Ing. Václav Kabourek, Ph.D.

This paper presents a two-dimensional (2D) metasurface (MTS) antenna array composed of mushroom cells coupled by thin slots in the top metallization. The antenna is fed through power dividers designed in substrate-integrated waveguide (SIW) technology. The antenna structure is therefore designed in a fully up to date integrated version. The array shows beam steering in the azimuthal plane controlled by signal amplitudes fed into particular ports at the edges of the matrix. The main advantage of this antenna is no need to use phase shifters applied in standard 2D antenna arrays. Two antenna versions have been designed, fabricated, and experimentally tested. The beam can be steered within 360deg (90deg in azimuth. The steering of the beam in elevation from backward to forward directions within 40deg is done by changing frequency from 21 up to 23.8 GHz. This interval is reduced to 30deg by exciting the antenna simultaneously at two adjacent ports at the same amplitude.

This paper presents the application of a substrate integrated waveguide (SIW) for the design of a leaky wave antenna (LWA). The antenna radiates through a wide slot in the top wall of the SIW structure in the forward direction. The effective width of the slot is varied by changing capacitances of two arrays of varactors connected between slot edges and inserted conducting strips. The radiation pattern of the antenna is by this way controlled by DC bias, which sets the capacitances of varactors. The maximum radiation direction in elevation can be varied within 35degree by changing the DC bias from 2 to 12 V. This elevation angle is measured from the broad side direction perpendicular to the antenna substrate. The measured antenna characteristics are in accord with those predicted by simulation. The antenna can be simply fabricated by a PCB technology.

A design of a reconfigurable leaky wave antenna in the form of an 1D array of mushroom cells working at around frequency 3.25 GHz is presented. The reconfigurability is obtained by controlling capacitances of varactors connected between particular cells. The antenna array shows a control of the direction of the main lobe of the radiation pattern within a given span of elevation angles, which is achieved by setting the DC varactor bias. Both simulations and measurements verify the effectiveness of the presented antenna design. Simulations show the variation of the main lobe radiation pattern within approximately 45 degrees at 3.25 GHz when changing the applied DC voltage between 15 and 29 V. Unfortunately, the fabricated antenna specimen reaches a narrower span of elevation angles. The overall behavior is, however, similar as predicted by simulation. The designed antenna has a simple structure that can be cheaply fabricated by PCB process.

In this paper, design of a prime-focus feed for a deep reflector, Earth–Moon–Earth space communication system is described. The feed is based on a circular waveguide equipped with two chokes in order to minimise sidelobes and illuminate the deep dish with a high aperture efficiency of 70% . Based on sun noise measurements, it is estimated that the antenna system presents very low noise temperature values, below 30 K, making this feed favourable for space communication.

A compact three-element shared-aperture waveguide antenna array for the 24–28 GHz microwave-frequency band is presented as a proof-of-concept of an array with steerable directional beam suitable for 5G telecommunication systems. The array is intended for use in a microwave photonic link and is sufficiently steerable only with the progressively phased excitation signals of equal magnitudes. The mutual interactions between the array elements are minimized to maintain the properties of the individual elements, even if they are embedded and closely spaced in the array. The proposed concept could be simply extended by adding more elements to further increase the directivity and enhance the steering properties of the array.

This article presents the design, simulations and measured results of a dual-band coaxial feed for satellite communication in the 2.4 and 10.45 GHz bands. The feed is designed for communication with the geostationary satellite. Es´hail 2 (scheduled to be lanched in late 2018), which will be equipped with a public amateur radio transponder covering nearly one-third of the Earth´s surface. A communication link can be established using a relatively low-power transmiller (Tx) employing conventional microwave technology. The proposed feed operates with linear polarization at the X-band and circular polarization at the S-band and has similar radiation patterns in both bands, providing high aperture efficiency for a broad range of reflector focal-to-diameter (f/D) ratios.

The design, performance and operation of the high resolution microwave spectrometer are described. The spectrometer is based on the Fabry-Perot resonator supplemented by a pulsed supersonic nozzle for adiabatic cooling of the sample. The spectrometer’s high sensitivity and resolution are demonstrated by several examples.

This paper brings a brief overview of the statistical method called Principal Component Analysis (PCA). It is used for clutter reduction in detection of hidden objects, targets hidden behind walls, buried landmines, etc. Since the measured data, imaged in time domain, suffer from the hyperbolic character of objects' reflections, the utilization of the Synthetic Aperture Radar (SAR) method is briefly described. Besides, the basics of PCA as well as its calculation from the Singular Value Decomposition are presented. The principles of ground and clutter subtraction from image are then demonstrated using training data set and SAR processed measured data.

The paper discusses the emission spectroscopic measurement in the Fabry-Perot resonator. The presented results compare the spectra evaluated from the measured characteristics, obtained using various methods.

This article presents the methods of broadband axial feeding of a Fabry-Perot resonator. The resonator was originally designed with the radial excitation for the absorption measurement in the frequency band ranging from 18 to 80 GHz. If the frequency stays below ~26.4 GHz, the excitation of resonator is less satisfactory, since at the frequency in question, the value of Fresnel number of resonator drops to one. For the broadband measurement of gaseous samples' emission spectra, the excitations for frequencies lower than 26.4 GHz were analyzed using the capacitive coupling and two newly proposed couplings.

In this paper, the data processing based on polarimetric features extraction from Synthetic Aperture Radar (SAR) processed data is discussed. For this purpose, fully polarimetric data were collected using the ultra-wideband Ground Penetrating Radar (GPR) and quad ridged horn antenna. The measurement of plastic landmine, metallic pipe and rocks buried in the sand was carried out so that three dimensional data correction and visualization could be applied. Since the landmine is detected in the presence of a metallic target, a standard GPR processing does not lead to satisfactory results. Therefore, polarization and orientation features were obtained by means of the polarimetric decomposition in order to classify and detect various objects.

The paper describes the plastic mine detection by Ground Penetrating Radar. The received data evaluation and imaging are based on two- and three-dimensional Synthetic Aperture Radar (SAR) and Stolt Migration methods. The results of the processing that are subject to discussion were presented using the examples of measurement of antitank mine situated on the sand surface and anti-personal mine located both on and under the sand surface.