Sami M. Alhumaidi

Characterization of Radar Backscatter Response of Sand-Covered Surfaces at Millimeter-Wave Frequencies

Radar imaging of deserts suffers from insufficient radar backscatter at low microwave frequencies due to the low permittivity of dry sand and relatively smooth sand surface roughness. Operating at millimeter-wave (MMW) frequencies, however, rectifies this deficiency as significant radar backscatter is generated by surface and volume scattering. This is due to the fact that sand surface roughness is electrically large and signal penetration into the dry sand, which is a homogeneous mixture of air and sand particles with dimensions comparable to a fraction of a wavelength, generates considerable volume scattering. This paper investigates both surface and volume scattering from dry sand surfaces, subject to the peculiar physical properties of sand surfaces found in sand dune-covered regions. An incoherent model is proposed that characterizes the angular dependence of volume scattering from dry sand in the presence of a 1-D rippled air/sand surface. A set of indoor experiments conducted on smooth and 1-D rippled sand surfaces at Ka-band confirms that significant volume scattering is present at MMW frequencies and that the proposed model correctly captures the observed angular dependence when 1-D surface ripples are present.

Up to 64 QAM/32 Gbaud flexible dual polarization transmitter for future elastic optical networks

Abstract. Next generation elastic optical networks will very likely require dual polarization (DP) optical transmitter with inherent flexibility to dynamically change its baud rate and/or modulation format. We develop a prototype of compact flexible DP M-ary quadrature amplitude modulation (MQAM) optical transmitter and demonstrate its reconfigurability to accommodate baud rates ranging from 8 to 32  Gbaud/s using the same hardware. The prototype has another advantage in that the modulation format can also be dynamically changed from binary phase shift keying up to 64 quadrature amplitude modulation (QAM) for single and DPs, all over a single optical carrier. This allows the generation of variable data rate up to 384-Gb/s over a single wavelength. Experimental results show that for the most challenging setting of DP-64 QAM/32 Gbaud, the worst case values of error vector magnitude and bit error rate are 6.7 and 3×10−2, respectively. For less stringent settings, i.e., lower baud rate and/or lower modulation format, forward error correction limit error free transmission is easily obtained. Further results are also reported to demonstrate transmitter flexibility and software definability, by measuring symbol streams showing instantaneous swapping between modulation schemes with a swapping time less than 10 symbols duration, i.e., 0.3 ns.

FPGA-based implementation of a CFAR processor using Batcher's sort and LUT arithmetic

This paper presents the realization of the forward automatic censored cell averaging detector (F-ACCAD), a novel CFAR algorithm for detecting targets in log-normal distribution clutter recently published in [1]. The algorithm is realized through an FPGA-based parallel architecture. The timing constraints of high resolution radar applications are considered and satisfied in the system. The sequential nature of the algorithm has been parallelized to achieve the desired processing delay. The intensive statistical calculations and the complexity of the algorithm have been significantly reduced by using lookup tables (LUTs). Batchers sort, a parallel sorting algorithm, is adopted in this work. The hardware synthesis results and timing analysis are reported at the end.

An Empirical Model of Volume Scattering From Dry Sand-Covered Surfaces at Millimeter-Wave Frequencies

This paper examines recently acquired polarimetric data of dry sand with a smooth air/sand interface at millimeter-wave (MMW) frequencies. The data characterize volume scattering from different types of sand as a function of the radar incidence angle, frequency, polarization, and particle size. The data show substantial volumetric response from dry sand at MMW frequencies with significant depolarization (between -12 and -7 dB). An empirical model is proposed and adapted for both smooth and 1-D periodic dry sand surfaces. Comparison between the expected volume scattering response of a dry sand medium with the surface scattering response of dry sand surfaces with rough interfaces shows that volume scattering is, in general, dominant, particularly at 95 GHz.

A neural network sea ice edge classifier for the NASA Scatterometer

The NASA Scatterometer (NSCAT) to be launched in August 1996 is designed to measure wind vectors over ice-free oceans. To prevent contamination of the wind measurements, by the presence of sea ice, an algorithm based on only NSCAT data is described. Results are presented for a neural network trained using dual linear polarized Ku-band backscatter measured by the SeaSat-A Satellite Scatterometer (SASS). These results demonstrate the utility of neural network classifiers to provide this ice flag. Results are presented for both multilayer perceptron (MLP) and a learning vector quantization (LVQ) neural networks. Classification skill is evaluated by comparisons with surface truth and with an independent ice-flagging algorithm.

Characterization and diagnostics of active phased array modules using non-invasive electro-optic field probes with a CW laser source

Electro-optic (EO) field probes can be used very effectively for simultaneous near-field and far-field characterization of radiating apertures. Due to their very small footprint and absence of any metallic parts at the signal pickup area, EO probes provide a non-invasive method for ultra-wideband measurement of aperture-level fields in RF circuits and antennas with very high spatial resolution. In this paper, we describe the use of EO field probes with a CW laser source to characterize a vertically integrated X-band active phased array tile and verify the measured results with simulation data and anechoic chamber measurements.

Range only target localization in multi-static passive radar system: A gradient descent approach

In this study, we present an iterative method for finding target position using only range measurements from multi-static passive radar system. We formulate an optimization problem and use the gradient descent approach to locate target position. In addition, we show that for multi-receiver-single-transmitter system, our method requires only three receivers in order to converge to the correct position without having local minima problem. Furthermore, we conduct Monte-Carlo simulation to evaluate the mean time and accuracy of our approach. Our method can be implemented in real-time and hence it can be applied in real-life situations.

384Gb/s per carrier Quad-DAC based dual-polarization software defined optical transmitter

We demonstrate a 32Gbaud Quad-DAC based software defined optical transmitter. Our transmitter is able to generate up to 128QAM and 64QAM for single and dual polarizations, respectively. In addition, this transmitter emulates laser phase noise effect.

Improving target signature in a software defined, multi-band, multi-channel passive radar

The use of passive radar for detection of targets of different type has gained considerable popularity in past few years. This radar uses the so-called the ”signals of the opportunities” which are already in the environment. These opportunistic signals can be of different types, both in terms of frequency and modulation type. Therefore, instead of designing a separate hardware receiving system, a better approach will be design a single software defined receiver having capability to capture any signal of interest by just changing antenna system. Also to obtain various signals of interests, a multi-channel receiver system is desired so that advance array processing algorithms like digital beamforming can be utilized. Therefore , a state of the art software defined, multi-band, and a multi-channel passive radar system has been designed and being tested. One important step in the processing of signals for final target detection is the cancelation of direct path signal coming from main transmitter. Usually this is done by a combination of digital beamforming and adaptive filters based interference cancelation algorithms. An improved digital beamformer is designed with complete control of side-lobes to suppress the direct path signal. Also improved interference cancelation is done by using a cascade (two-stage) of adaptive filters. By using the combination of these techniques it will be shown that a considerable weak target can be detected.

Characterization of volume scattering of dry sand at millimeter-wave frequencies

Fully polarimetric measurements of volume scattering contribution from dry layer of fine sand with smooth air/sand interface were performed at millimeter-wave frequencies. The measured radar response was compared to predictions made by the numerical solution of the DMRT model. Sand particles were modeled as spherical particles. The simulated response was able to predict the angular dependence of the data but was not able to predict accurately the absolute level, especially for the cross-polarized return. Furthermore, a simpler model, which was developed earlier for asphalt surfaces and is based on 1st order solution of RT for semi-infinite medium, was tested against the measured data. The model was not able to predict the angular dependence demonstrated by the measured data.