waveguide characteristics and measurement errors€¦ · waveguide • waveguide = hollow metal...
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![Page 1: Waveguide Characteristics and Measurement Errors€¦ · Waveguide • Waveguide = hollow metal pipe • Rectangular, 2:1 aspect ratio • Advantages – Conducts millimeter signals](https://reader031.vdocuments.net/reader031/viewer/2022013117/5b8b486e09d3f212498b4fc9/html5/thumbnails/1.jpg)
Keith AndersonAgilent Technologies
© Copyright 2011 Agilent Technologies, Inc.
Waveguide Characteristicsand Measurement Errors
IMS2011 in Baltimore: A Perfect Match
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Agenda
• Background• Characteristics• Conclusion
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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
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Millimeter Bands
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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)
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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)
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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
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Agenda
• Background• Characteristics• Conclusion
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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
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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
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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
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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
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LossLoss is due to skin effect & surface roughness
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Loss in perfect copper
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Agenda
• Background• Characteristics• Conclusion
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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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