29 research outputs found
A comparison of processing approaches for distributed radar sensing
Radar networks received increasing attention in recent years as they can outperform
single monostatic or bistatic systems. Further attention is being dedicated
to these systems as an application of the MIMO concept, well know
in communications for increasing the capacity of the channel and improving
the overall quality of the connection. However, it is here shown that radar
network can take advantage not only from the angular diversity in observing
the target, but also from a variety of ways of processing the received signals. The
number of devices comprising the network has also been taken into the analysis.
Detection and false alarm are evaluated in noise only and clutter from a theoretical
and simulated point of view. Particular attention is dedicated to the statistics
behind the processing. Experiments have been performed to evaluate practical
applications of the proposed processing approaches and to validate assumptions
made in the theoretical analysis. In particular, the radar network used for
gathering real data is made up of two transmitters and three receivers. More than
two transmitters are well known to generate mutual interference and therefore
require additional e�fforts to mitigate the system self-interference. However,
this allowed studying aspects of multistatic clutter, such as correlation, which
represent a first and novel insight in this topic. Moreover, two approaches for
localizing targets have been developed. Whilst the first is a graphic approach, the
second is hybrid numerical (partially decentralized, partially centralized) which
is clearly shown to improve dramatically the single radar accuracy. Finally the
e�ects of exchanging angular with frequency diversity are shown as well in some
particular cases. This led to develop the Frequency MIMO and the Frequency
Diverse Array, according to the separation of two consecutive frequencies. The
latter is a brand new topic in technical literature, which is attracting the interest
of the technical community because of its potential to generate range-dependant
patterns. Both the latter systems can be used in radar-designing to improve the
agility and the effciency of the radar
An investigation of a frequency diverse array
This thesis presents a novel concept for focusing an antenna beam pattern as a function
of range, time, and angle. In conventional phased arrays, beam steering is achieved by
applying a linear phase progression across the aperture. This thesis shows that by
applying an additional linear frequency shift across the elements, a new term is
generated which results in a scan angle that varies with range in the far-field.
Moreover, the antenna pattern is shown to scan in range and angle as a function of time.
These properties result in more flexible beam scan options for phased array antennas
than traditional phase shifter implementations. The thesis subsequently goes on to
investigate this phenomenon via full scale experimentation, and explores a number of
aspects of applying frequency diversity spatially across array antennas. This new form
of frequency diverse array may have applications to multipath mitigation, where a radio
signal takes two or more routes between the transmitter and receiver due to scattering
from natural and man-made objects. Since the interfering signals arrive from more than
one direction, the range-dependent and auto-scanning properties of the frequency
diverse array beam may be useful to isolate and suppress the interference. The
frequency diverse array may also have applications to wideband array steering, in lieu
of true time delay solutions which are often used to compensate for linear phase
progression with frequency across an array, and to sonar, where the speed of
propagation results in large percentage bandwidth, creating similar wideband array
effects. The frequency diverse array is also a stepping stone to more sophisticated joint
antenna and waveform design for the creation of new radar modes, such as simultaneous
multi-mode operation, for example, enabling joint synthetic aperture radar and ground
moving target indication
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
Time-Range FDA Beampattern Characteristics
Current literature show that frequency diverse arrays (FDAs) are able of
producing range-angle-dependent and time-variant transmit beampatterns, but the
resulting time and range dependencies and their characteristics are still not
well understood. This paper examines the FDA transmission model and the model
for the FDA array factor, considering their time-range relationship. We develop
two novel FDA transmit beampatterns, both yielding the auto-scanning capability
of the FDA transmit beams. The scan speed, scan volume, and initial mainlobe
direction of the beams are also analyzed. In addition, the equivalent
conditions for the FDA integral transmit beampattern and the multiple-input
multiple-output (MIMO) beampattern are investigated. Various numerical
simulations illustrate the auto-scanning property of the FDA beampattern and
the proposed equivalent relationship with the MIMO beampattern, providing the
basis for an improved understanding and design of the FDA transmit beampattern.Comment: 10 pages, 9 figure
Frequency Diverse Array Radar: Signal Characterization and Measurement Accuracy
Radar systems provide an important remote sensing capability, and are crucial to the layered sensing vision; a concept of operation that aims to apply the right number of the right types of sensors, in the right places, at the right times for superior battle space situational awareness. The layered sensing vision poses a range of technical challenges, including radar, that are yet to be addressed. To address the radar-specific design challenges, the research community responded with waveform diversity; a relatively new field of study which aims reduce the cost of remote sensing while improving performance. Early work suggests that the frequency diverse array radar may be able to perform several remote sensing missions simultaneously without sacrificing performance. With few techniques available for modeling and characterizing the frequency diverse array, this research aims to specify, validate and characterize a waveform diverse signal model that can be used to model a variety of traditional and contemporary radar configurations, including frequency diverse array radars. To meet the aim of the research, a generalized radar array signal model is specified. A representative hardware system is built to generate the arbitrary radar signals, then the measured and simulated signals are compared to validate the model. Using the generalized model, expressions for the average transmit signal power, angular resolution, and the ambiguity function are also derived. The range, velocity and direction-of-arrival measurement accuracies for a set of signal configurations are evaluated to determine whether the configuration improves fundamental measurement accuracy
Frequency Diverse Array MIMO Radar Adaptive Beamforming with Range-Dependent Interference Suppression in Target Localization
Conventional multiple-input and multiple-output
(MIMO) radar is a flexible technique which enjoys the advantages
of phased-array radar without sacrificing its main
advantages. However, due to its range-independent directivity,
MIMO radar cannot mitigate nondesirable range-dependent
interferences. In this paper, we propose a range-dependent
interference suppression approach via frequency diverse array
(FDA) MIMO radar, which offers a beamforming-based solution
to suppress range-dependent interferences and thus yields much
better DOA estimation performance than conventional MIMO
radar. More importantly, the interferences located at the same
angle but different ranges can be effectively suppressed by the
range-dependent beamforming, which cannot be achieved by
conventional MIMO radar. The beamforming performance as
compared to conventional MIMO radar is examined by analyzing
the signal-to-interference-plus-noise ratio (SINR). The CramĂŠr-Rao lower bound (CRLB) is also derived. Numerical results
show that the proposed method can efficiently suppress range-dependent
interferences and identify range-dependent targets. It is particularly useful in suppressing the undesired strong
interferences with equal angle of the desired targets