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Ansoft HFSS Engineering Note
Lumped RLC Elements in HFSS Version8
In Ansoft’s High Frequency Structure Simulator(HFSS),a specified impedance boundary condition has always referred to field values becau HFSS is a full-wave field simulator.You may wish to model a physical lumped resistance(R),inductance(L),or capacitance(C)element that is connected to the field or distributed model.
HFSS Version8enables you to specify any combination of parallel-connected lumped RLC elements on surfaces in terms of circuit definition by using lumped RLC boundaries.A typical application is the simu-lation of a Monolit Microwave Integrated Circuit(MMIC),in which the lumped elements are reprented by thin sheets.
HFSS Version8’s fast and interpolating frequency sweep options support the frequency dependence of an impedance,which consists of either a lumped inductance or a lumped capacitance,with the u of lumped RLC elements.HFSS’s3D Boundary Manager supports any combination of parallel-connected RLC elements on a surface.To model rial-connected lumped elements,define two rial-connected sur-faces for the rial elements.
This engineering note explains the difference between field and lumped impedances and prents applications for both cas.
Field and Lumped Impedances
Figure 1shows a thin,rectangular sheet on which a lumped impedance boundary condition will be defined.
Figure 1:Thin rectangular sheet
where:
•l is the length of the sheet
•W is the width of the sheet
•E t is the tangential component of the electric field on the impedance boundary surface
•H t is the tangential component of the magnetic field on the impedance boundary surface •I is the current flowing on the sheet
一团乱麻•c is a clod curve surrounding the sheet
•U is the voltage drop
•δis the thickness of the sheet
The definitions for the lumped and field impedances are:
The circuit quantities U and I can be expresd by the field quantities
as:
Z lumped U I ---=Z field E t H t
-----=U E t l òdl
E t l ==H t c ò°dc H t w I
==
Substituting the field quantities into the impedance definition yields:
党员转正介绍人发言稿
Z field is measured in ohms/square.It is also denoted by Z ϕ.
The shape of a lumped impedance surface is not always rectangular.An arbitrarily shaped surface is transformed into a rectangular-shaped surface by defining the length of the main current flow,as shown in the following figure:
Figure 2:Transformation of an arbitrarily shaped surface to an
equivalent rectangular-shaped surface
The width of the equivalent rectangular surface is:
where S is the area of the sheet.连接蓝牙耳机
The relationship between the lumped and field impedances is:
Define the length of the current flow in the 3D Boundary Manager.The area of the surface is calculated automatically.
Z lumped U I
---E t l H t w ---------Z field l w ---===Z field Z lumped w l
---=l
w S l
--≅Z lumped Z field l 2S ---=Z field Z lumped S l
2---=
The parallel-connected RLC lumped elements are assigned to the lected surface (e Figure 3)using the ur-defined current path:
The frequency dependence is taken into account as:
where:
•j is the imaginary unit,•ω is the angular frequency,2πf
Figure 3:Parallel-connected lumped RLC elements assigned to a boundary surface
饼形图R field R S l 2---=L field L S l 2---=C field C l 2
中华梦
S ---=1Z field ------------1R field ------------j ωC field 1ωL field ----------------–èø
+=1
–
Parallel Plate Waveguide Terminated with a
Parallel Lumped RLC Circuit
In the following example,a parallel plate waveguide is terminated by a parallel-connected RLC circuit,as shown in
Figure 4.
Figure 4:Parallel plate waveguide terminated by parallel lumped RLC elements
R =33.75Ohms,L =0.1nH,C =2.533pF
The magnitude of S 11was calculated using HFSS’s new lumped element boundary feature.The problem has an analytical solution.The magnitude of parameter S 11can be calculated as:
巨人的花园where:
and Z w =377Ohms The field values are given by:
Figure 5shows good agreement between the results calculated by the analytical method and the HFSS results.HFSS results were calculated using the interpolating sweep method,a frequency sweep in which solved frequency points are chon so that the entire solution lies within a specified error tolerance.Approximately 2000tetrahedra were ud and the solution time was approximately 71/2minutes on a Pentium/266MHz PC.
S 11Z 2Z w –Z 2Z w
+------------------=1Z 2-----1R field ------------j ωC field 1ωL field ----------------–èø
揣测是什么意思+=R field R w l ---=L field L w l ---=C field C l w
---=
