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An efficient, approximate but accurate method is presented for predicting the electromagnetic plane wave scattering from a dielectric filled antenna cavity recessed in a ground plane backed by an array of slots which are loaded by dominant mode rectangular waveguides. As in the earlier companion paper [1], the scattered fields are found via a Multiple Scattering Method (MSM) based formulation whereby the antenna cavity is broken up into three isolated regions. The three junctions which define these different regions are located at the cavity opening, the cavity back wall containing the waveguide array, and the loads terminating each of the dominant mode guides of the array. In [1] the scattering matrices associated with the first two junctions, namely the open end junction and the slot array junction, are determined via a Moment Method (MM) based solution of the integral equations for the unknown aperture electric fields pertaining to each of these junctions. In the present paper, it is shown that the eff...

In wireless mesh networks (WMNs), TDMA based link schedulingcan allow multiple concurrent transmissions, resulting in throughput improvements. In this paper, we identify certain link characteristics which reduce achieved spatial reuse and increase schedule length. It is shown that certain links (called loners) based on their length and position, introduce inherent difficulty in scheduling them with other links in network. Effects of such links on scheduling reveals important limitations of any such scheduling algorithm and motivates need of joint routing, scheduling and power control. We then present joint routing, topology control and scheduling algorithm to alleviate effects of loner links. Simulation results confirm throughput improvement with shorter schedule length.

An efficient approach is described for calculating the field distribution in the focal region of an electrically large, symmetric or offset parabolic reflector antenna with an arbitrary rim contour, when the concave reflector surface is fully illuminated by an obliquely incident arbitrary electromagnetic plane wave. The dominant contribution to the focal-region fields is found by transforming the physical-optics integral over the reflector surface into a plane-wave spectral (PWS) integral. The PWS integral is evaluated rapidly via the fast Fourier transform (FET) algorithm to furnish, in only a single computation, the field for every place in the focal plane (or any plane parallel to it) within the focal region for a given direction of the incident wave. The correction to the physical-optics field is relatively small in the focal region and may therefore be neglected. Numerical results based on this PWS approach are presented, and their accuracy is established by comparison with results based on other approaches. >

The phase retrieval algorithm has been widely used in adaptive optical systems. This presentation outlines a method to use the phase retrieval algorithm and microwave holographic surface reconstruction to synthesize contoured beam reflector antennas.

A novel Gaussian beam method, and a hybrid method, are developed for the efficient analysis of large reflector antenna systems, and large planar phased arrays, respectively. Several numerical results illustrating the speed and accuracy of these methods are described in this paper.

The present UTD solution provides a relatively simple yet accurate solution which is ideally suited analyzing conformal antenna and antenna array problems whose electrical size or shape preclude them from being solved by the standard numerical techniques. This solution which is valid for perfectly conducting convex surfaces with a material coating is valid uniformly within shadow boundary transition regions and is expressed in terms of a more general class of Fock (1965) functions that may be readily computed via a fast and efficient numerical procedure. In addition, this solution also explicitly shows the effect of surface ray torsion on the radiated fields in the shadow and transition regions.

The authors of the above named paper (see ibid., vol.36, no.10, p.1407-17, 1988) suggest that previous work on mixed-path radio ground wave theory is less general than their asymptotic analysis. The commenter clarifies the similarities to and differences from the earlier radiowave propagation studies, which span a period of several decades, and discusses the role of the Elliott mode in such problems. He also draws attention to the similarity of their eq.(12) to the generalized attenuation function in ground wave theory. In replying, Ersoy and Pathak note that for certain cases eq.(12) should be replaced by a more general expression, and they discuss in turn several other points raised by the commenter. >

A relatively efficient procedure is proposed, which combines a novel Gaussian beam (GB) approach for fast computation of reflector antenna radiation patterns with an iterative optimisation technique, to synthesise a shaped reflector surface for contoured beam applications. The GB approach employs relatively few Gaussian beams as electromagnetic basis functions to represent the field radiated by the feed; each of these GBs launched from the feed then reflects and diffracts from the reflector surface to yield the radiation field produced by the reflector antenna. Closed form expressions are used for calculating this GB reflection and diffraction; consequently, the reflector radiation pattern, which needs to be computed repeatedly in any iterative synthesis procedure, can be obtained in an extremely rapid fashion via the present GB method. In contrast, the conventional procedure, which requires a numerical integration of the currents induced by the feed over the large reflector surface to calculate the radiation field, is far less efficient and lacks physical insight. Furthermore, the GB approach is used in conjunction with a fast and convergent synthesis procedure which is developed via a modification of the usual steepest descent method (SDM) to ensure a more global reflector shaping optimisation and smooth contoured beam patterns. Numerical results are presented to validate the proposed approach.

Metallic tape is commonly used to cover the interpanel gaps which occur in paneled compact-range reflectors. It is therefore of interest to study the effect of the scattering by the tape on the field in the target zone of the range. An analytical solution is presented for the target zone fields scattered by 2D metallic tapes. It is formulated by the generalized scattering matrix technique in conjunction with the Wiener-Hopf procedure. An extension to treat 3D tapes can be accomplished using the 2D solution via the equivalent current concept. The analytical solution is compared with a reference moment method solution to confirm the accuracy of the former.

In this paper the geometrical theory of diffraction is extended to treat the radiation from apertures or slots in convex perfectly conducting surfaces. It is assumed that the tangential electric field in the aperture is known so that an equivalent infinitesimal source can be defined at each point in the aperture. Surface rays emanate from this source which is a caustic of the ray system. A launching coefficient is introduced to describe the excitation of the surface ray modes. If the field radiated from the surface is desired, the ordinary diffraction coefficients are used to determine the field of the rays shed tangentially from the surface rays. The field of the surface ray modes is not the field on the surface; hence if the mutual coupling between slots is of interest, a second coefficient related to the launching coefficient must be employed. In the region adjacent to the shadow boundary, the component of the field directly radiated from the source is represented by Fock-type functions. In the illuminated region the incident radiation from the source (this does not include the diffracted field components) is treated by geometrical optics. This extension of the geometrical theory of diffraction is applied to calculate the radiation from slots on elliptic cylinders, spheres, and spheroids.

A high-frequency approximation is presented for the fields radiated by a magnetic line or line dipole source which is located on an impedance surface patch that partly covers an electrically large, perfectly conducting convex cylinder. Relatively simple asymptotic approximations are developed for the currents induced on the impedance surface by the line sources, and the radiation patterns are calculated by incorporating these surface currents into the radiation integral. The latter integral exists only over the patch region as it uses a perfectly conducting cylinder Green's function which is expressed in terms of a uniform geometrical diffraction (UTD) solution. Numerical results are presented and shown to compare very well with other independent calculations and measurements. >

In recent years the geometrical theory of diffraction (GTD) has developed rapidly as a practical tool for calculating the radiation from complex shapes. At the present time it has progressed beyond the treatment of simple examples to the construction of user-oriented computer programs for antenna and scattering problems of engineering interest.