Mtt 08 Poster Holzman 3 14 08

Analyzing Broad-Band Electromagnetics Problems with

Commercial Software—Time Domain vs. Frequency Domain

Analyzing Broad-Band Electromagnetics Problems with

Commercial Software—Time Domain vs. Frequency Domain

Eric Holzman1, William Nelson1, Brian Swift1,

James Willhite2 and Shrikrishna Hegde2

1Northrop Grumman, Baltimore, MD 21240, USA2Sonnet Software, Syracuse, NY 13212, USA

Holzman ([email protected])

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Outline of Our Comparison

• Overview of finite element EM software• Solving in time vs. frequency domain• Analyze 4 problems in both domains• Use commercial software from CST*• Compare the CPU time and RAM• Which domain is superior?

*Computer Simulation Technology, www.cst.com


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Finite Element 3-D EM Software

• Time and Frequency domain

• Mature, cell-based algorithms

• Available commercially (CST, ANSOFT)

• Inputs: arbitrary 3-D structure geometry

• Outputs: S-parameters, radiation patterns, radar cross section, fields


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Theory: Time vs. Freq Domain

Feature Time Frequency

Number of cells (2L/)3 (2L/)3

Transient problems Yes No

Frequency response 1 solutionAll 1 solution1 pt

S-parameters N solutionsNxN 1 solutionNxN

Periodic structures Normal incidence Any , incidence(Direct solver only)


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Analyze real problems in time & freq

1) ring hybrid

2) 1:4 divider

3) conical antenna

4) pillbox antenna

time

freq

Analyze 4 devices in both solver domains

Comparison criteria

Use CST Microwave Studio™ for all analysis

CPU Time

RAM


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IBM PC platform for all problems

CPU featuresTime Freq Time Freq Time Freq Time Freq

No. of bits 32 32 32 32 32 32 32 64Speed (GHz) 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.0RAM (GB) 3 3 3 3 3 3 3 16

Ring Hybrid 1:4 dividerConical antenna Pillbox

antenna

Freq-domain analysis of pillbox requires a 64-bit CPU


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Ground Rules

• Generate a single model of each device

• Refine mesh to convergence

• Time domain mesh: uniform

• Frequency domain solver: iterative

• Frequency domain sweep: interpolating


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March’s Ring Hybrid in Stripline

ports

ports

-40

-30

-20

-10

0

0 1 2 3 4 5 6 7 8 9 10 11

Frequency (GHz)

(dB

)

return loss

isolation

insertion loss

FD

TD

S. March, “A Wideband Stripline Hybrid Ring,” IEEE Trans. Microwave Theory & Tech, p. 361, June 1968. Bandwidth: 7-11 GHz


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Stripline 1:4 Wilkinson Divider

output ports

common port-30

-25

-20

-15

-10

-5

0

5 7 9 11 13 15 17 19

Frequency (GHz)(d

B)

isolation

Common port return loss

insertion loss

FD

TD

Bandwidth: 6-16 GHzPort separation is large


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Conical Antenna over Ground

Coax feed

Antenna

Ground

Bandwidth: 0.15-1.00 GHz

Frequency (GHz)

-40

-30

-20

-10

0

0 0.2 0.4 0.6 0.8 1|S

11

| (d

B)

FD

TD


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Pillbox—a very large antenna

E. L. Holzman, “Pillbox Antenna Design for Millimeter-Wave Base Station Applications,” IEEE Ant. & Prop. Mag., Vol. 45, #1, pp.27-37, Feb. 2003.

Reflector surface

Waveguide Port

Radiating aperture

-40

-30

-20

-10

0

23 24 25 26 27 28 29 30 31 32

Frequency (GHz)

|S11

| (d

B)

FDTD

TD: 23-32 GHzFD: 28-32 GHz

~40


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ParameterTime Freq Time Freq Time Freq Time Freq

RAM (GB) 0.011 0.26 0.192 1.38 0.020 0.59 0.68 6.4CPU Time 0.9 m 10 m 26 m 86 m 0.5 m 17 m 3.6 h 13 h# of S-pars 16 16 25 25 1 1 1 1

# of freqs 1001 11 1001 14 1001 20 1001 86

Time Domain—fastest & least RAM

Ring Hybrid 1:4 dividerConical antenna Pillbox

antenna

Summary--TD advantage over FD

• 3 to 30 times in CPU time

• 6 to 30 times in RAM

• $ savings--less powerful PCs solve the same problems faster in time domain

• Time domain’s biggest advantages for–Broadband devices

–Electrically large devices
