# Major Advisor: Dr. Benjamin D. Braaten

Electronics - Devices

Nov 15, 2013 (4 years and 5 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

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
°

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

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:

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

Sharing Equal Power

Unequal Inter
-
element Phase Shift,

s
o complex control circuitry.

Summed up Attenuation

Parallel Phasers

Phase Shifters act independently

Simpler Control Circuit

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
-
pattern gets distorted.

Solution

By applying the concept of phase steering, correct

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

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

-
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

𝐜𝐬
𝜽
]

Phase Compensation Calculation

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

where

=

𝐬𝐢
𝜽
𝐜𝐬
𝜱


=

𝐬𝐢
𝜽

𝐜𝐬
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
𝐜𝐬
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

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

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
-
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
-