Electrically large arrays offer high resolution, however since cost is proportional to the number of elements, large dense arrays have a high cost. Sparse arrays on the other hand offer a cost-effective solution with less number of elements, but the problem is that with large element spacing, grating lobes, or equivalently aliasing, appears in the radiation pattern of analog sparse arrays. In this work, we show that in digital sparse arrays, this results in false detection of targets in direction finding applications. As a solution to this problem, we propose sparse digital arrays where the element locations are determined by shifted low discrepancy sequences. We present numerical results and show that the field of view of sparse digital arrays can be extended significantly by using our proposed approach.

Element failures degrade the performance of an antenna array. The rate of failure depends upon the aperture temperature as well as manufacturing defects. This paper presents a way to compensate for element failures in a thinned transmit array by turning on elements that were thinned in order to replace the failed elements. Both uniform and nonuniform failures are considered.

Physically large digital beamformers offer higher resolution, but since the cost is proportional to the number of elements in the array, designers try to minimize the number of elements by creating sparse arrays. Larger element spacing however results in grating lobes which in direction finding results in false signal detection. Aperiodic spacing can reduce the grating lobes, however random approaches typically increase the variation in element density. This paper explores the use of nonuniform element spacing based on the hierarchical, low-discrepancy van der Corput sequence for direction finding with sparse digital arrays. Numerical results are presented for linear arrays with average element spacings of one wavelength and taking into account multiple noise cases. We show that the proposed approach is capable of accurate direction finding with sparse arrays and provides a more uniform distribution compared to an equal set of uncorrelated random points.

In dynamic high-interference environments, classical approaches to digital beamforming typically can't distinguish between the intended signal and interferences, which disrupts the intended operation. We consider a dynamic scenario where carrier frequency offset, in addition to element location errors, severely corrupts the received signal. We show that while traditional methods fail, our solution is effective. We present a mathematical model for the signal under these conditions, and then implement an evolutionary search approach that minimizes the peak interference amplitude using this received signal model. Our numerical studies show that the proposed approach removes the issues with both phase drifts and element location errors in dynamic digital beamforming scenarios.

Phased arrays play an increasingly important role in communications and radar systems. These systems require wideband signals to achieve the desired high-performance goals. A phased array's bandwidth depends on much more than the bandwidth of its components. When designing phased arrays, the traditional time-harmonic analysis methods do not capture all of the frequency performance constraints imposed by the array architecture. Grating lobes limit the maximum element spacing, while pulse/symbol dispersion and beam squint limit maximum array size and bandwidth. Hardware frequency limits bound the operating bandwidth of the array. This article discusses time-dependent performance concerns of phased arrays that limit bandwidth, such as the constraints imposed on scan angle, frequency bandwidth, beam squint, dispersion, and hardware.

Sparse spherical arrays have grating lobes due to large element spacings. Aperiodic spacing can reduce the grating lobes, however random approaches typically increase the average sidelobe level. This paper explores the use of a deterministic hierarchical random-like distribution based on the low-discrepancy Van der Corput sequence. Array pattern results are presented for hemispherical arrays with element spacings larger than one wavelength and we show that this approach removes the grating lobes while allowing one to add or remove elements without needing to recalculate positions.

Sparse cylindrical arrays have grating lobe issues. Aperiodic spacing can reduce the grating lobes, however random approaches typically increase the average sidelobe level in addition to creating element clumping problems. This paper explores the use of a deterministic low discrepancy quasi-random distribution. The implementation of Sobol sequence on cylindrical platforms is outlined and we present numerical results for sparse array that are capable of removing the grating lobes.

Grating lobes in sparse arrays can be removed by using aperiodic element spacing, however, the traditional random sampling methods cluster some of the elements too close together, making fabrication impractical. We present a new constraint based design approach using guided random search. Numerical results are presented and we show that our approach is capable of removing the grating lobes and reducing the sidelobe level while keeping the elements from being too close together with an organized distribution within the aperture.

Sparse antenna arrays are effective at reducing array cost, but their design is challenging due to the large element spacings causing grating lobes. Aperiodic element spacing can remove the grating lobes, but random element positions increase the sidelobe levels and cluster some of the elements too close together. This paper explores the use of nonuniform element spacing based on Poisson-disk sampling. Array pattern results are presented for planar arrays with circular apertures with element spacings larger than one wavelength and we show that this approach is capable of removing the grating lobes and reducing the sidelobe level while keeping the elements from being too close together.

Airborne, atmospheric radars need to detect the presence of relatively weak weather echoes near the earth's surface. In order to accomplish this, both antenna sidelobes and range-time sidelobes must be suppressed considerably. This paper focuses on antenna sidelobe suppression by means of using a genetic algorithm to optimize both the thinning of the transmit aperture and the receive taper simultaneously in order to get desirable two-way sidelobe levels.

Digital beamforming is the holy grail of antenna array technologies, however implementing digital beamforming into practical antenna arrays has been slow due to hardware complexity and cost. We propose a relatively inexpensive new approach to digital beamforming using software defined radios. Using this system, we carried out experiments on adaptive interference cancellation. We present detailed description of the beamformer system along with the developed control software and experimentally verify the beamformer performance. Our results show that in high-interference and high-multipath environments, where carrier frequency offsets cannot be measured, conventional interference cancellation algorithms fail. We propose two new robust solutions to this problem and compare the results with multiple techniques, including the minimum variance distortionless response beamformer, which outputs the highest possible signal-to-interference-plus-noise-ratio (SINR). We experimentally demonstrate that both our approaches work well in the face of these types of signal corruptions and are capable of interference cancellation without degrading SINR or other system performance factors, and without the need for transmitter and receiver synchronization.

This issue of IEEE Antennas and Propagation Magazine (APM) starts with a special section "Artificial Intelligence in Electromagnetics." I am very grateful to the guest editors and editorial board members of APM, Prof. Randy Haupt and Prof. Paolo Rocca, for proposing and editing this cluster of excellent articles. The topic is attracting increasing interest in our community, and this special section can serve both the novice and the expert reader in this scientific subfield. Our readers will also find several other interesting feature articles in this issue. This is also the inaugural issue for a new column of the magazine: "COPE Corner." This column will support the IEEE Antennas and Propagation Society’s (APS's) Committee on Promoting Equality (COPE), which has been recently established. We additionally regretfully announce the recent passing of three very prominent colleagues, Prof. Tapan Sarkar, Prof. Theodoros D. Tsiboukis, and Prof. Tatsuo Itoh, who were extremely active in our scientific community. The magazine honors their memories in the "In Memoriam" column; see pages 156–159.

Sparse arrays have grating lobes in the far field pattern due to the large spacing of elements residing in a rectangular or triangular grid. Random element spacing removes the grating lobes but produces large variations in element density across the aperture. In fact, some areas are so dense that the elements overlap. This paper introduces a low discrepancy sequence (LDS) for generating the element locations in sparse planar arrays without grating lobes. This nonrandom alternative finds an element layout that reduces the grating lobes while keeping the elements far enough apart for practical construction. Our studies consider uniform sparse LDS arrays with 86% less elements than a fully populated array, and numerical results are presented that show these sampling techniques are capable of completely removing the grating lobes of sparse arrays. We present the mathematical formulation for implementing an LDS generated element lattice for sparse planar arrays, and present numerical results on their performance. Multiple array configurations are studied, and we show that these LDS techniques are not impacted by the type/shape of the planar array. Moreover, in comparison between the LDS techniques, we show that the Poisson disk sampling technique outperforms all other approaches and is the recommended LDS technique for sparse arrays.

Designing sparse cylindrical arrays without grating lobes is a challenging task due to the large element spacings. Aperiodic spacing can reduce the grating lobes, however random approaches typically increase the average sidelobe level. This paper explores the use of nonuniform element spacing based on the low-discrepancy Van der Corput sequence. Array pattern results are presented for cylindrical arrays with element spacings larger than one wavelength and we show that this approach is capable of removing the grating lobes.

This article provides an overview of a few applications of artificial intelligence (AI) in adaptive and reconfigurable antenna arrays. In particular, AI proves to be more robust than traditional approaches in noisy and high multipath environments compared to many signal processing algorithms. AI is highly dependent upon the array architecture and requires the signal control offered by digital beamforming. Five application areas are presented, including adaptive nulling, wireless localization, multiple-input, multiple-output (MIMO) communications, element failures, and calibration.

Discusses the importance of allocating the proper amount of time to accomplish tasks and goals. To effectively prioritize your tasks and goals, you must first honestly evaluate the amount of time required for you to complete these actions and so understand your bandwidth. People tend to be overly confident in their self-awareness, which leads to the Planning Fallacy. To appropriately plan within your bandwidth, it is important to first take an unbiased view on the amount of time required to meet your goals, whether personal or professional. It is also important to understand the number of prior commitments and urgent tasks and how they will impact your ability to meet these defined goals. True self-awareness requires an honest evaluation of what you can accomplish, and almost more importantly, what you cannot accomplish. This requires you to evaluate obligations and goals based on true capacity planning rather than a simple ranking of competing priorities.

The term “silver lining” originated from the 1634 poem “Comus” by John Milton. It describes the glistening edges of a cloud that blocks the sun. We use it when emphasizing the positive aspects of a very negative situation.

Discusses the importance of allocating the proper amount of time to accomplish tasks and goals. To effectively prioritize your tasks and goals, you must first honestly evaluate the amount of time required for you to complete these actions and so understand your bandwidth. People tend to be overly confident in their self-awareness, which leads to the Planning Fallacy. To appropriately plan within your bandwidth, it is important to first take an unbiased view on the amount of time required to meet your goals, whether personal or professional. It is also important to understand the number of prior commitments and urgent tasks and how they will impact your ability to meet these defined goals. True self-awareness requires an honest evaluation of what you can accomplish, and almost more importantly, what you cannot accomplish. This requires you to evaluate obligations and goals based on true capacity planning rather than a simple ranking of competing priorities.

4-arm spiral antennas have a wide bandwidth and circular polarization when operating in mode 1 (fundamental mode). Switching to mode 3 (to obtain opposite circular polarization) dramatically reduces the antenna bandwidth compared to mode 1. In this work we reduce the arm sizes of the spiral (for example with RF switches) to increase the bandwidth of mode 3 at the higher mode 1 frequencies. In this way the antenna has the same wide bandwidth for both polarizations (modes).