RF Basic
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Transcript of RF Basic
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BASIC RF
Components
CELL PLANNING
SMART Communications Inc.
-
OBJECTIVES:
Review the Basic Units, terminology
and RF components
Applications
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I. Basic of Telecom
a. Transmitter the equipment that generates and
amplifies a RF carrier signal, modulating the
carrier signal with intelligence, and feeding the
modulated carrier to an antenna for radiation into
space as electromagnetic wave.
b. Receiver an equipment used for receiving
radio waves and converting them into the original
intelligence
c. Information/Intelligence the actual message
that is being sent in a communication system.
-
Hi! Good
Morning
too.
Hi! Good
Morning.
Tx
Rx
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II. Terms and Units
a. Relative and Absolute
i. Ratios units which are in absolute form and
represent division of values. Ex. C/I, S/N, etc.
ii. Logarithmic units which are converted into
its equivalent logarithmic values. Ex. decibel
b. Amplitude or Signal Level
i. Watts
- it is named after the Scottish inventor
James Watt
- the SI unit of electric power that in
one second gives rise to energy to one joule.
- signifies the strength of the given signal
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Amplitude
Amplitude the value of a varying signal at a specific period
in time
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ii. Decibel a power measurement unit referred to another
unit.
dBm the power level of a certain signal taking 1
milliwatt as the reference
iii. Losses and Gains -energies that are either
added/absorbed and subtracted/released in a system
iv. C/I or S/N the ratio of the desired signal to the
undesired signal or interference/noise
- this is a measure of the strength of a
signal compared to any unwanted
signal.
-
c. Frequency - the number of complete cycle per unit of
time for a periodic quantity such as alternating current,
sound waves and radiowaves.
i. Hertz the SI unit of frequency equal to cycle
per second
T
Frequency = 1
Period ( T )
=Vel of PropagationFrequency
-
v. 3 dB points Half power points
- points on the waveform where of
the maximum signal is located
- this is the reference when we take the
bandwidth of a certain waveform
Max pt.
3dB pt
Bandwidth
amplitude
frequency
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ii. Center Frequency - the average frequency of the
emitted wave when modulated by a symmetrical signal
iii. Bandwidth the range of frequencies which have
been specified as performance limits for a filter, amplifier
or attenuator, defined as the 3dB points at the high pass
and low pass ends of the frequency response curve
CF
Bandwidth
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Spectrum Analyzer - an instrument
that measures the amplitudes of the
components of a complex waveform
throughout the frequency range of the
waveform.
d. SPECTRUM ANALYZER
-
Spectrum analyzer
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f. Law of Conservation of Energy
- this states that energy can neither be
created nor destroyed, instead it will
just transform from one form to
another.
-
IV. RF COMPONENTS
a. Active - components that introduces
additional energy and reprocess the received
signal
b. Passive components that do not introduce
any additional energy on the signal.
-
c. Basic RF Components
i. ANTENNA - a device that radiates and receives
radio waves
- British term is AERIAL
- they transition point in the
communication chain, where the signal
changes from a wireline signal to a radio
wave propagating signal and vice versa.
Types
Omnidirectional antennas : radiate with the same intensity to
all directions (in azimuth)
Directional antennas : main radiation energy is concentrated
to certain directions
- sometimes called RADIATOR
-
antennas
yagi
radiation pattern
pico
panel
-
a. Practical Requirements
i. Number of Antenna - reduce the required
number of antenna relative to the number of
radios. One to one ratio of antenna to radio is
impractical.
ii. Antenna isolation the separation
between two antennas that is usually
considered when employing a space
diversity technique. The distance should be
multiple of the half wavelength.
-
Antenna Isolation: Vertical
K
A
The following is valid for 900 Mhz.,
1800,1900Mhz and co-located 900 + 1800/1900
Mhz.
Requirements: Tx -Rx and Rx- Tx: 30 dB
Pre-condition: No influence from tower
structures More than 2m bet Ant and tower.
( A in figure)
Vertical Separation: Tx - Rx and Rx - Tx
Minimum 0.2 m
( K in figure)
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Antenna Isolation: Horizontal
D
Requirements: Tx -Rx and Rx- Tx: 30 dB
Vertical Separation: See Table Below
Table: Horizontal Separation
Gain dBi 900 Mhz 1800/1900 900+1800/1900
10 5m 2.5 m 1m
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There is a need for receiver diversity in cellular systems
to improve the uplink.
Space Diversity
TX1/RXA TX1/RXA
BTS Equipment
Common
TX/RX
Antenna
dd
Horizontal Separation, dd
for diversity = 12-18 (wavelength)
for isolation = 30 dB = 2 (wavelength)
[antennas with 65 degrees beamwidth,
all gain values]
DIVERSITY
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Polarization Diversity using dual-polarized antennas
vertical + horizontal polarization +/- 45 degrees polarization
vertical
array
horizontal
array
antenna
housing
connectors
feeders
+45
degrees
- 45
degrees
DIVERSITY
-
Polarization Diversity using dual-polarized antennas
1.5 dB downlink loss
TX1/RXA TX1/RXA
Required isolation >30 dB between
the two antenna parts...
DIVERSITY
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ii. Filters - a selective device that allows a
desired range of energy to pass through
and substantially attenuating all other
ranges.
- they are used to separate, combine or
suppress microwave frequencies.
- they are used to ensure that no
harmonics are transmitted
-
1. Low Pass Filter a filter that
attenuates frequencies higher than
the cut-off frequency
fcInput Output
Amplitude Amplitude
Frequency Frequency
-
2. High Pass Filter -a filter
that permits frequencies
higher than the cut-off
frequency.
Amplitude Amplitude
Frequency Frequency
fcInput Output
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3. Band pass Filter - a filter that
accepts a band of
frequencies and
considerably attenuates
higher and lower frequencies
than the desired band.
Amplitude Amplitude
Frequency Frequencyfc fc
Input Output
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4. Band stop/Notch Filter - a
filter that prohibits the
passage of a certain
band of frequencies and
allows other
frequencies.
Amplitude Amplitude
Frequency Frequencyfc fc
Input Output
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iii. Amplifier - a device that
increases the strength of a
signal without appreciably
altering its characteristic
waveform.
Input Output
Time
Amplitude
Time
Amplitude
-
iv. Circulator - a waveguide component that has a number
of terminals so arranged that energy entering one terminal
is transmitted to the next in a particular direction. This can
be used as a duplexer
-
v. Directional Coupler - a device that
couples a secondary system only to a
wave traveling in a particular
direction while completely ignoring
the wave traveling into the opposite
direction
-
vi. Splitter/Divider - a device that has
the capability to distribute one input
signal to two or more output
without introducing distortion to the
signal.
-
vii. Resistive Load - component that can absorb the
transmitted energy and behaves like an actual load such
as an antenna.
-
attenuator
viii. Attenuator - a device that uses resistive
components to reduce the strength of a
signal without introducing considerable
distortion.
Time Time
Amplitude Amplitude
-
ix. Isolator - allows a signal to pass through in one
direction and attenuates it in the other direction. This is
usually used to prevent a very high SWR.
Incident Wave
Reflected Wave
-
Connectors
x. Connectors - device that joins two or more circuit
-
Cables
xi. Cables - a transmission line
where energy can pass through
without considerable decrease
on the energy
-
xii. Leaky Cables - a cable which has a leak where
energy escapes out continuously
-
i. Combiners are needed to enable more than
one transmitter to be connected to one
common transmitting antenna.
In GSM, two different TX combiners can be
used -
FILTER COMBINER HYBRID COMBINER
Transceiver 1
Transceiver 2
Transceiver 3
Transceiver 4
d. Complex RF Components
-
ii. Duplexer - a switching device that permits
alternate use of the same antenna for both transmit
and receive.
TxRx
-
Tx Filter
Rx Filter LNA
Antenna
Rx
Tx
Duplexer Block Diagram
-
iii. Diplexer - a coupling system that allows two
different transmitters to operate simultaneously
or separately from the same antenna.
Tx1
Tx 2
-
Diplexer Block Diagram
Port 900
Port 1800
Dual Band
Antenna
-
vi. RECEIVER MULTICOUPLER UNIT (RMU)
- amplifies the received signals and divides them to the
receivers (Rx) of the Transceiver units (TRXs).
RX 1
RX 3
RX 4
RX 5
RX 6
RX 2
Amplifier
ModuleTest
Module
RX
Filter
ANT
TEST
Main Functional Part of the RMUA (1800)
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IV. Implementation
a. BTS Base Transceiver Station
- this is the outer most part of the network
and it interfaces the mobile subscriber to
the network
MS BTSMSC
BSC
-
Duplexer
Transceiver
Transceiver
Transceiver
Transceiver
Tx
Tx
Tx
Tx
Rx
Rx
Rx
Rx
RMU
Combiner
Antenna
Base Transceiver Station
-
b. Repeater - an amplifier that processes weak signals
and retransmits stronger signal without reshaping
their waveform
-
BPF BPF
BPFBPF
BPF
BPF BSF
BSF
ATT
ATT
Downlink
Uplink
PSU AlarmsTo BTS To MS
PA
PA
LNA LNA
LNALNA
REPEATER
-
D.A.S.
Splitter/divider
Splitter/divider
amplifier
c. DAS Distributed Antenna System
- a system employed wherein several
antennas can be used to cover several areas
with only one transmitter
-
V. Link Budget
- this is a calculation of the
signal strength seen at the receiver
considering the output power of the
transmitter and the possible gains and
losses that might be incurred within
the system.
-
Downlink Link BudgetMobile sensitivity = Bts transmit power - Combiner loss -
duplexer loss - Cable/feeder loss + Bts antenna gain - Maximum
path loss - fading margin - Building/Car penetration loss - body
loss + Mobile antenna gain
Uplink Link BudgetBts sensitivity = Mobile transmit power + mobile antenna gain -
body loss - Maximum path loss - fading margin - building/car
penetration loss + Bts antenna gain + - Duplexer loss
- cable/feeder loss + Low Noise Amplifier