REFLECTION SPECTROSCOPY OF PHOTONIC CRYSTAL HETEROSTRUCTURES BASED ON OPALS

Method of synthesis photonic crystal heterostructures based on polystyrene films with opal structure has been described in this work. Influence of structure parameters of single layers on reflectance spectra has been determined. Effect of boundary between layers on appearing allowed states in photonic band gap has been discovered in like structures

Ultra-wideband tapered-slot antenna with non-uniform resistive loading

Several designs of tapered-slot antennas for ultra-wideband applications such as ground penetrating radar are described. The antennas for subsurface imaging must be damped to decrease clutter arising from the ringing of the antenna. The ringing is caused by the internal or open-end reflections as well as multiple reflections between the antenna and ground surface. In the proposed design, the ringing has been partially suppressed by corrugations and/or resistive films applied on the antenna flares in different ways. Performance of the antennas has been estimated using the electromagnetic simulation software. It was found that resistive loading of the antenna flares results in decrease of the return loss and increase of the directivity at low frequencies that diminishes the clutter. This is demonstrated also in the simulations by the impulse waveform received by a small probe placed in the antenna near field

UWB antenna array development for GPR applications

Theoretical and experimental studies of the influence of mutual arrangement of wideband tapered slot antennas (TSA) in the array are presented. Major attention is paid to reducing antenna coupling. The modeling was done using a transient solver realized in the CST Microwave Studio software. It was found that a parallel displacement of the antennas in the array when the distance between antenna planes is kept, allows to suppress unwanted lateral coupling that leads in turn to reduction of clutter. The antenna array consisting of the TSA had been fabricated and tested in a test site for the detection of low-contrasted objects like anti-personnel mine

Development of the radiating part of an ultra-wideband tapered-slot antenna for GPR applications

This article presents some techniques of improving characteristics of planar ultra-wideband antennas based on the tapered slot line. Different antenna openings based on the elliptical taper with additional metal flares, smooth and corrugated bent blades had been studied. Several planar antennas with dimensions of 23 to 12 centimeters have been simulated using electromagnetic simulation software, and then designed, fabricated and tested. Results of computer simulations and measurements of the ultra-wideband antenna characteristics are presented

UWB antenna design concept for near field applications

Antennas and antenna systems are the most important components of the ground penetrating radar. That is why a lot of work had been done in the field of antenna modelling and design. One of the major points about the antenna working in the vicinity of the ground is to ensure stability of the antenna characteristics to the influence of nearby objects and ground surface.This work is devoted to the comparison of performance of different GPR antennas such as TEM horn, dielectric rod antenna fed by TEM horn and tapered-slot antennas operating as part of step-frequency ground penetrating radar. Presented antennas have been developed and manufactured by the authors in the framework of different international projects. In this work, the data have been obtained using both simulations by the CST Microwave Studio software and experimental studies.The advantages and disadvantages of each type of antenna when operating in the near field area for detection of both shallowly buried and deeper targets are described

Time-domain terahertz imaging of layered dielectric structures with interferometry-enhanced sensitivity

Abstract This article presents a time-domain imaging technique for layered dielectric slabs using a solid-state wavelet generator with subterahertz carrier frequency. The technique utilizes the dual nature of a wavelet, i.e., both the applicability of time-of-flight measurements and the ability of wavelets to interfere in thin dielectric layers at a carrier frequency that is preserved in spite of the ultrawideband character of the signal. This results in a very high sensitivity of the time delay of the resultant pulse to variations in the effective thickness (thickness × refractive index) of the dielectric layer. It is shown using a plane-wave analysis of the pulse propagation that under certain conditions, this sensitivity enhancement can reach an order of magnitude. The experimental setup for the reflection-mode operation is described and its performance in the discrimination of healthy and malignant tissues and in the detection of corrosion under paint is demonstrated