P. Horak

Czech Technical University in Prague, Praha, Praha, Czech Republic

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Publications (9)8.66 Total impact

  • Petr Horak, Pavel Pechac
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    ABSTRACT: Results of experiments focusing on high-elevation links with a ground terminal shadowed by a single tree are introduced. The measurement trials were carried out at 2.0, 3.5, 5.0 and 6.5 GHz utilizing a remote-controlled airship as a pseudo-satellite for four different deciduous trees in summer and winter when trees are in full leaf and defoliated. The complete range of elevation angles typical of satellite/HAP services was addressed. Empirical models were proposed to account for excess loss as a function of its geometry. The applicability of terrestrial vegetation attenuation models on the given scenario is discussed.
    IEEE Transactions on Antennas and Propagation 07/2012; 60(7):3541-3545. · 2.33 Impact Factor
  • P. Horak, P. Pechac
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    ABSTRACT: This paper presents the results of a series of measurements to investigate the vegetation shadowing loss of high elevation links at L, S and C frequency bands. The results are analyzed and presented with respect to a frequency dependence of the vegetation shadowing loss and are based on experimental investigation performed during two different seasons, for three measurement scenarios and in a total of twelve different measurement locations.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
  • P. Horak, P. Pechac
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    ABSTRACT: In this paper we report the results of a series of measurements to investigate the influence of vegetation on satellite communications in the L, S and C bands during the winter months. These measurements were performed by a 9m- long remote-controlled airship used as a pseudo-satellite to carry a narrowband transmitter while the receiver station was located on the ground at four different locations inside small groves in order to involve different types of vegetation. Flyovers were performed to obtain data for the widest range of elevation and azimuth angles. The measurements presented, performed during March 2010, are an extension to the results of the measurement campaign carried out in Stromovka Park in the city of Prague during June 2009. A short comparison with data acquired during the summer is also presented. I. INTRODUCTION
    01/2011;
  • Petr Horak, Pavel Pechac
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    ABSTRACT: Results of measurement trials at 2.0, 3.5, 5.0 and 6.5 GHz focused on high elevation links with a ground terminal inside a forested area are presented. Previous measurements during summer vegetation shadowing in full leaf were significantly expanded upon in new locations and, in addition, by conducting trials during winter. New empirical linear models were derived for both summer and winter at a broad frequency range taking into consideration elevation angles between 25 to 90 degrees. The models can be used to estimate average, minimum and maximum values of the additional vegetation attenuation in moderate climate wood- lands.
    IEEE Transactions on Antennas and Propagation 01/2011; 59(12):4865-4867. · 2.33 Impact Factor
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    ABSTRACT: Different methods of defining building penetration loss for high elevation angle paths exist. A key factor is the selection of the reference level. A comparison of four of the most common types of reference levels used to determine building penetration loss for high elevation angles is presented based on a measurement trial using unmodulated carriers at 2.0 GHz and 5.0 GHz performed at a three-storey office building. It was shown that the choice of reference level significantly affects the results obtained. Particular cases are discussed and general recommendations on the selection of the reference level for building penetration loss measurement are provided.
    IEEE Transactions on Antennas and Propagation 01/2011; · 2.33 Impact Factor
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    ABSTRACT: The aim of this paper is to describe tree attenuation measurements at 2 GHz in four different locations inside vegetation, and at three different positions for a single tree shadowing. The purpose of this measurement campaign was to use a 9-meter long remote-controlled airship as a pseudo-satellite. The transmitting station was located on the airship as a payload and receiving station inside or nearby the vegetation. Subsequently, the received signal strength was measured at each position as a function of elevation angles ranging from 25 to 90 degrees. Measurements taken in an open field were used as a reference. The measured data are still being processed, however, the initial results are shown. The results for locations inside the vegetation and the single tree are compared as well.
    Antennas and Propagation (EuCAP), 2010 Proceedings of the Fourth European Conference on; 05/2010
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    ABSTRACT: This paper presents preliminary results obtained from an extensive measurement campaign aimed at building penetration loss. We have concentrated on three different factors affecting this loss — the elevation, the frequency and the floor number of the investigated building. Results for two different measurement sites at 2.0 GHz and 5.0 GHz inside an old brick three-storey office building located in Prague are provided together with a brief description of the measurement system used during the measurement campaign.
    Antennas and Propagation (EuCAP), 2010 Proceedings of the Fourth European Conference on; 05/2010
  • P. Horak, M. Kvicera, P. Pechac
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    ABSTRACT: This letter presents the results of vegetation loss measurements at 2.0, 3.5, 5.0, and 6.5 GHz for elevation angles ranging from 20?? to 90??. The excess attenuation due to vegetation was measured at four different wooded locations using a remote-controlled airship as a pseudo-satellite. Measurements taken in an open field were used as a reference. The results are given as additional attenuation averaged over the whole range of azimuth and elevation angles for circular polarization. Average results from all four locations vary from 9 dB at 2.0 GHz to 14.5 dB at 6.5 GHz. Linear frequency dependence of vegetation attenuation was observed, and a corresponding empirical model providing the additional vegetation loss as a function of the frequency was derived in closed form. The results are then compared to the literature.
    IEEE Antennas and Wireless Propagation Letters 02/2010; · 1.67 Impact Factor
  • P. Horak, P. Pechac
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    ABSTRACT: The paper provides a study on possibilities of signal coverage for wireless systems provided from high altitude platforms (HAPs). Coverage by a single antenna forming a cell on the ground beneath the platform is considered. The presented study helps to understand that the coverage is not given just by geometry, i.e. the optical visibility to the platform is not sufficient. The key limiting factor is also the power budget requirements and the antenna. The platform altitude from 0 to 100 km is analyzed.
    Antennas and Propagation, 2009. EuCAP 2009. 3rd European Conference on; 04/2009