waveguide characteristics and measurement errors€¦ · waveguide • waveguide = hollow metal...
TRANSCRIPT
Keith AndersonAgilent Technologies
© Copyright 2011 Agilent Technologies, Inc.
Waveguide Characteristicsand Measurement Errors
IMS2011 in Baltimore: A Perfect Match
Agenda
• Background• Characteristics• Conclusion
Page 2
Waveguide• Waveguide = hollow metal pipe• Rectangular, 2:1 aspect ratio• Advantages
– Conducts millimeter signals– Low loss– High power– Good shielding– Can "flare" end into horn antenna
•Disadvantages– Bandwidth < 1 octave– Rigid, heavy, large– Expensive– No DC connection– Dispersive
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a
b a = 2 * b
Waveguide dimensions
Millimeter Bands
Page 4
Propagation Modes
• Electromagnetic wave modes• TEM• TE & TM• Hybrid
• Rectangular waveguide• Supports TE and TM• For TEmn, m & n give the "order" of mode • Mode propagates above its "cutoff frequency"
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a
b
x
y
TE10 electric field(end view)
Waveguide Frequencies
• Standard millimeter waveguide is 2:1• Fcutoff1 = c / (2 * a)
• No propagation below Fcutoff1• TE10 propagates between Fcutoff1 and 2*Fcutoff1• Other modes propagate above 2*Fcutoff1
• Operating range• Fmin = 1.25 * Fcutoff1• Fmax = 1.89 * Fcutoff1• FLinearMean = 1.57 * Fcutoff1• FGeometricMean = 1.54 * Fcutoff1
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a
b
x
y
TE10 electric field(end view)
Dispersion
• Wave propagation depends on frequency• Below Fcutoff1, no propagation• Above Fcutoff1, the wave "ping-pongs"
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Fcutoff1
Low frequencypropagation
High frequencypropagation
Agenda
• Background• Characteristics• Conclusion
Page 8
Propagation Velocity• Wave velocity: Free space propagation• Group velocity: Energy propagation • Phase velocity: Phase propagation
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V /
c
f / Fcutoff1
Vgroup
Vwave
Vphase
Vphase
Vwave
Vgroup
fcutoff1
f1
2Vphase = c
fcutoff1
f1
2Vgroup = c *
c2 = Vphase * Vgroup
Vwave = c
Fmin Fmax
1.67
1.18
0.600.85
FGMean
0.76
1.34
Group Delay
• GD is infinite at Fcutoff1 & approaches GDfreespace
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GD = GDfreespace
GD = (Physical Length) / Vgroup 1.671.181.34
FGMean
GD = 1ns / foot, in free spaceG
D /
GD
frees
pace
Fcutoff1
f1
2
f / Fcutoff1 Fmin Fmax
Guide Wavelength
• λguide is infinite at fcutoff1 & approaches λfreespace
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λguide = λfreespace
λ g/ λ
frees
pace
λguide = Vphase / f
f / Fcutoff1Fmin Fmax
1.67
1.18λfree space = 1mm @ 300GHz
Fcutoff1
f1
2
Impedance
• ZTE is infinite at Fcutoff1 & approaches Zfreespace
• Network analyzers assume Zo = "1"
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ZTE = Fcutoff1
f1
2
Zfreespace
Z TE
/ Zfre
espa
ce
f / Fcutoff1
ZFreespace = 377Ω
Fmin Fmax
628Ω
444Ω
LossLoss is due to skin effect & surface roughness
Page 13
Loss in perfect copper
Agenda
• Background• Characteristics• Conclusion
Page 14
Conclusion
• Waveguide is dispersive• Zo = 444Ω - 628Ω•Set Zo = "1" in VNA• Group delay is 18~67% longer than free space• Wavelength is 18~67% longer than free space• Skin effect loss is high (6.5dB/meter for WR7)
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