antenna systems: mono & multi beams beam forming...

Antenna Systems: Mono & Multi BeamsBeam Forming

Focal Plane Array

Enrico [email protected]

OBJECTIVES OF THE LECTURETo provide the technical backgrounds and tools for the analysis and the design of RF telescope like antenna system

To recognize the major incoming constraints and challenges of a telescope antenna

CONTENTS

• I n t r o du c t i o n

• Ba s i c Con c ep t s

• An tenna Pa rame te r s & Ru l e s O f Thumb

• Te l e s cope An tenna Con f i g u ra t i o n s

• Op t i c s & Beam Fo rm i n g Ne two r k

• S i n g l e & Mu l t i Beam

• SW Too l s Fo r Ana l y s i s And De s i g n

ELECTRIC FIELD

MAGNETIC FIELD

The nature of time harmonic wave of the Electromagnetic Field into the free space. Direct analogy with light, sound and … water waves

THE ELECTROMAGNETIC WAVES

y

x

z

THE ELECTROMAGNETIC WAVES

c = Light Velocity 30 x 1010 , mm

λ = Wavelenght , mm

ν = Frequency , GHz

τ = Time , sec

h = Planck Constant

E = Quantum Energy

λ = c τ

ν = c / λ

E = h ν

ELECTROMAGNETIC SPECTRUM

3‐30 kHz Very Low Frequency (VLF)30‐300 kHz Low Frequency (LF)300‐3000 kHz Medium Frequency (MF)3‐30 MHz High Frequency (HF)30‐300 MHz Very High Frequency (VHF)

300‐3000 MHz UltraHigh Frequency (UHF)3‐30 GHz SuperHigh Frequency (SHF) Microwaves30‐300 GHz Extreme High Frequency (EHF) Millimeter Waves

Near Infrared, Far Infrared,Light,UltraViolet, Far UltraViolet, X rays γ rays

MAXWELL EQUATIONSTHE BASIC LAWS OF THE EM WAVES PROPAGATION INTO THE FREE SPACE

Integral & Differential Form

If the E wave is travelling in the positive z‐direction, the instantaneus total vector field E is:

E1 = amplitude of wave linearly polarized in x direction

E2 = amplitude of wave linearly polarized in y direction

δ = time‐phase angle by which Ey leads Ex

The EM Field – Harmonic Wave

EM FIELD POLARIZATION

“ Polarization of a radiated wave” is defined as thatproperty of an electromagnetic wave describing thetime varying direction and relative magnitude of theelectric‐field vector; specifically, the figure traced as afunction of time by the extremity of the vector at afixed location in space and the sense in which it istraced, as observed along the direction of propagation

Polarization may be classified as linear, circular, orelliptical:

E1

General Spatial Representation of the E field

LINEAR POLARIZATION:

For E1 = 0 → linear polarization in y direction

For E2 = 0 → linear polarization in x direction

If δ = 0 and E1 = E2→ the wave is lin. pol. in a plane at an angle of °45 with respect to the x axis ( τ= °45 )

Circularly Polarised Field

ANTENNA AS A TRANSITION DEVICE

THE ANTENNA IS A MEANS FOR RADIATING OR RECEIVING RADIO WAVES.

THE ANTENNA SHOWS THE SAME BEHAVIOUR IN TRANSMITTING AND RECEIVING

ANTENNA : THE RADIATION MECHANISM

• When the electromagnetic waves are within the transmission line and antenna , their existence is associated with the presence of the charges inside the conductors.

• However, when the waves are radiated, they form closed loops and there are no charges to sustain their existence:

• The electric charges are required to excite the fields but are not needed to sustain them into the free space as electromagnetic waves

ANTENNA TELESCOPE : BASIC REFLECTOR ANTENNA PRINCIPLES

PARABOLIC REFLECTOR ANTENNA PRINCIPLES (Quasi Optic System)

The reflector antenna is conceptually oneof the simplest of antenna types,consisting in its basic form of a primaryradiator or feed to distributeelectromagnetic energy, and a curvedreflecting surface to collimate this energyover a larger secondary aperture.

DESIGN CRITERIA AND ANTENNA COMPONENTS

• Antenna Optics

• Feeds for Reflector Antennas

• Antenna Components

• Guidelines for Antenna Design

• Rules of thumb

CONIC SECTIONS GENERATING REFLECTOR ANTENNAS

REFLECTOR ANTENNA CONFIGURATIONS

• SINGLE ON SET OR FRONT FED

• SINGLE OFFSET

• DUAL REFLECTOR CASSEGRAIN ON SET

• DUAL REFLECTOR CASSEGRAIN OFFSET

• DUAL REFLECTOR GREGORIAN ON SET

• DUAL REFLECTOR GREGORIAN OFFSET

• SPECIAL OPTICS & SHAPED REFLECTORS

SINGLE ONSET REFLECTOR

Feed

Focus = Feed Phase Center

Axial Symmetrical Reflector

D=Aperture Diameter

F= Focal Lenght

DUAL ONSET REFLECTORCASSEGRAIN & GREGORIAN

Cassegrain :Main Reflector Paraboloid(Diameter D, Focal Lentgh f )Sub Reflector Hyperboloid(Eccentricity e >1)Gregorian :Main Reflector ParaboloidSub Reflector Ellipsoid(Eccentricity e <1)

Equivalent Focal Lenght=

feefe

11

−+

=

ONSET CONFIGURATION:THE BLOCKAGE

GEOMETRICAL CONSTRUCTION OF OFFSET PARABOLIC REFLECTOR

GLOSSARY AND DEFINITIONS

• D Diameter of Radiation Aperture

• ΨB Offset Angle

• ΨS Illumination Angle

• ΨL Clearance Angle

• Fe Equivalent Focal LengthBcosscos

scos1FFeΨ+Ψ

Ψ+=

DUAL OFFSET CASSEGRAIN

DUAL OFFSET GREGORIAN ANTENNA

BASIC FEED HORN CONFIGURATIONS

CORRUGATED HORN

Corrugated HornsCORRUGATED HORN

CLASSIFICATION OF REFLECTOR ANTENNAS BASED ON PATTERN, REFLECTOR AND FEED TYPES

FUNDAMENTAL PARAMETERS OF ANTENNA SYSTEM

RADIATION PATTERN

RADIATION POWER DENSITY

RADIATION INTENSITY

DIRECTIVITY

GAIN

ANTENNA EFFICIENCY

HALF POWER BEAM WIDTH

BEAM EFFICIENCY

BAND WIDTH

POLARIZATION

INPUT IMPEDANCE

ANTENNA RADIATION EFFICIENCY

EQUIVALENT AREA

ANTENNA TEMPERATURE


ANTENNA TEMPERATURE

NOISE FIGURE

EIRP

EIRP DENSITY

FRIIS EQUATION


POWER UNITS

dB = Log(P / Prif)

dBm = Log (P / 1mW)

dBW = Log (P / 1W)

dBi = Log (P / Piso)

dBc = Log (P / Piso‐c)

RADIATION PATTERN

It’s “ a mathematical function or a grafical representation of the radiation properties of the antenna as a function of space coordinates”

The Antenna is a point source coincident with the origin of the reference system

REFERENCE COORDINATE SYSTEMSCARTESIAN AND SPHEREICAL

PRINCIPAL PATTERNS

•The E‐PLANE is the plane containing the electric‐field vector and the direction of maximum radiation

•The H‐PLANE is the plane containing the magnetic‐field vector and the direction of maximum radiation

The polarization characteristics of an antenna can be represented by its POLARIZATION PATTERN that is the spatial distribution of the polarizations of a field vector excited (radiated) by an antenna taken over its radiation sphere. At each point on the radiation sphere the polarization is usually resolved into a pair of orthogonal polarization represented by its magnitude:

CO‐POLARIZATION & CROSS‐POLARIZATION

(The co‐polarization must be specified at each point on the radiation sphere)

RADIATION PATTERN LOBES

A RADIATION LOBE is a portion of the radiation pattern bounded by regions of relatively weak radiation intensity

MAIN BEAM: radiation lobe containing the direction of maximum radiation

SIDE LOBE: any lobe except a major lobe

NEAR‐IN SIDE LOBES: radiation lobes adjacent to the main lobe

FAR SIDE LOBES: radiation lobes that occupy the overall solid angle off the main lobe direction

BACK LOBE: radiation lobe whose axis make an angle of approximately ±180O with the respect to the beam direction

• DIRECTIVITY: is the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions

D = U/ Uo = 4πU/ Prad

D = directivity ( dimensionless)

U = radiation intensity ( W/ unit solid angle)

Uo= radiation intensity of isotropic source

( W/ unit solid angle)

Prad = total radiated power (W)

GAIN: is the ratio of the intensity, in a given direction, to the radiation intensity that would be obtained if the power accepted by the antenna were radiated isotropically:

G = 4π radiation intensity/total input

(accepted) power

G = 4πU(θ,Φ)/ Pin (dimensionless)

GAIN CALCULATION

DIRECTIVITY D(dBi) = 10Log( (G10 + G3) / 2 )

where: G3 = 31000 / (Фe3 x Фh3)G10 = 91000 / (Фe10 x Фh10)

Фe3, Фh3 = 3 dB beamwidths in the E‐planes and H‐planesФe10, Фh10 = 10 dB beamwidths in the E‐planes and H‐planes

INSERTION LOSS OF THE FEED SYSTEM ηf

Gain (dBi) = D (dBi) – ησ ‐ ηf

ANTENNA EFFICIENCY: takes into account losses at the input terminals and within the structure of the antenna

eo = er ec ed

eo = total efficiency

er = reflection eff. =

= (1‐ |Γ|2)

ec = conduction eff.

ed = dielectric eff.

Γ = (Zin‐ Zo)/ (Zin + Zo)

HALF POWER BEAMWIDTH: Is the angle between the two directions in which the radiation intensity is one‐half the maximum value of the beam.

MAIN BEAM 1st approximation :D = 10 log[cosn θ]

n = 150

MAIN BEAM vs u = k a sin (θ)

n = 150

BEAM EFFICIENCY: indicates the amount of power in the major lobe compared to the total power; for an antenna with its major lobe directed along the z axis (θ = 0), BE is defined by:

BE = (power transmitted (received) within

cone angle θ1 ) / (power transmitted

(received) by the antenna)

θ1 = angle where the first null or minimum

occurs

ANTENNA CLASSIFICATION

ISOTROPIC RADIATOR hypothetical lossless antenna having equal radiation in all directions (G = 0 dB). It is often taken as a reference for expressing the directive properties of actual antennas

DIRECTIONAL ANTENNA has the property of radiating or receiving electromagnetic waves more effectively in some directions than in others

RULES OF THUMBGAIN-HPBW-10dBBW-1dBBW

ηλ

π LogDLogdBiG 1020)( −=

DdB

λϑ 60(deg)3 =

cos shape beammain by the torelated 31

θϑϑ

n

dBdB ⎯ →⎯

dBdB 310 2 ϑϑ ×≅

RULES OF THUMB CROSS POL

pcdB HPBW θθ ≅= )21(3

‐ Relationship between HPBW and cross polar peaks:

‐ The cross polar energy radiated by the antenna isthe scalar product of two main components:

• cross polar scattered by the reflector

• cross polarised field produced by the feed chain

BANDWIDTH

It is the range of frequencies within which the performance of the antenna, with respect to some characteristics, conforms to a specified standard.

BW% = 100minmaxminmax2 •

+−

ffff

ANTENNA NOISE TEMPERATURE

TSYST = TLNA + TREF( 1 – 1/a ) + TANT/a

α = attenuation coeff. of transmission line [Np/m] a = feed losses = e2αl →α = log(a)/2 = B → αdB = 10Log[B]TREF = 290 K = 17°C (IEEE STANDARD)TANT = effective temperature seen by an antenna from its

surroundingsTLNA = low noise amplifier temperature

NOISE FIGURE:

G/ Ta [dB / °K]

G = Gain [dBi]

Ta = Antenna temperature [°K ]

WHERE ANTENNA NOISE COMES FROM:

NOISE AT THE OUTPUT TERMINALS

EXTERNAL NOISE PICKED UP

+

INTERNAL NOISE ( THERMAL NOISE)

Paris, May 2004Course on Antennas for Satellite Earth

Stations57

EXAMPLE: EXTERNAL NOISE SOURCES

EXTERNAL NOISE SORCES: includes static ( man made and natural), cosmic (solar and galactic), atmospheric, ionospheric and terrestrial (ground or sea) sources.

To study noise temperature, we use the BLAKE CURVES:

BLAKE CURVES

REALISTIC ANTENNAS

An expression for a realistic estimate of the antenna noise temperature is given by:

TANT = {Ta’ ( 1 – Tg/Ttg) + Tg } α + Tta (1 ‐ α)

TANT = external noise temperature + internal,where:

Ta’ = sky temperature given by the Blake curves

Tg = ground noise temperature comp.

Ttg = effective thermal temp. of the ground

Tta = effective thermal temp. of the lossy part of

the antenna

DESIGN GUIDELINESFROM RF SPECIFICATIONS

GAIN REFLECTOR DIAMETER

CROSS POLAR FOCAL LENGHT/ DIAMETEROPTICSFEED

1st SIDE LOBE PRIMARY PATTERN

NEAR IN SIDELOBES OPTICS

FAR SIDE LOBES OPTICS & STRUCTURE

ANTENNA EFFICIENCY

General Expression of Antenna Efficiency η

η = ηsr x ηss x ηi x ηb x ηcp x ηε x ηφ x ηr

THE FACTORS LIMITING THE ANTENNAEFFICIENCY

• ηsr Primary Spillover Efficiency (subreflector)

• ηsr Secondary Spillover Efficiency (reflector)

• η i Illumination Efficiency (aperture)

• ηb Blockage Efficiency (aperture)

• ηcp Cross Polar Efficiency (aperture)

• ηε Surface Error Efficiency (aperture)

• ηФ Phase Efficiency (aperture)

• ηr Radiation Efficiency (feed chain ohmic losses)

REFLECTOR SURFACEERRORS

The surface deviations of a antenna reflector

may be of three main different types:

• Systematic

• Random

• Periodic

SYSTEMATIC ERRORS

THE SYSTEMATIC ERRORS TYPICALLY COME FROM THE PRESSING PROCESS OF METALLIC OR SMC OR CFRP SHEETS WHEN EVERY REFLECTOR OF A LARGE SCALE PRODUCTION IS REMOVED FROM THE MOULD.

THESE EFFECTS CAN BE EASILY OVERCOME BY MOVING THE FEED HORN AROUND THE NOMINAL FOCAL POINT AND THEN CORRECTING THE BOOM AND THE HORN HOLDER.

RANDOM ERRORS

THESE ERRORS CAN BE CONSIDERED AS ARISING FROM THREE MAIN SOURCES:

SURFACE CONTOUR ROUGHNESS

MANUFACTURING IMPERFECTIONS IN THE MOULD

THERMOELASTIC AND MECHANICAL DISTORTIONS.

RUZE (“ANTENNA TOLERANCE THEORY”, Proc IEEE, Vol.54,1966)

TREATED A RANDOMNESS CAUSED BY BUMP AND DENTS WITH A GAUSSIAN PROFILE AND RANDOM HEGHT AND SPACING BY DEFINING AN RMS SURFACE ERROR TOLERANCE,ε, WITH A CORRELATION DISTANCE,c.

THE FEED SUB SYSTEM

THE PORPUSE OF THE FEED SUB SYSTEM:

TO ACHIEVE THE MOST “EFFICIENT” REFLECTOR ILLUMINATION IN AMPLITUDE AND PHASE AND IN COPOLAR AND CROSS‐POLAR

TO SEPARATE THE FREQUENCY BANDS AND POLARISATIONS

IN CASE OF CP ‐ TO CONVERT LINEAR IN CIRCULAR POLARISATION

TO MATCH THE LNA AND THE HPA INPUT PORTS

FEEDS FOR REFLECTOR ANTENNAS

FEED Passive Antenna Sub System may include (all or partly ):

• HORN

• WAVEGUIDE INTERFACES / DIRECTIONAL COUPLERS

• POLARISER

• DIPLEXER-DUPLEXER

• FILTERS

EXEMPLE OF FEED CHAIN

WAVEGUIDE PROPAGATION BACKGROUND

THE PROPAGATION OF EM FIELD WHICH FOLLOWS THE MAXWELL EQUATIONS IN THE FREE SPACE,

( PROPAGATION CONSTANT k 0 = 2π/λ0 ), IS MODIFIED INTO THE WAVEGUIDES BY THE CONDUCTIVE WALLS, (PROPAGATION CONSTANT k z = 2π/λg )

THE EM FIELD INTO THE WAVEGUIDE CAN BE CONSIDERED AS A SUM OF ORTHOGONAL FUNCTIONS WHICH ARE THE “MODES” OF THE WAVEGUIDE


TWO MAIN WAVEGUIDE STRUCTURES ARE CONSIDERED:

‐ SQUARE / RECTANGULAR WAVEGUIDE

‐ CIRCULAR WAVEGUIDE

EVERY MODE HAS A PROPAGATION VELOCITY WHICH CAN BE REAL (PROPAGATION MODE) OR IMAGINARY (EVANESCENT) MODE AS FUNCTION OF THE WG DIMENSIONS

)( 220 tz kkk −=


EVERY MODE WITH CUT OFF FREQ. fc ,PROPAGATES WITH WAVELENTGH λg.

Side = 2a

Diameter = 2r

20

1 ⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

ffc

gλλ

OMTBLOCK DIAGRAM

OMTCONFIGURATIONS

POLARISERMECHANISM

SCHEMES OF POLARISERS

MULTIBEAM ANTENNA

C O L L I M AT E D B E A M S :

Coaxial FeedsSub Reflectors FSS ( Frequency Selective Surfaces )

D I S P L A C E D B E A M S :

Feed Array on the Reflector Focal Plane

Coaxial Feed Double Band and Double Polarisation ( Cassini Mission)

COLLIMATED BEAMS – COAXIAL FEED

COLLIMATED BEAMS – BEAM FORMING

Off-Axis Reflector Antenna

On-Axis Reflector Antenna

Multi Displaced Beams

Snell Law

Fermat Principle



Snell Law

Θ2

E2, H2

Θ1

E1, H1

nΘi

Θr

Fermat Principle ( Conservation of Energy)


Example of Multi-Feed System

BEAM FORMING

Planck Array of Feeds on the Focal Plane

Effects of the Astigmatism of the Displaced Beams: Example by Grasp

Shaping of the surfaces of the antenna reflectors in order to reduce the astigmatism effects in the focal plane zones relevant to each beam.

By overlapping to the nominal conic surfaces with polynomials of different types and degrees.

Multi Displaced Beams : Design Method

SW Tools : ( Among several on the market)

Multi-reflector Antennas : Program GRASP

Waveguide Components Analysis :CST Microwave StudioHFSSFEKO

antenna systems: mono & multi beams beam forming...

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