Dan Busuioc

Taper Design of Vivaldi and Co-Planar Tapered Slot Antenna (TSA) by Chebyshev Transformer

A new method for the flares opening rate for a single radiator tapered slot antenna (TSA) is presented. A stepped quarter-wave Chebyshev transformer is calculated to minimize the frequency domain reflection and maximize the power transfer gain. Then slot widths are computed to match the Chebychev design, and smooth curves are fit to the computed steps. Different smoothing functions are compared, including the conventional exponential function, as well as cubic spline and Gaussian. The validity of the method is verified through simulations and measurements of experimental designs for the 1 to 3 GHz frequency range. In this work the TSA is fabricated on one side of a single layer Duroid substrate with dielectric constant 6.15. Although the Chebyshev transformer is an old concept, the novelty of this method is applying the transformer to design the TSA slotline taper profile, leading to a closed design procedure rather than an optimization. Advantages of this novel method are the straightforward mathematics of the design and that a simple simulation program can be written in a short time.

Low-cost, fused millimeter-wave and 3D point cloud imaging for concealed threat detection

The growing need to detect non-metallic, concealed threats at venues ranging from airports to sports arenas has created a demand for low-cost, close-range whole-body imaging systems. The adaptation of low-cost wireless communication hardware for millimeter-wave imaging has made possible to design a system that satisfies this demand. The integration of 3D point cloud data has created a multi-modal, fused system that leverages both imaging technologies.

Millimeter-wave nondestructive evaluation of pavement conditions

The United States is suffering from an aging civil infrastructure crisis. Key to recovery are rapid inspection technologies like that being investigated by the VOTERS project (Versatile Onboard Traffic Embedded Roaming Sensors), which aims to outfit ordinary road vehicles with compact low-cost hardware that enables them to rapidly assess and report the condition of roadways and bridge decks free of driver interaction. A key piece of hardware, and the focus of this paper, is a 24 GHz millimeter-wave radar system that measures the reflectivity of pavement surfaces. To account for the variability of real-world driving, such as changes in height, angle, speed, and temperature, a sensor fusion approach is used that corrects MWR measurements based on data from four additional sensors. The corrected MWR measurements are expected to be useful for various characterization applications, including: material type; deterioration such as cracks and potholes; and surface coverage conditions such as dry, wet, oil, water, and ice. Success at each of these applications is an important step towards achieving the VOTERS objective, however, this paper focuses on surface coverage, as whatever covers the driving surface will be most apparent to the MWR sensor and if not accounted for could significantly limit the accuracy of other applications. Contributions of the paper include findings from static lab tests, which validate the approach and show the effects of height and angle. Further contributions come from lab and in-field dynamic tests, which show the effects of speed and demonstrate that the MWR approach is accurate under city driving conditions.

Errata to “Taper Design of Vivaldi and Co-Planar Tapered Slot Antenna (TSA) by Chebyshev Transformer” [May 12 2252-2259]

In the above titled paper (ibid., vol. 60, no. 5, pp. 2252-2259, May 2012), a subscript in Eq. (8) appeared incorrectly. The correct form is presented here. The IEEE regrets the error.

Compact programmable ground-penetrating radar system for roadway and bridge deck characterization

A compact, high-performance, programmable Ground Penetrating Radar (GPR) system is described based on an impulse generator transmitter, a full waveform sampling single shot receiver, and high directivity antennas. The digital programmable pulse generator is developed for the transmitter circuit and both the pulse width and pulse shape are tunable to adjust for different modes of operation. It utilizes a step-recovery diode (SRD) and short-circuited microstrip lines to produce sub-nanosecond wide ultra-wideband (UWB) pulses. Sharp step signals are generated by periodic clock signals that are connected to the SRDs input node. Up to four variable width pulses (0.8, 1.0, 1.5, and 2.1 ns) are generated through a number of PIN switches controlling the selection of different microstrip lengths. A schottky diode is used as a rectifier at the output of the SRD in order to pass only the positive part of the Gaussian pulses while another group of short-circuit microstrips are used to generate amplitude-reversed Gaussian pulses. The addition of the two pulses results in a Gaussian monocycle pulse which is more energy efficient for emission. The pulse generator is connected to a number of UWB antennas. Primarily, a UWB Vivaldi antenna (500 MHz to 5 GHz) is used, but a number of other high-performance GPR-oriented antennas are investigated as well. All have linear phase characteristic, constant phase center, constant polarization and flat gain. A number of methods including resistive loading are used to decrease any resonances due to the antenna structure and unwanted reflections from the ground. The antennas exhibit good gain characteristics in the design bandwidth.