Microwave Communication PDF

Answer with “Yes” or “No” in [ ] and correct the “No” answer: 1. Microwaves don't need to be treated differently from low-frequency circuits. [NO] >> need 2. In microwaves, antenna gain is proportional to the electrical size of the antenna. [Yes] 3. Waveguides have more losses compared to two lin...

Answer with “Yes” or “No” in [ ] and correct the “No” answer: 1. Microwaves don't need to be treated differently from low-frequency circuits. [NO] >> need 2. In microwaves, antenna gain is proportional to the electrical size of the antenna. [Yes] 3. Waveguides have more losses compared to two lines and coaxial lines. [NO] >> less 4. waveguides have cutoff frequencies below which propagation is possible. [NO] >> is not 5. Microwave signals travel by line of sight and are not bent by the ionosphere. [Yes] 6. The dominant mode is the mode with highest cutoff frequency. [NO] >> lowest 7. In TE modes, the electric field is transverse to the direction of propagation. [Yes] 8. Klystron and Magnetron are microwave active devices. [Yes] 9. For the TE mode, if n or m is zero, all fields are zero. [NO] >> TM 10. More bandwidth (information-carrying capacity) can be realized at higher frequencies. [Yes] 11. For microwaves, the wavelengths are between 1mm and 1000 mm. [Yes] 12. The order of the mode is not refer to the field configuration in the waveguide. [NO] >> refer 13. Microwave communications systems began to be developed soon after the birth of radar. [Yes] 14. Rectangular waveguides have cutoff frequencies below which propagation is not possible. [Yes] 15. Waveguides are not effected by the surrounding electromagnetic waves[Yes] 16. The dominant mode is the mode with lowest cutoff frequency. [Yes] 17. In TM modes, the magnetic field is transverse to the direction of propagation. [Yes] 18. The design of the waveguide depends on the frequency and the power of the transmitted signals. [Yes] 19. The order of the modes change depending on the dimensions of the waveguide. [Yes] 20. The order of the next modes change depending on the dimensions of the waveguide. [Yes] 21. More bandwidth (information-carrying capacity) can be realized at lower frequencies. [NO] > higher 22. For the TE mode n and m cannot be both zero. [Yes] 23. Rectangular waveguides have cutoff frequencies below which the propagation is possible. [NO] >> is not 24. As per IEEE, electromagnetic waves between 30 and 300 GHz are called millimeter waves (MW). [Yes] 25. In TE modes, the magnetic field is transverse to the direction of propagation. [NO] >> TM 26. A particular mode is only supported above its cutoff frequency. [Yes] 27. For microwaves, the Frequencies are between 3x106 Hz and 3x109 Hz. [NO]>> 300 x106 & 300 x109 28. Microwaves need to be treated differently from low-frequency circuits. [Yes] 29. Waveguide can't support TE or TM modes. [NO] >> can 30. Rectangular waveguides have cutoff frequencies above which propagation is possible. [Yes] 31. The attenuator can pass the signal coming from any port to the next port in a circular direction. [NO] >> circulator 32. For the waveguide, the dominant mode is the mode with lowest cutoff frequency. [Yes] 33. The echo of radar is only affected by the shape and size of the target. [NO] >> is not 34. Repeaters can be placed at regular intervals to extend the range of the link. [Yes] 35. Diversity is used to increase the reliability of the system by decreasing its availability. [NO] >> increasing 36. The receiver threshold is not depending on the wideband noise power. [NO] >> depending 37. For Transverse Electromagnetic (TEM) Waves, ( Ez  0 , but H z  0 ).[NO] >> ( Ez  H z  0 ) 38. As per IEEE, electromagnetic waves between 300MHz and 300 GHz are called millimeter waves (MW). [NO] >> 30 GHz 39. The order of the modes is not depending on the dimensions of the waveguide. [NO] >> depending 40. Over the horizon radar has (high power, low resolution). [Yes] 41. For the TM mode, if n or m is zero, all fields are zero. [Yes] 42. Diversity is used to increase the capacity of the system. [NO] >> reliability 43. Attenuator passes the signal coming from any port to the next port in a circular direction. [NO] >> circulator 44. Rectangular waveguides has more attenuation than the circular waveguides. [Yes] 45. Propagation losses are due to Earth's atmosphere and terrain. [Yes] 46. Diversity is used to increase the capacity of the system by increasing its availability. [NO] >> reliability 47. The Airborne radar has (high power, low resolution). [NO] >> Over the horizon  ‫أسئلة الحفظ‬ 1. What is the function of: Attenuator, Isolator, and Filter.  Attenuator: It is used for measurement purposes or control the power level of the collected signals.  Isolator: Allows the microwave signal to travel in one direction and attenuates the signal in the opposite direction.  Filter: Allow a certain bandwidth to pass to the antenna or the receiver. 2. Explain the phenomenon of skin effect at microwaves?  The lumped circuits referred to in the definition are the carbon resistors, mica capacitors, and small inductors you see in your AM-FM radio or television set.  These components cannot be used with microwaves due to a phenomenon called skin effect, which is the concept that high frequency energy travels only on the outside skin of a conductor and does not penetrate into it any great distance. 3. What is a microwave communication system?  It is a communication system operating in the microwave frequency range and using microwave technology. 4. What is a waveguide?  It is Transmission line consists of one hollow conductor allows the high frequency signals to pass throw it at cutoff frequency based on its dimension. 5. What is the difference between the cutoff frequency of the mode and the cutoff frequency of the Waveguide? ‫ بينما لكل نمط تردد قطع خاص به‬.‫تردد القطع للدليل املوجي هو أصغر تردد قطع من األنماط‬ The cutoff frequency of the waveguide is the lowest cutoff frequency of all modes. Each mode has it's own cutoff frequency that must be above the cutoff frequency of the waveguide. 6. What is the cutoff frequency of the waveguide and the cutoff frequency of the mode? The cutoff frequency of the waveguide is the lowest cutoff frequency of all modes. Each mode has it's own cutoff frequency that must be above the cutoff frequency of the waveguide. 7. Why the lumped circuits components such as the carbon resistors, mica capacitors, and small inductors cannot be used with microwaves.  due to a phenomenon skin effect, which is the concept that high frequency energy travels only on the outside skin of a conductor and does not penetrate into it any great distance. 8. Give a brief definition for the term "Microwave.  The term microwaves refers to alternating current signals with frequencies between 300 MHz and 300 GHz with a corresponding electrical wavelength between 1m and l mm respectively. 9. In microwave system, what is the function of : circulator, magnetron and filter Which of them is an Active device?  circulator: a) Pass the signal coming from any port to the next port in a circular direction. b) Protects the receivers from the high power transmitted signals  magnetron: A diac generates microwave waves (2GHz – 70 GHz) with very high power more than 1 MW. (this is the active device).  Filter: Allow a certain bandwidth to pass to the antenna or the receiver. 10. Which special techniques are used to insert/eject the power to/from the waveguides. Explain the probe Method briefly.  techniques 1. Probe 2. Loop 3. Window Slot Or Aperture  the probe Method – The small probe inside the waveguide works as an antenna when supplies with power. – The probe transmits and receives the signal when the current at microwave frequencies flows in it. 11. In microwave system, what is the function of : klystron, terminator and isolator Which of them is an Active device?  klystron: Power amplifier and microwave signal oscillator. (this is the active device).  terminator: It is used to terminate the waveguides, circulators and directional couplers in order to prevent the leakage of the microwave signals  isolator: Allows the microwave signal to travel in one direction and attenuates the signal in the opposite direction. 12. Give a brief definition for: link budget, Diversity and waveguide.  The link budget: is a calculation involving the gain and loss factors associated with the antennas, transmitters, transmission lines and propagation environment, to determine the maximum distance at which a transmitter and receiver can successfully operate.  Diversity: suggests that there is more than one transmission path available between the transmitter and the receiver.  Waveguide: It is Transmission line consists of one hollow conductor allows the high frequency signals to pass throw it at cutoff frequency based on its dimension. 13. What is the function of: Repeater station, Circulator and Radar?  The repeater station : receives a signal, amplifies and reshapes it and then retransmits it to the next repeater or terminal station.  circulator: a. Pass the signal coming from any port to the next port in a circular direction. b. Protects the receivers from the high power transmitted signals.  Radar : is for RAdio Detection And Ranging and Radar systems attempt to infer information about remotely located objects from reflections of deliberately generated electromagnetic waves at radio frequencies. 14. Explain briefly the main applications of microwave systems.  Communications systems : – Cellular telephone system 1970, – Satellite systems, direct broadcast satellite (DBS) television – Wireless Local Area Networks (WLANs), – Ultra Wide Band (UWB) radio, where the broadcast signal occupies a very wide frequency band.  Radar systems, Military: detecting and locating air, ground, and seagoing targets, as well as for missile guidance and fire control. Commercial: air traffic control, motion detectors (door openers and security alarms), vehicle collision avoidance, and distance measurement. Microwave ovens (2.45 GHz). Scientific: weather prediction, remote sensing of the atmosphere, the oceans, and the ground, and medical diagnostics and therapy. 15. In microwave systems, what is the function of: isolator, circulator and magnetron.  isolator: Allows the microwave signal to travel in one direction and attenuates the signal in the opposite direction.  circulator: a) Pass the signal coming from any port to the next port in a circular direction. b) Protects the receivers from the high power transmitted signals  magnetron: A diac generates microwave waves (2GHz – 70 GHz) with very high power more than 1 MW. 16. In microwave communication, what is the diversity?. Mention the types of diversity.  Diversity : suggests that there is more than one transmission path available between the transmitter and the receiver.  types of diversity : 1. Frequency diversity 2. Space diversity 3. Polarization diversity 4. receiver diversity 17. What is the main function of microwave repeater ?.Mention the types of repeaters.  The repeater station : receives a signal, amplifies and reshapes it and then retransmits it to the next repeater or terminal station.  types of repeaters 1. IF repeaters 2. Baseband repeaters 3. RF-to-RF Repeater 18. What is the basic operation of the radar?. And mention the factors that affect the received echo?  In its basic operation, a transmitter sends out a signal which is partly reflected by a distant target, and then detected by a sensitive receiver.  factors that affect the received echo: 1. distance of the target, 2. its size, 3. its shape and 4. its composition 19. Mention some advantages and disadvantages of waveguides.  Advantages 1. Easy to fabricate waveguides 2. Less losses compared to two lines and coaxial lines. 3. Did not effected by the surrounding electromagnetic waves 4. They has high power to transmit electromagnetic waves  disadvantages 1. Difficult to install due to their hardness and the need for special tools. 2. More expensive than normal cables. 3. Only used with microwave systems. 20. Which special techniques are used to insert/eject the power to/from the-waveguides. Explain the probe Method briefly.  techniques 4. Probe 5. Loop 6. Window Slot Or Aperture  the probe Method – The small probe inside the waveguide works as an antenna when supplies with power. – The probe transmits and receives the signal when the current at microwave frequencies flows in it. 21. What is the main function of a radar system and how does it works?  Radar : is for RAdio Detection And Ranging. Radar systems attempt to infer information about remotely located objects from reflections of deliberately generated electromagnetic waves at radio frequencies.  In its basic operation, a transmitter sends out a signal which is partly reflected by a distant target, and then detected by a sensitive receiver. 22. In microwave systems, give a brief definition for: circulator, filter, and Triac.  circulator: a) Pass the signal coming from any port to the next port in a circular direction. b) Protects the receivers from the high power transmitted signals  Filter: Allow a certain bandwidth to pass to the antenna or the receiver.  Triac: Generate and amplify microwave frequencies. It is used in transmission systems for ground stations and satellites. 23. Why the microwave repeaters are needed?  Microwave path can not directly reach the distant end. – Path is too long, earth curvature blocks path. – Terrain between radio ends is too high and blocks path. – New building blocks the path. 24. For microwave Communication, what is the Link Budget?  The link budget: is a calculation involving the gain and loss factors associated with the antennas, transmitters, transmission lines and propagation environment, to determine the maximum distance at which a transmitter and receiver can successfully operate. 25. Mention the types of diversity in microwave communications. Why diversity is used.  types of diversity: 1. Frequency diversity 2. Space diversity 3. Polarization diversity 4. receiver diversity  Diversity is used to increase the reliability of the system by increasing its availability. 26. What do you know about waveguide in terms of (definition. Function and shape).  waveguide it is Transmission line consists of one hollow conductor allows the high frequency signals to pass throw it at cutoff frequency based on its dimension  Waveguides are used to connect the transmitters and antenna in the microwave and radar systems.  Waveguides Shapes 1. Rectangular 2. Circular 3. Elliptical flexible waveguide 27. What is the dominant mode of a waveguide? and how to prevent the propagation of higher order modes in the waveguide.  The dominant mode is the mode with lowest cutoff frequency. It’s always TE10. To prevent the propagation of higher order modes decrease the cutoff frequency of the waveguide. 28. Give a brief explanation for: a) Microwave communications system. b) Waveguides. Microwave communications system : a communication system operating in the microwave frequency range and using microwave technology. They began to be developed soon after the birth of radar. They offer wide bandwidths and line-of-sight propagation. Used in satellite communications systems. Waveguides : transmission line consists of one hollow conductor allows the high frequency signals to pass throw it at cutoff frequency based on its dimension. Used to connect the transmitters and antenna in the microwave and radar systems. 29. Explain why: a) The lumped circuit's components can't be used with microwave frequencies? b) Waveguides are not suitable for low frequencies? c) The reflected wave is generally smaller in amplitude than the direct wave? d) The fade margin is needed for the communication link? e) The rain attenuation is significant for frequencies above 15 GHz? a) due to a phenomenon called skin effect, which is the concept that high frequency energy travels only on the outside skin of a conductor and does not penetrate into it any great distance. b) At low frequencies, means that the waveguide dimensions must be very large. (Even at mega- hertz frequency range, the wavelength is in kilometers. ) Hence waveguides are commonly used at microwave frequency ranges or higher where wavelength is in the millimeter range. c) because of the larger distance it travels and because the ground is not a perfect reflector. d) The radio can handle anything that affects the radio signal within the fade margin but if it is exceeded, then the link could go down and therefore become unavailable. And to make sure that the signal received at the receiving antenna is above the threshold. And for any unpredictable loss. e) rain fading is the dominant fading mechanism. And it scatters and absorbs electromagnetic waves by rain drops in that frequency particularly.