DESIGNING OF A SMALL WEARABLE CONFORMAL PHASED ARRAY ANTENNA FOR WIRELESS COMMUNICATIONS

DESIGNING OF A SMALL WEARABLE CONFORMAL PHASED ARRAY ANTENNA FOR WIRELESS COMMUNICATIONSBySayan RoyMajor Advisor: Dr. Benjamin D. Braaten Dept. of ECE, NDSU, Fargo, ND, USAContentsIntroduction

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 toArray Antenna

Conformal Antenna

Phased Array Antenna

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

Todays Antenna Systems

Array AntennaArray means a collection of similar entities.Array Antenna Set of individual antenna elements connected together to behave as a single unitAdvantagesHigher GainBeam Steering CapabilityReliableHigher SNR

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 directionBeam Steering of a Patch Array Antenna

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

ApplicationsAerospace DesignsWearable AntennaSpacesuitMobile 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 FactorConcept of Phase ScanningPhase Compensation Technique of a Conformal Array Antenna

Defining Co-ordinate(,) 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

Array Factor (AF)is the complex weight for element nk=2/ is the wave number(xn, yn, zn) is the location of element nArray Factor (AF) (cont.)

Concept of Phase ScanningPhase Scanning Circuitry

Why?Electronic Beam Steering

TechniqueTime Delay ScanningFrequency ScanningPhase Scanning

Why Phase Scanning?Ease of ImplementationCheaper Digital Control CircuitryFast Response TimeHigh SensitivityConcept of Phase Scanning (cont.)How?By controlling the progressive phase difference between each individual elements of an array.

ImplementationDiode Phase ShifterFerrite Phase Shifter

Industrial SolutionDigitally controlled fixed step phase shifterAnalog controlled continuous phase shifter

Phase Scanning TechniqueImplementationSeries PhasersAdvantage:Sharing Equal PowerDisadvantages:Unequal Inter-element Phase Shift,so complex control circuitry.Summed up Attenuation

Parallel PhasersAdvantages:Phase Shifters act independentlySimpler Control CircuitDisadvantage:Each phase shifter does not share equal power

ExampleSwitched Line Phase ShifterFerrite Phase Shifter

Conformal Antenna-Challenges and SolutionChallengesFor 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.

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

Realization of Conformal Phased Array AntennaEquation 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 CorrectionDesigning 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 mmw=43.6 mm.Rogers 6002(r=2.94) 60 mil substrate.Resonant Frequency: 2.46 GHz

Four port Receiver RF Circuit BoardConsists ofVoltage controlled Analog Phase ShiftersVoltage Controlled AttenuatorsAmplifier andPower 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 SystemRT/duroid 6002 60 mil (r=2.94)Controlled by DAC Circuit through LabVIEW GUI

DAC Circuit12 bit, octal, 64 pin, low power DACOutput ranges from 0V to 33 V for unipolar operationAllows programmable gain of x4 or x6 w.r.t the applied reference voltageFeatures Serial Peripheral Interface that can be operated at 50 MHz and is logic compatible with 1.8V, 3V or 5VThe register consists of a R/W bit, 5 address bits and 12 data bitsOperated in both synchronous and asynchronous modeTQFP(Thin Quad Flat Package)-64 (10 x 10mm) usedLabVIEW GUINational Instrument LabVIEW USB 6008 peripheral device was used to communicate with the GUI4 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 CalculationReturn Loss Measurement

Properties on a cylinder (r=10cm)

Gain CalculationThe primary objective through this correction is to recover the gain.If the reference gain of the system for a particular orientation is Gr(,) and the compensated gain after the correction is Gc(,), then for ideal condition Gr (,) = Gc (,)

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 (Gs) has been measured for all conformal cases and compared with analytical result.

Gain Calculation (cont.)Gs (,) = Gc (,) - Gr (,)Test Platform ResultsAdvantages

Practically validates the theory of beam steeringAbility of recovering the radiation pattern has been demonstrated for a general arrayGain Calculation has been presented showing low loss of gain

Disadvantages

Manual control required for any changes of conformal surfaceThe 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 DesignSELFLEX Array DesignChallengesCan 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?

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

Proposed System Block Diagram

Corporate Feed NetworkFeed NetworkWhy?Matching.TechniqueCorporate Feed Structure by using quarter-wave transformerExampleBifurcated T waveguide or coaxial T-junctions.

SELFLEX Array DesignFeatures:Single feed pointInsertion of phase shifters into corporate feed networkIntroduce the sensor circuit as the feedback network with autonomous controller circuitry for radiation pattern recovery

Sensor Circuit Setup

How it WorksA 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 ArrayReturn Loss Measurement

Properties on a cylinder (r=10cm)

Gain CalculationGs (,) = Gc (,) - Gr (,)-0.9 dBi

-1.4 dBi-1.2 dBiConclusionConformal Phased Array AntennaTheory of Beam SteeringImplementation 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 userDesigning, printing and testing of a 1x4 self-adapting antenna that can autonomously preserve its radiation field during conformal applicationQuestions ?Thank You