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Oct. 16, 2006

Oct. 16, 2006. Midterm Next Class Assignment #4 is Marked Problem session in lab today – review for midterm More Antennas. Midterm Overview. Midterm Info: http://people.okanagan.bc.ca/dwilliams/courses/nten216/nten216_Quiz1.htm Sample questions:

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Oct. 16, 2006

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  1. Oct. 16, 2006 • Midterm Next Class • Assignment #4 is Marked • Problem session in lab today – review for midterm • More Antennas

  2. Midterm Overview • Midterm Info: • http://people.okanagan.bc.ca/dwilliams/courses/nten216/nten216_Quiz1.htm • Sample questions: • http://people.okanagan.bc.ca/dwilliams/courses/nten216/Tests/NTEN216_Midterm1SampleQuestions.pdf

  3. Antenna Characteristics • Gain and Directivity • Radiation Pattern • Polarization • Input Impedance • Antenna Efficiency • Bandwidth • Reciprocity

  4. Bandwidth • Range of frequencies over which antenna can transmit or receive signals effectively • Can apply to a certain antenna • Measurement is (Upper Frequency-Lower Frequency)/(Upper Frequency) • e.g. 2.4GHz Dipole antenna may be able to transmit signals from 2.28 to 2.52GHz without significant loss of signal power. BW = (2.52-2.28)/2.4 = 10% • Can apply to a certain type of antenna • E.g. Half-wave dipole antennas in general have a bandwidth of 6GHz (0-6GHz) as long as the specific dipole size is set to the half-wave length

  5. Antenna Input Impedance • Want input impedance to match impedance of incoming cable • Minimize reflections • Maximize signal in to antenna • Eliminate VSWR • Impedance mismatch will reduce the antenna efficiency

  6. Reciprocity • An antenna can be used for transmitting and receiving • If you know the transmit properties of an antenna, you know the receive properties of an antenna…they are the same • Applies to: Gain, Radiation Pattern, Polarization, Input Impedance, Efficiency, and Bandwidth

  7. Cutoff for Midterm Topics

  8. Types of Antennas • Omnidirectional • Half-wave dipole • Quarter-wave monopole • Directional • Yagi-Uda antenna • Patch antenna • Parabolic Dish • Phased Array • Sector Antennas

  9. Omnidirectional Antennas • Ideally, radiates energy equally in all directions • Isotropic antenna • In reality, radiates energy equally in one plane, but not in other plane • Omnidirectional in one plane

  10. Half-Wave Dipole • Dipole antenna consists of two conductors which stretch out in opposite directions • Best dipole is when length is equal to half the wavelength of EM being radiated

  11. Half Wave Dipole Characteristics • Gain: 2dBi • Typical Beamwidth: 80° x 360° • Omnidirectional in horizontal plane • Beamwidth in vertical plane can vary • Polarization: linear, and perpendicular to antenna • Bandwidth: 10%. • Effective from 0-6GHz

  12. Half Wave Dipole Radiation Pattern

  13. Quarter Wave Monopole • One conductor carrying the signal referenced to a ground plane • Virtual mirror image of conductor created on opposite side of plane • 2 x λ/4 = λ/2. This is effectively a half-wave dipole

  14. λ/4 Monopole Characteristics • Gain: 2-6dBi • Typical Beamwidth: 45° x 360° • Omnidirectional in horizontal plane • Beamwidth in vertical plane can vary • Polarization: linear, and perpendicular to antenna • Bandwidth: 10%. • Effective from 0 to very high

  15. λ/4 Monopole Radiation pattern

  16. Directional Antennas • Focus coverage more in one direction than others • Refers to all antennas that are not omnidirectional. Wide range of degrees of directionality • Semidirectional: smaller gain, wider coverage region • Highly directional: high gain, focused strongly in one direction, long distance range

  17. Yagi Antenna • One radiating dipole, one reflector to reflect signal in opposite direction, several directors to focus energy • Size and number of directors determines directivity and gain

  18. Yagi Antenna Characteristics • Gain: 5-15dBi • Typical Beamwidth: 50° x50° • Polarization: Horizontal • Bandwidth: 5% • Effective from 50MHz to 2.5GHz

  19. Yagi Antenna Radiation Pattern

  20. Patch or Panel Antenna • Consists of metallic plate and base sandwiching an insulating material • Easy to manufacture • Easy to mount • Similar to Yagi Antennas in terms of performance • Better than Yagis for cost, ease of use and aesthetics

  21. Patch/Panel Antenna Characteristics • Gain: 5-18dBi • Typical Beamwidth: 50° x50° • Polarization: • Bandwidth: • Effective from XXXHz to XXX Hz

  22. Patch/Panel Antenna Radiation Pattern

  23. Parabolic Dish or Grid Antenna • Highly directional antennas, beamwidth can be as small as a couple of degrees • Used for fixed location, long distance communications • E.g. satellite, microwave towers • Parabolic dish or grid focuses energy in one direction.

  24. Dish Antenna Characteristics • Gain: 20-30dBi • Beamwidth: 1-10 degrees • Polarization: can be linear or circular • Bandwidth: 30% • Effective from 400MHz to 13GHz

  25. Parabolic Dish Radiation Pattern

  26. Phased Array Antennas • Group of independently fed active elements • Input signals can be controlled to cause required constructive/deconstructive waveforms • Result: antenna can be aimed without any moving parts

  27. Phased Array Antenna Characteristics • Gain: Varies widely • Beamwidth: Varies Widely • Polarization: depends on array. • Bandwidth: depends on array. • Effective from 10MHz to 10GHz • Radiation Pattern: depends on array

  28. Sector Antennas • Generate “Pie Slice” radiation patterns • “Pie Slice” width depends on particular antenna • Because of predictability of slice, multiple antennas may be mounted together to give larger coverage area • E.g. want 270° of coverage, but have only 90° sector antennas, what do you do.

  29. Sector Antenna Characteristics • Gain: 10-21dBi. • A 90° sector antenna can still have variable gain by changing the vertical pattern • Beamwidth: Depends on Pie Slice size • Polarization: linear • Bandwidth: • Effective from

  30. Sector Antenna Radiation Pattern

  31. Increase coverage area by joining three 120° antennas together. • Omnidirectional in horizontal plane, controllable in vertical plane.

  32. Review • What are lobes and nulls? • If you have a right handed circularly polarized transmission antenna, what is the best kind of antenna to use as the reception antenna? • If the gain of an antenna is 5dBi for transmission, and its beamwidth for transmission is 90°x45°, what would the gain and beamwidth be if it was used for reception? What is this principle called? • A 1 watt signal is input to an antenna, but 200mW is reflected. The gain of the antenna is 10dBi, and the loss of power due to resistance is 50mW. What is the efficiency of this antenna?

  33. Review • What happens if there is an impedance mismatch between the antenna, and the cable coming into the antenna? • The center frequency of an antenna is 104.7MHz, and at 104.7MHz it radiates 50 Watts of power. If it radiates a 100MHz signal, it can only output 12.5W of power, and at 110MHz, it can only output 12.5W of power. What is the bandwidth of this antenna?

  34. Review • In terms of directionality, what kind of antenna is this ? • What are the horizontal and vertical beamwidths? • In the vertical plane, what is the signal strength at 45° if the strength at 90° is 50mW?

  35. Review • Describe at least two ways to provide full wireless coverage to a large rectangularly shaped warehouse. Explain the types of antennas you would use and why. • If you have need for long distance point to point communications, what kind of antenna would you use. • What would you use a Yagi antenna for?

  36. Resources • http://www.arrl.org/tis/info/whyantradiates.html • http://www.hp.com/rnd/pdf_html/antenna.htm • http://www.connect802.com/wcu_articles.htm

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