Microwave

Introduction to Microwave Communication

Dr. Hoda BoghdadyTransmission Department

National Telecommunication Institute

Microwave course 9-13 May 2010National Telecomm. Institute

Transmission Dep.Microwave Comm. Systems

9-13 May 2010

Course Schedule

Day 1: Introduction

Introduction.

Basic Concepts & Definitions.

Basic Microwave Measurements & Digital Transmission Analyzer . (Lab)

Day 2 : System Components

Passive Devices.

Mixers, Amplifiers And Oscillators.

Antennas.

T.L.

Day 3: Digital M.W. Radio System

Digital M.W. Radio System Overview.

Digital Commissioning Tests (Lab)

Day 4: Microwave Network Design

Digital Modulation.

System Power Budget.

Day 5:

Multiplexing+ Access Technique.

Introduction to SDH Frame



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Lecture Outline

Electromagnetic Spectrum

High frequency main characteristics

Guided and unguided transmission

The Microwave band: Advantages and disadvantages

Microwave Transmission Systems

Line of Sight vs. wireless system



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History of Wireless System



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The Electromagnetic Spectrum



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Commercial Broadcasting



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IEEE Frequency Band Designation

Microwave



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Microwave Frequency Band Designations



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Spectrum Management

To avoid interference between different communication system, a

management of the spectrum is required.

International organization: ITU (International Telecommunication Union)

ITU-R

Regional Organizations:

CEPT (Conference of European Post and Telecommunications administrations).

FCC (Federal Communications Commission) in the USA



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Terrestrial fixed network communication.

Maritime communication.

Navigational radio

Satellite communication.

Radio astronomy.

Public broadcast radio and television.

Mobile communication

Amateur radio

Bands allocated by ITU-R for:



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Spectral Mask

Spectral mask ensures that transmission in a channel doesn’t disturb or interfere with adjacent channels. It is usually specified by Standardization organization



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Wave Propagation

Electromagnetic waves travels in straight lines through the atmosphere

Wave is affected by atmospheric conditions

Temperature inversion (multipath fading)

Rain, fogs, snow

Waves can be received directly or through reflections (path clearance)



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Atmospheric Absorption of Electromagnetic Wave



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Layers of the Atmosphere



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Microwave vs. Low Frequency

Wavelength is the distance a wave travel to have a 2phase change (comes to the same point – assuming sinusoidal wave)

Phase Difference is very important

F=10Ghz, = 3cm ( /2 antenna = 1.5cm)

F=60hz, =5x106 m = 5000Km ( /2 = 2500km)



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Sinusoidal Wave

t2

d

F = 10 GHz = 3 cm

F = 50 Hz = 5000 Km



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Microwave Frequency Main Characteristics

Wave length = speed of light / frequency

The higher the frequency the smaller the wave length – (smaller dimensions, scattering, energy focusing, phase reference…etc.)

Lumped elements cannot be used

Different transmission lines

Frequency dependent components

Phase references



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Microwave Applications

Telecommunication transmission system

Remote sensing

Heating (cooking, industrial application)

Medical applications (although laser is replacing it – better resolution and more power focusing)



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Transmission System

Transmission systems can be categorized into two main category:

Guided system (cable system): a point to point connection must be made, a physical wire is installed, a frame is transmitted (baseband transmission)

Unguided system (free space): point to point is not necessary, only stations and antennas are installed, signal is transmitted by a carrier in air (carrier transmission)



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Wireless System (unguided)

A/D & signal

processing

Multiplexing

Modulation

Transmitter/

Receiver

Antenna

Information

Microwave

IF

B.B.

Microwave

Transceiver



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Microwave Communication - Advantages

Ease of installation (no digging), important over water, mountain, historical places etc.

Fast deployment of the system

Ease and flexibility of upgrading (capacity and services)

Low in vestment needed for large coverage area (pay as you build)

Mobility

Redeployment of radio hardware

Back-up link can be realized easily and efficiently

Broadcast applications (PMP)



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Microwave Communication - Disadvantages

Clearance for L.O.S

Frequency license and B.W. allocation permission

Some area restrictions

Electromagnetic radiation safety and power control

Fading, interference and jamming (security issues)

Standards are imposed by outside agencies



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Radio Communication

Radio communications can be split into 3 types:

Simplex

Full duplex

FDD (FD duplex)

Half duplex

TDD (TD duplex)

TX RX

TX RX

RX TX

TX RX

RX TX

F

F1

F2

F1

F1



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Microwave Systems

Line of Sight (microwave system)

Satellite system

Cellular system

Fixed (e.g. WLL)

mobile

Home networking (inside buildings)

WIFI, WMAX, Bluetooth



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Main Component of a Microwave system

IF stage

Up- and Down- conversion

Filters (very important)

Amplifiers (power and low noise)

T.L. and feeders

Towers

Antennas



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Microwave Transmitter and Receiver

One way system



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Line of Sight Communication

Clearance

Fresnel Zone

Up

to

10

0m

Up to 60km



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Point to Multi-Point Communication



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PTP vs PMP

PTP

1 Tx, 1Rx

Low power radiated

Line of site is a must

Path clearance

High tower

Directive antenna

Long distance cover.

PMP

1 Tx, multi-Rx

High power required

Interference

Multiple reflection

Omni antennas

Small coverage area

Access techniques



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Important Issues to Consider

EMI –Security, system performance

EMC – system immunity to interference

Interference problems – Freq. management

Output radiated power control for health and safety consideration

New wireless network’s terms : WIFI, WIMAX, Bluetooth, home networking, …..



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Standards and Regulations

Standards: Recommendations and mandatory

ITU: ITU-T, ITU-R, ITU-D

Analog microwave system – CCIR

Digital Microwave system – CCITT

FCC, IEEE in the USA

ETSI (European Telecommunications Standard Institute).



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Thank you

Concepts and Definitions

andSystem Overview



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Definitions

Decibel and Neper

S/N, C/N, E/N

Reflection and SWR

Noise Figure

G/T (high gain directive antennas)

System impairments

Passive vs. active devices

Linear and non-linear characteristics

Microwave system components



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Decibels (dB)

Decibels is a power ratio defined by

dB = 10 log(P2/P1)

P2 can the output and P1 the input, also in many occasions P1 is a reference power level, i.e. 1watt, 1mwatt, therefore

dBw, dBm

For antennas dBi is usually used to specify power referred to isotropic radiated power



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Note that :dBx represents an absolute value of power

While dB represents a relative power level

-20dBm

-10dBm

-10dB

dBx Abs. level

0dBm 1mwatt

10dBm 100mwatt

0dBw 1watt

-30dBw 0.001watt

10dB gain means 10 times

20 dB gain means 100 times

60 dB gain means million times



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Neper (Np)

The Neper is the unit for voltage or current ratio

8.686dB1Np ln

log20log10

matchingfor

/

/log10log10

1

2

1

2

2

1

2

21

1

2

1

2

2

2

1

2

V

VNp

V

V

V

VdB

RR

RV

RV

P

PdB



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As the receiving signal is very critical in telecommunication systems, noise contribution from the receiver is a critical issue.

Noise contribution of the receiver itself should be kept to a minimum.

Noise figure (NF) is always specified at the receiver only. It is the ratio of the S/N at the input to the S/N at the output.

Noise Figure



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Noise Figure – cont.

in

devdB

in

dev

in

devin

in

out

out

in

out

in

GN

NNF

GN

N

N

NGN

GNF

N

N

S

S

NS

NSNF

1log10

11

)/

)/ 0devNBest case

NF = 0 dB

Worst case

NF = 3 dB

indev GNN



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Noise Figure – cont.

For cascaded elements

1

321

21

3

1

21

1.... If

......11

NFNF

GGG

GG

NF

G

NFNFNF

NF1, G1 NF2, G2 NF3, G3



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S/N, C/N and Eb/N

At the receiver what matter is the ratio of the signal to the noise not the signal level

S/N is the amount by which the signal exceeds the noise level (analog signal)

C/N is the carrier level to the noise level

Eb/N is equivalent to S/N for digital signals, Eb is the energy contained in one bit, N is the noise power per 1Hz cycle, BER is specified at a given receiver threshold

All above ratios are measured in dB



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Reflection Coefficient

At any impedance mismatch there will be a reflected wave, therefore all terminations should be matched, it varies from 0 to 1 in magnitude

12

12

ZZ

ZZ

• Reflection should be measure at the point of

concern

• Reflection coefficient is used to measure

impedances at microwave frequencies



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Standing Wave Ratio (SWR)

SWR is standing wave ratio on a RF transmission lines, it is independent on position for lossless system, it varies from 1 up to ∞ (3.5)

It is used to measure reflection between the feeder and the antenna

It can be measure at any point in the T.L.

1

1

min

max

V

VSWR



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G/T – Receiver Figure of Merit

The higher this ratio the better the sensitivity of the system to weak signals

G is the gain of the antenna in dBi, it depends on the antenna size, wavelength and type (directive or omni-directional)

T is the total system noise temperature in degree Kelvin (Ta

and Tr)

G/T varies from –ve values up to 10 dB/K for omni-directional, can reach 35dB/K for directive antenna



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Passive vs. Active Devices

Passive: means devices that doesn’t add power to the system (T.L., circulator, filters, antennas, etc…

Passive devices are usually cheaper, easier to design, can have broadband c/cs

Active: means devices that adds power to the system (amplifiers)

Active devices need more critical designs, B.W. limited, power limited, more expensive and need special operation conditions (Temp.)



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Linear and Non-linear Characteristics

For microwave devices input-output characteristics and frequency response are very important

Most used devices are linear except:

Mixers and power amplifiers

Non linear devices can cause signal distortion (AM to PM, and intermodulation noise)



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System Performance

System performance can be affected by many factors: external and/or internal (station)

Noise level is a major problem in telecom systems, it can be internal or external

Interference (can be overcame by good system design and use of appropriate filters, it is usually external

Atmospheric effects – can be optimized by good design and diversity systems



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Noise & Interference

Internal noise can be caused by equipment and devices in the station itself it is usually a thermal noise coming from the electrons motions

External noise is any unwanted signal coming from the outside it usually has a white Gaussian distribution

Noise level should always be kept lower than the threshold level



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Noise & Interference – cont.

Interference is any unwanted signal in the operating band

Interference can be internally, antenna side lobes, antenna back radiation, bad branching unit, bad filters, bad design, or intentionally transmitted signal for jamming

Interference can be overcame by pre-frequency survey, and antenna adjustment



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System Performance – Cont.

System performance can also be affected by operational factors as well

Power supply back-up

Continuous system monitoring (local and remote)

Continuous system maintenance is a must (towers, antennas, feeders, local oscillators, power amplifier, etc…..)

Wiring system (MDF) – for ease of maintenance

Fire alarm



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Equipment Block Diagram

BB Unit

RF Unit

(IFU + Up-

Converter)

Information

• In the base band unit signal is digitized,

coded, framed and scrambled

• In the RF unit IF signal is modulated by the

BB signal then up-converted to the carrier

Telemetry & OW



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Microwave Transmitter and Receiver – One Way

One way system



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RFU – Mod. Demod.

A fixed IF intermediate frequency is modulated rather than the Carrier frequency

IF carrier is obtained from a crystal controlled oscillator operating typically at 70MHz.

The Modulated IF carrier is then up-converted to the final microwave frequency by a mixer



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RFU - Transceiver

The mixer (or up-converter) has two input and one output (Inp: IF, FLO and Out: Fc)

The mixer produces sum and difference products of the input frequencies

IF = 70MHz, FLO is chosen such that the final transmitted frequency is produced

Finally a filter is used to select one of the two produced side bands



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RFU - Transceiver

At the receiver side, same procedure is implemented

The mixer (or down-converter) converts input frequencies into IF signal

The input frequencies are the FC and the FLO



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RFU – Frequency Synthesis

The local oscillator input to the up-converter (down-converter) is obtained from a “frequency synthesiser”

A crystal reference oscillator is chosen to operate at between 5 and 10 MHz (best stability)

A frequency multiplier (typically X 4) provides the required output frequency



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RFU - Amplifier

There are two types of amplifiers in microwave systems:

Power amplifier placed at the last stage of the transmitter, it generates the high power necessary for transmission, it has high gain

Low noise amplifier (LNA) placed at the front end of the receiver, it is characterized by moderate gain but very low noise figure



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RFU - Branching Unit

In duplex system the transmitter and receiver station are both connected to the same antenna

A branching unit (circulator + filters) is used to direct microwave power in the transmit and receive side

Filter

Filter



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Thank you

System Components for Wireless Communications



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Wireless System



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Passive Components



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Filters

Low pass High pass Band Pass Band stop

F Filters are characterized by its power loss or insert ion loss behavior versus

frequency.

F Power Loss Rat io and Insert ion Loss (somet imes called reject ion)

PL R =Power available from source

Power delivered to load=

Pi nc

Pl oad

:

I L = 10 logPL R (dB)



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Filter Types

Maximally Flat (binomial or Butterworth response)

Equal ripple (Chebyshev filter)

Linear phase.

Elliptic filters.



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Filter Design

In low frequencies, the circuit can be realized using lumped L and Celements.

In microwave frequencies, different types of stubs and/or cavities are used.



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Microstrip filters

Low Pass Filters

Filters with bandpass characteristic,



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Coupler Hybrids and Power dividers

Couplers and hybrids are components used to combine and divide signals.

Directional coupler

Coupling Factor (in dB)

Directivity (in dB)

Isolation (in dB)

It is usually required to have the directivity and isolation as large as possible (P4=0).

3

1log10P

PC

4

3log10P

PD

4

1log10P

PI



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Hybrids (Hybrid Couplers)

They are 3-dB couplers. They can be divided as two types:

90º Hybrid

180º Hybrid

For both Hybrids the signal power is divided equally between the two output ports, but the phase shift is different.

Both Hybrids can be implemented as a lossless circuit.



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90º Hybrid

Microstrip implementation

Port 4 is isolated from Port 1



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180º Hybrid (Microstrip Ring Implementation)

Port 1 and 4 are isolated.

Path difference between ports 2 and 3 is λg/2 gives the 180º.



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180º Hybrid (Waveguide Implementation)



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In phase 3 dB divider

Wilkinson power divider

Port 2 & 3 are isolated from each other.

When port 2 and 3 are matched no power loss occurs in the resistance 2Z0.



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Switches, Phase shifters

These devices provides control over phase/amplitude of the RF signal.

They could be built using either:

solid state devices (p-i-n diodes or FET)

Ferrites

Advantages of p-i-n diodes over ferrites:

Fast speed.

Low cost.

Light weight and small size

Simple driver

Advantages of ferrites over p-i-n diodes:

Lower losses

Large power handling capability



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Switches

Switches are used in:

Time multiplexing (TDMA),

With the antenna to separate the receiver and the transmitter.

To build a digitally controlled phase shifter.

Types



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Thank you

Mixers, Amplifiers and Oscillators



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Mixers

An ideal mixer produce the product of two signals.

The main objective is to change the modulated frequency to another one.



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Mixers

Mixers are usually implemented using nonlinear elements such as diodes.

The diode nonlinear I-V characteristic can be approximated by: i= a1v(t)+ a2v(t)2+a3v(t)3

The input voltage to the diode is given by:

v(t)=Asin(ωRFt)+ Asin(ωLOt)

Different frequencies harmonics appear in the current:

a1v(t): ωRF, ωLO

a2v(t)2: 2ωRF, 2ωLO, ωRF±ωLO, DC

a3v(t)3: 3ωRF, 3ωLO, 2ωRF±ωLO, ωRF±2ωLO, ωRF, ωLO

Using Filter the desired frequency is obtained.



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Mixers

The conversion loss is:

A good mixer requires low conversion loss, low VSWR at the three ports and good isolation between any two of them.

LO and RF must be isolated to prevent leakage as radiation of LO through the receiving antenna.

IF

RFc

P

PdBL log10



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Oscillators

An oscillator is an active element, usually consisting of a device with negative resistance connected to a load with positive resistance.

The device impedance is generally a function of frequency, bias current, RF current and temperature



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Frequency Tuning

Electronics frequency tuning:

Bias tuning by changing the bias current I0.

Varactor tuning, changing C(V), thus changing ZC.



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Oscillator Noise and Stability

Oscillator noise: AM and FM noise.

Single sideband phase noise is measured as:

Its unit is dBc/Hz (decibels below carrier per Hertz).

Oscillator temperature stability specifies how much deviation in frequency occurs with temperature change, its unit is kHz/±C or ppm/±C.

powersignalcarrier

carrierfromoffsetfatbandwidthHzinpowerNoisefL m

m

1



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Reference Oscillators

Crystal oscillators have low noise and good stability of their frequency.

Other frequencies can be obtained from the reference crystal oscillator, using frequency multipliers and dividers.

Frequency multipliers and dividers are implemented using nonlinear elements (i.e. diodes) and PLL (Phase Locked Loop).



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Oscillators parameters

Output power.

DC-to-RF efficiency.

Noise.

stability.

Spurious signals (i.e. harmonics 2f, 3f …).



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Amplifier

An amplifier is a component that provides power gain to the input signal.

Types of Amplifiers:

Power Amplifier PA: Amplify the RF signal before the transmitting antenna.

Low Noise Amplifier LNA: Amplify the received signal fed by the receiving antenna.

G =Pout

Pin

; G(in dB) = 10logPout

Pin



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Performance of An Amplifier

Gain and bandwidth.

Stability and matching of the input and output.

Noise, specially for LNA

Efficiency, for PA.

1-dB compression point, specially for PA

Third-order intercept point.

Dynamic range.



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Amplifier Gain

Power gain: G=PL/Pin (depends on ZL)

Available gain GA=PAVN/PAVS (depends on ZS)

Transducer gain GT=PL/PAVS (depends on both ZL and ZS)

The behavior of the amplifier can be described by its S matrix parameters.



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Stability and Matching

Unconditional stability : no possible oscillations at all frequency band for all source and load impedance.

Conditional stability: it is occurred at certain range of source and load impedance.

Stability parameter K>1 for unconditional stability.



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Noise

A measure of noise added by an amplifier (or any device) to the input noise, is the so called noise figure F

o

o

i

i

NS

NS

outputatSNR

inputatSNRF

The output noise No=GNi+Nn

i

n

i

o

o

o

i

i

GN

N

GN

N

NS

NS

F 1



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Noise Figure for a cascaded circuit

The noise figure is mostly affected by the first stages. So a major design consideration to reduce the noise figure for the first stage amplifier which is called LNA

...................11

21

3

1

21

GG

F

G

FFF



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Amplifier Efficiency

Amplifier efficiency is major importance for PA and battery operating systems.

This can be measured in terms of Power Added Efficiency PAE

Where PDC is the DC bias power, it is around 50%

DC

io

P

PPPAE



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Amplifier nonlinearity

1-dB compression.

Dynamic range DR.

Linear region:

Pout(dBm)=G(dB)+Pin(dBm)

1-dB compression

Pout(dBm)=G(dB)+Pin(dBm)-1

Minimum Detectable Signal MDS

is given in terms of the minimum

SNR acceptable for demodulation.

Dynamic Range DR

DR=1-dB compression-MDS



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Amplifier nonlinearity (IM)

When two or more signals at frequencies f1 and f2 are applied to a nonlinear device, they generate IM products at mf1 +nf2.

2nd order IM products have frequencies f1 ±f2, are out of band.

3rd order IM products have in band frequencies 2f1-f2 and 2f2-f1, which make it of primary interest.



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Amplifier nonlinearity (IM)

Third order intercept point IP3.

Spurious Free Dynamic Range SFDR.

inin MDSIPSFDR 33

2



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Summary

Mixers: implemented using nonlinear device.

Parameters: conversion loss, isolation between ports, VSWR, noise figure, IM.

Oscillators

Phase noise

Reference Crystal Oscillator

Amplifier

Stability and matching

Gain and BW

Noise figure

Efficiency

Nonlinearity: DR, SFDR



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Thank you

Microwave Antennas



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National Telecomm. Institute


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What is an antenna?

It is a device used to transform electrical signal into traveling electromagnetic wave

It is required to transmit power over long distance with adequate gain and appropriate directivity

On the receiver side it should be able to recover very weak signal coming from the transmitter

The antenna size is related to the operating frequency (wavelength)



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Antenna main specifications

The antenna performance is affected by several parameters:

Antenna type (PTP or PMP)

Gain

Radiation pattern (3-dB beamwidth)

Band width (dual band)

Polarization (vertical, horizontal, dual)

Side and back lobes relative levels



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Field Regions

The region surrounding the antenna is usually divided into 3 regions:

Reactive near field: R < 0.62(D3/λ)

Radiative near field: 0.62(D3/λ)< R< 2D2/λ

Far field: this is the region where the angular distribution is dependent on the distance from the antenna R > 2D2/λ

D is the largest dimension of the antenna

R is the distance from the antenna



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Plane Wave Approximation



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Radiation Pattern

It is the distribution of signal power in space measured at the far field region

There exist an E-plane (elevation) and H-plane (azimuth)

The more the patterns are symmetrical the better the performance of the antenna

The pattern designate the antenna types: directive or non-directive



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Radiation Pattern – cont.

Antenna pattern can be

classified as:

Isotropic: equal radiation

in all direction (theoretical)

Directional: radiation is in

some directions more than

others

Omnidirectional:

directional in the elevation

but isotropic in the azimuth

plane



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Radiation Pattern – cont.

The pattern can be drawn in polar or cartisian (pencil beam antenna) form

The pattern features:

Main lobe

Minor lobes (Side, back)

3 dB beamwidth

Gain



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Antenna Parameters

The side lobes level should be kept to a minimum relative to the main lobe to reduce interference (> 35 dB)

The Back lobe level should be <-50dB for back to back transmission

3-dB beamwidth is the angle between points on the pattern where the response is 3dB below the maximum



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Antenna Parameters – cont.

Gain: the gain measure the antenna efficiency and its directional capabilities, always expressed in dB, (effective aperture)

• Antenna efficiency: it accounts for the

losses at the antenna inputs due to

mismatch or conduction and dielectric

loss I2R

2/4 eAG



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Bandwidth: it is the range of frequency within which the antenna characteristics are acceptable

Narrow band: the B.W. is a percent of the center frequency, i.e. 5%fc

Broad band: the B.W. is defined as the ratio of the max. to the min. frequency, i.e. 10:1

Dual band antenna also exist, e.g. 4/6 GHz, 900/1800 MHz



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Polarization: it is the polarization of the radiated wave when the antenna is excited. Polarization may differ from the center to the edges of the antenna. Polarization may be linear, circular or elliptical – Cross Polar discrimination

Input impedance: it is the impedance at the terminal of the antenna, it indicates the reflection at that terminal



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Antenna Type

Wire antenna: exhibit wide band wide pattern, they can made more directive by combining them into arrays

Aperture antenna: are used for higher frequencies (patch antenna)

Reflector antenna: parabola fed by a horn, very directive, the gain can be increased by increasing the dish size



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Dipole Antenna



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Parabolic Antenna

It consists of a parabolic dish and a feed at the focal point to illuminate the dish

Dish diameter are: 1m, 1.2m, 1.5m, 2m, 2.4m, 3m, 3.4m

The simplest is with single polarized feed, some can have dual polarized feed

VSWR feeds are of the order 1.05

Front to back ratio > 50dB for back to back transmission



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Side Lobe Control



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Grid Antenna

Used where light weight is a must

To account for wind loading

Lower performance than solid antenna

The surface is made of tubular members

High gain but bad front-to-back ratio



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Antenna Specs Summary

Gain – more than 30dB for directive

Size – the larger the higher the gain

Band (can be dual) - the higher the better the gain

Side lobes level – higher than 30dB

Front to back ratio F/B higher than 50 dB

Cross polar discrimination – around 6 dB



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Friis Formula

2

2

4

4

RGGP

AGR

PP

rtt

ett

r

s

rtt

r

T

G

RGP

N

P2

4



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Launch Unit (Horn)

Sectoral Horn: WG is

flared in one direction

Narrow E-beam but wide

H-beam

Pyramidal Horn: WG is

flared in both direction

Equal E and H plane but

unequal phase, greater

side lobes



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Launch Unit (Horn) – cont.

Corrugated Horn

Symmetrical E and

H plane better side

lobes

Dual polarised feed

Made of a circular WG



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Feeders (Coaxial)

Coaxial: the impedance depends on the ratio of the outer to the inner diameter b/a, as freq increases attenuation increase

Attenuation can be minimized by increasing the cable size but keeping the same ratio b/a to keep same impedance

Cut off depends on dimensions as well, so the size should be kept to an upper level

Ex: coaxial used in the 2GHz band, b/a = 3.6, b=41mm, a=11.4mm, the cut off is 3.6GHz



9-13 May 2010



9-13 May 2010

Feeders (Waveguide)

Rectangular: Group velocity is related to the frequency and dimension (larger), with wide band distortion can be significant between the upper and lower side bands

Ex: A system operating at 1.7 GHz with bandwidth 20MHz using EW17 waveguide, cut off=1.363GHz and the length of WG is 100m

100 m at 1.71GHz is 552.8ns

100 m at 1.69 GHz is 564.9ns

12ns difference corresponding to 40% of the bit at E3



9-13 May 2010



9-13 May 2010

WG disadvantages

Group velocity causes dispersion

In installation over long runs curved needs joints

Reflections from joints and bends, (about -30dB at each joint)

Regular spaced joints cause echo (reflections will be in phase over a given band – spacing between joints)



9-13 May 2010



9-13 May 2010

Feeders (Waveguide) - cont.

Circular: dominant mode is TE11, better dispersion and attenuation, difficult to make bends without introducing higher order modes (unwanted), larger B.W. than rectangular and elliptical

Elliptical: can be designed in continuous lengths so no joints, usually corrugated



9-13 May 2010



9-13 May 2010

Antenna Mounting Structure

Antenna are placed on support structures

Requirement for supporting structure

Weight loading of the antennas and feeders

The wind loading, structure tends to twist

Tilt and twist of the antenna affect the beam width of the antenna

Grid antenna can be used to reduce wind and antenna loading

Standards for wind loading definitions and calculations are EIA standards – RS222A for towers and RS-195S for antennas



9-13 May 2010



9-13 May 2010

Factors to consider

Earthing and lightning: structure must be earthed to provide path to earth for any lightning strikes

Aircraft warning lights which depends on location

There exist different type of mounting structures: Guy and self supported structure (3 or 4 legs)



9-13 May 2010



9-13 May 2010

Supporting Structure (Tower)

Guyed masts:

cheap but

requires large

area

Self supporting

towers less ground

space, very high

cost

Self supporting: less

area but the most

expensive, used in

cities



9-13 May 2010



9-13 May 2010

Area for Self Supporting

PRheight

21.815.450

28.920.5100

HWRHeight

23.426.613.850

29.333.517.3100



9-13 May 2010



9-13 May 2010

Area for Guyed Structure



9-13 May 2010



9-13 May 2010

Thank you

Microwave Transmission Line



9-13 May 2010

Lecture Outline

Types

T.L. parameters

Comparison of T.L.

Connectors and adaptors

Matching between T.L. and components

Antenna feeders



9-13 May 2010

Low vs. High Frequency

At low frequency V and I affect the entire circuit at the same instant of time

At high frequency at a given instant voltage and current waves have different values at different locations on the circuit

When voltage or current waves enter a transmission line at high frequencies it takes time to travel down the line



9-13 May 2010

Voltage and Current Wave

Voltage (current) on microwave T.L. are the sum of a two voltage (current) wave components: incident and reflected

ZjrefZjinc eVeVV

LoadVinc

Vref



9-13 May 2010

Line Parameters

)( ZjrefZjinc eVeVZ

I

0

1

ZjrefZjinc eVeVV

Total voltage and

current along the line

Z0 is the line

characteristic impedance

ß is the propagation

constant of the line

C

LZ 0

2



9-13 May 2010

Terminated Line

If the load terminating the line is not matched (Zload Z0) then a reflection will exist on the line

0

0

ZZ

ZZ

load

load

• The reflection coefficient has an amplitude and

phase depending on the load impedance, Zo is

always real, it is used to calculate unknown

impedance



9-13 May 2010

Reflection Coefficient

Short Circuit, ZL = 0, =-1 (=1, =180º)

Open circuit, ZL = , =1, ( =1, =0 º or 2n)

Matched load, ZL = Z0, = 0º, (No reflection) perfect case

je



9-13 May 2010

Standing Wave Ratio

Short circuit, = 1, SWR =

Open circuit, = 1, SWR =

Matched load, = 0, SWR = 1 (best value)

What is infinity means? In worst case half the power will be reflected, = ½ = 0.707, SWR= 5.8

SWR should vary from 1 up to 3 max. The higher the SWR the higher the reflection on the line

1

1

min

max

V

VSWR Note: SWR is a real value it has no phase



9-13 May 2010

Impedance Measurement

To measure an unknown impedance, connect it to a line with characteristic impedance Z0, then measure the reflection coefficient

is measured by measuring max and min. voltage on the line

The phase by measuring the position of the first minima from the load ( = - zmin)

1

1loadZ

1

1

0

0

load

load

load

load

Z

Z

ZZ

ZZ



9-13 May 2010

Measure Reflection From Antenna

An SWR meter is placed in the feed line

The max. and min voltages are recorded

SWR is calculated as the ratio of the max. to the min.

If SWR is close to “1” the reflection is low, if the SWR is higher than 2.5 too much power is reflected

Note: the measurement can be carried anywhere on the feed line



9-13 May 2010

Input Impedance

The concept of input impedance is very important as what we see at each port is different and at any point on the line as well

The input impedance depends on the line termination and the operating wavelength and the distance between observation point and the load



9-13 May 2010

Input Impedance – cont.

tan1

tan

L

Lin

Zj

jZZ

tanjZin Short circuit

termination

Open circuit

termination

Matched load

termination

cotjZin

1inZ



9-13 May 2010

Lumped Element in Microwave

OC =

capacitor

SC =

inductortanjZin

cotjZin

4/True for



9-13 May 2010

T.L. Types

A transmission line should be able to transmit power with minimum loss and radiation

2- wire – for low frequency, can carry up to 2Mb/sec over 200m

Coaxial – DC up to 1GHz maximum

Waveguide

Microstrip lines, not for transmission system but for circuits



9-13 May 2010

Coaxial

The dominant mode is the TEM,

This allows wide band operation starting at DC

The cut off of the coaxial cable gives the upper frequency limit, dimensions will be chosen such that higher order mode are prohibited

TE11 mode is the lowest higher order mode

)( bac



9-13 May 2010

Coaxial –cont.

Coaxial cables are used at frequencies below microwave

It can be used at high frequency with smaller diameter

The larger the diameter the lower the attenuation and the greater its power handling capability



9-13 May 2010

Coaxial - Power Handling

The power handling capability is limited since the it is easily dissipated in the inner conductor

The power is conducted through the dielectric between inner and outer conductor, good for radiation loss

At lower frequency power loss is lower and cable can handle more power



9-13 May 2010

Waveguide

Waveguide TL are hollow conducting pipes that can take different shapes

Rectangular, easier to manufacture and to excite, but has edge discontinuities, larger BW than circular

Circular, easier to manufacture good for circular polarization or dual polarizer, difficult power coupling

elliptical, difficult to manufacture, E and H plane not symmetrical

Waveguide are used for transmission over few hundreds of meters, because of unflexibility

circular and elliptical can be designed rigid or flexible



9-13 May 2010

Waveguide

Wave propagates in modes

As modes increase group delay increases causing signal distortion

Only one mode is usually excited, the dominant mode (TE01

for rectangular)

The dimensions of the guide designate the dominant mode cut off

Cut off is the lowest frequency that a guide can handle (High pass filter)



9-13 May 2010

Modes in Rectangular WG

22

, )()(b

m

a

nCf nmc

a

Cfc

201,

a is the smallest side of the rectangle

b is the largest side of the rectangle

n,m are the order of the mode

The dominant mode frequency

Dimensions are standard b=2a

a

Cfc 10,< Band <



9-13 May 2010

Rectangular Waveguide

Waveguide can handle more power than cables

They have narrow bandwidth, the cut off up to the next higher order mode

The physical size of the waveguide determines its operating characteristics, the larger the WG the lower the cut off freq., the lower the attenuation and the greater the power handling

BW depends on „a‟ as a decreases BW increases

Waveguide components also exist



9-13 May 2010

Feeders



9-13 May 2010

Feeder for Parabolic Antenna

The parabolic antenna is just a reflector

The antenna is the horn placed at the focal point of the reflector

The horn is also called the “feeder”

The feeder may be dual polarized or single polarized

Dual band feeder also can be designed (e.g. 6 and 11 GHz)



9-13 May 2010

Feed Unit

Wave propagating down the waveguide will spill out of the open end and radiate

To avoid sudden discontinuity the waveguide end is gradually flared out into a horn (rectangular or circular)

Sectorial horn: flared in one plane only narrow beam in the plane of the flare and wide on the other plane

Pyramidal horn: flared to a square aperture, has approximately equal E and H plane beamwidth

Corrugated horn: circular guide, improve side lobes and symmetry between E and H planes



9-13 May 2010

Feeder Type

A dipole or dipole array can be used with a coaxial feed line

Swan neck feed with a flared horn is the simplest form of feed

A circular waveguide can be used to enable dual polarization

Vertical Horizontal



9-13 May 2010

Coaxial Feeders

For air filled conductor, impedance = 76 ohm for b/a=3.6

a radius of the inner conductor

b is the inner radius of the outer conductor

The impedance of a coaxial line is

)/log(138 abZr

r



9-13 May 2010

Coaxial Feeder – cont.

The attenuation increases rapidly with frequency

The attenuation is minimized by increasing dimensions and keeping same ratio b/a

The lowest cut off mode is set by the dimensions

220

ba Upper freq. limit

Therefore for higher frequencies a waveguide is used



9-13 May 2010

Rectangular Waveguide Feeder

Pyramidal shape

Better side lobes

Limited in BW

Circular

Good for dual polarizer applications

Circular corrugated

Improve side lobes



9-13 May 2010

Feeder Pressurization

Water within a feeder causes excessive losses and lead to corrosion of the copper, water can be condensed with day/night temperatures changes

Water is excluded from air spaced T.L. by pressurizing the feeder with a dry gas

Static system: use of hand foot/pump equipped with desiccator

Gas bottles: Safe bottles are used for better monitoring (gas used is Nitrogen, oxygen free)

Mechanical pressurizers: electrically driven pump, desiccant is contained in transparent container for better monitoring



9-13 May 2010

Thank you

Microwave Network DesignPresented by

Eng / Yahia Ahmed



9-13 May 2010Microwave Course 9-13 May 2010



9-13 May 2010

AGENDA

Introduction to Microwave Network Design Types of Microwave Transmissions.

Microwave Transmission Frequency Bands.

Performance and availability objectives

Design aspects and main concepts Design Parameters

Antenna Theory

Digital Modulation

Microwave Link Budget

Assumptions in design

Design Steps






9-13 May 2010

Introduction to Microwave Network Design

The main objective for system planning is to ensure that the radio relay system will meet the given performance and availability requirements.

Quality and availability of communications line-of-sight (LOS) radio are closely related to propagation conditions.






9-13 May 2010

Transmission Types

Two methods of classifications

1. Point to point and point to multi point.

2. Line of sight and non line of sight.






9-13 May 2010

Transmission Types (1): Point to point and point to multi point

Point to point:

1 transmitter and 1 receiver.

Directive antennas used.

Low radiated power.

Point to multi point:

1 Base station connected to many stations.

Omni directional antenna used for base station.

High radiated power.






9-13 May 2010

Line of sight

Line of Sight (LOS):

Simple design.

Full or partial clearance of fresnel zone.

Suitable for long links.






9-13 May 2010

Frequency Bands

The following bands are available:

Long Haul:

2 , 6 , 7 and 8 GHz

Short Haul:

11 , 13 , 15 , 18 , 23 , 25 , 28 and 32 GHz

Micro Links:

38 GHz.






9-13 May 2010

Frequency Plans

Frequency

Lower band Upper band

Channel bandwidth

Channel spacing

According to ITU recommendation for each band.

The recommendation specifies the channel bandwidth, spacing and total number of

available channels.






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9-13 May 2010


Link Availability

A microwave link is available if communication is established in the two directions with an acceptable bit error rate (BER).

If the BER of the communication in at least one direction exceeds the BER specified, the link is considered unavailable.

%Availability=100-%Unavailability.






9-13 May 2010


Error performance parameters are derived from the

following events

Errored second (ES):

It is a one second period in which one or more bits are in error or during which loss of signal or alarm indication is detected..

Severely errored second (SES):

It is a one second period which has a bit error ratio≥10-3 .






9-13 May 2010


Parameters are:

Errored second ratio (ESR):

the ratio of ES to total seconds in available time during a fixed measurement interval.

Severely errored second ratio (SESR):

the ratio of SES to total seconds in available time during a fixed measurement interval.






9-13 May 2010

Availability performance parameters and objectives

Period of unavailable time

begins at the onset of 10 consecutive SES events. These 10 s are part of unavailable time.

Period of available time

begins at the onset of 10 consecutive non SES events. These 10 s are part of available time.

A path is available if, and only if, both directions are available.






9-13 May 2010

Availability performance parameters and objectives

Quality (SES) and Availability objectives are chosen according to different ITU recommendations.

Different ITU recommendations depend on the capacities and hop lengths.






9-13 May 2010

Design Aspects and Main Concepts






9-13 May 2010

Design Parameters

1. Propagation related issues

Free space loss

Surface reflection

The Line of Sight Concept

Atmospheric multipath

Rain Scattering property

Polarization

Gaseous attenuation

2. Equipment related aspects

Modulation

Radio protection switching

Antennas






9-13 May 2010

Design Parameters – Propagation related issues

Free space loss:

The free space loss (FSL) value is given in the equation below:

FSL= 92.44 + 20 log (f) + 20 log (d)

Where:

FSL: free space loss (dB)

f: frequency of radio (GHz)

d: distance between transmitter and receiver (km)






9-13 May 2010


Surface reflection

The influence of the reflected signal from the surface of the Earth on the performance of the Microwave link is important when it is sufficiently strong to interfere significantly with the direct signal, either constructively or destructively.

The strength of the reflected signal at the receiving antenna terminals will depend upon:

the directivity of the antennas,

the height of the terminals above the Earth’s surface,

the nature of the surface

and the length of the path.






9-13 May 2010

The Line of Sight Concept

An optical line of sight exists if an imaginary straight line can be drawn connecting the antennas on either side of the link.

A clear line of sight exists when no physical objects obstruct viewing one antenna from the location of the other antenna.

A radio wave clear line of sight exists if a defined area around the optical line of sight (Fresnel Zone) is clear of obstacles.



9-13 May 2010

LOS Propagation



9-13 May 2010

Fresnel Ellipsoid

The free space loss formula can only be applied if the direct line-of-sight (LOS) between transmitter and receiver is not obstructed

This is the case, if a specific region around the LOS is cleared from any obstacles

The region is called Fresnel ellipsoid

Transmitter

Receiver

LOS



9-13 May 2010

Fresnel Ellipsoid

21

21

dd

ddr

The Fresnel ellipsoid is the set of all points around the LOS where the total length of the connecting lines to the transmitter and the receiver is longer than the LOS length by exactly half a wavelength

It can be shown that this region is carrying the main power flow from transmitter to receiver

Transmitter Receiver

LOS

LOS + /2

Fresnel zone






9-13 May 2010


Atmospheric multipath

Under normal propagation conditions a radio wave follows a single path from the transmitter to the receiver.

Anomalous propagation conditions however make two or more paths possible. This phenomenon is known as “multipath”.

In the presence of multipath several rays arrive at the receiving antenna at slightly different angles in the vertical plane. The resulting signal is then the sum of various components whose mutual interference produces more or less deep fades, according to the relative amplitudes and phases of the components.






9-13 May 2010


Rain Scattering property

Rain precipitation scattering of microwaves is very important at frequencies above about 10 GHz.

At these frequencies the rain droplet sizes become comparable to the wave length of the radio waves and cause scattering of microwave energy.

The main effect of scattering is a heavy attenuation in the path.

Due to the asymmetrical approximately oblate spheroidal shape of the rain drops which has a vertical rotation axis, it cause larger attenuation for horizontally polarized waves than that for vertically polarized ones.






9-13 May 2010


Polarization

The plane of polarization is not affected by normal passage of the wave through the atmosphere except in case of rain or during multipath formation.

The wave is received by the receiver antenna as either “H” or “V” polarized.

Polarization is a very convenient and simple method available by which it is possible to increase the isolation between two signals and hence to increase the spectrum usage.






9-13 May 2010


Gaseous attenuation

Gases in the atmosphere such as water vapour and oxygen create additional attenuation over and above that produced during propagation in free space.

13 GHz 18 GHz 23 GHz 38 GHz

0.03 dB/km 0.08 dB/km 0.19 dB/km 0.12 dB/km






9-13 May 2010

Design Parameters – Equipment related aspects

ModulationLower modulation schemes use larger Bandwidth but provide higher system

gain (higher TX power and lower Rx threshold), while higher modulation schemes use smaller bandwidth but provide lower system gain.

As a result, lower modulation schemes are used for long links to provide optimum performance.

Higher modulation schemes are used in congested city areas to provide maximum use of the frequency bands.

For example:4 QAM 16 QAM

Higher BW (m) Lower BW (m/2)

High system gain [TX power – Rx threshold] spectrum efficiency






9-13 May 2010

Fading






9-13 May 2010

Fade margins – Parameters affecting the Link Quality

Thermal Fade Margin:

Is the difference between the free space received signal and the receiver threshold level.

Interference Fade Margin:

Is the additional attenuation to the free space received signal required to produce an outage due to interference (independent of thermal noise).

Flat Fade Margin:

Is the combination of the thermal and the interference fade margins.

Dispersive Fade Margin:

This is an equipment parameter which depends on the equipment design and is defined as the average depth of multi-path fade which causes an outage independent of thermal noise and interference.

Effective Fade Margin:

Is the combination of the flat and dispersive fade margin components.






9-13 May 2010

Diversity Systems

Failure time due to multipath can be limited by using diversity techniques:

Space diversity: two orthogonal paths are used

Frequency diversity: two orthogonal frequencies are used

Polarization diversity: Information can be transmitted using two different polarization






9-13 May 2010

Frequency Diversity

A single antenna can be used having broadband characteristics

Two transceivers are used at two different frequencies

Disadvantage is the used of wide spectrum for same channel transmission

Only used for very difficult conditions and vital applications






9-13 May 2010

Space Diversity

Two antennas are used and spaced vertically with distance half of the fringing space

In some applications antennas can be placed horizontally (mobile system)

Only one transceiver can be used






9-13 May 2010

Antenna Theory






9-13 May 2010

Antenna Theory

50 is the impedance of the cable

377 is the impedance of the air

Antennas adapt the different impedances

They convert guided waves, into free-space waves (Hertzian waves) and/or vice versa

Z =377Z =50






9-13 May 2010

Antenna Characteristics

Isotropic Antenna

A hypothetical, lossless antenna having equal radiation intensity in all directions. Used as a zero dB gain reference in directivity calculation (gain).

Gain

Antenna gain is a measure of directivity. It is defined as the ratio of the radiation intensity in a given direction to the radiation intensity that would be obtained if the power accepted by the antenna was radiated equally in all directions (isotropically). Antenna gain is expressed in dBi.

Radiation Pattern

The radiation pattern is a graphical representation in either polar or rectangular coordinates of the spatial energy distribution of an antenna.



9-13 May 2010

Antenna Characteristics (Cont.)

Antenna Beamwidth

The directiveness of a directional antenna. Defined as the angle between two half-power (-3 dB) points on either side of the main lobe of radiation.

EIRP (Effective Isotropic Radiated Power)

The antenna transmitted power. Equal to the transmitted output power minus cable loss plus the transmitting antenna gain.

)()()( dBGdBCdBmPEIRP ttout






9-13 May 2010

Antenna Pattern and HPBW

0 dB

-3 dB

-10 dB

0 dB

-3 dB

-10 dB

verticalhorizontal

sidelobe

null direction

main beam

HP

BW



9-13 May 2010

Microwave antennas, feeders and accessories

Microwave point to point systems use highly directional antennas

Gain

with G = gain over isotropic, in dBi

A = area of antenna aperture

e = antenna efficiency

Used antenna types

parabolic antenna

high performance antenna

horn lens antenna

horn antenna

GA e

104

2lg






9-13 May 2010

Antenna Data

Polarization

Specification due to certain wave polarization (linear/elliptic, cross-polarization)

Half power beam width (HPBW)

Related to polarization of electrical field

Vertical and Horizontal HPBW

Antenna pattern

Yields the spatial radiation characteristics of the antenna

Front-to-back ratio

Important for interference considerations






9-13 May 2010

Panel Antenna with Dipole Array

Many dipoles are arranged in a grid layout

Nearly arbitrary antenna patterns may be designed

Feeding of the dipoles with weighted and phase-shifted signals

Coupling of all dipole elements






9-13 May 2010

Dipole Arrangement

t Dipole

arrangement

Typical flat panel

antenna

Dipole

element

Weighted

and

phase

shifted

signals



9-13 May 2010

X 65° T6 900MHz 2.5m

Rural road coverage with mechanical uptilt

Antenna

RFS Panel Dual Polarized Antenna 872-960 MHz

APX906516-T6 Series

Electrical specification

Gain in dBi: 17.1

Polarization: +/-45°

HBW: 65°

VBW: 6.5°

Electrical downtilt: 6°

Mechanical specification

Dimensions HxWxD in mm: 2475 x 306 x 120

Weight in kg: 16.6Horizontal

Pattern



9-13 May 2010

Parabolic antenna

Parabolic dish, illuminated by a feed horn at its focus

Available sizes: 1’ (0.3 m) up to 16’ (4.8 m)

Sizes over 4’ seldom used due to installation restrictions

Single plane polarized feed vertical (V) or horizontal (H)

Also: dual polarized feeder (DP), with separate V and H connections (lower gain)

Front-to-back ratios of 45 dB not high enough for back-to-back configuration on the same frequency

Antenna patterns are absolutely necessary for interference calculations



9-13 May 2010

High performance antenna

Similar to common parabolic antenna, except for attached cylindrical shield

Improvement of front-to-back ratio and wide angle radiation discrimination

Available in same sizes as parabolic, single or dual polarized

Substantially bigger, heavier, and more expensive than parabolic antennas

Allow back-to-back transmission at the same frequency in both directions (refer to interference calculation)






9-13 May 2010

Specific Microwave Antenna Parameters (1)

Cross polarization discrimination (XPD)

highest level of cross polarisation radiation relative to the main beam; should be > 30 dB for parabolic antennas

Inter-port isolation

isolation between the two ports of dual polarised antennas; typical value: better than 35 dB

Return loss (VSWR)

Quality value for the adaption of antenna impedance to the impedance of the connection cable

Return loss is the ratio of the reflected power to the power fed at the antenna input (typical> 20 dB)






9-13 May 2010

Radiation pattern envelope (RPE)

Tolerance specification for antenna pattern (specification of antenna pattern itself not suitable due to manufacturing problems)

Usually available from manufacturer in vertical and horizontal polarisation (worst values of several measurements)

Weight

Wind load

Specific Microwave Antenna Parameters (2)



9-13 May 2010

Digital Modulation



9-13 May 2010

Digital modulation

Can be considered as varying certain characteristics of the carrier signal; according to the modulating signal “which is the signal to be transmitted”

x(t)=Acos(wct+)






9-13 May 2010

Demodulation and Detection

Demodulation

Process of removing carrier signal

Detection

Process of symbol decision

Coherent detection:

Receiver uses the carrier phase to detect signal

match within threshold to make decision

Non-coherent detection:

Doesn‟t explode phase to detect signal

less complex receiver, but worse performance






9-13 May 2010

Metrics for Modulation

Power Efficiency: is a measure of how much signal power should be increased

to achieve a particular BER for a given modulation scheme

Bandwidth Efficiency:

Trade off between data rate and bandwidth

Ability to accommodate data within a limited Bandwidth

Error Performance.






9-13 May 2010

Considerations in choice of modulation technique

High spectral efficiency

High power efficiency

Robust to multipath effects

Low cost and ease of implementation

Low out of band radiation due to the lobed

nature of modulation



9-13 May 2010

Handling Data

Binary Modulation

The stream of bits modulated as it comes so we have two signals one for each of the two cases (0,1) as

ASK, PSK, FSK

M-ary Modulation

the stream of bits is divided into symbols of m bits per symbol To form a set of M symbol where

m=log2 (M) then modulating the data

We have M signals one for each symbol



9-13 May 2010

Amplitude Shift Keying

The amplitude of the carrier is varied according with the binary source it can be told OOK

s(t)=A(1+m(t))cos(wct)

Since the carrier conveys no information we can eliminate it:

DSB-SC

s(t)=A(m(t))cos(wct)






9-13 May 2010

Amplitude Shift Keying

Band width the ASK bandwidth is BT=2B Where B is the base band bandwidth

Advantages :

ease of implementation

Disadvantage:

signal is transmitted at different amplitudes so it is power inefficient



9-13 May 2010

Frequency Shift Keying

The two binary characters 0/1 are represented by two different frequencies slightly offset from the carrier frequency

s1(t)=Acos((wc+w)t)

s0(t)=Acos((wc-w)t)






9-13 May 2010

Frequency shift keying






9-13 May 2010

Frequency Shift Keying

Modulation index m=f/B Where B is the base band

bandwidth while the FSK bandwidth is BT=2B(1+m)

Advantages :

1- signal is transmitted at constant amplitude so it is power efficient scheme.

2- more immune to noise than ASK

Disadvantage:

requires more analog bandwidth than ASK



9-13 May 2010

ASK & FSK

ASK in frequency domain FSK in frequency domain



9-13 May 2010

Phase Shift Keying

The two binary characters 0/1 are represented by two different phases namely 180 and 0 respectively

sj(t)=Acos(wct+j)






9-13 May 2010

Phase shift keying






9-13 May 2010

Phase Shift Keying

Advantages :

1. Simple to implement

2. signal is transmitted at constant amplitude so it is power efficient scheme

3. Very robust, used in sat. communications

Disadvantage:

inefficient use of bandwidth



9-13 May 2010

A binary signal

Frequency

modulation

Amplitude

modulation

Phase

modulation

Binary Modulation Techniques



9-13 May 2010

Comparison of binary modulation techniques



9-13 May 2010

Band width Power BER

ASK 2R BAD BAD

FSK 2R + Δf GOOD GOOD

PSK 2R GOOD Better

R: Bit Rate

Comparison of binary modulation techniques






9-13 May 2010

Binary modulation techniques

Good error performance due to simple implementation

Bandwidth inefficient specially at high bit rates

Power inefficient

So we have to introduce some complexity to the system to enhance its characteristics






9-13 May 2010

Quadrature Phase Shift Keying

It is clear that the bandwidth depends on the bit rate, so if we could reduce the bit rate to one half for example, we will obtain half the bandwidth.

The stream of bits is divided into two streams:

1. Odd (Q) : takes the odd bits, every even bit takes the same as the previous odd bit, so we have Ro=Rb/2

2. Even (I): takes the even bits, every odd bit takes the same as the next even bit, so we have Re=Rb/2

Then applying PSK to both I and Q streams with cosine and sine carriers respectively

The orthogonality between sine and cosine results in no interference and the overall bandwidth will be half that of binary PSK



9-13 May 2010

QPSK

Constellation diagram for QPSK Quadratic coefficients for 4-PSK






9-13 May 2010

M-ary Modulation

When we group stream of bits in 2 bits at a time we have reduced the bandwidth to one half.

If we could classify the stream into M symbols each of m=log2M we could save more bandwidth.

We have M-ary(ASK, PSK and FSK)






9-13 May 2010

M-ary PSK

M symbols are expressed as the set of equally spaced phase angles

sn(t)=Acos(wct+n) , 0<t<T , n=1,2,…,M

Where n=2(n-1)/M

This can be rewritten in the quadrature form as : sn(t)=A[pncos(wct)+Qnsin(wct)]

Where pn=cos n , Qn=sin n






9-13 May 2010

There are four different angles:

45 degrees

135 degrees

225 degrees

315 degrees

QPSK Modulation






9-13 May 2010

15 -10-2008 المعهد القومي لالتصاالت

M-ary Modulation Techniques



9-13 May 2010

M-ary Modulation Techniques

01 11

00 10

Q

I-1 +1+1

-1

0010 0110 1110 1010

0011 0111 1111 1011

0011 0101 1101 1001

0000 0100 1100 1000

Q

I-1-3 +3+1

+3

+1

-1

-3

000101 001101 011101 010101 110101 111101 101101 100101

000111 001111 011111 010111 110111 111111 101111 100111

000110 001110 011110 010110 110110 111110 101110 100110

000010 001010 011010 010010 110010 111010 101010 100010

000011 001011 011011 010011 110011 111011 101011 100011

000001 001001 011001 010001 110001 111001 101001 100001

000000 001000 011000 010000 110000 111000 101000 100000

000100 001100 011100 010100 110100 111100 101100 100100

Q

I-1-3-5-7 +7+5+3+1

+3

+5

+7

+1

-1

-3

-5

-7



9-13 May 2010

Microwave Link Budget



9-13 May 2010

Radio Link Design

Unlike terrestrial cellular networks, in a mobile-satellite network, transmissions are constrained by available power.

Efficient coding and modulation techniques need to be employed in order to achieve a system margin above the minimum needed to guarantee a particular Quality of Service (QoS).



9-13 May 2010

Link Budget Analysis

Link budgets are performed in order to analyze the critical factors in the transmission chain and to optimize the performance characteristics.

The strength of the received signal power is a function of the transmitted power, the distance between transmitter and receiver, the transmission frequency, and the gain characteristics of the transmitter and receiver antennas.

If we have an isotropic antenna as transmitter and receiver then the loss in dB is given by:

Where:

d is the path length in kilometers and f is the frequency in MHz.

fdLoss log20log204.32






9-13 May 2010

The aperture antenna

The antenna forms the interface between the ‘guided wave’ (for example in a coaxial cable) and the electromagnetic wave propagating in free space.

Antennas act in a similar manner irrespective of whether they are functioning as transmitters or receivers, and it is possible for an antenna to transmit and receive simultaneously.

Parabolic dishes used for microwave communications or satellite Earth stations are good examples of aperture antennas.



9-13 May 2010

The aperture antenna (Cont.)

The gain of a circular parabolic dish type of aperture antenna is given by the approximation:

where D is the diameter of the dish in meters and f is the frequency of operation in GHz.

The beamwidth is usually measured in degrees. A useful approximation is:

where D is the diameter of the dish in metres and f is the frequency of operation in GHz

fDdBigain log20log2018)(

reesDf

Beamwidth deg22



9-13 May 2010

Power Density

Assuming that the transmitting antenna is perfect, the power entering the antenna from its feed, Pt, is measured in watts. Once it has left the antenna, it creates a power density, Pd, in space that is measured in watts per square meter:

This equation reveals a very valuable generalization in radio wave

propagation: the „inverse square‟ law. It can be seen that the power density produced by an antenna reduces with the square of the distance.

24 r

PP t

d



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Power at the Receiver

The power entering the aperture (the received power, Pr) depends on the size of the aperture, Ae square meters (the suffix e taken to stand for „effective‟ when referring to a receiving antenna), and the power density of the radio wave:

This gives us the power received at distance r meters by an antenna

with effective aperture Ae square meters when an isotropic antenna

transmits power Pt watts.

edr APP

24 r

APP et

r



9-13 May 2010

Power at the Receiver (Cont.)

The power density is given more generally by:

where Gt is the gain of the transmitting antenna in any direction.

we can modify the equation for the received power:

where the effective aperture of the receiving antenna is now called Aer

to make it clear that it is the receiving antenna that is being referred to.

24 r

GPP tt

d

24 r

AGPP ertt

d



9-13 May 2010

The effective aperture

The effective aperture of an isotropic antenna, Aei, depends on the wavelength, λ, and is given by:

Practical antennas have a smaller aperture than that calculated from the diameter of the dish.

Where η is the aperture efficiency, which lies between 0 and 1 and D is the diameter of the parabolic dish.

4

2

eiA

4

2DAe



9-13 May 2010

General rules

If you double the frequency, the gain of an antenna will quadruple.

If you double the frequency, the beamwidth of an antenna will halve.

If you double the antenna diameter (keeping the frequency the same), the gain of the antenna will quadruple.

If you double the antenna diameter (keeping the frequency the same),the beamwidth of an antenna will halve.



9-13 May 2010

Point-to-point transmission

With knowledge about the gain of antennas and the free-space loss between two points it is possible to predict the received signal power for a particular situation and, thence, to design a link to a deliver a particular power to the receiver.

The power required by any radio receiver depends on a number of things:

the quality of the receiver.

the noise and interference being received.

the required bit error ratio.

the modulation scheme used and.

the bit rate being transmitted.



9-13 May 2010

Point-to-point transmission (cont.)

For Digital communication we almost use the term Eb / No to present the signal to noise ration.

The actual value of N0 depends on the quality of the particular receiver ,N0 can be written as generally:

Where: K is Boltzman constant, T is the temperature in Kelvin.

)1038.1( 23

0

kkTN



9-13 May 2010

Determining the power required

The power required by any radio receiver depends on a number of things:

The quality of the receiver.

The noise and interference being received.

The required bit error ratio.

The modulation scheme used.

The bit rate being transmitted.



9-13 May 2010

EXAMPLE1

A point-to-point system operates over a distance of 20 kilometers at a frequency of 26 GHz. The antennas are each of diameter 90 cm. Estimate the beamwidths of the antennas deployed and the power received if the transmit power is 20 dBm.

SOLUTION ?



9-13 May 2010

EXAMPLE2

A geostationary satellite is 39 000 km from an Earth station.

It is transmitting a digital signal at a bit rate of 36 Mbit/s using a 40-

dBm transmitter at a frequency of 11.2GHz. The transmitting antenna

has a diameter of 80 cm. Determine the required size of a receiving

antenna if the required Eb/N0 ratio is 12 dB and the noise temperature

of the receiving system is 160 kelvin.

SOLUTION ?



9-13 May 2010

EXAMPLE 3

a particular transmitter delivers a power of 20 dBm into the feeder of the transmitting antenna. We are operating at a frequency of 30 GHz over a distance of 12 km. The transmitting and receiving antennas are of 0.9 meters diameter. Estimate the gain of the two antennas

SOLUTION ?



9-13 May 2010




9-13 May 2010


More available information Less assumptions

Network design cannot begin without the following:

Sites coordinates

Estimation of transmitted capacity for equipment specification

Frequency band used

Assumptions:

Configuration “1+0 / 1+1 …”

Terrain Database

Antenna heights ensuring “LOS” and following assumed clearance criteria.

Quality and availability objectives

Frequency channels “Co-polar / dual polar / XPIC”

Network topology

Traffic

Protection






9-13 May 2010

Design Steps

Dimensioning:

1. Sites coordinates and network topology entering

2. Path profiles generation and achieving LOS criteria “Antenna Heights”

3. Climatic parameters setting

4. Equipment specification “Antenna and radio models”

5. Performance evaluation

------ End of dimensioning ------

6. Frequency plan

7. Interference analysis

------ Design complete ------






9-13 May 2010

Synchronization between Tendering and Designer

Information needed for Network Design:

Sites Coordinates

Configuration

Path profile and survey

Radio and capacity

Protection

Network Topology

Spectrum and frequency band

Quality and availability objectives

Traffic

Necessary

Coordinates

Path profile and survey

Radio, configuration, and

capacity

Protection

Topology

Spectrum and frequency band






9-13 May 2010

Synchronization between Tendering and Designer

More Information available Fewer assumptions & faster

design

Network Design needs time

Output of Network Design: Design + report

Better output needs time






9-13 May 2010

Thank you

Documents

Microwave