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PRINTED ACTIVE RADIATORS (from the active antenna concept till the usual technology)

Daniel Segovia Vargas

Vicente González Posadas

Carlos Martín Pascual

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Active Antenna Concept

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Radio channels (I)

Transmission line losses+…

Noise S/N?

R

Tx CIRCUITRY CIRCUITRY Rx

Pt

LtLr

PTPR

Pr

Gr(σ)Gt

d

Friis Equation

Gt, Gr are GAIN (include mismatch, Xpol, antenna losses)

Frequency

Distance

MispointingEIRP

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Radio channels (II)

In Friis Equation: If d is link range PR is the minimum detectable signal

What about noise? Incoherent Incorrelalated Random Polarization

S/N> threshold allowing information extraction

Power sum: i

iNN

Rx

NR

C

NA

Nb

Na

P

RA NN

C

N

C

N

S

In a link budget:

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Radio channels (III)

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2 TT

G

Noise Source B

4

2 RR

GΩT

ΩR

Brigthness

RTRT

RT

TRTT

RR Bd

Bd

PG

dP

dEIRP

P

22222

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Friis

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a) For a widespread source

Radio channels (IV)

ff

f

ff

f fRf

ff

f fRR

ffTRR

dfSdfPdfdDBP

df

dBBdDBdP

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,,

,,;,,

Spectral density of brigthness

Spectral density of fluxSpectral density of power

Directivity

b) For a “point” source: Ωs=(ΩT)<< θ3dB (rec. ant.): Sf Bfs Ωs

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Blackbody radiation (Planck)

1exp

122

3

kThfc

hfB f

(f ↓) Rayleigh-Jeans Law

2

1

2

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1...2

1exp

kT

BkThf

For

xx

xx

f

x

For f 300 GHz Bf(Rayleigh-Jeans)<1.03 Bf(Planck)

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AntennaTemperature

For a “non black” (i.e: grey) body: Bf =Bf(bb) • ε(θ,φ,f,surface)

Brigthness temperature T = ε •T

Random polarization

fTk

dD

dDT

fkfk

dDTfk

P

A

B

R

BRN

4

4

42

42

,

,,

....

,,2

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For Δf Bf almost constant

emissivity

Antenna temperature

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G/T

T

G

TT

G

fTkN

fTkN

GEIRPC

NN

C

N

C

RARR

AA

R

RA

• Characteristic of the whole receiving chain (constant value along chain)

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Hertz channels: absorption

Sky temperature, Ts(θ,Φ)

RX

Attenuation:A, Tm

Nm+N’sNA

As

mA

mm

sS

ss

TfkA

T

ATfkN

AfTkN

A

NN

fTkN

'1

1

11

'

If the absorbing medium occupies the wholemain lobe and Ts is constant:

Common absorbing media:-Atmosphere: T0, A0

- Radomes: Tr, Ar

- Dielectric masts: Td, Ad

….….

drdr

A

rr

rr

dr

AA

AAT

AT

AAAT

AT

AT

AT

AAAT

T

112

11

11

11

11

00

00

00

0

''

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Atmospheric absorption

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Antenna structure trade-off in 70´s

Performance Arrays Focusing

systems

Good e.m. pointing control

N degrees of freedom

Surface structure

Compact

RECONFIGURABILITY

Low losses

Low noise T

G/T

Bad Grating lobes

Cost

Losses

Mechanical pointing

A few degree of freedom

Volume, weigth

Optical aberrations

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Active antennas (I)

RX (Fn)

G’, T’AG, TA

L

11'1

'

00

nA FTLTTL

LGTG

RX (Fn)

G, TA

REAL

CIRCUITRY

IDEAL

(all ohmic losses including cables, lines,etc)

XD

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nA FTTG

TG

1) What about L if it corresponds to the “connecting” devices(cables,lines,...)?2) What about arrays, where “connecting lines” BFN are intrinsic constraintments of the antenna?

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Active antennas (II)

SOLUTION TO 1 Put an LNA as near as possible

to the antenna

The L contribution to noise is divided by GA

RX (Fn) G1, Fn1 Gi, Fni….

G, TA

L

RX (Fn)

G’, T’A

G1, Fn1

1

010

11'

'

G

TLFTT

GTG

nA

SOLUTION TO 2ACTIVE (Rx) ANTENNA

a, b, c, …are the places(by priority order) where to put LNA´S

….a

b

c

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Classical array concepts

Scanning Array

Multibeam Array

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Active array concept (I)

Other way of thinking: DISTRIBUTED CONTROL OF POWER

(several receivers).

CAN BE EXTENDED TO TX (several transmitters)

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Active array concept (I)

T/Rmodule

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T/R modules

MMICs in active antennas

A monolitic T/R module is adequate only for very big active systemsFor more reduced sytems, the preferred choice is a hybrid assembly of chips

-High reliability-Compactness-High cost-More losses than conventional devices, especially in switches and phase-shifters

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Active radiator

ActiveDevice

TransmissionLine

ANTENNA

RF

Block diagram of a conventional antenna

Power radiated

Block diagram of an active antenna

Device

RF Active Antenna Power radiated

NO (50Ω) interface!!!

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Active radiators

Amplifying radiators Rx Tx

Self oscillating radiators Simplicity of the BFN (good) All the radiators must work with phase-looking (difficult).

The IF I/O active radiators Mixer active device External LO

The fully active radiator Self diplexing antenna (!) HARD + ..................

New design concepts(Antenna-amplifier interface

not necessary)

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Active system vs. Array of active elements

One active module per subarray

Easy characterization (separate measurements of the radiators and active circuits)

Economy of diplexers

One active circuit per radiator

High beam agility Allows a large physical

separation between the antenna and the transceiver

Many diplexers are required, increasing the interest of self-diplexing elements

Active system Array of active elements

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Alternatives for active antenna systems (I)

Fully activeantenna (RX)

Partially activeantenna (TX)

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Alternatives for active antenna systems (II)Semiactive antennas

BFN1

Matrix

BFN2

Matrix

N radiators

…..….. …..

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Beam forming matrices

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Classification of active antennas

ACTIVE ANTENNAS

ACTIVE ARRAYS ACTIVE RADIATORS

Partially active

SemiactiveArrays

(mainly TX)

Quasi-conventional

arrays (T/R modules)

Totally active

Transmitters Receivers Self diplexed

ExternalDiplexer

OL AMP

* RF* IF (up and /or down converters)* optical

CircuitInterface

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General effects of active antennas

At Rx Increase of the system figure of merit G/T

At Tx Less effect of the control circuit losses (if BFN is done at low power

RF or IF level) Increase of EIRP Better efficiency if solid-state devices are used

Lower cost (higher conversion efficiency) Easier thermal control

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Adaptive antenna concept (I)

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Adaptive antenna concept (II)

ADAPTIVE ARRAYS ARE ACTIVE ARRAYS

Referencesignal

Demod.

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BFN for active antenna

Freq

Tech Analog Digital Notes

IF * * High speed

RF

orthog. B

Combiners

RF non

orthog. B

Blass matrices

Optics * Low volume

Usual frequency for phase shifting

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Today trade-off

Reflectors Arrays Active arrays Adaptive arrays

Weight

Volume

Planar structure NO YES YES YES

Cost

Compactness NO YES YES YES

Bandwidth

Losses Not applicable --

Isolation ? --

Reconfigurability

Reconf. in real time

-- -- --

Complexity

G/T --

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Printed active antennas

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Active radiators design

• No antenna circuit interface (virtual, not Z0)• Zant fixed by the amplifier (mixer, oscillator, etc…) design needs(minimum noise, stability, etc…)• The antenna must offer a great impedance margin: resonant antennas

Which parameter does controlthe impedance magnitude?

Which parameter does control the imaginary part slope?

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The core concept of the array design

Good aperture efficiency interelement spacing is about elementary radiator electrical size Interelement spacing is usually fixed by the desired beams. In general: 0.5λ (≈ 0.25λ) ≤ d ≤ λ

Is there a radiator with this degree of freedom?

CIRCULAR PATCHES

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a

hb

SQUARE RECTANGULAR LINEAR CIRCULAR

RECTANGULAR PATCH

ELIPTICAL TRIANGLE RING

and others ....(pentagone,..)

PATCH GEOMETRY

Patch antennas

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PRINTED NOT PRINTED

PLANAR STRUCTURE

LOW WEIGHT

EASY CONSTRUCTION

LOW COST

CONFORMABILITY

LOW LOSSES

EASY TO MODEL

POWER CAPABILITY

HIGH GAIN

GREAT NUMBER OF MODELS

SURFACE WAVES

HIGHER MODES

LOW EFFICIENCY

NARROW BAND

LOW POLARISATION PURITY

HEAVY

MANUFACTURING TOLERANCE NOT CONFORMABILITY

DIFFICULT TO INTEGRATE

Dis

adv.

Ad

v.Advantages and drawbacks of printed

antennas vs non printed

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The basic and useful geometries are:

Rectangular Circular

Ring Shortcircuited Ring

ONLY !!!!

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Patches behaviour

Patches are the dual elements (Babinet sense) of open waveguides:

Modes TMmnp=0

Azimuth period repetition

Radial pseudo period

The fundamental mode: TM11 (TM10 in rectangular patch)

Dipolar mode

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N=1

N=2

M=0 M=1 M=2 M=3

Field distribution of TMmn modes

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Field Ez   

Current Lines   

11Mode (Circular patch)

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Field HΦ Field Hr

11Mode (Circular patch)

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11Mode: Impedance (Circular patch)

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11Mode: Impedance (real part)

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11Mode: Impedance of the ring patch (real part)

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G

10

4

dBS.C: Ring Patch

Circular Patch

Ring Patch

f( )

f( )

f( )

f()f()

f()

f()

Summary of circular geometries

The most versatile radiator? Yes, at least for arrays

Electricalsize

λ/2

λ

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Patch impedance

Imaginary part slope depends onQ or bandwidth, which is (mainly)function of thickness

Z magnitude depends on radialposition of the feeding

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•Easy integration of circuits with antenna in the hidden feeding layer or on the patch surface. Several Technologies (FET,BIPOLAR,MESFET,HEMT...)

•High power is difficult because the heat dissipation (short circuited ring or center short circuited patches)

• Multilayer structures (BFN*, Phasing, Amplifiers, frequency conversion)

*2 BFN’s for layer in arrays (2 polarizations, or 2 beams, or 2 frequencies..)

Patches are very well suited:

Active and/or integrated technologies

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Some examples