Russell P. Jedlicka

Measured mutual coupling between microstrip antennas

Mutual coupling between L -band rectangular, nearly square, and circular microstrip antennas has been investigated experimentally by a series of measurements of the S -parameters. The mutual coupling level decreases monotonically with increasing separation between elements with the E -plane coupling down 20 dB and the H -plane coupling down 25 dB for typical adjacent element spacings. For 1/16 in and 1/8 in substrates at L -band the predominant coupling mechanism is via the space wave since the surface wave is shown experimentally to be small.

Coupling through tortuous path narrow slot apertures into complex cavities

A hybrid finite-element method/method of moments (FEM/MOM) model has been implemented to compute the coupling of fields into a cavity through narrow slot apertures having depth. The model utilizes the slot model of Warne and Chen (1988, 1989, 1990, 1992), which takes into account the depth of the slot, wall losses, and dielectrics with air gaps in the slot region. The cavity interior is modeled with the mixed-order covariant-projection elements of Crowley (1988). Results are given showing the accuracy and generality of the method for modeling geometrically complex slot-cavity combinations.

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.

Electromagnetic coupling into complex cavities through narrow slot apertures having depth and losses

We present results for coupling through narrow slot apertures into a variety of cavity configurations. The effects of slot geometry, slot material, cavity geometry, cavity wall losses and dielectric inhomogeneities within the cavity are considered. All results include both the calculated and experimental data to verify the validity of the numerical simulations. The equations are solved with a hybrid finite element method/moment method.

Experimental study of narrow slot, cavity-backed apertures with finite wall conductivity

The authors present results showing the effects of varying conductivity and surface preparations for half-space coupling as well as different loadings of the narrow slot apertures. The coupling through narrow slot apertures having depth was measured for a variety of resonant cavity loadings. The loadings were chosen such that the cavity resonant frequencies were above, near, and below the resonant peak of the half-space coupling curve. Measurements were made in the 2-4-GHz band with vertical polarization. Two cases were considered: the slot radiating into a half-space and a cavity-backed aperture. The half-space coupling was reduced when the slot width decreased and/or the depth was increased. For very narrow slots, the wall loss dominates and this lowers the Q of the aperture. A decrease in Q was observed for a corresponding reduction in conductivity. It was observed that the cavity fields measured were quite large when a resonant structure loaded the aperture.<<ETX>>

Design and implementation of a golay-based GPR system for improved subsurface imaging

A bench-top prototype GPR using Golay codes has been designed and implemented. The preliminary experimental results show a reasonable good improvement in terms of SNR. This work is still in progress. Improvements related to some of the other components and subsystems are underway. In particular, we are experimenting with innovative antenna designs having minimum influence on the transmitted waveform, and improved image processing algorithms.

Simple estimated beamformer design in symmetric ESPAR arrays

An exciting body of work regarding electronically steerable parasitic array radiator (ESPAR) antenna technology has been generated in recent years (E. Taillefer,et al). By utilizing mutual coupling as a benefit rather than a drawback ESPAR antennas move the spectrum of possible array structures a significant step closer to the widely-desired goal of a small, low-cost, and low-power electrically-steered enhanced-gain antenna. This paper is intended to contribute to the excellent body of existing knowledge by proposing a simplified ESPAR beamformer design technique. ESPAR design, based as it is on the complicated phenomenon of mutual coupling, is one of the more inefficient aspects of the current state of the technology. Simulations reveal surprisingly good results using the reduced-complexity beamforming technique, and future verification work is planned.

Efficient computational models of electromagnetic coupling through general tortuous-path, narrow-slot apertures into shielded systems

Electromagnetic coupling can adversely impact a multitude of applications. The primary coupling issues are electromagnetic compatibility and interference, either intentional or unintentional. The functionality of the systems involved, which typically consist of numerous subsystems operating concurrently, can be characterized in terms of their susceptibility, vulnerability and survivability in the electromagnetic environment in which they are expected to operate. Coupling through unforeseen apertures such as the tortuous-path, lapped seam depicted in the paper into conducting cavities containing multiple thin conducting elements is the major thrust of this work. To model realistic coupling problems, it is necessary to develop a model which includes a three-dimensional representation of the slot/cavity/wire configuration. Specifically, such a model should incorporate narrow slot apertures having depth, loss and gaskets, bolt loads, backed by arbitrarily-shaped cavities, filled with inhomogeneous, lossy dielectrics, and thin wires in arbitrary configurations. The widely varying scales in such a system provides a challenge to a numerical model in terms of both accuracy and efficiency. This is especially true in a development engineering environment in which the engineer typically has a desk-top workstation on which to perform an analysis.