Published on March 5, 2014
RADIATION & PROPOGATION -Broadband Antennas AJAL.A.J Assistant Professor –Dept of ECE, UNIVERSAL ENGINEERING COLLEGE, THRISSUR- 680123 - INDIA Mob: 8907305642 MAIL: firstname.lastname@example.org
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
Bandwidth Definition for center frequency: f C = fU − f L 2 Bandwidth can be expressed as a percentage of the center frequency or as a ratio The percentage is commonly used for small bandwidth antennas: f − fL BP = U × 100% fC The ratio is commonly used for large bandwidth antennas: BR = fU fL
Broad Spectrum of Types Helical Log Periodic Biconical Sleeve Spiral 6
Narrow Band Antennas Circularly Polarized Linearly Polarized Feed Horns Dipole Uniform Helical Yagi-Uda
Broad Band Antennas Circularly Polarized Linearly Polarized Array of narrow band antennas Tapered Helical Spiral Planar Tapered Yagi-Uda
Polarization helical antennas have circular polarization
Parameters Varied Conductor material Size of conductor
Cont. Parameters Varied SMA connector Tuning Feeding point
Biconical Antenna Types of Biconical Infinite Biconical Finite Biconical Discone
Log Periodic Antenna The antenna is ideally suited for reception of VHF/UHF point-topoint 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/ax 31b.htm
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-toair communications. Although originally developed for shore stations, there is a modified version for shipboard use. http://www.tpub.com/inch/32.ht m http://www.emartin.it/it9vky/Ris orse/opensleeve.htm
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
Helical Antenna Helix antenna was invented by J. D. Kraus. two modes of operation, normal axial
Helix Antenna Story Dr. John Kraus Professor of Electrical Engineering and Astronomy Emeritus Ohio State University
Radiation Patterns NORMAL MODE
Radiation Patterns AXIAL MODE
Geometrical Considerations Matching Network S D1 D2 L
Building the First Prototype
Building the Array
Increasing the Diameter Kapton Tape D1 Matching Network D2
Resonance and Matching Reflection SWR Return Loss Smith Chart Impedance Transmission
Gain Spectrum Analyzer Signal Generator
Helical Antenna Directional Circularly Polarized Polarization changes with time Both high gain and wide band
1989 Early Helix – 2 x 10 Turns
1991 2 x 15 Turn 70 cm Helix
About 1994 AO-13 Antennas
2001 AO-40 Antennas
2003 13 and 23 cm Helix Arrays
Geometry D= diameter of helix C= circumference of helix Lo= length of one turn = C2 + S2 S ) α= pitch angle = tan ( πD −1 S= spacing between turns N= number of turns Lw= length of helix d= diameter of conductor Antenna Theory, Constantine A. Balanis Theory,
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
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 3 52λ 2 C NS Directivity: C 2S 15 N 3 λ Typical Gain: 10dB Bandwidth: 52% Frequency limit: 100MHZ to 3GHz http://www.mobile.ss.titech.ac.jp/~ken/broadband-antennas.pdf
Helix Applications Space Telemetry Applications of satellites, space probes, and ballistic missiles Signals have undergone Faraday rotation Directional applications
Adaptation of Single Antenna for Multi-band Use.
Test Equipment Set Up
Antenna Test Range
double helix gps antenna
GPS & GLONASS
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