Hung-Jui Lam, Yingying Lu, Huilian Du,Poman P.M. So and Jens Bornemann

TimeTime--Domain Modeling ofDomain Modeling ofGroupGroup--Delay CharacteristicsDelay Characteristics

of Ultraof Ultra--WidebandWidebandPrintedPrinted--Circuit AntennasCircuit Antennas

Department of Electrical and Computer Engineering

University of Victoria, Victoria, BC, V8W 3P6 Canada

OutlineOutlineIntroduction/Motivation

Ultra-Wideband Printed-Circuit Antennas

Phase Center Calculations

Group Delay Calculations

Coplanar UWB Antenna

Microstrip UWB Antenna

Conclusions

Introduction/MotivationIntroduction/MotivationUltra Wide-Band (UWB) technology has received increased attention with the release of the 3.1-10.6 GHz band.UWB antennas in printed-circuit technologies within relatively small substrate areas is of primary importance in short-range and high bandwidth applications.UWB systems involve the transmission and reception of short pulses; the variations of radiated amplitudes and phases over frequency contribute to the distortion of the pulse.Phase distortions are represented by either a varying phase center over frequency or by the group delay.This presentation focuses on a time-domain approach (transient analysis) to determine the group delay of printed-circuit UWB antennas. The TLM method (MEFiSTo-3D) is used as a simulation tool.

Ultra-Wideband Printed-Circuit Antennas – Examples: Microstrip

Choi, Park, Kim, Park, MOTL, No. 5, March 2004

3.1 - 10.6 GHzVariations ≈ 300 ps

Chuang, Lin, Kan, Microw. J., Jan. 2006 and Lin, Kan, Kuo, Chuang, MWCL, Oct. 2005

Ultra-Wideband Printed-Circuit Antennas – Examples: Coplanar

Ma,Tseng,Trans AP, Apr. 2006 Nikolaou, Anagnostou, Ponchak,Tentzeris, Papapolymerou, ,APS Dig., 2006

measured

Phase Center Calculations - Method I

Frequency domain Far fieldCalculate the spherical wave front in the far field.Compute the apparent phase center along the antenna surface or axis.

Time consuming !

C1C2

Ф2=ФoФ1=Фo

Ф3=Фo

Ф3’=Фo’

Ф1’=Фo’

Ф2’=Фo’

Phase Center Calculations - Method IIFrequency domain Near field

From a reference point on the surface of the antenna, compute the phase variation in the near field over the main beam.A valid phase center location is detected if the phase variationover the main beam is within a few degrees.

phase center

microstrip circuit

Rambabu, Thiart, Bornemann, Yu, Trans. AP, Dec. 2006

No longer an option in HFSS !

Group Delay CalculationsTime domain

Generate a pulse covering the respective frequency spectrum.Excite antenna and detect radiated pulse. Fourier transform both pulses and record phase response. Calculate the group delay from the derivative of the phase response.

Setup in MEFiSTo-3D

Note that the model includes the coax-to-CPW transition.

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5t/ns

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

Nor

mal

ized

E-fi

eld

2 3 4 5 6 7 8 9 10 11f/GHz

-630

-540

-450

-360

-270

-180

-90

Phas

e / d

egre

es

Input pulse

E(t)

|Φ(f)|

Radiated pulse

2 3 4 5 6 7 8 9 10 11f/GHz

-60

-50

-40

-30

-20

-10

0

Nor

mal

ized

Am

plitu

de /

dB

|Eθ |

|Eϕ |

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5t/ns

-0.010

-0.008

-0.006

-0.004

-0.002

0.000

0.002

0.004

0.006

0.008

0.010

Nor

mal

ized

E-fi

eld

Eθ Eϕ

2 3 4 5 6 7 8 9 10 11f/GHz

-4000

-3000

-2000

-1000

0

Phas

e / d

egre

es

< ( Eθ )

< ( Eϕ )

2 3 4 5 6 7 8 9 10 11f/GHz

30

32

34

36

38

40

Nor

mal

ized

Am

plitu

de /

dB

|E(f)|

Coplanar UWB Antenna

θ

ϕx

y

z

Eθ

Eϕ

New CPW UWB antenna for 3.1- 10.6 GHz bandLam, Bornemann, EMC Symp., July 2007

Normalized Radiation Patterns0

30

60

90

120

150

180

210

240

270

300

330

-40 -30 -20 -10 0

E-plane (Eθ) 3 GHz 4 GHz 6 GHz 8 GHz10 GHz

0

30

60

90

120

150

180

210

240

270

300

330

-40 -30 -20 -10 0

H-plane (Eθ) 3 GHz 4 GHz 6 GHz 8 GHz10 GHz

0

30

60

90

120

150

180

210

240

270

300

330

-40 -30 -20 -10 0

H-plane (Eφ) 3 GHz 4 GHz 6 GHz 8 GHz10 GHz

0

30

60

90

120

150

180

210

240

270

300

330

-40 -30 -20 -10 0E-plane (Eθ) 3 GHz 4 GHz 6 GHz 8 GHz10 GHz

Eθ(θ,π/2)

Eθ(θ,0)

Eθ(π/2, ϕ)

Eϕ(π/2,ϕ)

Input Return Loss ( |S11|)

Input reflection coefficient: Comparison between HFSS and MEFiSTo

Note: Coax-to-CPW transition included in both models

2 3 4 5 6 7 8 9 10 11f/GHz

-50

-40

-30

-20

-10

0

|S11

| / d

B

HFSS

MEFiSTo

Group Delay and Amplitude

2 3 4 5 6 7 8 9 10 11f/GHz

-100

-90

-80

-70

-60

-50

-40

|E| /

dB

Amplitude Variation (3.1-10.6 GHz):

∆ |Eθ | < 8.7 dB

∆ |Eϕ | < 23 dB

2 3 4 5 6 7 8 9 10 11f/GHz

0.0

0.5

1.0

1.5

2.0

Gro

up d

elay

/ ns

Group Delay Variation (3.1-10.6 GHz):

∆ (Eθ ) < 163 ps

∆ (Eϕ ) < 620 ps

Note:

Group delay variation in principal polarization is better than other published values.

Variation in amplitudes are consistent with HFSS computations of radiation patterns.

Microstrip UWB Antenna

Lin, Kan, Kuo, Chuang, MWCL, Oct. 2005

probe

MEFiSTo

VSWR

2 3 4 5 6 7 8 9 10 11f/GHz

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

VSW

R

measured (incl connector)

HFSS (incl connector)

MEFiSTo (no connector)

Measured VSWR< 3.7 (3.1 – 10 GHz)< 2.5 (4.1 – 10 GHz)

Group Delay and Amplitude

Note:

Group delay variation is inferior to that of the CPW antenna.

Amplitude variations in main polarization are almost identical.

3 4 5 6 7 8 9 10f/GHz

0.0

0.5

1.0

1.5

2.0

2.5

Gro

up d

elay

/ ns

Group Delay Variation (3.1-10 GHz):

∆ (Eθ ) < 231 ps

∆ (Eϕ ) < 1.9 ns

3 4 5 6 7 8 9 10f/GHz

-120

-110

-100

-90

-80

-70

-60

-50

-40

|E| /

dB

Amplitude Variation (3.1-10 GHz):

∆ |Eθ | < 8.8 dB

∆ |Eϕ | < 31 dB

Comparison

Note:

Peak gain of CPW antenna: 1.7 – 5.1 dBi

Comparable nearly omnidirectional radiation patterns; characteristic deteriorates towards 10 GHz.

< 8.8 dB< 8.7 dBAmplitude variation

<231 ps< 163 psGroup Delay Variation

3.72.03VSWR

Microstrip Antenna

Coplanar Antenna

3.1 – 10.6 GHz

The Transmission-Line Matrix method in form ofMEFiSTo-3D is applied to determine the group delay characteristics of printed-circuit UWB antennas. It is found that transient (time-domain) analysis has several advantages over frequency-domain phase center computations.The method is applied to two different printed-circuit UWB antennas, and their performances are compared. The design in CPW technology outperforms a comparable design using microstip circuitry.

ConclusionsConclusions