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V. Broadband Antennas

V. Broadband Antennas. Broadband Antenna. Bandwidth Broadband Non-resonant type -traveling wave antenna, vee, rhombic antenna -helical, log-periodic antenna -conical antenna. Traveling wave antenna. For short-wave band: 2~30MHz. Traveling wave antenna.

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V. Broadband Antennas

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  1. V. Broadband Antennas

  2. Broadband Antenna • Bandwidth • Broadband • Non-resonant type • -traveling wave antenna, vee, rhombic antenna • -helical, log-periodic antenna • -conical antenna

  3. Traveling wave antenna For short-wave band: 2~30MHz

  4. Traveling wave antenna Traveling wave antenna in free space Unnormalized pattern factor Pattern with n forward lobe Element factor

  5. Traveling wave antenna

  6. Traveling wave antenna Traveling wave VEE antenna in free space

  7. Traveling wave antenna Rhombic antenna in free space

  8. Traveling wave antenna Ground effect (perfect ground)

  9. Traveling wave antenna Beverage antenna: Traveling wave ant. above the earth with imperfect conducting properties Tangential Electric field on earth is not zero =>1.inducing a current on the antenna conductor. 2.due to unbalanced operation, can radiate the field. Loss and standing wave

  10. Beverage antenna Loss:radiation and dissipation in earth Reflection from load end

  11. Helical antenna Mode of Helix

  12. Normal mode Helix Direction of maximum directivity: Normal to the axis of Helix Normal mode

  13. Normal mode Helix For circular polarization, Normal mode helix is usually operated as linearly polarized

  14. Normal mode Helix Resonant stub helix antenna on ground plane

  15. Axial mode Helix Hansen-Woodyard

  16. Axial mode Helix Useful axial mode helix design

  17. With tapered helix, bandwidth and axial ratio are improved uniform end taper continous taper nonuniform Polarization LHCP RHCP

  18. Biconical Antenna Analysis Spherical TEM wave Infinite bicone

  19. Biconical Antenna

  20. Finite biconical Antenna Non-ideal open: non TEM higher mode

  21. conical monopole antenna monopole bandwidth

  22. Discone antenna disc+cone

  23. Sleeve antenna(monopole) Virtual feed

  24. Sleeve antenna(dipole)

  25. Open-sleeve dipole

  26. Frequency independent antennas • Bandwidth over 10:1 -pattern, impedance, polarization, phase center.. • Frequency-independent antennas are designed to minimize finite length and maximize angular dependence. Helix - geometry of angular dependent • Self-complimentary structure • Thick metal biconical, bow-tie • Self-scaling property: most radiation takes place from the active region

  27. Self complimentary Self complimentary: A antenna and its complimentary are identical complimentary Frequency independent

  28. Equiangular antenna antenna of geometry enlarged antenna For enlarged surface coincides with original one

  29. Spiral antennas truncated Equiangular spiral Expansion ratio

  30. Equiangular spiral Frequency range(bandwidth) Antenna impedance Finite thickness Coaxial feed Pattern HPBW Polarization:circular as helix

  31. Archimedean spiral 1.feed to active region ->act as transmission line 2. active region ->radiation takes place 3. Beyond the active region ->currents can be neglected active region: portion of the antenna that is one wavelength in circumference Circular polarization

  32. Cavity-backed Archimedean spiral For unidirectional beam

  33. Conical equiangular spiral Main beam

  34. Log-periodic Antennas Logarithmically periodic structure The electrical properties vary periodically with the logarithm of the operating frequency Scaling of antenna dimension Scaling of operating frequency Spiral antenna: continuously scaled structure scaling->rotation of the structure

  35. Log-periodic Self complementary Active region: tooth with length of quarter wavelength

  36. Main beam direction: normal to the plane of antenna(bidirection) Polarization: linear polarization normal to that of bow-tie(without teeth) Operating band: determined by the length of the largest and the smallest tooth

  37. Log-periodic toothed wedge(unidirectional) Log-periodic toothed trapezoid Log-periodic wire Trapezoid zig-zag Log-periodic wire Trapezoid(circular pol.)

  38. Log-periodic dipole array(LPDA) Series-fed array of log periodically scaled parallel wire dipoles Main beam

  39. Log-periodic dipole array(LPDA) Log-periodic

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