3 3 4 Electromagnetic Simulation of Cavity Filters
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Transcript of 3 3 4 Electromagnetic Simulation of Cavity Filters
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Electromagnetic Simulation of Cavity
Filters and Dielectric Resonators
Mark Bedford [email protected]
Part Time Lecturer in Engineering, School of Engineering, Design & Technology / Visiting Researcher, Mobile and SatelliteComm unications Research Centre / University of Bradford.
Presentation notes for the 4 th CST European User Group Meeting,Darmstadt, March 17th 2009.
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Overview.
Rsum of BTS Filter Technology. Complementary rle for electromagnetic analysis in
filter synthesis/optimisation
Rationale for compact triple mode.
Development of basic filter response. Broadband analysis/Model Order Reduction (MOR).
Eigenmode searches.
Performance analysis and tuning.
Realisation. Discussion and Conclusions.
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Requirements for EM-analysis.
Require:
Fast and efficient
calculations.
Equally valid in timeand frequency domain.
Properly represent the
topology and geometry
of Maxwellsequations.
CST:
Inbuild AR filtering in
TD, MOR.
Leap-frog algorithm,dual grid.
Finite integration
technique (FIT)and
perfect boundaryapproximation (PBA).
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BTS Filter Technology.
Standard filter technology is multi-conductor coaxial (combline), withsome contribution from ceramics.
Next generation BTS filtering for advanced 3G and early 4Gsystems demand volume and weight reductions.
Need to produce filter technologies which are:
Smaller and lower cost. Similar or betterQ than combline.
SuperiorQu/Vol.
Single vs. multimode technologies.
Expect several new technologies to become available: Single Mode.
Dual Mode. Triple Mode.
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Cavity Filter Technologies.
1. Multi-conductor coaxial / combline.
2. Dielectric combline.
3. Dual mode ceramic (metallised).
1
2
3
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S-Plane Synthesis.
Generalised Chebyshev approximation
Symmetrical network analysis Form the transmission coefficient, S21, in terms of even- and odd-mode
admittances For a stable system, LHP poles of S21 are extracted using the alternating-
pole technique
Form even- and odd-mode admittances, Ye and Yo , from the polynomialcomprising the LHP poles
Form ABCD matrix from Ye and Yo Extract the circuit element from the ABCD matrix
Finite frequency transmission zero is extracted in the form of a phaseshifter, a shunt inductor in series with frequency invariant reactance
followed by another phase shifter Transform the synthesized network into a cross-coupled network
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Coupling Paths and Alignment.
Store reflected
phase across
passband and into
stopband.
Tune coupling andresonant
frequency of each
resonator to
approximate error
over stored band. Finite
Transmission
Zeros.RX path, 8
resonators,
3 cross
couplings
TX path, 7
resonators,
2 crosscouplings
M12
M23
M13
M34
M45M56
M67
M78 M68
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Dielectric Resonators.
Standard definition: an unmetallized piece of dielectric which functions as a resonant
cavity by means of reflections at the air-dielectric interface.
High permittivity, low loss microwave ceramic materials.
Single mode technologies: Compact TE01 Ceramic combline.
Ceramic waveguide.
Dual and triple mode technologies: Dual mode: HE
11 Dual and triple mode: TE01 Triple mode: TE01 & HE11
Metallization.
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The Spherical TE01 Resonator
First spur is TM10 Introduce central hole
Open to 30% of sphere diameter
Upwards frequency shift bounded below1%, with maximum SPFF of 1.42. Implies21% increase in spur free BW cf solid DR.
Hollow spheres, not mechanically sound. Circulation ofE with orthogonally varying
H of TE01 v.similar to cubic structure.
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Triple Mode DR Dielectric Sphere.
JDMJDMAKS
1.41071.34811.34101.366SPFF
2.59652.47112.47112.52561st spur
1.84141.83391.8337
1.84011.83271.8327
1.84011.83261.83261.8485Triplet
Meshing 40 lines /
No -refinement in initial conditions
Calc.Mode
Hollow,
di/do=0.3
Sphere, ro=12.4mm, r=45, 60mm
cube
JDMJDMAKS
1.41071.34811.34101.366SPFF
2.59652.47112.47112.52561st spur
1.84141.83391.8337
1.84011.83271.8327
1.84011.83261.83261.8485Triplet
Meshing 40 lines /
No -refinement in initial conditions
Calc.Mode
Hollow,
di/do=0.3
Sphere, ro=12.4mm, r=45, 60mm
cube
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The TE01 Resonator
TE01 , HEM11 , HEM21 ,TM01 depends ondimensions and .
When 1, the HEM11dominates as the lowestorder resonance.
The indicates less thanhalf a sine wave variationalong the direction ofpropagation.
For 35 approx. 95% ofthe stored electricalenergy of the TE01 -mode is confined withinthe resonator. The
corresponding figure forthe magnetic energy is60%.
The remaining EM energyis distributed through the
air in the neighbourhoodof the dielectric surface,and rapidly decays withdistance.
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The TE01 Resonator
Optimisation of , 0.4.
Introduction of central holeperturbs E, shifts resonanceand spurs having similar E-variation to higher frequencies.
In fact any mode having its E-field concentrated near theaxial line will be affected.
The central hole can beopened up to 35% withoutsignificantly affecting thefrequency.
Effect of supporting structure. Typically alumina, 9.5 9.9.
Polystyrene, 2.2.
Support has non trivial effecton TM can become first spur.
The downward frequency shiftis due to its E field lyingalmost entirely on the outsideflat surface of the dielectric.
Sensitive to metal tuningdiscs.
Possible strong coupling to
inter-cavity irises. Multi-criteria optimisation, but
constrained by synthesisrequirement.
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Compact TE01 .
Application: Full band filter.
HighQu.
Advantages:
Better SPFF than HE11dual.
Small cavity and singlemode flexible layout.
Disadvantage:
LowQu/Vol=310cm-3
. Minimum cavity size is
Diam 35 mm x 25 mmdeep height is a limitingfactor for someapplications.
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Chamfered Rectangular DR.
Mode 1: TE01 , e-field
Mode 2: HE11 , h-field.
Mode 3: HE11 , e-field
Mode 1: TE01Mode 2: HE11Mode 3: HE11
dualtriple
Chamfer 6mm, cavity width 35.3mm
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Field Distributions, Calculated Qu-factor.
Electric and magnetic field monitors at 2GHz (XY-plane):
Losses and unloaded Q-factor.
e-field h-field
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Coupling Mechanism.
The excitation probes are aligned along the dual modes(HE11 ) the M12 and M23 couplings controlled as afunction of the coupling hole diameters (to and from thecircularTE01 mode).
Dual mode coupling M13
is controlled in practice byhaving tuning screws above the DR.
M12
1
3M23
h-field, 2GHz
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Basic Filter
Response, N = 3.
1.9 2.32 2.05 2.1 2.15 2.2 GHz
-60
0
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
dB
S21
-50
0
-45.83
-41.67
-37.5
-33.33
-29.17
-25
-20.83
-16.67
-12.5
-8.333
-4.167
dB
S11
umts : Graph : S21 Mag dB / S11 Mag dB
1
1.9 2.31.96 2 2.04 2.09 2.14 2.19 2.24 GHz
-60
0
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
dB
S21
-50
0
-45.83
-41.67
-37.5
-33.33
-29.17
-25
-20.83
-16.67
-12.5
-8.333
-4.167
dB
S11
pcs_at_2 : Graph : S21 Mag dB / S11 Mag dB
1
UMTS
PCSCT-section
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Tuned Output of EM-analysis.
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Final Comparison, N = 3.
CH1 S22 LOG 5 dB/ REF 0 dB
Cor
PRm
CH2 S21 LOG 5 dB/ REF 0 dB
CENTER 2 000 .000 000 MHz SPAN 500 .000 000 MHz
Cor
PRm
15 Jul 2002 14:44:53
1
2
1:-19 .175 dB 1 937 .000 000 MHz
CH1 Markers2:-18 .359 dB2.00900 GHz1 2
3
4
5
5:-.16020 dB 1 975 .700 000 MHz
CH2 Markers1:-.16210 dB1.93700 GHz
2:-.24330 dB2.00900 GHz
3:-48 .886 dB2.05710 GHz
4:-8 .3259 dB1.83700 GHz
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Next Step: N = 6.
Internal Couplingsapproximately correct.
Input/output probes to beincreased.
EM-geometry of probesto be optimised.
Current Unloaded Qvalue 7000 9000.
CH1 S11 LOG 5 dB/ REF 0dB
START 1 894 .836 004 MHz STOP 2 144 .836 004 MHz
Cor
PRm
CH2 S21 LOG 10 dB/ REF 0 dB
Cor
PRm
1 ep 2 2 1 : 1:1
1
2
3
4
4:.25370 dB 2 070 .000 000 MHz
CH1 Markers1:-9 .2733 dB1.97500 GHz
2:-16 .391 dB2.01161 GHz
3:-19 .698 dB2.05000 GHz
1 2 3
4
4:-53 .609 dB
CH2 Markers1:-.83090 dB1.97500 GHz
2:-.14520 dB2.01161 GHz
3:-.55090 dB2.05000 GHz
CH1 S11 LOG 5 dB/ REF 0 dB
START 1 894 .836 004 MHz STOP 3 000 .000 000 MHz
PRm
CH2 S21 LOG 10 dB/ REF 0 dB
PRm
MARKER 52.66746807 GHz
1 ep 2 2 1 : 1: 5
1
23
4
5
5:-1 .7323 dB 2 667 .468 070 MHz
CH1 Markers1:-12 .762 dB
1.97500 GHz2:-17 .136 dB
2.01161 GHz3:-16 .030 dB
2.05000 GHz
4:-1 .5829 dB2.07000 GHz
1 2 3
4
5
5:-35 .030 dB
CH2 Markers1:-2 .2911 dB
1.97500 GHz2:-1 .7381 dB
2.01161 GHz
3:-3 .0676 dB2.05000 GHz
4:-56 .046 dB2.07000 GHz
Broadband
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Eventual Goal.
Diplexer unit.
N = 6 RX and TX.
Phased common junction,
physically using a simpletrough line construction.
Integrated with LNA
package.
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Discussion.
Proof of principle is apparent for compact triple mode,but not yet sufficient for useful application.
Practical implementation not clear, notably with respectto suspension of DR and also degree of external tuning.
Full identification of coupling mechanism, redundancy,proper linkage to network model. Experiment with use ofiris apertures. Space filling layout ?
Dual mode operation may be more sensible interim goal.
Eventual mixed dual and triple mode operation ?
Selective use of partial metal deposition directly toceramic.
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References.[1] Liang and Blair, High Q TE01 mode DR filters for PCS base stations, IEEE Trans. MTT-46, 12, 2493,
1998.
[2] Fiedziuszko et al, Dielectric materials, devices and circuits, IEEE Trans. MTT-50, 3, 706, 2002.[3] I.C.Hunter et al, Dual mode filters with conductor loaded dielectric resonators, IEEE Trans. MTT-47, 12,
2304, 1999.[4] I.C.Hunter et al, Triple mode hybrid reflection filters, IEE Proc. MAP-145, 4, 337. 1998.
[5] V.Walker and I.C.Hunter, Design of cross coupled dielectric loaded waveguide filters, IEE Proc. MAP-148,2, 91, 2001.[6] P.J.B.Clarricoats, Propagation along unbounded and bounded dielectric rods part 2, Proc. IEE 108C,
177, 1961.[7] J.D.Rhodes, General constraints on propagation characteristics of electromagnetic waves in uniform
inhomogeneous waveguides, Proc. IEE, 118, 7, 849, 1971.[8] T.Weiland, Eine methode zur losung der Maxwellschen Gleichungen fur sechs -komonentige Felder aufdiskreter Basis, AEU, 31, 116, 1977.
[9] G.Deschamps, Differential Forms, in E.C.Roubine (ed), Mathematics applied to physics, SpringerVerlag/UNESCO.
[10] T.Weiland, Finite integration and discrete electromagnetism, in C.Carstensen et al (eds), Lecture notes in
comp. sci. and eng. Vol. 28, Springer Verlag.[11] I.Munteanu and F.Hirtenfelder, Convergence of the FIT on various mesh types, Proc. German Microwave
Conference (GeMic05), Ulm, April 2005.[12] P.D.Sleigh, Asymmetric filter design for satellite communication applications, IEE colloquium on
microwave filters, IEE colloquium digest 1982/4, 1982 (6 pages).[13] R.J.Cameron, Advanced coupling matrix synthesis for microwave filters, IEEE Trans. MTT-51, 1, 1, 2003.[14] A.G.Lamperez, et al, Effective electromagnetic optimization of microwave filters and multiplexers using
rational models, IEEE Trans. MTT-52, 2, 508, 2004.