Pv Brennan

FMCW Based MIMO Imaging Radar for Maritime Navigation

The berthing of large ships in inclement weather with frequently poor visibility presents a challenge. To assist with this application, it may be beneficial to utilise standard radar imaging. Whilst this may be achieved using a mechanically-scanned system, reliability, cost and weight issues, coupled with the need to primarily image only a 1200 sector on the port and starboard of the ship, make phased array radar an attractive possibility. Multiple-Input Multiple-Output (MIMO) radar, with its ability to enhance the resolution available from a given number of elements, is particularly suited to a short-range application such as this in which there is sufficient time to switch between antenna elements as an alternative to more complex implementations. This paper describes a system of this nature from its basic architecture to development and validation, including some artefacts of the particular topology employed.

Active RFID location system based on time-difference measurement using a linear FM chirp tag signal

This paper introduces a new method for estimating location of radio frequency identification (RFID) tags for application in indoor environments. The proposed positioning scheme employs a time-difference of arrival (TDOA) range estimation algorithm. The time-difference measurement is performed by taking advantage of the de-ramp properties of a linear frequency modulation (LFM) chirp. The paper provides details of the mechanism of this LFM-TDOA scheme from the system point of view. Compared to other popular radio technologies in the indoor positioning field, this new scheme is easy to design and requires only moderate computation ability. According to the experiment results summarized in the paper, the LFM-TDOA system shows good range estimation accuracy and thus has the potential to be used in accurate indoor location application.

An experimental and theoretical study of self-phased arrays in mobile satellite communications

Communication with satellites from ships and aircraft requires the accurate pointing of a high-gain antenna. The self-phased array, which performs beam steering automatically by the use of a pilot carrier, offers a number of advantages in this application. The principles and properties of this type of array are outlined, and their implications for array design are discussed. An experimental self-phased system using a phase-locked loop, which receives signals from the Marecs satellite over the Atlantic Ocean, is described. Results are presented for a two-element laboratory prototype to illustrate its performance. The behavior of the self-phased-array concept under multipath conditions is particularly interesting and is examined both theoretically and experimentally. >

Determination of Sweep Linearity Requirements in FMCW Radar Systems Based on Simple Voltage-Controlled Oscillator Sources

Linear frequency modulated (FM), or chirp, pulse compression is a widely used technique for improving the range resolution of radar systems, although it often places quite stringent demands on FM sweep linearity. This paper examines the impact of sweep nonlinearities on the performance of frequency modulated continuous wave (FMCW) radar systems, particularly those employing simple voltage-controlled oscillator (VCO) sources, using a new and straightforward approach based on the fractional slope variation (FSV). Modeled results are presented, assuming a square-law source nonlinearity representation, showing the effect of such nonlinearities on point-target response and range resolution. These results are then related to the standard definition of linearity. Measurements from a commercial VCO are finally used to convincingly validate the work, resulting in a simple and practical method to predict the impact of source nonlinearity, as defined by the FSV parameter, on the performance of an FMCW radar system.

FMCW radar imaging of avalanche-like snow movements

High quality field measurements of avalanche flows are required for calibrating computational models which are an essential tool in managing the threat posed by these flows. In this paper we present a new C-band FMCW radar system developed at University College London for gathering highresolution avalanche flow data. The radar employs a full deramp hardware architecture, a diverse set of frequency ramps, and an 8-channel receiver array. We also show initial results of a small-scale field trial carried out using a single channel prototype radar deployed in a snow chute. The results are presented as range-time plots. A simple calculation of the expected flow velocity due to gravity agrees with the estimated experimental value. The results demonstrate the capability of the radar system to record high range resolution microwave images of snow movements. The experiments reported here were carried out as a precursor to full trials of the radar system during which images of full scale avalanche flows will be captured.

The dynamics of surges in the 3 February 2015 avalanches in Vallée de la Sionne.

Five avalanches were artificially released at the Vallee de la Sionne test site in the west of Switzerland on 3 February 2015 and recorded by the GEOphysical flow dynamics using pulsed Doppler radAR Mark 3 radar system. The radar beam penetrates the dilute powder cloud and measures reflections from the underlying denser avalanche features allowing the tracking of the flow at 111 Hz with 0.75 m downslope resolution. The data show that the avalanches contain many internal surges. The large or “major” surges originate from the secondary release of slabs. These slabs can each contain more mass than the initial release, and thus can greatly affect the flow dynamics, by unevenly distributing the mass. The small or “minor” surges appear to be a roll wave-like instability, and these can greatly influence the front dynamics as they can repeatedly overtake the leading edge. We analyzed the friction acting on the fronts of minor surges using a Voellmy-like, simple one-dimensional model with frictional resistance and velocity-squared drag. This model fits the data of the overall velocity, but it cannot capture the dynamics and especially the slowing of the minor surges, which requires dramatically varying effective friction. Our findings suggest that current avalanche models based on Voellmy-like friction laws do not accurately describe the physics of the intermittent frontal region of large mixed avalanches. We suggest that these data can only be explained by changes in the snow surface, such as the entrainment of the upper snow layers and the smoothing by earlier flow fronts.

Minimax robust jamming techniques based on signal-to-interference-plus-noise ratio and mutual information criteria

Jamming in defence applications is increasingly difficult because of advanced signal processing countermeasures. In this study, task-dependent power-constraint optimal jamming techniques are investigated. To prevent the target from being detected, a novel jamming technique is proposed to minimise the signal-to-interference-plus-noise ratio (SINR) of the radar for extended known and stochastic target. To impair the parameter estimation performance, another jamming technique is proposed which minimises the mutual information (MI) between the radar return and the stochastic target impulse response. The optimal jamming spectrum is obtained assuming that the jammer has intercepted the radar waveform generally. However, the precise characteristic of radar waveform is impossible to capture in practice. To model this, it is considered that the waveform spectrum lies in an uncertainty class confined by known upper and lower bounds. Then, the minimax robust jamming is designed based on the SINR and MI criteria, which optimises the worst-case performance. Results demonstrate that the two criteria lead to different optimal jamming results but they have a close relationship from the Shannons capacity equation which provides useful guidance on jamming power allocation for different jamming tasks. However, their behaviour with respect to the waveform uncertainty is the same.

A New Mechanism Producing Discrete Spurious Components in Fractional-

Fractional- frequency synthesizers have long been known to suffer from a set of spurious components, often referred to as fractional spurs, which are usually attributed to the operation of the modulator. This paper proposes a new phenomenon-based on cross-coupling and sampling of the nonharmonically related signals present in such synthesizers-which is capable of producing a family of spurious components of identical form to fractional spurs, with support from a range of analytic, simulated and measured results. A unique experimental arrangement is described, allowing controlled cross-coupling of signals within a synthesizer, which provides convincing experimental validation of this mechanism. Finally, techniques are suggested to allow at least partial mitigation of the effect.

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Frequency modulated continuous wave (FMCW) radar is widely adopted solution for low-cost, short to medium range sensing applications. However, a multistatic FMCW architecture suitable for meeting the low-cost requirement has yet to be developed. This paper introduces a new FMCW radar architecture that implements a novel technique of synchronizing nodes in a multistatic system, known as over-the-air deramping (OTAD). The architecture uses a dual-frequency design to simultaneously broadcast an FMCW waveform on a lower frequency channel directly to a receiver as a reference synchronization signal, and a higher frequency channel to illuminate the measurement scene. The target echo is deramped in hardware with the synchronization signal. OTAD allows for low-cost multistatic systems with fine range-resolution, and low peak power and sampling rate requirements. Furthermore, the approach avoids problems with direct signal interference. OTAD is shown to be a compelling solution for low-cost multistatic radar systems through the experimental measurements using a newly developed OTAD radar system.

Frequency Synthesizers

Describes a method for disrupting a standard, commercially available, nonlinear electronic system. In particular, we show how, with relatively little knowledge of the commercial system design, an in-band signal can be determined which will disrupt the operation of the circuit. Our approach is based on a nonlinear analysis of the most susceptible subsystem in the circuit. Analytical, numerical, and experimental results are reported to demonstrate the efficacy of our approach.