PRINTED ACTIVE RADIATORS (from the active antenna concept till the usual technology)
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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)
4
2 TT
G
Noise Source B
4
2 RR
GΩT
ΩR
Brigthness
RTRT
RT
TRTT
RR Bd
Bd
PG
dP
dEIRP
P
22222
144
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
4
,,
,,;,,
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
21
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
21
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
10
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