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