by sayan roy major advisor: dr. benjamin d. braaten dept...

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

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

𝒘𝒘𝒏𝒏 = 𝒂𝒂𝒏𝒏 𝒆𝒆𝒋𝒋𝜹𝜹𝒏𝒏

𝑨𝑨𝑨𝑨 = �𝒘𝒘𝒏𝒏𝒆𝒆𝒋𝒋𝝍𝝍𝒏𝒏𝑵𝑵

𝒏𝒏=𝟏𝟏

Array Factor (AF)

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.)

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

𝑨𝑨𝑨𝑨 = �𝒘𝒘𝒏𝒏

𝑵𝑵

𝒏𝒏=𝟏𝟏

𝒆𝒆𝒋𝒋𝒋𝒋[𝒙𝒙𝒏𝒏(𝒖𝒖−𝒖𝒖𝒔𝒔)+𝒚𝒚𝒏𝒏(𝒗𝒗−𝒗𝒗𝒔𝒔)+𝒛𝒛𝒏𝒏 𝐜𝐜𝐜𝐜𝐜𝐜𝜽𝜽]

Phase Compensation Calculation

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.)

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

0.43λ

0.35λ

non-uniform

Gs (θ,Φ) = Gc (θ,Φ) - Gr (θ,Φ)

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

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

0.43λ

0.35λ

non-uniform

Gs (θ,Φ) = Gc (θ,Φ) - Gr (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-adapting antenna that can autonomously preserve its radiation field during conformal application

Questions ?

Thank You