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Broadband Antennas

Broadband Antennas. Neal Mansfield Joseph Pete Matthew Robinson Steven Summers. Overview. Typical antennas are designed for a specific narrow band of operation Broadband antennas are designed to operate effectively over a wide range of frequencies Public two-way-radio VHF covers 130-174Mhz

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Broadband Antennas

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  1. Broadband Antennas Neal Mansfield Joseph Pete Matthew Robinson Steven Summers

  2. Overview • Typical antennas are designed for a specific narrow band of operation • Broadband antennas are designed to operate effectively over a wide range of frequencies • Public two-way-radio VHF covers 130-174Mhz • Public two-way-radio UHF 406-512Mhz • The challenge is to create an antenna which can operate in both the VHF and UHF bands

  3. Bandwidth • Definition for center frequency: • Bandwidth can be expressed as a percentage of the center frequency or as a ratio • The percentage is commonly used for small bandwidth antennas: • The ratio is commonly used for large bandwidth antennas:

  4. Broad Spectrum of Types • Helical • Log Periodic • Biconical • Sleeve • Spiral

  5. Biconical Antenna • Types of Biconical • Infinite Biconical • Finite Biconical • Discone • http://www.ik8uif.it/biconical-10ghz.htm

  6. Log Periodic Antenna • The antenna is ideally suited for reception of VHF/UHF point-to-point communication where its directional characteristics can significantly improve rejection of interfering signals. • In professional applications, this antenna is ideally suited for EMC pre-testing, surveillance and monitoring. • The antenna covers a frequency range of 230 to 1600 MHz (a much wider frequency range can be received with reduced gain). • http://www.winradio.com/home/ax31b.htm

  7. Sleeve Antenna • The sleeve antenna is used primarily as a receiving antenna. It is a broadband, vertically polarized, omnidirectional antenna. Its primary uses are in broadcast, ship-to-shore, and ground-to-air communications. Although originally developed for shore stations, there is a modified version for shipboard use. • http://www.tpub.com/inch/32.htm • http://www.emartin.it/it9vky/Risorse/opensleeve.htm

  8. Spiral Antenna http://www.emi.dtu.dk/research/afg/research/gpr/spiral_antenna.html http://www.naapo.org/Argus/docs/990702.htm • The spiral antenna is used primarily as a receiving antenna • Vertically polarized • Frequency Independent • Designed to minimize finite lengths and maximize angular dependence http://www.ece.uiuc.edu/pubs/antenna/slide03.html

  9. Helical Antenna • Directional • Circularly Polarized • Polarization changes with time • Both high gain and wide band http://www.wireless.org.au/~jhecker/helix/helical.html http://helix.remco.tk/

  10. Geometry D= diameter of helix C= circumference of helix Lo= length of one turn = α= pitch angle = S= spacing between turns N= number of turns Lw= length of helix d= diameter of conductor Antenna Theory, Constantine A. Balanis

  11. Normal Mode • Radiation pattern similar to linear dipole • The dimensions of the helix are small compared to the wavelength • Narrow in bandwidth • Radiation efficiency is small • Rarely used Antenna Theory, Constantine A. Balanis

  12. Axial Mode • Circular Polarization • ¾<C/λ<4/3 • C/λ=1:near optimum • S= λ/4 • Half-Power Beam width: 50 x 50 degrees • Directivity: • Typical Gain: 10dB • Bandwidth: 52% • Frequency limit: 100MHZ to 3GHz Antenna Theory, Constantine A. Balanis http://www.mobile.ss.titech.ac.jp/~ken/broadband-antennas.pdf

  13. Helix Applications • Space Telemetry Applications of satellites, space probes, and ballistic missiles • Signals have undergone Faraday rotation • Directional applications

  14. Adaptation of Single Antenna for Multi-band Use.

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