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