Adrian Eng-Choon Tan

Buried Object Characterization Using Ultra-Wideband Ground Penetrating Radar

In this paper, a method to characterize buried nonmagnetic objects in ground using ultra-wideband (UWB) ground penetrating radar (GPR) is proposed. In this method, UWB pulses are radiated by the radar, while scattered signals from the ground with the buried object are received. The received signals are then post-processed to estimate the depth, thickness, and electrical properties of the buried object. A constant depth and thickness is enforced at all frequencies while the signals are processed to extract the buried object characteristics, resulting in more accurate estimations and reduced processing time. In addition, path loss due to the close proximity of the radar to the ground is compensated analytically. The applicability of the proposed method is validated with several planar objects and a boulder that we typically encounter in the construction industry. The proposed method can achieve sufficient reliability in estimating the permittivity of buried objects for the purpose of material identification. Incorporating the proposed method into the GPRs enhances their existing imaging ability by adding material identification capability.

Estimation of Antenna Effect on Ultra-Wideband Pulse Shape in Transmission and Reception

This paper presents an analysis of the antenna effect on ultra-wideband (UWB) pulse shape in transmission and reception. This analysis consists of a derivation of the impulse response for frequently used UWB antennas like the ridged horn, transverse electromagnetic horn, and bicone in the transmitting and receiving modes. An analytical/semianalytical expression for the received pulse has been derived. Frequency-limited gain of the transmitting and receiving antennas has been accounted for in the estimation of the received pulse. To demonstrate the antenna effect on a UWB pulse, various antenna combinations have been considered to transmit and receive different Gaussian pulses. A combination of transmitting and receiving antennas has been proposed for faithful reception of the transmitted pulse. This paper also studies the pulse shape and amplitude due to oblique incidence of the pulse on a receiving antenna. Measurements have been presented to support the proposed analysis, and they show good agreement with the estimated received pulses.

Time Domain Characterization of Circularly Polarized Ultrawideband Array

The transmitted signal by a circularly polarized ultrawideband (CP-UWB) array is a short pulse of circularly rotating E-field vector in time domain. A mathematical model is derived for a transmitted pulse radiated by a CP-UWB array antenna. To validate the model, an array of four sequentially rotated ridged horns is constructed, and the transmitted pulse is measured in time domain. The measurement is done with a linearly polarized antenna in far-field, for different rotational angles. The E-field vector transmitted by the CP-UWB array is constructed with the measured time-domain pulses. The measured pulse is compared with the derived pulse for validation. Both measured and derived pulses are compared for various parameters such as the CP-UWB arrays sense of polarization, axial ratio, gain and phase difference between orthogonal signals.

Circularly Polarized Ultra-Wideband Radar System for Vital Signs Monitoring

A robust contactless vital signs monitoring system using circularly polarized ultra-wideband (UWB) radar is presented. The design of the proposed UWB radar system is based on a time-expanded correlation architecture. The circularly polarized antenna array of the radar has an axial ratio bandwidth from 3 to 10 GHz. Use of circular polarization has demonstrated improved accuracy for vital signs monitoring.

Design of Transverse Electromagnetic Horn for Concrete Penetrating Ultrawideband Radar

We propose a design for the specific class of trans- verse electromagnetic (TEM) horn that can effectively radiate the electromagnetic signals into soil or concrete. The designed horn antenna has the same aperture height and width, resulting in a square-shaped horn aperture. A design guideline for the horn that considers return loss and radiation performance is described in this paper. The proposed TEM horn is constructed and measured to validate the design. The constructed horn has a maximum dimension (including the balun) of 42.9 × 26.8 × 20 cm. Simulated and measured results suggest that the proposed horn is more effective in radiating electromagnetic energy into concrete, compared with existing TEM horn designs. For free space radiation, measured operating bandwidth of the horn is 0.75-12.0 GHz, with a gain of 3-13 dBi. When radiated into a concrete block, measured operating bandwidth of the horn is 1.0-12.0 GHz.

Material Characterization of Arbitrarily Shaped Dielectrics Based on Reflected Pulse Characteristics

The relative permittivity of materials is extracted using time domain radar pulse reflection measurements. The pulse reflected from an arbitrarily shaped dielectric object is compared with that reflected from its metallic equivalent to determine the objects dielectric constant. The proposed method achieves accuracies of over 85% for permittivity and within 2 mm for material thickness estimations. Using the proposed technique, the complex relative permittivity for various objects is extracted over a frequency range from 3 to 10 GHz. This method has been applied to determine the permittivity of a ridge of sand and to dielectric imaging.

Decade Bandwidth Circularly Polarized Antenna Array

A circularly polarized antenna array design comprising of a feed network that splits an input signal into four orthogonal (0°, 90°, 180°, and 270°) phased signals with equal magnitudes and connected to four anti-podal Vivaldi antennas sequentially rotated by 90° is presented. The proposed antenna array yields 10-dB return loss and 3-dB axial ratio bandwidths from 1-10 GHz. The symmetrical structure gives the antenna array almost identical azimuth and elevation radiation patterns. Pulse reception from various angles show equi-amplitude outputs and very little distortion. The proposed design is suited for high-resolution microwave imaging systems.

Modeling the Effects of Interference Suppression Filters on Ultra-Wideband Pulses

In this paper, we study the effects of interference suppression filters (multiple stopbands) on ultra-wideband (UWB) short pulses. Multiple stopbands of the filter, which is placed in the receiver, affect the UWB pulse amplitude, pulsewidth, and ringing; resulting in reduced signal-to-noise ratio and degradation in receiver performance. An analytical method is proposed in this paper to model the effect of stopbands on the pulse shape. In this paper, the effects of an interference suppression filter on three different Gaussian pulses are studied. Theoretical and measured pulses are compared and found to be in good agreement. The proposed method enables the UWB radio designer to predict the distortion of the received signals after passing through interference suppression filters.

Experimental Verification of Link Loss Analysis for Ultrawideband Systems

An experimental verification of energy link loss between the source at the transmitting antenna and the load at the receiver for ultrawideband systems is presented. The proposed closed-form approximations for the link loss analysis are verified experimentally for different types of antennas and pulse excitations. The measurements showed that the shape of the received pulse depends on the antenna transfer functions and the received pulse energy depends on effective height of the antenna.

Effect of Antenna Noise on Angle-of-Arrival Estimation of Ultrawideband Receivers

This paper presents a method for predicting the angle-of-arrival (AOA) using ultrawideband time-difference-of-arrival technique, when the received signal is corrupted by antenna noise. To predict the accuracy of the AOA, the probability density function of the estimated AOA and the standard deviation (rms error) are derived. Numerical simulations and measurements for AOA, in thermal noise conditions, are carried out for three different SNRs. The rms error of the measured and simulated AOAs is then compared with the theoretical standard deviation. The measurements are done with two ridged-horn antennas placed on a turn-table and the received signals are recorded (50 times) at intervals of 1° between -20° and +20°. Accuracy of the proposed AOA estimation model is validated by simulations and measurements.