Emr - Electro Magnetic Radiations

Electromagnetic Waves: (Electromagnetic radiation EMR) ek he baat hai

1 electromagnetic waves do not need medium (hawa pani wagara) to travel, they can travel through Vacume

2 They lie in the electromagnetic spectrum (jis main X-rays, gamma rays aur visible spectrum shamil hota hai)

3 Wo dual nature ki hoti hain... wave nature and particle nature

4 They Do not viberate other molecules, (matlab wo Air k molecules viberate nahi kertin hain so no sound is produced)

5 They are MUCH Faster than Mechanical waves

6 Electromagnetic radiation (EM radiation or EMR) is a form of energy emitted and absorbed by charged particles, which exhibits wave-like behavior as it travels through space.

7 EMR has both electric and magnetic field components, which stand in a fixed ratio of intensity to each other, and which oscillate in phase perpendicular to each other and perpendicular to the direction of energy and wave propagation (refer to my diagram in the mail)

8 Its speed is that of the speed of light

9 Electromagnetic waves are also called electromagnetic radiations (EMR)

10 and 11 and 12: EMR carries energy—sometimes called radiant energy—through space continuously away from the source (this is not true of the near-field part of the EM field). EMR also carries both momentum and angular momentum. These properties may all be imparted to matter with which it interacts. EMR is produced from other types of energy when created, and it is converted to other types of energy when it is destroyed. The photon is the quantum of the electromagnetic interaction, and is the basic "unit" or constituent of all forms of EMR. The quantum nature of light becomes more apparent at high frequencies (or high photon energy). Such photons behave more like particles than lower-frequency photons do.

Mechanical waves:

A mechanical or material wave is a wave that needs a medium to travel. The oscillating material does not move far from its initial equilibrium position, as only the energy is transferred by connected particles. Ocean waves and sound are examples of this phenomenon.

A mechanical wave requires an initial energy input. Once this initial energy is added, the wave travels through the medium until all its energy is transferred. Electromagnetic waves require no medium, but can still travel through one.

There are three types of mechanical waves: Transverse waves, longitudinal waves, and surface waves. Transverse waves cause the medium to vibrate at a 90-degree angle to the direction of the wave. Transverse waves have two parts—the crest and the trough. The crest is the highest point of the wave and the trough is the lowest. The wavelength is the distance from crest to crest or from trough to trough.

When the particles the wave is traveling through are close together, it is called compression. When the particles it is traveling through are spread apart, it is called rarefaction.

Pressure waves travel faster through solids and liquids than through gases such as air.

The final type of wave is a surface wave. This type of wave travels along a surface that is between two media. An example of a surface wave would be waves in a pool, or in an ocean, lake, or any other type of water body.

One important property of mechanical waves is that their amplitudes possess an unusual form, displacement divided by reduced wavelength. When this gets comparable to unity, significant nonlinear effects such as harmonic generation may occur, and, if large enough, may result in chaotic effects. For example, waves on the surface of a body of water break when this dimensionless amplitude exceeds 1, resulting in a foam on the surface and turbulent mixing.

Smart Antenna:

Smart antennas (also known as adaptive array antennas, multiple antennas and recently MIMO) are antenna arrays with smart signal processing algorithms used to identify spatial signal signature such as the direction of arrival (DOA) of the signal, and use it to calculate beamforming vectors, to track and locate the antenna beam on the mobile/target. The antenna could optionally be any sensor.

Smart antenna techniques are used notably in acoustic signal processing, track and scan RADAR, radio astronomy and radio telescopes, and mostly in cellular systems like W-CDMA and UMTS.

Smart antennas have two main functions: DOA estimation and Beamforming.

Direction of arrival (DOA) estimation

The smart antenna system estimates the direction of arrival of the signal, using techniques such as MUSIC (Multiple Signal Classification), estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithms, Matrix Pencil method or one of their derivatives. They involve finding a spatial spectrum of the antenna/sensor array, and calculating the DOA from the peaks of this spectrum. These calculations are computationally intensive.

Matrix Pencil is very efficient in case of real time systems, and under the correlated sources.

Beamforming

Beamforming is the method used to create the radiation pattern of the antenna array by adding constructively the phases of the signals in the direction of the targets/mobiles desired, and nulling the pattern of the targets/mobiles that are undesired/interfering targets. This can be done with a simple FIR tapped delay line filter. The weights of the FIR filter may also be changed adaptively, and used to provide optimal beamforming, in the sense that it reduces the MMSE between the desired and actual beampattern formed. Typical algorithms are the steepest descent, and LMS algorithms [4].

Types of smart antennas

Two of the main types of smart antennas include switched beam smart antennas and adaptive array smart antennas. Switched beam systems have several available fixed beam patterns. A decision is made as to which beam to access, at any given point in time, based upon the requirements of the system. Adaptive arrays allow the antenna to steer the beam to any direction of interest while simultaneously nulling interfering signals [3]. Beamdirection can be estimated using the so-called direction-of-arrival (DOA) estimation methods [6].

In 2008, the United States NTIA began a major effort to assist consumers in the purchase of digital television converter boxes.[1] Through this effort, many people have been exposed to the concept of smart antennas for the first time. In the context of consumer electronics, a "smart antenna" is one that conforms to the EIA/CEA-909 Standard Interface.

Limited Choice of EIA/CEA-909A Smart Antennas in the Marketplace

Prior to the final transition to ATSC Digital television in the United States on June 11, 2009, two smart antenna models were brought to market:

RCA ANT2000 -- no longer available from retailers

DTA-5000 -- manufactured by Funai Electric, marketed under the "DX Antenna" brand name, sometimes associated with the Sylvania brand name; no longer available from retailers

And two models are causing consumer confusion:

Although the Apex SM550 is capable of connecting to a CEA-909 port for the purpose of drawing electrical power, it is not a true smart antenna.[2]

The unfortunately-named Channel Master 3000A SMARTenna is a conventional antenna, not a smart antenna.[3]

Extension of smart antennas

Smart antenna systems are also a defining characteristic of MIMO systems, such as the IEEE 802.11n standard. Conventionally, a smart antenna is a unit of a wireless communication system and performs spatial signal processing with multiple antennas. Multiple antennas can be used at either the transmitter or receiver. Recently, the technology has been extended to use the multiple antennas at both the transmitter and receiver; such a system is called a multiple-input multiple-output (MIMO) system. As extended Smart Antenna technology, MIMO supports spatial information processing, in the sense that conventional research on Smart Antennas has focused on how to provide a beamforming advantage by the use of spatial signal processing in wireless channels. Spatial information processing includes spatial information coding such as Spatial multiplexing and Diversity Coding, as well as beamforming.