Jingye Cai

Waveform-Diversity-Based Millimeter-Wave UAV SAR Remote Sensing

To integrate a synthetic aperture radar (SAR) into an operational unmanned airborne vehicle (UAV), it should be as small as possible to meet stringent limitations of size, weight, and power consumption. It appears that the novel combination of millimeter-wave frequency-modulated continuous-wave (FMCW) technology and SAR techniques can provide an optimal solution. However, some efficient techniques should be applied to resolve range/Doppler ambiguities in FMCW UAV SAR systems. As such, a technique of waveform-diversity-based millimeter-wave UAV SAR imaging is presented in this paper. Along with the described system concept and signal model, the performance of the diversified waveforms evaluated by their cross correlations is detailed. As the conventional stop-and-go approximation is not valid for FMCW SAR, a modified wavenumber-domain algorithm with a consideration of continuous antenna motion during transmission and reception is derived. This imaging algorithm is validated with computer simulations. Furthermore, one parallel direct-digital-synthesizer-driven phase-locked-loop synthesizer with adaptive nonlinearity compensation, which has been validated by the experimental results, is proposed to obtain a millimeter-wave FMCW signal with fine frequency linearity.

A Technique for Jamming Bi- and Multistatic SAR Systems

Bi- and multistatic synthetic aperture radars (SARs) can achieve reduced vulnerability in military systems, especially in directional responsive jamming, and avoid physical attack to radar platforms. In this letter, a technique for jamming bi- and multistatic SAR systems is proposed, which is implemented with a novel transponder. This technique is based on a delayed retransmission of the received radar signal toward the scene. Unlike conventional delayed jamming, here, the jammers delay time is random in the whole range interval. Moreover, the jamming signal is not retransmitted to the receiver directly but to the areas with targets that need to be protected against being imaged by radar. By this, it is then possible to jam the radar echoes independent of the receiver location

MIMO SAR using Chirp Diverse Waveform for Wide-Swath Remote Sensing

Synthetic aperture radar (SAR) is a well-proven remote sensing technique; however, current single-antenna SAR systems cannot fulfill the increasing demands of future remote sensing in high-resolution and wide-swath imaging performance. This paper presents a scheme of multiple-input and multiple-output (MIMO) SAR using chirp diverse waveform for wide-swath remote sensing. This approach employs MIMO antenna configuration in elevation which is divided into multiple subpertures. In this way, multiple pairs of transmit-receive virtual beams directing to different subswathes are formed simultaneously. Equivalently a large swath is synthesized. The corresponding system scheme, chirp diverse waveform design, multi-beam forming algorithm and range ambiguity performance are investigated. A chirp-scaling-based image formation algorithm is presented to focus the MIMO SAR simulation data. Comprehensive numerical simulation examples are performed. It is shown that the proposed method enables the SAR systems to operate with high flexibility and reconfigurability which is particularly attractive for next generation remote sensing technique.

Range-Angle-Dependent Beamforming by Frequency Diverse Array Antenna

This paper proposes a range-angle-dependent beamforming for frequency diverse array (FDA) antenna systems. Unlike conventional phased-array antenna, the FDA antenna employs a small amount of frequency increment compared to the carrier frequency across the array elements. The use of frequency increment generates an antenna pattern that is a function of range, time and angle. The range-angle-dependent beamforming allows the FDA antenna to transmit energy over a desired range or angle. This provides a potential to suppress range-dependent clutter and interference which is not accessible for conventional phased-array systems. In this paper, a FDA radar signal model is formed and the range-angle-dependent beamforming performance is examined by analyzing the transmit/receive beampatterns and the output signal-to-interference-plus-noise ratio (SINR) performance. Extensive simulation examples and results are provided.

Near-Space Microwave Radar Remote Sensing: Potentials and Challenge Analysis

Near-space, defined as the region between 20 km and 100 km, offers many new capabilities that are not accessible to low earth orbit (LEO) satellites and airplanes, because it is above storm and not constrained by either the orbital mechanics of satellites or the high fuel consumption of airplanes. By placing radar transmitter/receiver in near-space platforms, many functions that are currently performed with satellites or airplanes could be performed in a cheaper way. Inspired by these advantages, this paper introduces several near-space vehicle-based radar configurations, such as near-space passive bistatic radar and high-resolution wide-swath (HRWS) synthetic aperture radar (SAR). Their potential applications, technical challenges and possible solutions are investigated. It is shown that near-space is a satisfactory solution to some specific remote sensing applications. Firstly, near-space passive bistatic radar using opportunistic illuminators offers a solution to persistent regional remote sensing, which is particularly interest for protecting homeland security or monitoring regional environment. Secondly, near-space provides an optimal solution to relative HRWS SAR imaging. Moreover, as motion compensation is a common technical challenge for the described radars, an active transponder-based motion compensation is also described.

Near-space SAR: A revolutionary microwave remote sensing mission

Inspired by the recent advances in near-space defined as the region between 20km and 100km, this paper proposed the concept of near-space SAR. To the authors knowledge, this is the first time that the near-space SAR is being proposed for microwave remote sensing missions. By placing the SARs transmitter/receiver in the near-space platforms, many functions that are currently performed with the satellites or airplanes could be performed much more cheaply and with much greater operational unity. These advantages make near-space SAR attractive for a variety of remote sensing missions. In this paper, the potential and challenges of the near-space SAR, compared to current spaceborne SAR and airborne SAR, were detailed. Various near-space SAR configurations are introduced, and their potential for different applications such as passive imaging, high-resolution and wide-swath imaging, and inverse SAR imaging were investigated. It is shown that, the use of near-space SAR can lead to the solutions that are previously thought to be out of reach for remote sensing scientists and customers.

Impacts of frequency increment errors on frequency diverse array beampattern

Different from conventional phased array, which provides only angle-dependent beampattern, frequency diverse array (FDA) employs a small frequency increment across the antenna elements and thus results in a range angle-dependent beampattern. However, due to imperfect electronic devices, it is difficult to ensure accurate frequency increments, and consequently, the array performance will be degraded by unavoidable frequency increment errors. In this paper, we investigate the impacts of frequency increment errors on FDA beampattern. We derive the beampattern errors caused by deterministic frequency increment errors. For stochastic frequency increment errors, the corresponding upper and lower bounds of FDA beampattern error are derived. They are verified by numerical results. Furthermore, the statistical characteristics of FDA beampattern with random frequency increment errors, which obey Gaussian distribution and uniform distribution, are also investigated.

Impact of frequency increment errors on frequency diverse array MIMO in adaptive beamforming and target localization

In this paper, we investigate the impacts of frequency increment errors on frequency diverse array (FDA) multiple-input and multiple-output (MIMO) radar in adaptive beamforming and target localization. Since a small frequency increment, as compared to the carrier frequency, is applied between the transmit elements, FDA MIMO radar offers a range-dependent transmit beampattern to suppress range-dependent interferences and thus yields better direction-of-arrival (DOA) estimation performance than conventional MIMO radar. But the frequency increment errors will degrade FDA MIMO performance such as adaptive beamforming and target localization precision. In adaptive transmit beamforming analysis, we analyze the FDA MIMO radar beampattern mainlobe offset in range dimension, angle dimension and signal to interference and noise ratio (SINR) performance under different frequency increment error cases. While for the target localization investigation, the performance analysis is based on an explicit expansion of the estimation error in the signal subspace and frequency increment error matrix. Simulation results show that the impacts of frequency increment errors are mainly on the range dimension, i.e., the range offset of mainlobe in beamforming and range estimation in target localization, especially for large frequency increment errors. The Data model for FDA MIMO radar is derived with frequency increment error.We analysis the FDA MIMO radar mainlobe offset.We investigate SINR degradation caused by frequency increment errors.The subspace-based localization performance of the FDA MIMO radar is analyzed.We derive expressions of FDA RMSEs based on the subspace processing algorithms.

MIMO Antenna Array Design with Polynomial Factorization

One of the main advantages of multiple-input multiple-output (MIMO) antenna is that the degrees-of-freedom can be significantly increased by the concept of virtual antenna array, and thus the MIMO antenna array should be carefully designed to fully utilize the virtual antenna array. In this paper, we design the MIMO antenna array with the polynomial factorization method. For a desired virtual antenna array, the polynomial factorization method can optimally design the specified MIMO transmitter and receiver. The array performance is examined by analyzing the degrees-of-freedom and statistical output signal-to-interference-plus-noise ratio (SINR) performance. Design examples and simulation results are provided.

Diversified MIMO SAR waveform analysis and generation

Inspired by recent advances in multiple-input and multiple-output (MIMO) radar, which has the potential to dramatically improve the performance of radar systems over single antenna systems. This paper proposes a waveform diversity-based MIMO synthetic aperture radar (SAR) concept. The fundamental difference between MIMO SAR and conventional SAR is that the latter seeks to maximize coherent processing gain, while MIMO SAR capitalizes on the diversity of target scattering to improve imaging performance. The system concept and signal models are developed. An example diversified waveform using for MIMO SAR is designed, along with several computer simulations that investigate the correlation performance of the designed waveform. Furthermore, a direct digital synthesizer (DDS)-based approach of diversified waveform generation, in which parallel DDSs are applied, is proposed for MIMO SAR systems.