Recently a general framework has been proposed for constitutive relations. This theoretical approach attempted to represent constitutive relations as spatiotemporal differential operators acting on the physically observable fields. The general statement is sufficiently broad to embrace linear and nonlinear systems, and dispersive as well as inhomogeneous systems. The present study investigates specific examples related to polarizable and chiral media. It was immediately realized that prior to working out the examples, we have to better understand the relation of the kinematics of particles to field concepts. Throughout, the Minkowski space notation and related relativistic ideas are exploited for simpler notation and deeper understanding.
Analysis of frequency selective surface with gridded square element using accurate integral equation technique is considered in this paper. An improved subsectional current approximation model is proposed. Two more terms of basis function, the downward half triangle (DHT) term and the upward half triangle (UHT) term, besides the commonly adopted rooftop function, are included to expand the induced current. The additional terms are used to account for the effect of the induced currents at the corners of the outer square of the unit cell. Green's functions are derived by using spectral domain immittance approach and the incident fields are derived by using the z-directed potential. The computed results are in good agreement with the measured results.
Groove guides have sharp corners in the guide proper so are not low loss and high power carrying wave guides. Proposed has been a groove rectangular waveguide with rounded internal angles [1]. However, the latter is not practical in having the infinite arms. Let us try the Conchoid of Nicomedes and Limacon of Pascal to see how can they be boundaries of static fields or high frequency waves. Also has been proposed the pentagon waveguide [2] for the high power transmission in high frequency. Yet we feel that we have very limited forms of waveguides, so we study the existing curves to see whether we can find some better guides such as rounded corner rectangular waveguide and others by starting from the boundary curves of ρ = a/ cos ϕ + l and ρ = a cos ϕ + l.
This paper presents a method of moments (MoM) analysis, obtains the non-uniform current distribution in closed form, and computes the resulted radiated patterns in both near and far zones, of regular hexagonal loop antennas with electrically large perimeter. An oblique incident field in its general form is considered in the formulation of the non-uniform current distributions. In the Galerkin's MoM analysis, the Fourier exponential series is considered as the full-domain basis function series. As a result, the current distributions along the hexagonal loops are expressed analytically in terms of the azimuth angle for various sizes of large loops. Finally, an alternative vector analysis of the electromagnetic (EM) fields radiated from thin hexagonal loop antennas of arbitrary length a is introduced. This method which employs the dyadic Green's function (DGF) in the derivation of the EM radiated fields makes the analysis general, compact and straightforward in both near- and far-zones. The EM radiated fields are expressed in terms of the vector wave eigenfunctions. Not only the exact solution of the EM fields in the near and far zones outside a are derived by use of the spherical Bessel and Hankel functions of the first kind respectively, but also the inner regions between √3a 2 and a are characterized by both the spherical Bessel and Hankel functions of the first kind. Validity of the numerical results is discussed and clarified.
The spectral structure of the reflected and transmitted fields due to a three dimensional electromagnetic X-wave incident on a planar air-dielectric interface is examined. Using a novel superposition of azimuthally dependent pulsed plane waves, it is shown that for oblique incidence the reflected pulse has a localized wave structure. On the other hand, the transmitted field maintains its localization up to a certain distance from the interface beyond which it starts disintegrating. A study of the effects of polarization on the amplitudes of the reflected and transmitted wave fields is presented.
In this paper, a general ray-theoretical representation of the X-wave pulse is introduced. This representation is based on pulsed plane waves having wave vectors lying on a conic surface. The pulsed plane wave representation is used to study the behavior of X-waves in the presence of planarly layered media. In the case of an interface separating two semi-infinite media, the pulsed plane wave representation provides a clear explanation for the disintegration of the transmitted field. It shows that unlike the incident and reflected fields, the wave vectors associated with the transmitted field do not lie on a cone. Furthermore, this approach allows one to estimate several characteristic properties of the layered media (e.g., dielectric constant and thickness of each layer) from the time of arrival of the reflected X-waves.
The dispersion relation and the wave polarisation coefficients of the electromagnetic waves in the ionospheric plasma have been obtained by considering the magnetic declination. If the magnetic declination is taken into account, the polarisation coefficients have real and imaginary parts. It is pointed out that the peculiarity of the real parts of the wave polarisation coefficients become more obvious in the vicinity of the frequency ω(= ωpe + ωpi) in the ionospheric plasma, while has no effect on the imaginary parts. This result is different from as in the absence of the magnetic declination.
In this paper antenna measurements in the presence of multipath waves are discussed. Methods are proposed to diagnose the degradation sources of a compact range measurement system operating at a frequency much lower than the designed frequency range. A range-gating technique is employed to improve the capability of the compact range measurement system. With this technique, the field responses over a bandwidth for each rotation angle are coherently measured, and the fast Fourier transform is applied to obtain the range profile. A suitable window function is applied to extract the desired path and eliminate all other undesired paths. The antenna pattern is plotted according to the filtered response of the desired path. We have expressed the receiving voltage of a testing antenna in terms of its gain pattern and input impedance of the testing antenna operating in multipath environment. If the bandwidth of the testing antenna is very narrow and the mismatch problem is very serious over the required bandwidth, an algorithm is proposed to compensate the mismatch effect so that the obtained radiation pattern and the antenna gain are more accurate. Numerical and experimental results have verified the effectiveness of our method.
The technique of dyadic Green's function (DGF) expressed in terms of the normalised cylindrical vector wave functions is adopted in this study for examining the electromagnetic fields excited by one thin circular loop antenna above a (un)grounded multi-layered chiral slabs. The current carried on such a circular loop antenna is expressed in a generalized Fourier series so as to incorporate practical situations. Thereby, exact representations of the radiated fields in both near and far zones are obtained in closed form, in a superposition of the rightand left-handed circularly polarized waves. Furthermore, numerical results are presented to show the radiation characteristics of the loop antenna in different layered chiral slab structures. The contributions of the lower- as well as higher-order current excitations to the far-zone field are examined in detail.
Unique effects of the double helical conductances of the surfaces (HCS) on the Mueller matrix (Mm) of a two-layer eccentrically bianisotropic cylinder linear array are investigated in this paper. The mathematical treatment is conducted based on the boundaryvalue approach combined with the technique of generalized separation variables. Both the TMz - and TEz-polarization of the obliquely incident waves are taken into account in the analysis. To gain insight into some physical mechanisms, numerical examples are presented to show the influences of the variations of the twist angles on the behavior of Mm of a linear array of four bianisotropic cylinders. Correspondingly, various magnetic symmetry groups (such as D∞(C∞), C∞v(C∞), D∞h(D∞), C∞h(C∞)) and some generalized symmetry and anti-symmetry relations, which govern all the elements of Mm or the scattering cross section under special chiral operations, are demonstrated. The present studies can be exploited to identify the constitutive characteristics of some bianisotropic media and to provide better understanding of the electromagnetic wave interaction with bianisotropic cylindrical objects with complex boundaries.
The analysis of a lossless helical slow-wave structure (SWS) using equivalent circuit approach, reported elsewhere, had been carried out for the fundamental mode only. This is essentially used to predict the transmission line parameters. Moreover, in the analysis the effect of permittivity on the radial propagation constant has not been considered. The radial propagation constant was considered to be same over the different structure regions. In this paper, the analysis has been developed for the space-harmonic modes considering different radial propagation constant over different structure regions. Due to it, the present analysis becomes more general, accurate and capable of dealing with a wide range of structure parameters. The dispersion relation developed here in terms of the equivalent line parameters for a lossless structure, namely, shunt capacitance per unit length and series inductance per unit length for the space-harmonic modes, as a special case, passes on to those obtained earlier by considering same radial propagation constants over different structure regions and for the fundamental mode. Besides the dispersion characteristics, characteristics impedance has also been predicted in terms of line parameters. The results presented here in terms of the structure parameters can be used for structure design and performance evaluation as well as for the control of any space harmonic of interest. The present analysis has also been validated with those experimental values reported elsewhere.
Green functions corresponding to various polynomial partial differential operators of second, fourth and higher order are derived and the results are collected in tabular form for quick reference. The results and the methods suggested for their derivation are of importance in solving electromagnetic field problems associated with various linear (bi-anisotropic) media.
We describe how antenna sum patterns can be controlled by modifying just the phase distribution of the excitation. As examples, we calculate linear and circular aperture distributions affording symmetric sum patterns with low side lobe levels, and linear aperture distributions affording patterns with low sidelobe levels on one side of the beam.
The adaptive integral method (AIM) is applied in this paper to calculate the capacitance coefficients for an arbitrarily shaped three-dimensional structure. The uniformity of multipole moment approximation is revealed theoretically and numerically; it is realized that the approach can guarantee the accuracy of AIM for computing capacitance of any structure. The memory requirement and computational complexity of the present method are less than O(N1.5) and O(N1.5 logN) for three-dimensional problems, respectively. Numerical experiments for several conducting structures demonstrate that the present method is accurate and efficient to compute capacitance of an arbitrarily shaped three-dimensional structure.
Modeling of long range propagation of collimated wavepackets poses some major difficulties with the conventional FDTD scheme. The difficulties arise from the vast computer resources needed to discretize the entire region of interest and the accumulation of numerical dispersion error. As a means for circumventing these difficulties, the moving frame FDTD approach is in this work. In this approach, the computational grid size is limited to the order of the pulse length, and it and moves along with the pulse. The issues discussed in conjunction with this method are those of numerical dispersion, which is shown to be reduced substantially compared with the stationary formulation, numerical stability, and absorbing boundary conditions at the leading, trailing and side boundaries, Numerical results of pulsed beam propagation in both homogeneous and plane stratified media are shown, and the capability of the method is demonstrated with propagation distances exceeding the order of 104 pulse lengths.
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