Abstract:
The present invention provides a support for an antenna. In particular, the present invention provides a substrate with conductive transition pads for a co-linear coaxial antenna array. The transition pads are constructed and arranged to properly provide power and phase shifting to the antenna array.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/390,947, filed Jun. 24, 2002, titled OMNI-DIRECTIONAL ANTENNA ARRAYS AND METHODS OF MAKING THE SAME. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to antenna arrays and, more particularly, to omni-directional antenna arrays. 
     BACKGROUND OF THE INVENTION 
     Radio frequency antennas are often designed as arrays to provide sufficient gain. The power feed network associated with antenna arrays, however, is often complex. The power feed network is complex because antenna pattern and gain depend on physical and network parameters. Some physical parameters include the number of elements and their spacing. Some feed network parameters include the phase and amplitude of the power signal at each of the antenna feeds as well as the impedance of the feed network delivering the power. 
     One omni-directional antenna array that has a relatively non-complex feed network is a co-linear coaxial antenna array. FIG. 1 shows a conventional co-linear coaxial (COCO) antenna array  100 . COCO antenna  100  comprises a feed coax cable section  102 , a plurality of coax cable sections  104 , and a termination coax cable section  106 . Connecting each section of coax  102 ,  104 , and  106  is a wire pair  108 . Wire pair  108  includes a center wire to shield wire  108   a  and a shield wire to center wire  108   b . A power feed  110  is connected between feed coax cable section  102  and the first of the plurality of coax cable sections  104 . Power feed  110  has a connection  110   a  to the shield of feed coax cable section  102  and a connection  110   b  to the shield of the first of the plurality of coax cable sections  104 . Connection  110   a  runs to a short connection  112  internal to feed coax cable section  102 , which also connects power to the center wire  114  of feed coax cable section  102 . Termination coax cable section  106  similarly has a center wire  116  connected to a short  118 . Other than the power feed  110  connection, feed coax cable section  102  and termination coax cable section  106  are images of each other. (Notice, determining lengths of the coaxial cable and other dimensions of the COCO antenna  100  are well known in the art and will not be explained further herein.) 
     The coax cable can be any conventional coax cable such as 50 ohm or 75 ohm coax cable. The coax cable can be flexible or in a semi-rigid sheath. Using 50 ohm cable, a ¼ wave transformer may be needed in the power feed coax cable section  110 . The cable sections  102 ,  104 , and  106  are stripped and soldered to wire pairs  108  to make the connections. Moreover, the shorts  112  and  118  are located and soldered. The above example, and the description of the present invention, below, relate to conventional 50 ohm coax cable, but one of skill in the art would recognize other cable or radiating elements are possible. 
     The COCO antenna  100  provides an omni-directional RF antenna with a good power gain for lower frequency operation. However, the conventional COCO antenna  100 , explained above, has several problems. The problems include: the construct is fragile, the electrical connections have defects, the solder placement lacks consistency, and the coax stripping is inconsistent. In general, the conventional COCO antenna  100  has a minimum error associated with its construction and handling the assembly is difficult. While these manufacturing and assembly errors can be tolerated at lower operating frequencies, at higher frequencies, such as the 5 GHz range, the errors become prohibitive. The prohibitive nature of the errors is due, in part, to the smaller lengths of coax and wires used. As the frequency increases, the wavelength, and the lengths of each section decrease. The smaller lengths of wire make the errors relatively higher, causing unacceptable degradation of the antenna pattern and gain. Also, the fragile nature of the conventional COCO antenna (coax cable sections soldered together) makes handling and assembly of the construct difficult if not prohibitive. 
     Thus, it would be desirous to provide a COCO antenna that had lower errors and was less fragile. 
     SUMMARY OF THE INVENTION 
     To attain the advantages of and in accordance with the purpose of the present invention, a support for an omni-directional antenna is provided. The support comprises a substrate with pre-placed transition pads and a feed pad. Coaxial cable could be soldered to the transition pads to form a co-linear coaxial antenna array. 
     The present invention further provides methods for designing the support including arrangement of transition pads on a substrate. A feed transition pad is also arranged on the substrate. Coaxial cable attached to the substrate at the transition pads would form a co-linear coaxial antenna array. 
     The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects and advantages of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
     FIG. 1 is a conventional co-linear coaxial antenna construct; 
     FIG. 2A is a top side plan view of a baseboard in accordance with the present invention; 
     FIG. 2B is a side elevation view of the baseboard of FIG. 2A; 
     FIG. 2C is a bottom side plan view of the baseboard of FIG. 2A; 
     FIG. 3 is shows a transition pad of FIG. 2A in more detail; 
     FIG. 4 is illustrative of connecting downstream coaxial cable and upstream coaxial cable using the transition pad of FIG. 3; 
     FIG. 5A is a top side plan view of a power feed in accordance with the present invention; 
     FIG. 5B is a side elevation view of the power feed of FIG. 5A; 
     FIG. 5C is a bottom side plan view of the power feed of FIG. 5A; 
     FIG. 6 is illustrative of connecting a downstream coaxial cable to a power feed shown in FIG. 5A; 
     FIG. 7 is illustrative of connecting a power feed cable in accordance with the present invention, and 
     FIG. 8 is a flowchart illustrative of a method of making omni-directional antenna arrays in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 2-8 and the following paragraphs describe some embodiments of the present invention. Like reference characters are used wherever possible to identify like components or blocks to simplify the description of the various subcomponents described herein. More particularly, the present invention is described in relation to a co-linear coaxial antenna, however, one of ordinary skill in the art will understand other antenna arrays are possible without departing from the spirit and scope of the present invention. 
     Referring to FIGS. 2A,  2 B, and  2 C, a co-linear coaxial antenna baseboard  200  exemplary of the present invention is shown. FIG. 2A shows a top side plan view of baseboard  200 . FIG. 2B shows a side elevation view of baseboard  200 . FIG. 2C shows a bottom side plan view of baseboard  200 . Baseboard  200  includes a substrate  202  having a plurality of transition pads  204 . Substrate  202  can be any non-conductive substrate, but it has been found conventional printed circuit board substrates work well. Transition pads  204  are generally a conductive material, such as copper. Transition pads  204  will be explained further below with reference to FIG.  3 . Baseboard  200  also includes a feed pad  524 , a feed cable connector  522 , and a ground plane  504 . Feed pad  524 , connector  522 , and ground plane  504  will be explained further below with reference to FIGS. 5A,  5 B, and  5 C. 
     Connecting coaxial cable to the transition pads  204  will be explained with reference to FIGS. 3 and 4. FIG. 3 shows one transition pad  204  in more detail. Transition pad  204  includes two center wire connections  302  and  304  and two shield connections  306  and  308 . A Transition connection  310  connects center wire connection  302  and shield connection  306  and a transition connection  312  connects center wire connection  304  and shield connection  308 . 
     Referring now to FIG. 4, transition pad  204  is connected to downstream coaxial cable  410  and upstream coaxial cable  420 . Downstream coaxial cable  410  has a jacket  412 , a shield (or braid)  414 , an insulator  416 , and a center wire  418 . Similarly, upstream coaxial cable  420  has a jacket  422 , a shield  424 , an insulator  426 , and a center wire  428 . Center wire  418  is soldered (or otherwise electrically coupled) to center wire connection  304  and shield  414  is soldered to shield connection  306 . Center wire  428  is connected to center wire connection  302  and shield  424  is connected to shield connection  308 . In this configuration, downstream coaxial cable  410  has its center wire  418  electrically coupled to shield  424  of upstream coaxial cable  420 . Similarly, downstream coaxial cable  410  has its shield  414  electrically coupled to center wire  428  of upstream coaxial cable  420 . 
     As shown in FIG. 4, the placement of center wires  418  and  428  do not need to be perfectly placed prior to soldering the wires to center wire connections  304  and  302 . Also, shields  414  and  424  do not need to be perfectly placed prior to soldering the shields to shield connections  306  and  308 . Moreover, because the transition pads  204  can be placed with a degree of accuracy, because some of the human factors errors associated with soldering the downstream cable to the upstream cable are removed, and because some of the error associated with stripping the coaxial cable is removed, using the baseboard  200  allows manufacturing co-linear coaxial antenna arrays that can be used at higher frequencies, such as the 5 GHz range. 
     While transition pad  204  is shown using generally rectangular portions, the geometric configuration of the transition pad is largely a matter of design choice. In other words, the connections could be round, elliptical, square, triangular, or a combination of multiple or random shapes. For example, connection  304  is shown having a dimple  430  (which could also be a slot, a groove, a semi-circle, or the like) located substantially adjacent where center wire  428  connects to center wire connection  302  to allow for more or less overhang to accommodate for machine stripping tolerances, human error relating to center wire  428  placement, or the like. Further, the gaps between the conductive pads can be widened or narrowed to accommodate errors in placement, stripping or the like. 
     Although transition pads  204  have been described as being used to solder coaxial cables  410  and  420  and the like, it is possible to connect the coaxial cables at transitions  204  using other means, such as coaxial connectors, press-in connections, adhesives, or other means, while still maintaining the intent of the present invention. 
     FIGS. 5A,  5 B, and  5 C illustrate a power feed  500  for the omni-directional antenna array described above. FIG. 5A shows a top side plan view of power feed  500  on baseboard  200 . FIG. 5B shows a side elevation view of the power feed  500  on baseboard  200 . FIG. 5C shows a bottom side plan view of power feed  500  on baseboard  200 . FIG. 5A further shows power feed  500  comprises a feed transition pad  502 , a ground plane  504 , and two vias  506  and  508 . Feed transition pad  502  has ¼ wave transformer connection  510  and shield connection  512  connected by feed connection  514 . ¼ wave transformer connection  510  includes via  508 . Power feed  500  further comprises a ground  516  connected to ground plane  504  by ground connection  518 . 
     FIG. 5C shows the bottom side plan view of power feed  500 . The bottom side of power feed  500  includes the vias  506  and  508 . Via  508  is connected to a ¼ wave transformer  520  to match the 50 ohm coaxial cable used in the omni-directional antenna array, although one of skill in the art would recognize on reading the disclosure other coaxial cable, the most common of which are 50 ohm and 75 ohm coaxial cable, could be used. ¼ wave transformer  520  is any conductive material, but generally is constructed of the same material as the transition pads  204 . Via  506  is connected to connector  522 . Connector  522  provides a mechanism to attach a power feed (not specifically shown in FIG. 5C, but shown in FIG. 7) to the omni-direction antenna array. 
     FIG. 6 shows connecting the omni-directional antenna array to feed transition pad  502 . FIG. 6 shows coaxial cable  550  having a jacket  552 , a shield  554 , an insulator  556 , and a center wire  558 . The center wire  558  is connected to ground  516 , which in turn is connected to the ground plane  504  by ground connection  518 . Shield  554  is connected to shield connection  512 , which in turn is connected to ¼ wavelength transformer  520  through feed connection  514  and ¼ wave transformer connection  510 . The same comments given above regarding transition pad  204  about the geometry, shape, and benefits of the present invention at the point the coaxial cable is attached, apply equally to feed transition pad  502 . 
     FIG. 7 illustrates connecting a power feed cable  700  to the omni-directional antenna array. Power feed cable  700  includes a jacket  702 , a shield  704 , an insulator  706  and a feed center wire  708 . Feed center wire  708  is attached to ¼ wave transformer connection  524 , which connects to ¼ wave transformer  520 , which connects to ¼ wavelength transformer connection  510  and shield  554  through via  508 . Feed shield  704  connects to ground plane  504  through via  506 , which connects to center wire  558  through ground  516 . 
     Notice that while FIG. 7 shows providing the power feed using a feed cable  700 , other means of feeding the array are possible as would be evident to one skilled in the art. For example, a coaxial connector could be attached to ¼ wavelength transformer  520  and ground plane  522 , using suitable geometry. Other means, including capacitively coupled feeds are possible and may be envisioned by one skilled in the art. 
     FIG. 8 is a flowchart  800  illustrative of a method of making an omni-directional antenna array in accordance with the present invention. While other transmission line elements are possible, the flowchart assumes the use of coaxial cable. First, at least one transition pad is arranged on a top side of a substrate, step  802 . The ground plane and feed transition pad are arranged on the top side of the substrate, step  804 . The ¼ wavelength transformers and connector are arranged on the bottom side of the substrate, step  806 . Vias are provided from the ground plane to the connector and the ¼ wavelength transformer to the feed transition pad, step  808 . Notice, steps  802 ,  804 ,  806 , and  808  could be performed in numerous orders or performed substantially simultaneously. In other words, the order of steps  802 ,  804 ,  806 , and  808  should be considered exemplary and not limiting. 
     Once the baseboard is prepared, steps  802  through  808 , the omni-directional antenna array is built by, for example, cutting and stripping coaxial cable to the appropriate lengths, step  810 . Notice the coax could be cut and stripped before the baseboard is prepared. Next the stripped coaxial cable is placed on the baseboard and soldered (or otherwise electrically connected), as explained with reference to FIGS. 4 and 6, step  812 . Finally, the power cable is electrically connected, as explained with reference to FIG. 7, step  814 . 
     The conductive portions, such as transition pads  302 , can be placed on substrate  202  using any conventional attaching means. For example, the conductive portions can be built up on substrate  202  or etched away on substrate  202 . 
     While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the invention.