Jean-Pierre R. Bayard

Target identification using optimization techniques

A scheme for synthesizing bandlimited radar waveforms for detection and discrimination of targets is presented. The procedure, which involves a maximization of the ratio of the energy within a specified time interval to the total energy of the received waveform, can be used to synthesize a bandlimited generator waveform that produces a target response with the majority of its energy concentrated in the specified time duration. For an appropriate time interval, which depends on the bandwidth, such response exhibits energy concentration comparable to that produced by the K-pulse and E-pulse waveforms. The analysis does not require a numerical or empirical determination of the targets complex poles, since the desired waveform is obtained directly from the knowledge of the system transfer function over the frequency band of interest. The procedure is based on an analytical optimization, so no iterations or nonlinear programming techniques are required. The method is illustrated using simple thin-wire models as targets and antennas. Numerical examples are given, and the effects of bandwidth, duration of optimization, and aspect angle are discussed. >

Analysis of infinite arrays of printed dipoles on dielectric sheets perpendicular to a ground plane

The analysis of infinite arrays of printed dipoles on finite-height dielectric sheets is described. A full-wave solution is obtained by using a combination of the Greens function-moment method approach and mode matching techniques. Numerical calculations and experimental results validating the theory are shown for the air-dielectric case and for epsilon /sub r/ not=1. Scan blindnesses are identified in arrays with epsilon /sub r/ not=1. Pertinent numerical considerations and issues of convergence are discussed. >

Analysis of infinite arrays of microstrip-fed dipoles printed on protruding dielectric substrates and covered with a dielectric radome

A method for analyzing infinite arrays of antennas printed on both sides of substrates protruding from a ground plane and covered with a dielectric radome is described. Using the equivalence principle, the array unit cell is decomposed into homogeneous regions where the fields are expressed as Floquet summations, and an inhomogeneous cavity region where the fields can be found by a combination of the method of moments and modal analysis. The approach is rigorous in the sense that the combined effects of the radiating element and feed geometry printed on opposite sides of a protruding substrate are taken into account. The method is quite general, capable of modeling any antenna elements with substrate currents that are perpendicular and/or parallel to the ground plane. In addition, both the radiating and scattering/receiving modes of operation are treated in the analysis. The method is used to calculate the active element impedance of an infinite array of dipoles transmission line-coupled to microstrip feeds. Examples of numerical results are presented for various scan conditions and the effects of a near-field dielectric radome are demonstrated. >

E-plane scan performance of infinite arrays of dipoles printed on protruding dielectric substrates: coplanar feed line and E-plane metallic wall effects

The effects of coplanar feed lines and of E-plane cavity walls on the performance of infinite arrays of dipoles printed on protruding dielectric substrates are investigated. In order to do so, two unit cell configurations are studied: (1) the dipole element fed by coplanar transmission lines and (2) the dipole element fed by coplanar transmission lines with finite-height metallic walls added parallel to the H-plane of the array. The element active impedances are calculated for these configurations, and they are compared with those obtained from arrays of dipoles without coplanar feed lines. Effects of the dielectric substrate permittivity and of its thickness on the array element active impedance are included. The results show that the arrays of dipoles with the coplanar feed lines exhibit feed-line-induced blindnesses which reduce considerably the scan volume of the array. It is also shown that these feed line effects are reduced for thicker or higher permittivity substrates, and that the insertion of electric walls is one possible avenue for eliminating these anomalies. >

A general method for treating infinite arrays of antennas printed on protruding dielectric substrates

A full-wave approach has been developed to analyze a wide variety of radiating elements (including the dipole element with feed lines) printed on one side of a protruding substrate in an infinite array environment. The method is outlined, and examples of results are presented for the dipole element fed by a coplanar strip transmission line.<<ETX>>

Optimization method versus E-pulse method in the context of target discrimination

The performances of the optimization method and the extinction pulse method are evaluated for idealized data as well as experimental data from scaled-model targets. Although both methods use the late-time response to discriminate targets, the discriminant waveform is synthesized differently; from the target pole singularities in the E-pulse method, and from an energy maximization in the optimization method. Responses from waveforms synthesized using calculated wire data and laboratory measured data are presented, and the early-time energy confinements produced by the two methods are found to be generally comparable. The robustness of the optimization and E-pulse methods in the presence of noise is demonstrated by results for calculated and measured data. >

Multimedia teaching tools for an introductory circuit analysis course

The paper discusses the use of computer technology as a tool for increasing access to and quality of our electrical engineering program at the California State University, Sacramento. Using readily available software and Internet access, a comprehensive set of lecture materials, student exercises and basic laboratory demonstrations are produced in electronic format in order to promote learning, reinforcement and consistency. While the central focus of this work is on learning, the convenience aspect of this method of delivery has proven to be effective tool for increasing performance as well as enrolment.

Scan performance of infinite arrays of microstrip-fed dipoles with bent arms printed on protruding substrates

E-plane scan results are presented for infinite arrays of microstrip-fed dipoles printed on protruding dielectric substrates. Active impedance values are calculated for dipoles with bent arms and for the array with a near-field dielectric radome cover. It is found that bending the dipoles arms produces a small improvement in the scan range, as compared to the element with the arms straight, and that a dielectric radome with a low permittivity causes a small shift in the impedance curves. The scan limitation of the array is dictated, however, by the presence of the coplanar feedlines with improvement achievable by varying the substrates thickness and permittivity as well as the dipole/feed geometry. A dipole element with a modified coplanar feed design is introduced for wider scan coverage. >

Transient response of a receiving dipole array: bounds and maximization

The optimum solution for a receiving array of dipole antennas connected to a load through a feed network is obtained. It is given in terms of the incident electric field waveform that maximizes, at a specific time t/sub 0/, the received voltage across a specified load impedance. This result is used to set an upper limit on the peak voltage that the antenna can deliver to a load, thus providing guidelines for the design of pulse-protection circuits. The analysis uses the method of moments to approximate the currents induced in the wires by the incident field and S-parameter techniques to describe the feed incident electromagnetic plane waves. The Lagrange multiplier technique is then used to maximize the receive load voltage. The solutions presented are based on an idealized model for the feed network; however, the analysis can be extended easily to account for loss and asymmetry of physically realizable feed networks. >

Applications of computer technology in tandem with the traditional classroom

Electronic teaching methods are used to stimulate the teaching and learning of basic electrical circuits at California State University, Sacramento (CSUS). Television and the world wide web are combined with traditional classroom teaching to address the issues of attendance, or lack thereof, poor performance and timely assessment at a comprehensive urban university. While the circuits course is taught in the regular classroom, it is simultaneously broadcast through cable television in the larger Sacramento area. The course is also entirely available through the worldwide web including audio-video segments captured from the classroom, as well as testing/assessment modules. The significance of this experiment lies in that the instructor promotes the technology portion of the teaching as complementary to the classroom environment, not as an equivalent self-paced learning option. This paper describes the process in detail, including how web-based materials are used to assess students performance, provide dynamic feedback to the instructor and give students an opportunity for timely remedial action.