Patent Publication Number: US-7215294-B2

Title: Antenna with reflector

Description:
BACKGROUND OF THE INVENTION 
   In antenna design, there are at least three overall design criteria; size relative to wavelength, directivity (or antenna gain), and frequency operating bandwidth. Generally, the first limiting design factor is frequency bandwidth and gain versus antenna size trade-off. Gain to size aspect ratios favor center feed corner reflector antennas, which is a well-understood design. 
   Design of the antenna feed assembly is also a relevant concern. To achieve broader frequency bandwidth, the conventional bow-tie feed is often chosen. There are two problems associated with this design, one, the conventional bow-tie feed has a 300 ohm balanced input impedance, which is a large mismatch for the typical 50 ohm unbalanced coaxial line, and two, the conventional bow-tie uses a full wavelength corner reflector, which is too large to fit into reduced space requirements. 
   SUMMARY OF THE INVENTION 
   Exemplary embodiments of the present invention may be directed to an antenna with a reflector, which do not suffer from antenna input impedance mismatch, provide increased operating frequency bandwidth, and/or reduce the antenna physical size. 
   Exemplary embodiments of the present invention may be directed to an antenna, which includes a monoconical antenna feed assembly. The feed assembly has a base and an apex, a ground plane adjacent to the monoconical antenna feed assembly near the apex, and an antenna reflector coupled to the ground plane. The antenna reflector at least partially surrounds the monoconical antenna feed assembly. 
   Exemplary embodiments of the present invention may be directed to an antenna has increased operating bandwidth and a modest amount of gain. A monoconical feed assembly may be used to illuminate a reflector antenna. The broadband characteristics of the monoconical antenna (typical ground plane geometry) may be used as the feed assembly for the reflector to give modest amount of gain, while maintaining larger than previously developed bandwidths. The reflector may provide improved antenna directivity and thus increases the antenna gain. 
   Exemplary embodiments of the present invention may be directed to an antenna having increased operating bandwidth. The antenna may have an impedance matched to a 50 ohm transmission line, and a modest amount of antenna gain. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the present invention will become more fully understood from the detailed description given below and the accompanying drawings, which are given for purposes of illustration only, and thus do not limit the invention. 
       FIGS. 1A ,  1 B and  1 C illustrate antennas with reflectors in accordance with exemplary embodiments of the present invention. 
       FIG. 2  illustrates operating results when using a 30° monoconical cone according to at least one exemplary embodiment of the present invention. 
   

   It should be emphasized that the drawings of the instant application are not to scale but are merely schematic representations, and thus are not intended to portray the specific dimensions of the invention, which may be determined by skilled artisans through examination of the disclosure herein. 
   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Regarding antenna design, the bandwidth criteria can be approached using the same broadband characteristics of a bi-conical cone antenna, where two cones are arranged apex-to-apex. Substituting half of this design, known as an image antenna, i.e., vertical ground plane antenna, provides a broadband feed mechanism for the reflector. 
   The antenna input impedance can be made to match the coaxial transmission line by determining the appropriate cone apex angle and spacing. With an image antenna feed structure, the reflector size may be reduced (to up to half the normal size), while still maintaining performance. Further, a reflector may be used to transform an omniidirectional “doughnut” shaped pattern into a pattern with increased directivity or gain. 
     FIGS. 1A and 1B  illustrates an antenna with reflector in accordance with at least one exemplary embodiment of the present invention. As shown, the antenna  10  includes a ground plane  12 , an antenna reflector  14 , and a monoconical antenna feed assembly  16 . The monoconical feed assembly may be incorporated to increase the bandwidth. The ground plane  12  is coupled to an outer conductor of the adapter  20  and located adjacent to the monoconical antenna feed assembly  16  near the apex of the assembly  16 . The antenna reflector  14  is coupled to the ground plane  12  and the antenna reflector  14  at least partially surrounds the monoconical antenna feed assembly  16 . As shown in  FIG. 1B , the feed assembly  16  is coupled to a center conductor  18  of the adapter  20 . In exemplary embodiments of the present invention, the antenna reflector  14  is a modified corner antenna reflector, as shown in  FIG. 1A . In exemplary embodiments of the present invention, the antenna reflector  14  is a solid metal antenna reflector, a mesh antenna reflector, or a plurality of bars. In other exemplary embodiments of the present invention, the antenna reflector  14  is a combination of solid metal, mesh, and/or bars with or without varying thickness  22 . 
   In exemplary embodiments of the present invention, the antenna  10  has a reduced size in terms of wavelength, improved directivity, and wider bandwidth. In exemplary embodiments of the present invention, the bandwidth is 1800–2200 MHz to accommodate cell phone systems, PCS, UMTS and other wireless systems. 
   In exemplary embodiments of the present invention, the antenna  10  is vertically polarized and an image antenna, however, both of these need not be the case, as would be known to one of ordinary skill in the art. 
   In exemplary embodiments of the present invention, the antenna reflector  14  partially surrounds the monoconical antenna feed assembly  16 . The degree of surrounding may be from 90° to 180°. In exemplary embodiments of the present invention, the antenna reflector  14  is a corner antenna reflector, which surrounds 180° of the monoconical antenna feed assembly  16 . 
   In exemplary embodiments of the present invention, the orientation of the antenna reflector  14  to the monoconical antenna feed assembly  16  is not vertical, as shown in  FIGS. 1A and 1B  by angel α, but rather sloped at another angle, for example, 10°, 20°, 30°, 45°, or 60°, as shown by  FIG. 1C . 
   In exemplary embodiments of the present invention, an outer surface of the monoconical antenna feed assembly  16  and/or the outer surface of the ground plane  12  comprises a conductive material. 
   In other exemplary embodiments of the present invention, the ground plane  12  is made of conductive metal and the monoconical antenna feed assembly  16  comprises an insulating material coated with conducting metal material. 
   In exemplary embodiments of the present invention, the adapter  20  is a coaxial cable adapter. In other exemplary embodiments of the present invention, the adapter  20  may be any type adapter of either sex. Such types may be standard or special and include, but not be limited to, DIN series connectors, including DIN 7/16, N-type, TNC, SMA, and MMX. 
   In exemplary embodiments of the present invention, the feed point spacing can be adjusted with the center conductor  18  of the adapter  20 . In exemplary embodiments of the present invention this adjustment can be made utilizing a threaded mechanism. 
   Antenna return loss measurements were conducted. Measurements were conducted using a 90°, 45°, 30°, 20°, and 10° apex angle monoconical antenna feed assembly. The reflector to feed probe distance was adjusted to obtain improved return loss values while observing the antenna operating frequency bandwidth.  FIG. 2  shows the operating results when using the 30° cone (experimentally, the best match to 50 ohms). As shown, an 18.7 dB return loss (Standing Wave Ratio of 1.23) was obtained, which is a highly desirable value. 
   Exemplary embodiments of the present invention can operate in multiple bands, for example, the standard PCS wireless band and the new UMTS wireless band simultaneously. This encompasses a frequency range from 1900 to 2200 MHZ, or a frequency bandwidth of 15% centered at 2050 MHZ. 
   Additionally, exemplary embodiments of the present invention are small enough to be installed into limited space areas and have predictable operating performance, and/or be low cost. 
   Initial antenna testing with various feed configurations has determined antenna feedpoint impedance and reflector to feed spacing. Antenna gain and beamwidth tests have gains from 4–5 dB with a half wavelength corner reflector. 
   Although exemplary embodiments of the present invention are generally described in the context of wireless telephony, the teachings of the present invention may be applied to other systems, wired or wireless, voice, data or a combination thereof, as would be known to one of ordinary skill in the art. 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as departure from the spirit and scope of the exemplary embodiments of the present invention, and all such modifications are intended to be included within the scope of the following claims.