A Multilayered Broadband Reflect-Array

Manuel Romero

Outline

Introduction and Project Goals

Ideal Reflect-Array Cell

Proposed Cell

Experimental Results

Conclusions

Introduction – Reflect-Arrays

Reflect-arrays alter the scattered EM field to form a radiation maximum in a desired direction

The reflection phase of the individual array elements is modified to form the desired scattered beam pattern

A phase agility of 360 degrees per array element allows for a beam maximum at any angle

Many applications in radar and communication systems.

...Δφ 2Δφ NΔφ

d d

Δφ 2Δφ NΔφ

Introduction – Microstrip Reflect-Arrays

Microstrip reflect-arrays are low cost, low loss and low profile Potential substitutes for parabolic reflector antennas used in terrestrial

and satellite communication systems.

Previous work has focused on the patch antenna as the main array element

Vary patch size, stub length and tilt angle to modify the reflection phase.

The resonant nature results in poor phase agility and bandwidth

Project Goals

To design a reflect-array at a center frequency of 10GHz Non-resonant structure unit cell

Linear reflection phase as function of frequency

Fully printable structure low cost low profile low loss

Frequency

Ref

lect

ion

Ph

ase,

Φ

Typical Phase of Resonator

Non-resonant Phase

Ideal Reflect-Array Cell

Sample phase characteristic of each cell at fo

These samples create the phase gradient across the surface

Large bandwidth if ΔΦ constant over frequency Linear phase profile desired

Matching helps achieve linear reflection phase

cell at (N-1)Δx

Position

Re

flect

ion

Ph

ase

2ΔxΔx (N-1)Δx NΔx

Re

flect

ion

Ph

ase

Frequency

ΔΦ

fo

cell at Δxcell at 2Δx

cell at NΔx

Final Surface Unit Cell and Equivalent Circuit Center frequency of

10GHz Vary radii (r1 and r2)

to obtain required phase

Achieve high phase agility by increasing mismatch with free space

Equivalent Circuit

2βh, ZTL

Input

βh, ZTL

TL βh, ZTL

TL

TL

L2

L1

Dielectric(εr=10)

metal

ground plane

r1

r2

Input

2h

d

Chosen Structure

d=5mm

h

h=1.9mm

Three layers provide sufficient phase agility > 360° Use minimum mismatch for required phase agility

Measurements

Measurements agree with theory High side lobes of -5dB due to phase errors in fabrication Achieved small error of ± 4° in maximum beam direction within

20% bandwidth around 10GHz

-40dB

-30dB

-20dB

-10dB

0dB

60

210

30

240

0

270

-30

300

-60

330

-90 90

Reflect-Array Measured Pattern at 10GHz

Measured Pattern

Theoretical Angle of Maximum Radiation9 9.2 9.4 9.6 9.8 10 10.2 10.4 10.6 10.8 11

-35

-34

-33

-32

-31

-30

-29

-28

-27

-26

-25Direction of Radiation Beam Maximum vs Frequency

Frequency (GHz)

Dire

ctio

n of

Max

imum

Bea

m (

deg)

Measured

Theoretical

Conclusions

Radiation beam direction controlled by reflection phase Linear phase gradient equivalent to slanted metal sheet

Not limited to linear phase gradient

Designed unit cell at 10GHz cell with phase agility > 360° Phase agility - by increasing impedance mismatch with free space Smaller unit cell possible at the expense of phase agility

Thicker dielectric can offset the loss in phase agility for smaller cells

Designed, built and tested a reflect-array at 10GHz with proposed cell

Works for both TE and TM polarizations at various incidence angles

Achieved small beam direction error over 20% bandwidth