In this paper, an efficient method to obtain the elements current distribution for a non uniformly spaced array is presented. For a given far field pattern, after sampling the array factor the proposed method uses the least mean square error technique to solve the system ofequations rather than solving the previously published Legendre function method. It's shown that the average side lob level obtained by this proposed method is some 5 dB lower in comparison with the existing Legendre function method ofsolution. Ifthe Legendre function method published in the literature is to be used to solve for the current distribution, in the final part ofthis paper, a criteria on how to choose suitable vectors that would result in a 3 dB lower side lobe level performance will be provided.

An exponentially tapered structure is introduced into multimode interference (MMI) devices. Compared with a parabolically tapered structure,which has been successfully used in MMI devices, this structure can further reduce the length of these devices. The performances of the 1 × 2 MMI coupler with exponentially tapered structure,such as the optical transmission,the wavelength response and the fabrication tolerance,are investigated by the 2D finite difference beam propagation method. Results show that the exponentially tapered MMI coupler exhibits a similar property to that with a parabolically tapered structure.

A LAser raDAR (LADAR) system was described in previous papers for detecting and tracking cooperative targets. The LADAR system was optimized to achieve accurate tracking with a high probability of detection and low False Alarm Rate (FAR). However, the operation range was limited to about thirty km's under clear sky conditions and less in low visibility and bad weather conditions. To obtain operation ranges in the order of hundreds km's without affecting tracking accuracy a LADAR/RADAR dual mode system was developed. Moreover, very bulky, expensive and powerful RADAR equipments are required. In this paper, we propose a tactical mobile tracking LADAR/RADAR systems based on a multi-mode LADAR/RADAR combination using active transponders on cooperative targets for predetection and tracking at higher range distances. The optimal solution described in this paper is based on a six-step multimode operation procedure, which starts from an L-band active transponder for maximal distance detection and tracking, and with decreasing distance it switches to an L-band RADAR , Ka-band RADAR with and without active transponder, LADAR with transponder and then to a LADAR without transponder for the final tracking step. Although relatively complicated (6 steps), our proposed solution requires significantly lower power levels and produces less radio interference than the former dualmode system as shown in Table 1.

Continuous current spectrum of an integrated open waveguide structure is identified as the branch cut contribution to singularity expansion of those currents in the complex axial transform plane. Those singularities in that plane include poles associated with the guiding structure and branch points contributed by layered background environments. The manner in which singularities in background environments manifest themselves as branch points in the complex axial transform plane is reviewed. Based on spectral integral equation formulation, approximate and analytical expression for spatial microstrip current is obtained. That approximation is based on Maxwellian distribution for the transverse current profile. This result is the representation of currents in terms of proper propagation mode spectrum. During the integration around branch cuts, singularities in the transverse transform plane migrate in a complicated manner. The trajectories of this migration are identified and suitably accommodated during the real axis integration in that plane. This overall procedure leads to a decomposition of the total currents into bound modes and continuous spectrum contributions. This representation is validated by real axis integration in the axial transform plane. The quasi TEM characteristic impedance of bound mode is calculated and validated by comparison with well-known empirical formula.

Most previous multiple-scattering theories for electromagnetic waves in strongly fluctuating media are limited by the assumption of statistical homogeneity of media. In the paper, a lossy electrically isotropic random medium is considered whose mean permittivity distribution, as well as the multipoint permittivity's moments are invariant under arbitrary rotations about and translations along a fixed symmetry axis, and are inhomogeneous in the radial direction. The goal of the paper is to calculate the effective permittivity operator (EPO) for such medium in the case of strong permittivity fluctuations. For this purpose, one has to eliminate the secular terms from the spectral representation of the-EPO in the basis set of waves suited to a statistically inhomogeneous medium. This is achieved via a renormalization approach which takes into proper account a delta function singularity of the spectral Green's function (rather than that of the spatial Green's function accounted for in the past) referring to a spatially inhomogeneous electrically anisotropic background medium. On this basis, the permittivity matrix of the background medium is explicitly found, a full perturbation series solution and a bilocal approximation for the EPO are derived, the macroscopic properties of the spatially dispersive effective medium are studied, and a perturbative solution for the propagation constants of guided modes of the mean field is obtained.

The high frequency diffraction of E_z-polarized plane waves by a dielectric loaded thick-walled parallel-plate impedance waveguide is investigated rigorously by using Fourier transform technique in conjunction with the mode-matching method. Relying upon the image bisection principle, the original problem is splitted up into two simpler ones and each individual boundary-value problem is formulated with this mixed method which gives rise to a scalar Wiener-Hopf equation of the second kind. The solution of each Wiener-Hopf equation contains infinitely many constants satisfying an infinite system of linear algebraic equations. A numeric solution of this system is obtained for various values of the dielectric constant, plate impedances plate thickness, and the distance between the plates through which the effect of these parameters on the diffraction phenomenon is studied.

The diffraction and scattering of a first-order ultrawideband TE X-wave by a perfectly conducting circular disk is investigated using an augmented time-domain incremental theory of diffraction. The analysis relies on a pulsed plane wave representation of the incident X-wave. The diffraction and scattering of each constituent pulsed plane wave component is calculated at the observation point. A subsequent azimuthal angular superposition yields the diffracted and scattered field due to the incident X-wave pulse. Making use of the localization and symmetry properties of the incident TE X-wave, a novel four-sensor correlated detection scheme is introduced which is particularly effective in detecting the edges of the scattering disk and has an exceptional resolving power.

A new formulation of a time domain incremental theory is introduced. This approach is applied to the scattering of a pulsed plane wave incident on a circular disk. It is shown that the scattered field is free from singularities at caustics and exhibits a notable wave structure outside Keller's cone.

The paper discusses the methodological questions arising in the study of open electrodynamic structures of resonance quasi optics via time-domain technique. As demonstrated, all of the interesting physical characteristics inherent in these objects (including the objects with various frequency-selective elements) can be obtained through the numerical solution of the relevant model initial bowldaryvalue probhxns. For the first time, a finite difference method equipped with the exact local 'absorbing' conditions on artificial boundaries has been applied for the solution of this kind of open problems. The results of the computational experiments performed have verified the possibility of the efficient selection of oscillations in dispersive open resonators with diffraction gratings, among them the resonators with gratings operating in the quasitotal nonspecular reflection mode.

This paper studies the radiation properties of aperture antennas above imperfect ground using Discrete Complex Image Method (DCIM). The present method is simple and has high accuracy. In this approach, based on linear approximating a function to an exponential series, equivalent complex images have been obtained. Number, intensity and location of images are obtained using Generalized Pencil Of Function (GPOF) technique. We assume current distribution over the aperture be combination of electric and magnetic currents in vertical and horizontal direction. The obtained results are comparable with analytical computation in limited cases. In spite of Sommerfeld integral based methods, this method is simple with lower computational time.