Dihedral corner reflector backscatter using higher order reflections and diffractions

The uniform theory of diffraction (UTD) plus an imposed edge diffraction extension is used to predict the backscatter cross sections of dihedral corner reflectors which have right, obtuse, and acute included angles. UTD allows individual backscattering mechanisms of the dihedral corner reflectors to be identified and provides good agreement with experimental cross section measurements in the azimuthal plane. Multiply reflected and diffracted fields of up to third order are included in the analysis for both horizontal and vertical polarizations. The coefficients of the uniform theory of diffraction revert to Keller's original geometrical theory of diffraction (GTD) in far-field cross section analyses, but finite cross sections can be obtained everywhere by considering mutual cancellation of diffractions from parallel edges. Analytic calculations are performed using UTD coefficients; hence accuracy required in angular measurements is more critical as the distance increases. In particular, the common "far-field" approximation that all rays to the observation point are parallel is too gross of an approximation for the angular parameters in the UTD coefficients in the far field.     

Comments on “Analog layout using ALAS!” [and reply]

For the original article see ibid., vol. 31, no. 2, p. 271-4 (1996). In the aforementioned paper the authors consider the advantages of laying out matched pairs of transistors, resistors, capacitors, etc., with interdigitated geometries and common centroid. Then they show six examples of “matched devices”. However, the commenters point out that not one has a common centroid. This leads to the conclusion that the computer program ALAS! seems to have a remarkable consistency in making layouts where the centroids are never in common. In reply, the authors thanks R.A. Pease for his comments on their paper and respond to his concerns, especially clarifying the issues regarding common-centroid versus interdigitated layout     

Comments on ``The QPSX MAN' [with authors' reply]

For original article see ibid., vol.26, no.4, p.20 (1988). The commenter contends that the authors of the above-mentioned article miscompare dual bus and dual ring topologies. He addresses what he believes should be the main point of interest to the telephone companies when they are assured that QPSX will measure up to the public network requirements, namely, reliability and maintainability. He uses QPSX and FDDI to compare dual bus/dual ring reliability, showing that QPSX is less reliable. The original authors refute Dr. Rocher's comments regarding the reliability of QPSX, and they emphasize that the numerous other advantages of QPSX listed in their article stand undiminished     

Comments `Surface losses in transmission lines' [and reply]

The commenter argues that the treatment of a uniform plane wave impinging obliquely on a lossy half plane in the above-titled paper by D.A. de Wolf (see ibid., vol.34, no.4, p.22-6, Aug.1992) is fundamentally incorrect. In reply, de Wolf agrees with the commenter's objections, but points out that they pertain only to his first, heuristic, derivation. He then examines why his apparently absurd derivation yielded the right answer     

Comments on `A practical end-of-life model for semiconductordevices' [and reply]

Several observations are made on the above-named work by M.S. Ash and H.C. Gorton (see ibid., vol.38, no.4, p.485-93, Oct. 1989) concerning gradual performance deterioration in semiconductor devices. The commenter suggests that the development of predictive tools for reliability assessments involving long-term deterioration in such devices requires that careful attention be paid to the operational physics of the device, including temperature-dependent characteristics. An author's reply is included     

Comments on `Minimum variance beamforming with phase-independentderivative constraints' [and reply]

The commenter points out that the idea of controlling only the magnitude response of a beam to achieve a flat main beam response, as discussed in the above-titled paper by C.-Y. Tseng (ibid., vol.40, no.3, p.285-94, Mar. 1992), is not new and was discussed by M.H. Er (1988). The author apologizes for the oversight and points out that the paper also covers issues that were not addressed by Er     

Comments on “Hall Effect Imaging” [and reply]

Recently, Wen, Shah, and Balaban (The Encyclopedia of Physics, 2nd ed., New York, VCH, 1990) presented two novel and elegant methods for imaging electrical conductivity. In their first method, they placed a conducting sample in a steady magnetic field and applied an ultrasound pulse. The resulting motion of the conductor in the magnetic field produced a measurable voltage. In their second method, they applied a high-frequency voltage to a conducting sample in a steady magnetic field and recorded the ultrasound signal. Here, Roth and Wikswo make two points about this work: 1) The “Hall effect” is not the physical basis for Wen et al.'s techniques, and 2) their work has close experimental and theoretical connections to previous studies of magnetoacoustic imaging. In their reply, disagreeing with Roth et al., Wen and Balaban say that they did not propose two imaging methods. Their paper presented two realizations, the forward and reverse modes, of the same imaging method. They are the reciprocal versions of the same linear electrodynamic process, namely, the conversion between electrical energy and mechanical energy by the Lorentz force. In reply to Roth et al.'s statement that “the name “Hall effect imaging” is misleading” Wen and Balaban say that they extended the idea of the classical Hall effect to describe “Hall-effect imaging” because the initial motion of the charges is not driven by an electric field but by direct mechanical force     

Comments on `Two-port higher mode circular microstrip antennas'[and reply]

The commenter maintains that the definitions of the line current and line voltage given in the above paper (ibid., vol.36, no.3, p.309-21, Mar. 1988) do not follow the standard transmission line equations. He offers an alternative definition. The author replies that the problem is due to a misleading figure, and he clarifies his work     

Comments on "Synthesis of adaptive monopulse patterns" [and reply]

In the recent paper (see ibid., vol.47, no.5, p.773-4, May 1999) Fante determines the weight vector w/sub /spl Delta// for the difference beam subject to the constant slope of the ratio /spl Delta///spl Sigma/. Junhao Xie states that the method is quite general and that the sum/difference beam weight vector should be simplified further.     

Comments on `18-GHz 1/8 dynamic frequency divider using Si bipolartechnologies [and reply]

For the original article see ibid., vol.24, no.12, p.1723-8, (1984). The author asserted that the circuit configuration of a regenerative frequency divider employing a modulator with a parallel-feedback amplifier instead of load resistors is novel. The commenter gives citations to prove that similar results have been published earlier. In reply, Ichino indicates that the circuit has a new feature, i.e. the inclusion of emitter followers in the parallel feedback path, which increases the gain and bandwidth of the transimpedance amplifier. A further purpose was to provide an analytic explanation and simulation results on top of experimental proof for why a frequency divider having this configuration can operate up to the limits of the transistors     

Comments on “Multiphase systolic algorithms for spectraldecomposition” [and reply]

Comments that the paper by Liu and Yao (see ibid., vol.40, no.1, p.190, 1992) presented an efficient algorithm for spectral decomposition, but the parallel algorithm and architecture for the Hessenberg reduction has a problem. The matrix obtained from the unitary similarity transformation is not necessarily a Hessenberg matrix. The authors reply that the Hessenberg reduction described is not in the Hessenberg form. Only the first column is in its proper form. There are many ways to overcome such a problem. One simple way is to use the multiphase rectangular systolic array     

Comments on `Protecting EFIE-based scattering computations fromeffects of interior resonances' [and reply]

It is pointed out that the above-titled paper by F.X. Canning (ibid., vol.39, no.11, p.1545-52, Nov. 1991) neglects an earlier paper by the commenter (ibid., vol.37, no.12, p.1559-65, Dec. 1989) which describes the determination of the resonances of integral equation operators. The commenter suggests that the method used by Canning for correcting scattered fields is incorrect or impractical since it is based on an integral equation that is ill posed. Canning responds by showing that the matrix problem one must solve is not ill posed, and that the objections raised by Marks stem from failing to properly distinguish the properties of the matrix from the properties of the integral equation. Responses are also given to several specific statements made in the above comments     

Comments on "Ill conditioning in self-heating FET models" [and reply]

A recent letter by S. A. Maas (see ibid., vol.12, no.3, p.88-9, March 2002) reported ill conditioning in nonlinear circuit simulators caused by the introduction of self-heating effects into FET models. This is true for circumstances outlined in that work but is a consequence of using an incomplete thermal model. This letter points out that an account for both thermal potential and mobility variation with temperature will eliminate the problem.     

Comments on “Anomalous mutual coupling between microstripantennas” [and reply]

The paper by Haddad and Pozar (see ibid., vol.42, no.11, p.1545, 1994) contains important observations about the mutual coupling between printed antennas. It presented the oscillatory behavior of the mutual coupling between two printed dipoles as the separation between elements is increased. The authors used a closed form asymptotic Green's function to evaluate the mutual impedance between the elements. The oscillatory behavior of the mutual coupling is supposed to be a consequence of the interference between the surface waves and the space waves. The authors of the aforementioned paper stated that this behavior was previously unreported. Rosales here comments that the "anomalous" oscillatory behavior of the mutual coupling between microstrip antennas was in fact reported in a paper presented at the Ninth Computing Conference on the Computation of Electromagnetic Fields, and by Haddad and Pozar in their paper, almost simultaneously. The results and conclusions of both papers confirm each other. Haddad and Pozar reply to the Comment     

Comments on Transient analysis of stored charge in neutral baseregion [and reply]

The commenter addresses questions raised in the above-titled paper by K. Suzuki et al. (ibid., vol.39, p.1164-9, May 1992) concerning the validity of bipolar transistor models using the partitioned-charge (PC) approach for transient simulations. Suzuki et al. assert that the concept of charge partitioning applies only to discharge transients and thus the charge-partition ratio depends on the sign of the emitter-base voltage gradient, which, if true, would greatly reduce the utility of PC-based models. The commenter shows that this is not the case and that their conclusion is due only to a misinterpretation of the PC model. The authors reply     

Comments on "Transitional combline/evanescent-mode microwave filters" [and reply]

For the original paper see ibid., vol. 45, no. 12, p. 2094-99 (1997). In the aforementioned paper, Levy et al. refer to the phenomenon of combline-filter bandwidth expansion (i.e., practical bandwidth versus theoretical TEM-analyzed bandwidth). Levy et al. explain that this phenomenon is mainly caused due to evanescent waveguide modes propagating through the structure, affecting the overall coupling coefficients and bandwidth. The commenters point out that this explanation, known for many years, is only one among other explanations such as coupling between nonadjacent resonators, also known for many years. They suggest that these explanations and derived equivalent models are not fully compliant with practical results and may be applicable only in limited frequencies and structural dimensions. In conclusion, the commenters consider it important to mention that their explanation, based on deviation from quasi-static 2-D cross-sectional TEM-derived coupling coefficients, and modified equivalent model were successfully adopted by others to achieve fast and accurate design procedure, thus proving the validity of their explanation and the practical value of their modified equivalent circuit. In reply Levy et al. say that, on the whole, they disagree with most of the arguments of Shapir and Sharir, but think that they have raised some interesting points which deserve careful consideration, and the authors are grateful for the opportunity both to respond and to clarify certain aspects of their paper which may be subject to misunderstanding.     

Comments on “Near-zone gain of open-ended rectangularwaveguides” [and reply]

The author comments that formulating the problem of radiation from open-ended rectangular waveguides (OEG) using an electric field integral equation (EFIE), Kawalko and Kanda (see ibid., vol.39, p.408-13, 1997) present results for the near-zone gains as a function of both the frequency and distance from the OEG aperture. These values can be considered to be exact. On the alternative methods, this paper observes that the approximate formulas need the measured values of the aperture reflection coefficient and the total radiated power. Kawalko and Kanda reply that the formula for the on-axis gain presented by Selvan (see Inst. Electron. Telecommun. Eng. J. Res., vol.43, p.61-4, 1997) certainly has an advantage over Yaghjian's formula (1984) in that it does not require knowledge of the total radiated power or the reflection coefficient at the aperture. However, this formula still does not account for all of the diffraction effects that occur at the aperture of the OEG     

Comments on “High frequency performance of multilayercapacitors” [and reply]

For the original paper see ibid., vol.43, no.9, p.2007-15 (1995). The commenters state that are pleased to see this addition to the analysis of high-frequency (HF) capacitors as given in the aforementioned paper. They go on to discuss various points which have arisen in the analysis owing to the use of the transmission-line model. In reply the author clarifies several of the aspects considered