Patent Application
20120262358
The present invention relates to a high frequency (HF) beam forming antenna that satisfies the need for a high performance gain antenna.
Beam forming high frequency (HF) (2 to 30 MHz) antennas, such as Yagi and Log-Periodic antennas, are usually horizontally polarized. When mounted low above the ground, horizontally polarized antennas have high radiation angles resulting in poor long distance performance.
Long distance communications at HF frequencies rely on the ionosphere refracting signals back to earth. These refractions occur at heights of 200 to 300 kilometers. To reach long distances (2000 to 4000 km), signals must be launched at low angles so they reach the ionosphere as far from the transmitter as possible and thus, after refraction, return to earth the farthest possible. Signals launched at high angles return to earth much closer and often need multiple reflections and refractions (so called hops) to reach the distant receiver. Multiple hops result in significant signal loss and thus poor reception. Therefore, low angle radiation is a very desirable characteristic of long distance (DX) HF antennas. Radiation angles of 20 degrees or less are considered to be good for these purposes.
Radiation from horizontally polarized antennas (where the electrical field is parallel to the ground) is out of phase with radiation reflected from the ground. This results in the two radiations cancelling each other at low angles. This can be overcome by raising the antenna above the ground, effectively shifting its phase to reduce signal cancellation at low angles. Ideally, a horizontally polarized antenna, such as a Yagi antenna, should be raised to a height of one wavelength above ground to achieve optimum low angle radiation. Compromise heights of 0.5 to one wavelength result in compromised performance and significant ground losses. At lower heights the horizontally polarized antenna is almost useless for long distance communications.
To obtain the necessary heights, horizontally polarized HF beam antennas are installed on towers or other high structures. This requirement severely restricts their use in residential areas where either local ordinances or community covenants restrict the height and visibility of structures. For example, to be an effective long distance antenna, a Yagi beam antenna designed to operate in the 14 MHz radio amateur band, should be installed at a height of at least 15 meters (45 feet). In practice, tower heights range between 45 and 120 feet. A large number of amateur radio operators, who live in neighborhoods with antenna restrictions, are not able install towers and therefore are seriously disadvantaged. They are limited to low dipole or ground mounted vertically polarized antennas that have either no, or limited beam forming capabilities, and suffer from ground losses.
Although, most existing beam forming antennas in the HF service are horizontally polarized (such as Yagi and Log-Periodic antennas), there are also some vertically polarized beam forming antennas that may be used in the HF frequency range. Vertically polarized beam forming antennas are usually phased vertical arrays that require extensive radial fields, and therefore they often suffer from high ground losses. Their performance is strongly dependent on ground quality, and can be very poor when mounted over low conductivity ground.
Beam forming antennas are desirable as they concentrate the radiated radio energy in the direction of the receiver. They can easily achieve gains of 10 dB, which provides a ten fold signal increase at the receiving end. Accordingly, it is desirable to have a high gain HF antenna beam forming antenna that does not have the above mentioned angle, height and ground requirements of the prior art HF antennas.
This invention describes a beam forming HF antenna that satisfies the need for a high performance gain antenna that provides low angles of radiation when installed at 0.1 to 0.2 wavelength above ground. The antenna eliminates the need for a tower in the HF service.
In general, one aspect of the invention provides a high frequency (HF) beam antenna including a set of radiating vertical monopole elements and a set of horizontal dipole elements. The horizontal dipole elements are parasitically coupled to corresponding radiating vertical monopole elements and are configured to counterpoise radiation from the radiating vertical monopole elements and to effectively isolate the vertical monopole elements from the underlying ground.
Implementations of this aspect of the invention include the following. The set of radiating vertical monopole elements includes at least three vertical monopole elements arranged inline and parallel to each other. The three monopole elements include a fed element, a reflector element and a director element. The fed element is connected to a signal feed line and is configured to emit radiated energy and the reflector and director elements are parasitically coupled to the fed element. The reflector and director elements are sized and spaced apart from the fed element so that they cause phase shifts in the radiated energy and the phase shifts cause the radiated energy to add constructively in a forward direction and to cancel in a rearward direction, thereby forming a radiated energy beam. The antenna further includes a horizontally extending boom and the set of radiating vertical monopole elements are mounted perpendicularly onto the boom and the set of horizontal dipole elements are mounted coplanar and perpendicular to the boom. The antenna further includes a vertical mast and the vertical mast is secured in the underlying ground and the boom is mounted on top of the vertical mast. The mast has a height of less than 5 meters above ground. The mast has a height in the range of 0.1 to 0.2 wavelength above ground. The antenna further includes a rotating mechanism for rotating the set of radiating vertical monopole elements and the set of horizontal dipole elements. The antenna may further include a plurality of sets of radiating vertical monopole elements configured to emit radiation in multiple ranges of frequencies and a plurality of sets of horizontal dipole elements. The sets of horizontal dipole elements are parasitically coupled to the sets of radiating vertical monopole elements and are configured to counterpoise radiation from the sets of radiating vertical monopole elements and to effectively isolate the sets of vertical monopole elements from the underlying ground. Each horizontal dipole element includes first and second components and the first and second components are arranged and dimensioned so that they provide current return paths for the corresponding vertical element.
In general in another aspect the invention provides a method for generating a high frequency (HF) beam including providing a set of radiating vertical monopole elements, providing a set of horizontal dipole elements and coupling the horizontal dipole elements parasitically to corresponding radiating vertical monopole elements so that radiation from the radiating vertical monopole elements is counterpoise by the horizontal dipole elements and the vertical monopole elements are effectively isolated from the underlying ground.
Among the advantages of this invention may be one or more of the following. The rotatable vertically polarized beam forming antenna achieves low radiation angles from moderate heights (0.1 to 0.2 wavelength above ground) and does not suffer from excessive ground losses. Because this antenna does not require a tower, it can be installed in neighborhoods with restrictions on tall structures.
Referring to the figures, wherein like numerals represent like parts throughout the several views:
Beam forming antennas in the HF service are either vertically or horizontally polarized. Referring to
Referring to
The antenna of this invention is a ground independent vertically polarized multi-element parasitic array that has low angles of radiation even when mounted at moderate heights, i.e., 3 to 4 meters. Referring to
Unlike on a Yagi antenna, the present antenna's horizontal elements 105, 112, 114 do not radiate. Only the vertical elements 102, 103, 104 radiate, which generates a vertically polarized signal. The horizontal elements 105, 112, 114 act as counterpoise to the vertical elements 102, 103, 104 and effectively isolate the radiating elements from the underlying ground, thereby avoiding the ground losses that affect horizontally polarized antennas or vertical antennas over ground. All elements 102, 103, 104, 105, 112, 114 are supported onto a horizontal boom 101. Boom 101 is mounted on the top of a vertical mast 106, which is secured in the ground 120.
The boom 101 provides mechanical support for the entire antenna structure. When made out of metal, the boom also provides grounding for all the elements. This ground plays a negligible role in the RF performance of the antenna, but is generally provided for lightning protection.
The fed element 102 is the active element that is fed the radio frequency (RF) energy from the feed line 107 (coaxial cable). The fed element 102, which is vertically polarized, and may also contain an impedance matching structure, is parasitically coupled to the two vertical parasitic elements 103 and 104.
The rear parasitic element 103 (reflector) is sized to be longer than the fed element 102. The forward parasitic element 104 (director), is sized to be shorter. There may be more than one director in an array. The size differences between the fed element 102, the reflector 103 and the director 104 result in phase-shifts that cause the radiated energy to add constructively in the forward direction, and cancel in the rearward direction. Thus the antenna forms a beam of radiation in the forward direction 111. The antenna thus has a gain in the forward direction 111 at the expense of the side and rear directions. When the antenna is pointed in the desired direction of communications this gain results in increased signal strength at the other end of the link. Likewise, the received signal also experiences gain, while the noise received from the other directions is attenuated.
Each of the horizontal elements 105, 112, 114 includes a set of two horizontal elements 105a, 105b, 112a, 112b, and 114a, 114b, respectively. Each set of the two horizontal elements (i.e., 105a, 105b) provides a current return path for the corresponding vertical element (i.e., 103), and enables the vertical element to resonate at the appropriate frequencies. Because of the opposing phases of currents in the horizontal elements 105a, 105b, these elements do not radiate, although they play an important role in the beam-forming function of the antenna. The horizontal elements are sized the same as their corresponding vertical counterparts. Importantly, they “shield’ the antenna from the lossy ground. The feed cable 107, usually a coaxial cable, carries RF power from the transmitter to the antenna.
The antenna is installed on a short (3 to 4 meter) mast 106, that is between 0.1 to 0.2 wavelength above ground and may be equipped with a rotating mechanism. The antenna may be made to work on multiple ranges of frequencies by adding additional sets of elements sized for those frequencies (interlaced or forward staggered).
Several embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
This application claims the benefit of U.S. provisional application Ser. No. 61/474,787 filed on Apr. 13, 2011 and entitled BEAM FORMING ANTENNA which is commonly assigned and the contents of which are expressly incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61474787 | Apr 2011 | US |
