Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
  • H01Q9/04—Resonant antennas
  • H01Q9/16—Resonant antennas with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole

Definitions

• the present invention relates to a directional antenna of the half-wave dipole type, particularly intended for transmission or reception in the frequency range from approximately 88 to 108 MHz, known as the FM band.
• the known antennas used for radio transmission or reception in the FM band are generally not very directive.
• the radiation patterns of neighboring antennas partially overlap.
• Each antenna is associated with a frequency different from the frequencies associated with neighboring antennas to avoid unwanted interference.
• SFN Single Frequency Network
• all the antennas transmit with the same frequency.
• the radiation patterns of these antennas must be adjusted very precisely so that the diffusion zones associated with these antennas are adjacent but do not overlap so that there is no interference between neighboring diffusion zones.
• the antennas in an SFN network are very large. Very often, for example when the antennas are arranged one behind the other, such as along a motorway axis, a large reflector is fixed behind each antenna. in order to avoid destructive interference between the electromagnetic field radiated by the antenna and that radiated by the previous antenna.
• the typical dimensions of these antennas are of the order of several meters. These dimensions increase the cost of manufacture of antennas, and complicate their installation and maintenance. Finally installed, these antennas degrade the landscape and present a significant wind resistance which causes damage in case of a storm.
• the present invention aims to provide a directive antenna with a small footprint and whose shape of the radiation diagram is easily adaptable to the operating conditions of a single frequency broadcasting network.
• an antenna comprising a powered radiating source and a non-powered radiating source
• the powered source is a half-wave dipole extending along a longitudinal axis
• the unpowered source comprises a first elongated element conductor extending along a longitudinal axis intersecting with 0 the longitudinal axis of the half-wave dipole, a first insulation means connecting a first end of the elongate element substantially at the center of the half-wave dipole, and a first insulating means connecting a second end of the first elongate element to a first end of the half-wave dipole.
• the directivity of the antenna is better controlled when the non-powered source, called parasitic, further comprises a second elongated conductive element and a second insulating means.
• the second elongate element extends along a longitudinal axis intersecting with the longitudinal axis of the first elongate element and with the longitudinal axis of the half-wave dipole.
• the first isolation means extends from a first end fixed at the center of the half-wave dipole towards a second end to which the first end of the first elongate member and a first end of the second elongate member are attached.
• the second insulating means connects a second end of the second elongate element to a second end of the half-wave dipole.
• the first and second elongate elements form acute angles, preferably equal, with the longitudinal axis of the half-wave dipole.
• the antenna can radiate along this axis, either mainly in a direction, or in a symmetrical or asymmetrical way according to the two directions along the axis.
• the unpowered source further comprises third and fourth elongated conductive elements, a second insulation means, and third and fourth insulating means.
• the third and fourth elongate elements extend respectively along longitudinal axes intersecting each other and with the longitudinal axis of the half-wave dipole.
• the second isolation means extends from a first end fixed at the center of the half-wave dipole to a second end to which first ends of the third and fourth elongate elements are fixed.
• the third and fourth insulating means' respectively connect second ends of the third and fourth elongate elements to the first and second ends of the half-wave dipole.
• the first and second insulation means extend along an axis of symmetry which is perpendicular to the longitudinal axis of the half-wave dipole and with respect to which the first and third elongate elements are respectively symmetrical with the second and fourth elongated elements.
• the directivity of the antenna can be more accentuated in the second embodiment compared to the first embodiment, thanks to the third and fourth elongated elements.
• the first end of a long element can be connected to a reference potential such as earth through, among other things, an additional reactance, preferably variable in order to adjust the characteristics of the antenna diagram, for example as a function of 'other surrounding broadcast areas, or to periodically select predetermined antenna patterns.
• an additional reactance preferably variable in order to adjust the characteristics of the antenna diagram, for example as a function of 'other surrounding broadcast areas, or to periodically select predetermined antenna patterns.
• the antenna comprises the first and second elongate elements
• the first ends of the first and second elongate elements can be connected together through at least one additional, preferably variable, reactance.
• the antenna comprises the third and fourth elongate elements
• the first ends thereof can be connected together in a similar manner through an additional reactance.
• - Figure 2 is a horizontal top view of an antenna according to a first embodiment of the invention
• - Figure 3 is a horizontal top view of an antenna according to a second embodiment of 1 • invention.
• a single frequency broadcasting network known as the Single Frequency Network (SFN)
• SFN Single Frequency Network
• contiguous broadcasting zones also called diffusion cells, arranged linearly to cover a motorway axis AR.
• a portion of the motorway axis AR is covered by four contiguous diffusion zones ZDi, ZDi + i, ZDi + 2 and ZDi + 3 comprising transmitting antennas Ai, Ai + i, Ai + i and Ai + 3, respectively.
• the broadcasting network transmits with a carrier frequency common to all the broadcasting areas.
• the carrier frequency is included in the VHF band, and more particularly in the FM frequency band from approximately 88 to 108 MHz.
• the broadcast areas are perfectly defined to minimize interference between neighboring areas.
• the antenna Ai mainly comprises two radiating sources.
• a first radiating source is supplied and constitutes a pilot 1.
• the second radiating source is non-supplied and constitutes a parasite 2.
• the antenna Ai has a generally substantially triangular shape and is symmetrical with respect to a plane perpendicular to the plane of FIG. 2 and having for trace the axis PP in figure 2.
• the pilot 1 is a half-wave dipole extending along a longitudinal axis DD perpendicular to the axis PP and comprises two identical metal masts 11 and 12 aligned along the axis DD.
• the mast 11 has, transversely an isosceles or equilateral triangular section and is formed by three metallic cylindrical rods 111, 112 and 113 parallel to the axis DD. Alternatively, the cross section may be circular, square or polygonal, while still being perforated. Two rods 111 and 112 are only visible in FIG. 2. The three rods 111, 112 and 113 are secured by a lattice of spacers 114. The structure of the mast 11 is rigid, while being light and having little wind resistance .
• the mast 12 is identical to the mast 11 and comprises three rods 121, 122 and 123 secured by a lattice of spacers 124.
• First ends 115 and 125 of the masts 11 and 12 close to the axis PP are rigidly fixed to a first end 31 of an isolation foot 3 which mechanically maintains, while electrically insulating, the various parts connected to it.
• the foot 3 is elongate and centered on the axis P- P. The foot 3 is thus perpendicular to the masts 11 and 12 and is fixed to the latter substantially at the center of the half-wave dipole 1.
• Second ends 116 and 126 of the masts 11 and 12 form the ends of the dipole 1.
• the base 3 comprises a cylindrical central core 32 of dielectric material and a protective sheath 33 of plastic material.
• the ends 115 and 125 of the masts 11 and 12 are embedded in the protective sheath 33 so as to be electrically insulated.
• the foot has a rectangular section or is conical.
• the parasite 2 comprising first and second electrically identical conductive shrouds 21 and 22 extending in the plane of Figure 2 along axes Hl-Hl and H2-H2, respectively.
• the axes Hl-Hl and H2- H2 are intersecting with each other and intersecting with the axis PP at the end of the foot 34.
• Each of the shrouds 21, 22 is formed by a slender element such as a metallic cylindrical rod, the first of which end 211, 221 is embedded in the protective sheath 33 of the foot 3 at the end 34 and a second end 212, 222 is fixed to an insulating element 41, 42.
• the insulating element 41, 42 is a tensioned wire Nylon type synthetic connecting the second end of the guy line 212, 222 to the second end 116, 126 of the mast 11, 12.
• the parasite 2 thus has the shape of a vee, the point of which is on the axis PP and the branches are directed towards the ends 116 and 126 of the pilot 1.
• the ends 212 and 222 of the branches of the vee are separated from the ends 116 and 126 of the pilot 1.
• the shrouds are replaced by elongated metal blades or elongated cages of metallic wires.
• the masts 11 and 12, the shrouds 21 and 22 and the foot 3 can be removable from each other.
• the foot 3 has a length of approximately 40 to 55 cm and a diameter of the order of approximately 5 to 10 cm.
• Each of the masts 11 and 12 has a length of approximately 70 to 90 cm, typically a quarter of a wavelength A / 4 ⁇ 75 cm for a transmission frequency equal to 100 MHz.
• the sides of the triangular section of the masts 11 and 12 are each about 3 to 4 cm long.
• the shrouds 21 and 22 have a length substantially equal, that is to say somewhat less or greater, to the quarter of a length wave, about 60 to 80 cm, and a diameter of 22 mm, and the insulating wires 41 and 42 have a length of 10 to 20 cm and a diameter of 0.2 mm.
• the angle between a stay cable and the foot is approximately 60 °, that is to say the angle between a stay cable and the DD dipole axis is an acute angle of approximately 30 °.
• the foot 3 has a length between 35 and 40 cm and a diameter between 60 and 80 mm.
• the lengths of the masts, foot and shrouds as well as the angle between the shrouds and the foot, or even the relative position of each of the shrouds and of the dipole, are interdependent and define the shape of the radiation diagram, the gain and the directivity of the antenna for a given transmission frequency of the antenna A ⁇ .
• the antenna Ai is supported, for example by the end of the foot 31, by a support (not shown) of the foot arranged on the ground so that the masts 11 and 12 and the foot 3 are located in a horizontal plane as shown in top view in Figure 2, or are located in a vertical plane, depending on the desired diffusion area contour.
• the masts 11 and 12 are each supplied with an emission signal by two respective supply terminals 117 and 127 embedded in the sheath 33 at the end 31 of the foot 3.
• the terminals 117 and 127 are thus protected from the unfavorable influence rain or frost on the electrical characteristics of the antenna A ⁇ .
• the terminals 117 and 127 are respectively supplied by the inner conductors of two coaxial cables 51 and 52 of the same length connected to the outputs of a balun 5.
• the sy erizer distributes the power of a transmission signal SE in FM band transmitted by a source 7 installed at the base of the support, through a coaxial antenna cable 70 winding through the support.
• the outer conductors of the coaxial cables are connected to a reference potential, such as earth, by means of a metal plate 53 fixed to the end 31 of the stand 3.
• the symmetrization of the transmission signal SE into symmetrical signals supplying the masts 11 and 12 is integrated in the first end 31 of the stand 3.
• the coaxial cable 70 is directly connected to a first coaxial section of a balun having two coaxial, elongated, parallel and identical sections. First ends of the outer conductors of the two coaxial sections are interconnected by a short circuit, one of these first ends being connected to the outer conductor of the cable 70. Second ends of the inner conductors of the coaxial sections are connected to the terminals mast 117 and 127.
• the shrouds 21 and 22 have an intrinsic reactance XI21 and XI22, depending in particular on their length.
• the ends 211 and 221 of the shrouds are connected in series at the end 34 of the foot 3.
• two additional adaptation reactors XS21 and XS22 are inserted in series between the ends 211 and 221 of each guy at the second end 34 of the foot 3.
• the additional reactors XS21 and XS22 have a common terminal connected to a metal plate 23, similar to the plate 53, and fixed to the end 34 of the foot 3. According to a simplified variant, the two additional reactors are replaced by a single connected reactance between the ends 211 and 221 of guy lines 21 and 22. In all cases, the pilot 1 is electrically isolated from the parasite 2.
• the core 32 of the foot 3 is conductive, for example metallic, the sheath 33 being insulating.
• the plates 23 and 53 at the two ends 31 and 34 are then brought to the same reference potential, or common ground. Consequently the ends 211 and 221 of the shrouds are brought to the reference potential.
• the total reactances XT21 and XT22 have equal values in the majority of applications so that the maximum of radiation is directed along the axis PP of the foot 3 perpendicular to the half-wave dipole 1. More generally, the values of the reactances directly influence on the antenna radiation.
• the antenna Ai radiates mainly in the parasitic direction 2 towards pilot 1 substantially along the axis PP, that is to say from the top towards the bottom in figure 2.
• the intrinsic reactance XI21, XI22 increases when the length of the stay 21, 22 increases and the additional reactance XS21, XS22 increases with the value of the inductance inserted between the shroud 21, 22 and the foot 3.
• the antenna Ai radiates in the pilot direction 1 towards parasite 2.
• the reactance XT21, XT22 becomes more capacitive when the length of the guy line 21, 22 decreases or when a capacitor of higher capacity as additional reactance is inserted between the stay 21, 22 and the stand 3, for a given emission frequency.
• additional reactors XS21 and XS22 which are variable, it is possible either to modify the radiation pattern of the antenna A ⁇ for a given emission frequency, or to modify the emission frequency then to adjust the radiation pattern of 1 antenna A ⁇ , for example so that the antenna is very directive, or substantially bidirectional along the axis PP.
• This variation in the directivity and the gain of the antenna A ⁇ can be used to impose for example a broadcast of the emission signal SE during a first period, for example during the day, in a bidirectional manner, that is to say - say almost omnidirectional, and for a second period, for example at night, in a directive manner. If the total reactances XT21 and XT21, or more precisely the variable additional reactances XS21 and XS22 are adjusted more and more differently, the directivity of the antenna A ⁇ is modified relative to the axis of foot P-P.
• the variable reactors XS21 and XS22 can be controlled by remote-controlled gearmotors from the base of the antenna support.
• a second embodiment of an Aai antenna according to the invention has a general diamond shape and is symmetrical with respect to a Pa-Pa trace plane perpendicular to FIG. 3. Only the main differences of the antenna Aai with respect to the previous embodiment Ai are described.
• the antenna Aai comprises a pilot analogous to pilot 1, a first parasite 2a analogous to parasite 2, a second parasite 6a analogous to the first parasite 2a and placed symmetrically with the latter relative to the longitudinal axis Da-Da of the pilot la , and a foot 3a.
• the pilot 1a is supplied in the same manner as the pilot 1 by a transmission signal SEa transmitted by an FM source 7a through a balun 5a analogous to the balun 5.
• the foot 3a is substantially twice as long as the foot 3 and extends on either side of the pilot along the axis Pa-Pa.
• the second parasite 6a comprises two shrouds 61a and 62a fixed between one end 34a of the foot 3a and two insulating wires 43a and 44a respectively fixed to the ends 116a and 126a of the pilot la.
• the third and fourth shrouds 61a and 62a extend along axes H6la-H61a and H62a-H62a, respectively.
• the axes H61a-H61a and H62a-H62a are intersecting with each other and intersecting with the axis Da-Da of the pilot la, and are preferably coplanar with the axes Hla-Hla and H2a-H2a of the first and second shrouds 21a and 22a.
• the first ends 211a, 221a, 611a and 621a of the four shrouds 21a, 22a, 61a and 62a are connected two by two in series at the ends of the foot 3a, as illustrated in FIG. 3, or by means of a additional reactance, preferably variable, such as reactance XS21, XS22, in addition to the intrinsic reactance of each of the shrouds.
• the lengths of the shrouds, the inclinations of the shrouds relative to foot 3a and the values of the additional reactances condition the shape of the radiation diagram and therefore the directivity and the gain of the antenna Aai, which can be more directive or bidirectional than the antenna Ai.
• the antenna Aai is not necessarily symmetrical with respect to the axis Da-Da, if the antenna must radiate asymmetrically with respect to the axis Da-Da of the pilot dipole la.
• the foot 3a has different lengths on either side of the pilot la.
• the lengths of the stays 61a and 62a, a priori equal to each other, are different from the length of the stays 21a and 22a.

Landscapes

• Variable-Direction Aerials And Aerial Arrays (AREA)
• Details Of Aerials (AREA)
• Aerials With Secondary Devices (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9469014

Family Applications (1)

Country Status (9)

Citations (2)

• 1994
  • 1994-11-18 FR FR9413939A patent/FR2727249B1/fr not_active Expired - Fee Related
• 1995
  • 1995-11-15 SK SK610-97A patent/SK280107B6/sk unknown
  • 1995-11-15 ES ES95940313T patent/ES2125057T3/es not_active Expired - Lifetime
  • 1995-11-15 EP EP95940313A patent/EP0792528B1/fr not_active Expired - Lifetime
  • 1995-11-15 PL PL95320029A patent/PL178126B1/pl not_active IP Right Cessation
  • 1995-11-15 HU HU9702083A patent/HU217725B/hu not_active IP Right Cessation
  • 1995-11-15 WO PCT/FR1995/001499 patent/WO1996016453A1/fr not_active Ceased
  • 1995-11-15 DE DE69505149T patent/DE69505149T2/de not_active Expired - Fee Related
  • 1995-11-15 CZ CZ971499A patent/CZ284949B6/cs not_active IP Right Cessation

Patent Citations (2)

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