The present invention pertains generally to antennas. More specifically, the present invention pertains to the design of antennas that extend the frequency range of antennas.
In order to operate over a wide frequency range, a plurality of dedicated antennas that operate in specific radio frequency bands are typically installed on, for example, shipboard systems. For example, ultra high frequency (UHF) antennas that operate in the range of 225 MHz to 400 MHz may be installed on the shipboard system for use by radios operating in this range. Other antennas operating in other bands may also be provided for radios operating in those other bands, resulting in an “antenna farm” on the ship. However, antennas in the antenna farm may electrically interfere with each other and create holes in the antenna pattern. To minimize the electrical interference while maintaining the frequency range, it is therefore desirable to eliminate the number of antennas by combining multiple antennas.
One way to do this is by using bi-cone antennas. However, the classic bi-cone configuration can be too large (given the physical space available) for the required lowest frequency range. A current broadband antenna that can be used for a number of communication systems while maintaining a minimal size can be limited to 8.09 GHz because of the feed point design. Accordingly, there can be a need for a broadband antenna with an extended frequency range that allows other antennas to be eliminated from the antenna farm.
Some embodiments can be directed to an antenna that can include a feed disk, which can terminate at a feed disk apex, and a top element, which can include a nipple that terminates a top element apex. The feed disk and top element can be positioned so that the feed disk apex and the top element apex can be spaced-apart by a distance “d”, which can be chosen according to the desired frequency range. The feed disk and top element can also have respective bottom conical and top conical surfaces. When the feed disk and top element are positioned as described above, the top and bottom conical surfaces can establish a respective first predefined angle relative to a horizontal plane and a second predefined angle relative to the horizontal plane, thereby extending the antenna frequency range. The predefined angles can be chosen according to the desired frequency range of operation.
Other objects, advantages and features will become apparent from the following detailed description when considered in conjunction with the accompanied drawings.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
Antenna 100 incorporates a bi-conical antenna configuration 102 and can include a pair of coaxially disposed cones 108 and 110, each of which has an apex region and a base. Cones 108 and 110 are arranged such that the apex regions are adjacent. Antenna 100 can be feed from the bottom with a coaxial feed cable 104. A relatively small diameter cable may be used to reduce the feed point in order to optimize higher frequency impedance matching. In an embodiment, the impact of the feed cable 104 may be reduced by using, for example, a 0.144″ diameter coaxial cable. With such a feed point cable 104, antenna 100 may operate at a frequency of 18 GHz with a wavelength of 0.6562″. Smaller RF Cables 104 in diameter can allow the invention to go even higher in frequency above 18 GHz.
Referring now to
As shown in
A spacer 114, as shown in
The initial angle θ1 (i.e., the 22.5 degrees conical angle relative to the horizontal) can be approximated by the impedance of an infinite bi-cone according to the following Equation (1):
where θhc can be the half angle of the cone with respect to the vertical plane and n can be the desired impedance (for example, 50Ω). In the invention, CST Microwave Studio® was utilized to further optimize the angles, although other simulator tools that are known in the art could be used to further optimize the angle. For 67.5 degrees, impedance Z can be 48.3Ω. As noted above, the highest frequency of the classic bi-cone can depend on the details of the feed point. The classic bi-cone has a one wave length diameter. The impedance of the bi-cone depends on the reflection from the end of the cone. The cone can be rolled to reduce the reflections from the end of the cone.
A disk-cone antenna has one cone and a disk ground plane. The cone can be ¼ of the wavelength of the lowest frequency. A disk-cone antenna with a rolled cone has four-octave bandwidth. An embodiment replaces this cone with a section of a sphere to reduce the size and reflection from the end of the cone. The sphere section can be hollow to reduce weight.
Each time the angle changes in antenna 100, there can be a reflection and the impedance also changes. In an example where the feed point region has an initial impedance of 48.3 Ohms, at a radial distance of 0.375″, the impedance will change (distance on surface can be 0.4059″) causing a reflection. This will also cause a small reflection with a 0 degree phase shift plus propagation delay to feed point. In this example, a second transition to 15 degrees occurs at a radial distance of about (0.735 bottom-0.744 top; distance on surface can be 0.7956 for bottom and 0.8205 for top). This will also cause a reflection and propagation delay. The two reflected signal will modify the impedance at high frequencies. Impedance closer to 50 Ohms will have a lower Voltage Standing Wave Ratio (VSWR). The above dimensions are based on a design that meets the performance requirements for VSWR and pattern. An antenna designer could alter the design parameters and obtain similar or better performance antennas. Antenna 100 can therefore be used to transmit from 400 MHz to 18 GHz. For lower frequencies, for example, 150 MHz to 400 MHz, the antenna may be receiving only.
Referring now to
As shown by step 72 in
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.
The United States Government has ownership rights in this invention. Licensing inquiries may be directed to Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif., 92152; telephone (619) 553-5118; email: ssc_pac_t2@navy.mil, referencing NC 101630.
Number | Name | Date | Kind |
---|---|---|---|
2511849 | Smith | Jun 1950 | A |
2762045 | Stavis et al. | Sep 1956 | A |
6268834 | Josypenko | Jul 2001 | B1 |
6667721 | Simonds | Dec 2003 | B1 |
6845253 | Schantz | Jan 2005 | B1 |
7079079 | Jo | Jul 2006 | B2 |
7538737 | Black et al. | May 2009 | B2 |
7764236 | Hill | Jul 2010 | B2 |
8314744 | Libonati et al. | Nov 2012 | B2 |
8576135 | Krivokapic | Nov 2013 | B1 |
20060284779 | Parsche et al. | Dec 2006 | A1 |
20070241980 | Smith | Oct 2007 | A1 |
20120044119 | Libonati | Feb 2012 | A1 |
Entry |
---|
Schantz, Hans, “The Art and Science of Ultrawideband Antennas”, 2005, pp. 203-206, Artech House, Boston/London. |