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High cross-polarization isolation (CPI) is crucial to the accurate polarization measurement using polarimetric phased array radar (PPAR). In this article, we propose an adaptive direction-dependent polarization state configuration (AD2PSC) method to improve the polarization isolation. Compared with the conventional fixed polarization state of radiated wave whether it is linear, circular, or elliptical polarization state, our AD2PSC approach configures the polarization state on basis of beam steering. To achieve the adaptive configuration of magnitude and phase of the dual-polarization antenna, an improved steepest descent algorithm is put forward. To facilitate the uniform representation for the polarization measurement application of PPAR, the universal expressions of intrinsic and measured backscatter matrices are derived for arbitrary polarization state. The dual-polarization dipole array is used to assess the priority of our proposed method. Compared with the conventional approaches, our approach could obtain higher CPI while being available for a larger scanning range. The configured CPI meets the specific polarization requirement for PPAR. [ABSTRACT FROM AUTHOR]

In this article, a hybrid radar configuration for automotive radar applications is proposed, with the system architecture, design, and measured results reported. The hybrid radar system consists of a vertically distributed phased transmitting array (PTA) and a horizontally aligned digital beamforming (DBF) receiving array, thereby enabling 2-D beam scanning with a reduced channel number. In contrast to time-division multiplexing (TDM) multiple-input multiple-output (MIMO) radars, in which only a single transmitter is active at a time in the TDM MIMO radar configuration due to the working principle of switching between different transmitting elements, here, all the phased array transmitters of the proposed radar work simultaneously. The demonstrated system realizes a higher transmitted power and signal-to-noise ratio, provided that the equivalent isotropically radiated power (EIRP) is not limited and the radiated power of each transmitter is equal in these two radar configurations. In addition, only 1-D DBF is required for the proposed hybrid radar because beamforming in another dimension is accomplished by the PTA, thus alleviating the baseband complexity and signal processing burden. As a proof-of-concept example for system validation, a hybrid radar prototype is fabricated and measured at around 24 GHz, without considering any specific EIRP limitations in this band, thus confirming the validity of the proposed concept. [ABSTRACT FROM AUTHOR]

A dual-polarized planar phased array antenna with enhanced polarization and isolation characteristics for multifunction applications is presented. A bent crossed dipole is selected as the element of the array antenna. The bend angle is optimized to widen the E-plane active element pattern of the dipole resulting in a pair of matched co-polar patterns. Contrary to common patch array antennas, this design does not require a continuous grounded substrate. This diminishes the surface wave propagation along the ground plane. Efficient techniques, applied to the element design, isolate the two polarizations from each other. Higher than 40 dB port isolation is achieved within the entire frequency range of 2.7–3.0 GHz in principal plane scanning. In order to preserve the symmetry of the array antenna, a mirrored arrangement in both orthogonal directions is applied to the array configuration. This enhances the co- to cross-polarization levels to better than 45 dB in scanning up to ±45° in the principal planes. The proposed phased array antenna with enhanced polarization purity can potentially improve polarimetric performance. [ABSTRACT FROM AUTHOR]

This article has developed a new approach to combine transmit beamforming techniques and 4-D antenna array theory for simultaneously improving the detection and low probability of intercept (LPI) capabilities of radar. This new approach enjoys most of the advantages of multiple-input multiple-output (MIMO) and phased arrays, providing excellent detection and LPI capabilities. The essence of the proposed approach is to utilize a 4-D variable to extend the detection dimension and increase the signal uncertainty. Specifically, the flexible choices of a time-modulation scheme can greatly improve the detection and LPI capabilities of radar. The substantial improvements achieved by the proposed method compared with basic MIMO and phased-MIMO arrays are demonstrated by simulations through analyzing the corresponding beampatterns. In addition, a basic experiment with reference to transmit beampatterns of 4-D antenna arrays is presented to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, challenges and limitations of using cross-polarization suppression methods for dual-linear polarization antenna arrays are presented. A simple probe-fed patch antenna and high-performance, dual-polarized hybrid-fed patch antennas are used for this article. The image feed method is used for improving the cross-polarization level and increasing the geometrical symmetry of a very large phased array antenna. It is shown that decomposing the antenna radiation pattern to its even and odd components for calculating $2\times $ 2-element subarray radiation pattern has fundamental limitations and none of four different $2\times $ 2-element and $4\times $ 4-element subarray configurations will entirely suppress the sidelobe issue of configured arrays. The accuracy of using embedded element pattern for calculating the radiation pattern of very large array antennas with identical subarrays is studied, and an accurate procedure for predicting array antenna radiation pattern is proposed. The appearance of undesired sidelobes has been examined, and optimal design for mitigating the sidelobe issue associated with the large array of identical subarrays with image configuration is presented. [ABSTRACT FROM AUTHOR]

This article presents a technique designed to extend the scanning range of a probe-fed patch array whose performances are limited by scan blindness, due to a strong surface wave coupling. The current framework relates to the context of radar applications requiring a large scanning range (up to 60°) and where no inter-element spacing modification is possible as a result of strong T/R modules integration constraints. The proposed solution is based on the introduction of an additional correcting coupling within the array, by means of microstrip lines connecting the sources two by two. A thorough step-by-step description of the design methodology is introduced. It is then implemented in the case of a single-polarized ten-element patch array operating in $X$ -band. Simulation results as well as an experimental validation of the concept are presented. They assess the effective improvement of the active impedance matching and realized gain resulting from the use of connecting lines. [ABSTRACT FROM AUTHOR]

This article presents the synthesis of isophoric (equally fed), wideband wide-scan sparse concentric ring antenna arrays (CRAs) with low sidelobe level (SLL). The technique utilizes the characteristics of Bessel functions (BFs) of the first kind for representing the array factor (AF) and propose deterministic design guidelines for SLL reduction. It is shown that higher order BFs are necessary to predict nonsymmetry in the azimuth pattern of CRA. A design process for deriving ring radii and number of elements in the rings is presented to achieve highly sparse CRAs. Numerical test case studies are presented demonstrating the design procedure and its validation with the prior literature. The effect of the mutual coupling on the array performance over wideband and wide-scan volume is also presented. The results show sparser CRAs with comparable values of peak SLL (PSLL) and −3 dB beamwidth. This work may complement the existing stochastic or other efficient optimization techniques in reducing their computational time, especially for large arrays (more than hundreds of elements). This work focuses on phased array antennas for radar applications. [ABSTRACT FROM AUTHOR]

Compact phased-array antennas embedded in flip-chip ball grid array (BGA) packages are proposed to operate over the unlicensed 60 GHz frequency band. Radiation properties are enhanced by designing novel corrugated soft-surface structures and implementing them using the low-temperature co-fired ceramic process with no extra cost and fabrication complexity. This is achieved by adjusting via land diameters of periodic grounded vias in top four layers of the package, which in fact create perfect magnetic boundaries between the phased-array antenna elements to modify the electric near-field distributions and consequently improve far-field characteristics including gain, cross polarization, sidelobe level, and beam steering. Low-loss transitions from flip-chip IC to antenna elements are designed with less than 0.1 dB amplitude and 2° phase imbalance over 50–70 GHz. Prototypes with/without soft-surface structures are fabricated to work with flip-chip ICs with/without switches. A USB-interface adapter and a waveguide-interface module with a compact vertical power combiner are proposed for the first time to experimentally evaluate the phased-array antenna while connected to the flip-chip RF IC. Significant miniaturizations and improvements are achieved over the wide frequency range of 56–67 GHz, demonstrating up to 7 dB reduction in sidelobe level, up to 4 dB reduction in cross polarization, and up to 3 dB enhancement in gain at different directions. [ABSTRACT FROM AUTHOR]

Sum ($\Sigma$) and difference ($\Delta$) beampatterns are commonly utilized to estimate the bearings of targets in the radar system. However, the nulls of $\Delta $ -pattern are not always aligned with those of $\Sigma $ -pattern, and this phenomenon would become more severe in practical scenario since the array errors exist. Meanwhile, the sidelobe level (SLL) of the array would also increase due to the unavoidable errors. The above-described factors would dramatically decrease the performance of radar in the adaptive suppression of interference. To increase the output signal-to-interference-plus-noise ratio of a radar system, this paper presents an approach to design the low SLL $\Sigma \Delta $ -patterns where the nulls of the $\Delta $ -pattern, excluding the central null, are always aligned with those of the $\Sigma $ -pattern in the presence of errors. Two schemes are addressed to obtain the covariance matrix for null-alignment constraint, which is exploited to force nulling in desired angles accordingly. In the sequel, the matrix tapering method is adopted to broaden the nulls and enhance the robustness for the possible errors. With the proposed approach, the low SLL and nulls alignment can be achieved simultaneously. Numerical examples are provided and discussed to demonstrate the effectiveness of the proposed solution, including the results based on a linearly spaced microstrip array antenna. [ABSTRACT FROM AUTHOR]

This paper discusses the impact of a wet flat radome on the performance of a line replaceable unit active phased-array antenna developed for a dual-polarized phased-array weather radar. Water formations, such as film and droplets, were fully characterized over flat and curved radome surfaces using an analytical model as a function of the precipitation rate. Numerical simulations and experimental results validated the proposed analytical model. An active dual-polarized phased-array of $8\times 2$ elements was used to evaluate the degradation of the cross-polarization component as well as the mismatch and the phase of scanned antenna radiation patterns for vertical and horizontal polarizations. In addition, a radome panel of an $S$ -band weather radar (WSR-88D) was characterized in the far field using a single radio-frequency probe. It is demonstrated that even at the $S$ -band, the water formation on the radome affects both copolarization and cross-polarization components, degrading the overall performance of the dual-polarized radar system under rain conditions. [ABSTRACT FROM AUTHOR]

In this reply, we refer to comments made by a reader on our publication “Overlapped phased array antenna for avalanche radar.” The authors would like to thank the reader for reading this article. In this article, the authors provided detailed answers to the comments made by the reader. [ABSTRACT FROM AUTHOR]

A frequency reconfigurable phased array element is presented. The operational band of the single port L/S-band antenna can be selected by modifying the element apertures with p-i-n diode switches. The antenna element satisfies strict requirements on its frequency band separation (2.2:1), size, feeding structure, and control lines to be integrated into a phased array system. A multiscale array topology is proposed to achieve wide angle scanning (±60°) in both operational bands of the array. [ABSTRACT FROM AUTHOR]

Snow avalanche is a natural phenomenon, which annually causes infrastructure damage and leads to human casualties in many countries all over the world. As a result, a detailed hazard mapping is required to be able to understand the avalanche risk levels. Also, the scarcity of the areas suitable for constructing infrastructures in the mountains places a high premium on providing high precision hazard mapping. This paper presents the design and development of an advanced phased array antenna for an FMCW radar to produce a high resolution image of snow avalanche in range and cross-range. The proposed antenna is a 16-element fully populated phased array with ±14° azimuth beamwidth and ±22.5° fixed elevation angle. The designed phased array antenna has 14.4 dBi gain and −20.3 dB sidelobe level. In this design, subarraying overlapping technique has been used to eliminate undesirable grating lobes by means of spatial antialias filtering. A phased array power divider is proposed to allow tapering of the amplitude of the elements to achieve low sidelobe level. [ABSTRACT FROM PUBLISHER]

This communication presents the experimental results of a ultrawideband 2–18-GHz dual-polarized Vivaldi antenna array for airborne radar measurements of snow. The antenna design is based on the previously reported all-metal flared-notch array by Kindt and Pickles for operation over the frequency range 0.7–9 GHz. An antenna array prototype consisting of $8 \times 8$ active dual-polarized elements was fabricated with precise aluminum machining and tested in the anechoic chamber. Beamsteering upto 30° was experimental demonstrated from 2 to 18 GHz. The measurement results are in a good agreement with the full-wave simulation results in both polarization configurations. Preliminary sample results from data collected using the Vivaldi array are also presented. The antenna array enables full polarimetric measurements of snow-over-sea-ice for estimating the snow-water-equivalent (SWE), as well as fine-resolution mapping of snow-air and snow-ice interfaces for estimating thickness. [ABSTRACT FROM PUBLISHER]

Modern phased-array radar systems increasingly require customized transmit patterns, implemented using only phase shifts, to illuminate or suppress interference from specific regions. Multiple custom patterns may be required at every beam position, requiring either precomputation of a large library of phase weights or real-time computation. Presented here is a weighted pattern-error formulation that offers efficient FFT-based calculation of both the objective and its gradient vector and is well suited for solving with efficient quasi-Newton methods. Although deliberately simple, the objective has several heuristic parameters for flexibility and can be used to simultaneously customize the mainbeam shape and selectively suppress the sidelobes. Examples demonstrate the feasibility of 1000+ element 2-D array designs, as well as a characterization of point nulls that commonly occur in the mainbeam of suboptimal local minima. [ABSTRACT FROM AUTHOR]

We describe a novel iterative methodology for computing a set of low-sidelobe beamforming weights for an airborne, electronically-steered phased-array radar using an in-flight stochastic optimization routine performed over a number of coherent processing intervals (CPIs). The proposed approach is notable in that it does not rely upon a good antenna calibration and only requires digitization of the radar's sum beam. By observing the radar ground clutter, the algorithm iteratively adjusts the beamformer. Furthermore, it is computationally inexpensive and scales favorably to radars comprising very large numbers of antenna elements and requiring extremely low sidelobes. [ABSTRACT FROM PUBLISHER]

A memetic particle swarm optimization (MPSO) algorithm is applied to fine-tune the asymmetrical difference pattern of a linear array, which is useful for tracking targets, for example, in radar applications. The side-lobe level of the asymmetrical difference pattern with various peak differences can be successfully reduced, while maintaining the desired squint angle and the side-lobe difference. Conventional PSO, genetic algorithm (GA) and memetic GA (MGA) have also been applied, with the initial conditions of uniformly-excited and Bayliss linear arrays, to compare their performance of optimization. [ABSTRACT FROM PUBLISHER]

We present an efficient solution for the fast computation of wideband radiation patterns of large planar arrays with overlapped subarray architecture, subject to beamforming errors. We obtain very good results fully hosting the simulation on a desktop platform, and even better results implementing a small portion of code on commercially-available graphical processing units (GPUs). Errors can be introduced throughout the beamforming chain and include random phase/magnitude errors, element failures, and surface deformation errors. At the core of the computational architecture are interchangeable primitives that quickly compute the entire far-field subarray pattern, subject to errors and user-defined tapers. The primitives are routines that address the general case of arrays with non-uniformly spaced elements (to model surface distortion) and the special case of arrays with uniformly-spaced elements. Both grid-type primitives are CPU hosted, while only the general non-uniform grid primitive type is GPU hosted due to its excellent run-time performance. The simulation quickly generates wideband patterns for the entire forward-looking hemisphere with sufficient resolution to accurately evaluate directivity and sidelobe metrics. Using only the non-uniform grid type hosted on the GPU, we show significant run-time improvement over both CPU-hosted implementations: 18.0\times over the general non-uniform grid and 5.7\times over the uniform grid. [ABSTRACT FROM PUBLISHER]

The proposed time-interleaved phased array is a functional integration of a space-time domain filter in antenna arrays and a time-frequency domain filter in mixer arrays. Spatially sampled signals by the antenna arrays will be interleaved in time by the mixer arrays to increase modulation speed while leveraging relatively low-frequency carriers. In M-element time-interleaved arrays, the carriers frequency can be reduced by the factor of M to realize an equivalent functionality as in conventional phased arrays based on fundamental carrier modulations. Depending on the array configuration, the time-interleaved phased array can be categorized as “correlated-noise time-interleaved (CNTI)” array or “uncorrelated-noise time-interleaved (UNTI)” array. In the CNTI-array, both signal and correlated noise will be interleaved resulting in the same filter response for the signal and noise, whereas in the UNTI-array only signal will be interleaved in time domain: uncorrelated noise will not participate in the time-interleaving process. An extensive noise analysis for both array types is provided in the paper. To achieve maximum SNR, noise filtering techniques are proposed and verified through CAD behavioral simulations. In essence, the time-interleaved array architecture is a mix of parallel signal processing at RF and LO domains, which can have an advantage in compensating system performance deficits due to an active device speed limitation at high frequencies at the expense of an endurable system complexity. [ABSTRACT FROM PUBLISHER]

This paper presents an analytical transient analysis of electromagnetic field radiation from a time-delayed and finite periodic array of antennas for the near- and far-field focused applications. The elemental current moments of array are assumed with a transient impulse input for the excitations whose signals are delayed to radiate near-zone focused fields. The transient field phenomena for each of the Floquet mode expansion were analyzed. The solution reduces to the case of far-zone field radiation by moving the focus point to the far zone. The analysis shows that the radiation exhibits an impulse field at the focused point, and finite pulses at locations away from the focus point. Phenomena of partial cylindrical wave functions have been observed. [ABSTRACT FROM PUBLISHER]

A phase-only method of generating notches in the beam pattern of a phased array antenna is described. It is shown how the problem can be formulated as a semidefinite programming problem, and solved with readily available solvers. Numerical results simulating the performance of a 32 element uniform linear array are presented. [ABSTRACT FROM PUBLISHER]

This communication presents results for the low sidelobe synthesis using amplitude-only tapering applied on the turned ON elements of large circular thinned arrays. The low sidelobe synthesis was carried out with the same iterative Fourier transform method that was developed earlier to restore the original sidelobe performance in case of defective array elements. The presented low sidelobe results refer to highly thinned circular arrays with diameters ranging from 25 to 133.3 wavelengths and involved both sum and difference patterns. In addition, sector nulling in combination with low sidelobes was numerical investigated. [ABSTRACT FROM PUBLISHER]

A double rhombus antenna fed through a microstrip 1800 phase shifter is presented. The 1800 phase shifter is a novel design of microstrip-to-coplanar waveguide (CPW)-to-microstrip transition. The proposed phase shifter is obtained without changing the layer of the second microstrip line for an easy embedding into the feedline. Via holes are used to transfer the current from the top to the bottom substrate layer and vice versa. The antenna with the phase shifter is operating in a wide bandwidth from 5.7 and 18.6 GHz (106%), and provides stable endfire radiation patterns. This design is tested in a modified two-element array configuration and proved to have a wide usable bandwidth. [ABSTRACT FROM AUTHOR]

Directional constraints are imposed on the weights of an antenna array to obtain solutions of some constrained beam- forming problems. For broadband antenna arrays, formulation of a constrained beamforming problem typically requires presteering the array using steering delays. These delays create implementation problems and cause loss of system performance in the presence of implementation errors. This paper presents new kind of constraints referred to as convolution constraints, which are easy to implement, eliminate the need for presteering the array and can be used for broadband pattern synthesis. Examples are presented to demonstrate many applications of these constraints on an array weights. [ABSTRACT FROM AUTHOR]

We present the design of miniaturized resonant inclusions to be employed in the practical realization of meta-material samples with anomalous values of the real part of the permeability. Such inclusions, in fact, can be employed in the design of both μ-negative (MNG) materials and artificial magnetodielectrics (with negative and high-positive values of the real part of the permeability, respectively). The inclusions here considered are the multiple split-ring resonators (MSRRs), that represent a straightforward extension of the commonly used split-ring resonators (SRRs), and the spiral resonators (SRs), that enable a greater miniaturization rate. Some physical insights on the resonance mechanism and on the inherent saturation of the resonant frequency when increasing the number of the rings of the MSRRs and the number of the turns of the SRs are given in the paper. New and accurate analytical design formulas, based on a quasi-static model, for both MSRRs and SRs are derived and tested through a proper comparison with the existing formulas and full-wave numerical results. Both MSRRs and SRs are shown to be useful to reduce the electrical dimensions of the resonant inclusions when synthesizing artificial metamaterials. [ABSTRACT FROM AUTHOR]

Static and rotating phased array radars are analyzed using conformal co-ordinate transformations on Riemann manifolds. By the use of a suitable metric tensor on a Riemann surface we obtain an expression for the parametric distance between two points that is used to calculate the area of surveillance mapped onto the uv-plane. The invariance of the beamwidth in uv-space allows us to determine the total number of beams required for scanning while the total search function time is obtained as an integral representing the volume under a Riemann time-manifold. Co-ordinate transformations are obtained for rotating arrays based on Sanson-Flamteed projections and we derive the corresponding search function times for each radar type. The packing densities of the beams are examined for both static and rotating arrays and we examine the number of radiating elements that are required so that free-space surveillance time is maintained on the basis of the number of array faces in simultaneous use. [ABSTRACT FROM AUTHOR]

A broadband microstrip-fed printed antenna is proposed for phased antenna array systems. The antenna consists of two parallel-modified dipoles of different lengths. The regular dipole shape is modified to a quasi-rhombus shape by adding two triangular patches. Using two dipoles helps maintain stable radiation patterns close to their resonance frequencies. A modified array configuration is proposed to further enhance the antenna radiation characteristics and usable bandwidth. Scanning capabilities are studied for a four-element array. The proposed antenna provides endfire radiation patterns with high gain, high front-to-back (F-to-B) ratio, low cross-polarization level, wide beamwidth, and wide scanning angles in a wide bandwidth of 103%. [ABSTRACT FROM AUTHOR]

A wideband low profile phased array using long slot aperture was recently developed for radar and EW applications. A prototype UHF array with 4 × 8 (32) elements (1.12 m × 2.24 m × 23 cm) was built and tested for 150–600 MHz operation. Array patterns, gain, and cross-pol level were measured. Excellent performance was observed. The array is 23 cm thick, and it weighs 7 kg (2.8 kg/m²). Lossy loading material may be used to make it thinner, but this is believed to be the lightest and thinnest UHF array reported for wideband applications without gain penalty. [ABSTRACT FROM AUTHOR]

A modified printed bow-lie antenna is designed to simultaneously cover the operations in the C and X-bands from 5.5 to 12.5 GHz. The presented antenna has an end fire radiation pattern that makes it suitable for integration in single and dual polarized phased array systems. The antenna exhibits small size and wide bandwidth of 91%. The radiation characteristics are presented for a single element and a linear array of this antenna. [ABSTRACT FROM AUTHOR]

Radar cross-section (RCS) measurements of a target performed in an anechoic chamber with the conventional one antenna calibration technique may yield erroneous results at frequencies lower than those for which the chamber has been initially designed, essentially because the absorbers become ineffective and the field emitted by the antenna no longer satisfies the plane-wave I (PW) condition on the target. A possible way to circumvent these difficulties is to use a phased antenna-array that synthesizes a PW in a bounded domain, usually called the quiet zone (QZ). In this paper, we propose a calibration technique that allows an accurate reconstruction of the RCS of a target located in the near-field of the array, even when electrically conducting walls are present. A theoretical study of the problem at hand is presented that allows one to specify clearly the hypotheses that are being made and to identify the parameters that govern the accuracy of the RCS reconstruction. When the target-array, antenna-antenna, and target-walls-target interactions are neglected, it is demonstrated that this calibration technique synthesizes a PW in QZ if the calibration object is a line source (two-dimensional) or an infinitesimal dipole (three-dimensional). Three-dimensional full-wave numerical simulations, that take all the previously mentioned interactions into account, illustrate the efficiency of this technique when the array and conducting walls are a few wavelengths apart from the target. [ABSTRACT FROM AUTHOR]

The paper is devoted to the development of a phased array antenna for avalanche radar providing electrical scanning of beam within the angular sector of ±14°. The paper contains useful information being of interest for the antenna society; however, there are a few comments given in the following. [ABSTRACT FROM AUTHOR]