Zeland Software, Inc. has introduced the IE3D Electromagnetic Simulation and Optimization Package since 1993. IE3D, a method of moment (MOM) simulator, has many good features in modeling planar and 3D circuits and antennas in layered dielectric environment. The IE3D is easy-to-use where it is accurate and efficient in modeling wide range structures such as microstrip circuits and antennas, strip-line circuits, CPW circuits and antennas, coaxial structure with uniform dielectric filling, inverted-F antennas, dipoles and other wire antennas, high speed transmission lines, high speed digital circuit interconnects, high speed digital circuit packaging. However, moment method codes have some rooter disadvantages in modeling 3D dielectric structures, waveguide structures and structures emphasizing near field distribution.
FIDELITY is a finite-difference time domain (FDTD) based full-wave electromagnetic simulator. Many researches had been focusing on the development of FDTD algorithm within the past 20 years. FDTD has the following unique features compared to frequency domain simulation algorithms such as MOM and finite element method (FEM):
- FDTD is easy to implement where its basic principle is to use finite difference to represent the differentials in the Maxwell's equations. By allocating the Yee-algorithm, we combine the electric field and magnetic field together so as to convert the Maxwell's equations into algebraic equations.
- The final algebraic equations for FDTD are in the time-marching style. As the large matrix equations in MOM and FED are common, thus FDTD does not have to create large them. The memory requirement for FDTD is proportional to N compared to N to N2 for FEM and N log(N) to N2 for MOM. The time requirement of FDTD is also more proportional to N compared to N2 for FEM and N2 to N3 for MOM. The basic computational requirement for FDTD is normally much higher than that for MOM for modeling small and medium size structures, for large structures, although FDTD may require much less computational resources than MOM. Moreover, FDTD normally requires much less computational resources than FEM.
- A FDTD simulation normally can create a wide-band frequency response. MOM and FEM always require sweeping in frequency domain.
- FDTD simulators have the pros where it can handle complicated dielectric structures much easier than MOM and FEM.
As it is, the FDTD simulator, FIDELITY, is complementary to the MOM simulator IE3D developed by Zeland Software, Inc.
On the other hand, these are some equations that are used by the simulator to predict the required results:
where er is the real dielectric constant; s is the conductivity; w is the angular frequency; e0 is the complex dielectric constant in free space (8.86 10-12 F/m); tand is the loss tangent. In the other word, we have,
The Loss Tangent is always a non-negative number and the imaginary part of permittivity is always a non-positive number. In practical applications, users normally use either tand or s as frequency independent values. However, we can see from (3) that, when tand is frequency independent, s will be frequency dependent, or vice-versa. In order to resolve this inconsistency, we define the tand and s in the IE3D as in (3):
You should understand that this is not the true definition of the tand and s. It is just for the convenience of users. If you want to define the material with frequency independent tand, you should define s = 0 for the dielectrics. If you want to define the material with frequency independent s, should define tand = 0 for the substrate. However, if you define non-zero values for both tand and s, both will be used to calculate the erc