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This article presents a dual-band composite reflector antenna by embedding an array of metallic phase alignment elements (PAEs) on a selected area of reflector. As a result, this phase-configurable reflector may radiate two relatively arbitrary beams at two widely separated frequency bands, respectively. In this concept, a conventional parabolic surface is first created for ordinary field radiation by a focal feed in the low-frequency band. Afterward, a feed of high-frequency band is offset from the focal point to result in defocused radiation due to the phase distortion of reflection from the parabolic reflector. Metallic PAEs are subsequently implemented on the reflector to configure their phases of reflections for distortion compensation, and thus to refocus the radiation power along a desired direction. Here, the resonance of PAEs also specifies a valid high-frequency range. In this article, the methodology is first presented with radiation discrepancy evaluated to validate the design concept, which is further validated by full-wave simulations. Numerical examples are presented to demonstrate the feasibility. [ABSTRACT FROM AUTHOR]

A dual-band circularly polarized horn antenna of completely inhomogeneous corrugations is efficiently designed for simultaneous good polarization, aperture efficiency (AE), sidelobe level (SLL), and symmetric radiation pattern (SRP). The method employs two steps to integrate a mode-matching method and a genetic algorithm by introducing a modal expansion of the aperture field as an intermediate interface for optimization, where the selected modes’ weightings are first optimized to resemble the desirable far-field patterns. Afterward, the aperture distribution serves as the goal to subsequently optimize the entire corrugation structure by formatting related scattering matrices using the weighting coefficients of available modes on the aperture and inside the horn section. In the implementation of design, the developed corrugated horn comprises six and 19 completely inhomogeneous corrugations in mode conversion and radiation sections, respectively, providing sufficient design freedom. Simulated and measured results are shown to validate the optimized horn design, which simultaneously meets all above-mentioned requirements in both the K-band (19.6–21.2 GHz) and the Ka-band (29.4–31 GHz). [ABSTRACT FROM AUTHOR]

In this paper, a design of reflector antennas to produce near-field focused (NFF) radiation is presented. Instead of focusing the radiation at a single focal point, which results in an ellipsoidal reflector, this new reflector antenna application concept designates a finite zone, especially a finite curved surface, for NFF illumination. This finite zone may consist of several subzones for multi-NFF radiation. The design concept employs equal path lengths of wave propagation from the feed’s phase center toward the focal zone via reflections from the reflector’s surface in a one-to-one correspondence, which results in a confluence of reflection points found from a set of ellipsoidal surfaces. Based on a definition of the mapping mechanism to extract the reflection points to form the reflector, the field can be properly focused in the target zone by the concept of geometric optics (GO). In this paper, the basic theoretical concept is first summarized with a design equation developed for easy implementation. The focus property is demonstrated by a time-domain physical optics (TD-PO) analysis of spherical wave illumination with a transient-step field behavior to show the focusing responses of electromagnetic scattering from the reflector. The focusing characteristics of the frequency domain (FD) are also shown by PO simulation at 20 GHz. [ABSTRACT FROM AUTHOR]

The diffraction mechanisms of electromagnetic (EM) transient scattering from large scatterers are examined by applying a general time-domain aperture integration (TD-AI) technique when the scatterer is illuminated by an incident EM field. This incident field exhibits a transient-step field response and can be the radiation from a relatively arbitrary EM source located at any place. The mechanism is interpreted by considering an equal time-delay curved aperture (ETDCA) where a set of EM equivalent current sources are defined to radiate the scattering field. The transient responses at any instant time are then found by considering the effects of equal net time-delay in propagation when the incident wave propagates to the field point via EM scattering from the scatterer. A contributing contour in the radiation integral of the equivalent currents define on the ETDCA by its intersection with a time-varying equal path-length sphere defined by the field point is therefore extracted to reduce the surface integral into a line one. The characteristics of this contributing contour are employed to interpret the EM scattering mechanisms. Practical numerical examples are presented to demonstrate the validity and feasibility of this general TD-AI technique. [ABSTRACT FROM AUTHOR]

This article presents an investigation into the radiation characteristics of broadband, all-metallic reflectarray antennas with nonresonant convex elements for directional beam applications. The metallic reflecting elements demonstrate advantages over conventional elements that are realized on printed circuit board (PCB)-type dielectric substrates because of the superiority in energy efficiency of these metal elements. The use of the metallic elements results in more radiation power to compensate for the energy loss that occurs during propagation in air. These radiation characteristics cause the antennas to radiate a broader beam with a smaller physical size and with the same gain achievement as that of a PCB-based antenna, resulting in better coverage. [ABSTRACT FROM AUTHOR]

This paper presents uniform formulations of radiation mechanisms, analogous to the ray decompositions of diffraction theory, from a semi-infinite and periodic array of antennas. The antenna array is excited to radiate the electromagnetic (EM) fields focused at a relatively arbitrarily selected location. The ray decomposition results from a closed-form formulation by asymptotically evaluating the radiation integral of Floquet modes that are obtained by applying the Poisson sum formula to the summation of elemental radiations. The analysis is relatively general and will reduce to the case of a conventional phased array antenna that is excited to radiate directive beams focused in the far zone, and exhibits consistent phenomena. Theoretical investigations as well as numerical examinations are presented to demonstrate the radiation mechanisms. [ABSTRACT FROM PUBLISHER]

This paper presents an analytical transient analysis of electromagnetic field radiation from a time-delayed and finite periodic array of antennas for the near- and far-field focused applications. The elemental current moments of array are assumed with a transient impulse input for the excitations whose signals are delayed to radiate near-zone focused fields. The transient field phenomena for each of the Floquet mode expansion were analyzed. The solution reduces to the case of far-zone field radiation by moving the focus point to the far zone. The analysis shows that the radiation exhibits an impulse field at the focused point, and finite pulses at locations away from the focus point. Phenomena of partial cylindrical wave functions have been observed. [ABSTRACT FROM PUBLISHER]

A time-domain (TD) analysis of ellipsoidal reflector antennas is presented to predict the transient scattered fields when it is illuminated by a cosine-tapered and transient-step feed radiation whose phase center is located at the nearby focus. A transient-step function of the feed's radiation is considered because it will produce an impulsive response near the second focus of the reflector as interested in the applications of impulse-radiating antennas. This TD solution is in a closed form and remains valid both near and far from the reflector, and can be used via the convolution theorem to efficiently obtain the early time transient fields generated by the same ellipsoidal reflector antenna when it is illuminated by a realistic finite-energy pulse which emanates as a spherical wave from the focus. Numerical results are presented for the transient fields both near and far from the reflector. [ABSTRACT FROM PUBLISHER]

We present an efficient procedure for the synthesis of planar array antennas to radiate contoured patterns in the near zone of array aperture, as desired in RFID applications. It first grids the target area, and then utilizes a global basis set to span the array's excitations. Each basis's excitation of the array radiates a focused spot beam in the near zone and serves as a local basis function for representing the radiation field. The unknown coefficients of the array's basis set are then found via a minimum least square error (MLSE) technique. It is found that only a small number of basis functions are sufficient to synthesize the radiation pattern, and make the present approach very fast. [ABSTRACT FROM AUTHOR]