19468768 Tambahan Antenna

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Antenna - How it Works

The antenna converts radio frequency electrical energy fed to it (via

the transmission line) to an electromagnetic wave propagated into

space.

The physical size of the radiating element is proportional to the

wavelength. The higher the frequency, the smaller the antenna

size.

Assuming that the operating frequency in both cases is the same,

the antenna will perform identically in Transmit or Receive mode



The type of system you are installing will help determine thetype of antenna used. Generally speaking, there are two

‘types’ of antennae:

1. Directional

- this type of antenna has a narrow beamwidth; with the

power being more directional, greater distances are usually

achieved but area coverage is sacrificed

- Yagi, Panel, Sector and Parabolic antennae

- an EUM, NCL Station/Master will use this type of

antenna in both Point to Point and Point to Multipoint



2. Omni-Directional

- this type of antenna has a wide beamwidth and radiates

3600; with the power being more spread out, shorter

distances are achieved but greater coverage attained

- Omni antenna

- a CCU or an NCL Master will use this type of antenna



Yagi

- better suited for shorter links

- lower dBi gain; usually between 7 and 15 dBi



Typical Radiation Pattern for a Yagi



Parabolic- used in medium to long links

- gains of 18 to 28 dBi

- most common



Typical Radiation Pattern for a Parabolic



Sectoral

- directional in nature, but can be adjusted anywhere from 450 to

1800

- typical gains vary from 10 to 19 dBi

0

0



0

90

180

270 0 -3 -6 -10

-15-20

-30

dB

0

90

180

270 0 -3 -6 -10

-15-20

-30

dB

Typical Radiation Pattern for a Sector



Omni- used at the CCU or Master NCL for wide coverage

- typical gains of 3 to 10 dBi



Typical Radiation Pattern for an Omni



Antenna Radiation Patterns

Common parameters

– main lobe (boresight)

– half-power beamwidth (HPBW)

– front-back ratio (F/B)

– pattern nulls

Typically measured in two planes:

• Vector electric field referred to E-field

• Vector magnetic field referred to H-field



An antennas polarization is relative to the E-field of antenna.

– If the E-field is horizontal, than the antenna is Horizontally

Polarized.

– If the E-field is vertical, than the antenna is Vertically

Polarized.

Polarization

No matter what polarity you choose, all antennas in the same RF

network must be polarized identically regardless of the antennatype.



Polarization may deliberately be used to:

– Increase isolation from unwanted signal sources (Cross

Polarization Discrimination (x-pol) typically 25 dB)

– Reduce interference

– Help define a specific coverage area

Horizontal

Vertical



Antenna ImpedanceA proper Impedance Match is essential for maximum power

transfer. The antenna must also function as a matching load for

the Transmitter ( 50 ohms).

Voltage Standing Wave Ratio (VSWR), is an indicator of how

well an antenna matches the transmission line that feeds it.

It is the ratio of the forward voltage to the reflected voltage. The better the match, the Lower the VSWR. A value of 1.5:1 over the

frequency band of interest is a practical maximum limit.



Return Loss is related to VSWR, and is a measure of the

signal power reflected by the antenna relative to the forward

power delivered to the antenna.

The higher the value (usually expressed in dB), the better. Afigure of 13.9dB is equivalent to a VSWR of 1.5:1. A Return

Loss of 20dB is considered quite good, and is equivalent to a

VSWR of 1.2:1.



VSWR Return Loss Transmission Loss

1.0:1 ∞ 0.0 dB

1.2:1 20.83 dB 0.036 dB

1.5:1 13.98 dB 0.177 dB

5.5:1 3.19 dB 2.834 dB

19468768 Tambahan Antenna

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