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MICROWAVE INTRODUCTION

MICROWAVE INTRODUCTION. Prepared by Mrs.A.A.Nikam Subject:Microwave Engineering Class: BE E&TC A.Y. 2017-18 SEM I. Contents. Introduction to Microwaves Properties of Microwaves Advantages/Disadvantages of Microwaves Waveguide Applications of Microwaves Microwave oven Radar

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MICROWAVE INTRODUCTION

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  1. MICROWAVE INTRODUCTION Prepared by Mrs.A.A.Nikam Subject:Microwave Engineering Class: BE E&TC A.Y. 2017-18 SEM I

  2. Contents • Introduction to Microwaves • Properties of Microwaves • Advantages/Disadvantages of Microwaves • Waveguide • Applications of Microwaves • Microwave oven • Radar • Wireless Mobile Charging • Others Applications

  3. Waves In physics, a wave is disturbance or oscillation that travels through matter or space, accompanied by a transfer of energy. There are two main types of waves. Mechanical Waves Electromagnetic Waves • Radio waves • Microwaves • Infrared radiation • Visible light • Ultraviolet radiation

  4. Microwaves Microwaves are electromagnetic waves 300MHz- 300Ghz Frequency range Microwaves is the shortest wavelength region of the radio spectrum and a part of the electromagnetic spectrum 100cm- 1mm Wavelengths range in air The word microwave means “very short wave”

  5. Microwaves Frequency Bands

  6. Properties of Microwaves 1.Electromagnetic radiation of short wavelength 2.Can reflect by conducting surface like optical waves. 3.M.W current flows through outer layer of conductor 4.Microwaves are easily attenuated 5.They are not reflected by ionosphere

  7. Advantages and Limitations Microwaves have large bandwidths Improved Directive properties.Can be focused in a specified direction Fading effect and reliability. Due to LOS and high frequency fading effect is very low Transmitter/Receiver power requirements are pretty low at microwave frequencies

  8. Advantages and Limitations Microwave band ranging from 300MHz-10GHz are capable of freely propagating through atmosphere This helps in astronomical research of space in the study of microwave radiations from the sun and stars

  9. Advantages of Microwave communication High bandwidth,higher speeds Because of high frequency, more data can be sent. Smaller antennas produce a more focused beam Because of their short wavelength,microwaves use smaller antennas

  10. Disadvantages of microwave communication • They require no obstacle is present in the transmission path • The cost of implementing the communication infrastructure is • high • Microwaves are susceptible to rain,snow,electromagnetic interference

  11. Functional Block Diagram of a Communication System Input signal (Audio, Video, Data) Input Transducer Transmitter Wire or Wireless Channel Output signal (Audio, Video, Data) Output Transducer Receiver Electrical System

  12. Antenna and Wave Propagation Microwave & Millimeter Wave Satellite communication Ionsphere Sky Wave Repeaters(Terrestrial communication) 50Km@25fts antenna Direct Wave Surface Wave Receiving Antenna Transmitting Antenna Earth

  13. Waveguide A Hollow metallic tube of uniform cross section for transmitting electromagnetic waves by successive reflections from the inner walls of the tube is called waveguide.

  14. Why we need Waveguide?? Electromagnetic waves at frequencies greater than 3GHz; transmission through cables becomes difficult. Reason This is due to losses in the solid cable and the dielectric use to support the cable. So, we use waveguide which is a hollow metallic

  15. Basic features e.g. In Antennas transmitter power to antenna and microwave signal from antenna to receiver Waveguides are used to carry energy from one equipment to another The metals are extruded into long rectangular or circular pipes Waveguides are made from copper, aluminum or brass The electric and magnetic field of signals bounce off the walls back and forth. The energy to be transmitted is injected from one end of the waveguide through probes

  16. Em field configuration within the waveguide EM field configuration can be determined from Maxwell’s equation. There are number of configurations and each configuration is known as mode. Possible modes Hybrid Transverse Electromagnetic Transverse Electric Transverse Magnetic

  17. Components of Electric and Magnetic Field Intensities in an EM wave

  18. Possible types of Modes 1.Transverse Electro Magnetic (TEM) wave: Here both electric and magnetic fields are directed components.(i.e.) Ez=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 2.Transverse Electric (TE) wave: The electric field component is purely transverse to the direction of propagation.(i.e.) Ez=0 and Hz0

  19. Possible types of Modes 3.Transverse Magnetic (TM) wave: The magnetic field component is purely transverse to the direction of propagation.(i.e.) Ez0 and Hz0 4.Hybrid (HE) wave: Here neither electric nor magnetic fields are purely transverse to the direction of propagation.(i.e.) Ez0 and Hz0

  20. Rectangular Waveguides • Any 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 waveguide

  21. Rectangular waveguide Dimensions of the waveguide which determines the operating frequency range

  22. Dimensions of the waveguide which determines the operating frequency range: 1.The size of the waveguide determines its operating frequency 2.The frequency of operation is determined by dimension ‘a’ which is usually made one half the wavelength at lowest frequency of operation. 3.At cutoff frequency and below, the waveguide will not transmit energy.

  23. Wave paths in a waveguide at various frequencies • At high • frequency (b) At medium frequency ( c ) At low frequency (d) At cutoff frequency

  24. Wave propagation • When 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.

  25. At 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.

  26. Flexible Waveguide • It 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:

  27. Applications of Microwaves

  28. How a Microwave Oven Works?

  29. History • Invented Accidentally By Dr. Percy Lebaron Spencer.

  30. Working Principle Microwave radiations generated by a magnetron pass through the exposed food, create dielectric heating within the food, this is the basic principle on which a microwave oven works. Dielectric Heating

  31. How the Oven Works • Electricity from the wall outlet travels through the power cord and enters the microwave oven through a series of fuse and safety protection circuits • When the oven door is closed, an electrical path is also established through a series of safety interlock switches

  32. Sensing That All Systems Are Set To Go, The Signal Activates Triac Producing A Voltage Path To The High-voltage Transformer. • The High-voltage Transformer Along With A Special Diode And Capacitor Arrangement Increases The Typical Household Voltage From ~220 Volts To ~3000 Volts

  33. The magnetron converts the high voltage into the microwave frequency for cooking. • The microwave energy is transmitted into a waveguide. • The waveguide feeds the energy to the stirrer blade and into the cooking area. • When the door is opened, or the timer reaches zero, the microwave energy stops.

  34. How Foods Get Cooked • The microwaves that penetrate the food have an electric field that oscillates 2.45 billion times a second, a frequency that is well absorbed by polar liquid molecules such as water, sugars, fats and other food molecules. • Water interacts with the microwave: • flipping its orientation back and forth very rapidly • bumping into one another and producing heat, cooking the food.

  35. Radar

  36. Introduction Radar Radio Detection and Ranging • A System For Detecting The Presence, Direction, Distance, And Speed Of Aircraft, Ships, And Other Objects, By Sending Out Pulses Of Radio Waves Which Are Reflected Off The Object Back To The Source. • The Time Delay Between The Transmitted Pulse And The Received Echo Can Be Used To Determine The Distance To The Target .

  37. Basic Principle and Operation Of Radar

  38. RADAR FUNCTIONS TRANSMITTER: • Generate radio waves • Perform modulation • Amplification to high power RECIEVER: • High sensitivity • Very low noise • Ability to discern a received signal from background noise PROCESSING & CONTROL: • It regulates the rate at which pulses are sent (PRF). • Synchronizes the function between Transmitter, Receiver, display, duplexer etc.

  39. ANTENNA: • Takes radar pulses from transmitter and puts into the air. • Focuses energy into the well designed beam. • Antenna is of two types • Physically moving • Electronically steered DISPLAY: Display received information to the operator. It is of two types • PPI • Used for surface search and navigation • A-Scan • Used for gunfire control DUPLEXER: • A switch to alternatively connect Tx and Rx to antenna.

  40. MAIN TYPES OF RADAR There are two main types of radar: 1)Primary Radar • Continuous wave Radar • Pulse Radar 2)Secondary Radar SSR

  41. 1)CONTINUOS WAVE RADAR: • Employs continual RADAR transmission • Separate transmit and receive antennas • Relies on the “DOPPLER SHIFT”

  42. 2)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. • Since radar waves travel at the speed of light, range from the return can be calculated.

  43. Applications of Radar

  44. MILITARY • Target Detection, Target Tracking & Weapon Control • Tracks The Targets, Directs The Weapon To An Intercept And Assess The Effectiveness Of Engagement

  45. REMOTE SENSING • Weather Observation • Planetary Observation • Below Ground Probing

  46. AIR TRAFFIC CONTROL • Used To Safely Control Air Traffic In The Vicinity Of The Airports. • Mapping Of Regions Of Rain In The Vicinity Of Airports & Weather.

  47. LAW ENFORCEMENT & HIGHWAY SAFETY • Radar Speed Meters Are Used By Police For Enforcing Speed Limit.

  48. AIRCRAFT SAFETY & NAVIGATION • Airborne Weather Avoidance Radar Outlines The Regions Of Precipitation & Dangerous Wind Shear • Low Flying Military Aircrafts Rely On Terrain Avoidance & Terrain Following Radars To Avoid Collision With High Terrain & Obstructions

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