Robert J. Mailloux

Array failure correction with a digitally beamformed array

A technique is presented for replacing the signals from failed elements in a digitally beamformed receive array. The technique is shown to be useful in a multiple signal environment and does not impose special restrictions on the correlation properties of the received signals. Experimental data confirm the operation of this algorithm for the case of one signal and one interfering source. The technique is shown to be accurate when the incident signal locations are not precisely known, and even when the signals are distributed over a broad angular region or are only known to be located within a broad angular region.

Unconventional Phased Array Architectures and Design Methodologies—A Review

The proliferation of wireless services is driving innovative phased array solutions that are able to provide better cost/performance tradeoffs. In this context, the use of irregular array architectures provides a viable solution. This paper reviews and highlights some of the most recent advances in this field, including clustered, thinned, sparse, and time-modulated arrays, and their proposed design methodologies.

A low-sidelobe partially overlapped constrained feed network for time-delayed subarrays

Completely overlapped space-fed subarrays have been shown to provide sufficient pattern control to enable (modestly) wide-band arrays using time delays at the input to each subarray and phase shifters at the array face. These configurations are bulky, but have been proposed for space-based use as well as for certain ground-based applications that do not have severe volume constraints. Other applications for space-based and airborne radar require much more compact, constrained array feed networks, but until now there have been few appropriate constrained networks for inserting time delay at the subarray ports without causing high sidelobes. This paper describes one such network that, at the outset, provided far lower sidelobes than the usual contiguous subarrays, but retained closely spaced high lobes near the main beam. This paper presents a synthesis procedure that alters the subarray patterns and reduces nearly all array sidelobes to levels determined by tolerance errors. Several examples are presented that synthesize sidelobes at -40 dB. The resulting network operates over 70% to 80% of the maximum theoretical bandwidth.

Pattern synthesis for TechSat21 - a distributed space-based radar system

The TechSat21 space-based radar employs a cluster of free-floating satellites, each of which transmits its own orthogonal signal and receives all reflected signals. The satellites operate coherently at the X band. The cluster forms essentially a multielement interferometer, with a concomitantly large number of grating lobes and significant ground clutter. A novel technique for pattern synthesis in angle-frequency space is proposed, which exploits the double periodicities of the grating lobes in the angular domain and of the radar pulses in the frequency domain, and allows substantial gains in clutter suppression. Gains from 7 to 17 dB relative to the normal random, sparse array appear feasible.

Military antenna design using simple and competent genetic algorithms

Over the past decade, the Air Force Research Laboratory (AFRL) Antenna Technology Branch at Hanscom AFB has employed the simple genetic algorithm (SGA) as an optimization tool for a wide variety of antenna applications. Over roughly the same period, researchers at the Illinois Genetic Algorithm Laboratory (IlliGAL) at the University of Illinois at Urbana Champaign have developed GA design theory and advanced GA techniques called competent genetic algorithms-GAs that solve hard problems quickly, reliably, and accurately. Recently, under the guidance and direction of the Air Force Office of Scientific Research (AFOSR), the two laboratories have formed a collaboration, the common goal of which is to apply simple, competent, and hybrid GA techniques to challenging antenna problems. This paper is composed of two parts. The first part of this paper summarizes previous research conducted by AFRL at Hanscom for which SGAs were implemented to obtain acceptable solutions to several antenna problems. This research covers diverse areas of interest, including array pattern synthesis, antenna test-bed design, gain enhancement, electrically small single bent wire elements, and wideband antenna elements. The second part of this paper starts by briefly reviewing the design theory and design principles necessary for the invention and implementation of fast, scalable genetic algorithms. A particular procedure, the hierarchical Bayesian optimization algorithm (hBOA) is then briefly outlined, and the remainder of the paper describes collaborative efforts of AFRL and IlliGAL to solve more difficult antenna problems. In particular, recent results of using hBOA to optimize a novel, wideband overlapped subarray system to achieve -35 dB sidelobes over a 20% bandwidth. The problem was sufficiently difficult that acceptable solutions were not obtained using SGAs. The case study demonstrates the utility of using more advanced GA techniques to obtain acceptable solution quality as problem difficulty increases.

GA-Based Optimization of Irregular Subarray Layouts for Wideband Phased Arrays Design

The design of phased arrays generating low sidelobes and grating-lobes-free patterns over wide frequency bandwidths is addressed. The array structure is decomposed in subarrays with irregular polyomino tiles whose locations and orientations are optimized by means of a genetic algorithms-based approach. A set of representative results is reported and discussed to give some insights on the performance of the proposed approach also in comparison to state-of-the-art solutions.

Guest Editorial for the Special Issue on Innovative Phased Array Antennas Based on Non-Regular Lattices and Overlapped Subarrays

There has been a renewed interest in phased arrays based on non regular lattices or overlapped subarrays for different types of applications ranging from spaceborne to ground antennas, from civil to military systems. The objective of this special issue consists in providing an overview of the current state-of-the-art in this field, highlighting the latest developments and innovations, and proposing new applications, solutions and challenges for the future. The main topics considered are: 1. sparse and thinned arrays; 2. overlapped and interlaced subarrays; 3. beamforming and multibeam excitation of irregular arrays; 4. fabrication and signal distribution networks for large arrays; 5. overlapped and non-regular conformal arrays; 6. synthesis using irregular and overlapped subarrays. Most of the papers selected are in the area of array antennas based on nonregular lattices. Papers were selected based on detailed peer review and relevance to the topic. Papers are grouped into two main categories: a) array antennas based on non-regular lattices and b) array antennas organized in overlapped subarrays. The papers are briefly summarized.

Polyomino subarraying through genetic algorithms

The synthesis of subarrayed phased antenna arrays for limited-field-of-view (LFOV) and wideband applications is addressed in this work. The tiling of the antenna aperture is obtained using polyomino subarrays of irregular shape. The position and orientation of each subarray are properly optimized by means of a strategy based on a genetic algorithm in order fill the aperture and obtain the desired radiation pattern. Preliminary results are reported to show the effectiveness of the proposed method in synthesizing subarray configurations whose resulting patterns are characterized by low sidelobes and high main-beam directivity.

Technology for array control

Throughout the years, electronic scanning of arrays has been accomplished using a variety of electromechanical and electronic components or frequency dependence to introduce phase shift or time delay at each of the antenna array radiators. Ferrite and diode phase shifters and MMIC modules are the technologies that have developed to address the control task. There is a continuing need to further develop these technologies in addition to the several new modalities that address the needs of wideband time-delayed arrays. This paper assesses the current state of the art of array control devices and the role of optical and digital control of future arrays. The paper also discusses the relevant array configurations appropriate to these technologies.

Operating Modes and Dynamic Range of Active Space-Fed Arrays With Digital Beamforming

Narrow band space-fed (lens) scanning arrays have played a major role in many military and commercial applications. However, wider bandwidth space-fed arrays with phase shifters in the objective aperture, and subarrayed time delay have not found many ready applications because of network losses, complexity, and more recently because of a perceived incompatibility with active solid state module technology. This paper demonstrates that a feed array with transmit/receive (T/R) modules and digitally reconfigured control, can accommodate both narrow band and radiation with relatively efficient use of the active sources