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Coverage in mobile communications systems requires an acceptable link gain over a maximum service area, with areas of low link gain being problematic. A standard approach to maximize link gain is to deploy multiple-input–multiple-output (MIMO) antennas that adapt to the changing multipath. There is also recent interest in using active surfaces for adaptive reflections within the multipath environments, and this calls for new ideas at the system and component levels. A critical mechanism in urban propagation is corner diffraction, which illuminates shadow areas but with low link gain. We present a simple add-on system for corners, comprising a simple scattering dipole or scattering array, which can significantly improve link gain in the shadow region over a wide bandwidth. The concept is demonstrated through analysis, simulation, and physical measurement. Only shadowed areas are boosted, and the line-of-sight coverage is not significantly affected. Our demonstration is for a passive, fixed configuration, which is suitable for retrofitting to existing systems. [ABSTRACT FROM AUTHOR]

Waveguide arrays comprise slot radiators cut into hollow, single-mode, standing wave structures. Their impedance bandwidth and compactness are limited by the waveguide cutoff. By using the TEM mode of a coaxial waveguide, a more compact structure with a larger bandwidth is possible at the expense of increased ohmic loss in the waveguide. Using this basis, a new type of slotted coaxial waveguide antenna is presented. A compact waveguide array means that the element and array aspects are not independent, and with no accurate transmission line models for the structure, the design is from a parametric study by simulation. Two basic designs are demonstrated: the first with no constraint on the azimuthal extent of the slots, and the second where some mechanical strength of the waveguide is maintained by constraining the azimuthal extent of the slots to be 90° or less. The parametric studies provide insight for realizing the high bandwidth, and measurements of prototypes confirm the performance. These antennas are useful for integration with cylindrical structures such as masts or bicycle and drone frames. [ABSTRACT FROM AUTHOR]

New designs of slot elements and a new configuration for array antennas for synthetic aperture radar (SAR) at L- and X-bands are presented. The L-band elements are cavity-backed crossed slots for dual polarization, and for X-band, interleaved ridged waveguide slot subarrays are used. The height of the L-band cavity is reduced by adopting an inverted-T configuration. Each of the crossed slots is fed by a pair of differential probes to ensure the correct modal excitation with high isolation. For evaluation, the X-band slot subarray is center fed by a coax probe although slot excitation is also possible. An initial prototype array comprising $4 \times 3$ L-band elements interleaved with X-band subarrays was fabricated to allow initial measurements. This element design is applicable for larger arrays and can be readily configured to frequency ratios other than L- and X-bands. A construction advantage of the slot design over SAR patch arrays is the use of all-metallic surfaces. [ABSTRACT FROM AUTHOR]

Multiple element antennas (MEAs) support multiple-input multiple-output (MIMO) communications and other antenna diversity techniques, resulting in better communications performance than available from single antenna systems. The space occupied by MEAs becomes important when the antennas are integrated into small or portable devices, and a metric would be helpful for the design of compact MEAs. A figure of merit for the spatial efficiency is presented here for evaluating the MEA compactness with respect to the MEA bandwidth and the potential communications performance. A spherical volume is used and different propagation scenario models can be incorporated. The impact of element efficiencies, mutual coupling, correlation, diversity scheme, and propagation scenario are included. [ABSTRACT FROM PUBLISHER]

We address the optimization of the geometric design of two classes of multifaceted antenna arrays, namely, pyramids and pyramidal frusta. The optimization involves choosing the face elevation and the number of arrays. The optimal face elevation minimizes the maximum scan angle encountered by the arrays, given a general hemispherical coverage requirement. Firstly, an approach is presented to compute the face elevation of the pyramidal frustum, based on equalizing the maximum scan angles. It is demonstrated that the equalization-based approach is not always optimal. Secondly, a new optimal approach based on minimax optimization is presented and used for both pyramids and pyramidal frusta, along with a comparison of the two approaches. Finally, the choice of the number of arrays is addressed using different cost functions including scan angles, scan losses, antenna dimensions, geometric directivity, and total number of antenna elements. Quantitative guidelines on how to choose among planar, pyramidal, and pyramidal frustum antenna systems are outlined. [ABSTRACT FROM AUTHOR]

An approach is presented for optimizing the geometry of pyramidal antenna arrays, given a full azimuth and a full or limited elevation scan requirement. It involves choosing the best face elevation and number of faces of the pyramid, which minimize the maximum scan angle while maximizing the geometric directivity. The analysis shows that the 4-face pyramid is the best choice. The derivation assumes that the distance to the antenna is infinite (the true far-field case). However, when finite distances are considered, the maximum scan angle increases only slightly at the minimum far-field distance used for low sidelobe pattern measurement. [ABSTRACT FROM AUTHOR]

Presents information on a study which described the use of two-dimensional pattern measurements as a tool for evaluating an antenna configuration for reducing power absorbed in the head. Principal pattern cut technique and experiment; Experimental results and discussion; Conclusions.

Presents a study on conditions for angle diversity for antenna beams. Correlation operations in a circular support; Rotation of an elliptic beam; Conclusions.