Application of the FD-TD method to the analysis of circuitsdescribed by the two-dimensional vector wave equation

A class of microwave circuits described by a two-dimensional vector wave equation is defined. It is proposed to refer to them as vector two-dimensional or 2-DV circuits to distinguish them from circuits described by a two-dimensional scalar wave equation (typically referred to as 2-D circuits). It is shown that the 2-DV class contains some planar circuits filled with anisotropic media, two-dimensional waveguide discontinuities, and circular waveguide discontinuities. Calculation of dispersion characteristics of inhomogeneously filled hollow waveguides is an eigenvalue problem belonging to the 2-DV class. Application to the finite-difference-time-domain (FDTD) method to the analysis of 2-DV circuits is described. Examples show the efficiency of the method for several types of circuit     

Properties of the FDTD method relevant to the analysis of microwave power problems

The objective of the paper is to provide a systematic consideration and generalization of properties and features of the FDTD method in the context of its use in solving microwave power problems. This is aimed at filling the gap between the general theory of the FDTD method and the specific practice of its applications by microwave power engineers. The paper starts with a comparison of FDTD to other methods like FEM, from the perspective of microwave power simulations. It then discusses FDTD-specific models of lossy and dispersive media, conformal boundaries, field singularities, and modal excitation as well as error bounds due to numerical dispersion. Theoretical overview is illustrated with examples. References are provided to the literature where more details and application notes can be found.     

A transformed symmetrical condensed node for the effective TLManalysis of guided wave problems

A transmission line matrix (TLM) algorithm for the effective solution of arbitrary guided wave problems is proposed. The algorithm uses an appropriately transformed symmetrical condensed node (SCN) introduced herein. In comparison with the previous SCN TLM formulation for the analysis of guiding structures, the approach maintains equivalent accuracy and generality while providing a 50% gain in terms of required computer memory and time. The advantages of the new algorithm are verified by means of several examples, including full-wave analysis of waveguides filled with anisotropic and lossy media     

Comments on 'A new finite-difference time-domain formulation and its equivalence with the TLM symmetrical condensed node' (and reply)

For the original article see ibid., vol.39, no.12, p.2160-9 (1981). The commenters summarize the conclusions of the above-titled paper by Z. Chen et al. in five statements. They show that the first four are partly incorrect and the fifth is misleading. In their reply, Chen et al. argue that these five statements are the commenter's conclusions, not theirs. They discuss these statements, agreeing with some of the commenters' points and disagreeing with others.<>     

Portable Automated Radio-Frequency Scanner for Non-destructive Testing of Carbon-Fibre-Reinforced Polymer Composites

A portable automated scanner for non-destructive testing of carbon-fibre-reinforced polymer (CFRP) composites has been developed. Measurement head has been equipped with an array of newly developed radio-frequency (RF) inductive sensors mounted on a flexible arm, which allows the measurement of curved CFRP samples. The scanner is also equipped with vacuum sucks providing mechanical stability. RF sensors operate in a frequency range spanning from 10 up to 300 MHz, where the largest sensitivity to defects buried below the front CFRP surface is expected. Unlike to ultrasonic testing, which will be used for reference, the proposed technique does not require additional couplants. Moreover, negligible cost and high repeatability of inductive sensors allows developing large scanning arrays, thus, substantially speeding up the measurements of large surfaces. The objective will be to present the results of an extensive measurement campaign undertaken for both planar and curved large CFRP samples, pointing out major achievements and potential challenges that still have to be addressed.     

Computer-aided analysis of arbitrarily shaped, coaxialdiscontinuities

The author proposes a method of analyzing a coaxial discontinuity arbitrarily shaped in two dimensions (radial and longitudinal) but maintaining its axial symmetry. It is shown that under such assumptions the equations to be solved correspond to the equations describing an equivalent planar circuit filled with a nonuniform medium. These equations are solved by a version of the finite-difference time-domain method. The method produces a universal computer algorithm capable of solving a wide range of practical problems with no analytical preprocessing. The examples presented show that the method can be effectively used in engineering applications     

An alternative approach to FD-TD analysis of magnetized ferrites

This paper presents a new approach to the finite difference-time domain (FD-TD) analysis of magnetized ferrites. An equivalent lumped circuit of an FD-TD cell filled with such a medium is developed. Then the lumped circuit is used to propose a new FD-TD algorithm. This algorithm is verified on canonical examples and is shown to be simple, accurate, robust and computationally more effective than the previously published approaches.     

Analysis of sub-THz radiation detector built of planar antenna integrated with MOSFET

In this paper an approach to analysis of responsivity of MOSFET-based detectors of THz radiation has been presented. The authors have analyzed the substrate modes that affect performance of antennas that are always used as a part of detecting structures, and should be accounted for by proper choice of the substrate geometry. Then, a methodology to combine extracted properties of an arbitrary antenna with properties of the transistor channel has been described and employed to estimate responsivity of a detector built of a particular MOSFET integrated with several antenna structures. Finally, example detectors were fabricated and measured using sub-THz radiation sources operating in the combined bandwidth 220–360 GHz. Measurement results were compared with predictions which lead to conclusions on possible levels of the impedance of the transistor channel at these frequencies.     

Wide-band S-parameter extraction from FD-TD simulations for propagating and evanescent modes in inhomogeneous guides

This paper proposes a new method of S-parameter extraction from finite-difference time-domain simulations. Unlike the previously published methods, the present method extracts the frequency-dependent mode impedance and propagation constant directly from the three-dimensional simulations. This makes it accurate and computationally effective in wide-band analysis. This paper provides examples of calculations including difficult cases of inhomogeneous or lossy structures, with the frequency band spanning below and above the cutoff frequency. Special attention is given to the S-parameter extraction for evanescent modes. It is shown that the available literature provides insufficient and sometimes confusing background in this regard. Thus, a new consistent theoretical background is presented.     

Analysis of arbitrarily shaped two-dimensional microwave circuitsby finite-difference time-domain method

A version of the finite-difference time-domain method adapted to the needs of S-matrix calculations of microwave two-dimensional circuits is presented. The analysis is conducted by simulating the wave propagation in the circuit terminated by matched loads and excited by a matched pulse source. Various aspects of the method's accuracy are investigated. Practical computer implementation of the method is discussed, and an example of its application to an arbitrarily shaped microstrip circuit is presented. It is shown that the method in the proposed form is an effective tool of circuit analysis in engineering applications. The method is compared to two other methods used for a similar purpose, namely the contour integral method and the transmission-line matrix method