Abstract:
The invention relates to an antenna ( 1 ) for a transmitting operation and/or a receiving operation with a decoupling apparatus ( 2   a ) and/or a coupling apparatus ( 2   b ) for electromagnetic waves. The antenna ( 1 ) according to the invention comprises a horn funnel ( 4 ) which is composed of at least two side walls ( 3   a   , 3   b   , 3   c   , 3   d ), and also comprises at least two fins ( 5   a   , 5   b ) which extend into the interior of said horn funnel ( 4 ). The at least two side walls ( 3   a   , 3   b   , 3   c   , 3   d ) have a cutout ( 7   a,    7   b ) in each case.

Description:
FIELD OF INVENTION 
     The invention relates to a horn antenna for transmitting and receiving electromagnetic waves in the frequency range from, for example, about 1 GHz to about 18 GHz. 
     BACKGROUND 
     U.S. Pat. No. 6,995,728 B2 describes a horn antenna with a pyramid-shaped horn funnel and a ridge. Said horn antenna comprises a first and a second conducting wall, which walls are disposed so as to form an angle in relation to one another. The horn antenna also has a first ridge in the vicinity of the first conducting wall and a second ridge in the vicinity of the second conducting wall, the first ridge extending over the averted end of the first wall and the second ridge extending over the averted end of the second wall. The curvature of the first ridge corresponds to an arc which is tangent to a line that is perpendicularly upright on the surface of the first wall. 
     The disadvantage of the horn antenna described in U.S. Pat. No. 6,995,728 B2 lies in the fact that the antenna gain is subject to major fluctuations, particularly at low frequencies. Furthermore, the antenna gain drops to less than 0 dBi at low frequencies, such as frequencies around 1 GHz for example. 
     A further disadvantage of this horn antenna consists in the fact that the voltage standing wave ratio in the lower frequency range is very unfavorable, with values of between 2 and 5, since it is scarcely possible to operate the horn antenna from a VSWR of about 3. 
     BRIEF SUMMARY 
     The underlying object of the invention is to indicate an antenna which has a good antenna gain without fluctuations at low frequencies and which has a lower VSWR, even in the lower frequency range. 
     The aforesaid object is achieved, according to the invention, by means of the features in the pre-characterizing clause of claim  1 , in combination with the characterizing features. Advantageous further developments form the subject of the subclaims which are referred back to these. 
     The antenna according to the invention for a transmitting operation and/or a receiving operation thus comprises a coupling apparatus and/or a decoupling apparatus for electromagnetic waves. Provided around said coupling or decoupling apparatus is a horn funnel which is composed of at least two side walls and comprises at least two fins, the coupling apparatus and/or decoupling apparatus being preferably provided at a narrow end of said horn funnel. The fins of the antenna according to the invention are disposed substantially inside the horn funnel, the at least two side walls having two cutouts which are preferably trapezoidal in each case. 
     One advantage consists particularly in the fact that the two cutouts are congruent, a fact which reduces the expenditure on production when manufacturing the incised side walls. 
     In addition to this, the two side walls preferably have the same tolerances, so that no asymmetries are produced in the radiating characteristic of the antenna according to the invention as a result of different tolerances in the material of the antenna. 
     It is also advantageous that the two cutouts are disposed substantially symmetrically in relation to one another, a fact which, once again, has a favorable effect on a radiating characteristic of the antenna according to the invention that is as symmetrical as possible. 
     Furthermore, it is advantageous if each trapezoidal cutout has a longitudinal axis of symmetry in each case. The side walls having the cutout are thereby easier to position, since the said longitudinal axis of symmetry can be oriented in a simple manner and with a high degree of accuracy at a specific angle to the coupling or decoupling apparatus. 
     In addition, it is of advantage if one direction component, in each case, of one fin, in each case, is oriented parallel to the longitudinal axis of symmetry. This ensures precise adjustment of the fins, relative to the coupling or decoupling apparatus. 
     In addition to this, it is of advantage if the two fins of the antenna according to the invention are disposed symmetrically within the horn funnel and extend through the cutout, so that, in each case, a first part, which is smaller in terms of area, of the two fins projects, in each case, beyond the side wall that forms the horn funnel. 
     In each case, a second part, which is larger in terms of area, of the two fins advantageously projects into the horn funnel in each case, so that even electromagnetic waves with a high frequency can be conducted inside said horn funnel, since the electrical field develops, above all, between the two fins, in the event of excitation with a high frequency. 
     A further advantage is obtained if the two fins each have a rounded-off end in the direction of a broad opening of the horn funnel, so that the boundary conditions for the profile of the fields are constant. 
     In addition to this, it is of advantage that the radiation diagram of the antenna according to the invention has no breakdown. This guarantees uniform illumination of a test specimen when the antenna according to the invention is used, for example, as a measuring antenna in an EMC (electromagnetic compatibility) laboratory. 
     In addition, it is of advantage if the profile of the antenna gain in dependence upon the frequency is relatively smooth. The user of the antenna according to the invention is thereby able to estimate or calculate the field strengths more easily. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplified embodiments of the present antenna according to the invention will be described below. Both the structure and also the mode of operation of the horn antenna, and also its other advantages, can be best understood with the aid of the following description, in conjunction with the appertaining drawings, in which: 
         FIG. 1  shows a side view, in perspective, of a first exemplified embodiment of the antenna according to the invention, from above; 
         FIG. 2  shows a front view of the exemplified embodiment of the antenna according to the invention, with the preferred dimensions; 
         FIG. 3  shows a side view of one fin of the exemplified embodiment of the antenna according to the invention, and the essential preferred dimensions; 
         FIG. 4  shows a plan view of one side wall of the antenna according to the invention, with a cutout and the preferred dimensions; 
         FIG. 5  shows, in an enlarged representation, a region which is marked by V in  FIG. 4 ; 
         FIG. 6  shows an antenna according to the prior art, without a cutout; 
         FIG. 7  shows a frontal view, in perspective, of a second exemplified embodiment of the antenna according to the invention; 
         FIG. 8   a  shows a profile of the antenna gain in dependence upon the frequency used, in the case of a conventional antenna; 
         FIG. 8   b  shows a profile of the antenna gain in dependence upon the frequency used, in the case of one exemplified embodiment of the antenna according to the invention; 
         FIG. 9   a  shows a profile of the VSWR (voltage standing wave ratio) in dependence upon the frequency used, in the case of a conventional antenna; 
         FIG. 9   b  shows a profile of the VSWR (voltage standing wave ratio) in dependence upon the frequency used, in the case of one exemplified embodiment of the antenna according to the invention; 
         FIG. 10   a  shows a radiation diagram of an antenna according to the invention at a frequency of 14.03 GHz; and 
         FIG. 10   b  shows a radiation diagram of an antenna according to the invention at a frequency of 17.526 GHz. 
     
    
    
     DETAILED DESCRIPTION 
     In all the figures, parts that correspond to one another are provided with the same reference symbols. 
       FIG. 1  shows a side view, in perspective, of a first exemplified embodiment of the antenna  1  according to the invention, from above. The horn funnel  4  of the antenna  1  according to the invention consists of four side walls  3   a ,  3   b ,  3   c ,  3   d , two opposed side walls  3   a ,  3   b  each having a cutout  7   a ,  7   b  through which one of the two fins  5   a ,  5   b  extends in each case. Disposed at the narrow end  6  of the horn funnel  4 , which funnel is dimensioned, above all, as a reflector at lower frequencies, is the decoupling or coupling apparatus  2   a ,  2   b , the side walls  3   a ,  3   b ,  3   c ,  3   d  being fastened thereto via a folded edge  17  by means of a number of screws  18  or rivets. In this first exemplified embodiment, the decoupling apparatus  2   a  and the coupling apparatus  2   b  are integrated in an overall casing  2 . A flange  19  with a coaxial plug  20  is fastened, preferably by means of screws  18 , to a side wall of the decoupling or coupling apparatus  2   a ,  2   b . This coaxial plug  20  serves to feed in high-frequency electromagnetic waves via a coaxial cable, or to conduct out, via said coaxial cable, high-frequency electromagnetic waves that have been received. A matching circuit may also be accommodated in the casing  2 , so that the horn antenna  1  according to the invention can be operated at very much lower frequencies in spite of an unfavorable VSWR with values between 2 and 3. 
       FIG. 2  shows a front view of the first exemplified embodiment of the antenna  1  according to the invention, with the preferred dimensions. The two fins  5   a ,  5   b  together have a maximum overall length  11  within the range from 200 mm to 400 mm for example, and preferably, in the exemplified embodiment, an overall length  11  of about 303 mm. 
     A broad edge  14   a ,  14   b  of a first side wall  3   a  and a second side wall  3   b  at an opening  10  of the horn funnel  4  has a length  23  within the range from 50 mm to 150 mm for example, and preferably, in the exemplified embodiment, a length of about 105 mm, and delimits the cutout  7   a.    
     A broad edge  12  of a third side wall  3   c  and a fourth side wall  3   d  at an opening  10  of the horn funnel  4  has a length  24  within the range from 50 mm to 150 mm for example, and preferably, in the exemplified embodiment, a length of 100 mm. 
     A length of the decoupling apparatus  2   a  or of the coupling apparatus  2   b  that corresponds to the overall length  25  of a narrow edge  13  of the first side wall  3   a  and of the second side wall  3   b  at the narrow end  6  of the horn funnel  4 , lies within the range from 50 mm to 150 mm, for example, the length which is preferred in the exemplified embodiment being about 87 mm. 
     Each cutout  7   a ,  7   b , which is substantially trapezoidal in the exemplified embodiment, has a longitudinal axis of symmetry  8  in each case, so that symmetrical fastening of the side walls  3   a ,  3   b  to the decoupling or coupling apparatus  2   a ,  2   b  is easily possible. 
     A length of the decoupling apparatus  2   a  or of the coupling apparatus  2   b  that corresponds to the overall length  26  of a narrow edge  28  of the third side wall  3   c  and of the fourth side wall  3   d  at the narrow end  6  of the horn funnel  4 , lies within the range from 50 mm to 100 mm, for example, the preferred length in the exemplified embodiment being about 66 mm. 
     The distance  15  of the two fins  5   a ,  5   b  from, in each case, an edge  30  of a first and second side wall  3   a ,  3   b  respectively, at the outermost rim of the opening  10  of the horn funnel  4  lies, for example, within the range from 25 mm to 35 mm, the distance which is preferred in the exemplified embodiment being about 30 mm. 
     A thickness  29  of the fins  5   a ,  5   b  lies, for example, in the range between 5 mm and 15 mm, the thickness or the gauge of material which is preferred in the exemplified embodiment being about 9 mm. 
     An absorber  40 , which is made, for example, of a carbon-containing foam material and which damps the reflections of the electromagnetic radiation radiated or received, is preferably located in the center of the narrow end  6  of the horn funnel  4 , or inside the casing  2  disposed thereon. 
       FIG. 3  shows a side view of a fin  5   a  of the antenna  1  according to the invention, and its essential preferred dimensions. The overall length  31  of a fin  5   a , which corresponds to the length of the section SF, lies within the range from 150 mm to 200 mm for example, but is preferably 172 mm. The first height  16  of the fin  5   a , which corresponds to the section GB, lies within the range from 100 mm to 200 mm, but the height  16  which is preferred in the exemplified embodiment is about 151.5 mm, the point B lying at a rounded-off end  9  of said fin  5   a . The distance  32  of the point A from the point F, which distance corresponds to a second height  32  of the fin  5   a , lies within the range from 100 mm to 150 mm for example, the preferred length being about 120 mm. The angle α about the vertex S lies within the range 45° to 55° for example, the preferred angle in the exemplified embodiment being about 50.5°. The angle β about the vertex S lies within the range 30° to 40°, the preferred angle in the exemplified embodiment being about 35°. The section SG, which corresponds to a boundary section  33  of the fin  5   a , has a length which lies within the range from 100 mm to 150 mm for example. Its length which is preferred in the exemplified embodiment is about 125 mm. 
       FIG. 4  shows a plan view, onto the antenna, of a first side wall  3   a  with a cutout  7   a , and also shows the preferred dimensions of the antenna  1  according to the invention, a third height  34  of the fin  5   a  with respect to a base region  37  of the coupling or decoupling apparatus  2   a ,  2   b  lying within a range from 150 mm to 200 mm for example, and preferably being about 172 mm in the exemplified embodiment. The height  35  of the horn funnel  4  in the longitudinal direction of the antenna lies within a range from 100 mm to 150 mm for example, the height which is preferred in the exemplified embodiment being about 120 mm. Moreover, it can be inferred, from  FIG. 4  as well as from  FIG. 2 , that the horn funnel  4 , and in particular its lateral edge  30 , is at an increasing distance from the fin  5   a ,  5   b . In the exemplified embodiment, this distance lies in the region of about 4 mm in the base region  37  of the fin  5   a ,  5   b  and about 30 mm at the rim of the opening  10  of the horn funnel  4 . 
       FIG. 5  shows, in an enlarged representation, a region which is marked by V in  FIG. 4 . The distance  36  of the folded edge  17  for fastening the side walls  3   a ,  3   b ,  3   c ,  3   d , and in particular the first side wall  3   a  and second side wall  3   b  of the horn funnel  4 , from the base region  37  of the fin  5   a  lies, for example, within the range from 2 mm to 6 mm in each case, the distance which is preferred in the exemplified embodiment being about 4 mm. 
       FIG. 6  shows an antenna according to the prior art without a cutout in the region of the two fins  5   a ,  5   b , the connecting bars  3   c ,  3   d  being optional. It can be clearly seen that the two fins  5   a ,  5   b  do not project beyond the side walls  3   a ,  3   b . Furthermore, the ends of the two fins  5   a ,  5   b  terminate with the opening  10  of the horn funnel  4 . 
       FIG. 7  shows a frontal view, in perspective, of a second exemplified embodiment of the antenna  1  according to the invention with a cutout  7   a ,  7   b  in each of the two side walls  3   a ,  3   b , the measurements of the area of said cutout  7   a ,  7   b  being such, in each case, that the two fins  5   a ,  5   b  are able to project beyond the said side walls  3   a ,  3   b.    
     A first part  21  of the two fins  5   a ,  5   b  which is smaller in each case, area-wise, projects beyond the side walls  3   a ,  3   b , in each case, that form the horn funnel  4 . A second part  22  of said two fins  5   a ,  5   b  which is larger, area-wise, is disposed inside the horn funnel  4  in each case. 
       FIG. 8   a  shows a profile of the antenna gain (in dB) in dependence upon the frequency used (in GHz), in the case of a conventional antenna according to  FIG. 6 . It can be clearly seen that the antenna gain breaks down at an operating frequency between 14 GHz and 15 GHz. 
       FIG. 8   b  shows a profile of the antenna gain (in dB) in dependence upon the frequency used (in GHz), in the case of an exemplified embodiment of the antenna according to the invention, the said profile displaying no breakdown in the abovementioned frequency range. In addition to this, it can be seen that the profile of this curve is subject to only minor fluctuations, so that the said curve extends in a smoother manner, compared to the curve shown in  FIG. 8   a.    
       FIG. 9   a  shows a profile of the VSWR (voltage standing wave ratio) in dependence upon the frequency used, in the case of a conventional antenna according to  FIG. 6 , and  FIG. 9   b  shows a profile of the VSWR (voltage standing wave ratio) in dependence upon the frequency used, in the case of an exemplified embodiment of the antenna according to the invention. It can be clearly seen that the antenna according to the invention has a more favorable standing wave ratio in the frequency range from 1 GHz to about 5 GHz. This guarantees that the antenna according to the invention can be operated with greater efficiency in this frequency range. 
       FIG. 10   a  shows a radiation diagram of an antenna according to the invention at a frequency of 14.03 GHz. Under these circumstances, only a slight breakdown  38  in the intensity distribution  39  of the electrical field can be seen at 90°. This represents a marked improvement compared to the prior art, since this breakdown  38  is more markedly pronounced in the case of a conventional antenna according to  FIG. 6 , in the case of which it can be several dB. 
       FIG. 10   b  shows a radiation diagram of an antenna according to the invention at a frequency of 17.526 GHz. The breakdown  38  shown in  FIG. 10   a  scarcely remains pronounced in the intensity distribution  39  of the electrical field in this radiation diagram. 
     The invention is not restricted to the exemplified embodiments represented in the drawings, and particularly not to an antenna in a laboratory operation. All the features described above and/or represented in the drawings can be combined with one another in any desired manner.