3 3 4 electromagnetic simulation of cavity filters

7/31/2019 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.


2/24

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.


3/24

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).


4/24

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.


5/24

Cavity Filter Technologies.

1. Multi-conductor coaxial / combline.

2. Dielectric combline.

3. Dual mode ceramic (metallised).

1

2

3


6/24

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


7/24

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


8/24

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.


9/24

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.


10/24

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


11/24

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.


12/24

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.


13/24

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


16/24

Field Distributions, Calculated Qu-factor.

Electric and magnetic field monitors at 2GHz (XY-plane):

Losses and unloaded Q-factor.

e-field h-field


17/24

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


18/24

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


19/24

Tuned Output of EM-analysis.


20/24

Final Comparison, N = 3.

CH1 S22 LOG 5 dB/ REF 0 dB

Cor

PRm


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


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


START 1 894 .836 004 MHz STOP 3 000 .000 000 MHz

PRm


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


22/24

Eventual Goal.

Diplexer unit.

N = 6 RX and TX.

Phased common junction,

physically using a simpletrough line construction.

Integrated with LNA

package.


23/24

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.

3 3 4 electromagnetic simulation of cavity filters

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