filterdesign and tuning using cst studio suite€¦ · filter design and tuning using cst studio...
TRANSCRIPT
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Filter Design and Tuning
using CST Studio Suite
Franz Hirtenfelder
Applications Engineer
CST Branch Office Munich
Elsenheimer Strasse 55
D-80687 München (Munich)
Germany
Tel: +49 89 2420 828 101, Mob: +49 170 9160 110, Fax: +49 89 2420 828 198
Email: [email protected], Web: www.cst.com
Abstract: Bandpass filters with small fractional bandwidths are quite challenging to design and tune.
After reviewing various tuning techniques using CST Studio Suite a further approach to compute
coupling factor bandwiths simultaneously is demonstrated. A combination of 3D and circuit models
team up with new built in optimizers to efficiently tune bandpass filters. The new System and
Assembly Modelling (SAM) in CST Studio Suite enables the interdisciplinary usage of coupled EM-
Thermal- Structural and Sensitivity analyses within parameter-sweeps and optimization loops and is
demonstrated on a simple test vehicle. Some accuracy considerations with respect to various meshing
techniques conclude this presentation.
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Agenda
Introduction
Tuning Methods
Solver selections, accuracy
System Assembly and Modeling (SAM)
Guidelines and Summary
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Specifications Circuit Design
Analytical models
Empirical adjustments
on the structure Measurements
Typical Flow Chart of the Filter design and Tuning process
Introduction: Flow Chart
3D EM Simulation
Dimensioning
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Introduction: from equations to a 3D model
3D
o
jjii
ijf
cc
ccbw *
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Introduction: from equations to a planar model
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Parameterization Definition of Goal function Optimizer Choice
1. Define structure parameters
2. Define parameter ranges
Introduction: General Optimizer Setup
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
local global
Genetic Algorithm
Particle Swarm Optimization
Nelder-Mead Simplex Algorithm
Trust Region Framework
Interpolated Quasi Newton
Classic Powell
Initial parameters already
give a good estimate of the
optimum, parameter ranges
are small
Initial parameters give a
poor estimate of the
optimum, parameter
ranges are large
x
y Example:
Waveguide Corner Goal:
Minimize S11
x
y
CMA Evolutionary Strategy
Introduction: Optimizers
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Classic Powell: Quasi Newton: Nelder Mead
Particle Swarm Genetic Algorithm
Trust Region Framework
(TRF)
Introduction: Optimizers
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Nelder Mead: 70 Iterations
TRF: 15 Iterations
Introduction: Convergence Speed
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Introduction: Summary
To summarize
• In general many parameters to consider
• Wide parameter ranges necessary in order not to
miss an optimum
-> global optimizer strategies required
A possible solution to speed up the tuning effort
is „pretuning“:
Advantage:
local optimizers can be used in addition
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Agenda
Introduction
Tuning Methods
Solver selections, accuracy
System Assembly and Modeling (SAM)
Guidelines and Summary
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Tuning Methods: Introduction
Classification of Filters
LP-Prototype
90º 90º 90º
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Coupling Bandwidth,
Group delay
GroupDelay-Macros and
ResultsTemplates available for CST-
MWS and CST-DS
Coupling-Coefficients and Td-Values
computations are available via Macro
Tuning Methods: Group Delay
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Tchebychev Filter
===================
Order = 4
Bandwidth = 25 MHz (rel. BW=2.3%)
Center Frequency = 1100 MHz
Passband ripple = 0,01 dB (1,100747 VSWR)
Return loss = -26,3828 dB
Normed g values:
-------------------------------------------
g1 = 0,7129
g2 = 1,2004
g3 = 1,3213
g4 = 0,6476
g5 = 1,1008
Corresponding coupling coefficients in MHz / (rel):
-------------------------------------------
k_E = 35,07 (0,0318809)
k1_2 = 27,03 (0,0245688)
k2_3 = 19,85 (0,0180464)
k3_4 = 27,03 (0,0245688)
k_out = 35,07 (0,0318809)
Group Delay Time
----------------
t_d1 = 18,153 ns
t_d2 = 30,566 ns
t_d3 = 51,798 ns
t_d4 = 47,057 ns
t_d5 = 71,78 ns
1
2
dtke
2
..1 ode
ftQ
Only two variables at a time!!
Tuning Methods: Group Delay
90º 90º 90º
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Tuning of a Dual Mode Filter Iris Coupled Cavity
Filter
Hairpin
Filter
Short
Tuning Methods: Group Delay Examples
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Port 1 is excited
Tuning Methods: Field Strengths
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
The E-max is recorded vs. frequency. What can be observed is that the
peaks of E-max coinside with the peaks of the transmission-groupdelay,
as expected. The groupdelay may act here as a probability function of
energy: High fields when there is a high chance of energy concentration
Tuning Methods: Field Strengths
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Add two small discrete ports or
Face ports to excite the modes
Even-Mode F1 Odd-Mode F2
2
2
2
2
1
2
2
2
1
2
2
2
2
1
2
2
2
1
1
2
2
1
2
1_
SS
SS
FF
FF
S
S
S
ScorrectedCBW
Tuning Methods: Pin-Probes and Eigenmodes
CBW
S1, S2… single cavity modes
Pin Probes:
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Discrete Ports or Face-
Ports are assigned at
the Resonators
Tuning Methods: Port-Tuning
Initial 3D results
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Use Tuner for C3 and C4 to
manually adjust a good filter
response (resonance-tuning)
Tuning Methods: Port-Tuning
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Coupling between resonators are designed as negative Cs (act as TLs 90 deg)
1. Use Tuner for C34
and C45 to manually
adjust a good filter
response
Tuning Methods: Port-Tuning
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Correlation to the real Geometry (Space Mapping):
Once the optimum for a certain capacitor has been found, we need to find out their relation to the real 3D geometry.
This is done by slightly changing the 3D model for the given resonator where the capacitor is attached to. Then we
need to retune the circuit again to account for this geometrical change. Now we have two positions in 3D and two
values for the capacitance C of the circuit. With a linear extrapolation we are able to find out the desired
mechanical change to set the capacitance to zero, meaning that the lumped capacitance has no impact anymore and
can be eliminated in the circuit.
Mech. Position p1 Ca= x1 F
Mech. Position p2 Ca= x2 F
p1 p2
Ca@p1 =x1F
Ca@p2=x2F
Ca
p px
0
21
1211
xx
ppxppx
Tuning Methods: Port-Tuning
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
To compute the coupling factors k12,k23,
etc…, the Input and Output converters are
separated from the main part of the filter.
Ports of 50 Ohms are assigned and connected
to each resonator. S-Parameter and Y-
Parameter are computed via a DS task. The
imaginary parts of the Y-matrix are used to
compute the coupling factors simultaneously.
3 4 5 6
k12 k23 k34
Tuning Methods:Tuning via Slope Susceptance
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
k12
k34 k23
))_().(_(((/)(.2.2
derivYimderivYimsqrYim
df
dB
df
dB
Bk jjiiij
jjii
ij
ij
Tuning Methods:Tuning via Slope Susceptance
Templates:
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Circuit setup for Coupling Coefficients
To get the coupling coefficients simultaneously the circuit is modified such that each resonator is
attached to a e.g. 50 Ohm port. The resulting Y-Matrix is used to compute all couplings:
Tuning Methods:Tuning via Slope Susceptance
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
The chirp Z-Transformation can be used as a
more flexible means to calculate discrete Fourier
transforms. In particular, the unit circle version
(known as chirp-transform) can be used to create
a high-quality zoom function.
Golden (reference) Filter required
S-Parameter
ICZ-Bandwidth
fo
Inverse Chirp-Z response
1 2 3 4
Tuning Methods:Inverse Chirp Z
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Tuning of 1st resonator
Tuning of 2nd resonator
1 2
Tuned to a min.dip
Tuning Methods:Inverse Chirp Z
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Example of a Diplexer: Groupdelay
Rx part is considered,
but not shown here,
posts are short out Red curve: Inital groupdelay for the
first two posts next to the common
port after the separate tuning of TX
and RX
Green Curve: tuned Groupdelay
TX
RX
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
1D Results > invChiprZ_TX
1D Results > invChiprZ_RX
InvChirpZ transformation is applied to the
open filter and it can clearly be seen that
some of the resonators are not tuned to
their center frequency f1 and/or f2. This
is indicated by the dips of the response.
The coupling seems to be rather ok,
repesented by the time-delay.
The advantage of this method is that the
individual mistuned resonators can be
identified!
2nd resonator mistuned
Example of a Diplexer: InvChirpZ
f1 f2
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Agenda
Introduction
Tuning Methods
Solver selections, accuracy
System Assembly and Modeling (SAM)
Guidelines and Summary
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Time Domain (TD) Frequency Domain (FD)
Eigenmode (E)
Modal (Resonant Fields)
Lossy/Lossless
Solver Selection
Resonant: Fast S-parameter (MOR)
General Purpose
Resonant: S-Parameter, Fields (Modal Analysis)
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Accuracy vs. Meshdensity
20/20 30/30
10/10
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Re_tuner_L_2
Re_tuner_L_1
Coupl_tuner_23
Ke_offset
Variable / Mesh Coarse 10/10 Medium
20/20
Fine 30/30 40/40 60/60
Coupl_tuner_23 7.5 mm 6.35 6.35 6.35 6.35
Ke_offset 5.68 5.6 5.6 5.45 5.45
Re_tuner_L_1 6.107 5.8 5.85 5.722 5.731
Re_tuner_L_2 5.165 4.94 4.97 4.924 4.942
k23 18.2 18.2 18.2 18.22 18.22
CPU Time (HEX MOR) 26s 129s 485s 18m 60m
Accuracy vs. Meshdensity
k12
k23
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
FD General Purpose Tet-Mesh
Curved Tetras To avoid Mesh Noise:
•Dummy-elements
•Slicing of tuners
(switching of materials)
•Grid-Movement
•Sensitivity
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Agenda
Introduction
Tuning Methods
Solver selections, accuracy
System Assembly and Modeling (SAM)
Guidelines and Summary
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
SAM: Multiphysics Simulation
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Coupling between Simulation Projects
SAM: Multiphysics Simulation
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Parameter Sweep / Optimization
aperture
S-Parameter (pure EM)
S-Parameter
(including Therm./mech.
Deformation)
SAM: Multiphysics Simulation
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Agenda
Introduction
Tuning Methods
Solver selections, accuracy
System Assembly and Modeling (SAM)
Guidelines and Summary
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Some Guidelines
• Start out with a rather coarse mesh models
• Don‘t use meshadaptation
• Pretuning is helpful to apply local optimizer
strategies
• Select the appropriate solver
• Refine the mesh and retune again
(Parameter ranges are a lot smaller)
until parameter changes are smaller than a
given manufactoring tolerance
CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com | May-12
Summary
• CAD Modeler easy to use with respect to
parameterization
•CST Complete Technology™: TD, FD, E, Th, Mech, MP
•Various optimizer strategies
•Optimization and parameterization control via
complex post processing templates
•Flexible link to circuit simulator CST- DESIGN
STUDIO including CST- MICROWAVE STUDIO –
submodels
• Various tuning procedures available for a successful
tuning