Broadband AntennasBroadband AntennasNeal MansfieldNeal MansfieldJoseph PeteJoseph Pete

Matthew RobinsonMatthew RobinsonSteven SummersSteven Summers

OverviewOverview

Typical antennas are designed for a specific Typical antennas are designed for a specific narrow band of operationnarrow band of operation

Broadband antennas are designed to operate Broadband antennas are designed to operate effectively over a wide range of frequencieseffectively over a wide range of frequencies Public two-way-radio VHF covers 130-174MhzPublic two-way-radio VHF covers 130-174Mhz Public two-way-radio UHF 406-512MhzPublic two-way-radio UHF 406-512Mhz The challenge is to create an antenna which can The challenge is to create an antenna which can

operate in both the VHF and UHF bandsoperate in both the VHF and UHF bands

BandwidthBandwidth

%100

C

LUP f

ffB

L

UR f

fB

2LU

C

fff

Definition for center frequency:Definition for center frequency:

Bandwidth can be expressed as a percentage of the center Bandwidth can be expressed as a percentage of the center frequency or as a ratiofrequency or as a ratio

The percentage is commonly used for small bandwidth antennas:The percentage is commonly used for small bandwidth antennas:

The ratio is commonly used for large bandwidth antennas:The ratio is commonly used for large bandwidth antennas:

Broad Spectrum of TypesBroad Spectrum of Types

HelicalHelical

Log PeriodicLog Periodic

BiconicalBiconical

SleeveSleeve

SpiralSpiral

Biconical AntennaBiconical Antenna

Types of BiconicalTypes of Biconical Infinite BiconicalInfinite Biconical Finite BiconicalFinite Biconical Discone Discone

http://www.ik8uif.it/bichttp://www.ik8uif.it/biconical-10ghz.htmonical-10ghz.htm

Log Periodic AntennaLog Periodic Antenna

The antenna is ideally suited for The antenna is ideally suited for reception of VHF/UHF point-to-reception of VHF/UHF point-to-point communication where its point communication where its directional characteristics can directional characteristics can significantly improve rejection of significantly improve rejection of interfering signals. interfering signals. In professional applications, this In professional applications, this antenna is ideally suited for EMC antenna is ideally suited for EMC pre-testing, surveillance and pre-testing, surveillance and monitoring. monitoring. The antenna covers a frequency The antenna covers a frequency range of 230 to 1600 MHz (a range of 230 to 1600 MHz (a much wider frequency range can much wider frequency range can be received with reduced gain). be received with reduced gain). http://www.winradio.com/home/http://www.winradio.com/home/ax31b.htmax31b.htm

Sleeve AntennaSleeve Antenna

The sleeve antenna is used The sleeve antenna is used primarily as a receiving primarily as a receiving antenna. It is a broadband, antenna. It is a broadband, vertically polarized, vertically polarized, omnidirectional antenna. Its omnidirectional antenna. Its primary uses are in broadcast, primary uses are in broadcast, ship-to-shore, and ground-to-ship-to-shore, and ground-to-air communications. Although air communications. Although originally developed for shore originally developed for shore stations, there is a modified stations, there is a modified version for shipboard use. version for shipboard use.

http://www.tpub.com/inch/http://www.tpub.com/inch/32.htm32.htm

http://www.emartin.it/it9vky/http://www.emartin.it/it9vky/Risorse/opensleeve.htmRisorse/opensleeve.htm

Spiral AntennaSpiral Antenna

The spiral antenna is used The spiral antenna is used primarily as a receiving antennaprimarily as a receiving antennaVertically polarizedVertically polarizedFrequency IndependentFrequency Independent

Designed to minimize finite lengths Designed to minimize finite lengths and maximize angular dependenceand maximize angular dependence

http://www.naapo.org/Argus/docs/990702.htm

http://www.emi.dtu.dk/research/afg/research/gpr/spiral_antenna.html

http://www.ece.uiuc.edu/pubs/antenna/slide03.html

Helical AntennaHelical Antenna

DirectionalDirectional

Circularly PolarizedCircularly Polarized Polarization changes Polarization changes

with time with time

Both high gain and Both high gain and wide bandwide band

http://helix.remco.tk/

http://www.wireless.org.au/~jhecker/helix/helical.html

GeometryGeometry

Antenna TheoryAntenna Theory, Constantine A. Balanis, Constantine A. Balanis

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

Normal ModeNormal Mode

Radiation pattern similar Radiation pattern similar to linear dipoleto linear dipole

The dimensions of the The dimensions of the helix are small compared helix are small compared to the wavelengthto the wavelength

Narrow in bandwidthNarrow in bandwidth

Radiation efficiency is Radiation efficiency is smallsmall

Rarely usedRarely used

Antenna TheoryAntenna Theory, Constantine A. Balanis, Constantine A. Balanis

Axial ModeAxial Mode

Circular PolarizationCircular Polarization ¾<C/¾<C/λλ<4/3<4/3 C/C/λλ=1:near optimum=1:near optimum S= S= λλ/4/4

Half-Power Beam width: 50 x 50 degreesHalf-Power Beam width: 50 x 50 degrees

Directivity:Directivity:

Typical Gain: 10dBTypical Gain: 10dB

Bandwidth: 52%Bandwidth: 52%

Frequency limit: 100MHZ to 3GHzFrequency limit: 100MHZ to 3GHz

http://www.mobile.ss.titech.ac.jp/~ken/broadband-antennas.pdfhttp://www.mobile.ss.titech.ac.jp/~ken/broadband-antennas.pdf

Antenna TheoryAntenna Theory, Constantine A. Balanis, Constantine A. Balanis

NSC

23

52

3

2

15SC

N

Helix ApplicationsHelix Applications

Space Telemetry Applications of satellites, Space Telemetry Applications of satellites, space probes, and ballistic missilesspace probes, and ballistic missiles Signals have undergone Faraday rotationSignals have undergone Faraday rotation

Directional applicationsDirectional applications

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