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We propose a lightweight radar that autonomously measures snow depth over sea ice from an unmanned aerial vehicle (UAV). Development of this snow radar and its integration with an octocopter UAV is presented. Field trials of the UAV-mounted snow radar, conducted in Antarctica during the summer season of 2017/2018, are also described. The radar allows measurements of snow depths on sea ice between 10 and 100 cm. Additional reflections due to internal layers within the snow are evident at a few measurement points. The snow radar is evaluated for various flight parameters: stationary; flying at speeds between 1 and 3 m/s, and at heights from 5 to 15 m. Evaluation of snow-depth results indicates that a depth accuracy of ±3.2 cm is achieved with stationary measurements, and of ±9.1 cm with measurements at the various flight speeds. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results of using a non-invasive time domain reflectometry (TDR) sensor to image and parameterize the moisture content of basecourse materials used in road construction. Imaging, resulting from the amplitude losses of a pulsed signal travelling down TDR transmission lines, is found to produce excellent information on the relative changes in basecourse moisture content to a spatial resolution <5 mm in the plane of the road surface. A simple model relating the volumetric moisture content to the TDR measured propagation time is shown to provide a consistent transform between the two. The experimental data also indicate that the smallest transform error of $\sim 0.25$ % in volumetric moisture content is achieved when model coefficients are separately fitted for each of the two basecourse aggregate types tested. [ABSTRACT FROM PUBLISHER]

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 object’s 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. [ABSTRACT FROM AUTHOR]

A circularly polarized antenna array design comprising of a feed network that splits an input signal into four orthogonal (0^\circ, 90^\circ, 180^\circ, and 270^\circ) phased signals with equal magnitudes and connected to four anti-podal Vivaldi antennas sequentially rotated by 90^\circ 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. [ABSTRACT FROM PUBLISHER]

In this paper, a method to estimate the characteristics of ultra-wideband (UWB) pulse scattered from metal planar objects in far-field is proposed. When the object is in near-field, the transition of the scattered pulse shape is studied. In addition, we define a frequency averaged radar cross section (RCS) of the metal planar object in terms of the effective height of the transmitting and receiving antennas, and the energy of the excitation and received pulses. We find excellent agreement between the estimated and measured scattered pulses for metal planar objects of sizes 100\times 100\ \ mm^2, 160\times 160\ \ mm^2, and 200\times 200\ \ mm^2. For the same objects, the estimated frequency averaged RCS are close to narrowband conventional RCS. The agreement validates the proposed method, allowing us to compute the scattered pulse shape and energy based on the conventional RCS of the object. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a method for modeling the transient radiated and received pulses of ultra-wideband (UWB) planar aperture antennas. The proposed method is able to analytically model the angle-dependent pulse distortion of the antennas. The method relates the input pulse of an antenna to its transient radiated fields, and the incident transient fields to its output pulse. This method needs to estimate the antenna's aperture field distribution from time-domain antenna measurements. Using the proposed method, the received pulses from three different antennas—a ridged-horn, a dielectric loaded horn, and a Vivaldi antenna—are modeled and compared with the measured received pulses. A comparison of pulse shape, amplitude, and energy shows very good agreement. Different input pulses are also examined for the experimental evaluation of the proposed method. The method allows designers to analytically estimate the antenna effect on transmitted pulse enabling the inclusion of pulse distortion by the antenna into the ultra-wideband transceiver design. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

We propose a design for the specific class of transverse 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\times 26.8\times 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 array's sense of polarization, axial ratio, gain and phase difference between orthogonal signals. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]