antennas & their associated patterns

7/27/2019 Antennas & Their Associated Patterns

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Antennas & theirassociated patterns

Mr.Song KepingEngineer of Management of station and network Division

State Radio Monitoring Center

[email protected]+8610-68318264

Radio Monitoring and Spectrum Management Training

(China,23-31,May,2005)


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Definitions associate with antenna

HF antenna types

VHF and UHF omnidirection types

VHF and UHF directional types

Antennas for frequencies above3 000 MHz

Antennas & theirassociated patterns


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HF antenna types




Definitions associate withantenna


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Antenna

-Definition:

System of wires or other conductors that used to transmit

or receive radio waves or electromagnetic fields

-Transform between current and radio wave



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Antenna gain

-Definition:

When produce same field strength of the same powerflux-density at the same distance in a given direction, the

ratio of the power required at the input of a loss free

reference antenna to the power supplied to the input of a

given antenna.

-Refers to the direction of maximum radiation

-Considered for a specified polarization



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Antenna gain (2)

-Gi: isotropic antenna as reference (expressed in dBi)

-Gd: half-wave dipole as reference (expressed indBd)

-Gv: linear conductor as reference (expressed in dBv,not in common use)

dBi = dBd + 2.15 dB



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Antenna directivity diagram(pattern)

-A curve representing a quantity proportional tothe gain of antenna in the various direction in aparticular plane

-Main lobe and side lobe

-Horizontal directivity diagram

-Vertical directivity diagram



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Example of main lobe and side lobe


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Horizontal (left) and vertical (right) radiation pattern of an antenna


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Polarization of a radio wave

-The orientation of the electric flux in the EM field

-Linear polarization (vertical, horizontal)

-Circular polarization (right hand, left hand)

Polarization of an antenna

-Polarization of the signals it transmit



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Bandwidth of antenna

-Range of frequencies over which its effective

-Techniques that can increase the bandwidth

Active antenna

-Active processing before intercepting or producing

-Has active elements in front of the output



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Active antenna (2)

-Wide bandwidth

-Good shape of radiation pattern

-Small size

-Frequency-impendence parameters

-Influenced by intermodulation and cross-modulation

-Weak to nearby lightning



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HF antenna types




HF antenna types


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Rotatable horizontally polarized log-periodic

antenna

-Broadband

-Rotatable for different direction-Consistent pattern over the entire frequency range

-Typical gain: 12dBi

-Suitable for medium and long range skywave

-Suitable for short range ground wave

HF antenna types


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Horizontally log-periodic HF antenna in Beijing monitoring station

and typical horizontal(top) and vertical(bottom) radiation pattern

HF antenna types


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HF Quadrant antenna

-Consist of horizontal bent dipoles

-Bent angle different for required horizontal pattern

-Cannot cover entire HF band

-Dipole is performed as an open multi-wire cage

HF antenna types


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Quadrant antenna and typical horizontal (top) and vertical (bottom)

radiation pattern

HF antenna types


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Quadrant antenna in Beijing monitoring station

HF antenna types


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Vertically polarized monopole omnidirectionalantenna

-Broadband

-Composed of a biconical cage of wire

-Typical gain: 4~5dBi

-Suitable for short range ground wave-Suitable for moderate to long range skywave

HF antenna types


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Broadband vertical omnidirectional antenna and typical horizontal

(top) and vertical (bottom) radiation pattern

HF antenna types


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Magnetic loop antenna

-Very small size

-Detects the magnetic field

-Can be installed in low height.

-Sometimes active

-Suitable for monitoring and measurement

HF antenna types


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Example of magnetic loop antenna

HF antenna types


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HF antenna types




VHF and UHF omnidirectiontypes


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Active Receiving Dipole antenna

-Small size

-High sensitivity-Wide dynamic range

-Wide bandwidth

-Typical gain: 5dBi



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Active receiving dipole antenna



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Rod antenna

-Cover different frequency range

-Sometimes active


Active rod antenna


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Coaxial Dipole antenna

-Vertically polarize

-Suitable for mobile use-Typical gain : 2dBi @800MHz



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Coaxial dipole antenna and typical horizontal (top) and vertical

(bottom) radiation pattern



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HF antenna types






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VHF/UHF Log-periodic antenna

-Suitable for both wide and narrow band application

-Very wide frequency range

-Frequency-independent radiation patterns

-Sometimes be individual calibrated-Typical gain: 6.5dBi



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Log-periodic antenna and typical horizontal (top) and vertical(bottom) radiation pattern



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Yagi antenna

-Widely used in VHF/UHF band

-Include the driven element, reflectors and directors

-Concentrates the radiation and response

-More directors, greater gain

-More directors, more directional



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Number of directors -6dB beam width Gain (dB)

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9 37 14

13 31 15

20 26 16

Relationship between the number of directors, beamwidth and gain ofYagi antenna


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Yagi antenna and typical radiation pattern



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Portable directional antenna

-For portable use-Normally active

-Broadband, small size and low weight



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Active portable antenna and typical horizontal (left) and vertical(right) radiation pattern



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HF antenna types






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Dish and feed form

-To achieve the necessary of high gain-A feeder in the focus of a parabolic reflector

Gain depend on:-Relation between dish diameter and wavelength-Efficiency



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Examples of typical dishand feed antenna with afeeder and a parabolic

reflector


Examples of a log-periodicantenna as a feeder


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Narrow-band application

-Need very high gain

-To achieve high efficiency

-Minimize the losses caused by insufficientreflection and side radiation

Monitoring or surveillance application

-Need high gain and broad beamwidth-Focusing and defocusing the antenna feed

-By a motor-driven mechanical equipment



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Wideband application

-Need high gain and broad bandwidth

-Often use log-periodic antenna

-Minimizing the losses caused by defocusing

-By a motor-driven mechanical equipment



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Horn antenna

-Broadband

-Compact-Frequency-dependence high gain-Suitable for accuracy measurement



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Horn antenna



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Mount on a tripod or a tower

-For stably face to a certain direction

-Match the direction of the antenna and the signal

-Adjust to desired direction



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Electric antenna rotator


antennas & their associated patterns

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