Dual Frequency Continuous Wave Radar for Small Displacement Detection

In several field such as structure health monitoring, landslide monitoring and medical measurement, small displacement is used as the indicator of any problem that may rise in such fields. High resolution radar system is required for small displacement detection in millimeter of centimeter scale. Continuous wave (CW) radar with its narrow bandwidth feature, has a simpler system comparing with other radar system. However, the modification is needed to present the ability of CW radar in detecting small displacement. In this paper, dual frequency CW radar was investigated and proposed for small displacement detection. Computer simulation has been conducted to study the capability of the proposed radar system. The result shows that the dual frequency CW radar at 10.525 GHz is capable to detect a small displacement in millimeter scale. The frequency difference of the radar signal needs to be adjusted to avoid the ambiguity in the detection resul

DUAL FREQUENCY CONTINUOUS WAVE RADAR FOR SMALL DISPLACEMENT DETECTION

Many studies have been developing RADAR for small displacement detection including Synthetic Aperture RADAR (SAR) to detect the landslide, where a wide bandwidth is commonly used. This thesis propose a small displacement detection by using Continuous Wave (CW) RADAR. CW RADAR with its narrow bandwidth feature, make system realization become more simple compared to the system using a wide bandwidth. CW RADAR can only detect the velocity of a dynamic target. Then, it underlie this thesis to modify the CW RADAR system by using dual frequency. This dual frequency, helps the system to recognize the displacement of a static target by processing its phase component on the echo signal. This thesis performs a computer simulation by MATLAB and an experiment by HB100 motion sensor. The computer simulation result shows that the proposed RADAR is capable to detect a small displacement in milimeter scale. It simulated -3.5625 mm until 3.5625 mm of displacement with three value of bandwidth. The narrowest bandwidth that can be simulated is 0.3 MHz. In the experiment result, the bandwidth is set to 0.87 MHz. Then, it needs some improvement in order to make the result better. Keywords: continuous wave (CW) RADAR, small displacement, phase shift

Confocal Ellipsoidal Reflector System for a Mechanically Scanned Active Terahertz Imager

We present the design of a reflector system that can rapidly scan and refocus a terahertz beam for high-resolution standoff imaging applications. The proposed optical system utilizes a confocal Gregorian geometry with a small mechanical rotating mirror and an axial displacement of the feed. For operation at submillimeter wavelengths and standoff ranges of many meters, the imaging targets are electrically very close to the antenna aperture. Therefore the main reflector surface must be an ellipse, instead of a parabola, in order to achieve the best imaging performance. Here we demonstrate how a simple design equivalence can be used to generalize the design of a Gregorian reflector system based on a paraboloidal main reflector to one with an ellipsoidal main reflector. The system parameters are determined by minimizing the optical path length error, and the results are validated with numerical simulations from the commercial antenna software package GRASP. The system is able to scan the beam over 0.5 m in cross-range at a 25 m standoff range with less than 1% increase of the half-power beam-width

Orbital Angular Momentum Waves: Generation, Detection and Emerging Applications

Orbital angular momentum (OAM) has aroused a widespread interest in many fields, especially in telecommunications due to its potential for unleashing new capacity in the severely congested spectrum of commercial communication systems. Beams carrying OAM have a helical phase front and a field strength with a singularity along the axial center, which can be used for information transmission, imaging and particle manipulation. The number of orthogonal OAM modes in a single beam is theoretically infinite and each mode is an element of a complete orthogonal basis that can be employed for multiplexing different signals, thus greatly improving the spectrum efficiency. In this paper, we comprehensively summarize and compare the methods for generation and detection of optical OAM, radio OAM and acoustic OAM. Then, we represent the applications and technical challenges of OAM in communications, including free-space optical communications, optical fiber communications, radio communications and acoustic communications. To complete our survey, we also discuss the state of art of particle manipulation and target imaging with OAM beams

Wireless Health Monitoring using Passive WiFi Sensing

This paper presents a two-dimensional phase extraction system using passive WiFi sensing to monitor three basic elderly care activities including breathing rate, essential tremor and falls. Specifically, a WiFi signal is acquired through two channels where the first channel is the reference one, whereas the other signal is acquired by a passive receiver after reflection from the human target. Using signal processing of cross-ambiguity function, various features in the signal are extracted. The entire implementations are performed using software defined radios having directional antennas. We report the accuracy of our system in different conditions and environments and show that breathing rate can be measured with an accuracy of 87% when there are no obstacles. We also show a 98% accuracy in detecting falls and 93% accuracy in classifying tremor. The results indicate that passive WiFi systems show great promise in replacing typical invasive health devices as standard tools for health care.Comment: 6 pages, 8 figures, conference pape

Ocean waves and turbulence as observed with an adaptive coherent multifrequency radar

An adaptive coherent multifrequency radar system is developed for several applications. The velocity distribution (Doppler spectrum) and spectral intensity of 15 different irregularity scales (waves and turbulence) can be measured simultaneously. Changing the azimuth angle of the antennas at regular intervals, the directivity of the wave/turbulence pattern on the sea surface can also be studied. A series of measurements for different air/sea conditions are carried out from a coast based platform. Experiments in the Atlantic are also performed with the same equipment making use of the NASA Electra aircraft. The multifrequency radar allows the measurement of the velocity distribution (""coherent and incoherent component'') associated with 15 different ocean irregularity scales simultaneously in a directional manner. It is possible to study the different air/sea mechanisms in some degree of detail

Spacecraft applications of advanced global positioning system technology

The purpose of this study was to evaluate potential uses of Global Positioning System (GPS) in spacecraft applications in the following areas: attitude control and tracking; structural control; traffic control; and time base definition (synchronization). Each of these functions are addressed. Also addressed are the hardware related issues concerning the application of GPS technology and comparisons are provided with alternative instrumentation methods for specific functions required for an advanced low earth orbit spacecraft

Time-Delay Multiplexing of Two Beams in a Terahertz Imaging Radar

We demonstrate a time-delay multiplexing technique that doubles the frame rate of a 660–690-GHz imaging radar with minimal additional instrument complexity. This is done by simultaneously projecting two offset, orthogonally polarized radar beams generated and detected by a common source and receiver. Beam splitting and polarization rotation is accomplished with a custom designed waveguide hybrid coupler and twist. A relative time lag of approximately 2 ns between the beams’ waveforms is introduced using a quasi-optical delay line, followed by spatial recombination using a selectively reflective wire grid. This delay is much longer than the approximately 20-ps time-of-flight resolution of the 30-GHz bandwidth radar, permitting the two beams’ reflected signals from a compact target to be easily distinguished in digital post-processing of the single receiver channel