TWC3401Wireless Computing

Lecture 3 Lecture 3

AntennaAntennaTrimester 3

Session 2008/2009

Outlines:

- Outline the purpose of an antenna

- Define Decibel, gain, and loss

-Listing the different antenna types, shapes, sizes, and

their applications

- Explain RF signal strength and direction

- Describe how antenna work

- Antenna system implementation

Antenna

– RF system components: Amplifier, Filter, Mixer, Antenna.

– Modulation: loading the signals with some king of useful information-audio, music, digital data.

– Antenna:

– The purpose of antenna is to convert electricity into electromagnetic waves and radiate those waves into a medium (air or free space).

– Antenna installation needs proper planning to ensure good signal coverage, user mobility, and eliminate interference

Antenna: Gain and Loss-Understanding of RF Signal transmission involves knowing:

1.The strength or power with which the transmitter is sending the signal.2.The amount of reduction in signal strength caused by cables, connectors.3.The transmission medium (air or free-space).4.The minimum strength of the signal required by the receiver to be able to properly recover the data sent by the transmitter.

-Gain: Strength in the signal‘s power.-Loss: Weakness in the signal’s power.

-Both gain and loss are relative concepts and they expressed in terms of Decibel (dB). Gain = 3dB (+3dB)/ Loss = 3dB (-3dB).-Decibel is a ratio between two signal levels

-Knowing how much gain or loss occurs in RF system composed of radio transmitter, receivers, cables, connectors is necessary to assist the RF engineers to select appropriate components and installation.

Gain and Loss-

In dBin milliWatt (mW)

in milliWatt (mW)

Gain and Loss-

RULE1: x = by , then y = logb (x)RULE2: logb (x/y) = logb (x) - logb (y)

RULE3: 1 W = 1000 mW

Antenna Categories- Antennas categorized as: Passive and Active.1.Passive Antenna - Constructed of a piece of metal, wire or similar conductive material-Does not amplify the signal. It radiate the signal with the same amount of energy that appears at the antenna connector.

2.Active Antenna- Passive antenna with amplifier build in.-The amplifier is connected directly to

the piece of metal that forms the antenna itself

Antenna Sizes and Shapes-The size and shape of antenna depend on three characters:

1. The frequency (range of frequencies) on which antenna will transmit and receive.

2. The direction of radiated electromagnetic waves.3. The power in which the antenna must transmit and receive

- The size of Antenna is inversely propositional to the wavelength of the signal it is designed to transmit and receive.

- Lower frequency signals Larger Antenna.- Higher frequency signals shorter antenna.

- Antenna shapes vary according to their specific application:- Omnidirectional, Directional, Patch, Parabolic dish, Yagi.

Antenna Sizes and Shapes1.Omnidirectional Antenna

- Used to transmit and receive the signal to/from all directions

2.Directional Antenna- Used to transmit and receive the signal to/from ONE direction ONLY.

3.Yagi Antenna emits wider, less focused RF energy.- Used to send and receive radio station signals

4. Parabolic Dish Antenna emits narrow, more concentrated beam of RF energy.

- Used to send and receive satellite signals5. Patch/Panel Antenna

- Emits RF energy beam that is horizontally wide BUT vertically taller. - Used to send RF down a long corridor, Cellular telephone tower.

Antenna

Antenna (Signal strength/direction/wavelength)

- Distance between transmitter and receiver determiners the strength of signal we want to send. This in turn determines the size and shape of antenna we need to use.

- Larger antenna has higher gain than shorter antenna.

- AM station antenna over 566 meters long, Cellular phone antenna over 33cm long.

Antenna Radiation Patterns- Antenna performance is a measure of how efficiently an antenna can radiate RF signal.- The design, installation, size, and shape of antenna can affect its performance.

-Antenna pattern indicates the direction, width, and shape of RF signal beam coming from the antenna.

Antenna Patterns viewed from above

Antenna Radiation Pattern

Antenna Patterns viewed from side

Antenna Radiation Pattern

Different Antenna Radiation Patterns

Antenna Polarization- The orientation of wave leaving the antenna (Horizontal OR Vertical). - Hand Phone up. Vertical Polarization ( up and down).

- Hand Phone laying down. Horizontal Polarization (side to side)- Most efficient signal transmission and receiving when sending and receiving antennas are equal polarized.- Different polarization between devices can cause poor communication between them.

Horizontal and Vertical Polarization

Antenna Dimensions1.One dimensional Antenna

- Basically length or straight piece of wire or metal

2. Two dimensional Antenna- Organized in two dimensional pattern with both high and width.- examples are Patch , Horn, and dish antenna.

Satellite dish antenna Horn Antenna

Patch Antenna

Smart Antenna1

- Smart antenna system combines an antenna array with a digital signal-processing capability to transmit and receive in an adaptive manner. - It focus the RF energy in particular direction according to place of mobile receiver to avoid wasting energy and prevent interference.

Directional Antenna vs Smart Antenna

Smart Antenna

Smart Antenna

- Two class of smart antennas.

1.Switched beam antenna- use several narrow beam antennas pointing in

different directions and turns each ON or OFF as the receiver moves across the path of beams.

Smart Antenna

2. Adaptive or phased array antennas- Like patch antenna. Single piece of metal divided into matrix of

radiating elements. - A computer-based signal processor controls circuits in the antenna system, turning elements of the matrix On or OFF as the mobile user moves in front of the antenna

Antenna System Implementation- Proper installation of antennas requires knowing the users requirements and dealing with various challenges such as physical obstacles.-Cellular services providers spend a great time and effort designing their network of antennas and studying user traffic pattern in order to provide best signal coverage (best service to customers) and minimizing interference.

1.Antenna Cables.- Most Antennas are connected to the transmitter or receiver using

coaxial cable .- Almost all conducting materials offer a resistance to flow of electricity on a

wire- Designers must consider the signal loss caused by cables and connectors

- Cables' signal loss is measured in relation to the length of the cable.- The longer the cable, the more loss occurs.

coaxial cables different sizes

Antenna System Implementation2. Antenna RF Propagation-The way radio waves propagate (move) between the transmitter and receiver through the atmosphere depend on the frequency of the signal. - Three Groups:

1. Ground Waves: follow curvature of the earth.2. Sky Waves: bounce between ionosphere and the surface of earth.3. Line-of-sight waves: follow straight path.

Antenna System Implementation2. Point-to-Multipoint Links- One transmitter communicates with several mobile clients.- Omnidirecional antenna with directional antenna.

2. Point-to-Point Links- Two devices connect with each other.- Telephone companies make extensive use of point to point microwave links

Point-to-Multipoint Links Point-to-Point Links

Antenna System Implementation3. Link Budget- Calculate if you have enough signal strength to meet the receiver’s minimum requirements.- Need information from equipment specifications include antenna gain, cable and connector loss for receiver and the transmitter, receiver sensitivity…etc

4. Antenna Alignment- Point-to-point links need to position the antennas at same height and point them toward one another to maximize strength of the signal.- Spectrum Analyzer: tool display the signal amplitude, frequency, and detect interference in particular frequency or channel.