The present invention relates to the field of antennas, and, more particularly, to dipole antennas with broad pattern bandwidth and related methods.

A particular type of antenna may be selected for use in an electronic device based upon a desired application. For example, a different type of antenna may be used for terrestrial communications versus satellite communications. The type of antenna used may also be based upon a desired operating frequency of the antenna.

One example of a type of antenna is a broadband antenna. A broadband antenna is an antenna that operates over a wide range of frequencies. The broadband antenna may be formed to provide increased gain along the horizon, for example, during terrestrial communications.

One type of broadband antenna is a biconical dipole antenna. A biconical dipole antenna has inherent broadband characteristics as it functions as a self excited horn. The conical horn walls fit different sized waves. However, the diameter of a biconical antenna becomes increasingly large at lower operational frequencies. A larger diameter or size may be restricted in a mobile wireless communications device as the size of the housing carrying the biconical antenna may be limited in size. To reduce the size of the biconical antenna, the biconical antenna may be truncated. As a result, a dipole-type structure is formed.

Increased antenna performance at lower frequencies may correspond to increased antenna length. However, at higher frequencies the increased length may result in the formation of lobes in the antenna pattern, thus resulting in relatively low gain on the horizon. In fact, another radiation pattern lobe is formed for every half wavelength of wire dipole length. Electrically large thin wire dipole antennas have nearly endfire radiation rather than broadside radiation.

For example, referring now to the biconical antenna 170 in FIG. la, and the graphs in FIGS, lb-lc, the biconical antenna has relatively satisfactory performance at the horizon both for low (FIG. lb) and high (FIG. lc) frequencies. However, the biconical antenna has a relatively large diameter, for example, 15.5" tall by 15.3" in diameter, for a desired operating frequency range.

Additionally, referring to the truncated biconical antenna 180 (i.e. dipole with biconical feed) in FIG. 2a, and the graphs in FIGS. 2a-2c, the truncated biconical antenna feed has relatively satisfactory performance at the horizon at low frequencies (FIG. 2b). The dominate dipole structure may be too long for the higher frequencies, which illustratively causes a lobe to form at the horizon (FIG. 2c). Example dimensions for the truncated biconical dipole are 15.5" tall x 4" in diameter for the desired operating frequency range.

U.S. Patent No. 7,221,326 to Ida et al. discloses a biconical antenna. More particularly, the biconical antenna includes a columnar dielectric member having frustum-shaped cavities extending respectively from an upper and lower surface toward the center of the columnar member. Flat surfaces of apex portions of the frustum-shaped cavities are parallel and in opposition to one another.

U.S. Patent No. 2,175,252 to P.S. Carter discloses conical monopole and conical dipole antennas with a coaxial cable feed. The cone forms a sleeve over the coaxial cable.

U.S. Patent No. 7,339,542 to Lalezari. discloses an ultra-broadband antenna system that combines an asymmetrical dipole element and a biconical dipole element to form a monopole. The asymmetrical dipole element includes upper and lower asymmetrical dipole elements. The antenna system also includes a plastic expander ring coupled to the lower asymmetrical dipole element. The expander ring is also coupled to a canister sub-assembly. A choke sub-assembly is provided within the canister sub-assembly.

However, there may still be a need for a reduced diameter antenna profile, such as a cylindrical "whip" profile, including an increased radiation pattern bandwidth and a satisfactory pattern on the horizon.

In view of the foregoing background, it is therefore an object of the present invention to provide an increased radiation pattern bandwidth and a satisfactory pattern on the horizon in a biconical-type antenna. This and other objects, features, and advantages in accordance with the present invention are provided by an antenna assembly including first and second adjacent antenna elements each comprising a tapered or conical antenna body having a base and an apex opposite the base, an elongated or cylindrical antenna body extending from the base of the conical antenna body, and including a plurality of adjacent elongated or cylindrical antenna body portions, and a respective dielectric member separating adjacent cylindrical antenna body portions. Each of the first and second adjacent antenna elements are aligned along a common longitudinal axis with respective apexes in opposing relation to define a dipole antenna.

Each of the plurality of cylindrical antenna body portions may comprise a tubular cylindrical antenna body portion, a solid cylindrical antenna body portion, a mesh electrical conductor and/or a continuous electrical conductor. Each of the dielectric members may comprise a cylindrical dielectric member, and a diameter of each of the cylindrical dielectric members may be different than a diameter of adjacent cylindrical antenna body portions. The mesh electrical conductor may comprise insulated wire.

An antenna feed assembly may be coupled to the first and second adjacent antenna elements. The plurality of adjacent cylindrical body portions may include at least three cylindrical body portions with respective dielectric members therebetween.

A method aspect is directed to making an antenna assembly including forming first and second adjacent antenna elements each comprising a conical antenna body having a base and an apex opposite the base, a cylindrical antenna body extending from the base of said conical antenna body, and including a plurality of adjacent cylindrical antenna body portions, and a respective dielectric member separating adjacent cylindrical antenna body portions. The method further includes aligning each of the first and second adjacent antenna elements along a common longitudinal axis with respective apexes in opposing relation to define a dipole antenna.

FIG. 1 A is a schematic view of a biconical antenna in accordance with the prior art. FIGS. IB and 1C are respective graphs of low and high frequency radiation patterns of the biconical antenna of FIG. 1A.

FIG. 2 A is a schematic view of a truncated biconical antenna in accordance with the prior art.

FIGS. 2B and 2C are respective graphs of low and high frequency gain patterns of the truncated biconical antenna of FIG. 2 A.

FIG. 3 A is a perspective view of an antenna assembly in accordance with the present invention.

FIGs. 3B and 3C are schematic diagrams illustrating various embodiments of portions of the antenna assembly of FIG. 3 A.

FIG. 4A is a schematic diagram illustrating a sample radiation pattern of the antenna of FIG. 2 A in accordance with the prior art.

FIG. 4B is a schematic diagram illustrating a sample radiation pattern of the antenna assembly of FIG. 3.

FIGS. 5A and 5B are respective graphs of low and high frequency gain patterns of the antenna of FIG. 3.

FIG. 6 is an exploded view of an inductive mesh in the antenna embodiment of FIG. 3B.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

Referring initially to FIG. 3, an antenna assembly 20 includes first and second adjacent antenna elements 21a, 21b. Each of the first and second adjacent antenna elements 21a, 21b includes a tapered or conical antenna body 22a, 22b having a base 32a, 32b and an apex 31a, 31b opposite the base. Each conical antenna body 22a, 22b has two-stages defining a step therebetween. As will be appreciated by those skilled in the art, the two-step conical antenna body 22a, 22b may be used to match a return loss. An approximation of a curve corresponding to a desired return loss at a desired frequency may be accomplished by adding additional stages to form the conical antenna body 22a, 22b. The two-stage conical antenna body 22a, 22b provides improved return loss performance over a single -plane conical antenna body. Of course, each conical antenna body 22a, 22b may be formed having a single stage or more than two stages. Moreover, the stages may be formed to define any shape, but an overall spherical shape of the conical antenna body is less desired, for example, for wideband frequency operation.

An increase in the size or diameter of each conical antenna body 22a, 22b advantageously increases performance. For example, an increase in the diameter of the base 32a, 32b of the conical antenna body 22a, 22b corresponds to an increase in frequency bandwidth. Thus, the diameter of each conical antenna body 22a, 22b may be determined based upon a compromise of desired size and desired performance.

Each of the first and second adjacent antenna elements 21a, 21b also includes an elongated or cylindrical antenna body 26a, 26b extending from the base 32a, 32b of the conical antenna body 22a, 22b. Each cylindrical antenna body 26a, 26b includes a plurality of elongated or cylindrical antenna body portions 27a, 27b. Also, each of the first and second adjacent antenna elements 21a, 21b includes a respective dielectric member 29a, 29b separating adjacent cylindrical antenna body portions.

Such dielectric members 29a, 29b may be formed of foam, graphite or PTFE, for example. The plurality of cylindrical antenna body portions 27a, 27b and dielectric members 29a, 29b may be secured together in various ways included being threaded together, slid together and/or adhered together, for example.

The longitudinally spaced distance between the cylindrical antenna body portions 27a, 27b due to the dielectric members 29a, 29b advantageously affects the performance of the antenna. For example, the longitudinally spaced distance between cylindrical antenna body portions 27a, 27b affects the radiation pattern and/or return loss by altering the location of lobes in the gain pattern. The gaps created by the separation may control the phasing of current, and the plurality of cylindrical antenna body portions 27a, 27b may be considered to operate as a series-fed array.

Additional dielectric members (not shown) may be included in the cylindrical antenna body 26a, 26b. Thus additional lobe control may be provided. Reduction of "lobing" at other or additional frequencies may be accomplished by adjusting the location and number of the dielectric members 29a, 29b relative to the center of the antenna assembly 20. Moreover, the location and number of the dielectric members 29a, 29b may be chosen based upon a desired operating frequency, bandwidth, return loss, and lobe location, for example. Other factors may be considered in determining the number and location of choke members and thus choke slots.

As illustrated in FIG. 3B, each of the plurality of cylindrical antenna body portions 27a' comprises a tubular cylindrical antenna body portion and/or a mesh electrical conductor. Each of the dielectric members 29a' comprises a cylindrical dielectric member, and a diameter d of each of the cylindrical dielectric members may be different than a diameter D of adjacent cylindrical antenna body portions 27a', as also illustrated in FIG. 3B. As illustrated in FIG. 3C, each of the plurality of cylindrical antenna body portions 27a" comprises a solid cylindrical antenna body portion, and/or a continuous electrical conductor.

Referring to Fig. 6 an exploded view of an inductive mesh is provided. The inductive mesh may be used to form individual cylindrical antenna body portions 27a, 27b and it provides a distributed self inductance that may reduce the physical length requirements, e.g., inductive loading. In Fig. 6, metal wires 60, preferentially a copper metal wire, is coated with an insulation coating 62 such as enamel paint or lacquer. The weave may be a plain or linen weave with the insulated metal wires 60 oriented on a diagonal bias relative the antenna 20 elongate axis. The insulated metal wires are soldered to metal bands 64 to provide to prevent fraying. As can be appreciated by those in the art, the electrical currents should follow a diagonal and weaving path which provides increased conductor electrical length and increased self inductance. This in turn reduces antenna operating frequency and or physical size of the antenna 20.

The conical antenna body 22a of the first antenna element 21a has an opening 25a at the apex 31a thereof. A tubular dielectric spacer 24 is positioned in the opening 25a for receiving an inner conductor 41 of a coaxial cable 40, or other conductor, for example. The conical antenna body 22b of the second antenna element 21b may be similarly configured with an opening 25b at an apex 31b thereof, and may have a connector (not shown) therein for receiving the inner conductor 41.

The antenna assembly 20 includes a hollow shaft 28a in the first antenna element 21a, and the coaxial cable 40 extends through the hollow shaft 28a. The inner conductor 41 is coupled to the conical antenna body 22b of the second antenna element 21b. The inner conductor 41 passes through the tubular dielectric spacer 24 in the apex 31a of the first antenna element 21a to couple with the conical antenna body 22b of the second antenna element 21b. A coaxial cable connector (not shown) may be included in the conical antenna body 22b of the second antenna element 21b for coupling to the center conductor 41.

The coaxial cable 40 also includes an outer conductor 42 surrounding the inner conductor 41 and coupled to the cylindrical antenna body 26a of the first antenna element 21a. Other types of conductors may extend through the hollow shaft, for example a rigid conductor. Additionally, a second hollow shaft 28b may also be included, thus reducing manufacturing costs by reducing the amount of material used and the machining of two different antenna elements 21a, 21b. In some

embodiments, the cylindrical antenna body portions 26a, 26b may not be hollow (e.g., as shown in FIG. 3C).

Each of the first and second conical antenna bodies 22a, 22b are illustratively aligned along a common longitudinal axis 23 with respective apexes 31a, 31b in opposing relation to define a symmetrical biconical-type dipole antenna.

The overall height of the first and second adjacent antenna elements 21a, 21b is typically determined by the desired highest operating frequency. The overall height of the antenna 20 is typically determined by the lowest operating frequency. The height of the antenna may also be determined based upon a size limitation of a device housing, for example. The lengths of the individual cylindrical antenna body portions 27a, 27b may be unequal so each cylindrical body portion may provide tuning to a portion of the radio frequency spectrum.

The antenna assembly 20 may further include a balun (not shown). A balun may be desired based upon how the coaxial cable 40 or conductor is attached to the conical antenna body 22a, 22b. The balun may advantageously balance the RF signals in each of the first and second adjacent antenna elements 21a, 21b.

Referring now to the elevation plane radiation patterns in FIGS. 4 A and 4B, the dielectric separators advantageously reduce "lobing" at certain frequencies, thus reducing nulls in the radiation pattern of the antenna assembly 20 that are located on the horizon, for example. The antenna is oriented along the Z axis so the XY plane represent the horizon. The gain patterns in the graphs illustratively have improved performance over the prior art antennas, whose gain patterns are illustrated in the graphs of FIGS. IB, 1C, 2B, and 2C.

A method aspect is directed to making an antenna assembly 20 including forming first and second adjacent antenna elements 21a, 21b each comprising a conical antenna body 22a, 22b having a base 32a, 32b and an apex 31a, 31b opposite the base. A cylindrical antenna body 26a, 26b extends from the base 32a, 32b of the conical antenna body, and includes a plurality of adjacent cylindrical antenna body portions 27a, 27b, and a respective dielectric member 29a, 29b separating adjacent cylindrical antenna body portions. The method further includes aligning each of the first and second adjacent antenna elements 21a, 21b along a common longitudinal axis 23 with respective apexes 31a, 31b in opposing relation to define a dipole antenna.

For example, an antenna assembly was formed to have a height of 12 inches and a diameter of 1.5 inches. The antenna assembly exhibits operation from 240 MHz to 3 GHz with reduced or no nulls on the horizon, for example as illustrated in the graphs of FIGS. 4 A and 4B. In contrast, a prior art antenna, without the dielectric separators, exhibited nulls between 800 and 900 MHz.

The antenna assembly 20 matches to very broad bands, with the lowest band of operation being dictated by the length of the antenna, and the highest band of operation being dictated by the accuracy of the dimensions near the center of the antenna. Desirable radiation pattern performance is achieved while a relatively small diameter.

Accordingly, the antenna assembly 20 may be particularly advantageous in a frequency range of about 240 MHz to 3 GHz, and in ultra- wideband applications, for example. Of course, the antenna assembly 20 may be used for other frequency ranges and other applications.