Optical Interconnects Group The University of Texas at Austin

Polymer-based Photonic Phased-array Antenna System based on Detector-

switched optical Blass Matrix True-time Delay Steering

Ray T. Chen(1), Bing Li(1), Yihong Chen(1),

W. Steier(2), L. Dalton(2), H. Fetterman(3) and Charles Lee(4)

University of Texas, Austin(1)

University of Southern California(2)

University of California, Los Angeles(3)

Air Force Office of Scientific Research(4)

Sponsors: AFOSR and BMDO.

Advantages of Proposed Photonic PAA

• Ultra-wide instantaneous radiation bandwidth without beam squint.

• Easily work at high RF frequency (18-26.5GHz in demo).

• Compact and low weight.

• Reliable and avoid EMP attack.

• Remote control.

• Wavelength tuning ability to provide fine-tuning of beam steering angles.

• Easily reconfigured and high steering speed.

Beamforming Matrix of PAA

Blass matrix for multi-beam forming

or steering.

BeamPorts

(Signal in)

Terminator

directionalcoupler

1

2

3

M

...

.....

0

No.M

No.0No.1

...

.....

m

normalsteeringangle wavefront

antennaarray

Polymer-based Substrate-guided Wave optical True-time

Delay Module

MM-1

21

0

0A

N-1A

2A

1A

guide-wavesubstrate

subregion ofhologram grating

....

..

B 0B 1

B 2

BN-2BN-1

x

y

GRIN lensarray

m..

..

Design of the hologram grating on guide-wave substrate

Delay introduced at No. m fanout:

dngnb kKk ,,

K g,n

kb,n

kd

1

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5

E xp o sure D o sa ge (J /cm 2 )

A n+1

A n

dngnb kKk 1,1,

K g,n+1

kb,n+1

kd

2

])cos(

1

)cos(

1[

2

1 nnm c

nhmm

Polymer-based 2-Dimensional Waveguide fanout for Uniform

Blass Matrix

0 1 2

-1 -2

Delay step: 50 ps

TTD Module Package Design and PIN Array PCB

Substratelocation

Slot for angle lock

Couple in GRINlens array

Fanout beamswindow

actuator screw forangle adjustment

GRIN lens array

The objective of this package design is to couple the 8×8 asymmetric fanout beam array into fibers, through a corresponding GRIN lens array.

The PCB layout (half) of the PIN photodetector bank (linear array), which will be used to convert the optical signals from one column of the fanout array.

System Configuration

PARAMETER GOALFrequency 18.0-26.0 GHzNumber of Elements 24 (3x8 array)Nominal Gain +17 dBiNominal Beamwidth 9 degrees x 52 degrees (fan beam)Illumination Function Uniform (-13dB nominal sidelobes)Polarization LinearGain 22 dBNoise Figure 3.0 dBPower Out +5 dBm

Elements’s number K = 8Steering resolution 3-bitScanning range: 0 ~ +/-45°

LD

LD

MOD EDFA

OpticalBlassmatrix

based onsubstrate-

guidedwaveTTD

module

PD

PD

PD

PD

PD

PD

PD

PD

PD

PD

PD

PD

PD

PD

PD

PD

Heterodyne opticalRF source

Optical TTD feeding network for antenna steeringpoweramp.

Antennaarray

Photodetectorbanks power

combiner

0

12

M

7

6

5

4

3

2

1

0

beam splitter

data in

k

LD

ED

FA

microwavepower amplifier

RF in

Power splitter andinitial delay tuning

toOpticalBlassMatrix

modulatorarray providedby USC/UCLA

2-D Phase-array Antenna Lattice

59

Radiating Element

• Printed circuit notches• 18-26 GHz operation• Crossed pair• Hybrid combiner for

circular polarization

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16

17 18 19 20 21 22 23 24

NotionalArray Lattice

• Triangular lattice• 24-elements, 8-subarray• X = 0.38”, Y = 0.19”,• Size ~ 3 x 0.6 x 2 inches

Y

X

18 GHzY-plane Pattern

18 GHzX-plane Pattern

22 GHzX-plane Pattern

26 GHzX-plane Pattern

22 GHzY-plane Pattern

26 GHzY-plane Pattern

Squint-free Technique for PAA with Subarray

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15

at 22GHz

at 18GHz

TTD line

Phase control line

)cos( tA

)cos( tA

E1

E2

)2/cos()2/cos(2 tA E9

)cos( tA

)cos( tA

E1

E2

E9

90

Beamwidth: 10.38º ~ 16.85º

0 15 30 45 60 75 90-60

-40

-20

0 18GHz 26GHz

Pow

er (

dB)

Angle (degree)

Heterodyne Photonic RF Source

• Power coupled into fiber: -4 dBm/ch

• RF frequency: ~ 30 GHz

• RF signal power: -35 dBm

Theoretical limit of conversion efficiency:

2.

2 )(8

1poptLRF PRZP

Or, in dBm:dBm9.32

9.36)log(20 .

poptRF PP

LD #1

LD #2

MSA

coupleinto fiber

verticalpolarization

PD

OSA

Block diagram of experiment

Switching Operation of Wide-band Photodetectors

-21

-18

-15

-12

-9

-6

-3

0

0 1 2 3 4 5 6

Bias voltage (V)

RF

ou

tpu

t (d

B) 1.5GHz

3.0GHz

5.5GGHz

10.0GHz

15.5GHz

21.0GHz

Switching characteristic of MSM.

Metal Semiconductor Metal

h

X0 d

V bias

Ve

x( ) qe

0 5 10 15 20 25 30-50

-40

-30

-20

-10

0

A B C D E F G

Res

pons

e (d

B)

Frequency (GHz)

Switching of PIN: VJ0=1.9V (A&B), 0.5V(C&D), 0.05V(E&F), 0.1V(G), A, C, E are experiment data,

B, D, F, G are theoretical curve.

hPIN

IR 0Z RF out

C b

eR

bV

Cp

BVJ0 is adjusted by this circuit

Conclusion:

• Novel detector-switched optical Blass matrix for phase-array antenna true-time delay steering have been proposed and designed.

• The photonic phase-array antenna system based on above optical TTD module has been designed and under preparing.

• A new squint free technique for photonic phase-array antenna based on sub-array structure is proposed. Simulated result of the far-field radiation pattern has been presented.

• The heterodyne system for photonic RF signal generation has been built, which conversion efficiency approaches to theoretical limit.

• The switching mechanism of wide-band MSM and PIN photodetector has been studied.

• The whole system will work on 18-26GHz, which will be of the photonic PAA demonstration with the highest RF frequency.