Vladimir Schejbal

Radar technology in the Czech Republic

A contemporary status of radar technology in the Czech Republic is reviewed in this paper. We may find activity in many different directions in this field now. Those are: new primary radar development both for military and civil application, primary and secondary radar upgrades, new passive radar development for civil application, ELINT and ESM equipment, intruding alarm radar sensors for commercial application/high mass production, radar warning and seeking receivers and military targets RCS minimization.

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.

Microwave imaging using indirect holographic techniques

This work describes how indirect holographic techniques, previously applied to the determination of antenna radiation patterns, can be adapted for the imaging of passive objects. It provides details of how complex scattered field values can be obtained in a simple and inexpensive manner from sampled scalar intensity measurements taken over a single scanning aperture. This work provides a brief outline of the basic theory of indirect microwave holography, and how the transformation of the holographic intensity pattern into the Fourier domain enables the isolation of the terms required for complex field reconstruction to be isolated from the remaining terms. The work is supported by a range of experimental results, illustrating the reconstructed complex fields for a number of simple test objects. Back-propagation techniques have also been included to reconstruct complex fields at the position of the scattering objects.

A Method of Cross-Polarization Reduction

A method for the reduction of cross-polarized radiation is described. The method can be used for various antenna array systems made up of radiating elements with higher cross-polarized radiation. This solution enables numerous possibilities for selecting the position, the spacing, and the excitation coefficient of any array element. It is even possible to use two different linearly polarized arrays that use the same or different polarizations. Two examples are given: a quarter-wave microstrip antenna system operating in two frequency bands, and a suspended patch array

Czech radar technology

Recently Czech radars have been known almost only within the previous Eastern Bloc. Tesla Pardubice, a European manufacturer of radars with more than 1200 various radars manufactured and delivered, has achieved the leading role among other radar manufacturers in Central and Eastern Europe. Radar production has been based on the companys own research and development of systems and technologies. A brief history of Czech radars is presented. The most important parts of radar systems are dealt with. Several typical Tesla radar system are described. Descriptions are completed with numerous figures and tables. >

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.

Directivity of planar antennas

Starting with a common formula for directivity, given beamwidths, the author gives the modifications needed to improve the accuracy when the distribution is known. Also included is a nomograph that shows the parameters of the Taylor single-parameter distribution, and allows trade studies versus the sidelobe level.

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.

Mathematical elimination of unwanted signal decrease due to satellite spatial motion

The satellite signal drop can be caused either by atmospheric attenuation (rain, clouds, snow, ...) either by unwanted satellite motion. This contribution demonstrates the software methods to extract the atmospheric attenuation from signal level record influenced by space satellite motion. Contribution is devoted to the construction of so called template (signal course in the case there is no atmospheric attenuation) using clear day signal, Fourier transform and cosine or polynomial approximation.

Antenna Beamwidth Control [Antenna Designer's Notebook]

Some methods for controlling antenna beamwidth are briefly proposed for aperture widths approximately equal to one wavelength. They can be used as primary feeds to create fan beams for radar antennas. The mouth modifications can improve the radiation patterns and the matching of the input impedance. This allows narrowing the radiation pattern, and therefore increasing the gain. On the other hand, similar modifications are advantageous for dual orthogonal polarization or octave-frequency-bandwidth operations of aperture antennas, such as horns. The proposed modifications have been performed for a hoghorn antenna. The measurements of the conventional and modified hoghorn designs are compared in detail.