97 research outputs found
Communications techniques and equipment: A compilation
This Compilation is devoted to equipment and techniques in the field of communications. It contains three sections. One section is on telemetry, including articles on radar and antennas. The second section describes techniques and equipment for coding and handling data. The third and final section includes descriptions of amplifiers, receivers, and other communications subsystems
Radar Technology
In this book āRadar Technologyā, the chapters are divided into four main topic areas: Topic area 1: āRadar Systemsā consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: āRadar Applicationsā shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: āRadar Functional Chain and Signal Processingā describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: āRadar Subsystems and Componentsā consists of design technology of radar subsystem components like antenna design or waveform design
An introduction to the interim digital SAR processor and the characteristics of the associated Seasat SAR imagery
Basic engineering data regarding the Interim Digital SAR Processor (IDP) and the digitally correlated Seasat synthetic aperature radar (SAR) imagery are presented. The correlation function and IDP hardware/software configuration are described, and a preliminary performance assessment presented. The geometric and radiometric characteristics, with special emphasis on those peculiar to the IDP produced imagery, are described
Non-Contact Human Motion Sensing Using Radar Techniques
Human motion analysis has recently gained a lot of interest in the research community due to its widespread applications. A full understanding of normal motion from human limb joint trajectory tracking could be essential to develop and establish a scientific basis for correcting any abnormalities. Technology to analyze human motion has significantly advanced in the last few years. However, there is a need to develop a non-invasive, cost effective gait analysis system that can be functional indoors or outdoors 24/7 without hindering the normal daily activities for the subjects being monitored or invading their privacy. Out of the various methods for human gait analysis, radar technique is a non-invasive method, and can be carried out remotely. For one subject monitoring, single tone radars can be utilized for motion capturing of a single target, while ultra-wideband radars can be used for multi-subject tracking. But there are still some challenges that need to be overcome for utilizing radars for motion analysis, such as sophisticated signal processing requirements, sensitivity to noise, and hardware imperfections. The goal of this research is to overcome these challenges and realize a non-contact gait analysis system capable of extracting different organ trajectories (like the torso, hands and legs) from a complex human motion such as walking. The implemented system can be hugely beneficial for applications such as treating patients with joint problems, athlete performance analysis, motion classification, and so on
Target recognition techniques for multifunction phased array radar
This thesis, submitted for the degree of Doctor of Philosophy at University College London, is a
discussion and analysis of combined stepped-frequency and pulse-Doppler target recognition methods
which enable a multifunction phased array radar designed for automatic surveillance and multi-target
tracking to offer a Non Cooperative Target Recognition (NCTR) capability. The primary challenge
is to investigate the feasibility of NCTR via the use of high range resolution profiles. Given stepped
frequency waveforms effectively trade time for enhanced bandwidth, and thus resolution, attention is
paid to the design of a compromise between resolution and dwell time. A secondary challenge is to
investigate the additional benefits to overall target classification when the number of coherent pulses
within an NCTR wavefrom is expanded to enable the extraction of spectral features which can help
to differentiate particular classes of target. As with increased range resolution, the price for this extra
information is a further increase in dwell time. The response to the primary and secondary challenges
described above has involved the development of a number of novel techniques, which are summarized
below:
ā¢ Design and execution of a series of experiments to further the understanding of multifunction
phased array Radar NCTR techniques
ā¢ Development of a āHybridā stepped frequency technique which enables a significant extension
of range profiles without the proportional trade in resolution as experienced with āClassicalā
techniques
ā¢ Development of an āend to endā NCTR processing and visualization pipeline
ā¢ Use of āDoppler fractionā spectral features to enable aircraft target classification via propulsion
mechanism. Combination of Doppler fraction and physical length features to enable broad
aircraft type classification.
ā¢ Optimization of NCTR method classification performance as a function of feature and waveform
parameters.
ā¢ Generic waveform design tools to enable delivery of time costly NCTR waveforms within operational
constraints.
The thesis is largely based upon an analysis of experimental results obtained using the multifunction
phased array radar MESAR2, based at BAE Systems on the Isle of Wight. The NCTR
mode of MESAR2 consists of the transmission and reception of successive multi-pulse coherent bursts
upon each target being tracked. Each burst is stepped in frequency resulting in an overall bandwidth
sufficient to provide sub-metre range resolution. A sequence of experiments, (static trials, moving
point target trials and full aircraft trials) are described and an analysis of the robustness of target
length and Doppler spectra feature measurements from NCTR mode data recordings is presented. A
recorded data archive of 1498 NCTR looks upon 17 different trials aircraft using five different varieties
of stepped frequency waveform is used to determine classification performance as a function of
various signal processing parameters and extent (numbers of pulses) of the data used. From analysis
of the trials data, recommendations are made with regards to the design of an NCTR mode for an
operational system that uses stepped frequency techniques by design choice
Low Correlation Interference OFDM-NLFM Waveform Design for MIMO Radar Based on Alternating Optimization.
The OFDM chirp signal is suitable for MIMO radar applications due to its large time-bandwidth product, constant time-domain, and almost constant frequency-domain modulus. Particularly, by introducing the time-frequency structure of the non-linear frequency modulation (NLFM) signal into the design of an OFDM chirp waveform, a new OFDM-NLFM waveform with low peak auto-correlation sidelobe ratio (PASR) and peak cross-correlation ratio (PCCR) is obtained. IN-OFDM is the OFDM-NLFM waveform set currently with the lowest PASR and PCCR. Here we construct the optimization model of the OFDM-NLFM waveform set with the objective function being the maximum of the PASR and PCCR. Further, this paper proposes an OFDM-NLFM waveform set design algorithm inspired by alternating optimization. We implement the proposed algorithm by the alternate execution of two sub-algorithms. First, we keep both the sub-chirp sequence code matrix and sub-chirp rate plus and minus (PM) code matrix unchanged and use the particle swarm optimization (PSO) algorithm to obtain the optimal parameters of the NLFM signal's time-frequency structure (NLFM parameters). Next, we keep current optimal NLFM parameters unchanged, and optimize the sub-chirp sequence code matrix and sub-chirp rate PM code matrix using the block coordinate descent (BCD) algorithm. The above two sub-algorithms are alternately executed until the objective function converges to the optimal solution. The results show that the PASR and PCCR of the obtained OFDM-NLFM waveform set are about 5 dB lower than that of the IN-OFDM
The Goldstone solar system radar: A science instrument for planetary research
The Goldstone Solar System Radar (GSSR) station at NASA's Deep Space Communications Complex in California's Mojave Desert is described. A short chronological account of the GSSR's technical development and scientific discoveries is given. This is followed by a basic discussion of how information is derived from the radar echo and how the raw information can be used to increase understanding of the solar system. A moderately detailed description of the radar system is given, and the engineering performance of the radar is discussed. The operating characteristics of the Arcibo Observatory in Puerto Rico are briefly described and compared with those of the GSSR. Planned and in-process improvements to the existing radar, as well as the performance of a hypothetical 128-m diameter antenna radar station, are described. A comprehensive bibliography of referred scientific and engineering articles presenting results that depended on data gathered by the instrument is provided
FMCW Signals for Radar Imaging and Channel Sounding
A linear / stepped frequency modulated continuous wave (FMCW) signal has for a long time been used in radar and channel sounding. A novel FMCW waveform known as āGated FMCWā signal is proposed in this thesis for the suppression of strong undesired signals in microwave radar applications, such as: through-the-wall, ground penetrating, and medical imaging radar. In these applications the crosstalk signal between antennas and the reflections form the early interface (wall, ground surface, or skin respectively) are much stronger in magnitude compared to the backscattered signal from the target. Consequently, if not suppressed they overshadow the targetās return making detection a difficult task. Moreover, these strong unwanted reflections limit the radarās dynamic range and might saturate or block the receiver causing the reflection from actual targets (especially targets with low radar cross section) to appear as noise. The effectiveness of the proposed waveform as a suppression technique was investigated in various radar scenarios, through numerical simulations and experiments. Comparisons of the radar images obtained for the radar system operating with the standard linear FMCW signal and with the proposed Gated FMCW waveform are also made.
In addition to the radar work the application of FMCW signals to radio propagation measurements and channel characterisation in the 60 GHz and 2-6 GHz frequency bands in indoor and outdoor environments is described. The data are used to predict the bit error rate performance of the in-house built measurement based channel simulator and the results are compared with the theoretical multipath channel simulator available in Matlab
Millimetre-Resolution Photonics-Assisted Radar
Radar is essential in applications such as anti-collision systems for driving, airport security screening,
and contactless vital sign detection. The demand for high-resolution and real-time recognition in
radar applications is growing, driving the development of electronic radars with increased bandwidth,
higher frequency, and improved reconfigurability. However, conventional electronic approaches are
challenging due to limitations in synthesising radar signals, limiting performance.
In contrast, microwave photonics-enabled radars have gained interest because they offer numerous
benefits compared to traditional electronic methods. Photonics-assisted techniques provide a broad
fractional bandwidth at the optical carrier frequency and enable spectrum manipulation, producing
wideband and high-resolution radar signals in various formats. However, photonic-based methods
face limitations like low time-frequency linearity due to the inherent nonlinearity of lasers, restricted RF bandwidth, limited stability of the photonic frequency multipliers, and difficulties in achieving
extended sensing with dispersion-based techniques.
In response to these challenges, this thesis presents approaches for generating broadband radar
signals with high time-frequency linearity using recirculated unidirectional optical frequency-shifted
modulation. The photonics-assisted system allows flexible bandwidth tuning from sub-GHz to over 30
GHz and requires only MHz-level electronics. Such a system offers millimetre-level range resolution
and a high imaging refresh rate, detecting fast-moving objects using the ISAR technique. With
millimetre-level resolution and micrometre accuracy, this system supports contactless vital sign
detection, capturing precise respiratory patterns from simulators and a living body using a cane toad.
In the end, we highlight the promise of merging radar and LiDAR, foreshadowing future
advancements in sensor fusion for enhanced sensing performance and resilience
- ā¦