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Measurements of Surface Waves Radiated by a Vertically Polarized Antenna Over Planar Seawater at 5 Mhz

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Measurements of Surface Waves Radiated by a Vertically Polarized Antenna Over Planar Seawater at 5 Mhz Measurements of surface waves radiated by a vertically polarized antenna over planar seawater at 5 MHz. comparison to planar Earth models Mathilde Bellec, Sébastien Palud, Pierre Yves Jezequel, Stéphane Avrillon, Franck Colombel, Philippe Pouliguen To cite this version: Mathilde Bellec, Sébastien Palud, Pierre Yves Jezequel, Stéphane Avrillon, Franck Colombel, et al.. Measurements of surface waves radiated by a vertically polarized antenna over planar seawater at 5 MHz. comparison to planar Earth models. Radar Conference, 2014 IEEE, May 2014, Cincinnati, United States. pp.245 - 250, 10.1109/RADAR.2014.6875592. hal-01114363 HAL Id: hal-01114363 https://hal.archives-ouvertes.fr/hal-01114363 Submitted on 9 Feb 2015 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Measurements of Surface Waves radiated by a Vertically Polarized Antenna Over Planar Seawater at 5 MHz. Comparison to Planar Earth Models. M. Bellec, S. Palud, P.Y. Jezequel, S. Avrillon, F. Colombel , Ph. Pouliguen Abstract — High Frequency propagation over the surface of Introduced at the beginning of the last century, surface-wave the Earth or sea is a relevant subject today, especially for High- propagation has been largely investigated starting by Frequency Surface Wave Radars (HFSWR) over the horizon. In Sommerfeld [1] and followed by Norton [4] [5] and King [6] this paper, we present measurements of Electric field [7][8]. These pioneer researchers provided mainly theoretical propagating over sea water in HF Band compared to K.A. studies and analytical solutions to this problem. Sommerfeld Norton, R.W.P. King and G. Millington’s theories, thanks to a reliable measurement setup. The transmitter antennas are started by calculating the EM field radiated by an infinitesimal located on the coast while the receiver antenna is installed on a vertical electric dipole located on the surface of the planar boat which sails at constant azimuth. The Electric field Earth. Then, Norton introduced the attenuation function, the measurements are carried out with a shielded loop antenna and ground effect, and the frequency dependence of the surface we measured the field strength attenuation versus distance wave radiated by a vertical dipole. Based on Maxwell’s between the transmitter and the boat along a sea water path. In equations, R.W.P. King established the EM field expression order to take into account the media change (the coast and the generated by a vertical electric dipole placed on or in the sea water), Millington’s solution has been added to King’s and vicinity of the surface of a planar Earth and described the Norton’s theories with the planar Earth model. At 5 MHz over surface-wave propagation behavior. King also introduced the sea water, the environment of propagation is an attractive feature for the trans-horizon radar application. Indeed, the characteristic distances to explain the attenuation factor attenuation along the path in the planar model is similar to the variation along the path. To introduce the environmental attenuation in free space but over the horizon. The measurements constraints, Millington developed an analytical method which performed at 5 MHz and the calculations are in a good takes into account the ground characteristics changes along the agreement. path [9]. All these studies are mainly theoretical and the measurements are unusual. Keywords— HF band measurements, surface-wave propagation, ground-wave field, vertical electric dipole, planar This paper presents the measurements of the surface waves Earth model. over the sea at 5 MHz and gives the comparison between the I. INTRODUCTION experimental studies and the theoretical models provided in the literature, especially in order to validate the surface wave The surface waves propagation phenomenon presents decrease as 1/d all along the planar seawater path. attractive and useful features for industrial applications In this paper, we first present the surface-wave propagation because the surface waves propagate along the surface of the theories proposed by Norton, King and Millington where the Earth and beyond the radio-electric horizon. Thanks to these radiating element is a vertically polarized antenna located properties, the surface waves allow communication in hard above the ground. In the second part, we present environments (forest…) or target detection at very low measurements performed over the sea. Firstly, the elevation and at large distances. Furthermore, the temporal measurement process is carefully described including the stability of the surface wave propagation is an attractive design of the electrically small antenna used to radiate the feature in a defense or civil context. Few examples already surface waves. Secondly, we provide a comparison between exist mainly operating in VLF, LF and in the HF band [1] [2]. the measurements and the theoretical results. II. PROPAGATION THEORIES This work was supported in part by TDF and the “Direction Générale de l’Armement”. M. Bellec, S. Avrillon and F. Colombel are with the institute of Electronics This section describes theoretical approaches and then and Telecommunication of Rennes (IETR), UMR CNRS 6164, University of provides an interpretation of the surface wave propagation Rennes 1, Campus de Beaulieu, Rennes Cedex 35042, France. (e-mail: [email protected]; [email protected]; theories on a planar Earth thanks to the research of [email protected]) Sommerfeld [1], K.A. Norton [5] and R.W.P. King [6] [7] [8]. S. Palud and P-Y Jezequel are with TDF, Centre de Mesure d'Antennes, These authors have provided electromagnetic field formulas La Haute Galesnais, 35340 Liffré, France. radiated by an infinitesimal vertical electric dipole located at a (e-mail : [email protected]; [email protected]) Ph. Pouliguen is with the « Direction Générale de l’armement » (DGA), specified height h e, over an imperfectly conducting half-space. DGA-DS/MRIS, 7-9, rue des Mathurins, Bagneux Cedex 92221, France In this section, we have summarized these theories with a (e-mail : [email protected]) standardized notation system. We have employed a harmonic 1 -iωt time factor e throughout. The infinitesimal dipole is fed by a Where Z0=120 π is the free space impedance, Rv the Fresnel’s unit electric Fig. 1. Set of coordinates and location of an infinitesimal vertical electric dipole (D) at a height he in the air (wave number k 0) over the ground (wave number k g). moment Idl=1 A.m (current I, infinitesimal length dl). reflection coefficient and F the attenuation function of the Fig. 1 describes the set of coordinates and the geometry surface wave. Rv and F(p) are defined with the following parameters. Since the propagation characteristics are formula : dependent on ground properties, we use the wave numbers k0 and kg, respectively in the air and in the ground, where εrg and σg are respectively the relative permittivity and the conductivity of the ground. These media are assumed to have the same permeability µ 0 than free space. ( 5 ) ( 1 ) ( 1- 2 ) j ( 6 ) ( 3 ) Where p0 is the Sommerfeld numerical distance. Where N is the complex refractive index of the ground. The relation between the magnetic field and the Hertz vector is: A. Presentation of Norton’s Model The EM field radiated by an infinitesimal vertical electric ( 7 ) dipole on the surface of the planar Earth was firstly analyzed by A. Sommerfeld [1]. Then, K.A. Norton simplified the B. Presentation of King’s Model calculation, the formalism and the interpretation [4][5] by introducing the attenuation function. Norton’s formalism starts from the Hertz vector and Norton’s model is valid whatever R.W.P. King established the EM field expression generated by the transmitter or the receiver height. The Hertz vector a vertical electric dipole located on or in the vicinity of the Earth surface from Maxwell’s equations. According to [6], the expression Πz contains 3 terms: a direct wave, a reflected wave and the surface wave. transverse magnetic induction B2φ and associated electric field E2 are: ( 8 ) ( 4 ) 2 Physically, the transition between the two areas is smooth. We call this transition area the “smoothly” attenuation (dotted ( 9 ) zone). ( 10 ) 3 2 Where P0=k 0 d/2k g is the Sommerfeld numerical distance and F(P 0) is defined by the following formula: Fig. 2. Two mains areas of propagation behavior around the ( 11 ) “smoothly” area (dotted zone). Where, C2(P 0)+iS 2(P 0) is the Fresnel integral and ω is the The trans-horizon radar application requires a long coverage pulsation. (200 nmi). Even if the sea water is a favorable medium to the surface wave propagation, the frequency is an important These formulas have been proposed with the following choice relative to the characteristic distances (d c and d i). The conditions issued from [4] and [6] respectively: 5 MHz frequency is a special case (Fig. 2- a): the intermediate distance (d i=270 km) is superior to the critical distance (d c=90km). Knowing that d i>d c, the surface wave propagation decreases as 1/d all along the planar model range (90 km). ( 12 ) This behavior is an attractive feature to the need of large coverage and detections at large distances . ( 13 ) C. Millington’s Model Where, r 0 is defined in Fig. 1. The King’s theory describes physically surface-wave The Millington’s model is applied as soon as the environment propagation behavior by defining characteristic distances: the contains several ground types along the propagation path.
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