Sergey Kharkovsky

Measurement and monitoring of microwave reflection and transmission properties of cement-based specimens

The results of measurement and monitoring of reflection and transmission properties of cement-based specimens (blocks of mortar, concrete) during long time of their service lives, including hydration process, and different curing conditions at microwave frequencies (X-band) are presented. A simple and inexpensive measurement system that utilizes the nondestructive and contactless free space method is used. Dependencies of the reflection and transmission coefficients on water-to-cement ratio, preparing and curing conditions of the specimens are demonstrated. It is shown that the reflection coefficient is approximately stable after hydration process while the transmission coefficient changes during long time of the specimens service life. The complex dielectric permittivity of the cement-based materials is calculated by a new method using only the amplitudes of the reflection and transmission coefficients. The expected applications of the results are discussed.

Compact and Small Planar Monopole Antenna With Symmetrical L- and U-Shaped Slots for WLAN/WiMAX Applications

A small and compact triple-band microstrip-fed printed monopole antenna for Wireless Local Area Network (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX) is presented. The proposed antenna consists of a rectangular radiating patch with L- and U-shaped slots and ground plane. A parametric study on the lengths of the U- and L-shaped slots of the proposed antenna is provided to obtain the required operational frequency bands-namely, WLAN (2.4/5.2/5.8 GHz) and WiMAX (2.5/3.5/5.5 GHz). The proposed antenna is small (15 × 15 × 1.6 mm 3) when compared to previously well-known double- and triple-band monopole antennas. The simulation and measurement results show that the designed antenna is capable of operating over the 2.25-2.85, 3.4-4.15, and 4.45-8 GHz frequency bands while rejecting frequency ranges between these three bands. Omnidirectional radiation pattern and acceptable antenna gain are achieved over the operating bands.

Portable Real-Time Microwave Camera at 24 GHz

This paper presents a microwave camera built upon a two-dimensional array of switchable slot antennas. The camera borrows from modulated scattering techniques to improve isolation among the array elements. The camera was designed to measure vector electric field distribution, be compact, portable, battery operated, possess high dynamic range, and be capable of producing real-time images at video frame-rate. This imaging system utilizes PIN diode-loaded resonant elliptical slot antennas as its array elements integrated in a simple and relatively low-loss waveguide network thus reducing the complexity, cost and size of the array. The sensitivity and dynamic range of this system is improved by utilizing a custom-designed heterodyne receiver and matched filter for demodulation. The performance of the multiplexing scheme, noise-floor and dynamic range of the receivers are presented as well. Sources of errors such as mutual-coupling and array response dispersion are also investigated. Finally, utilizing this imaging system for various applications such as 2-D electric field mapping, and nondestructive testing is demonstrated.

Millimeter-wave detection of localized anomalies in the space shuttle external fuel tank insulating foam

The Space Shuttle Columbias catastrophic accident emphasizes the growing need for developing and applying effective, robust, and life-cycle-oriented nondestructive testing (NDT) methods for inspecting the shuttle external fuel tank spray on foam insulation (SOFI). Millimeter-wave NDT techniques were one of the methods chosen for evaluating their potential for inspecting these structures. Several panels with embedded anomalies (mainly voids) were produced and tested for this purpose. Near-field and far-field millimeter-wave NDT methods were used for producing images of the anomalies in these panels. This paper presents the results of an investigation for the purpose of detecting localized anomalies in several SOFI panels. To this end, continuous-wave reflectometers at single frequencies of 33.5, 70, or 100 GHz representing a relatively wide range of millimeter-wave spectrum [Ka-band (26.5-40 GHz) to W-band (75-110 GHz)] and utilizing different types of radiators were employed. The resulting raw images revealed a significant amount of information about the interior of these panels. However, using simple image processing techniques, the results were improved in particular as it relates to detecting the smaller anomalies. This paper presents the results of this investigation and a discussion of these results.

Depth Evaluation of Shallow Surface Cracks in Metals Using Rectangular Waveguides at Millimeter-Wave Frequencies

This paper presents a resonant technique, which is founded on previous extensive work on millimeter-wave surface crack detection and sizing, for the accurate depth evaluation of long and shallow surface damages (scratches or cracks), which are represented as rectangular slots, in metal plates. A crack in a metal plate may be considered a short-circuited rectangular waveguide, which presents certain resonant characteristics when its electrical depth coincides with a quarter of the operating wavelength. Furthermore, a shallow crack may be filled with a dielectric material to electromagnetically make it appear deeper and hence facilitate its depth evaluation. The resonant properties of a crack depend on the dielectric properties of the material filling the crack and the crack dimensions. It is shown that a slight amount of loss, which is associated with the dielectric material, causes a relatively significant and characteristic change in the reflection coefficient measured using a probing rectangular waveguide aperture. In particular, this change affects the magnitude of the reflection coefficient, which is an easier parameter to measure than the phase. This information, as a function of frequency, may then be used to determine the shallow crack depth. This paper presents the foundation of this technique at millimeter-wave frequencies, along with supporting electromagnetic simulations and experimental results.

Rapid Rotary Scanner and Portable Coherent Wideband Q-Band Transceiver for High-Resolution Millimeter-Wave Imaging Applications

Millimeter-wave imaging techniques, based on synthetic aperture focusing (SAF), have been successfully used for nondestructive testing (NDT) of various composite and aerospace structures. Most current imaging mechanisms utilize raster scanning platforms, whereby the imaging system is scanned in a rectangular grid over the structure-under-test (SUT). Most raster scanning platforms, although relatively simple in design and construction, are inherently slow. Furthermore, SAF techniques necessitates the use of vector-measuring instruments such as a vector network analyzer (VNA), which are typically: 1) bulky; 2) cannot be mounted on scanning platforms; 3) are not suitable for in-field use; and 4) expensive. These factors limit the effectiveness of these millimeter-wave imaging techniques in applications where frequent and rapid inspection of large structures is required. Hence, there is a great demand for rapid mechanical scanning systems combined with portable wideband transceivers in order to increase the utility of these imaging techniques, and provide a real solution to many practical NDT applications. To this end, a unique rotary scanner system, capable of scanning a relatively large area in a relatively short span of time, was designed and constructed. In addition, a custom-designed portable transceiver system operating in the frequency range of 35-45 GHz (Q-band) was developed and incorporated into the rotary scanner system for producing coherent (amplitude and phase) and accurate data suitable for synthetic aperture imaging and the 10-GHz bandwidth allows the generation of relatively high-resolution millimeter-wave holographical images. This paper presents the design of the rotary scanning system, the associated Q-band transceiver and the integration of the two systems via a custom-designed software. To illustrate the efficacy of the complete imaging system, SAF of several complex structures produced using the proposed system, are presented and discussed.

Modulated Elliptical Slot Antenna for Electric Field Mapping and Microwave Imaging

Microwave and millimeter wave imaging has shown significant potential in various applications. An imaging system commonly consists of a sensitive electric field mapping array devised to measure the spatial distribution of the scattered field from an object to be imaged. One of the most prominent methods used to realize a cost-effective real-time imaging system is the modulated scatterer technique (MST). Although the conventional MST, using small loaded dipole antennas, performs well at lower microwave frequencies, its utility at high microwave and millimeter wave frequencies is limited. To improve upon the conventional MST, a novel modulated elliptical slot antenna, loaded with a PIN diode, is introduced and analyzed in this paper. The modulation-depth (effectiveness in modulating the slot), current distribution around the slot, and the influence of PIN diode bias structure are discussed based on numerical simulation results and experiments. Finally, the efficacy of the proposed slot for electric field measurements at 24 GHz is demonstrated using a prototype slot.

A Compact High-Gain and Front-to-Back Ratio Elliptically Tapered Antipodal Vivaldi Antenna With Trapezoid-Shaped Dielectric Lens

A modified compact antipodal Vivaldi antenna is proposed with good performance for different applications including microwave and millimeter wave imaging. A step-by-step procedure is applied in this design including conventional antipodal Vivaldi antenna (AVA), AVA with a periodic slit edge, and AVA with a trapezoid-shaped dielectric lens to feature performances including wide bandwidth, small size, high gain, front-to-back ratio and directivity, modification on E-plane beam tilt, and small sidelobe levels. By adding periodic slit edge at the outer brim of the antenna radiators, lower-end limitation of the conventional AVA extended twice without changing the overall dimensions of the antenna. The optimized antenna is fabricated and tested, and the results show that S11 <; -10 dB frequency band is from 3.4 to 40 GHz, and it is in good agreement with simulation one. Gain of the antenna has been elevated by the periodic slit edge and the trapezoid dielectric lens at lower frequencies up to 8 dB and at higher frequencies up to 15 dB, respectively. The E-plane beam tilts and sidelobe levels are reduced by the lens.

Novel and Simple High-Frequency Single-Port Vector Network Analyzer

Portable, accurate, and relatively inexpensive high-frequency vector network analyzers (VNAs) have great utility for a wide range of applications, encompassing microwave circuit characterization, reflectometry, imaging, material characterization, and nondestructive testing to name a few. To meet the rising demand for VNAs possessing the aforementioned attributes, we present a novel and simple VNA design based on a standing-wave probing device and an electronically controllable phase shifter. The phase shifter is inserted between a device under test (DUT) and a standing-wave probing device. The complex reflection coefficient of the DUT is then obtained from multiple standing-wave voltage measurements taken for several different values of the phase shift. The proposed VNA design eliminates the need for expensive heterodyne detection schemes required for tuned-receiver-based VNA designs. Compared with previously developed VNAs that operate based on performing multiple power measurements, the proposed VNA utilizes a single power detector without the need for multiport hybrid couplers. In this paper, the efficacy of the proposed VNA is demonstrated via numerical simulations and experimental measurements. For this purpose, measurements of various DUTs obtained using an X-band (8.2-12.4 GHz) prototype VNA are presented and compared with results obtained using an Agilent HP8510C VNA. The results show that the proposed VNA provides highly accurate vector measurements with typical errors on the order of 0.02 and 1° for magnitude and phase, respectively.

30 GHz Linear High-Resolution and Rapid Millimeter Wave Imaging System for NDE

High-resolution millimeter-wave imaging for nondestructive testing applications offers certain unique and practical advantages. Traditionally, imaging for this purpose is performed by raster scanning a single probe/antenna across a two-dimensional (2D) grid. Raster scanning requires bulky, slow and expensive scanning platforms, in addition to being a slow process. Utilizing an array of probes significantly reduces these limitations. This paper presents the design of a linear one-dimensional millimeter wave imaging array operating at 30 GHz and capable of rapid image production. The imaging array is 150 mm long, operates in quasi-mono-static reflection mode, and provides coherent vector reflection coefficient data for generating high spatial resolution synthetic aperture radar images. This imaging array performs fast electronic scan along one dimension and may be readily moved along the other direction to produce 2D images, greatly reducing the required scan time compared to raster scanning. The design and utility of this imaging array along with several imaging examples are presented in this paper.