Major Advisor: Dr. Benjamin D. Braaten

fatfallenleafElectronics - Devices

Nov 15, 2013 (3 years and 7 months ago)

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By

Sayan Roy

Major Advisor: Dr. Benjamin D. Braaten
Dept. of ECE, NDSU, Fargo, ND, USA

Contents


Introduction



Defining the Problem



Phased
Array
Antenna



Realization of Conformal Phased Array Antenna



Designing of Phased Array Antenna Test
Platform



Scanning Properties of Phased Array Antenna Test Platform



Four Element SELFLEX Array
Design



Scanning Properties of SELFLEX
Array



Conclusion


Introduction
to






Array
Antenna




Conformal Antenna




Phased
Array Antenna


Antenna


For any communication device, an antenna system
serves the purpose for external communication
wirelessly.


Today’s Antenna Systems

Array Antenna


Array means a collection of similar entities.


Array Antenna


Set of individual antenna elements connected together
to behave as a single unit


Advantages


Higher Gain


Beam Steering Capability


Reliable


Higher SNR

Beam

Steering


In any Antenna system, the
transmitting or receiving signal
has two attributes:



Amplitude (A) and



Phase (
φ
).




Beam Steering can be achieved in
an array antenna by changing the
progressive phase differences
between antenna elements.

Beam steered 45
°

from Broadside direction

Beam Steering of a Patch Array Antenna

Conformality



Conformality can be described as a map
projection which has the property of
preserving relative angles over small
scales.




In Mathematics, a conformal map is a
function which preserves angles.


Conformal Antennas


Often mechanical design of a communication system requires
that the associated antenna should be mounted on a curved
surface.



Applications


Aerospace Designs


Wearable Antenna


Spacesuit


Mobile Devices





For last couple of years, designers have been showing interest in
simulating conformal antenna performance to optimize antenna
parameters in presence of conformal surface.

Defining the
Problem


Relation between Conformality and
Beam Steering


A conformal surface changes
its curvature with time and
may be planar or non
-
planar.



When an antenna system lies
on a planar conformal
surface, the field pattern of
the antenna behaves
normally.

Relation between Conformality and
Beam Steering
(cont.)


However, when the surface of the antenna becomes
non
-
planar, the performance of the antenna starts to
degrade.



Relation between Conformality and
Beam Steering (cont.)


Beam Steering concept can be implemented to recover
the field pattern of the antenna system by
proper
correction in relative phases between
elements of the
array.


This type of antenna is known as
Phased Array
Antenna
.









Defining the Problem:

Can we recover the radiation
pattern of a conformal array ?


Phased Array Antenna



Defining Co
-
ordinate



Theory
of Array Factor




Concept of Phase Scanning







Phase Compensation Technique of a Conformal

Array Antenna

Defining Co
-
ordinate


(
θ
,
φ

is the direction in space


The array factor due to isotropic point sources is the
weighted sum of the signals received by the elements.



Mathematically,



where
N

=
number of elements






𝒏
=

𝒏

𝒆

𝜹
𝒏

𝑨
=



𝒏
𝒆

𝝍
𝒏
𝑵
𝒏
=
𝟏

Array Factor (AF)

is the complex weight for element n

k=2
π
/
λ

is the wave number

(
x
n
,
y
n
,
z
n
)
is the location of element n

Array Factor (AF) (cont.)


Unique for each array



Depends on


number of elements,


relative magnitude and phase
of current on
each
element,


relative inter
-
element
spacing and


geometrical orientation of the elements.



Use


Pattern Multiplication Rule


If the response of a single element of a linear array is






then the total response of the array


total

can be written as,






total

=


𝑨



Concept of Phase Scanning


Phase Scanning Circuitry



Why?


Electronic Beam Steering



Technique


Time Delay Scanning


Frequency Scanning


Phase Scanning



Why Phase Scanning?


Ease of Implementation


Cheaper Digital Control Circuitry


Fast Response Time


High Sensitivity

Concept of Phase Scanning (cont.)


How?


By controlling the progressive phase difference between each
individual elements of an array.



Implementation


Diode Phase Shifter


Ferrite Phase Shifter



Industrial Solution


Digitally controlled fixed step phase shifter


Analog controlled continuous phase shifter

Phase Scanning Technique



Implementation


Series Phasers


Advantage:


Sharing Equal Power


Disadvantages:


Unequal Inter
-
element Phase Shift,

s
o complex control circuitry.


Summed up Attenuation



Parallel Phasers


Advantages:


Phase Shifters act independently


Simpler Control Circuit


Disadvantage:


Each phase shifter does not share equal power



Example


Switched
Line Phase Shifter


Ferrite Phase Shifter


Conformal Antenna
-


Challenges and Solution


Challenges


For a conformal antenna, the surface of the substrate
changes with time during operation.


When the surface remains planar, the antenna behaves
normally.


However for non
-
planar orientation, the radiation
pattern gets distorted.



Solution


By applying the concept of phase steering, correct
radiation pattern can be recovered.


Realization of Conformal
Phased Array Antenna





Equation
for
Phase
Correction


Proposed System Block

Determining possible conformal
surfaces in terms of application

Conformal Antennas
are used basically as
wearable antennas
which may be shaped as
wedge or cylindrical in
non
-
planar orientation.


A linear conformal array antenna
placed on a Wedge shaped surface

A linear conformal array antenna
placed on a
Cylindrical surface

Equation for Phase Correction


An
x
-

and
z
-

translation is incurred from the original flat
position for each array element.


Fields arriving at the reference plane associated with
A
±
2
lagged
from fields arriving at the reference plane associated
with
A
±
1.


So, the phases of current at
A
±
2

should be positive enough to
compensate the phase delay by that free space propagation to
maintain equivalent planar orientation.


As the phase has being corrected towards the source, the phase
correction will be additive in nature.


For wedge shaped surface, this correction can be achieved by
introducing phase
𝚫
𝜱
𝒏


to each element where


𝜱
𝒏

=

+
𝑳
|
𝒏
|
𝐬𝐢
𝜽



For
cylindrical surface
, this correction can be achieved by
introducing phase
𝚫
𝜱
𝒏


to each element where

𝜱
𝒏

=
+


 𝒏
𝜱
𝒏


 𝒏
𝜱
𝒏

𝟏



Designing of Phased Array
Antenna Test Platform

Phased Array Antenna Test
Platform

4
-
element antenna array with
connectors



g=2.0 mm, h=35.6 mm, t=1.3 mm

w=43.6 mm.


Rogers 6002(
ε
r
=2.94) 60 mil substrate.


Resonant Frequency: 2.46 GHz

Four port Receiver RF Circuit Board


Consists of


Voltage controlled Analog Phase Shifters


Voltage Controlled Attenuators


Amplifier and


Power Combiner



Industry Available



Each component was tested and verified
prior to application with single prototype

Control Voltage vs. Normalized
Phase of the Phase Shifter

Four port Receiver RF Circuit
Board
(cont.)


Multiple Input Single Output System


RT/duroid 6002 60 mil (
ε
r
=2.94)


Controlled by DAC Circuit through LabVIEW GUI

DAC Circuit


12 bit, octal, 64 pin, low power DAC


Output ranges from
0
V to 33 V for unipolar operation


Allows programmable gain of x4 or x6 w.r.t the applied
reference voltage


Features Serial Peripheral Interface that can be operated at
50 MHz and is logic compatible with 1.8V, 3V or 5V


The register consists of a R/W bit, 5 address bits and 12
data bits


Operated in both synchronous and asynchronous mode


TQFP(Thin Quad Flat Package)
-
64 (10 x 10mm) used

LabVIEW GUI


National Instrument LabVIEW USB 6008 peripheral
device was used to communicate with the GUI


4 phase shifters and 4 attenuators can be controlled by
8 separate output channels from
DAC with precision
up to 300 mV


Connection Setup of the system

Scanning Properties of
Phased
Array Antenna Test Platform


𝑨
=



𝒏
𝑵
𝒏
=
𝟏
𝒆

[

𝒏






+

𝒏






+

𝒏

𝐜𝐬
𝜽
]

Phase Compensation Calculation


The expression for Array Factor can be redefined in Spherical
coordinate as:





where

















=

𝐬𝐢
𝜽
𝐜𝐬
𝜱





=

𝐬𝐢
𝜽

𝐜𝐬
𝜱






=

𝐬𝐢
𝜽

𝐬𝐢
𝜱





=

𝐬𝐢
𝜽
𝐬𝐢
𝜱



θ
s

is
the elevation steering angle



Φ
s

is
the elevation steering
angle



A is the amplitude to each element



Element factor
𝒆
𝜽
=
𝑨
𝐜𝐬
𝜽


and


𝒏
=
𝒆

𝜽

𝒆
𝜶


Then the compensated Array Factor (
𝑨

) will be



𝑨

=
𝑨
𝒆

𝜱
𝒏


Return Loss Measurement

Properties on a flat surface (
𝜽

=0
°
)

Properties on a
wedge
(
𝜽

=
3
0
°
)

Properties on a wedge (
𝜽

=
45
°
)

Properties on
a cylinder (r=10cm)

Gain Calculation


The primary objective through this correction is to recover the
gain.


If the reference gain of the system for a particular orientation is
G
r
(
θ,Φ
)
and the compensated gain after the correction is
G
c
(
θ,Φ
)
,

then for ideal condition




G
r
(
θ,Φ
) =
G
c

(
θ,Φ
)



However, the projected spacing between the elements deviates
from
λ
/2 value for any non
-
planar orientation.


Due to this geometrical limitation, compensated gain can never
be achieved to be equal to the reference gain. This gain shift (
G
s
)
has been measured for all conformal cases and compared with
analytical result.






Gain
Calculation (cont.)

Surface

(
𝜽

=
3
0
°
)

(
𝜽

=
45
°
)

Cylinder

G
s
,
analy
.

-
0.6
dBi

-
1.3
dBi

-
0.8
dBi

G
s
, meas.

-
1.0
dBi


-
1.8
dBi

-
1.6
dBi

Projected
Spacing

0.43
λ


0.35
λ

non
-
uniform

G
s

(
θ,Φ
) =
G
c

(
θ,Φ
)
-

G
r

(
θ,Φ
)

Test Platform Results


Advantages



Practically validates the theory of beam steering


Ability of recovering the radiation pattern has been demonstrated
for a general array


Gain Calculation has been presented showing low loss of gain



Disadvantages



Manual control required for any changes of conformal surface


The array was formed by individual element with separate feeding
points. But an array should be acting as an individual element.


Gain shift

Four Element SELFLEX Array
Design

SELFLEX Array Design


Challenges


Can we design a conformal array on a single substrate
with phase correction capability?


Can we achieve radiation pattern recovery for a
conformal array in an autonomous manner?


Can we reduce the gain shift?



Solution


By designing a SELFLEX (SELF
-
adapting
FLEXible
) array
antenna.



Proposed System Block Diagram

Corporate Feed Network


Feed Network


Why?


Matching.


Technique


Corporate Feed Structure by using quarter
-
wave transformer


Example


Bifurcated T waveguide or



coaxial T
-
junctions
.


SELFLEX Array Design


Features:


Single feed point


Insertion of phase shifters into corporate feed network


Introduce the sensor circuit as the feedback network
with autonomous controller circuitry for radiation
pattern recovery

Sensor Circuit Setup

How it Works


A flexible
r
esistor senses the amount of curvature of
the surface each time and feed that value to the
controller circuit.


The controller circuit consists of an instrumentation
Op
-
Amp AMP04 that offers the phase shifter with
necessary voltage correction for any conformal
orientation.


The phase shifters placed on the corporate feed
network then process the signals from each array
element resulting correction of radiation pattern of
the array autonomously.

Scanning Properties of SELFLEX
Array

Return Loss Measurement

Properties on a flat surface (
𝜽

=
3
0
°
)

Properties on a flat surface (
𝜽

=
45
°
)

Properties on a cylinder (r=10cm)

Gain
Calculation

Surface

(
𝜽

=
3
0
°
)

(
𝜽

=
45
°
)

Cylinder

G
s
,
analy
.

-
0.6
dBi

-
1.3
dBi

-
0.8
dBi

G
s
, meas.

(Test Platform)

-
1.0
dBi


-
1.8
dBi

-
1.6
dBi

G
s
, meas.

(SELFLEX)

Projected
Spacing

0.43
λ


0.35
λ

non
-
uniform

G
s

(
θ,Φ
) =
G
c

(
θ,Φ
)
-

G
r

(
θ,Φ
)

-
0.9
dBi


-
1.4
dBi

-
1.2
dBi

Conclusion


Conformal Phased Array Antenna


Theory of Beam Steering


Implementation of RF block


Designing, printing and testing of a primitive
conformal array that has the ability to compensate
phase on each element with external manual control
by the user


Designing, printing and testing of a 1x4 self
-
adapting
antenna that can autonomously preserve its radiation
field during conformal application

Questions ?

Thank You