Abstract:
A modular antenna has a primary radiating aperture which can either be an array of radiating elements or a passive reflector. In regards to the array of radiating elements, a feed network interfaces with the radiating elements to form the modular antenna array. The feed network has a number of output ports wherein each output port of the feed network is adapted to interface with each feed port of the radiating elements. The feed network can be placed at various locations along the antenna array to change to radiation characteristics of the antenna array. When passive reflector is used, a modular feed interfaces with the waveguide. The feed module controls the sector radiation pattern. The vertical reflector surface controls the elevation radiation pattern. The feed module can consist either of an antenna array or a single element utilizing beam shaping.

Description:
FIELD OF THE INVENTION 
     This invention relates to sector antennas, but more particularly to a sector antenna which can make use of various beam forming modules wherein the physical antenna aperture remains the same, while the beam forming module can vary to give the required beam width. 
     BACKGROUND OF THE INVENTION 
     Wireless transmission systems that make use of basestation antennas are configured according to the customer and network requirements. In particular, fixed broadband wireless networks which operate within a range of frequencies on different frequency bands can make use of several different types of antennas to enable the transmission and reception of the radio signals between various sites. Although a fixed wireless system may operate on as few as three different frequency bands, a system which may need to operate on a few different polarization scheme may require as many as 60 different antennas. 
     The problem associated with previous antenna designs is that if a different radiation pattern is required, a new antenna would have to be selected to provide this radiation pattern. Since multiple radiation patterns may be required in a multiband wireless network, several different types of antennas will be required thereby increasing the infrastructure cost of the network. In addition, once the antenna is installed in the field, there is very little flexibility which permit the modification of the radiation pattern without having to change the entire antenna. 
     For example, within each frequency band an antenna operating within say, a 90, 60, 45, 30 and 15 degree sector may be required. Since the system may require horizontally and vertically polarized antennas, many different styles of antennas are required. 
     A need therefore exists for a modular antenna which can overcome the problems associated with the prior art antennas. In particular, a need exists for an antenna arrangement which can be modified to change the beamwidth capability of the antenna without having to change the physical antenna aperture portion of the antenna. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided a modular antenna comprising an antenna panel having a number of antenna radiating elements forming an array, each radiating element having a feed port. A feed network interfaces with the radiating elements to form the modular antenna array. The feed network has a number of output ports, each output port of the feed network being adapted to interface with each feed port of the radiating elements. 
     The advantages of using the modular antenna of the present invention is that one antenna can be used in many different applications offering different radiation patterns. For volume manufacturing, only one antenna is required to be manufactured. The modular array provides flexibility by enabling a new module to be interfaced with the array to change the radiation pattern without having to disassemble the radio. In another embodiment, an active module can be used to dynamically modify the radiation pattern of the array. 
     The use of the array of antenna elements of the present invention permits the shaping of the beam into many different types of radiation patterns by adjusting the amplitude weighting of the elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustration of a polarized sectional antenna according to the prior art; 
     FIGS. 2 a ,  2   b  and  2   c  are front, cross-sectional top and back views respectively of an antenna panel according to a first embodiment of the present invention; 
     FIGS. 3 a ,  3   b  and  3   c  are front, top and back views respectively of the phase and power distribution module for use with the antenna panel of FIGS. 2 a ,  2   b  and  2   c;    
     FIGS. 4 a  and  4   b  are top and side views of the combination antenna panel and power distribution module of the present invention; 
     FIG. 5 is a diagram illustrating a power distribution module according to one embodiment of the invention; 
     FIG. 6 is a diagram illustrating a power distribution module according to another embodiment of the invention; 
     FIG. 7 is a diagram illustrating a power distribution module according to yet another embodiment of the invention; 
     FIGS. 8 a ,  8   b  &amp;  8   c  are front, side and rear views, respectively of a panel array antenna according to another embodiment of the invention; and 
     FIGS. 9 a  and  9   b  are front and side views, respectively of a power distribution network according to yet another embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, we have shown a diagram illustrating a polarized sectored antenna according to the prior art. This particular antenna design offers a 90° sector radiation pattern which is either vertically or horizontally polarized. If a different polarization pattern is required, a different type of antenna will be required. 
     With reference to FIG. 2 a , we have shown a front view of an antenna element panel according to the first embodiment of the present invention. The antenna element panel  20  comprises a plurality of antenna elements  21  laid out to radiate vertically and horizontally in a matrix to form the array. In the embodiment depicted in FIG. 2 a , the first two rows of antenna elements provide horizontally polarized radiators. Each antenna element  21  includes a horizontal feed port  22  thereby polarizing the transmitted/received signal horizontally. The last two rows of antenna elements provide vertical polarization to the transmitted/received signal. The antenna elements  23  are each provided with a vertical feed port  24 . A cross-sectional top view of the panel is illustrated in FIG. 2 b . This top view shows the arrangement of antenna elements  21  having horizontal feed ports  22 . 
     Although the radiating elements illustrated in FIGS. 2 a  and  2   b  are comprised of horn elements, the antenna array of the present invention can also make use of lens or printed radiating elements. Similarly, circularly polarized elements can also be used instead of linearly polarized elements. 
     Referring now to FIG. 2 c , we have shown a back view of the antenna element panel of FIG. 2 a . One side of the antenna panel as illustrated in FIG. 2 a  consists of radiating elements and the other side of the panel as illustrated in FIG. 2 c  contains the feed ports of the radiating elements. As indicated above, the first two rows of radiating elements provide horizontal polarization and the last two rows of radiating elements provide vertical polarization. This is achieved using a horizontal feed port  22  for each of the radiating element of the first two rows and a vertical feed port  24  for each radiating element of the bottom two rows of the array. Each row of radiating elements is provided with a number of alignment dowel pins  26  to enable the alignment of feed network modules (not shown) when the modules are secured to the back of the antenna element panel. 
     Referring now to FIGS. 3 a ,  3   b  and  3   c , we have shown a front, top and back view respectively of the phase and power distribution module of the present invention. As indicated earlier, the power distribution module is used in conjunction with the antenna element panel of FIGS. 2 a ,  2   b  and  2   c . Each module is provided with a series of output ports adapted to mate with the feed port of each antenna element. A corresponding number of dowel pin receptacles  31  are provided on the front of the module to enable easy and quick installation of the module on the back of the antenna panel. The module can thus be moved vertically along the back of the panel to provide the required radiation pattern. The module is assembled from two parts. A cover  32  and a base portion  33  into which is formed the power distribution network  34  shown in a dotted line in FIG. 3 b . The power distribution network  34  enables a signal coming in at an input port  35  to be equally distributed among a number of output ports  30 . This is achieved by means of one or more transmission lines which, in this embodiment, act as a waveguide. As will be shown further below, variations of the output signal can be achieved by changing the distribution pattern of the network. As indicated earlier, each output port is adapted to mate with a feed port of an antenna element to provide the required radiation pattern. The module, and in particular the power distribution network, can either be molded into the base portion  33  or designed as a printed structure on the surface of the base portion  33 . The back view is shown in FIG. 3 c.    
     In combination, the antenna panel and module are set up as illustrated in FIG. 4 a , which is a top view of the panel/module combination. The antenna panel is illustrated at reference numeral  40  and the module at reference numeral  41 . As indicated earlier, the panel  40  and module  41  are quickly aligned by means of dowel pins and receptacles. This enables the proper alignment of the module output ports  30  and the antenna panel feed ports  42  which depending on the alignment of the module along the panel can either be a horizontal feed port or a vertical feed port as shown in FIG. 2 c.    
     A side view of the panel module combination is illustrated in FIG. 4 b . In this embodiment, a first and second module  43  and  44  respectively are disposed on the first two rows of radiating elements to provide a horizontal/horizontal module configuration. In this configuration, a horizontally/horizontally polarized radiation pattern is provided from the antenna array. Similarly, the first and second module  43  and  44  can be lowered by one row to provide a horizontal/vertical module configuration wherein the radiation pattern is horizontally/vertically polarized. 
     A vertically/vertically polarized radiation pattern can be also be obtained by lowering the first and second modules to the last two rows of the array  45  and  46  to the vertical/vertical module configuration shown in FIG. 4 b.    
     Referring now to FIG. 5, we have shown the power distribution network of FIG. 3 b . In particular, as indicated previously, the power distribution network  34  which when provided with a predetermined number of transmission lines forming a predetermined pattern can give a normalized signal at each output port. For example, given an input signal at input port  35 , a normalized output amplitude is provided at the six (6) output ports  30 . Thus, assuming we have an input signal of the order of 6 watts at input port  35 , each output port  30  will produce a normalized output signal equal to ⅙ of the amplitude of the input signal, i.e. 1 watt. 
     Referring now to FIG. 6, we have shown another power distribution network  50  wherein the output amplitude at each output port is varied by introducing a different power distribution pattern. In this embodiment, the first two output ports  51  and  52  will provide an output which is half of the output of the third and fourth output ports  53  and  54  respectively. Similarly, the last two output ports  55  and  56  will also provide an output amplitude which is half of the third and fourth  53  and  54 . Thus, the power distribution can be changed by making use of power dividers. Power dividers can be used to give a balanced or unbalanced power division. For example, in order to obtain a balanced power division network, an input signal is divided into two even amplitudes by splitting the output transmission line. On the other hand an unbalanced power division network is accomplished by dividing the distributing network such that one transmission line is split a second time for example, whereas the first one isn&#39;t. We can therefore achieve an unbalanced power division network. For example, as shown in FIG. 6, what would normally be the first output port  57  is split to two output ports  51  and  52 , whereas output port  53  remains unchanged. Thus in the example given above, wherein an input signal of the order of 6 watts is provided at the input port  58 , the resulting output power at each of the output ports will vary according to the power division provided by the power distribution network. In particular, in FIG. 6, output ports  51  and  52  will provide an output of ¾ of a watt, output ports  53  &amp;  54  will provide an output power of 1.5 watts and output ports  55  and  56  will provide output power of ¾ of a watt each. 
     Referring now to FIG. 7, we shown yet another power distribution network wherein a phase shift of an input signal is achieved at the output. A change in phase at an output port can be provided by varying the length of the transmission line which carries the signal. For example, a 180 degree phase change can be obtained by varying the length of the output transmission line by λ/2 wherein λ is equal to c/f and c is the speed of light and f is the frequency of the input signal. Thus in the power distribution network of FIG. 7, a signal provided at the input port  60  having a predetermined phase will be modified at output port  61  by the introduction of a transmission line  62  which is of greater length than transmission line  63 . Thus, even though the output signal of transmission lines  62  and  63  will have the same output amplitude, these signals will have different phase shifts. 
     Referring now to FIG. 8 a , we have shown a front view of an antenna element panel with a printed antenna array and horizontal and vertical polarized antenna elements. Horizontal polarization is provided by means of horizontal antenna array elements  70  and horizontal feed port which is shown in the form of an aperture-coupled slot  71 . Similarly, vertical polarization is provided by means of vertical antenna array elements  72  and vertical feed ports, again in the form of an aperture-coupled slot  73 . As shown in FIG. 8 b , the printed antenna array is formed by placing the antenna elements  74  on a microstrip substrate  75 . FIG. 8 c  is a rear view of the antenna element panel of FIG. 8 a . The antenna element panel is shown with a ground plane  76  and horizontal and vertical feed ports  71  and  73  respectively. As discussed earlier, alignment dowel pins  77  are provided to enable the placement of the feed network modules. 
     In operation, the antenna elements are energized by a feed network which electromagnetically couples slots  71  and  73  in the ground plane  76 . As illustrated in FIG. 8 a  and  8   c , one side of the antenna panel consists of radiating elements and the other side contains the radiating elements feed ports. The placement of the feed network modules on the antenna panel will determine how the output radiation pattern is polarized. 
     Referring now to FIG. 9 a , we have shown a side view of a phase and power distribution module according to another embodiment of the invention. The module is a printed structure having a microstrip substrate  80 , a radome cover  81  and input port  82 . In the embodiment of FIG. 9 a  and  9   b , the distribution module makes use of microstrip transmission lines. The module electro-magnetically couples to the antenna through slot coupling  82 . The module is a power/phase distribution network. Microwave energy is input into the module and the appropriate amplitude/phase is distributed to the output ports. The dowel pin holes  83  interface with the dowel pins of the antenna panel. 
     As indicated previously, the advantages of using the modular antenna of the present invention is that one antenna can be used in many different applications by simply aligning the module to the antenna ports offering the required polarization pattern. Since only one antenna is required to be manufactured, there is considerable cost savings in simply exchanging a module without having to modify the array.