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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. Index Terms--Geometric directivity, hemispherical scan coverage, maximum scan angle, multibeam antennas, pyramidal antenna arrays.

A new concept in single-port adaptive antennas using parasitic elements with switched terminating impedances is presented including results from a concept prototype. Each parasitic element can be effectively terminated in three impedance values. The antenna concept provides multiple radiation patterns with a single RF signal port without the need for RF switches or phase shifters in the direct RF signal path. Impedance variations in the active antenna element are minimized by use of only rotationally symmetric configurations. Measured patterns are used to demonstrate the performance improvement expected using switched diversity combining in a simulated uniform scattering scenario. The concept prototype having one active element and four parasitic elements, is shown to have equivalent diversity performance to between three and four uncorrelated branches. Index Terms - Adaptive, averaged uniform scattering scenario, diversity gain, single-port diversity antenna, switched parasitic antenna elements, wire monopole antenna.

Switched parasitic elements provide a useful implementation of antenna pattern diversity. The basic principle is presented with some examples of wire antennas computed using the method of moments. The modeled diversity gain available from selection combining of uncorrelated signals is used to quantify the expected improvement relative to nondiversity antennas. The advantage of the switched parasitic concept is that it is a relatively simple system, which can give the adaptive antenna performance of many branch selection or switched diversity. Index Terms - Antenna arrays, antenna radiation patterns, diversity, mobile communications, multibeam antennas, personal communications.

In the uncorrelated scenario model, a continuous source distribution illuminates a receiver with waves bearing signals that are uncorrelated with respect to their angle of arrival. This model is used for multipath situations such as scintillating atmospheres, but also can be applied to optical beams for indoor communications, acoustic beamforming, and, of particular interest here, mobile communications. For diversity antennas operating in such a scenario, patterns that produce uncorrelated signals are required. An angular separation of directive beams in multipath scenarios acts to decorrelate the received signals. It is of interest to quantify the minimum angular spacing required of beams in order to provide a framework for the design and configuration of the antennas. The approach is to consider only the main lobe of the antenna pattern and to take it as a real function. This is reasonable as long as most of the energy is conveyed via the main beam. In practice, the sidelobe structure and nonuniformity in the phase of an actual pattern act to improve the situation in the sense that the decorrelation angles become smaller. The conditions for angular diversity result in a simple rule-of-thumb for the minimum beam separation requirement, which is essentially independent of the directivity. Finally, both scalar (acoustic case and circularly polarized case) and vector (linearly polarized case) elliptic beams rotated about their boresight axes are analyzed for the decorrelation rotation angle as a function of the ratio of the ellipticity. The resulting design curves offer a guideline to beam configuration for multipath scenarios. Index Terms - Multibeam antennas.

A method for evaluating antenna diversity systems is presented with an example of a handset using up to four antennas in indoor mobile communication. The method includes a 'two-at-a-time' measurement test setup that uses maximum likelihood estimation of the covariance matrix and compensation for the imperfect match, which typically occurs during the design and evaluation process for compact antennas. The diversity performance of the antenna system can be presented as an effective order of diversity, which is the equivalent number of equal power, uncorrelated diversity branches for the same diversity gain at a given probability. Index Terms--Antenna arrays, covariance matrices, diversity methods, estimation, fading channels, mobile antennas, signal processing.

The Fourier relations between channel transfer function and scattering distribution can apply to personal and mobile communications where multipath is a prevalent phenomena. In this paper, the transform relations are reviewed and interpreted for the mobile radio channel. The effective scattering distribution is the vector product of the antenna pattern and the incident waves and is a scalar function of angle and delay time. The space base-band frequency correlation function transforms with the averaged power of the effective scattering distribution. If the angular power density marginal of the effective scattering distribution is known, then the transform relations can be used for configuring antennas for spatial diversity. Similarly, if the delay time marginal is known, then conditions for frequency diversity are available. The two-dimensional (2-D) transform gives a convenient route for assessing tradeoffs between combined frequency and space diversity. Using modeled distributions, solutions are given for spaced directive antennas and an example is discussed for the space-frequency tradeoff. Index Terms--Land mobile radio, land mobile radio diversity systems, multipath interference.