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: Beam steered 45° from Broadside direction  Amplitude (A) and

 Phase (φ).

 Beam Steering can be achieved in an array antenna by changing the progressive phase differences between antenna elements. 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.  Mathematically, = 𝑵𝑵 = 𝒋𝒋𝝍𝝍𝒏𝒏 𝑨𝑨𝑨𝑨 � 𝒘𝒘𝒏𝒏𝒆𝒆 where N = number of elements𝒏𝒏 𝟏𝟏 = is the complex weight for element n 𝒋𝒋𝜹𝜹𝒏𝒏 k=2𝒏𝒏 π/λ 𝒏𝒏is the wave number 𝒘𝒘 𝒂𝒂 𝒆𝒆 (xn, yn, zn) is the location of element n Array Factor (AF) (cont.)  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 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

 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 

[ ( )+ ( )+ ] = 𝑵𝑵 = 𝒋𝒋𝒋𝒋 𝒙𝒙𝒏𝒏 𝒖𝒖−𝒖𝒖𝒔𝒔 𝒚𝒚𝒏𝒏 𝒗𝒗−𝒗𝒗𝒔𝒔 𝒛𝒛𝒏𝒏 𝐜𝐜𝐜𝐜𝐜𝐜 𝜽𝜽 𝑨𝑨𝑨𝑨 � 𝒘𝒘𝒏𝒏 𝒆𝒆 𝒏𝒏 𝟏𝟏 Return Loss Measurement

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)

Projected Surface G G s, analy. s, meas. Spacing

-0.6 dBi -1.0 dBi 0.43λ

-1.3 dBi -1.8 dBi 0.35λ

non- Cylinder -0.8 dBi -1.6 dBi uniform 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 cylinder (r=10cm) Gain Calculation

Gs (θ,Φ) = Gc (θ,Φ) - Gr (θ,Φ)

Gs, meas. Gs, meas. Projected Surface G s, analy. Spacing (Test Platform) (SELFLEX)

-0.6 dBi -1.0 dBi -0.9 dBi 0.43λ

-1.3 dBi -1.8 dBi -1.4 dBi 0.35λ

non- Cylinder -0.8 dBi -1.6 dBi -1.2 dBi uniform 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