An Introduction to the Finite Difference Time Domain (FDTD) Method & EMPIRE XCcel

Transcription

1 An Introduction to the Finite Difference Time Domain (FDTD) Method & EMPIRE XCcel Simulation Model definition for FDTD DUT Port Simulation Box Graded Mesh six Boundary Conditions 1

2 FDTD Basics: Field components Yee cell H z Spatial discretization H x E z E y H y Ex FDTD Basics: Field components Yee cell H z Spatial discretization H x E z E y H y Ex 2

3 FDTD Equivalent Circuit H z H x E y H y E z Ex Basics: Time discretisation Time step ~ min E 0 E n-1 E n E n+1 Initial values t t t t steady state H 0 H n-1 H n H n+1 Time t Time domain tracking of EM field Time Step limited by spatial resolution avoid small details in simulation model εr t min c x y z 0 1 IMST GmbH - All rights reserved 3

4 Typical Simulation flow Geometric model setup import geometry create objects Electric Property definition material properties Excitation definition Ports, Plane wave Simulation settings frequency range meshing structure type Simulation Simulation results check results (time domain pulses, s-parameters, ) IMST GmbH - All rights reserved Geometric Model Setup 1 Layer Concept Objects are grouped on different layers which have a predefined default height (new objects created on this layer will have these height) each layer defines for all objects a certain electrical property / special property layer name layer direction & height material property Hint: Objects can have a direct property definition. This definition would overwrite the definition on the layer 4

5 Geometric Model Setup 2 Object Creation Objects are created on the current layer (green colored layer name) Box and Polygon objects are created with the default height (can be changed later) create polygon current layer create box V5.20: Object Library Wire Objects Example All values may be parametric Vorlage 5

6 Scripting Interface examples complex polygon objects parabolic shapes bended polygon lines user defined solid objects wrapped sheets transformed objects patch antenna feed network Feb-08 IMST GmbH - All rights reserved Electric property definition Define Layer/Object Properties (dielectric, conductor, ) layer properties Hint: Start simulating without losses for basic investigations IMST GmbH - All rights reserved 6

7 Supported Materials... Materials Library Lumped resistors, capacitors, inductors Line resistors for, e.g. bond wires, power lines Sheet resistors (R-square, distributed loads) Conductive sheet model for efficient broadband loss calculations Dielectrics with loss tangent Frequency dependent dielectrics (Debye model 1 st to n th order) Double negative Metamaterials with Drude characteristic Anisotropic dielectric and magnetic tensors including losses Surface metallization Voxel Model supporting tissues Vorlage Boundaries Boundary Conditions (BCs) absorbing hard PML sheet electric magnetic PML (Perfectly matched layer): consists of several lossy layers needed for antenna simulations which are matched to each other sheet : resistive sheet with n x 377 Ω Rsquare, faster than PML, only for used for circuit simulations perpendicular waves no reflection 7

8 Supported Excitations... Feed Library Lumped ports, e.g. for differential ports Microstrip feed Coplanar waveguide feed Triplate waveguide (symmetric / asymmetric) Coaxial line feed (circular, square) TE / TM waveguide modes (arbitrary cross section) (multiple) Plane waves (e.g. RCS calculation, homogeneous field) Voltage / current sources (e.g. for user defined ports) Multiple weighted excitations including time delay User defined pulse shape Vorlage Ports in Empire Ports Absorbing (via absorbing BC) resistively terminated Transmission Line-Ports Wave Guide Ports Concentrated Ports (w/ TL) Lumped Ports 8

9 Resistive terminated ports 1 Port is perpendicular to drawing plane Ports can be placed inside simulation area Simulation Settings Define drawing unit, frequency range, boundary conditions Drawing unit Frequency range Mesh type Hint: start simulating for a new project with a coarse mesh; refine mesh later use Open 4 or Open 6 for antennas (4 or 6 cells thick pml boundary) use magnetic (open) or resistive sheet for circuit structures without radiation Boundary conditions 9

10 Time Domain Simulation: Digital Pulse Port 2 voltage in V /sub-1/ut1./sub-1/ut2./sub-1/ut3./sub-1/ut timesteps Simulation Results Voltage: Time domain ports S-parameters Hint: S-parameters can be created at any time during simulation: - switch to simulation control tab - select Postprocessing -> Start -> PostProc 10

11 2D Results Time Signals Impedances, Admittances Scattering parameters Smith Chart, Touchstone Files Field path & Integration Radiation Pattern User Defined Equations Vorlage 3D Results Near fields (E, H, J, P) Arrows, contour- & surface plots 3D far field visualization Animation (Phase loop, frequency loop, time stepping) refraction at metamaterial wedge 4x4 array antenna Vorlage 11

12 Near-to-Farfield Transformations Metal dipole source λ/2 Near to far field transformation Near-to-Farfield Transformations Far field Near field Far field Far field Near field Far field Near field: local resonance (reactive) Far field: Waves are relieving (radiation) 12

13 Near-to-Farfield far Transformations field transformation Near field box: λ/16 Distance to radiator and boundary Simulation domain: Open Boundaries Near field recording: E, H is recorded on surface Near field: local resonance (reactive) Far field: Waves are relieving (radiation) Near-to-Farfield Transformations non-uniform radiation: certain directions are preferred Directivity = D(θ,ϕ) 13