Comments on “Radiation and scattering from thin wires inchiral media”

Comments that the above paper (see Jaggard, Liu, Grot and Pelet, IEEE Trans. Antennas Propagat., vol.40, p.1273-1282, Nov. 1992) lacks the generality of the paper published by Monzon (see Antennas Propagat., vol.38, p.227-235, Feb. 1990). The latter paper contains an analysis for thin wires, including an explicit integral equation and method for numerical solution (summing impedance matrices), which renders the problem of trivial numerical implementation. Further, the analysis applies to full biisotropic regions, and is therefore more general than chiral since chiral is just a special case of biisotropic. It appears that Jaggard et. al. use the integral equation of Monzon and follow the numerical scheme therein literally     

Comments on “A new model for calculating the input impedanceof coax-fed circular microstrip antennas with and without airgaps” [and reply]

For original paper by Abboud et al. see IEEE Trans. Antennas Propagat., vol.38, p.1882-5 (1990). In the original paper, the resonance frequency of coax-fed circular microstrip antennas with and without air gaps has been modeled (in its Section III) by incorporating and rearranging some results previously reported by others. The present author, while working with the formulas of that Section III noticed a discrepancy in (8) and (9). This has been investigated thoroughly and the observations are presented. A brief reply is given by Damiano et al     

Comments on "Simple and accurate formula for the resonant frequency of the equilateral triangular microstrip patch antenna"

For original paper by Kumprasert and Kiranon see IEEE Trans. Antennas Propagat., vol.42, p.1178-9 (1994 August). Discusses the calculation of the resonance frequencies and provides some corrected calculations.     

Two-dimensional pulsed propagation from extended planar aperture field distributions through a planar dielectric layer via quasi-ray Gaussian beams

A previously developed Gabor-based quasi-ray narrow-waisted (NW) Gaussian beam (GB) algorithm for time-harmonic propagation of aperture-excited two-dimensional (2-D) electromagnetic fields through a planar dielectric layer is extended here to the time domain (TD) to deal with short-pulse excitation. The dielectric layer is assumed to be nondispersive; however, slight Ohmic losses can be accommodated. The frequency domain (FD) algorithm is based on a self-consistent discretization of the aperture field distribution in terms of basis NW-GBs in conjunction with an efficient quasireal ray tracing scheme for tracking the individual basis beams. The TD results are obtained by analytic Fourier inversion from the FD in terms of pulsed beam wavepackets, following a procedure similar to that utilized by Galdi et al. (see IEEE Trans. Antennas Propagat., vol.49, p.1322-32, Sept. 2001) in connection with free-space aperture radiation. The proposed algorithm is validated and calibrated against a rigorous numerical reference solution via an extensive series of numerical experiments. A priori accuracy assessments in terms of critical nondimensional estimators, and computational costs, are also given attention.     

Volume/surface formulation for analyzing scattering from coatedperiodic strips

A surface/surface formulation was used by Perte et al. (see IEEE Trans. Antennas. Propagat.) to analyze the scattering from periodic planar coated strips. This paper is an extension of that work where a combined volume/surface formulation has been used to solve the same problem. This formulation can be applied to problems which involve an inhomogeneous dielectric medium or/and a thick dielectric which requires the inclusion of the edge currents which were neglected as a simplification. Results obtained using the volume/surface formulation have been compared with the results published in the paper written by Petre et al. which were obtained using a surface/surface formulation     

Comments on “Radial line planar monopulse antenna”

The author points out that Miyashita and Katagi (IEEE Trans. Antennas Propagat., vol.44, p.1158-65, Aug. 1996) claim a new type of planar monopulse antenna, without reference to Kelly and Goebels (1964) that described their “invention” of the radial line planar monopulse antenna. Further, scant mention is made of the pioneering work by Goebels and Kelly (1961) and by Kelly and Goebels (1964) in various other papers by Goto, Ando, Nakano and others     

Comment on "Scattering by a bi-isotropic body" [and reply]

The author comments on a paper by Monzon (IEEE Trans. Antennas Propagat., vol.43, p.1288-96, Nov. 1995). The author comments that Monzon gave no indication as to whether the nonreciprocal variety of bi-anisotropic media can or do exist. The present comment notes that there is no reason to suggest that these can or do exist. A reply is presented by Monzon where he feels that the situation regarding these materials is not yet settled.     

Comments on “Exact solutions of electromagnetic fields inboth near and far zones radiated by thin circular loop antennas: ageneral representation” [and reply]

For original paper see Li et al. (IEEE Trans. Antennas Propagat., vol. 45, p.1741-8, 1997 Dec.). The paper by Li et al. presents closed form expressions in series form for the electromagnetic (EM) fields for both near and far zones due to thin circular loop antennas. Special cases such as fields due to sinusoidal and uniform current distribution in the circular loop antenna are given in the equations (14)-(18) of Li et al. However, the assumption of taking just the first term in the summation in (18) for electrically small loops compromises the accuracy of the field calculations for the near zone where the observation point is on or around the sphere r=a. Since the current in the loop is filamentary, the magnetic field will be singular in nature at r=a when &thetas;=π/2. However, this behavior is not displayed by the magnetic field, which is computed by taking just the n=1 term of (18b), as shown in Fig. 2(b) and Fig. 3 of Li et al.. The present comment has recast (18b) and (18c) of Li et al. to illustrate the need for more terms for accurate representation of fields in the near field. A reply is given by Li et al. in which they explain the simplification of equation (18) into (20 and then (23)     

Experimental verification of the generalized Schelkunoff'shorn-gain formulas for sectoral horns

An approximate formula has been recently proposed for the on-axis gain of rectangular waveguide antennas, that include open-ended rectangular waveguides and sectoral and pyramidal horns (see Selvan, K.T., IEEE Trans. Antennas Propagat., vol.47, p.1001-4, 1999). This formula is an approximate generalization of S.A. Schelkunoff's horn-gain formulas (see "Electromagnetic Waves", Van Nostrand, p.360-4, 1943). Gain measurements are reported for the gains of E plane and H plane sectoral horns and are used in an examination of the accuracy of Selvan's formulas. To the best of the authors' knowledge, these are the first ever measurement efforts on the gain of H-plane sectoral horns     

Comments on “Variational nature of Galerkin and non-Galerkinmoment method solutions”

For original paper see Peterson et al. (IEEE Trans. Antennas Propag. vol.27, p.241-2, April 1996). Peterson et al. compared moment method solutions by Galerkin and non-Galerkin procedures. They point out that their results are at odds with some commonly held beliefs in the superiority of the Galerkin method. The purpose of the present comments is twofold: 1) to add support to their position and 2) to add some justification and refinement to their findings. We frame our remarks in a complex Hilbert space S, where the usual operations of addition and multiplication by a complex scalar apply     

Mode Converter Synthesis by the Particle Swarm Optimization

Particle Swarm Optimization (PSO) is an effective, simple and promising method intended for the fast search in multi-dimensional space [Kennedy and Eberhart, "Particle Swarm Optimization", Proc. of the 1995 IEEE International Conference on Neural Networks, 1995]. Besides special testing problems a number of engineering tasks of electrodynamics were solved by the PSO successfully [Robinson and Rahmat-Samii, "Particle Swarm Optimization in Electromagnetics", IEEE Trans. Antennas Propag., 2004; Jin and Rahmat-Samii, "Parallel Particle Swarm Optimization and Finite-Difference Time-Domain (PSO/FDTD) Algorithm for Multband and Wide-Band Patch Antenna Designs", IEEE Trans. Antennas Propag., 2005]. On the other hand, the scattering matrix technique is a fast and accurate method of mode converter analysis. We illustrate PSO by a number of converter designs developed for high-power microwaves control: a matching horn for output maser section, a corrugated converter of linear-polarized hybrid modes, a TE₀₁ mitre bend.     

Comments on “Nondispersive waves: interpretation andcausality”, by P.T.M. Hillion [and reply]

Heyman and Felsen comment on a paper by Hillion (IEEE Trans. Antennas Propag., vol.AP-40, p.1031-5, 1992). Hillion gives a reply. The articles discuss nondiffracting wave objects and how they can be excited by physical aperture antennas     

A novel adaptive beamforming algorithm for antenna array CDMA systems with strong interferers

Blind beamforming based on the maximum signal-to-noise ratio (MSNR) can improve the performance of an array system only when the processing gain of the given code-division multiple-access (CDMA) system is high enough such that the desired signal can become dominant after despreading (see Choi, S. and Shim, D., IEEE Trans. Veh. Technol., vol.49, p.1793-1806, 2000; Choi, S. and Yun, D., IEEE Trans. Antennas Propagat., vol.45, p.1393-1404, 1997). We consider a maximum signal-to-interference-plus-noise ratio (MSINR) beamforming. The MSINR performance criterion is chosen to deal with strong interferers effectively. It is shown that blind MSINR beamforming is possible by directly utilizing the input and output signals of correlators of the CDMA systems. In addition, we propose an adaptive beamforming algorithm at a lower computational complexity - about O(7.5N) - where N is the number of antenna elements of the array system. Simulation results are presented in various signal environments to show the performance of the proposed adaptive algorithm.     

Periodicity-induced generalized Fourier transform pair

The field radiated by an infinite periodic structure can be expressed in terms of Floquet waves (FWs), both in the frequency domain (FD) and time domain (TD) (see Felsen, L.B. and Capolino, F., IEEE Trans. Antennas Propagat., vol.48, p.921-31, 2000). A new periodicity-induced generalized Fourier transform (FT) pair is derived relating FD-FWs to TD-FWs and vice versa, based on tabulated transforms and physical conditions at infinity. The new FTs are directly related to the simple canonical problem of a line array of sequentially excited dipoles that is a basic building block for more general phased periodic structures.     

Three-dimensional CAD-based mesh Generator for the Dey-Mittra conformal FDTD algorithm

It is well-known that the finite-difference time-domain (FDTD) method is subject to significant errors due to the staircasing of surfaces that are not precisely aligned with major grid planes. Dey and Mittra introduced a locally conformal method (D-FDTD) that has shown substantial gains in the accuracy of modeling arbitrary surfaces in the FDTD grid. A mesh generator for this purpose was reported by Yu and Mittra. In this paper, we present the formulation and validation of an alternative CAD-based mesh generator for D-FDTD that has improved capabilities for arbitrary three-dimensional (3-D) perfect electric conductor (PEC) geometries. This mesh generator is capable of importing AutoCad and ProE files of 3-D PEC scatterers and resonators. It can reduce the required FDTD grid resolution by up to 4:1 in each Cartesian direction in 3-D relative to conventional staircased FDTD models when modeling cavity resonances of complex PEC structures such as twisted waveguides.     

A method for designing high-power offset Cassegrain antennas

Starting from the geometrical parameters of the feed and the desired gain of the Cassegrain antenna, a method to determine the design starting parameters for a high-power offset Cassegrain antennas is discussed. Then, by numerically solving the equations governing the antenna geometry, a set of design curves are obtained, with which the structure of the antenna can be determined by trading off the electrical and geometrical system requirements. The method presented can be applied to both high or low gain feeds for constructing a high power microwave electromagnetic environment, where complex electronic systems can be tested. For linearly polarized feeds with high gain, the structure parameters of antenna with zero cross polarization can be obtained, which is equal to the design results of Brown and Prata (see IEEE Trans. Antennas Propagat., vol.42, no.8, p.1145-53, 1994)     

On the canonical grid method for two-dimensional scatteringproblems

The banded matrix iterative approach with a canonical grid expansion (BMIA/CAG) has been shown by Tsang et al. (see ibid., vol.43, p.851-9, 1995) to be an efficient method for the calculation of scattering for near planar two-dimensional (2-D) geometries such as one-dimensional rough surfaces. However, in the article of Tsang et. al, only the first three terms in the canonical grid series for TE polarization above a perfectly conducting surface were discussed and methods for implementing only a portion of these terms were presented. In this paper, a general form for all terms in the canonical grid series is provided for both TE and TM polarizations above an impedance surface and an efficient algorithm for calculating their contributions is described. The relationship between the canonical grid and operator expansion methods is also discussed. A sample surface scattering problem is shown to illustrate the utility of higher order terms in the canonical grid method     

Improvement in heuristic UTD diffraction coefficient

Holm (see IEEE Trans. Antennas Propag., vol.48, p.1211-19, 2000) has proposed a heuristic UTD diffraction coefficient for nonperfectly conducting wedges as an extension to the heuristic one given by Luebbers (see IEEE Trans. Antennas Propag., vol.32, p.77-6, 2000). The present work improves limitations of Holm's diffraction coefficient in the illumination region. The improved diffraction coefficient gives results that are very close to the Maliuzhinets (i.e. rigorous) diffraction coefficient. The improvement is valid for parallel and perpendicular field polarisations.     

Comments on "Generalized discrete Hartley transform"

The author comments on the paper by Hu et al. (IEEE Trans. Signal Processing, vol.40, no.12, p.2951-60, 1992). Information is provided about prior published work that precedes the transforms and convolution procedures defined in the above paper.<>     

Comments on “Analysis of wide inclined slot coupled narrowwall coupler between dissimilar rectangular waveguides”[and reply]

Comments by D. Satyanarayana and Ajay Chakrabarty claim that the original paper [see IEEE Trans. Antennas Propagat., vol. AP-37, no. 9, p. 1116-23, 1989] has not considered the contribution of TE_no mode in the scattered fields in the waveguide region and imply that the Green's function employed is incomplete. However there is a discussion on the singular contribution with a mathematical expression containing the appropriate Dirac delta function. It is also obvious that the specific terms of the cavity Green' s functions that treat the waveguide wall thickness do not have such a singular contribution present. Therefore, Green's functions employed in the paper are complete and rigorous. D. Satyanarayana and Ajay Chakrabarty reply to these further comments by the original author