmission line (50 ohm, for example), and matches it to the free space "impedance" of 377 ohms. The most critical parameter is the change of VSWR with frequency. The pattern usually does not vary much from acceptable to the start of unacceptable VSWRs (> 2:1). For a given physical antenna geometric size, the actual radiation pattern varies with frequency.