Habeeb Ur Rahman Mohammed

Analysis of Brillouin Precursor Propagation Through Foliage for Digital Sequences of Pulses

In this letter, we investigate the propagation of Brillouin precursors through dispersive foliage media, using leafy vegetation dielectric models proposed by Fung-Ulaby, El Rayes-Ulaby, Brown-Curry-Ding, Maetzler, and Pearce. A fast-Fourier-transform-based formulation is used to analyze the peak amplitude decay and pulse broadening effect (or effective oscillation frequency) related to the precursor formation for both single pulse and sequence of pulses traveling through the leafy vegetation. The influence of the Brillouin precursor on the receiver structure is also investigated. Simulations have been carried out in frequency bands between 100 MHz and 6 GHz allocated for remote sensing applications and digital satellite communications.

Empirical Pseudo-Optimal Waveform Design for Dispersive Propagation Through Loamy Soil

Using a fast Fourier transform-based theoretical formulation as a starting point for a near-optimal waveform design, three near-optimal or pseudo-optimal pulses are empirically derived in this letter to achieve near-optimal penetration depth through the sample of loamy soil considered in this study. We describe three methods to derive these waveforms with improved features valid for any dispersive media: the first of them establishes a close approach of the Brillouin pulses; and the other two analyze structures that reinforce the Brillouin precursor formation to simultaneously achieve improved peak decay and reduced pulse broadening. The pulses are tested for experimental data achieved within a reduced range of frequency, 0.5-3 GHz, even that any theoretical dielectric model can be also used.

Experimental Detection and Characterization of Brillouin Precursor Through Loamy Soil at Microwave Frequencies

This study reports experimental results on detecting Brillouin precursors through loamy-soil dispersive media in the frequency range of 500 MHz to 3 GHz. An experimental technique to collect and analyze the data is presented. Brillouin precursors are shown to be superimposed on the sine-modulated rectangular and Gaussian pulses. The detected Brillouin precursor is shown to have an algebraic amplitude decay behavior through the wet loamy soil considered in this study. Further, a method is proposed to extract the complex dielectric permittivity of the soil from limited experimental data. The experimental results are validated using a theoretical Fast Fourier Transform-based formulation and the experimentally achieved complex dielectric permittivity. These results are also compared with those of using existing theoretical dielectric models. Three different tests are also applied to validate the hypothesis of Brillouin precursor formation.

Low sidelobe level radar techniques using Golay based coded sequences

A radar system operating at a carrier frequency of 500 MHz and using different coded sequences is built and tested at NMSU. A limited set of experimental results at various ranges for both sequences: pseudorandom binary sequences (PRBS) and Golay were obtained and the comparison between them was done. Our tests indicate, though not conclusively, that Golay sequence seems to offer lower sidelobe level than PRBS sequences. Moreover, Golay sequences may yield higher dynamic range and results in improvement in estimation of the delay spread.

Software tool for simulation of Brillouin precursors in dispersive dielectrics

It has been long known that propagation through dispersive media give rise to Brillouin and Sommerfeld type precursors. The mathematical model to represent these precursors, in most dispersive media, results in mathematically intractable complex differential and integral equations. However, modern asymptotic theory of pulse propagation through dispersive media gave rise to closed-form formulations for Brillouin type precursors [1–3]. There are, however, very few experimental studies [4] reported in the literature to experimentally observe the existence of the precursors and characterize the evolution of these precursors in a given dispersive media.

Design and Implementation of Ground Peneration Radar System using Coded Sequences and Improved Target Detection using Golay Codes

Ground penetration radar (GPR) is one of the non-destructive and non-intrusive data collecting technologies used in geophysical measurements. A GPR system operating at carrier frequency 500 MHz and a bandwidth of 250 MHz was designed and developed. The major problem in most of the existing Ground Penetration Radar systems is masking of the weaker returns by the strong sidelobes. This problem can be minimized to a great extent with the help of complementary Golay sequences. The performance of Golay sequences in terms of reduced sidelobe levels is considered better than that of pseudorandom (PN), Barker or other maximal length sequences. We have tested the performance of Golay and PRBS sequences using 4096 and 8192 length sequences, respectively. When the correlation obtained using two M length Golay sequence is compared with one 2M length PRBS sequence, sidelobe level for Golay sequence is almost eliminated. This results in better performance to detect weaker returns. However, this claim may not hold true at low SNRs. We have shown the results in anechoic chamber. Our tests indicate that Golay sequence has lower sidelobe level than PN sequences.

Breast cancer detection utilizing Brillouin precursors at microwave frequencies

For early detection of breast cancer, ultrawideband microwave imaging techniques, among others, are a useful tool. This paper presents some of our numerical results showing the formation of Brillouin precursors from the back-scattered components of the microwave electromagnetic waves propagating through both normal and malignant breast tissues. The advantageous nature of these precursors is also highlighted.

Estimation of Sidelobe Level Variations of Phased Codes in Presence of Random Interference for Bistatic Wideband Noise Radar

We discuss the importance of using the sidelobe level of the cross-correlation function as a criterion to implement a noise radar based on the transmission of wideband binary waveforms. Theoretical expressions are introduced for the parameters Peak-Sidelobe, Secondary-Sidelobe, and Integrated-Sidelobe levels for both Golay and pseudorandom binary sequences in presence of additive white Gaussian noise, relating the sequence length to the spectral power of the interfering noise. These expressions offer a valuable method for adaptive radar waveform design in order to determine sequence requirements which allow facing the noise present in the frequency band of interest. We also show a comparison of the ambiguity functions for Golay and PRBS sequences to analyze their performance in terms of Doppler and range accuracy. We describe a practical implementation of a pseudonoise waveform-based bistatic radar with reduced sidelobe level due to the use of Golay codes in combination with single side band modulation and operation at UHF band. Experimental measurements were performed in actual scenarios for ranging test of single and double targets. Linear polarizations were combined with different length sequences to determine their influence on the sounder performance under field test conditions.