BASIC RF

Components

CELL PLANNING

SMART Communications Inc.

OBJECTIVES:

Review the Basic Units, terminology

and RF components

Applications

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

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

Amplitude

Amplitude the value of a varying signal at a specific period

in time

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

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

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

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)

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

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

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

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

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

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

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)

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