Microwaves

MicrowavesMicrowaves are electromagnetic waves whose frequencies range from about 300 MHz 300 GHz (1 MHz = 10 6 Hz and 1 GHz = 10 9 Hz) or wavelengths in air ranging from 100 cm 1 mm.

The word Microwave means very short wave, which is the shortest wavelength region of the radio spectrum and a part of the electromagnetic spectrum.

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Microwaves Frequency BandsProperties of MicrowavesMicrowave is an electromagnetic radiation of short wavelength.They can reflect by conducting surfaces just like optical waves since they travel in straight line.Microwave currents flow through a thin outer layer of an ordinary cable.Microwaves are easily attenuated within short distances.They are not reflected by ionosphere 3Advantages and Limitations 1. Increased bandwidth availability:Microwaves have large bandwidths compared to the common bands like short waves (SW), ultrahigh frequency (UHF) waves, etc. For example, the microwaves extending from = 1 cm - = 10 cm (i.e) from 30,000 MHz 3000 MHz, this region has a bandwidth of 27,000 MHz. 2. Improved directive properties:The second advantage of microwaves is their ability to use high gain directive antennas, any EM wave can be focused in a specified direction (Just as the focusing of light rays with lenses or reflectors) 4Advantages and Limitations 3. Fading effect and reliability:Fading effect due to the variation in the transmission medium is more effective at low frequency. Due to the Line of Sight (LOS) propagation and high frequencies, there is less fading effect and hence microwave communication is more reliable. 4. Power requirements:Transmitter / receiver power requirements are pretty low at microwave frequencies compared to that at short wave band.PH0101 Unit 2 Lecture 55Advantages and Limitations 5.Transparency property of microwaves:

Microwave frequency band ranging from 300 MHz 10 GHz are capable of freely propagating through the atmosphere. The presence of such a transparent window in a microwave band facilitates the study of microwave radiation from the sun and stars in radio astronomical research of space.PH0101 Unit 2 Lecture 56Advantages of microwaves over radio wavesbecause of high frequency, more data can be sent through microwaves -> increased bandwidth, higher speedsbecause of their short wave length, microwaves use smaller antennassmaller antennas produce a more focused beam which is difficult to interceptDisadvantages of microwave communicationthey require no obstacle is present in the transmission paththe cost of implementing the communication infrastructure is highmicrowaves are susceptible to rain, snow, electromagnetic interferenceApplicationsMicrowaves have a wide range of applications in modern technology, which are listed below

Telecommunication: Intercontinental Telephone and TV, space communication (Earth to space and space to Earth), telemetry communication link for railways etc.Radars: detect aircraft, track / guide supersonic missiles, observe and track weather patterns, air traffic control (ATC), burglar alarms, garage door openers, police speed detectors etc.

PH0101 Unit 2 Lecture 59Functional Block Diagram of a Communication SystemInput signal(Audio, Video, Data)Input TransducerTransmitterOutput TransducerReceiverOutput signal(Audio, Video, Data)ChannelElectrical System

Wire orWirelessAntenna and Wave PropagationSurface WaveDirect WaveSky WaveSatellitecommunicationMicrowave & Millimeter WaveEarthIonsphereTransmitting AntennaReceiving AntennaRepeaters(Terrestrial communication)50Km@25fts antenna1112Waveguide13Introduction to waveguidesA Hollow metallic tube of uniform cross section for transmitting electromagnetic waves by successive reflections from the inner walls of the tube is called waveguide.

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At frequencies higher than 3 GHz, transmission of electromagnetic energy along the transmission lines and cables becomes difficult.

This is due to the losses that occur both in the solid dielectric needed to support the conductor and in the conductors themselves.

A metallic tube can be used to transmit electromagnetic wave at the above frequencies15Basic featuresWaveguides may be used to carry energy between pieces of equipment or over longer distances to carry transmitter power to an antenna or microwave signals from an antenna to a receiver

Waveguides are made from copper, aluminum or brass. These metals are extruded into long rectangular or circular pipes.

An electromagnetic energy to be carried by a waveguide is injected into one end of the waveguide.

The electric and magnetic fields associated with the signal bounce off the inside walls back and forth as it progresses down the waveguide.

1516EM field configuration within the waveguide In order to determine the EM field configuration within the waveguide, Maxwells equations should be solved subject to appropriate boundary conditions at the walls of the guide.

Such solutions give rise to a number of field configurations. Each configuration is known as a mode. The following are the different modes possible in a waveguide system Components of Electric and Magnetic Field Intensities in an EM wave17

Possible Types of modes181. Transverse Electro Magnetic (TEM) wave:Here both electric and magnetic fields are directedcomponents. (i.e.) E z = 0 and Hz = 0

2. Transverse Electric (TE) wave: Here only the electric field is purely transverse to the direction of propagation and the magnetic field is not purely transverse. (i.e.) E z = 0, Hz 0 19Possible Types of modes 3. Transverse Magnetic (TM) wave: Here only magnetic field is transverse to the direction of propagation and the electric field is not purely transverse. (i.e.) E z 0, Hz = 0.4. Hybrid (HE) wave: Here neither electric nor magnetic fields are purely transverse to the direction of propagation. (i.e.) E z 0, Hz 0. 20

PH0101 Unit 2 Lecture 521Rectangular WaveguidesAny shape of cross section of a waveguide can support electromagnetic waves of which rectangular and circular waveguides have become more common.

A waveguide having rectangular cross section is known as Rectangular waveguidePH0101 Unit 2 Lecture 522Rectangular waveguide

Dimensions of the waveguide which determines the operating frequency rangePH0101 Unit 2 Lecture 523Dimensions of the waveguide which determines the operating frequency range:The size of the waveguide determines its operating frequency range. 2. The frequency of operation is determined by the dimension a. 3. This dimension is usually made equal to one half the wavelength at the lowest frequency of operation, this frequency is known as the waveguide cutoff frequency.4. At the cutoff frequency and below, the waveguide will not transmit energy. At frequencies above the cutoff frequency, the waveguide will propagate energy. PH0101 Unit 2 Lecture 524Wave paths in a waveguide at various frequencies

At high frequency(b) At medium frequency( c ) At low frequency(d) At cutoff frequencyPH0101 Unit 2 Lecture 525Wave propagationWhen a probe launches energy into the waveguide, the electromagnetic fields bounce off the side walls of the waveguide as shown in the above diagram.

The angles of incidence and reflection depend upon the operating frequency. At high frequencies, the angles are large and therefore, the path between the opposite walls is relatively long as shown in Fig.

PH0101 Unit 2 Lecture 526At lower frequency, the angles decrease and the path between the sides shortens.

When the operating frequency is reaches the cutoff frequency of the waveguide, the signal simply bounces back and forth directly between the side walls of the waveguide and has no forward motion.

At cut off frequency and below, no energy will propagate.

PH0101 Unit 2 Lecture 527Cut off frequencyThe exact size of the wave guide is selected based on the desired operating frequency. The size of the waveguide is chosen so that its rectangular width is greater than one half the wavelength but less than the one wavelength at the operating frequency. This gives a cutoff frequency that is below the operating frequency, thereby ensuring that the signal will be propagated down the line.

PH0101 Unit 2 Lecture 528Flexible WaveguideIt is used for bends, twists or in applications where certain criteria may not be fulfilled by normal waveguides.

Figure below shows some of the flexible waveguides:

PH0101 Unit 2 Lecture 529UsesTo reduce attenuation lossHigh frequenciesHigh powerCan operate only above certain frequenciesActs as a High-pass filterNormally circular or rectangularWe will assume lossless rectangular30Applications of Microwave:1. Telephone communications. 2. Radar 3. Space Communications 4. Heating ABOUT RADARRadar (radio detection and ranging) is an electronic systemfor transmitting electromagnetic signals and receiving echoes from objects of interest (targets).

Most radars work by transmitting a pulse of electromagnetic energy at a target and then listening with a receiver for the reflected echo from the target. Since electromagnetic waves travel at the velocity of light [186,411 miles (300,000 kilometers) per second] CONTDThe time delay between the transmitted pulse and the received echo can be used to determine the distance to thetarget (distance = speed time).

Radar is standalone system active system having its own transmitter, receiver, antenna, processor etc.

In radar strong radio waves are transmitted and receiver listens for scattered echoes very weak but can be amplified easily.

SIMPLE RADAR DIAGRAM

RADAR FUNCTIONS TRANSMITTER:Generate radio wavesPerform modulationAmplification to high power

RECIEVER:High sensitivityVery low noiseAbility to discern a received signal from background noiseCONTDPROCESSING & CONTROL:It regulates the rate at which pulses are sent (PRF). Synchronizes the function between Transmitter, Receiver, display, duplexer etc.

DUPLEXER:A switch to alternatively connect Tx and Rx to antenna. Protects receiver from high power of transmitter during transmission it aligns to transmitter. After pulse has been sent, it aligns antenna to receiver. CONTDANTENNA:Takes radar pulses from transmitter and puts into the air. Focuses energy into the well designed beam. Antenna is of two types Physically movingElectronically steered

DISPLAY:Presents received information to the operator. It is of two typesPPI (Plan Position Indicator)A-scope or A-scan PPI IMAGE

SOME HISTORY1886-88: Hertz demonstrated the Generation, reception and scattering of e.m waves.1903-04: Hulsmeyer developed and patented a primitive form for ships collision avoidance radar for ships.1925: Beginning of Pulsed Radars.1937: CHAIN HOME RADAR SYSTEM in Britain designed by Prof Watson Watt.1941: US, FM band Early Warning Radar at Oahu made.RADAR TYPES Detection and search radars Missile guidance systems Battlefield and reconnaissance radar Air Traffic Control and navigation Space and range instrumentation radar systems Weather-sensing Radar systems Radars for biological research

MAIN TYPES OF RADARThere are two main types of radar:

1)Primary Radar

Continuous wave RadarPulse Radar

2)Secondary Radar

PRIMARY RADARS1)CONTINUOS WAVE RADAR:Continuous-wave radar system is a radar system where a known stable frequency continuous wave radio energy is transmitted and then received from any reflecting objects. The return frequencies are shifted away from the transmitted frequency based on the Doppler effect if they are moving. The main advantage of the CW radars is that they are not pulsed and simple to manufacture.

CW radars also have a disadvantage because they cannot measure range. Range is normally measured by timing the delay between a pulse being sent and received, but as CW radars are always broadcasting, there is no delay to measure.

PRIMARY RADARS2)PULSE RADAR: The PULSE radar is the more conventional radar, which transmits a burst of radar energy and then waits for the energy (or echo) to be reflected back to the antenna. After a specific period of time (depending on how far the radar is searching) another pulse will be sent followed by another listening period. Since radar waves travel at the speed of light, range from the return can be calculated.

BASIC PULSE RADAR TERMS:Pulse DurationPulse Repetition TimePulse Repetition FrequencyListening TimeBASIC RADAR TERMS1)PULSE DURATION: The time a radar set is transmitting radio frequency (RF) energy. It is also referred to as pulse width (PW). Pulse duration is measured in millionths of a second or microseconds (usec).

2)PULSE REPETITON TIME: This is the time required to complete one transmission cycle. It is the time from the beginning of one radar pulse to the beginning of the next. It is the reciprocal of our next term, Pulse Recurrence Frequency (PRF). This term represents the period for one transmission cycle.

CONTD3)PULSE REPETITON FREQUENCY: The PRF equals the number of pulses per second the radar transmits. If you want the radar to look at long ranges, a low PRF is required (this allows time for the radar energy to be reflected by the target and to return to the antenna before the next pulse is transmitted). For shorter ranges, a higher PRF can be used.

4)LISTENING TIME: Listening time is the part of the Rest Time that the radar can receive and process the echoes of radar returns. It is measured is usec.

Applications of Radar

FIELDS OF APPLICATIONMILITARYREMOTE SENSINGAIR TRAFFIC CONTROLLAW ENFORCEMENT AND HIGHWAY SECURITYAIRCRAFT SAFETY AND NAVIGATIONSHIP SAFETYSPACEMISCELLANEOUS APPLICATIONSMILITARYIMPORTANT PART OF AIR DEFENCE SYSTEM,OPERATION OF OFFENSIVE MISSILES & OTHER WEAPONSTARGET DETECTION, TARGET TRACKING & WEAPON CONTROLTRACKS THE TARGETS, DIRECTS THE WEAPON TO AN INTERCEPT AND ASSESS THE EFFECTIVENESS OF ENGAGEMENTALSO USED IN AREA, GROUND & AIR SURVEILLANCE.

WEATHER OBSERVATION-T.V.REPORTINGPLANETARY OBSERVATIONBELOW GROUND PROBINGMAPPING OF SEA ICE

REMOTE SENSING

USED TO SAFELY CONTROL AIR TRAFFIC IN THE VICINITY OF THE AIRPORTS AND ENROUTEGROUND VEHICULAR TRAFFIC & AIRCRAFT TAXINGMAPPING OF REGIONS OF RAIN IN THE VICINITY OF AIRPORTS & WEATHER

AIR TRAFFIC CONTROL

RADAR SPEED METERS ARE USED BY POLICE FOR ENFORCING SPEED LIMITSIT IS USED FOR WARNING OF PENDING COLLISION, ACTUATING AIR BAG OR WARNING OF OBSTRUCTION OR PEOPLE BEHIND A VEHICLE OR IN THE SIDE BLIND ZONELAW ENFORCEMENT & HIGHWAY SAFETY

AIRBORNE WEATHER AVOIDANCE RADAR OUTLINES THE REGIONS OF PRECIPITATION & DANGEROUS WIND SHEARLOW FLYING MILITARY AIRCRAFTS RELY ON TERRAIN AVOIDANCE & TERRAIN FOLLOWING RADARS TO AVOID COLLISION WITH HIGH TERRAIN & OBSTRUCIONSAIRCRAFT SAFETY & NAVIGATION

RADAR IS FOUND ON SHIPS & BOATS FOR COLLISION AVOIDANCE & TO OBSERVE NAVIGATION BUOYS, WHEN THE VISIBILITY IS POORSHORE BASED RADARS ARE USED FOR SURVEILLANCE OF HARBOURS & RIVER TRAFFICSHIP SAFETY

SPACE VEHICLES HAVE USED RADAR FOR CLOCKING & FOR LANDING ON THE MOONUSED FOR PLANETARY EXPLORATIONGROUND BASED RADARS ARE USED FOR DETECTION & TRACKING OF SATELLITES & OTHER SPACE OBJECTSUSED FOR RADIO ASTRONOMYSPACE

IT IS USED FOR NON CONTACT MEASUREMENT OF SPEED & DISTANCEUSED FOR OIL & GAS EXPLORATIONUSED TO STUDY MOVEMENTS OF INSECTS & BIRDS

OTHER APPLICATIONS GPR APPLICATIONS SHALLOW GPR SURVEYSLOCATE PIPES AND UTILITIESBURIED OBJECTSCEMETERLY & GRAVE LOCATION DEEP GPR SURVEYSLANDFILL & TRENCH DELINEATIONBEDROCK DEPTH STUDIESSINK HOLE LOCATIONHHR APPLICATIONSSECURITY & BORDER SURVEILLANCE SYSTEMUNDER GROUND, THROUGH-WALL & OCEAN IMAGINGAUTOMOTIVE SAFETY, INCLUSING COLLISION-AVOIDANCE & INTELLIGENT CRUISE-CONTROL SYSTEMSMART DIVICE SUCH AS LIGHTS, HEATERS & TOOLS THAT AUTOMATICALLY TURN ON OR OFFMEDICAL DIAGNOSTICS DAY TO DAYAPPLICATIONS

MICROPOWER IMPULSE RADAR SENSORS USED IN PROXIMITY FUSES HAVE BEEN SUCCESSFULLY TESTED. THE FUSES TRIGGER SMALL BOMBS TO DETONATE AT ABOUT 1 METER FROM THE GROUND. DETONATORS

LIVERMORE ENGINEERING TECHNOLOGIST USED A MICROPOWER IMPULSE RADAR SENSOR ATTACHED TO AN EXTENDER TO SEARCH FOR TRAPPED PEOPLE THROUGH RUBBLE AT GROUND ZERO OF THE WORLD TRADE CENTER FOLLOWING THE SEPTEMBER 11, 2001, TERRORIST ATTACKS.

A LIFE SAVER

A) THE HERMES (HIGH-PERFORMANCE ELECTROMAGNETIC ROADWAY MAPPING AND EVALUATION SYSTEM) BRIDGE INSPECTOR IS A RADAR-BASED SENSING SYSTEM MOUNTED IN A TRAILER. (B) THE ARRAY OF 64 RADAR MODULES LOCATED BENEATH THE TRAILER PRODUCES IMAGES OF THE INSIDES OF BRIDGE DECKS. (C) THIS IMAGE SHOWS A SUSPECT AREA WHERE A DELAMINATION IN THE CONCRETE MAY HAVE OCCURRED.

HERMES- ROAD MAINTAINANCE

THIS VEHICLE TOWS THE ANTENNA TRANSCEIVER GROUP (ATG) WITH THE INTEGRATED MODULAR AZIMUTH POSITIONING SYSTEM (MAPS) MOUNTED ON THE TRAILER. THIS IS CONTROLLED BY AN OPERATOR EITHER LOCATED WITHIN THE SHELTER OR REMOTELY LOCATED GHANTATUNNEL WALL INSPECTION

MINE INSPECTION

63LOCATING UNDER GROUND PIPES

LOCATING GRAVE

Homeland Security ApplicationsPotential Security Applications Detection of hidden weapons and explosives Detecting non-metallic weapons Postal screening of envelopes for bacteria Chem/bio detection

Security screening wand

ExplosivesStand-off detectionPostal screeningEnvelope

Terahertz Images Can Reveal Objects Concealed Under Cloth, Paper, Tape, Even Behind Walls

Objects Concealed Under clothes

Knife Wrapped in Newspaper

Microwave Applications

Wireless Charging of Mobile Phones Using Microwaves

69INTRODUCTIONMobile phones becoming basic part of life

Recharging of mobile phones is a big problem

Objectiveto recharge any mobile phone independent of manufacturer and battery make

Achieved by recharging battery while talking using microwaves

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CONTD More you talk more the mobile get charged!

No separate mobile charger

Removal of talk time and battery stand by from mobile specifications

Additives to mobile handsets:SensorRectenna71WHATS HAPPENING?Microwave signal is transmitted from transmitter along with message signal using slotted waveguide antenna at frequency 2.45 GHz

Charging made universal72

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Microwave region of electromagnetic spectrumWe choose s band of microwave region(2-4GHz)

74DesignationFrequency rangeL Band1 to 2 GHzS Band2 to 4 GHzC Band4 to 8 GHzX Band8 to 12 GHzKu Band12 to 18 GHzK Band18 to 26 GHzKa Band 26 to 40 GHzQ Band 30 to 50 GHzU Band40 to 60 GHzFREQUENCY SELECTION Select license free 2.45 GHz Industrial, Scientific and Medical (ISM) radio bands

ISM bands are reserved internationally for non-commercial use of RF electromagnetic fields for industrial, scientific and medical purpose

75Principle of Operation & Block DiagramTransmitting station with the microwave transmittersensorRectennaRF cablecirculatorwaveguideSlotted waveguideAntennamobile signal

The microwave signal is transmitted along with message signal using slotted wave guide antenna.

The sensor search for the mobile signal , in addition it has a RECTENNA.

Rectenna receives the transmitted power and converts the microwave power to DC power.

TRANSMITTERThe MAGNETRON is a self-contained microwave oscillator.

Efficiency of this high power oscillator lies between 50% and 80%.

Electron beam EnergyMicrowave Energy

Cross Field DeviceSlotted waveguide antenna

It is used as ideal power transmitter (because of its high aperture efficiency >95%) .

It has high power handling capacity .

It has 64 slots of power uniformly through free space to the rectenna.

SENSORSThe sensor circuitry is a simple circuit, which detects if the mobile phone receives any message signal. This is required, as the phone has to be charged as long as the user is talking. Thus a simple F to V converter would serve our purpose.

A simple yet powerful F to V converter is LM2907. Using LM2907 would greatly serve our purpose. It acts as a switch for triggering the rectenna circuitry

RECTENNAA rectifying antenna called a rectenna receives the transmitted power and converts the microwave power to direct current (DC) power.

This demonstration rectenna consists of 6 rows of dipoles antennas where 8 dipoles belong to each row. Each row is connected to a rectifying circuit which consists of low pass filters and a rectifier.

The rectifier is a GaAs Schottky barrier diode that is impedance matched to the dipoles by a low pass filter. The diode rectifies the current induced in the antenna by the microwaves.

A simple rectenna element consists of adipole antennawith an RFdiodeconnected across the dipole elements. The dioderectifiestheACcurrent induced in the antenna by the microwaves, to produce DC power, which powers a load connected across the diode.Schottky diodesare usually used because they have the lowest voltage drop and highest speed and therefore have the lowest power losses due to conduction and switching. Large rectennas consist of an array of many such dipole elements.RECTENNA DESIGNImplementationRecently NOKIA has launched this wireless charging technology in its new recent mobile model NOKIA LUMIA 1020.

Energy efficient chargers of all size and shape to match our phone.

They are all quiet compactable , which means we can use any chargers as we like.

AdvantagesThe need of different types of chargers by different manufacturers is totally eliminatedLower risk of ELECTRICAL SHOCK or shorting.Convenience.Wireless energy transfers can potentially recharge the mobile phones without chords.

DisadvantagesWireless transmission of the energy causes some drastic effects to human body, because of its radiationProcess is of high cost.