Antenna Basics

Let's get right down to the study of antennas and
Or perhaps you have never heard of (or are a little rusty) on the above parameters.
Well then, you've come to the right place. Before we can design an antenna or discuss antenna types, we
must understand the basics of antennas, which are the fundamental parameters
that characterize an antenna.
So let us learn something. We'll start with frequency and step through radiation patterns, directivity and gain,
and ultimately close with an explanation on why antennas radiate.
Jump ahead if this is already familiar to you.
A discussion on how all waveforms in the universe are made up of the sum of sinusoids (simple waves) This helps explains
why in antenna theory we always discuss wavelength and frequency no matter what signal (information) we want to transmit.
The radiation pattern for an antenna is defined on this page. We have 3D graphs of real antenna
radiation patterns, with a discussion on isotropic, omnidirectional and directional radiation patterns.
Radiation patterns are of the utmost importance in the discussion of antenna basics.
The introduction to antennas continues with a discussion of Field Regions. The Far Field, Near Field
and Fresnel Regions for an antenna is presented.
Directivity is fundamental to antennas. It is a measure of how "directional" an antenna's radiation pattern is.
An antenna's efficiency is a measure of how much power is radiated by the antenna relative to
the antenna input power. The subject of Antenna Basics also includes a discussion of Antenna Gain, which is
real power radiated in a particular direction.
An antenna's radiation pattern in the far field is often characterized by it's beamwidth and
sidelobe levels. This introduction to antenas illustrates this with an example.
Antenna Impedance is presented as the ratio of voltage to current at the antenna's terminals.
Low- and High-Frequency models are presented for transmission lines. The fundamentals of antenna
theory requires that the antenna be "impedance matched" to the transmission line or the antenna
will not radiate. The concept of VSWR is introduced as a measure of how well matched an antenna is.
The bandwidth of an antenna is the frequency range over which the antenna radiates.
The bandwidth can be defined in different ways; this page presents an introduction to antenna
bandwidth.
All electromagnetic plane waves have an associated polarization. The antenna concepts of Linear, Circular
and elliptical polarization are presented.
Antennas are also classified by their polarization; this defines the type of plane wave polarization
the antenna is most sensitive to. This is a fundamental antenna concept.
Effective aperture is a basic antenna concept that is a measure of the power captured by an antenna
from a plane wave. Effective aperture can be expressed as a function of the antenna gain and
the wavelength of interest.
Friis Transmission Formula is the most fundamental equation of antenna theory. This equation
relates transmit power, antenna gains, distance and wavelength to received power. This page
is a must-read for those interested in antenna theory.
Antenna Temperature is a property of an antenna and the environment it operates in. It is a measure
of the noise received by the antenna due to thermal (or temperature) effects.
The antenna basics section concludes with a discussion of Why Antennas Radiate. The idea here is to
explain the physical concepts that produce radiation in terms of electrons flowing on a wire.
After concluding the study of Antenna Fundamentals, the next step in the understanding of antenna theory
is to move on to the
types of antennas page,
where basic antenna types are discussed. You will find that the understanding of the above concepts is
crucial for understanding real antennas.

Frequency
## Antenna Fundamentals

**Antenna Basics**.
Suppose one day you're walking down the
street and a kind but impatient person runs up and asks you to design an antenna
for them. "Sure", you quickly reply, adding "what is the desired frequency, gain,
bandwidth, impedance, and polarization?"

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