Aspects of RF Simulation and Analysis Software Methods. David Carpenter. Remcom. B = t. D t. Remcom (Europe)

Transcription

1 Remcom (Europe) Central Boulevard Blythe Valley Park Solihull West Midlands England, B90 8AG (fax) Aspects of RF Simulation and Analysis Software Methods David Carpenter Remcom E B t H J + D t

2 Solving Maxwell s Equations Differential, integral and asymptotic approaches Popular examples: FEM (finite element method) normally frequency domain FDTD (finite difference time domain) BEM (boundary element method) MoM (Method of Moments) GTD/UTD (Geometrical/uniform theory of diffraction) with SBR (shooting and bouncing rays) PO Physical Optics B µh B 0 D E

3 Finite Difference Time Domain Method Explicitly solves Maxwell s Equations in time domain Subdivide geometry into spatial grid Grid is small compared to wavelength Grid is small compared to geometry features Step through time B µh B 0 D E

4 FDTD Applications Antennas-impedance, radiation, efficiency, matching SAR determination for Cell Phones, Pagers, WiFi MRI design FCC Acceptance for Medical Implant Communications Service (MICS) Microwave Circuits, Waveguides, Fiber Optics, S-Parameters EMC/EMI, Shielding, Coupling Scattering, Radar Cross Section Propagation Photonics Special Materials, including Nonlinear, Dispersive, Negative Index (NIM) and Anisotropic Plasmas (Exhaust, Re-entry) Lightning, EMP B µh B 0 D E

5 FDTD Advantages Simplicity: no Green s functions, no matrices, no asymptotics, no shape functions Wide frequency bandwidth from one calculation Wide variety of materials: dielectric/magnetic, frequency-dependent, nonlinear, anisotropic General geometries (computer memory not dictated by shape) Scales well so suitable for electrically large problems Fits well in parallel computer architectures B µh B 0 D E

6 FDTD Disadvantages Moment Method does not need to solve for fields in free space At very low frequencies the FDTD time step may be very small compared with the period of the sine wave, so many time steps may be needed. B µh B 0 D E

7 Maxwell Curl Equations Faraday s Law Ampere s Law Now assume 1-D propagation in z-direction 1-D Curl Equations B µh B 0 D E

8 Apply Finite Difference Approximation Quantize Space and Time z k z t n t Locate E and H fields centered in time and space Apply finite differences B µh B 0 D E

9 Horn Antenna - Typical Application (1) Pyramidal Horn Antenna Illustrate some of the capabilities of FDTD The horn geometry could be generated using CAD import, or using sweeping and/or shelling For this example a built-in horn primitive of XFDTD will be used B µh B 0 D E

10 Horn Antenna - Typical Application (2) Enter the Horn Parameters for the Horn and Waveguide Feed as shown in the menu B µh B 0 D E

11 Horn Antenna - Typical Application (3) FD CAD object and mesh B µh B 0 D E

12 Horn Antenna - Typical Application (4) Near Field display B µh B 0 D E

13 Horn Antenna E-Plane Gain Pattern Antenna Far Zone Gain B µh B 0 D E

14 BioEM Applications (1) FDTD well suited for Bio-EM analysis such as SAR (Specific Absorption Rate) Usual to start with a model of the human body including all tissue details FDTD models this well with a small mesh throughout B µh B 0 D E

15 E x, y, z BioEM Applications (2) SAR calculated from the electric fields and tissue characteristics SAR σ x E 2 x x 2 + σ y E 2 y y 2 + σ z E 2 z z 2 where SAR σ x, y, z E x, y, z x, y, z Specific Absorption Rate (W/kg) -electrical conductivity (S/m) -magnitude of electric field (V/m) -material density (kg/m3) B µh B 0 D E

16 E x, y, z BioEM Applications (3) B µh B 0 D E

17 GTD/UTD General purpose ray-based electromagnetic analysis for radiation, antenna, scattering, propagation and EMC applications A ray-based EM solver based on the UTD (Uniform Theory of Diffraction) Evaluate E-fields using UTD with material dependent reflection, transmission and diffraction coefficients Combine E-fields with antenna patterns to find received power, time and frequency domain E-field, far-zone radiation patterns, path loss, RCS, etc B µh B 0 D E

18 Hybrid SBR/GTD Approach Objects and features are represented by vector data Positions of Tx/Rx point are required Find geometrical ray paths by using a fast ray tracing procedure based on the Shooting and Bouncing Ray (SBR) method Construct the geometrical optics and the edge diffracted paths from geometrical paths Evaluate E-fields using the Uniform Theory of Diffraction (UTD) and material dependent reflection and transmission coefficients Combine E-fields with antenna patterns to find signal strength, angle of arrival, etc. B µh B 0 D E

19 Line-of-Sight Rays and Reflected Rays B µh B 0 D E

20 Diffracted Rays B µh B 0 D E

21 Multiple Transmitters and Interactions B µh B 0 D E

22 Suitable for electrically large models (1) Geometric features should be greater than a wavelength B µh B 0 D E

23 Suitable for electrically large models (2) Model size/computation time limited by number of facets, edges and vertices B µh B 0 D E

24 May include creeping waves Creeping wave propagation allows propagation across surfaces and around cylinders etc. B µh B 0 D E

25 May be used for propagation studies (1) Indoor B µh B 0 D E

26 May be used for propagation studies (2) Outdoor B µh B 0 D E

27 May be used for propagation studies (3) Time of arrival B µh B 0 D E

28 May be used for propagation studies (4) Outdoor - Indoor B µh B 0 D E

29 Summary There are a number of methods for EM simulation All have strengths and weaknesses Select the correct method for the application Most commercial packages are relatively easy to use based on latest GUIs Graphical images provide an insight into results that hand calculations and simple numerical methods may not. B µh B 0 D E