Patent Document

This invention was made with Government support under Contract No. N00019-98-C-0003 awarded by the Department of the Navy. The Government has certain rights in this invention. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates to RF antennas, and more particularly to L-band antennas. 
     BACKGROUND OF THE INVENTION 
     Log-periodic antennas have been used for L-band applications, but are generally relatively large. Dipole stub antennas have also been used for certain L-band frequencies, but provide unsatisfactory performance at higher frequencies in the L-band range from 500 MHz to 2 GHz. 
     Bi-conical antennas have been employed for low frequency applications below L-band 
     It would therefore be advantageous to provide an L-band antenna which is relatively small and has good wide-band performance. 
     SUMMARY OF THE INVENTION 
     An L-band antenna is described, and includes a plurality of elongated radiating elements arranged in a conical configuration, the radiating elements having first and second ends, the first ends of the elements attached in a tapered fashion to provide a conductive tapered end. The tapered end is attached to a connector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     These and other features and advantages of the present invention will become more apparent from the following detailed description of an exemplary embodiment thereof, as illustrated in the accompanying drawings, in which: 
     FIG. 1 is a side view of an L-band antenna embodying this invention. 
     FIG. 2 is a top view of the antenna of FIG.  1 . 
     FIG. 3 is an enlargement of a portion of the side view of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An exemplary embodiment of an L-band antenna  50  in accordance with aspects of this invention is illustrated in FIGS. 1 and 2. The antenna includes in this exemplary embodiment ten elements  52 A- 52 N, which in this exemplary embodiment are bus wires fabricated from # 20 American Wire Gauge (AWG). In this exemplary embodiment, the antenna is attached to an SMA rear mount bulkhead connector  54 , although other structures could alternatively be employed to mount the antenna and electrically connect the antenna to a transmitter or receiver. 
     The elements  52 A- 52 N are equally spaced and form a cone that is 60 degrees wide. In this exemplary embodiment, the connector  54  is secured through an opening in a ground plane structure  60 , which can be a metal plate having an extent at least 2-3 times as large as the diameter subtended by the distal ends of the elements  52 A- 52 N. The ground plane acts as a mirror for the antenna, and so the larger the ground plane the better the performance. 
     The length of the wires  52 A- 52 N that form the cone is three inches in this exemplary embodiment. The elements are soldered together at the tip of the cone, with one wire, here  52 C having an end protruding from the tip of the cone to provide a center conductor to which an electrical connection can be made. In this embodiment, the transition  58  from the ten soldered wires to one central wire for the bulkhead connector is tapered at a taper angle in the range of 45° to 60°. This tapering improves the electrical performance, in that the antenna reflects less energy and is more efficient. 
     An exemplary form of the connector  54  is illustrated in the enlarged side view of FIG.  3 . The connector includes a center conductor  54 A and a cylindrical outer conductor  54 B with an external threaded surface. The ground plane structure  60  is captured between the shoulder  54 C and the threaded nut  54 D and washer  54 E to secure the connector and the antenna to the ground plane structure. 
     In an exemplary embodiment, the connector  54  includes a center conductor  54 A with a solder cup  54 D at its distal end. The solder cup is hollowed out at a diameter just large enough to receive therein the tip  52 C 1  of one of the wire elements  52 A- 52 N, here shown as element  52 C, which is then soldered in place. Thus, the center conductor  54 A has a diameter only slightly larger than the diameter of the wire element  52 C. A standard SMA connector has a center conductor diameter of 0.050 inch, which is about equal to the diameter of # 20 AWG wire. 
     The antenna can be mechanically supported by packing dielectric material, preferably with a relative dielectric constant equal to that of air, about the base of the antenna at the connector. Alternatively, a dielectric potting compound could be employed, if required for a particular application. 
     The number of wires  52 A- 52 N can be varied depending on the application. In general, the more elements, the better the antenna performance. To reduce the cost, and maintain temperature stability, simple bus wire, i.e. wire without insulation, can be employed as the material for the antenna elements. For this exemplary embodiment, the maximum number of wires that could be grouped into a manageable bundle is ten, but for other applications, a larger or small number could be employed. 
     For best performance, the conical angle for a particular application was determined to be 60°. Angles below 50° had reduced performance, and angles above 70° made the antenna larger than desired for a particular application. 
     The length of the antenna elements is an important parameter. The cutoff frequency of the antenna is directly related to the element length, in an inverse relationship, so that the longer the elements, the lower the cutoff frequency. With elements of length 3 inches, this exemplary embodiment of the antenna does not work below 450 MHz. 
     The connector  54  provides a connection for a coaxial cable running to an RF transmit source or receiver. The antenna  50  provides an omnidirectional azimuth pattern. 
     It is understood that the above-described embodiments are merely illustrative of the possible specific embodiments which may represent principles of the present invention. Other arrangements may readily be devised in accordance with these principles by those skilled in the art without departing from the scope and spirit of the invention.

Technology Category: 5