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Information about WIDE BAND RADIATORS ajal

Published on March 5, 2014

Author: ajal4u

Source: slideshare.net



RADIATION & PROPOGATION -Broadband Antennas AJAL.A.J Assistant Professor –Dept of ECE, UNIVERSAL ENGINEERING COLLEGE, THRISSUR- 680123 - INDIA Mob: 8907305642 MAIL: ec2reach@gmail.com

Broadband Antennas

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



Return Loss


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 ONWARDS

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

Spiro-Helical Antenna

double helix gps antenna


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