Nicholas V. Shuley

On the fast approximation of Green's functions in MPIE formulations for planar layered media

The numerical implementation of the complex image approach for the Greens function of a mixed-potential integral-equation formulation is examined and is found to be limited to low values of /spl kappa//sub o//spl rho/ (in this context /spl kappa//sub 0//spl rho/ = 2/spl pi//spl rho///spl lambda//sub 0/, where /spl rho/ is the distance between the source and the field points of the Greens function and /spl lambda//sub 0/ is the free space wavelength). This is a clear limitation for problems of large dimension or high frequency where this limit is easily exceeded. This paper examines the various strategies and proposes a hybrid method whereby most of the above problems can be avoided. An efficient integral method that is valid for large /spl kappa//sub 0//spl rho/ is combined with the complex image method in order to take advantage of the relative merits of both schemes. It is found that a wide overlapping region exists between the two techniques allowing a very efficient and consistent approach for accurately calculating the Greens functions. In this paper, the method developed for the computation of the Greens function is used for planar structures containing both lossless and lossy media.

Scan performance of infinite arrays of microstrip patch elements loaded with varactor diodes

The analysis and scanning characteristics of an infinite array of rectangular microstrip patches each loaded with a varactor diode is presented. The analysis is based on full-wave moment method theory and uses attachment modes to accurately model the current through the feed and the diode. The effect of the biased varactor diode on the scan performance is presented, and it is shown that the impedance mismatch caused by a scan blindness can be eliminated. Other characteristics are also given such as: the active element gain, the efficiency of each loaded microstrip element, and the level of cross polarization generated by the loading of the patch. The effect of the diode biasing level as well as the position of the diode on each radiating element on these scan characteristics is also considered. >

Electromagnetic wave wireless communication in shallow water coastal environment: theoretical analysis and experimental results

Shallow water coastal environments are very important from the biological, social and economic point of view. Wireless technologies - and in particular wireless sensor networks (WSN) - are critical for enabling their efficient and pervasive monitoring. Electromagnetic (EM) communication is considered as the physical layer because, in shallow water coastal environments, it presents distinct advantages with respect to acoustic and optical communication. The benefit of lateral wave EM propagation in shallow water environment is explained. A theoretical analysis of EM propagation in a typical shallow water environment is then conducted, where the maximum distance coverable for a given transmitter power is calculated. The results are then compared with simulations and measurements: their differences with respect to theoretical predictions are assessed. A prototype of underwater communication system constituted by an underwater sensor and a hub buoy that relays data to the mainland is finally presented. Conclusions are drawn in terms of its performance, also in comparison with existing underwater EM communication systems and solutions.

Frequency agile microstrip rectangular patches using varactor diodes

A technique for controlling the operating frequency of microstrip rectangular antennas was investigated experimentally and theoretically. The method consists of placing varactor diodes at appropriate locations and then biasing the diodes. Measurements and theoretical calculation were performed for a 5.3-cm*4.5-cm edge-fed patch using Arlon LX with a thickness of 0.7874 mm and a relative dielectric constant of 2.17. BB 405B silicon UHF variable-capacitance varactor diodes were used as tuning devices. Good agreement between experimental results and theory was achieved.<<ETX>>

Sampling Procedures for Resonance Based Radar Target Identification

The performance of radar target identification using the natural E-Pulse technique is significantly degraded if the sampling rates of the target response and the E-Pulse filter are ignored. In this work, improved sampling procedures over that previously reported by Antony and Shuley (Electron. Lett., vol. 40) in 2004 are proposed. Numerical results demonstrate that the proposed procedures significantly improve the target identification performance.

Reducing solution time in monochromatic FDTD waveguide simulations

Rectangular waveguide is modelled using the Finite-Difference Time-Domain Method. It is shown that when using a monochromatic excitation that the steady state solution can take an undue amount of time to achieve. A simple technique is presented which minimises the duration of the resulting transient time enabling the steady state to be reached in a much shorter amount of time. >

Subsurface Target Recognition Based on Transient Electromagnetic Scattering

The E-pulse technique which typically uses transient scattering data from radar targets in free space is one of the most well known resonance based radar target recognition schemes on which target recognition is based. In this communication, the possibility of subsurface target recognition based on the E-pulse technique is investigated using numerical examples of a metallic hip prosthesis embedded in models of realistic human tissue.

Numerical analysis of an aperture coupled microstrip patch antenna using mixed potential integral equations and complex images

A full wave analysis of the aperture coupled microstrip patch antenna using a Mixed Potential Integral Equation (MPIE) approach is proposed. The problem is formulated as three coupled integral equations where the unknowns are the electric surface currents on the patch and feedline and the magnetic surface current on the aperture. Method of Moments (MOM) is then applied to solve for the various current distributions. With the sole use of closed-form Greens functions, integration in the spectral domain or Sommerfeld integral is completely avoided. The technique results in a very efficient algorithm whose computational speed is generally superior to that of spectral domain approach.

Robust Target Identification Using a Modified Generalized Likelihood Ratio Test

In order to correctly identify a remote target, an efficient and robust target signature identification technique is required. Radar target identification based on complex natural resonances (CNRs) has drawn the interest of many researchers following the development of the singularity expansion method (SEM). As evident from the literature, statistical techniques such as the generalized likelihood ratio test (GLRT) have produced a better identification result, in the presence of noise, compared to some other SEM-based identification methods such as the extinction pulse (E-pulse) technique. However, one of the issues related to a resonance based target classifier is that it requires the commencement of the late time period for the unknown target response to be determined accurately in order to avoid false alarms during target classification process. For automatic target recognition (ATR) applications, usually such information is not known a priori. In view of this problem, a modified GLRT technique that utilizes time-frequency analysis is presented in this paper. The improved GLRT method does not require prior knowledge of the beginning of the late time period for the transient response of the unknown target. Simulation results using various targets show that our method is comparable to the original GLRT technique when the commencement of the late time period for the unknown target response is correctly determined and outperforming the original GLRT technique when the commencement of the late time period for the unknown target response is incorrectly determined.

A Novel, Fast, Approximate Target Detection Technique for Metallic Target Below a Frequency Dependant Lossy Halfspace

The extinction pulse (E-Pulse) technique has been widely applied to problems involving radar target identification. In this paper a fast approximate target detection and recognition scheme based on the E-Pulse technique is proposed and applied to a subsurface target detection and recognition scenario. Previous studies have demonstrated that the target resonances for subsurface targets are closely related to the target resonances for a target within a homogenous environment. In the proposed method, the target resonance for the target in the homogenous medium will be used to construct the E-Pulse for target detection and recognition purposes. The details of the proposed method will be described in this paper. The obvious example of a target below a dielectric halfspace is the use of ground penetrating radar (GPR) for detecting and recognizing unexploded ordnance (UXO). However, instead of a GPR related scenario, a numerical example of a biomedically related problem, of a hip prosthesis model sited within a halfspace of homogenous human tissue model with realistic dielectric properties will be used to demonstrate the feasibilities of the proposed technique for target detection and recognition. The reasons for the choice of this particular example will also be explained in the paper.