Bijan Houshmand

FDTD analysis of dielectric resonators with curved surfaces

In this paper, the finite-difference time-domain (FDTD) method is applied to calculate the resonant frequency of dielectric resonators (DRs) with curved surface. The contour-path integral FDTD (CFDTD) is modified to deal with the curved surface of the dielectric body while the traditional rectangular cells are maintained. Results are compared with theoretical values and staircase approximation, and show that the present method is more accurate than the staircase approximation.

Full-wave analysis of packaged microwave circuits with active and nonlinear devices: an FDTD approach

This paper presents a comprehensive full-wave analysis of packaged nonlinear active microwave circuits by applying the extended finite-difference time-domain (FDTD) method. Based on the approach of using equivalent sources, the device-wave interaction is characterized and incorporated into the FDTD time-marching scheme. As a consequence, analysis of linear and nonlinear properties, including harmonic generation and intermodulation, can be accomplished by employing a large-signal device circuit model. The implementation is first validated by comparing results of FDTD and HP MDS simulation of the circuit without the packaging structure. The analysis then goes beyond the capability of the circuit simulator to include the packaging effect. This analysis is useful in circuit design involving electromagnetic compatibility/electromagnetic interference (EMC/EMI) problems.

Modeling of microwave active devices using the FDTD analysis based on the voltage-source approach

This letter describes a voltage-source-based formulation of the extended finite-difference time-domain algorithm for the purpose of modeling microwave devices. The device-wave interaction is fully characterized by replacing the lumped devices with equivalent voltage sources in the device region, which in turn generate electromagnetic fields according to Faradays law. This formulation is applied to the analysis of a typical microwave amplifier, which includes a three-terminal active MESFET device. Simulation results are in good agreement with measured data.

Modeling of nonlinear active regions with the FDTD method

The finite-difference time-domain (FDTD) method is extended to include nonlinear active regions embedded in distributed circuits. The procedures necessary to produce a stable algorithm are described, and a single device cavity oscillator is simulated with this method.<<ETX>>

Coupled-mode theory of the Raman effect in silicon-on-insulator waveguides

Coupled-mode theory is used to calculate Raman gain and spontaneous efficiency in silicon waveguides with cross-sectional areas ranging from 0.16 to 16 microm2. We find a monotonic increase in the Raman gain as the waveguide cross section decreases for the range of dimensions considered. It is also found that mode coupling between the Stokes modes is insignificant, and thus polarization multiplexing is possible. The results also demonstrate that for submicrometer waveguide dimensions the Einstein relation between spontaneous efficiency and stimulated gain no longer holds.

Small signal analysis of active circuits using FDTD algorithm

The FDTD method is extended to analyze a microwave amplifier. This amplifier includes matching circuits, DC bias circuits, and an active device. Equivalent current sources are used to model the active element. With the small signal model of the active element, the FDTD full-wave simulations show good agreement with measured results. >

Global time-domain full-wave analysis of microwave circuits involving highly nonlinear phenomena and EMC effects

The global time-domain analysis of microwave circuits involving highly nonlinear phenomena such as injection locking and intermodulation, along with parasitic effects and electromagnetic compatibility (EMC) issues is presented in this paper. Employing the concept of equivalent sources, the device-wave interaction is characterized and incorporated into the finite-difference time-domain method. The investigation of nonlinear phenomena is accomplished by utilizing a large-signal device circuit model. Measured results are also provided for comparisons with simulated results. The applicability of this equivalent-source algorithm for investigating EMC effects is also demonstrated. A correspondence between simulated and measured EMC phenomenon indicates the usefulness of this algorithm in providing an effective tool for real world radio-frequency front-end circuit designs.

FDTD analysis of a metal-strip-loaded dielectric leaky-wave antenna

The finite-difference time-domain (FDTD) method is used to analyze a dielectric leaky-wave antenna comprising metal strips etched on a rectangular dielectric rod. The radiation patterns of the leaky-wave antenna with and without the transition are determined by using FDTD. The effects of the launching discontinuity on the performance of the antenna are discussed. In addition, the application of the perfectly matched layer (PML) technique to the three-dimensional (3-D) dielectric waveguide and its performance, compared to those of the Murs (1981) first-order and super-absorbing Murs first-order absorbing boundary conditions (ABCs) are described. In addition, the effects caused by perturbation on the wave propagation characteristics of dielectric waveguide are also discussed. The FDTD results are verified by a W-band experiment and found to be in good agreement.

The implementation of time-domain diakoptics in the FDTD method

The time-domain diakoptics is implemented in the finite-difference time-domain (FDTD) method with two types of connecting interfaces: i) directional interface (TLM-type), and ii) total-field interface (FDTD-type). The FDTD-type interface provides a more efficient way to realize time-domain diakoptics than TLM, especially for device optimization problems. To emulate the TLM-type interface in FDTD, two novel algorithms are developed in this paper. One is to implement an ultra-wideband absorbing boundary on the excitation plane during excitation. The other is to separate directional waves without the knowledge of incident waves. For a large circuit with cascaded modules, sequential and parallel algorithms are provided to connect them. With these connecting algorithms, time-domain diakoptics is one candidate method to realize modular and parallel computation in FDTD simulations. The validity of these algorithms is confirmed by comparison with simulated results from Microwave SPICE. >

Efficient modes extraction and numerically exact matched sources for a homogeneous waveguide cross-section in a FDTD simulation

Using the orthogonality of modes, an efficient real-time modes extraction is available for the finite-difference time-domain (FDTD) simulation of a waveguide. This paper demonstrates that, even at one cell beyond the discontinuity, S-parameters still can be accurately extracted. Combined with numerically exact matched sources, the computational volume for S-parameter computation can be reduced to a minimum.<<ETX>>