Patent Publication Number: US-11031698-B2

Title: Broad-band slot antenna covered on the rear side, and antenna groups comprising same

Description:
The invention concerns a broad-band slot antenna covered on the rear side, and antenna groups comprising the same. 
     Antenna systems according to the cavity back-end slot principle are known, which are usually accommodated in steel pipes with attached wings for graph generation and a GRP pipe for the radome with appropriate size. Modified T-Bar Fed slot antennas are known for example from the U.S. Pat. No. 4,101,900 A. Wideband slot antennas with low VSWR are known e.g. from the U.S. Pat. No. 6,150,988 A, and Wideband Cavity back-end antennas are known e.g., from the U.S. Pat. No. 7,339,541 B2. 
    
    
     
       In the following, preferred embodiments of the invention are explained in greater detail based on the attached drawing. It shows: 
         FIG. 1  a front view of the slot antenna according to an embodiment of the present invention. 
         FIG. 2  a top view of a cross-section by a slot antenna according to an embodiment of the present invention. 
         FIG. 3  a rear view of a group antenna, comprising two subgroups, each consisting of 2 slot antennas, according to an embodiment of the present invention. 
         FIG. 4  a feed element with single-sided slots according to an embodiment design of the present invention. 
         FIG. 5  a feed element with open slots on both sides according to an embodiment of the present invention. 
         FIG. 6 a    a 3D view of a slot antenna according to an embodiment of the present invention. 
         FIG. 6 b    an enlarged 3D view of a detail with the feed point according to an embodiment of the present invention. 
     
    
    
     In the following description of the figures, identical elements or functions are marked with the same reference characters. 
     As shown in the figures, the invention is designed as follows. 
     The invention replaces two columns of standard 8-unit fields, which usually cover the radiated area (HPBW˜160°). In contrast to the construction with 8-unit fields, the antenna system according to the invention is fully integrated with only the smallest space requirement. Components from mobile communications technology are used as radome, which are unusual in this type of construction in the radio antenna technology. For this frequency and performance range, the invention has an extraordinarily compact cross-section as well as a very flat one in respect to the ratio of width to depth. 
     In order to enable this flat design, the following construction elements were used in the proposed antenna system, i.e. these design criteria were specified:
         only the sides of the radiating elements of the antenna are used for supplying the transmission energy; a usually rear-mounted installation is waived,   the necessary parasitic elements are very close to the emitter,   a broad-band radiation of e.g. 470 to 790 MHz or other frequency ranges, depending on the application, is enabled by a special line shape with slots (T-bar fed slot),   the required power distributor is integrated longitudinally.       

     Advantages 
     
         
         
           
             low wind load due to compact dimensions, 
             low costs by using radomes from mobile communications technology, 
             simple installation by compact dimensions, as well as flat construction, 
             easy and convenient shipping by means of transport options in standard cartons instead of wooden crates or the like. 
           
         
       
    
       FIG. 1  shows an embodiment of a proposed slot antenna  100 . This comprises a circumferential housing wall  10 , a rear wall  11  connected to the housing wall  10 , a feed element  12  arranged within the housing formed from the housing wall  10  and the rear wall  11  with a feed point  101  for supplying the feed element  12 . The feed element  12  is electrically connected via two connecting points  121 ,  122 , opposite each other, to the housing wall  10 . More precisely, the connection points are located on a section of the housing wall  10 , on which the feed point  101  is not arranged. Furthermore, the feed element  12  is narrower at the connecting points  121 ,  122  than in the middle range between the connection points  121 ,  122 . The feed point  101  is located at the edge, thus a section near the housing wall  10  of the central area between the connection points  121 ,  122 , preferably In the extension of the maximum width BS of the feed element  12 . At the feed point  101  in the housing wall  10 , a conductor  200  can be connected for feeding the slot antenna  100  via an opening  101   a  corresponding to the feed point, as shown in  FIG. 2, 3 or 6   b . Furthermore, the feed element  12  has at least two slots  123 . 
     Advantageously, the feed element  12  shows approximately the shape of a parallelogram or a diamond, wherein the side opposite the feed point  101  is preferably flattened. Furthermore, the distance B from the bending edge M to the housing wall  10  on the side of the flattened area of the feed element  12  is greater than the distance A between the edge of the flattened area and the housing wall  10 , i.e. A&lt;B, wherein it is advantageous if A&lt;¼ B. The bending edge M is a line and/or edge extending approximately through the middle of the feed element  12  and substantially parallel to the flattened area. Approximately shall be understood here that the bending edge M extends with a deviation of 10-20%, but also more than 20%, of the width BS of the feed element  12 , measured on a (virtual) line at the widest area between feed point  101  and the opposite housing wall or flattened area. At the bending edge M, the part of the feed element  12  can be bent with the flattened area in the direction of the rear wall  11  of the housing, preferably at an angle of up to 30°. However, it may not be bent at all, then the bending angle would be 0°. 
     Furthermore, the conductor  200  connected to the feed point  101  is connected to the inner conductor of a plug-in connection  300  via an internal housing conductor  400 , as shown in  FIG. 2 or 3 . 
     Furthermore, the external conductor of the plug-in connection  300  is connected to the surrounding housing wall  10 . The housing wall  10  is preferably made from an electrically conductive or conducting material. 
     Furthermore, the feed element  12  is made from an electrically conductive or conducting material such as sheet metal or from an electrically conductive layer. The inner conductor  200  can be connected to the internal housing conductor  400  via an insulating disc. 
     Furthermore, the length AS of the feed element  12  is greater than 0.05 or 0.1 or 0.2 or 0.3 or 0.4 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9 or 1.0 or 1.2 or 1.5 or 2 wavelengths. Furthermore, the length AS of the feed element  12  is less than 0.05 or 0.1 or 0.2 or 0.3 or 0.4 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9 or 1.0 or 1.2 or 1.5 or 2 wavelengths. The length AS is advantageous greater than 0.3 and less than 2 wavelengths, further advantageous greater than 0.5 and less than 1.5 wavelengths. It is particularly advantageous for the length AS to be approximately equivalent to one wavelength. The wavelength refers to the medium frequency fm of the frequency range covered by the antenna. 
     Through the suitable selection of the size ratios of the components of the slot antenna  100  described above, a relative bandwidth Br of 50% can be achieved with a VSWR standing wave ratio of e.g. better than 1.1. Relative bandwidth B r  is calculated as follows: 
               B   r     =         f   o     -     f   u         f   m             
wherein
 
               f   m     =         f   o     +     f   u       2           
fo describes the upper operating frequency, fu the lower operating frequency, and fm represents the medium frequency.
 
     Furthermore, the (maximum) width BS of the feed element  12  is greater than 0.01 or 0.02 or 0.05 or 0.1 or 0.2 or 0.3 or 0.4 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9 or 1.0 wavelengths. Furthermore, the maximum width BS of the feed element  12  is smaller than 0.01 or 0.02 or 0.05 or 0.1 or 0.2 or 0.3 or 0.4 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9 or 1.0 wavelengths. The width BS is advantageously greater than 0.01 and smaller than 1 wavelength; further advantageous the width BS is greater than 0.1 and smaller than 0.5 wavelengths. The width BS=0.3×length AS is preferred. 
     In  FIG. 4  and  FIG. 5 , different embodiments of the slots  123  are shown, e.g., each slot  123  is open on one side, as shown in  FIG. 4 . Additionally, each slot  123  is open on both sides, as shown in  FIG. 5 . Alternatively, each slot  123  can be closed on both sides. The opening or openings are advantageously shown in the direction of the outside of the feed element  12 , i.e. the nearest housing wall  10 , as shown in the figures. The slots  123  of the feed element  12  and their adjacent areas  124  can have radii or curvatures. 
     Furthermore, the slots  123  in the areas, which lie closer to the connection points  121 ,  122 , form an angle W 1 , as shown in  FIG. 4  and  FIG. 5 . The angle W 1  is preferably measured between the inner edges of the outer sections of the slots  123 , but can also be measured between the outer edges of the outer sections of the slots  123 , since the slot  123  or the slot width is very low, so that no significant deviations result here. 
     In addition, the angle W 1  is smaller than 80°, 70°, 60°, 50°, 40°, 30°, in particular smaller than 65°. In addition, the angle W 1  is smaller than 80°, 70°, 60°, 50°, 40°, 30°, in particular smaller than 45°. The angle W 1  is preferably between 45° and 65°. 
     In addition, the slots  123  extend in the areas, which are each further distanced from the connecting points  121 ,  122 , essentially parallel to one another, as shown in  FIGS. 1, 4 and 5 . 
       FIG. 2  shows a cross section through a slot antenna  100  or a radome, wherein at least at one outer side, preferably at both outer sides, a covering longitudinal plate  104  is located, which, together with parts of the circumferential housing wall  10 , each defining in different areas respectively a free space for the wiring  102 . Here, the longer width BA 2  of the covering longitudinal plate  104  is greater than the shorter width BA 1  of the covering longitudinal plate  104 . 
     The covering longitudinal plate  104  comprises two sections AL 1  and AL 2 , which form a section of the covering longitudinal plate AL. The two sections are preferably formed from one piece, but have an angle in reference to one another. The section AL 1  of the covering longitudinal plate  104  forms an angle WA with the surrounding housing wall  10 , which ranges from 10° to 80°, preferably from 20° to 45°. 
     Preferably, the covering longitudinal plate  104  comprises a second section or section AL 2 , angled in reference to the first section AL 1 . The second section AL 2  can also have a curvature instead of an angle, which implies a kink. The covering longitudinal (sheet metal) plate  104  is made from an electrically conductive material as already indicated by the term sheet. 
     Preferably, the slot antenna contains at least two parasites, mirror-symmetrical to the middle of the antenna, wherein each parasitic shows a parasitic element  106 , which extends in a section P 1  essentially parallel to section AL 1  of the covering longitudinal plate  104 , or deviates slightly from being parallel, showing at an angle thereto, which is preferably smaller than ±10°, ±20°, ±30°. 
     Preferably, the parasitic element  106  comprises a section P 2  angled in the direction of the rear wall  11  or bent, preferably extending parallel to the rear wall  11 , which is formed such that the section P 1  is angular in reference thereto, meaning that sections P 1  and P 2  form an angle WP to each other. This angle WP ranges preferably from 100° to 150°. 
       FIG. 3  shows a rear view of a group antenna, comprising two subgroups  100   a ,  100   b , each consisting of at least two slot antennas  100  as described above and aligned serially along each other, with here serially meaning that the subgroups  100   a ,  100   b  each are connected with each other at the areas on which the connection points  121 ,  122  are located. In the profile of the housing wall  10 , an internal housing conductor  400 , which can consist of a different electrically conductive material than the housing, e.g. aluminum or silver-plated brass or copper or silver-plated or tin-plated copper, connects via an internal conductor  200  each the feed points  101  of two slot antennas  100  arranged serially using a plug-in connection  300  with a feed cable  500 . 
     In each of the subgroups  100   a ,  100   b , the inner conductor of a plug-in connection  300  is connected in the middle between the feed points  101  of the slot antennas  100  or at a predetermined offset V 1  from the middle between the feed points  101  of the slot antenna  100  to the internal housing conductor  400  in the profile via a feed cable  500 , in order to create a phase difference between the feed points  101  of the slot antenna  100  and a corresponding beam deflection, with the offset V 1  being less than 5%, 10%, or 20% of the length of the feed cable  500 . 
     The two feed cables  500  embodied as coaxial cables each extend through the free spaces for the wiring  102  of the slot antennas  100  and end in a distribution  600 , from which the group antenna is fed via a coaxial input  700 . The plug-in connection  300  between the inner conductor  400  and the cable  500  can also be designed as a fixed connection. 
     For illustration of the construction of a slot antenna  100  according to the invention,  FIG. 6 a    shows a 3D view of a slot antenna  100  according to an embodiment of the present invention, and  FIG. 6 b    shows an enlarged 3D view of a detail with the feed element  12  of the slot antenna  100 . Same reference characters as in the previous figures describe the identical elements. The description for this is discernible respectively from the previous descriptions. Alternatively, the feed element  12 , or parts thereof, as well as connecting lines such as the inner housing conductor  400  and the inner conductor of the plug-in connection  300  and the inner conductor  200  may be embodied as a conductive layer on a carrier like a circuit board.