Muhammad Dawood

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.

Experimental Dynamical Evolution of the Brillouin Precursor for Broadband Wireless Communication through Vegetation

In this paper, we report experimental results on detecting and analyzing the Brillouin precursor through vegetation at frequencies from 500MHz to 3GHz. An experimental method to collect data is reported. The outcomes in terms of energy and time-spreading are presented using modulated rectangular and Gaussian pulses, as well as a sequence of rectangular pulses. Using fleld-collected data, this study shows the estimated dynamical evolution of the Brillouin precursor flelds for wideband wireless systems, such as those represented by IEEE 802.16. The advantages of Brillouin precursors in terms of power spectrum density and bit energy are discussed. Complex relative permittivity is extracted from the experimental data and is used in theoretical formulation to analyze dispersive propagation for any kind of input waveform. Finally, a near-optimal pulse is proposed to achieve maximum propagation distance and/or signal-to-noise ratio for the transmission of bit stream sequences through vegetation.

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.

Temporal and Frequency Evolution of Brillouin and Sommerfeld Precursors Through Dispersive Media in THz-IR Bands

The evolution of rectangular and Gaussian pulses through dispersive media is analyzed using a frequency-domain technique, valid for any kind of modulated input signal propagated through any dispersive medium. Three different metals-aluminum, silver, and gold-are considered using the Drude dielectric model to characterize them, at operating frequencies of 1 and 100 THz. A Lorentz model was also tested in the picohertz frequency band. The frequency-domain approach facilitated to separate the different components of the signal after propagating through the dispersive medium: carrier, Brillouin and Sommerfeld fields. In combination with the electric-field intensity plots, the dynamical evolution related to Brillouin and Sommerfeld precursor has shown a different trend in the chosen media, undergoing also an opposite effect on the effective frequency deviation. The case of a finite thickness propagation medium is compared to half-space model showing differences in the precursor evolution behavior. Finally, with Drude model material parameters at an operating frequency of 100 THz, we demonstrated that the impinging wave is coupled through surface plasmon polaritons which are capable of coupling in the output facet of the finite thickness slab to radiating waves.

Superresolution Doppler Estimation using UWB Random Noise Signals and MUSIC

The application of the superresolution multiple signal classification (MUSIC) algorithm is extended to overcome the Doppler frequency estimation limitations due to the Fourier transform- (FT-) based techniques for ultrawideband (UWB) random noise radar signals. Simulated and experimental results are compared for single and multiple moving targets within a range bin, for narrowband (200 MHz) and UWB (1 GHz) noise radar signals. The simulated percentage error in Doppler estimation is parameterized as a function of the velocity ratio of two targets in a given range bin.

Evaluation of the Brillouin precursor performance for ultra wide band intra-body technologies

In this letter, we describe the formation and the evolution of Brillouin precursor fields through human tissues by using a frequency-domain analysis technique and a multi-pole Cole–Cole model to characterize the dielectric properties of the human body tissues, in a frequency band designated by the FCC for ultra wide band medical applications, which extends from 0.5 to 20 GHz. A 3D representation of the human body model has been implemented by employing a discretized mesh of cuboids with a resolution of 8 mm3 in which the frequency dispersive material parameters for different tissues have been considered. The dispersive propagation is analyzed for the purposes of radar imaging and intra-body communications. The performance of a classical rectangular pulse, a Brillouin pulse and a medium-matched waveform is described. The results show the potential application of this type of communication scheme in order to improve the achievable measurement range and provide better signal to noise ratios.

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.

Quadrature-Modulated Circular Microstrip Patch Antenna for Phased Arrays

An approach to complex-plane field manipulation in an antenna element using amplitude-based control has been developed. Such a capability is expected to be especially useful in phased array applications. This specific example of the general approach uses a circular microstrip patch (CMSP) antenna. The theoretical basis for the approach is presented along with a summary of simulation data that validate the theory. A new accuracy analysis across angular space is presented.

Performance evaluation of medium-matched waveforms and pulse shaping for application in ultrawideband intra-body technologies

In this letter we analyze the use of medium-matched signals and pulse shaping techniques to improve the performance of intra-body technologies. Firstly, we describe the evolution of the Brillouin precursor fields through human tissues by using a frequency-domain analysis technique and a multi-pole Cole-Cole model to characterize the dielectric properties of the human body tissues, in a frequency band designated by the FCC for UWB medical applications, 3-20GHz. A 3D representation of the body has been achieved by cuboids with a resolution of 8mm3. The dispersive propagation is analyzed for purposes of radar imaging and intra-body communications. The performance of a classical rectangular and a medium-matched waveform, the Brillouin pulse, are described.