Boris Tomasic

Element pattern of an axial dipole in a cylindrical phased array, Part I: Theory

Cylindrical array antennas are attractive for applications requiring uniform 360\deg azimuthal pattern performance. For very low sidelobe or precise angle measurement designs, an accurate knowledge of the mutually coupled element pattern becomes important. A modal solution is presented for an element pattern in a periodic array of axial dipole radiators placed coaxially over a circular cylindrical ground. This solution avoids the problems associated with asymptotic appproaches and displays a number of advantages: 1) it is exact, subject only to truncation errors; 2) it is uniformly valid in all spatial regions for both rectangular and, with a simple modification, for triangular isosceles lattice configurations; and 3) it provides absolute gain information. The analysis is presented along with numerical results for representative parameter values, selected to illustrate the various trade-offs. Comparison with published data employing the asymptotic approach and with planar array results is given.

The geodesic dome phased array antenna for satellite control and communication - subarray design, development and demonstration

In this paper we present the design, development and demonstration of an L/S band subarray - a basic building block of a geodesic dome phased array antenna. As previously reported, the geodesic dome array is a highly effective, multi-function, low cost spherical phased array antenna that provides hemispherical coverage. The antenna consists of a number of near-equilateral triangular, planar subarrays arranged in an icosahedral geodesic dome configuration. This novel architecture design preserves all the advantages of a spherical phased array antenna while its fabrication is based on well-developed, easily manufacturable, and affordable planar array technology. The antenna is used for simultaneous, full-duplex communication and control of multiple satellites, and for air/space surveillance over the entire sky.

Analysis of finite arrays-a new approach

A novel method for the analysis of finite arrays is presented. The method is based on a global array concept where the array problem (for single-mode elements) is reduced to a solution of a single Fredholm integral equation of the second kind. This formulation offers several types of solutions (not all explored yet) with illuminating results. The approximate solution of this integral equation, for example, yields finite array characteristics in terms of equivalent infinite array scattering parameters and mutual admittances. The method is general, i.e., applicable to any element-type and periodic array geometry. Presently, the method applies to single-mode elements (one unknown per element), however, it can be extended to a multimode analysis.

Spherical Arrays - Design Considerations

In this paper we present design trade-offs of array architectures for hemispherical coverage. We show that a spherical array geometry is the optimal choice for this application in terms of performance and cost. It is a natural array geometry that provides scan-independent hemispherical coverage with a uniform gain pattern. We also show that a spherical array requires fewer elements than a comparable multi-planar phased array with significantly larger instantaneous bandwidths, lower polarization and mismatch losses

Element pattern of an axial dipole in a cylindrical phased array, Part II: Element design and experiments

The design and construction of a cylindrical array of axial dipoles is described. Dipole pattern amplitude measurements performed over practical scan and frequency ranges show excellent agreement with theoretically predicted results. Dipole pattern phase, feed line effects and radiator match are also discussed. These results provide strong evidence of the correctness of the analysis and numerical results presented in Part I of this paper, and furnish a firm basis for accurate prediction of array performance.

Digital Beamforming in a large conformal Phased Array Antenna for satellite operations support — Architecture, design, and development

This paper describes the development of Digital Beamforming (DBF) architectures, techniques, and hardware performance demonstrations that can be incorporated into the Geodesic Dome Phased Array Antenna (GDPAA), a large multi-beam conformal phasedarray antenna. The DBF system can provide functions for satellite Tracking, Telemetry and Commanding (TT&C), with significant improvements in adaptive pattern control for anti-jamming or interference suppression control, direction finding with high-resolution, ultra low sidelobes, and flexible antenna resource management and beam scheduler. For most of the design, Commercial Off-the-Shelf (COTS) components were used to reduce costs and complexity. Three (3) candidates DBF architectures were analyzed and compared with respect to their performance, complexity and cost. For the selected (optimal) architecture the key COTS components were evaluated and the results are reported.

Analysis of cylindrical array of infinitely-long slots fed by connected dipoles

We have developed an accurate analysis of a cylindrical array structure of long slots with connected dipole feeds, [1]. The array exhibits wide-band characteristics, about 3:1 frequency band at broadside scan. The code we generated could be used to accurately predict the impedance and radiation characteristics of the array.

Minimum Q of the element in an infinite phased array

A general method has been presented for evaluating the Q of the element in an infinite array environment. In essence the method consists of transforming the active array fields to a unit cell representation in terms of Floquet modes where it is easy to calculate the reactive time-average stored energy and radiated power. Although the method was demonstrated on a simple canonical 2D array, it gives first order min Q-values possible as a function of array geometry and scan. It demonstrated that for small element spacings, the min Q is lower or comparable to the single element Q in free space.

A fragmented aperture-coupled microstrip antenna

This paper summarizes an effort to obtain a wideband aperture-coupled fragmented microstrip antenna. The antenna is modeled as a 2.5D structure, and is optimized using a genetic algorithm (GA). The realistic physical feed, a microstrip-fed slot, is also included in the optimization process.

The geodesic dome phased array antenna for satellite operations support - antenna resource management

The smart antenna resource manager, the brain of the GDPAA, has been developed. The manager, with optimal spherical array geometry and unique concept of operation makes the GD an optimum antenna for multiple, simultaneous TT&C SATOPS. Some of the GD features, that the manager facilitates are: gain-on-demand, beam assignment and management, beam steering, beam shaping, adaptive pattern control, self-healing/compensation for failed elements, antenna health status, O&M under hot conditions, and/operation.