By Sayan Roy Major Advisor: Dr. Benjamin D. Braaten Dept. of
ECE, NDSU, Fargo, ND, USA Slide 2 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 Slide 3 Introduction to Array Antenna Conformal Antenna
Phased Array Antenna Slide 4 Antenna For any communication device,
an antenna system serves the purpose for external communication
wirelessly. Slide 5 Todays Antenna Systems Slide 6 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 Slide 7 Beam Steering In any Antenna system,
the transmitting or receiving signal has two attributes: Amplitude
(A) and Phase (). Beam Steering can be achieved in an array antenna
by changing the progressive phase differences between antenna
elements. Beam steered 45 from Broadside direction Slide 8 Beam
Steering of a Patch Array Antenna Slide 9 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. Slide 10
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.
Slide 11 Defining the Problem Slide 12 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. Slide 13 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. Slide 14 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. Slide 15 Defining
the Problem: Can we recover the radiation pattern of a conformal
array ? Slide 16 Phased Array Antenna Defining Co-ordinate Theory
of Array Factor Concept of Phase Scanning Phase Compensation
Technique of a Conformal Array Antenna Slide 17 Defining
Co-ordinate ( , ) is the direction in space Slide 18 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 Array Factor (AF) is the complex weight for element n
k=2/ is the wave number (x n, y n, z n ) is the location of element
n Slide 19 Array Factor (AF) (cont.) Slide 20 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 Slide 21 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 Slide 22 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 Slide 23
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. Slide 24
Realization of Conformal Phased Array Antenna Equation for Phase
Correction Proposed System Block Slide 25 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. Slide 26 A linear conformal
array antenna placed on a Wedge shaped surface Slide 27 A linear
conformal array antenna placed on a Cylindrical surface Slide 28
Equation for Phase Correction Slide 29 Designing of Phased Array
Antenna Test Platform Slide 30 Phased Array Antenna Test Platform
Slide 31 4-element antenna array with connectors g=2.0 mm, h=35.6
mm, t=1.3 mm w=43.6 mm. Rogers 6002( r =2.94) 60 mil substrate.
Resonant Frequency: 2.46 GHz Slide 32 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 Slide 33 Control Voltage vs.
Normalized Phase of the Phase Shifter Slide 34 Four port Receiver
RF Circuit Board (cont.) Multiple Input Single Output System
RT/duroid 6002 60 mil ( r =2.94) Controlled by DAC Circuit through
LabVIEW GUI Slide 35 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 Slide 36 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 Slide 37
Connection Setup of the system Slide 38 Scanning Properties of
Phased Array Antenna Test Platform Slide 39 Phase Compensation
Calculation Slide 40 Return Loss Measurement Slide 41 Slide 42
Slide 43 Slide 44 Properties on a cylinder (r=10cm) Slide 45 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 (,) and the compensated gain after
the correction is G c (,), then for ideal condition G r (,) = G c
(,) However, the projected spacing between the elements deviates
from /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. Slide 46 Gain Calculation (cont.) Surface Cylinder Gs,
analy. -0.6 dBi-1.3 dBi-0.8 dBi Gs, meas. -1.0 dBi -1.8 dBi -1.6
dBi Projected Spacing 0.43 0.35 non- uniform G s (,) = G c (,) - G
r (,) Slide 47 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 Slide 48 Four Element SELFLEX Array Design
Slide 49 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. Slide
50 Proposed System Block Diagram Slide 51 Corporate Feed Network
Feed Network Why? Matching. Technique Corporate Feed Structure by
using quarter-wave transformer Example Bifurcated T waveguide or
coaxial T-junctions. Slide 52 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
Slide 53 Sensor Circuit Setup Slide 54 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. Slide 55
Scanning Properties of SELFLEX Array Slide 56 Return Loss
Measurement Slide 57 Slide 58 Slide 59 Properties on a cylinder
(r=10cm) Slide 60 Gain Calculation Surface Cylinder Gs, analy. -0.6
dBi-1.3 dBi-0.8 dBi Gs, meas. (Test Platform) -1.0 dBi -1.8 dBi
-1.6 dBi Gs, meas. (SELFLEX) Projected Spacing 0.43 0.35 non-
uniform G s (,) = G c (,) - G r (,) -0.9 dBi -1.4 dBi -1.2 dBi
Slide 61 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 Slide 62 Questions ? Thank You
