Patent Publication Number: US-6342855-B1

Title: Mobile radiotelephony planar antenna

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a planar antenna, in particular for mobile radio, the planar antenna having two conductive layers arranged at a predefined distance from one another. 
     2. Background of the Invention 
     The application area of the invention relates primarily to the mobile radio field and, in this case, in particular to E and D networks. 
     Known antenna solutions for the field of mobile radio applications are based on linear antenna designs in the form of monopole arrangements in shortened or unshortened embodiments. These linear antennas are known both as externally mountable onboard antennas and components directly coupled to the terminal, and are subject to different directionality and efficiency, these components being exclusively omnidirectional in the azimuthal plane. Known patch antenna solutions are based on dipole-like configurations which are arranged in two-dimensional fashion and whose directional diagrams is irregular and, in connection with the respective background, exhibit the features of significant radiation field deformation. The radiation properties relating to the application field are significantly inferior to those of conventional linear antennas. Likewise, controlled masking properties of the radiation diagram are not demonstrable. No further solutions are known whose electromagnetic or radiation properties are obtained on the basis of asymmetric and open waveguide technology, in particular microstrip technology, with the use of self-supporting conductive sheet conductors or sheet-like conductor surfaces. 
     EP 0 176 311 discloses a planar antenna which has a ground plane which is kept at a distance from the radiator element by means of a dielectric substrate layer. The radiator element is fed by means of a coaxial waveguide and is electrically conductively connected by means of short-circuit connections on one side to the ground surface. The radiator element is a geometrical subregion of the ground plane. EP 0 176 311 also discloses a two-dimensional short-circuit connection between the ground plane and the radiator element. 
     DE 195 04 577 discloses a mobile radio antenna for motor vehicles, which also has a radiation element that is in connection with the inner conductor of a coaxial waveguide. One side of the radiator element is in conductive connection with a ground surface via a short-circuit connection. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a two-dimensional radiator component with the property that it can produce linearly polarized and spatially wide sector radiation both in the azimuthal and in the elevation plane, as well as pronounced back-radiation attenuation and therefore useful radiation exclusively within a space hemisphere preferably in the spectral ranges of between 890 MHz and 960 MHz or 1710 MHz and 1890 MHz. 
     This object is achieved by the invention according to the distinguishing part of claim 1. Through the conductive connections of the two layers, a reduction in the overall size by approximately a factor of 2 is obtained, since λ/ 2  waves can advantageously be received. By virtue of the fact that the distance between the rectilinear edge and the short-circuited border changes, it is possible to receive and transmit in a relatively broad spectral range. In this case, it is advantageous if the first layer is circular and the second layer is reduced compared with the first by a chord portion, the chord portion forming a rectilinear edge. In this case, the conductive connections on the border side remote from the rectilinear edge may be produced by means of connection elements in point form or strip form. It may, however, also be advantageous to configure the base surface first layer elliptically, in a triangular shape, square or hexagonally. 
     The oscillation conditions of the planar radiator can advantageously be implemented by simulation software to investigate field problems of radio frequency radiation. In this regard, it should be noted that, for each spectral range, a comprehensive set of different oscillation conditions need to be taken into consideration depending on the radiator characteristic. Since full calculation taking these boundary conditions into account is not possible, the person skilled in the art is inevitably led to simulation trials if he wants to configure the planar radiator according to the invention to his circumstances. 
     The oscillation conditions of the planar radiator can also advantageously be influenced using diaphragms produced in the second layer by holes in the conductive layer. In this regard, the diaphragms form implemented capacitors with distributed parameters, which in this form electrically extend the waveguide geometry or provide the possibility of geometrical miniaturization. The arrangement of the diaphragms is in this selected symmetrically, since the symmetry condition represents the prerequisite for preserving the preferential polarization of the electric field vector. In this case, by means of the diaphragm position, the possibility is provided of altering the oscillation direction of the field vectors, which are primarily affected by the diaphragms, and therefore the resultant field profiles which are created by superposition. The location where the diaphragms are introduced and, subordinately, the diaphragm contour determine the degree to which the conduction currents, as well as the associated electric and magnetic field components, are affected. To that extent, the position and contour of the diaphragms primarily dictate the raising or lowering of the capacitive and inductive components within the reactive component budget. Since the diaphragms which are introduced basically influence the complex waveguide properties, besides alteration of the spectral oscillation conditions, the possibility is thereby provided of affecting the spectral bandwidth of the type of oscillation excited. The surface of each diaphragm may in this case either be circular, elliptical, rectangular, square, triangular, hexagonal or irregular. The optimum shape of the diaphragms and their arrangement can in turn usually be established only empirically by simulation tests. The electromagnetically resonating oscillation arrangement is excited or fed by means of a coaxial waveguide, the inner conductor of the waveguide being conductively connected to the second layer and the outer conductor of the waveguide being conductively connected to the first layer, the inner conductor being arranged through a diaphragm within the first layer, axially symmetric to the diaphragm border and without electrical connection to the latter. 
     The way in which the two layers are in connection with one another along border remote from the rectilinear edge is freely selectable. It is thus possible to connect these two layers to one another by means of conductive pins. This is advantageous especially when no dielectric is arranged between the two layers, and the two layers are formed, for example, by copper plates. The conductive connection pins are then used, as it were, as spacers. 
     If a dielectric is arranged between the two layers, it may be used as a support for the two conductive layers, the conductive connection then being advantageously made outside the dielectric, to which end the dielectric may be coated in linear or two-dimensional form on its outer edge. 
     The shape of the border on which the two layers are conductively connected to one another, is in principle freely selectable, although care must be taken to comply with the oscillation conditions. If the border remote from the rectilinear edge or chord extends parallel to the chord, only a monochromatic frequency response can be obtained. It is therefore necessary to design this border edge non-parallel to the rectilinear edge or chord of the second layer if a frequency spectrum or band is desired. 
     The planar radiator according to the invention forms an optimum antenna component or replacement component for the external vehicle antenna with the possibility of being mounted inside the passenger compartment. The application field further relates to general indoor applications, in that the radiator component forms a component spatially remote from the terminal in question and can be mounted on the inside and in two-dimensional fashion on the relevent room glazing. It is also possible for the room glazing itself to serve as the dielectric support of the conducting two layers. 
     The radiator component or planar antenna according to the invention can advantageously be used in all cases in which the space lying behind the antenna aperture is to be kept free of radiation or at a low radiation level, and the exposure of the user to electromagnetic radiation is therefore to be minimized. 
     Further, the radiator component according to the invention forms a base module for short or medium range transmission systems for communication, sensor or safety applications. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The planar antenna according to the invention will be explained in more detail below with reference to Figures, in which: 
     FIG. 1 shows a plan view of a first layer; 
     FIG. 2 shows a plan view of the second layer of the planar radiator with the underlying first layer (FIG.  1 ), the first and second layers being conductively connected to one another over a length L 1 ; 
     FIG. 3 shows a plan view of another embodiment of a planar antenna according to the invention with point-like conducting connections; 
     FIG. 4 shows a plan view of the second layer associated with the first layer according to FIG. 3; 
     FIGS. 5,  6  show another illustrative embodiment of a planar antenna according to the invention with circular hole in the second layer; 
     FIGS. 7-9 show a planar radiator with a circular dielectric and conductive coatings applied to the latter; 
     FIG. 10 shows a spacer or support cylinder; 
     FIG. 11 shows a point-like connection element; 
     FIGS. 12-15 show plan views of various embodiments of planar radiators; 
     FIG.  16  and FIG. 17 side views of planar radiators with electrically conducting connection elements applied to the outer edge of the dielectric. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a low-loss low dielectric structure support, preferably polypenco Q 200.5, polycarbonate or polystyrene, with a diameter of 93 mm. and a base height of 5 mm, which on one side has a continuous conductive layer  2 , preferably consisting of copper or aluminum with a layer thickness of between 5 μm and 800 μm. The conductive layer is preferably produced by means of additive or substractive techniques. 
     There is a conductive layer  3  on the side of the structural support remote from the continuous conductive layer  2 . This layer  3  is a segment of a circle, which is reduced by a chord portion in comparison with the first layer  2 , the chord  4  being arranged at right angles to the symmetry axis of the layers  2 ,  3 . On the outer edge or boundary edge  8  opposite the rectilinear boundary edge or chord  4  of the conductive layer  3 , the two conducting layers  2  and  3  are conductively connected to one another over the length L 1 , the half-length L 1 / 2  counting of the respectively starts at the line which is perpendicular to the rectilinear boundary edge  4 , or at the symmetry axis  15 . The planar radiator is fed by means of a coaxial waveguide, the outer conductor of the waveguide (not shown) being in connection with the conducting layer  2  in the region of the diaphragm  7 , and the inner conductor of the waveguide (not shown) being fed through the diaphragm  7  to the connection point  6  of the second layer  3 . The characteristic impedance of the waveguide is preferably 50 ohms. The electromagnetic diaphragm  7  is formed through a circular opening in the conductive layer  2  having a diameter of 3.2 times the inner conductor diameter of the coaxial waveguide. The length of the perpendicular  20  changes continuously in the region L 1 , with the result that a defined spectral range can be received or transmitted. 
     FIGS. 3 and 4 show an illustrative embodiment of a planar antenna for the frequency range between 1710 MHz and 1890 MHz. According to FIG. 3, a conductive metal plate  20  with circular border and diameter 90 mm is coupled plane-parallel over a distance of 4.8 mm to a second conductive metal plate  30 , which is designed as a portion of a circle, the centers both of the full-circle surface and of the circle portion surface are arranged on an identical symmetry axis  15  and, according to FIG. 4, the conductive plate  30  is conductively coupled to the conductive plate  20  at five points  50 , one of the five points  50  being positioned or the arrangement&#39;s symmetry line  76  extending in the plane of the circle portion surface, by fitting conductive connection elements  5  according to FIG. 11 at the position marked in FIG. 3 between the conductive plate  20  and the conductive plate  30 . The inner conductor of the coupling coaxial waveguide is electrically coupled with the conductive plate  30  at point  60 . In this case, the inner conductor is taken by means of a dielectric bush, preferably a PTFE bush, centrally between the conductive plates  20  and  30  through the hole  70  within the conductive plate  20 . The PTFE bush is in this case designed as a cylindrical sleeve with a length of 4.8 +/−0.1 mm, whose external diameter measures 1.4-0.1 mm and whose internal diameter measures 1.4 mm over a length of 3.8-0.1 mm and with an internal diameter of 2.2 mm over a length of 1 mm. The outer conductor of the signal-coupling coaxial waveguide is coupled in the immediate vicinity of the hole  70  with the conductive plate  20  arranged plane-parallel with the plate  30 . Another embodiment of the invention for a planar antenna for the frequency range between 890 MHz and 960 MHz is shown by FIGS. 5 and 6. According to FIG. 1, a conductive metal plate  20 ′ with circular border and diameter 90 mm is coupled plane-parallel over a distance of 4.8 mm to a second conductive metal plate  30 ′, which is designed as a portion of a circle, the centers both of the full-circle surface and of the circle portion surface are arranged on an identical axis and, according to FIG. 6, the conductive plate  30 ′ is provided with four circular hole  10  in a line extending parallel to the chord and is conductively coupled to the conductive plate  20 ′ at three points  50 ′, one of the three points  50 ′ being positioned on the arrangement&#39;s symmetry line extending in the plane of the circle portion surface, by fitting conductive connection elements  5  according to FIG. 11 at the position marked in FIG. 5 between the conductive plate  20 ′ and the conductive plate  30 ′ . To provide mechanical stabilization, a support cylinder  9  according to FIG. 10 with a diameter of 6 mm, which is positioned on the symmetry line of the arrangement is inserted between the conductive plate  20 ′ and the conductive plate  30 ′. The inner conductor of the coupling coaxial waveguide is electrically coupled with the conductive plate  30 ′ at point  60 ′. In this case, the inner conductor is taken by means of a dielectric bush, preferably a PTFE bush, centrally between the conductive plates  20 ′ and  30 ′ through the hole  70 ′ within the conductive plate  20 ′. The PFTE bush is in this case designed as a cylindrical sleeve with a length of 4.8 +/−0.1 mm, whose external diameter measures 1.4-0.1 mm and whose internal diameter measures 1.4 mm over a length of 3.8-0.1 mm and with an internal diameter of 2.2 mm over a length of 1 mm. The outer conductor of the signal-coupling coaxial waveguide is coupled in the immediate vicinity of the hole  70 ′ with the conductive plate  20 ′ arranged plane-parallel with the plate  38 ′. Another illustrative embodiment is shown by FIGS. 7 to  9 . According to FIGS. 7 to  9 , on one side of a low-loss and low-dielectric structural support  11 , preferably polypenco Q 200.5, polycarbonate or polystyrene, with a diameter of 93 mm and a base height of 5 mm, a continuous conductive layer  12 , preferably consisting of copper or aluminum with a layer thickness of between 5 μm and 800 μm, is produced by means of additive or subtractive techniques, preferably substractive techniques. 
     On the opposite side of the dielectric support  11  from the continuous and conductive surface  12 , according to FIG. 8, a surface segment  13  with a conductive layer, preferably consisting of copper or aluminum with a layer thickness of between 5 μm and 80 μm, is placed, the conductive layer  13  that is produced being conductively connected to the continuous conductive surface  12  on the outer edge  18  of the conductive surface segment  13  opposite the rectilinear boundary edge  14  of the conductive layer. Feeding is carried out by means of contact with a coaxial waveguide, in that, at point  16  according to FIG. 8, the inner conductor of the coaxial waveguide, with a characteristic impedance of preferably 50 ohms, is conductively connected to the surface segment  13 , and the outer conductor of the coaxial waveguide is connected to the opposite continuous and conductive layer  12  with a full-circle surface, the inner conductor of the coaxial waveguide being fed through an electromagnetic diaphragm  17  in the form of a circular opening within the conductive layer  12  having a diameter of 3.2 times the inner conductor layer of the coaxial waveguide. 
     FIG. 10 shows a support cylinder  9  made of a nonconducting material. FIG. 11 represents an electrically conducting connection element for connecting the points  50 ,  50 ′ according to FIGS. 3 to  6 . FIGS. 12 to  15  show various possible embodiments or border shapes of the planar antenna according to the invention, the nature of the frequency response, as well as of frequency range, being adjustable through special selection of the angle φ or φ′ in FIGS. 14 and 15. Thus, FIG. 12 shows that, at an angle φ of between 0 and 90 degrees of angle in the case of a polygon, the borders  8  may be conductively in connection with one another by means of point-like connection elements at points  50 . FIGS. 14 and 15 show that the number and shape of the electromagnetic diaphragms  10  is likewise freely selectable. 
     FIGS. 16 and 17 respectively show a side view of the planar antenna according to the invention, the lateral edge of the dielectric support material L having strip-like connection elements  19  applied to it, so that at these locations the two conductive layers  12  and  13  are in connection with one another. FIG. 17 shows a side view of the planar antenna explained according to FIGS. 1 and 2, the two conducting layers  12  and  13  being in connection over a length L 1  via the conductive connection element  19 .