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Angle of arrival (AoA) for target echo signal detection is crucial in vehicular radar systems, where the estimation of signal parameters via rotational invariance (ESPRIT) provides a high-resolution estimation. A subarray decomposition strategy is presented in this article to create two ESPRIT antenna arrays with enhanced echo signal strengths, applicable to multi-input–multioutput (MIMO) operations for creating a large virtual array. The concept intends to maximize the echo signal’s strength with minimum signal interferences by increasing the aperture sizes of the two ESPRIT antenna arrays. The decomposition produces two virtually overlapped subarrays to increase the subarray aperture sizes in the spatial or spectral representations. It is applied to the MIMO-based arrays for two-way radiation patterns for ESPRIT estimation of AoA. Numerical simulation examples are shown to validate the feasibility and demonstrate the applications. [ABSTRACT FROM AUTHOR]

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 study to reduce the peak sidelobe level (SLL) of a radar two-way array factor is presented. It applies the condition that the first significant sidelobe of the transmitting array is in the same direction as the first null of the receiving array. Moreover, it is supposed that in the two-way array pattern, two consecutive sidelobes near the main beam become equal. Moving one step further, by combining the advantages of taper distribution and the simplicity of the feed network of uniform arrays, a two-weight amplitude distribution for the radar transmit and receive arrays is designed. The resulting peak SLL of the two-way pattern becomes less than −45 dB. [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]

We propose a compact circularly polarized series-fed patch array with enhanced radiation performance at $S$ -band. To our best knowledge, no similar single-layer structure has been designed, measured, and reported in the literature with equivalent radiation performances in terms of reduced sidelobe level (SLL) and aperture efficiency as well as compactness and simplicity. The planar array consists of a 50- $\Omega $ microstrip single feed point, offering uniform and efficient excitation of all its elements that enable a broadside beam with high-gain and low sidelobes. A feeding network for such aperture control is designed and optimized to provide good impedance matching with a two-point excitation per radiating element, which is based on 0° and 90° meander lines to enable circularly polarized radiation. A structure made by a $4\!\!\times \!\!1$ arrangement of square patches is simulated, optimized, and manufactured, providing a realized gain of about 10 dBic and an SLL below −15 dB. Very good axial ratios and high efficiencies are obtained. The proposed antenna may be of interest for next-generation far-field wireless power transmission systems and other applications including target tracking, radar, and internet of things technologies requiring efficient circularly polarized radiation. [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]

In this article, we consider the problem of beampattern synthesis with sidelobe control using constant modulus weights. We specifically focus on two applications, i.e., notching and sidelobe-level (SLL) control (SLC). The considered problem is a challenging NP-hard due to the employed constant-modulus weights. Here, we convert the problem into an intermediate form by incorporating auxiliary variables and changing the form of the constant modulus. Then, we decompose the intermediate form into subproblems of single constraint each. Finally, we propose an iterative solution following the alternate direction method of multipliers (ADMM) and Proximal frameworks. The proposed solution solves the original problem by iteratively solving the subproblems in coordinated logical order. Importantly, it combines the convergence speed of ADMM and convergence property of Proximal methods. In addition, it always satisfies the constant modulus constraint. The solution has a significant contribution to mitigate interference using notching and to realize RadCom. Simulation results show that the proposed solution has a better performance in terms of computational speed, notching, and constant SLL than the previous works. [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]

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]

This contribution presents the results of a dual-polarized radiating element designed to achieve low cross-polarization (lower than −40 dB measured for the E-and H-plane, at least −30 dB in the D-plane based on simulations) and large fractional bandwidth (18%) over wide scanning angles (±60°). The proposed design includes multiple features that enable high isolation between ports, reduction of spurious radiation, highly symmetrical radiated fields, and suppression of diffracted fields between contiguous subarray gaps. To verify the polarimetric requirements for a weather radar, simulated and measured results, including electronic scanning of the array and embedded element patterns of the antenna, are shown. [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]

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]

Highly crevassed ice surfaces at ice-sheet margins and fast-flowing glaciers significantly scatter radar signals. The scattered signals, often known as surface clutter, mask weak echoes from the ice-bed interface. Large wing-mounted antenna arrays are essential to synthesizing low-sidelobe patterns to reduce surface clutter. However, wing-mounted arrays are susceptible to structural flexure, which causes amplitude and phase errors that result in shifting and filling of desired array pattern nulls. In this communication, we characterize the effects of wing flexure on array beamformation using a scaled array model, and we present a compensation method to mitigate phase center errors caused by wing flexure. The compensation greatly improves clutter suppression through improved null formation. Experimental results show that we obtain an average of 7.5 dB improvement in the signal-to-interference noise ratio. [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]

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]

The need to reduce the number of active elements in radar arrays claims for developing new synthesis approaches able to reduce the control points, i.e., the number of transmit/receive modules (TRM) needed to fulfill the design constraints, is presented. As the large part of the TRM costs are related to the active parts (HPA—high power amplifier), a hybrid method for reducing the number of amplitude controls is proposed. This allow the design of new array architectural solutions where the scanning capabilities only rely on phase controls. [ABSTRACT FROM PUBLISHER]

A triangular grid single polarized tapered-slot array antenna for radar applications is studied. Compared with a rectangular grid an equilateral triangular grid allows a larger unit cell without any onset of grating lobes. Since single polarized tapered-slots in triangular grids support guided modes, which cause scan blindness, the increase in unit cell size is smaller than the optimal 15%. The design presented in the paper is capable of scan angles out to 600 from broadside in the E and H planes. To improve the match over the radar band a local minimum in the active reflection coefficient is positioned at the most critical scan direction, resulting in a reflection coefficient that is less than -12 dB in the X-band. To reduce the radar cross section for the cross-polarization an absorbing layer is positioned above the ground plane, which affects some of the guided modes that lead to scan blindnesses. An experimental antenna with 16 × 16 elements was built, and it was found that the H-plane performance for large scan angles for the finite antenna deviates more than expected from the infinite array approximation. Otherwise both mutual coupling measurements and embedded element patterns agrees well with the numerical results. [ABSTRACT FROM AUTHOR]

A method for scanning of the main beam of phased array antennas in a wide angular range is presented. The method utilizes several smaller flat antenna panels, arranged in an array of panels, each of the panels pointed in the direction of the main beam of overall antenna. The output signal of the overall antenna is summation of the signals from all antenna panels. Investigation of the array performance of such structure with respect to the distance between the panels and sidelobe level of the antenna structure is presented. [ABSTRACT FROM AUTHOR]

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]

With the recent emergence of various radio frequency identification (RFID) applications, the desire for simpler, more efficient, and lower cost passive transponders has increased. Retrodirective arrays have been demonstrated as a good candidate for such systems due to their unique function of high-speed, automatic source tracking. A four-element, high-performance retrodirective transponder array is presented in this paper. The architecture uses a sparse array design to reduce the amount of radiating elements. A time sharing switching feature is used in conjunction with this architecture to further reduce RF hardware requirements and cost of the system. The switching network can also serve as a built-in modulator for simple data transfer tasks. [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 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]

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]