Amelia Buerkle

Compact slot and dielectric resonator antenna with dual-resonance, broadband characteristics

The goal of this study is to improve the bandwidth of a miniaturized antenna. The proposed technique combines a slot antenna and a dielectric resonator antenna (DRA) to effectively double the available bandwidth without compromising miniaturization or efficiency. With proper design it is observed that the resonance of the slot and that of the dielectric structure itself may be merged to achieve extremely wide bandwidth over which the antenna polarization and radiation pattern are preserved. In addition, using the DRA, a volumetric source, improves the radiation power factor of the radiating slot. A miniaturized antenna figure of merit (MAFM) is defined to simultaneously quantify aspects of miniaturized antenna performance including the degree of miniaturization, efficiency, and bandwidth. Figures for various common types of antennas are given and compared with that of the proposed structures. In order to determine the effects of varying design parameters on bandwidth and matching, sensitivity analysis is carried out using the finite-difference time-domain method. Numerous designs for miniaturized slot-fed dielectric resonator antennas are simulated and bandwidths exceeding 25% are achieved. Two 2.4 GHz antennas are built, characterized, and the results compared with theory.

Compact Wideband UHF Patch Antenna on a Reactive Impedance Substrate

The goal of this letter is to design a compact, planar UHF antenna operating over the frequency range 420¿450 MHz. A microstrip patch antenna is selected as the elementary radiating structure because it has a low profile and is simple to fabricate. Compact size and enhanced bandwidth are simultaneously achieved through the use of a reactive impedance surface (RIS) in place of a PEC ground plane. The inherently limited bandwidth of the patch is overcome by incorporating a U-shape resonant slot radiator within the patch area. The design, fabrication, and measurement results are presented. It is shown that a patch with a U-shape slot whose dimensions are only

A wide-band, circularly polarized, magnetodielectric resonator antenna

0.136~lambda times 0.228~lambda

Tracking of Metallic Objects Using a Retro-Reflective Array at 26 GHz

at the lowest frequency of operation can provide more than 20% bandwidth, covering a frequency range of 410¿485 MHz.

Fabrication of a DRA Array Using Ceramic Stereolithography

Previously insurmountable challenges posed by stringent requirements of simultaneous compact size, high bandwidth, high to moderate efficiency, and circular polarization operation at UHF have been surpassed by a unique design employing layered magnetodielectric materials. To achieve percentage bandwidth values in excess of 50% for an antenna with a maximum dimension of 0.15/spl lambda/ three approaches for bandwidth enhancement are combined in a proper fashion. A volumetric source, as opposed to printed planar or wire sources, inherently provides higher bandwidth and is used as the fundamental radiating element of the antenna. The radiating structure is made up of layered magnetodielectric material with proper design of permittivity and permeability values forming a magnetodielectric resonator antenna (MDRA). Noting that miniaturization and wave impedance in the MDRA are, respectively, proportional to the square-root of the product and ratio of the permeability and permittivity, moderate values of permittivity and permeability are used to enhance the bandwidth while achieving considerable miniaturization. The third method for bandwidth enhancement is based on the integration of a resonant feed and many parasitic elements into the MDRA structure. Square symmetry of the MDRA is used to obtain circular polarization operation. A prototype small UHF antenna operating over 240-420 MHz with a linear dimension smaller than 0.15/spl lambda/ at the lowest frequency is fabricated and tested; the results are summarized in this paper.

Non-Destructive Evaluation of Elastic Targets Using Acousto-Electromagnetic Wave Interaction and Time Reversal Focusing

The detection and tracking of targets in highly cluttered environments often poses a difficult engineering challenge as the strong clutter backscatter contained in the scene makes it difficult to distinguish the target of interest. A design concept to aide in standoff detection and tracking of large metallic objects in a warehouse setting is presented. This includes the design and implementation of an active retro-reflective array system that is able to determine the precise location and identification of an object. To accomplish this, a unique series fed grounded coplanar waveguide patch antenna is designed and implemented with minimal cross coupling among elements. This compact array has a relatively large radar cross-section (RCS) while maintaining the desired retro-reflectivity. Additionally, a tilted beam is incorporated in the linear series-fed array to isolate the large RCS of the planar array structure at boresight from the desired modulated, retro-reflective RCS. This method for enhanced detection is implemented at 26 GHz. The incorporation of the high-speed PIN switches into the array structure provide the tag with a unique identification. Measurement results for the modulated RCS from such an array in a cluttered environment are presented.

Analysis of Acousto-Electromagnetic Wave Interaction Using Sheet Boundary Conditions and the Finite-Difference Time-Domain Method

The purpose of this letter is to demonstrate monolithic fabrication of an array of dielectric resonator antennas (DRAs) using ceramic stereolithography. Design and measurements of a eight-by-eight array of rectangular DRAs composed of four monolithic four-by-four array blocks are presented. The array elements are designed over a ground plane and fed by a standard aperture-coupled microstrip corporate feed network. It is shown that the corporate feed, and not the DRAs, is mainly responsible for losses in the radiating structure

Analysis of Acousto-Electromagnetic Wave Interaction Using the Finite-Difference Time-Domain Method

The objective of this research is to demonstrate the efficacy of using acoustic and electromagnetic (acousto-EM) wave interaction and time-reversal focusing in the non-destructive evaluation of an object. Acousto-EM wave interaction occurs when an electromagnetic wave scatters from an object under seismic or acoustic illumination; the acoustic vibration of the object gives rise to a frequency modulated scattered electromagnetic field which is a function of the object and both the electromagnetic and acoustic source parameters. A recently developed model, which is capable of predicting the first Doppler component of the frequency modulated scattered field for arbitrary two-dimensional objects over a wide bandwidth, is used in the analysis. Time reversal focusing is also used to improve sensitivity and obtain information about the location of flaws within the target. Both the unshifted electromagnetic fields scattered from the stationary target and the Doppler component are analyzed. The sensitivity of the Doppler component to the presence of flaws, which perturb the mechanical mode shape and resonance frequency, is demonstrated for application in non-destructive evaluation.

Enhanced Detection of On-Metal Retro-Reflective Tags in Cluttered Environments Using a Polarimetric Technique

Acousto-electromagnetic wave interaction occurs when an electromagnetic wave scatters from an object under seismic or acoustic illumination. The vibration of the object under acoustic excitation gives rise to a frequency modulated scattered field which depends on both the object and electromagnetic and acoustic source parameters. The objective of this study is to accurately calculate the Doppler spectrum of the bistatic scattered field which is usually orders of magnitude smaller than the fundamental component of the scattered field (the stationary target response). In this analysis the recently developed sheet boundary conditions are used to set up a duplicate problem of a stationary object having time varying sheet impedance and admittance accounting for the object vibration. The problem is formulated using the two-dimensional finite-difference time-domain (FDTD) method in an iterative scheme in order to find the broadband response of the scattered field Doppler component. Two-dimensional analytical solutions for a canonical geometry are used to verify the FDTD simulation results.

A 26 GHz retro-reflective array for long-range RFID applications

We model electromagnetic scattering from two-dimensional objects under seismic or acoustic illumination. The vibration of the object gives rise to a frequency modulated, or Doppler, component in the scattered electromagnetic field. The Doppler component is primarily produced by two mechanisms, the boundary perturbation on the surface of the object and the density modulation within the object. The contributions from the boundary perturbation, which are analyzed in a previous publication, are reviewed and expanded upon herein; the contributions from density modulation are also presented. The wave interaction is analyzed with a unique, two-step approach. First, a finite element acoustic simulation is used to obtain the displacements within the acoustically excited object. This information is then input to a specialized formulation of the finite-difference time-domain method to simulate electromagnetic scattering. Analytical solutions for a cylinder are used to verify the computational modeling approach. Results for a more complex geometry are also presented.