Dusan Cermak

Synthesized-reference-wave holography for determining antenna radiation characteristics

Synthesized-reference-wave holographic techniques offer relatively simple and cost-effective measurement of antenna radiation characteristics and reconstruction of complex aperture fields using near-field intensity (power) pattern measurement. The near field is over-sampled. The phase is obtained indirectly, using the reference signal shifted linearly with the position of the probe. These methods allow utilization of advantages for probe compensation for near-field amplitude and phase measurements for planar and cylindrical scanning, including accuracy analyses. Descriptions are given of holographic near- field measurements using probe compensation for planar and cylindrical scanning, and numerical simulations. A comparison of holographic near-field and far-field measurements with and without probe compensation is presented.

Accuracy Analyses of Synthesized-Reference-Wave Holography for Determining Antenna Radiation Characteristics

Synthesized-reference-Wave holographic techniques offer relatively simple and cost-effective measurements of antenna radiation characteristics, and reconstruction of complex aperture fields using near-field intensity-pattern measurements. These methods allow utilization of the advantages of the methods for probe compensation for near-field amplitude and phase measurements for planar and cylindrical scanning, including accuracy analyses. Accuracy analyses using mathematical models considering random processes with correlation intervals are presented. Numerical simulations, taking into account random as well as deterministic errors and the processing of measurement statistics, are also presented. It is demonstrated that the given analyses correspond to our measurements and/or numerical simulations.

UWB through-wall propagation measurements

The propagation of ultra-wideband (UWB) signals is analyzed. The UWB radar output signals are formed both with transmitter and antenna. Moreover, they can be substantially affected due to electromagnetic wave propagation through walls. Experimental results and numerical simulations are analyzed and compared. The given examples show that the numerical simulations, which are very fast, could be reliable, when suitable wall parameters are used.

Multipath Propagation Effects of UWB Radars

The propagation of ultra wide band (UWB) signals is analyzed. The UWB radar output signals are formed both with transmitter and antenna. Moreover, they can be substantially affected due to electromagnetic wave propagation through walls and multipath effects. Multipath effects are analyzed and simulated numerically for various cases with several heights and distances.

Through-Wall Propagation Measurements

The propagation of signals for ultra wide band (UWB) systems is analyzed. Signals can be substantially affected due to electromagnetic wave propagation through walls or similar obstacles. New experimental results and numerical simulations for frequency band from 4 to 8 GHz are analyzed and compared. That is briefly compared with the time domain experiments, which have been performed using very short pulses. Experiments performed for frequency and time domains demonstrated that the numerical simulations, which are very fast, could be reliable, when suitable wall parameters are used. Some questions concerning electromagnetic compatibility (EMC) are briefly mentioned.

Numerical simulation of uwb radar propagation effects

The ultra-wideband (UWB) radar propagation through walls is analyzed. For UWB propagation studies, it is necessary to consider not only propagation at a single frequency but in the whole band. The UWB radar output signal is formed by both transmitter and antenna. The effects of antenna receiving and transmitting responses for various antenna types (such as small and aperture antennas) and ultra-wideband (UWB) radar propagation through walls are simulated in the frequency as well as time domain.

Study of electromagnetic scattering by rain drops

Communication performance demands ask for higher frequency bands, which are affected by precipitation. Particular attention should be devoted to the size of the particles, which are called hydrometeors such as rain (water drops), hail and snow [I]. This paper analyses the electromagnetic scattering by rain drops because train is the most important precipitation in our climatic conditions Rain consists of rain drops of various diameters from 0.01 to 0.7 cm and of various frequency (drop size distribution-DSD). The next problem is due to fact that water drops are created by material, which can be considered as lossy dielectric (exact series for scattering have been published as well [2], [3] and [4]). Therefore, both the reflected and transmitted wave should be analysed. That means that two various mechanisms creating the energetic losses of propagating electromagnetic wave exist. A part of energy is absorbed by water drops and the other part is scattered by water drops at various (also unwanted) directions. That creates several problems.

Diffraction over an earth — Comparison of methods

Diffraction over an earth is evaluated using several methods. An enhanced analysis of propagation over irregular terrain, which offers more reliable numerical simulations for low altitude propagation and diffraction field zone without any auxiliary procedures using physical optics approximation of vector problem, is used for comparison with Focks series and ITU.

Through-wall propagation measurements

The propagation of signals for ultra wide band (UWB) systems is analyzed. Signals can be substantially affected due to electromagnetic wave propagation through walls or similar obstacles. New experimental results and numerical simulations for frequency band from 4 to 8 GHz are analyzed and compared. That is briefly compared with the time domain experiments, which have been performed using very short pulses. Experiments performed for frequency and time domains demonstrated that the numerical simulations, which are very fast, could be reliable, when suitable wall parameters are used. Some questions concerning electromagnetic compatibility (EMC) are briefly mentioned.