Mariana Pralon

Optimization of antenna arrays for 2D DoA estimation using EADF for Cramér-Rao Lower Bounds computation

This paper presents results on optimization of antenna arrays to be used for Direction of Arrival (DoA) estimation using Cramér-Rao Lower Bounds computation. In our work, we apply the optimization to an L-quad antenna array and to a nonuniform patch array and compare the results in terms of direction finding capability. The aim of the optimization procedure is to increase the DoA estimation ability for the most compact antenna array the possible without losing focus on the antenna radiation constraints.

An eigen-analysis of a compact L-quad antenna array for direction finding

The aim of this paper is to analyze the coupling between elements in an array designed for direction of arrival (DoA) estimation for different arrangements, using an eigen-analysis approach. When designing an array for applications such as DoA estimation, it is important not only to focus on the antenna performance but also to analyze parameters such as the Cramér-Rao Lower Bound (CRLB), which will be reviewed in this work for direction finding. The connection between the CRLB and the coupling between elements in an antenna array will be drawn using the eigenefficiencies computed. The paper focuses on compact antenna arrays, and their performance for several inter-elements spacing will be analyzed in order to evaluate the array configuration that renders both maximum direction finding capability and maximum radiation efficiency.

Angular estimation for phased array surveillance radars considering orthogonal beamforming

Phased array antennas have been extensively used in radar systems. Each application requires an adequate design, to comply with specific requirements that involves both the radiation pattern as well as the beams spacing. Within this context, Orthogonal Beamforming arises as an interesting solution for surveillance radar applications. Besides optimum sidelobe isolation around the center of the beams, the orthogonality provides better coverage efficiency using the minimum number of beams to fill a given angular sector. On the other hand, since a single target can be detected in multiple beams, angular estimation in such configuration poses as a challenge when no windowing is applied to the radiation pattern (e.g. in long range applications) and the system can not cope with the additional computational burden of multi channel estimation. In the present work, closed form expressions describing the targets angular position in linear phased array systems with orthogonal beam shapes are derived, allowing full modeling of the beams, including side lobes positions. A combined algorithm for angular estimation is then proposed considering surveillance phased array systems with orthogonal beam spacing. Finally, the proposed algorithm performance, in terms of accuracy and precision, is evaluated using a Monte Carlo simulation approach, and compared to the simple centroid standalone solution.

On the polarization effects of decoupling and matching networks on compact single-polarized antenna arrays for direction finding

We investigate in this paper the effects of Decoupling and Matching Networks (DMNs) to the polarization characteristics of single-polarized microstrip patches used for the Direction of Arrival (DoA) estimation of impinging waves. Additionally, we present results on the Cramer-Rao Lower Bound (CRLB), used as a performance metric, with the aim of evaluating the impact of polarization on the capabilities of the array for direction finding. The effects of DMNs, designed with the goal of decoupling and matching radiating elements, will be analyzed for compact antenna arrays with different inter-element spacings smaller than half of the free-space wavelength.

Near-thumbtack ambiguity function of random frequency modulated signals

Noise radar is an emerging technology which employs random signals as their transmit waveforms. Relying on its stochastic properties, with the proper choice of system s parameters, high performance with respect to the suppression of range ambiguity and low range sidelobes can be achieved. Many works have been published in the literature addressing systems that transmit carriers modulated in amplitude by a given stochastic process, generally generated by a hardware noise source. Nevertheless, the characterization of random frequency modulation (more suitable for several applications) is still an on going subject matter. Within this context, in this paper closed form expressions of the narrowband ambiguity function of random frequency modulated signals are presented, and, as a consequence, its Doppler tolerance is better addressed.

Suitability of Compact Antenna Arrays for Direction-of-Arrival Estimation

The suitability of compact antenna arrays for the direction-of-arrival (DoA) estimation of radio emissions is investigated. Some applications may set constraints with respect to the antenna array physical size. If we increase the number of radiating elements in a given array size to maximize the degrees of freedom (DoF), the spacing between neighboring elements reduces to less than half of the free-space wavelength. Consequently, the electromagnetic coupling between the antenna elements becomes stronger. The result is a distortion of the radiation patterns, and mismatch at the antenna ports. This will have serious effects on the performance of any DoA estimator. Whereas the radiation pattern distortion, which is known from calibration measurements, can be considered by the DoA estimator, the power mismatch causes a loss of received signal power, and therefore, the SNR is reduced. This can only be mitigated by an analog decoupling and matching network (DMN), applied directly at the antenna array outputs, before digitalization. The DMN together with the antennas will exhibit mutually orthogonal radiation patterns, referred to as eigenpatterns. The output ports are, as a consequence, ideally “decoupled,” and the power spread of the eigenmodes will reflect the available DoF. We investigate the influence of the DMN design to the DoA performance in terms of the Cramér–Rao lower bound (CRLB). We show that both decoupling and matching will have a positive impact on the average CRLB. Moreover, for the application case of DoA estimation using small flying unmanned aerial vehicle platforms, we describe the performance of a specific circular array with L-quad antenna elements, and demonstrate the need for dual-polarimetric design and calibration.

On a probabilistic approach to detect Noise Radar random transmit waveforms based on a simple circularity test

Noise Radars are electromagnetic systems that use random signals for detecting and locating reflecting objects. Besides high performance with respect to the suppression of range ambiguity in the detection of targets and low range sidelobes, they also present an intrinsic property of low probability of interception by other systems, due to the stochastic nature of their transmit waveforms. Traditional methods and equipment are often ineffective to detect the presence of such kind of radars, both in time and frequency, since they generally adopt an ultra-wide bandwidth (UWB) configuration, spreading its power through a broad portion of the spectrum. Within this context, this paper proposes a probabilistic approach based on a statistical property of random vectors, the circularity, to detect the presence of pulses of this nature in the scenario under study.