Study of Refraction Effects for Propagation over Terrain

This chapter investigates the radio-wave propagation above irregular ground, including the troposphere, using physical optics computation. We briefly describe used simplifications, which substantially reduce numerical simulations. Using the principle of stationary phase, we can approximate the propagation over a terrain (the PO approximation of the vector problem with a 3-D surface) with a 2-D surface. Moreover, we approximate the reflection coefficient for a surface with random deviations considering the surface standard deviation and the local Fresnel reflection coefficient for the smooth ground. We present the novel computations of physical optics for investigations of radar coverage diagrams. We consider both monostatic and bistatic radars, the far-field antenna measuring ranges, and studies of air refraction index. We validate the calculations by both experimental results and the other numerical simulations. The experimental results changed during seasons and according to terrain and troposphere conditions including vegetation, cultivation, snow, and air temperature and pressure

Statistics of Radio Refractivity Derived from Prague Radiosounding Data

Vertical gradient of radio refractivity in the lowest 100 m is derived from the meteorological radio-sounding data of the Prague-Libus station. The data cover the measurements at the terms 00, 06, 12, and 18UTC, and the extent of data is 20 years. Diurnal, monthly, and annual distributions are presented and the relative role of the dry and wet components of the refractivity gradient is discussed. The b0 values, expressing the percentage of the time with the refractivity gradient below -100 km-1, are presented. This work should enable the effective radio-relay link design with respect to the radiowave bending

Microwave Tomography System for Methodical Testing of Human Brain Stroke Detection Approaches

In this work, a prototype of a laboratory microwave imaging system suitable to methodically test the ability to image, detect, and classify human brain strokes using microwave technology is presented. It consists of an antenna array holder equipped with ten newly developed slot bowtie antennas, a 2.5 D reconfigurable and replaceable human head phantom, stroke phantoms, and related measuring technology and software. This prototype was designed to allow measurement of a complete S-matrix of the antenna array. The reconfigurable and replaceable phantom has currently 23 different predefined positions for stroke phantom placement. This setting allows repeated measurements for the stroke phantoms of different types, sizes/shapes, and at different positions. It is therefore suitable for large-scale measurements with high variability of measured data for stroke detection and classification based on machine learning methods. In order to verify the functionality of the measuring system, S-parameters were measured for a hemorrhagic phantom sequentially placed on 23 different positions and distributions of dielectric parameters were reconstructed using the Gauss-Newton iterative reconstruction algorithm. The results correlate well with the actual position of the stroke phantom and its type

Assessment of the thermal tissue models for the head and neck hyperthermia treatment planning

Purpose: To compare different thermal tissue models for head and neck hyperthermia treatment planning, and to assess the results using predicted and measured applied power data from clinical treatments. Methods: Three commonly used temperature models from literature were analysed: “constant baseline”, “constant thermal stress” and “temperature dependent”. Power and phase data of 93 treatments of 20 head and neck patients treated with the HYPERcollar3D applicator were used. The impact on predicted median temperature T50 inside the target region was analysed with maximum allowed temperature of 44 °C in healthy tissue. The robustness of predicted T50 for the three models against the influence of blood perfusion, thermal conductivity and the assumed hotspot temperature level was analysed. Results: We found an average predicted T50 of 41.0 ± 1.3 °C (constant baseline model), 39.9 ± 1.1 °C (constant thermal stress model) and 41.7 ± 1.1 °C (temperature dependent model). The constant thermal stress model resulted in the best agreement between the predicted power (P = 132.7 ± 45.9 W) and the average power measured during the hyperthermia treatments (P = 129.1 ± 83.0 W). Conclusion: The temperature dependent model predicts an unrealistically high T50. The power values for the constant thermal stress model, after scaling simulated maximum temperatures to 44 °C, matched best to the average measured powers. We consider this model to be the most appropriate for temperature predictions using the HYPERcollar3D applicator, however further studies are necessary for developing of robust temperature model for tissues during heat stress.</p

From Internationalization to Development: Czechoslovak Economic and Scientific-Technical Cooperation in the Gottwald and Novotný eras (1948-1968)

During the period of communist supremacy, Czechoslovakia teetered between two geopolitical blocs. On the one hand, it was an official constituent of the socialist wing with far-reaching responsibilities to the other member states of the Council for Mutual Economic Assistance, but on the other, Czechoslovakia’s economy was traditionally pro-Western, and even the political drawing of the Iron Curtain could not completely deconstruct the deep-rooted ties with its Western neighbors. This thesis examines how senior officials of the Czechoslovak Communist Party (Klement Gottwald, Antonín Zápotocký, Antonín Novotný, Viliam Široký, Ota Šik, etc.) as well as individual rank-and-file workers and the scientific-technical intelligentsia dealt with Czechoslovakia's delicate position on the border of two geopolitical blocs. Specific attention is paid to the factors that guided Czechoslovak foreign economic policy, as well as to the question of how the individual actors, forms, platforms, and projects of Czechoslovak intra- and inter-bloc cooperation demonstrate the precariousness of the Czechoslovak position on the international stage. In pursuit of these goals, documents from the Czechoslovak Communist Party and Czechoslovak industrial ministries stored in the Prague archives are consulted and supplemented by the records of international organizations such as the UN Economic Commission for Europe and GATT. These often recently disclosed archival materials have proved capable of opening new doors to grasp the history of the Cold War in a revolutionary way and to expand its hitherto rather one-sidedly antagonistic and conflictual characterization with a new dimension of constructive cooperation

Optimizing Bias Point Of High Efficiency Class-B Gan Power Amplifier For The Best Efficiency

High performance amplifiers are always a demanding component in the world of wireless communication. The amplifier is the heart that drives each radio system. We have designed and developed a high performance one-stage class-B GaN power amplifier for drone applications in the S-band (at 1,6 GHz) with maximum output power 6 W. This paper compare fixed settings of the bias point option and optimized bias point for the best efficiency within the entire output power range. Applying the proposed method, that is particularly advantageous for low power performance to improve efficiency by more than 15 %

Long-Term Propagation Statistics and Availability Performance Assessment for Simulated Terrestrial Hybrid FSO/RF System

Long-term monthly and annual statistics of the attenuation of electromagnetic waves that have been obtained from 6 years of measurements on a free space optical path, 853 meters long, with a wavelength of 850&#8201;nm and on a precisely parallel radio path with a frequency of 58&#8201;GHz are presented. All the attenuation events observed are systematically classified according to the hydrometeor type causing the particular event. Monthly and yearly propagation statistics on the free space optical path and radio path are obtained. The influence of individual hydrometeors on attenuation is analysed. The obtained propagation statistics are compared to the calculated statistics using ITU-R models. The calculated attenuation statistics both at 850&#8201;nm and 58&#8201;GHz underestimate the measured statistics for higher attenuation levels. The availability performance of a simulated hybrid FSO/RF system is analysed based on the measured data.</p