PRINTED ACTIVE RADIATORS
(from the active antenna concept till the usual technology)
Daniel Segovia Vargas
Vicente González Posadas
Carlos Martín Pascual
1
Active Antenna Concept
2
Radio channels (I)
R
d
Tx
Gr(σ)
Gt
CIRCUITRY
Lt
Lr
Noise
Friis Equation
PR  PT  Gt  eˆT  t , t   eˆR  r , r 
Mispointing
S/N?
Frequency
Transmission line losses+…
EIRP
Pr
PR
PT
Pt
Rx
CIRCUITRY
2
1
2


 Gr
2
4d 4
Distance
Gt, Gr are GAIN (include mismatch, Xpol, antenna losses)
3
Radio channels (II)
In Friis Equation:


If d is link range
PR is the minimum detectable signal
In a link budget:

S/N> threshold allowing information extraction

What about noise?



Incoherent
Incorrelalated
Random Polarization
Power sum: N
  Ni
i
P
C
Rx
Na
NA
Nb
NR
S
C
C
 
N N N A  NR
4
Radio channels (III)
GT  2
T 
4
Noise
Source
ΩR
ΩT
GR  2
R 
4
B
Brigthness
Friis
PR 
EIRP
PT GT
1 T
 T  R







P





B

 B  T   R
R
R
T
R
2
2
2
2
2
4  d
d 4
d 
d
5
Radio channels (IV)
a) For a widespread source
Directivity
Spectral density
of brigthness
dB f  ,  
dPR   R  B ,    D ,    dT ; B f  ,   
PR   R  
f  f
f
 B f  ,   D ,   d  df  
4
f  f
f
df
Pf  df  
Spectral density of power
f  f
f
 R  S f  df
Spectral density of flux
b) For a “point” source: Ωs=(ΩT)<< θ3dB (rec. ant.): Sf
Bfs Ωs
6

Blackbody radiation (Planck)




2hf 3 
1

Bf  2 

c
 hf  
exp

 1 

kT

 

(f ↓) Rayleigh-Jeans Law
x2
exp  x   1  x   ...  1  x
x 1
2
hf
2kT
For
 1  B f  2
kT

For f  300 GHz Bf(Rayleigh-Jeans)<1.03 Bf(Planck)
7
AntennaTemperature
For Δf
Bf almost constant
1
2k  f
PN   R 
2
2
Random polarization
 T  ,   D ,   d 
B
4
 T  ,  D ,  d

 k  f  2R   .... k  f  4
 4
B
 D ,   d
 k  TA  f
4
Antenna temperature
For a “non black” (i.e: grey) body: Bf =Bf(bb) • ε(θ,φ,f,surface)
Brigthness temperature T = ε •T
emissivity
8
G/T
C  EIRP  GR 
C
C
G
G




 N A  k  TA  f  
N N A  NR 
TA  TR T

 N R  k  TR  f 
• Characteristic of the whole receiving chain
(constant value along chain)
9
Hertz channels: absorption
Attenuation:
A, Tm
RX
NA
Nm+N’s
If the absorbing medium occupies the whole
main lobe and Ts is constant:
N s  k  Ts  f



1


N m  k  Tm  f  1  
 A 
N S' 
Ns
A
Sky temperature, Ts(θ,Φ)
TA'' 

Common absorbing media:
-Atmosphere: T0, A0
- Radomes: Tr, Ar
- Dielectric masts: Td, Ad
….….



TA
1 
1 
1 
 T0  1    Tr  1    Tr  1  
A0  Ar  Ad
 Ar 
 Ar 
 A0 


TA
1 
1
1 

 T0  1    T0   2  
A0  Ar  Ad
Ar Ad 
 A0 


 1 T 
 N A  k  f   Tm  1    s   k  f  T ' A
 A A 

10
Atmospheric absorption
11
Antenna structure trade-off in 70´s
Performance Arrays
Good
Bad
Focusing
systems
e.m. pointing control
N degrees of freedom
Surface structure
Compact
RECONFIGURABILITY
Low losses
Low noise T
Grating lobes
Cost
Losses
Mechanical pointing
A few degree of
freedom
Volume, weigth
Optical aberrations
G/T
12
Active antennas (I)
IDEAL
L
(all ohmic losses including cables, lines,etc)
REAL
CIRCUITRY
RX (Fn)
RX (Fn)
G, TA
G
G

T TA  T0  Fn  1
X
G’, T’A
D
G, TA
G
G' L

T 1 T ' T  L  1  T  F  1
A
0
0
n
L
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?
13
Active antennas (II)
SOLUTION TO 1
Put an LNA as near as possible
to the antenna

RX (Fn)
G1, Fn1
SOLUTION TO 2
ACTIVE (Rx) ANTENNA
…. Gi, Fni
….
a
L
b
G1, Fn1
RX (Fn)
c
G’, T’A
G, TA

G
G'

T T ' T  F  1  L  1  T0
A
0
n1
G1
The L contribution to noise is
divided by GA

a, b, c, …are the places(by
priority order) where to put
LNA´S
14
Classical array concepts
Scanning Array
Multibeam Array
15
Active array concept (I)
Other way of thinking:
DISTRIBUTED CONTROL OF POWER
(several receivers).
CAN BE EXTENDED TO TX
(several transmitters)
16
Active array concept (I)
T/R
module
17
T/R modules
MMICs in active antennas
-High reliability
-Compactness
-High cost
-More losses than
conventional devices,
especially in switches and
phase-shifters
A monolitic T/R module is adequate only for very big active systems
For more reduced sytems, the preferred choice is a hybrid assembly of chips
18
Active radiator
Block diagram of a conventional antenna
RF
Active
Device
Power
radiated
Transmission
Line
ANTENNA
Block diagram of an active antenna
RF
Active Antenna
Power
radiated
Device
NO (50Ω) interface!!!
19
Active radiators

Amplifying radiators



Self oscillating radiators



New design concepts
(Antenna-amplifier interface
not necessary)
Simplicity of the BFN (good)
All the radiators must work with phase-looking (difficult).
The IF I/O active radiators



Rx
Tx
Mixer active device
External LO
The fully active radiator

Self diplexing antenna (!)
+
..................
HARD
20
Active system vs. Array of active elements
Array of active elements
Active system



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
21
Alternatives for active antenna
systems (I)
Fully active
antenna (RX)
Partially active
antenna (TX)
22
Alternatives for active antenna
systems (II)
Semiactive antennas
…..
BFN1
Matrix
…..
BFN2
Matrix
…..
N radiators
23
Beam forming matrices
24
Classification of active antennas
ACTIVE ANTENNAS
ACTIVE RADIATORS
Partially
active
Transmitters
OL
Receivers
AMP
Totally
active
External
Diplexer
ACTIVE ARRAYS
Semiactive
Arrays
(mainly TX)
Quasiconventional
arrays
(T/R modules)
Self
diplexed
Circuit
Interface
* RF
* IF (up and /or down converters)
* optical
25
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
26
Adaptive antenna concept (I)
27
Adaptive antenna concept (II)
Demod.
Reference
signal
ADAPTIVE ARRAYS ARE ACTIVE ARRAYS
28
BFN for active antenna
Tech
Freq
IF
RF
orthog. B
RF non
orthog. B
Optics
Analog
Digital
Notes
*
*
High speed
Combiners
Blass
matrices
*
Usual frequency for phase shifting
Low
volume
29
Today trade-off
Reflectors
Arrays
Active arrays
Adaptive arrays
NO
YES
YES
YES
NO
YES
YES
YES
Losses
Not applicable
--
Isolation
?
--
Weight
Volume
Planar structure
Cost
Compactness
Bandwidth
Reconfigurability
Reconf. in real
time
--
--
--
Complexity
G/T
--
30
Printed active antennas
31
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 control
the impedance magnitude?
Which parameter does control
the imaginary part slope?
32
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
33
Patch antennas
PATCH GEOMETRY
RECTANGULAR PATCH
h
b
a
ELIPTICAL
TRIANGLE
RING
and others ....(pentagone,..)
SQUARE
RECTANGULAR
LINEAR
CIRCULAR
34
Disadv.
Adv.
Advantages and drawbacks of printed
antennas vs non printed
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
35
The basic and useful geometries are:
Rectangular
Ring
Circular
Shortcircuited Ring
36
Patches behaviour
Patches are the dual elements (Babinet sense) of open waveguides:
Modes TMmnp=0
Radial pseudo period
Azimuth period repetition
The fundamental mode: TM11 (TM10 in rectangular patch)
Dipolar mode
37
Field distribution of TMmn modes
M=0
M=1
M=2
M=3
N=1
N=2
38
11Mode (Circular patch)
Field Ez
Current Lines
39
11Mode (Circular patch)
Field HΦ
Field Hr
40
11Mode: Impedance (Circular patch)
41
11Mode: Impedance (real part)
42
11Mode: Impedance of the ring patch
(real part)
43
Summary of circular geometries
Electrical
size
λ
f()
f()
f()
f()
λ/2
The most versatile radiator?
Yes, at least for arrays
44
Patch impedance
Imaginary part slope depends on
Q or bandwidth, which is (mainly)
function of thickness
Z magnitude depends on radial
position of the feeding
45
Active and/or integrated technologies
Patches are very well suited:
•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..)
46
Some examples
47