Patent Application
20050057425
1. Technical Field
The present invention relates to the art of RF broadcasting antenna systems and, more particularly, to such a system employing a vertically oriented radiator together with a plurality of top loading wires extending therefrom, the electrical length of the wires being adjustable so that the antenna may be resonated over a wide range of operating frequencies.
2. Description of the Prior Art
Antenna systems employing an electrically conductive vertical radiator, together with top loading wires extending outward from the radiator have been known in the art. Such top loading wires have been used to increase the electrical length of such a vertical radiator and to lower its self-resonance at a particular frequency. Such a system is disclosed, for example, in the above-referenced U.S. patent application.
It is to be noted, however, that the above-noted patent application does not disclose that the top loading wires may be adjusted so as to vary the electrical length thereof whereby the antenna may be adjusted to resonate at different frequencies over a wide area. This permits a fixed length, short, and vertical antenna to be used over a range of frequencies without adding a series inductor to the antenna which would reduce the operating bandwidth and add losses and result in a higher voltage at the base of such an antenna. The use of top loading wires of variable electrical lengths improves bandwidth, reduces losses and improves the system efficiency by increasing the radiation resistance of the antenna.
In accordance with one aspect of the present invention, there is provided an antenna system that includes an electrically conductive vertical mast radiator. Also, a plurality of top loading electrical conductive wires extend from the radiator. Each wire has an inner end electrically connected to the radiator and an outer end that is located away from the radiator. The electrical length of each wire, as measured from the radiator to the outer end, is adjustable to thereby vary the operating frequency of the antenna system.
In accordance with another aspect of the invention, the system includes a vertical radiator mast of electrically conductive material that extends generally in a vertical direction relative to earth ground. The mast has a lower end for receiving RF energy for radiation thereby at an operating RF frequency, and having an upper end. A plurality of top loading electrically conductive wires is provided. Each wire has an inner end and an outer end with the outer end being spaced radially outward from the upper end of the mast. An electrically conductive wire guide is provided for each wire. The guide is electrically connected to the mast and is in slidable contact with the wire intermediate its ends so that the wire may be extended and retracted therefrom to vary the electrical length of the wire from the wire guide to the outer end to thereby vary the operating frequency of the antenna system.
The foregoing and other objects and advantages of the invention will become more readily apparent from the following description as taken in conjunction with the accompanying drawings, wherein:
Reference is now made to
As shown in
The top loading wires, which are made of electrically conductive material such as copper or the like, are placed directly above and in registry with the radial wires. For example, the top loading wire TL1 is in registry with and directly over radial wire R1 so that they define a common vertical plane with the mast M. As viewed from above, the top loading wires are spaced from each other by about 90°. The top loading represents a capacitance to the radial wires to lower the self-resonant frequency of the vertical radiator. The radial wires may be tuned by circuitry within the tuning unit TU and they may resonate at a frequency corresponding to the operating frequency of the vertical radiator. As will be described hereinafter, the electrical length of each of the top loading wires is adjustable to thereby adjust the operating frequency of the antenna system.
The antenna system disclosed herein has an operating frequency in the range from approximately 1200 KHz to approximately 1700 KHz. However, the technology could be applied to systems that operate at much lower and much higher frequencies. The radiation resistance of the antenna system is about ⅓ that of a quarter-wavelength radiator so that minimizing ground resistance is important and this is achieved with the structure as described herein.
The mast M is preferably designed to be of a height that is less than a quarter wavelength of the highest operating frequency above ground level G.
The radial wires R1, R2, R3, and R4 are electrically resonated at the operating frequency.
The outer or far ends of the radial wires R1-R4 are each connected to an insulator and thence to respective mounting poles P1, P2, P3 and P4. These poles are constructed of suitable electrical insulating material and extend from the level of ground upward to an extent of approximately 10 feet and are suitably secured to the ground to provide support. The inner or near ends of the radial wires R1-R4 extend through insulators located in the respective sidewalls of the tuning unit TU. These wires may extend inwardly of the tuning unit and are connected together in common and thence through an adjustable series inductor to ground. This inductor is employed for adjusting the operating frequency of the radial system. As stated before, additional adjustment of this operating frequency is obtained by varying the electrical length of each of the top loading wires TL1-TL4.
The vertical mast M extends upwardly from the tuning unit TU and is suitably secured thereto. The tuning unit may take the form of a metal box having sidewalls, a floor and a roof. The mast may be secured with suitable insulated mechanical connections. Although not shown in the drawings, the lower end of the mast may be connected via the antenna tuning unit to a coaxial transmission line that extends from the tuning unit to a transmitter.
In accordance with the present invention, the electrical length of each of the top loading lines TL1-TL4 may be varied to thereby adjust the operating frequency of the antenna system so that the antenna system may be used over a wide range of frequencies. Variable electrical length top loading wires may reduce the need to employ a series inductor. Also reducing the reliance on such a series inductor or the elimination thereof may reduce losses and improve the system efficiency and bandwidth by increasing the radiation resistance of the antenna.
The features that permit this operation are described hereinbelow with emphasis on the features illustrated in
The electrically conductive top loading wire portion of each guy line-wire loop arrangement is in slidable electrical contact with the wire guide WG mounted on the upper end of the mast M. This wire guide includes a tubular wire guide member associated with each guy line-wire loop arrangement. Thus, as shown in
The mast M is constructed of electrically conductive material such as three vertical metal bars that are interconnected with reinforcing metal cross members to provide a three-sided structure. A rain cover may be wrapped about the mast from the tuning unit TU to the upper end of the mast.
Although the foregoing has been described in conjunction with the preferred embodiment, it is to be appreciated that various modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.
This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/407,709, filed Apr. 4, 2003 and entitled “An Antenna System Utilizing Elevated, Resonant, Radial Wires”.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10407709 | Apr 2003 | US |
| Child | 10963207 | Oct 2004 | US |
