Wen-Jiao Liao

Characteristic Evaluation of an Active Patch Antenna Structure with an Embedded LNA Module for GPS Reception

The concept of antenna design with an embedded LNA module is proposed in this work. To demonstrate the concept, a microstrip patch antenna for GPS reception is considered. The antenna is a conventional patch antenna with corners truncated to produce RHCP radiation for GPS reception at 1.575 GHz. A cavity is formed within the substrate of the antenna to accommodate the LNA module so that the built-in LNA may enhance the antenna reception capability without adding external circuits. The resulting patch has the same footprint and thickness as an ordinary passive patch. Simulations and measurements of the prototype antenna indicate that the built-in LNA module introduces no significant changes to the antenna properties except slight shifts on the resonance frequency, which can be corrected by rescaling. The proposed antenna configuration is an attractive option in practical applications for making antennas with small footprints and large gains.

A multiband microstrip dipole antenna

We have developed a hybrid multiband antenna that integrates a loop antenna into the feed structure of a planar dipole. The planar dipole is tuned to handle GSM and 802.11b WLAN signals while the fundamental and higher order modes of the loop antenna can be used for 802.11a WLAN communications. We first introduce the basic design principles of the planar dipole, and then describe the techniques used to package a loop antenna with a planar dipole using a parallel stripline structure. Measured reflection coefficients comply with simulation predictions and exhibit low return loss in the desired communication bands. Measured radiation patterns reveal an omnidirectional coverage in the lower bands and a wide coverage in the higher band. Such an antenna configuration is suitable for portable devices that integrate multiple wireless communication systems.

Predicting sensor fusion performance using theoretical models

Simple theoretical models can be constructed to study the behavior of sensor-fused systems using idealized sensor suites. Models are available for feature-level and decision-level fusion, both of which are now being used with demining sensors. These models are attractive as design tools and for estimating the expected performance of new sensor suites, since their performance can be evaluated with relatively little effort. In this paper we review some simple idealized models and their predictions for fused system performance. The data produced by demining sensors are often correlated, and the effect of correlation is explored for both feature-level and decision-level fusion.

Algorithms for detection of surface mines in multispectral IR and visible imagery

Algorithms are presented for detecting surface mines using multi-spectral data. The algorithms are demonstrated using visible and MWIR imagery collected at Fort A.P. Hill, VA under a variety of conditions. For imagery with a resolution of a few centimeters there is significant correlation in the clutter. Using a first-order Gauss Markov random field model for the clutter, an efficient pre-whitening filter is proposed. A significant improvement in detection is demonstrated as a result of this whitening. Further improvement in the detection of specific mine types is demonstrated by using a random signal model with a known covariance matrix. That approach leads to an estimator-correlator formulation, in which the random signature estimate is the output of a Wiener filter. It is suggested that by fusing the output of a bank of such filters one could improve detection of all mine types.

Beamwidth Control for Directive Antennas using RF Lens

Broadband antennas such as horn and spirals are suitable for testing range references, direction-of-arrival estimation and other UWB applications. However, one problem with most broadband antennas is the frequency dependency of the antenna beamwidth as well as antenna gain. In this work, a beamwidth compensation measure is proposed by adding an RF lens in front of the broadband antenna. By adjusting the curvature profile, the RF lens can be made to reduce the antenna beamwidth. Simulation results show that the main beam becomes more compact after adding a spherical RF lens. Experiment results show that by adding an elongated bullet-shaped RF lens, the antenna patterns can be drastically reduced and hence improve the antenna directivity

Using physical models to improve thermal IR detection of buried mines

Many aspects of a buried mines thermal IR signature can be predicted through physical models, and insight provided by such models can lead to better detection. Several techniques for exploiting this information are described. The first approach involves ML estimation of model parameters and followed by classification of those parameters. We show that this approach is related to an approximate evaluation of an integral over the parameters that arises in a Bayesian formulation. This technique is compared with a generalized likelihood ratio test (GLRT) and with computationally efficient, model-free approaches, in which soil temperature data are classified directly. The benefit of using the temporal information is also investigated. Algorithm performance is illustrated using broadband IR imagery of buried mines acquired over a 24 hour period. It is found that the detection performance at a suitably selected time is comparable to the performance achieved by processing all times. The performance of the GLRT, for which detection is based only on the residual error, is inferior to a classifier using the parameters.

The role of grounding in automotive EMC

We discuss grounding issues specific to automotive applications. We review the components of a typical automotive ground system, their intended functions, and known limitations. Some sources of automotive emissions are identified and the role of ground in mitigating these emissions is discussed.

Detectability of surface-laid landmines with a polarimetric IR sensor

Polarimetric scattering models are developed to predict the detectability of surface-laid landmines. A specular polarimetric model works well only under the condition that there is either no sunlight or the sun is not close to the specular reflection direction. Moreover, this model does not give insight why certain man-made objects like landmines give a higher polarimetric signature than natural background. By introducing a polarimetric bidirectional reflectance distribution function (BRDF) the specular model is extended. This new model gives a better prediction of the polarimetric signature and gives a close match to the measurements of landmines with different casings as well as the sand background. The model parameters indicate that the landmines have a lower surface roughness and a higher refractive index, which is the reason why these objects are detectable from the background based on their polarimetric signature.

Fusion of acoustic LDV and GPR data

We investigate the potential for improving land mine detection by fusing data from ground penetrating radars (GPRs) and sensors of acoustically induced soil motion. We present a case study involving data from the SRI forward-looking radar and a laser Doppler vibrometer (LDV) system developed by the University of Mississippi. The LDV sensor detects acoustically induced soil vibrations, while the GPR detects scattering from dielectric discontinuities or metal objects in the soil. Since these sensors exploit different target physical properties, it is reasonable to expect a benefit in fusion. Although the sensors are relatively new, the LDV and GPR data exhibit evidence for complementarity, in that the GPR is significantly better at detecting metal mines, while the LDV is somewhat better at detecting plastic mines. Decision-level fusion is shown to improve performance. A simple OR fusion approach is found to perform similarly to an optimum hard decision fusion algorithm.

An Active Patch Antenna with Embedded LNA Module

In this work, an LNA module is moved into a corner-truncated patch antenna, which is intended for GPS reception use. A cavity is formed within the substrate of the patch to accommodate the LNA module. The built-in LNA enhances the antenna reception capability without adding external circuits. Hence, the resulting patch has the same footprint and thickness as ordinary passive patches. Simulations and measurements on prototype antenna indicate that the built-in LNA module imposes limiting influences on the antenna properties, which can be corrected by rescaling the patch, and is hence an attractive option for making small antennas with large gains