Chi-Chih Chen

Buried unexploded ordnance identification via complex natural resonances

A classification technique focused on the identification of buried unexploded ordnance (UXO) using complex natural resonance (CNR) signature is considered. The total least square (TLS) Pronys (1795) method is used to extract CNRs from time-domain data, Full-scale UXO computational models and the body of revolution moment method (BORMM) code is used to obtain the backscattered fields, which are then used to give the theoretical free-space CNRs. Baums (1993) transformation is used to relate a CNR in a lossy simple medium to the corresponding CNR in free space. A practical UXO classification yields an estimate of the UXO length from its CNR information. Successful UXO classification examples from actual measured data are presented.

Ultrawide-bandwidth fully-polarimetric ground penetrating radar classification of subsurface unexploded ordnance

An ultrawide-bandwidth (UWB) ground penetrating radar (GPR) was used to collect fully-polarimetric backscattered data from 10 to 800 MHz using a dual-polarization version of the previously developed dielectric-loaded horn-fed bow-tie (HFB) antenna. Special processing algorithms were developed to extract the polarization, orientation, depth, and length features of the target under investigation. The polarization and resonance features were utilized to discriminate subsurface ordnance from false-alarm objects that do not have elongated bodies. The classification of a specific type of unexploded ordnance (UXO) was also performed using the known length information. The processed results obtained from an initial blind field test show a very encouraging discrimination performance.

A Portable Low-Power Harmonic Radar System and Conformal Tag for Insect Tracking

Harmonic radar systems provide an effective modality for tracking insect behavior. This letter presents a harmonic radar system proposed to track the migration of the Emerald Ash Borer (EAB). The system offers a unique combination of portability, low power and small tag design. It is comprised of a compact radar unit and a passive RF tag for mounting on the insect. The radar unit transmits a 5.96 GHz signal and detects at the 11.812 GHz band. A prototype of the radar unit was built and tested, and a new small tag was designed for the application. The new tag offers improved harmonic conversion efficiency and much smaller size as compared to previous harmonic radar systems for tracking insects. Unlike RFID detectors whose sensitivity allows detection up to a few meters, the developed radar can detect a tagged insect up to 58 m (190 ft).

Distributed Lumped Loads and Lossy Transmission Line Model for Wideband Spiral Antenna Miniaturization and Characterization

A lossy transmission-line model that incorporates the radiation resistance of small loop antennas is introduced to characterize the input impedance of a spiral antenna over a large frequency range. This model also leads to a concept of controlling the current velocity and impedance on a spiral antenna by introducing distributed reactive loading along the spiral arms. An important application of the concept is to reduce antenna size and this is demonstrated by numerical simulation examples.

Modeling and investigation of a geometrically complex UWB GPR antenna using FDTD

A detailed analysis of ultrawide-band (UWB), dual-polarized, dielectric-loaded horn-fed bow-tie (HFB) antennas is carried out using the finite-difference time-domain (FDTD) method. The FDTD model includes realistic features of the antenna structure such as the feeding cables, wave launchers, dielectric loading, and resistive-film loading. Important antenna characteristics that are usually difficult to obtain via measurements can be obtained more directly from this FDTD model. Since the HFB antennas under consideration are intended for ground penetrating radar (GPR) applications, the effects of the half-space medium are also investigated. The simulated results serve to verify the performance of the HFB antenna design, and to optimize various antenna parameters.

Single-fed Circularly Polarized Antenna Element With Reduced Coupling for GPS Arrays

A single-fed circularly polarized stacked patch antenna is proposed to cover all GPS bands, including the E5a/E5b band for the Galileo system. The small aperture size (lambda/8 at 1176 MHz, the L5 band) makes this antenna attractive for small GPS arrays. Also, in contrast to previous GPS antennas, the presented design uses a single feed for circular polarization. In this paper, we present the design procedures and performance of the designed GPS antenna and discuss issues relating to coupling between array elements. Modifications to reduce coupling are then presented.

Size Reduction of a Low-Profile Spiral Antenna Using Inductive and Dielectric Loading

This letter discusses a miniature low profile ultrawideband (UWB) spiral. The antenna is miniaturized using a combination of dielectric and inductive loading. In addition, a ferrite coated ground plane is adopted in place of the traditional metallic ground plane for profile reduction. Using full-wave simulations and measurements, it is shown that the miniaturized spiral can achieve similar performance to a traditional planar spiral twice its size.

Near-field dipole radiation dynamics through FDTD modeling

We use finite-difference time-domain (FDTD) numerical simulations to study horizontal dipole radiation mechanisms and patterns near half-space interfaces. Time snapshots illustrating propagation of wavefronts at an instance in time are included with antenna patterns to provide a visualization tool for understanding antenna radiation properties. Near-field radiation patterns are compared with far-field asymptotic solutions and the effects of electrical properties, antenna height, and observation distance are investigated through numerical simulations. Numerical simulations show excellent agreement with measured data collected over a water-filled tank. Near-field H-plane radiation patterns are broader and contain radiation maxima beyond the critical angle predicted by far-field solutions. A large amplitude E-plane radiation lobe is located directly below the antenna in all simulations, while the two large amplitude sidelobes are less distinct and occur at larger incidence angles than predicted by far-field solutions. Radiation patterns resemble far-field solutions by a distance of 10 wavelengths, except near the critical angle where H-plane radiation maxima and E-plane sidelobes occur at larger incidence angles than predicted by far-field solutions.

A Compact Dual-Band GPS Antenna Design

This letter discusses a small slot-loaded, proximity-fed patch antenna designed for GPS operation at L1 (1575 MHz) and L2 (1227 MHz) bands. High-dielectric substrate and meandered slots are employed to reduce the antenna size down to 25.4 mm in diameter and 11.27 mm in thickness. The thickness is important for achieving the wide bandwidth (>30 MHz) in support of modern GPS coding schemes. The dual-band coverage is achieved by utilizing the patch mode in L2 band and slot mode in L1 band. This design features additional slot stubs for independently tuning the L1 frequency. The right-hand circularly polarized (RHCP) field property is achieved by connecting two proximity probes to a small surface-mount 0°-90° hybrid chip. Simulated and measured antenna performance will be presented. This compact GPS antenna design is suitable for small GPS antenna arrays and portable GPS devices.

Patch-antenna miniaturization using recently available ceramic substrates

The recent availability of high-contrast, low-loss ceramic materials provides us with possibilities for significant antenna miniaturization. This paper explores the use of low-temperature co-fired-ceramic (LTCC) substrates in producing a miniaturized patch-antenna design. Of particular interest in the design are parameters such as substrate thickness, input impedance, radiation efficiency, and bandwidth due to the high-contrast ceramic. We propose a thick substrate to increase bandwidth. However, the substrate is truncated to mitigate surface-wave loss, with possible texture to provide dielectric-constant control for improved impedance matching. Utilizing these proposed design modifications, a miniaturization factor of more than eight was achieved, with a return-loss half-power bandwidth greater than 9%. Moreover, respectable gain was maintained, given the achieved miniaturization