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
Array Factor (AF)
 The array factor due to isotropic point sources is the
weighted sum of the signals received by the elements.
𝑵
 Mathematically,
𝒘𝒏 𝒆𝒋𝝍𝒏
𝑨𝑭 =
𝒏=𝟏
where N = number of elements
𝒘𝒏 = 𝒂𝒏 𝒆𝒋𝜹𝒏 is the complex weight for element n
k=2π/λ is the wave number
(xn, yn, zn) 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 𝑬𝒔
then the total response of the array 𝑬total can be written as,
𝑬total = 𝑬𝒔 𝑨𝑭
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,
so 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 AntennaChallenges 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 𝚫𝜱𝒘
𝒏 to each element where
𝜱𝒘
𝒏 = +𝒌𝑳|𝒏|𝐬𝐢𝐧𝜽𝒃
 For cylindrical surface, this correction can be achieved by
introducing phase 𝚫𝜱𝒄𝒏 to each element where
𝜱𝒄𝒏 = +𝒌𝒓 𝒔𝒊𝒏 𝜱𝒏 − 𝒔𝒊𝒏 𝜱𝒏−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(εr=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 (εr=2.94)
 Controlled by DAC Circuit through LabVIEW GUI
DAC Circuit
 12 bit, octal, 64 pin, low power DAC
 Output ranges from 0V 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
Phase Compensation Calculation
 The expression for Array Factor can be redefined in Spherical
coordinate as:
𝑵
𝒘𝒏 𝒆𝒋𝒌[𝒙𝒏 𝒖−𝒖𝒔 +𝒚𝒏 𝒗−𝒗𝒔 +𝒛𝒏 𝐜𝐨𝐬 𝜽]
𝑨𝑭 =
𝒏=𝟏
where
and
𝒖 = 𝐬𝐢𝐧 𝜽 𝐜𝐨𝐬 𝜱
𝒖𝒔 = 𝐬𝐢𝐧 𝜽𝒔 𝐜𝐨𝐬 𝜱𝒔
𝒗𝒔 = 𝐬𝐢𝐧 𝜽𝒔 𝐬𝐢𝐧 𝜱𝒔
𝒗 = 𝐬𝐢𝐧 𝜽 𝐬𝐢𝐧 𝜱
θs is the elevation steering angle
Φs is the elevation steering angle
A is the amplitude to each element
Element factor 𝒆 𝜽 = 𝑨 𝐜𝐨𝐬 𝜽
𝒘𝒏 = 𝒆 𝜽 𝒆𝒋𝜶
Then the compensated Array Factor (𝑨𝑭𝒄 ) will be
𝑨𝑭𝒄 = 𝑨𝑭𝒆𝒋𝜱𝒏
Return Loss Measurement
Properties on a flat surface (𝜽𝒃 =0°)
Properties on a wedge (𝜽𝒃 =30°)
Properties on a wedge (𝜽𝒃 =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
Gr(θ,Φ) and the compensated gain after the correction is
Gc(θ,Φ), then for ideal condition
Gr (θ,Φ) = Gc (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 (Gs)
has been measured for all conformal cases and compared with
analytical result.
Gain Calculation (cont.)
Gs (θ,Φ) = Gc (θ,Φ) - Gr (θ,Φ)
Surface
Gs, analy.
Gs, meas.
Projected
Spacing
(𝜽𝒃 =30°)
-0.6 dBi
-1.0 dBi
0.43λ
(𝜽𝒃 =45°)
-1.3 dBi
-1.8 dBi
0.35λ
Cylinder
-0.8 dBi
-1.6 dBi
nonuniform
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 resistor 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 (𝜽𝒃 =30°)
Properties on a flat surface (𝜽𝒃 =45°)
Properties on a cylinder (r=10cm)
Gain Calculation
Gs (θ,Φ) = Gc (θ,Φ) - Gr (θ,Φ)
Surface
Gs, analy.
(𝜽𝒃 =30°)
-0.6 dBi
(𝜽𝒃 =45°)
-1.3 dBi
Cylinder
-0.8 dBi
Gs, meas.
Gs, meas.
(Test Platform)
(SELFLEX)
-1.0 dBi
-0.9 dBi
0.43λ
-1.8 dBi
-1.4 dBi
0.35λ
-1.6 dBi
-1.2 dBi
nonuniform
Projected
Spacing
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