Reconfigurable Wave Velocity TransmissionLines for Phased Arrays

Advisors: Chi-Chih Chen John L. Volakis

1

By: Nicholas Host

NASA Mentor: Félix MirandaWork supported by NSTRF, NASA Grant #NNX11AN16H

https://ntrs.nasa.gov/search.jsp?R=20120015258 2018-07-01T21:48:33+00:00Z

2

Current Technology

Phased Array Features:Wideband

Element Design allows for widebandoperation

Beam Scanning AbilityElement phase control allows for beamscanning

Phased Array Challenges:Complex

Backend used to achieve beam steering isvery complex

HeavyThe backend adds significant weight

CostlyComponents are very expensive

Addressed byour approach

3

Novel Aspects

Design Goals:Reduce ComplexityReduce Weight

Large contributions for both come from thebackend

Reduce Cost

Methodology:Replace backend with simpler feeding mechanism

Replace withsimplermechanism

4

Approach

Replace Backend With SimplerMechanism

Get rid of all splitters, phase shifters, and ampsUse Series Fed Array:

Array fed at one point (side)Magnitude at each element controlled by variedmismatch at element terminalsBeam Steering will be accomplished by acontrollable propagation constant betweenelements

A motor can bring two fixed sheets closer tochange the effective dielectric constant

Varied

Motor to movesheets closer or

farther apart

Field mostly inair, so low eff

Field mostly indielectric, so high eff

By changing (through change of keff) scanning is accomplished:

Reconfigurable transmission line

5

Achieving Scanning

Move platescloser

Scanning is achieved with one mechanical motion and no phase shifters

k eff /

k 0• Needed Transmission Line Agility

Assume each transmission line is the same Scan Angle

d )

d >< ~ Zg < ~ cU Z, Z2 ryo, k'ff Z3 rlo, k eff

••• JZn • -t • 2¢

• ¢

• • • 3¢ 4¢

¢ = ted, keff )

~----=ec=-~£t J For d = 0.4;1 and 11>_ uu~ keff -+ e = 0°

-=5 41--------------f!'..

2

O~I ----~--------~--------~--------~

0.2 0.3 0.4 0.5 Element Spacing, d (*A)

ko

For e = -60 to 60 at d = 0.25;1 -+

Need k

3.1 < ~~f < 4.9

•

• n¢

6

7

Process to Scan

Theoretical 10Element array with

element spacing

As the parallel plates close (left) (right top)

For givenScan angle (right top)Pattern (right bottom)

k eff /

k 0

k eff /

k 0

9

Array as a Circuit Network

Equal Power Distribution Power at the

element

Uniform patternMatching at Feed

minimized at Feed

Feed ( )

10

General Impedance Distribution Elements

So:

knowing:

Equal Power Distribution Circuit Matching

To be matched:Valid for all

Or:

11

Analytical Formulation of

Equal Power Distribution Condition:

In This Case:

So:

1

For Equal PowerDistribution

Element Element

Use same antenna element

Derivation Graphical Representation

Not dependent on

Impe

danc

e of

Lin

e (

)

k eff /

k 0k ef

f / k 0

• Transmission Line Attributes • 4

~} 3

2

1

O~I --~~------~--------~--------~

0.2 0.3 0.4 0.5 Element Spacing, d (*A)

k ff Range - E =25 e r

5c~------.-------~------~------~

4

X: 0.001524 Y: 4.078

AirGan~~

3 f-.U-----------+-----------'-f

2

10

-------+.-----------1--- Chaos e -.. -.--... --.-.. ----J. '"'" i I

0.001524 < 9 < 0.042

0.1 0.2 0.3 0.4 Air Gap, g (mm)

A d=-

2

k ---+ Can scan to all angles 2 < eff < 4

- ko -

Impedance of Line 140~c------~----~~----~------~

120 t-------------------L----------J--- ---1---------c I!! 1 00 ------------------r-------- -r---------+---------

. I I 80 f---------------------i ------------r--------- ! ---------

x: 0.042 : 1 y. 5233 : : 60 r-------; ,. · . j-----------r------------L----------

4°1f--1----+-1 ZO_de~~:nose 32[1 . 20·-----------------t------------c------------'----------l x: 0.001524 I I I o Y: 19.23 o J.1 0.2 0.3 0.4

Air Gap, g (mm) 12

13

Simulation of Connected Array

Separate plates tofacilitate scanning

Gap

3.75

Z=22

Z0

.375

.05

Gap.05

1.2

*All labels in mm

@ 40GHz = 7.5mm

Z=42

Thickness=0.05

Rea

lized

Gai

n (d

B)

Rea

lized

Gai

n (d

B)

14

Traditional Array vs. Connected ArrayR

ealiz

ed G

ain

(dB

)

Rea

lized

Gai

n (d

B)

-

3 9

15

22 Element Prototype Design

Rea

lized

Gai

n (d

B)

RT6002R03010

60mil

60mil

10mil

g

Practical Transmission Line DesignCircuit printed on two 60mil thick RT6002 boards

o RO3010 becomes ripply when unsupportedRO3010 material bonded to inside of one of boards

g=0.73mil g=9mil

16

Assembly of Prototype

Pinch togethertwo boards with

metal frames

Fit top dielectricon with shims as

spacers

Alignment PinsTightening Bolts

CompressingFrame

Top Dielectric

Bottom Dielectric

Spacing Shims

17

Results

RT6002R03010

120mil

120mil

10mil

g Rea

lized

Gai

n (d

B)

Gai

n (d

B)

Scanning ObservedAchieving gap impreciseo Patterns shiftedo Gain Lowered

Ways to achieve gap being devised

18

Future Work

2-D ScanningOne feedIndependent control of each scanning axis

Hard with current transmission line

Transmission Line DesignIndependent control of

Wave VelocityImpedance