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Multistatic radar is a promising option for the low-cost collection of multiple-Doppler weather observations. However, due to the use of low-directivity antennas at the receivers in these systems, they typically suffer from extremely high two-way sidelobe levels compared to monostatic radars. Doppler velocity estimation biases induced by sidelobe contamination have proved to be a significant obstacle to more widespread adoption of this technology. It has been noted in the existing literature that the technique of sidelobe whitening, first developed for use in monostatic systems, has the potential to mitigate this issue. However, the existing sidelobe whitening algorithm is not suitable for use in this application, as it is only capable of achieving whitening in the two-way antenna pattern, whereas an algorithm to be used in the multistatic case must be able to achieve this result in the transmit pattern alone. This article proposes an alternate sidelobe whitening technique based on the method of alternating projections which allows for effective whitening in the one-way antenna pattern. A multistatic weather radar time-series simulator is used in conjunction with numerical weather prediction data to demonstrate the effectiveness of this method in mitigating multiple-Doppler measurement biases. [ABSTRACT FROM AUTHOR]

As low-cost fully digital array technology becomes more commercialized, techniques need to be developed to be able to deal with many of the inherent problems of these systems. This article focuses on mitigating the intermodulation distortion (IMD) caused by the low-input third-order intercept point (IIP3) of the low-noise amplifier (LNA) in a digital array element’s channel. The performance of solid-state electronics also varies with the temperature of the device, thus changing the device’s nonlinear characteristics. This article proposes an adaptive solution for nonlinear equalization (NLEQ) with the use of the least mean-square (LMS) algorithm. Data from a modern digital array channel are corrected using the proposed method; the channel nonlinearities are also characterized for further simulations. A simulation using these nonlinear coefficients shows that NLEQ can effectively mitigate the IMD of two strong interferers that had previously distorted the weak signal of interest. Finally, a nine-element fully digital array is simulated, showing the correlation of IMD with specific, predictable directions, and the decorrelation of these spurs after NLEQ is applied to each element of the array. [ABSTRACT FROM AUTHOR]

With an incredible increase in the number of wireless devices and an ever-growing demand for high data rates, 5G needs to provide a solution to satisfy the demand for the next decade. Multiple-input multiple-output (MIMO) systems are seen as one of the primary solutions—allowing for spatial multiplexing and the use of millimeter-wave (mmWave) frequencies, which can provide much larger bandwidths and, thus, data rates. MIMO is very closely related to phased arrays, which have been used for radar for the past few decades and requires many antennas and transceivers—on the order of hundreds or thousands for massive MIMO. To make such systems affordable, low-cost, low-power, and low-complexity is required—inherently compromising other system characteristics, such as linearity. The main focus of this paper will be in summarizing the challenges, recent advances, and potential future breakthroughs concerning MIMO/digital array sensitivity to interferers and nonlinear distortion. Specifically, this paper gives an overview of MIMO/digital array architectures and different techniques currently researched for the characterization and mitigation of spatial and spectral interferers and nonlinearities, which can be used to extend the effective dynamic range of low-cost MIMO/digital array systems. [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]

Spectral regrowth and waveform distortion caused by wideband signals input into active phased array antenna systems is the problem this paper addresses. The paper's unique contribution is the development of the impedance-dependent memory polynomial model, capable of solving nonlinear predistortion model parameters for a solid-state high power amplifier with varying load impedance resulting from active electronic beamsteering. Wideband load impedance mismatched tests demonstrate the effectiveness of this technique on a 2.7 GHz, 8 W amplifier. [ABSTRACT FROM PUBLISHER]

Future weather radar systems will need to provide rapid updates within a flexible multifunctional overall radar network. This naturally leads to the use of electronically scanned phased array antennas. However, the traditional multifaced planar antenna approaches suffer from having radiation patterns that are variant in both beam shape and polarization as a function of electronic scan angle; even with practically challenging angle-dependent polarization correction, this places limitations on how accurately weather can be measured. A cylindrical array with commutated beams, on the other hand, can theoretically provide patterns that are invariant with respect to azimuth scanning with very pure polarizations. This paper summarizes recent measurements of the cylindrical polarimetric phased array radar demonstrator, a system designed to explore the benefits and limitations of a cylindrical array approach to these future weather radar applications. [ABSTRACT FROM PUBLISHER]

The mitigation of third-order intermodulation distortion produced by a nonlinear tunable bandpass filter (BPF) in a digital receiver channel is demonstrated. An iterative solution is proposed, in the use of the least-mean-square algorithm, as an effective way to allow the correction coefficients to adapt to the changes in the system characteristics when the center frequency is changed. Results are shown using a two-pole, varactor-loaded BPF, and an Analog Devices AD9371 transceiver. [ABSTRACT FROM AUTHOR]

Digital beamforming (DBF) has long been heralded as the next frontier in phased array technology, and not without reason. The digitization of transmit and receive signals at the element level opens the door to new processing and beamforming schemes and promises to deliver maximum flexibility and unprecedented dynamic range in large systems. However, it is not without inherent technological risks and practical challenges associated with the amount of data to process and the use of less sophisticated transceivers. This paper provides broad overviews of several interrelated aspects of the resulting DBF trade spaces for these systems. In particular, emerging concepts are highlighted for the roles and interconnection of distributed beamforming/processing for fixed and adaptive beamforming. These are then related to digital array calibration mechanisms that can potentially reduce the need for data- and processing-intensive beamforming algorithms. [ABSTRACT FROM PUBLISHER]

A computer-aided technique is proposed to obtain the embedded characteristics of the elements in a cylindrical phased array using a unitcell approach in Ansys High Frequency Structure Simulator (HFSS). The proposed technique is general and can be used with other commercially available electromagnetic (EM) products that support periodic boundary conditions. Therefore, it can be widely adopted by engineers and researchers to analyze arbitrary element structures in cylindrical phased arrays. The implementation of the technique is discussed in detail, and the related formulation is presented. The method is verified by comparing its results with published literature as well as results obtained through full-wave analysis of a ring of microstrip patch antennas in HFSS. [ABSTRACT FROM AUTHOR]