BARKATULLAH UNIVERSITY INSTITUTE OF TECHNOLOGY BARKATULLAH UNIVRSITY, BHOPAL

PRESENTATION ON ANTENNA

Submitted to:- Submitted by:-Ms. Anita Jhamalia Praveen Kumar

Prajapati

IntroductionAn antenna is an electrical conductor or system of

conductorsTransmission - radiates electromagnetic energy into spaceReception - collects electromagnetic energy from space

In two-way communication, the same antenna can be used for transmission and reception

Antenna DefinitionAn antenna is a circuit element that

provides a transition form a guided wave on a transmission line to a free space wave and it provides for the collection of electromagnetic energy.

ReciprocityAn antenna ability to transfer energy form the

atmosphere to its receiver with the same efficiency with which it transfers energy from the transmitter into the atmosphere

Antenna characteristics are essentially the same regardless of whether an antenna is sending or receiving electromagnetic energy

PolarizationPolarization is the direction of the electric field and is the

same as the physical attitude of the antennaA vertical antenna will transmit a vertically polarized wave

The receive and transmit antennas need to possess the same polarization

Types of AntennasIsotropic antenna (idealized)

Radiates power equally in all directionsDipole antennas

Half-wave dipole antenna (or Hertz antenna)Quarter-wave vertical antenna (or Marconi antenna)

Parabolic Reflective Antenna

BeamwidthBeamwidth is the angular separation of the half-power points of the radiated pattern

Half-wave Dipole (Hertz) Antenna

An antenna having a physical length that is one-half wavelength of the applied frequency is called a Hertz antenna or a half-wave dipole antenna. Hertz antennas are not found at frequencies below 2MHz because of the physical size needed of the antenna to represent a half-wave

Vertical (Marconi) AntennaVertical Antennas are used for frequencies

under 2 MHz. It uses a conducting path to ground that acts as ¼ wavelength portion the antenna above the ground. The above ground structure represents a /4 wavelength

CounterpoiseCounterpoise is a grounding grid

established where the earth grounding cannot satisfy electrical requirements for circuit completion. It is designed to be non-resonant at the operating frequency

Antenna Array

Antenna array is a group of antennas or antenna elements arranged to provide the desired directional characteristics. Generally any combination of elements can form an array. However, equal elements in a regular geometry are usually used.

Yagi-Uda AntennaThe Yagi-Uda antenna is a simple form of a directional antenna based off of a reflector placed /4 from the dipole antenna’s placement. Complex analysis to define the radiated patterns are experimental rather than theoretical calculations

reflector/2

dipole antenna

/4

Radiation ResistanceRadiation Resistance is the portion of the

antenna’s impedance that results in power radiated into space (i.e., the effective resistance that is related to the power radiated by the antenna. Radiation resistance varies with antenna length. Resistance increases as the increases

Radiation PatternRadiation pattern is an indication of radiated

field strength around the antenna. Power radiated from a /2 dipole occurs at right angles to the antenna with no power emitting from the ends of the antenna. Optimum signal strength occurs at right angles or 180° from opposite the antenna

Radiation PatternsRadiation pattern

Graphical representation of radiation properties of an antenna

Depicted as two-dimensional cross section

Beam width (or half-power beam width) Measure of directivity of antenna

Reception patternReceiving antenna’s equivalent to radiation pattern

Antenna GainAntenna gain

Power output, in a particular direction, compared to that produced in any direction by a perfect omnidirectional antenna (isotropic antenna)

Effective areaRelated to physical size and shape of antenna

Antenna GainAntenna gain is the measure in dB how

much more power an antenna will radiate in a certain direction with respect to that which would be radiated by a reference antenna

Propagation ModesGround-wave propagationSky-wave propagationLine-of-sight propagation

Ground Wave Propagation

Ground Wave PropagationFollows contour of the earthCan Propagate considerable distancesFrequencies up to 2 MHzExample

AM radio

Sky Wave Propagation

LOS Wireless Transmission Impairments

Attenuation and attenuation distortionFree space lossNoiseAtmospheric absorptionMultipathRefractionThermal noise

Thermal NoiseThermal noise due to agitation of electronsPresent in all electronic devices and transmission mediaCannot be eliminatedFunction of temperatureParticularly significant for satellite communication

Antenna HeightAntenna height above the ground is directly related to

radiation resistance. Ground reflections causing out-of-phase signals to be radiated to receiving antennas will degrade the transmission. Physical length and electrical length of most antennas are approximately 95% of the physical length. Ideal antenna height is usually based on trial and error procedures

Phased Array AntennaPhased Array antennas are a combination of antennas in which there is a control of the phase and power of the signal applied at each antenna resulting in a wide variety of possible radiation patterns

Antenna Installation Considerations

Safetystandard operating procedure priority

Groundinglightning strikesstatic charges

Surge protectionlightning searches for a second path to ground

Antenna Installation Considerations

Base, mast, and supporting structure needs clearance, serviceability (access), and complies with state, federal, and municipal guidelines