1st IET Colloquium on Antennas, Wireless and Electromagnetics 29 May 2013, Loughborough University, Loughborough, UK

Substrate Integrated Waveguide Technology for the

Development of 60 GHz Photonic Transmitters

Ivan Flammia, Besher Khani, Andreas Stöhr

Affiliation University of Duisburg-Essen

Centre for Semiconductor Technology and Optoelectronics

Lotharstr. 55

47057 Duisburg, Germany

Email: ivan.flammia@uni-due.de

Introduction

The 7 GHz bandwidth recently allocated worldwide in the 60 GHz band for unlicensed wireless communication has opened the possibility to a wide range of indoor and outdoor wireless gigabit-per-second applications [1].

In this scenario, the fiber-like wireless connectivity guaranteed by Radio-over-Fibre (RoF) technology plays a fundamental role in allowing the development of new high-data rate systems, without the need for complicated modulation formats [2].

In this work we discuss the development a 60 GHz photonic transmitter for indoor RoF applications, based on substrate integrated waveguide (SIW) technology implemented on high-frequency laminates.

Radio-over-Fibre (RoF)

• Potentially able to provide multi-gigabit data rates, allowing fibre-like wireless connectivity.

• Expansion of existing optical networks.

• Indoor/outdoor applications.

Photonic transmitter:

Operates the optical-to-electrical conversion by means of a high-frequency photodiode (PD) and transmits the RF signal via an opportune antenna.

Fig. 1. Typical Radio-over-Fibre link.

60 GHz • 57-64 GHz band (7 GHz of unlicensed

spectrum bandwidth).

• Multi-gigabits data rate possible.

• Wireless PANs intended range: 10m.

• Replace various cables used today in office/home environment (gigabit Ethernet, USB, or IEEE 1394, HDMI).

• Increased mobility within the home.

• Frequency reuse / security (attenuation of oxygen, walls) [4].

• Several international standards for HD video streaming and file transfer (WirelessHD , ECMA-387 , 802.15.3c , 802.11ad , WiGig) [5].

Fig. 2. Typical scenario of in-building Radio-over-Fibre [3].

60 GHz Photonic Transmitter based on SIW Technology

Integration approach:

• Use of RF laminates as integration platform for RoF applications: – Successfully demonstrated [6]:

– E-Band photonic transmitter with off-the-shelf horn antenna.

• Integration of photodiode (wire bonds).

Use of SIW technology:

• No need for external (horn) antennas (eliminates mounting steps, tolerances, enables higher frequency operation).

• Requires transition from GCPW-to-SIW and suitable antennas.

Fig. 3. Interface between the high-frequency PD and the RF laminate. Wire bonds are used to connect the PD output to a grounded coplanar waveguide (GCPW) on the RF laminate.

G S G

Wire bonds

ROGERS 5880

PD Chip (InP)

Substrate Integrated Waveguide

W

Fig. 4. Substrate integrated waveguide transmission line, with highlighted via holes parameters.

H

• Promising candidate for the implementation of millimetre-wave integrated circuits [7, 8].

• Cost-effective technology suitable for mass production. d

p

Fig. 5. Field propagation (60 GHz) in SIW on ROGERS 5880 laminate. Geometrical parameters: W = 2.9 mm, H = 0.38 mm, d = 0.2 mm, p = 0.4 mm, Z0 ~ 75 Ω.

H

W

d

p

Substrate Integrated Waveguide • Proper dimensioning is necessary

to guarantee single mode operation:

–

• RF laminate: ROGERS 5880

– Low-loss high-frequency substrate: εr =2.2, tgδ = 0.0009.

αTE20 Single mode

operation

Fig. 7. Propagation constant of the SIW depicted in Fig. 4.

αTE10

βTE10

βTE20

Fig. 6. Electric field distribution for the TE10 (top) and TE20 (bottom) modes.

TE10

TE20

GCPW-to-SIW Transition Requirements:

• Must allow biasing of the photodiode!

• DC block and RF choke:

– Use of coupled lines [9]:

–

• Constrains due to line/gap etching resolution (~100 µm):

• Z0e= 187 Ω, Z0o= 76 Ω.

• Zin=46 Ω, Zout= 78 Ω.

Fig. 8. Layout of the transition.

Fig. 9. S-parameters of the transition. Fig. 10. 3D view of the transition.

GCPW-to-SIW Transition Requirements:

• Must allow biasing of the photodiode!

• DC block and RF choke:

– Quarter-wave capacitive stubs + quarter-wave transformer.

Fig. 12. S-parameters of the RF choke.

RF IN

RF OUT DC

Fig. 11. 3D view of the RF choke.

GCPW-to-SIW Transition • Allows correct biasing of the photodiode!

– DC block and RF isolation.

• In the 57-64 GHz band guarantees:

– Low loss (IL < 0.8 dB), excellent matching (RL > 19 dB) and excellent isolation (IS > 28 dB ).

• Opens the possibility to the development of 60 GHz photonic transmitters based on SIW technology!

Fig. 13. 3D view of the transition.

Fig. 14. S-Parameters of the transition. Fig. 15. Integration concept for SIW photonic transmitter.

60 GHz Photonic Transmitter for Indoor Applications

Indoor HD video streaming:

• Uncompressed HDMI wireless streaming (carrier: 60 GHz).

• Requires sector antenna to increase energy efficiency.

• Focus of the radiated power in a predefined „user area“.

• Possible candidate:

• SIW H-plane horn antenna!

Fig. 16. Indoor distribution of uncompressed

HD video signal.

Note: the size of the photonic transmitter is in

the order of a few centimetres; for

visualization purposes, the antenna and the

room are not represented in scale.

Dielectric-filled H-Plane Horn Antenna

• H-plane horn antenna on thin laminate (H = 381 um):

– Poor return loss (RL ~ 2 dB).

– Poor front-to-back ratio (FTBR < 3 dB).

-200 -150 -100 -50 0 50 100 150 200-50

-40

-30

-20

-10

-0

10

Angle (degree)

Ga

in (

dB

)

Fig. 17. Antenna model (left) and its RL (right). Fig. 18. Radiation pattern: 3D view (top) and

rectangular plot (bottom).

50 55 60 65 70-15

-10

-5

0

Frequency (GHz)

S11

(dB

)

-2

H-Plane

E-Plane

SIW H-Plane Horn Antenna with Grating Transition

• Equivalent SIW H-plane horn antenna:

– Use of grating transition [10] to achieve satisfying matching (RL > 9 dB) and high front-to-back ratio (FTBR > 23 dB)!

-200 -100 0 100 200-50

-40

-30

-20

-10

-0

10

Ga

in (

dB

)

Angle (degree)

Fig. 19. Antenna model (left) and its RL (right). Fig. 20. Radiation pattern: 3D view (top) and

rectangular plot (bottom).

H-Plane

E-Plane

50 53 55 58 60 63 65 68 70-15

-13

-10

-8

-5

-3

0

Frequency (GHz)

S11

(d

B)

-9

60 GHz Photonic Transmitter based on SIW Technology

~ 2.5 cm

Integration platform:

• Use of laminate-based SIW for photonic transmitters!

– GCPW-to-SIW transition with planar bias tee.

– SIW sector antenna with engineered radiation pattern.

Fig. 21. Integration concept for SIW photonic transmitter.

Fig. 22. GCPW-to-SIW transition and SIW H-plane horn antenna.

Conclusions

• 60 GHz Radio-over-Fiber.

• Integration approach for novel photonic transmitter:

– Substrate Integrated Waveguide (SIW) technology

• Novel GCPW-to-SIW transition:

– Integrated fully planar bias tee (DC-block, RF choke).

– 0.8 dB, RL > 15 dB, IS > 28 dB.

• 60 GHz photonic transmitter for indoor applications:

– SIW H-plane horn antenna.

– Sector antenna (improved efficiency).

– RL > 9 dB, FTBR > 23 dB.

Acknowledgements

The University Duisburg-Essen acknowledges financial support by the European Commission and cooperation within the Marie Curie initial training network MITEPHO (grant agreement 238393).

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