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This paper describes how an optimal target discrimination in a noisy environment can be obtained by an array antenna of angular beam steering and polarization agility. Results are proposed for a linear array of N elements spaced by a distance λ/2.
We consider the electromagnetic fields which can exist in the presence of two perfectly conducting spheres in free space in the absence of external sources, i.e. the free oscillations. An asymptotic analytical solution for the natural frequencies and natural modes is presented, which is exact in the limit of infinite sphere separation. To our knowledge this is the first analytical treatment of the...
Testing has indicated the sensitivity of the performance of Microwave Landing System antennas to the presence of water on the antenna radomes. Effects include degradation of system accuracy, effective radiated power, and system monitoring. Research has also been conducted in an attempt to find suitable radome materials with water shedding (hydrophobic) properties that would eliminate the problem....
Microstrip antennas are inherently narrowband due to the resonant nature of the top and bottom metal plates. Their typical bandwidths are between 0.1 to 3 %, although this can be improved somewhat by increasing the thickness of the substrate. However, if one intends to integrate MMIC circuitry and microstrip antennas onto the same substrate for phased array applications, the thickness and material...
The software EMsim™∗ has a graphical shell and a field theory “engine” WATMIC. This paper discusses the adjustments to the engine to improve the accuracy to 1 % error or less. The only limitation for new WATMIC is that it does not account for surface wave of substrates thicker than 0.05λd (in the substrate).
Integrated antenna design utilizing Resonant Tunneling Diodes (RTDs) as the active element is described, where the intent is to integrate RTDs with printed microstrip dipoles on GaAs substrates for operation at mm-wave frequencies. RTDs are capable of operation at frequencies of up to 200 GHz, making them a good candidate for use as a mm-wave source. Issues involved in RTD and dipole modelling are...
The determination of the propagation constants and fields for conductors embedded in a lossy half-space is of interest in low frequency radio transmission, remote sensing applications in geoelectromagnetics, and in the power engineering field for buried cable analysis. It is important to be able to determine the effect of the interface on the propagation and radiation characteristics of the geometry...
Radio wave propagation characteristics in snow, wet ice and mixed phase hydrometeors along a propagation path are investigated. Included are further studies on differential propagation effects in snow, the melting region in stratiform precipitation, wet snow and ice on elevated paths. Results from radar measurements, at both linear and circular polarizations on elevated radar and satellite paths are...
The objective of this paper is to present a numerical technique for the analysis of printed circuits and antennas using the grounded dielectric slab Green's functions. For the dynamic case, the Green's functions are quite complicated and require the numerical computation of certain semi-infinite integrals commonly known as the Sommerfeld integrals. In this paper certain approximations have been made...
Interest in the use of microstrip patches for array antennas has prompted investigations into numerous feed mechanisms. One of the most interesting, which offers considerable advantages over the others, is aperture coupling. In the paper that follows, the coupling of a feedline to a rectangular patch, through an aperture in the ground plane separating them, is described. Modal field expansion is used...
The modular approach to scattering is designed to facilitate the computation of complex problems in a gradual manner, resolving them into a series of sub-problems. In addition to the “Add-On” method [1-4], described earlier by the author, we introduce the following two modular schemes: 1. A rapid computation of different incident fields in the Conjugate Gradient context, where a basis of incident...
A new model for analyzing discontinuities in MIC devices is being proposed. The technique is based on the boundary element method. An MIC device with an arbitrarily shaped discontinuity can be treated as a one-dimensional problem. Two numerical examples are given for checking the validity of the model.
The NASA Deep Space Network (DSN) is constructing a new 34-meter research and development antenna as a precursor to introducing beamwaveguide antennas and Ka-band frequencies into the operational network. The basic design of the center-fed beamwaveguide is shown in Figure 1. It consists of a beam magnifier ellipse in a pedestal room located below ground level that transforms a JPL standard 22-dB gain...
An analysis of slot-coupled double layer microstrip lines is presented. A modal field expansion method and the Poynting theorem are applied to derive the input impedance as seen by the feed line at the slot. By comparing the theoretical results with measured values, the accuracy of the method is verified.
A land-mobile or a maritime antenna for local-area satellite ccmmunications of relatively low G/T can be realized by using a circularly polarized antenna generating a conical pattern. Because of its omnidirectional pattern in a horizontal plane and fairly wide beamwidth in a vertical plane, there is almost no need for tracking the satellite.
In passive remote sensing techniques, the radiometric temperature emitted from a forested canopy is related to the canopy biophysical characteristics. In this study the radiative transfer theory is applied to study the radiometric temperature of a coniferous forest at the microwave band. The forest is modeled as layer above a rough soil surface. The layer is occupied by the leaves and the branches...
For remote sensing of forests, knowledge of the electromagnetic scattering characteristics of tree leaves, branches and trunks is important. Various theoretical models based on the analytic solution of the Helmholtz integral have been developed for tree components. The trunks, branches, stems and coniferous leaves are treated as lossy dielectric cylinders. The deciduous leaves are treated as elliptic...
A rigorous analysis of an aperture-coupled stacked microstrip antenna is described. Developed from a coupled integral equation set employing spectral-domain Green's functions, the analysis includes all coupling, radiation and surface-wave effects. Optimization of the patch dimensions yielded VSWR bandwidths of greater than 20%. Theoretical and measured responses exhibited excellent agreement.
The symmetrical condensed node (SCN) TLM method is used to compute S-parameters of various waveguide components. A discontinuous ridge waveguide, a resonant iris, a double plane waveguide transition and a symmetrical waveguide T-junction are analysed. The conditions which must be satisfied in the S-parameter computation of such circuits are defined. The validity of the method is verified by comparison...
As a general numerical technique for solving electromagnetic problems, the finite element method[FEM] appears to compete favorably with other numerical methods. As an example, when used for solving circuit discontinuities and EM scattering, it can handle arbitrarily shaped discontinuities, including anisotropic waveguide components such as ferrite devices. Various forms of FEM have been used in EM...
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