Preliminary PresentationPreliminary Presentation
CHARACTERISATION OF WAVEGUIDE CHARACTERISATION OF WAVEGUIDE
COMPONENTS AT MILLIMETRECOMPONENTS AT MILLIMETRE
WAVELENGTHSWAVELENGTHS
Hasnain PanjwaniHasnain Panjwani
Supervisor: Dr. P. G. HuggardSupervisor: Dr. P. G. Huggard
December 2006December 2006
RALRAL
ContentsContents
Millimetre Waves
Wave propagation through waveguide
Losses within a waveguide
Theoretical Results– Formula
– HFSS
Experimental Results– Direct Measurements
– Ring Cavity
Future Work– Ring Cavity development
– Photonic Crystal
Conclusion
Millimetre Wavelengths & The Millimetre Wavelengths & The
Terahertz Terahertz ““GapGap””
Millimetre Wave usesMillimetre Wave uses
EM Wave TheoryEM Wave Theory
Maxwells equations
lead to the wave
equations for the B
and E fields.
The solutions to these
in the media we are
interested in give a full
set of components,
but…
2
2
00
2
t
BB
∂
∂=∇ µε
2
2
00
2
t
EE
∂
∂=∇ µε
Remembering Boundary conditions.
EM Wave TheoryEM Wave Theory
θ
x
y
zWaves reflecting off two infinite perfect conductors separated by distance a.
a
k1
E1
B1
k2
E2
B2
)]cos(exp[)sinsin(2 0 θωθ kztjkyjEeE x −=
The boundary conditions can be satisfied.
At y = 0, Ex = 0
At y = a, Ex = 0 – IF
k.a.sinθ = n.π n = 1, 2, 3…
Where: E0 = Amplitude, k = Wavenumber
k.a.sinθ = n.π n = 1, 2, 3…
When sin θ = 1 � MAX
n.π/k.a ≤ 1
λ = n/2a ���� Cut-off Wavelength
EM Wave TheoryEM Wave Theory
θ
x
y
z
a
k1
E1
B1
k2
E2
B2
By adding top and bottom walls and creating a finite length, the boundary conditions for the Transverse Electric and Transverse Magnetic Waves have not been invalidated.
This is now a rectangular waveguide.
22
2
22
2
22
gkka
n
b
m−=+
ππ
b
Waveguide Equationk = Wavenumber
kg = Guide Wavenumber
Modes of OperationModes of Operation
Electric Field
n = 1
n = 2
n = 3
TEnm – Mode
n signifies the
variation of field
with “y” (a wall)
m signifies
variation of field
with “x” (b wall)
LossesLosses
r
sf
SkinDepthµµπ
ρδ
02
2==
Why is power lost in a waveguide?
Dielectric Losses
Conductor Losses
Metals used have finite conductivity
Leads to currents in the walls and associated heating and loss effects.
These currents occur within the skin depth of the material.
Designers do not therefore require to make waveguides with lots of material in order to reduce losses but just to coat them with high conductivity materials e.g. Gold.
ρ = Bulk Resistivity (ohm-meters)
µ0 = Permeability Constant
µr = Relative Permeability
f = Frequency (Hertz)
Poynting Theorem:
Ampère’s Integral Law:
Leads to:
Theoretical LossesTheoretical Losses
∫=S
sdSP .2
10HES ×=
∫ ∫=s
fsdjldH ..
mNpkabbka
R
g
sc /)2( 232
3+= π
ηα
Rs = Surface Resistance, η = Free space Impedence
Theoretical LossesTheoretical Losses
Waveguides under test – W-Band
Signifies waveguide dimensions of 2.54mm x 1.27mm.
Frequency Cut-off: 59.1 GHz
Optimum frequency range 1.2Fc –1.9Fc
���� ~ 75 – 110 GHz
Theoretical Attenuation W-Band Waveguide of 1 metre length.
2.00
2.50
3.00
3.50
4.00
4.50
75 80 85 90 95 100 105 110
Freq (GHz)
Lo
ss
(d
B/m
)
Attenuation Copper
Attenuation Silver
Attenuation Aluminium
Theoretical Attenuation W-Band Waveguide of 1 metre length.
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
55 65 75 85 95 105 115
Freq (GHz)
Lo
ss
(d
B/m
)
Attenuation Copper
Attenuation Silver
Attenuation Aluminium
Theoretical Losses Theoretical Losses -- HFSSHFSS
Ansoft HFSS – 3D CAD programme which models
propagation of EM Radiation
Finite Element Method
Meshes network into Tetrahedrons and calculates
fields at vertices.
HFSS ModelsHFSS Models
Field Animation Power Lost in dB from port 1 � 2
HFSS + FormulaHFSS + Formula
Theoretical Attenuation W-Band Waveguide of 1 metre length.
2.10
2.30
2.50
2.70
2.90
3.10
3.30
3.50
75 80 85 90 95 100 105 110
Freq (GHz)
Lo
ss
(d
B/m
)
Attenuation Copper
HFSS
Vector Network AnalyserVector Network Analyser
Direction of Transmission
DUT
CONTROL, DETECTION & DISPLAYMAIN UNIT
Xx n
f1 = 8 – 18 GHz f2 = 8 – 18 GHzfIF
Frequency Multiplier
(� fmeas = n • f1)
Harmonic Mixer
(� fIF = n • f1 – n • f2)
Analysing Vector properties of waves through a “network”
“Network”: System of input and output ports. Simple is waveguide – 2 Ports
Measures amplitude and phase properties.
Oscillator directly provides a source which passes through the DUT.
Harmonic Mixer made of a Shottky diode mixes received signal and secondary generated signal which is phase locked to the original.
VNA TestingVNA Testing
Early Findings:
Initially test waveguides measured.
Noticed measurements of same waveguide changed over time.
Some tests carried out to check the effects of “warming up”
Conclusion: The VNA requires a warming up time of approximately 30 minutes in order to produce consistent results.
VNA TestingVNA Testing
Just after switch on:
Black – Forward Direction
Red – Reverse Direction
Dark Blue: Forward
direction after switch
on.
Light Blue: Forward
Direction after 40
minutes.
Forward and Reverss
Sweeps after 40 minutes.
VNA TESTINGVNA TESTING
Attenuation of Straight
Waveguide of 110cm Length.Losses from VNA below Cut-off
ComparisonComparison
Excess Losses maybe due to:
Dirty guide
Surface roughness
Faulty Contacts
Other anomalous effects.
Theoretical and Experimental results of WGD attenuation at W-Band
0.00
2.00
4.00
6.00
8.00
10.00
12.00
75.00 80.00 85.00 90.00 95.00 100.00 105.00 110.00
Frequency (GHz)
Att
en
uati
on
(d
B/m
)
VNA
ANALYTICAL
HFSS
Poly. (VNA)
New TechniqueNew Technique
Port 4
Port 1
Port 3
Port 2
Quality “Q” Factor
Relationship with
attenuation.
Resonant
Frequencies.
λ / 4
A B
D C
At A and B the wave diffracts through the holes.
However at D the wave coming from B would have travelled half a wavelength and therefore would be 1800 out of phase. These waves will destructively interfere.
The waves moving to the right in the upper waveguide will constructively interfere.
This set up is known as directional coupling.
Coupler HFSS DesignCoupler HFSS Design
HFSS Coupler Animation
S Parameter plot S31 and S41
Future WorkFuture Work
Complete design of Ring Cavity
Build and measure ring cavity
Investigate properties of Photonic Crystal
ConclusionConclusion
Millimetre Waves
Wave Propagation
– Maxwell Equation, Wave equation, Losses
Predicting losses analytically from formula
and HFSS
Experimental results and differences.
Ring Cavity and Resonance
Future work
QUESTIONS?QUESTIONS?
CHARACTERISATION OF WAVEGUIDE
COMPONENTS AT MILLIMETRE
WAVELENGTHS
Hasnain Panjwani
Supervisor: Dr. P. G. Huggard
December 2006
RAL
