Patent Application
20200373676
The present disclosure can pertain generally to antennas. More particularly, the present disclosure can pertain to bicone antennas having surfaces that can be shaped with a particular geometry, so that the antenna can act as a traveling wave antenna, to allow for multi-directional operation over a wide frequency range.
Standard bicone antennas can have insufficiently narrow operating frequency ranges. To extend the frequency range and improve gain, antenna arrays have been designed with multiple antennas, which are designed to cover respective multiple frequency ranges. This configuration can require multiple radio frequency cables and complex electronics. Typical antenna designs can also have positioning or rotary joints to allow an antenna to move in order to receive and/or transmit in multiple directions.
While antenna arrays and positioning/rotary joints provide a multi-directional extended frequency range, this antenna design increase the power required, resulting in high return loss. Also, the use of positioning or rotary joints can induce noise. As a result, such designs typically suffer from low gain.
In view of the above, it can be an object of the present invention to have a stationary antenna design that can have a multi-directional extended frequency bandwidth with improved gain and improved return loss. Another object of the present invention can be to provide a bicone antenna having surfaces that can be shaped with a particular geometry, so that the antenna can act as a traveling wave antenna. Yet another object of the present invention can be to provide a bicone antenna, which can allow for multi-directional operation over a wide frequency range, but with a minimum of moving parts. Still another object of the present invention can be to provide a bicone antenna that can be easy to manufacture, including by additive manufacturing techniques, in a cost-effective manner.
A bicone antenna and methods for manufacture therefor can include a feed portion centered on a vertical axis, and a top section and a bottom section that can be attached to the feed portion so that the top and bottom sections are also centered on the vertical axis. The top section and bottom section can each have a respective conical surface, which can each extend radially outward from the vertical axis at a respective inner portion at a constant angle θ1 with respect to a horizontal axis of the antenna. For both sections, the inner portion can merge into an outer portion that can have a curved surface, with curved surface extending radially outward from the conical surface so that the curved surface has a logarithmic profile when the antenna can be viewed in side profile.
The above structure can allow for a multi-directional antenna with a minimum of moving parts, which can be easily manufactured, including by additive manufacturing techniques. These, as well as other objects, features and benefits will now become clear from a review of the following detailed description, the illustrative embodiments, and the accompanying drawings.
The accompanying drawings, which are incorporated in and form a part of the specification, illustrate example embodiments wherein specific reference characters refer to specifically-referenced parts, and further wherein:
According to illustrative embodiments, a bicone antenna can be provided with a top section and a bottom section that each can include a conical surface having an inner portion and an outer portion. The outer portion of each of the top section and the bottom section can extend logarithmically outward, as described more fully below. Logarithmically extending the conical surface can result in wideband performance with high gain and low return loss.
Referring initially to
The top section 110 of the bicone antenna 100 can include a conical surface 115, and the bottom section 120 can include a conical surface 125. The top section 110 of the bicone antenna may also include a top cap 130 with rounded edges to improve reflections.
The conical surface 115 can include a straight inner portion 115A extending outward from the feed portion 105 at a constant angle θ1 with respect to a horizontal axis x of the bicone antenna 100. The conical surface 115 also can include a transition portion 115B extending from the inner portion 115A and an outer portion 115C extending logarithmically outward.
Similarly, the conical surface 125 can include a straight inner portion 125A extending outward from the feed portion 105 at a constant angle θ1 with respect to a horizontal axis x of the bicone antenna 100. The conical surface 125 also can include a transition portion 125B extending from the inner portion 125A and an outer portion 125C extending logarithmically outward.
As shown in
With respect to inner portions 115A, 125A, the angle θ1 may be selected based on a desired input impedance of the bicone antenna 100. To understand how the angle θ1 is selected, consider an approximation of the input impendence Zin of an infinite bicone which can be given as:
Z
in=(120/n)ln(cot θhc/2) (1)
where θhc is the half-angle of each conical surface of the bicone antenna with respect to the vertical axis y, and n is the desired input impedance (e.g., 50 Ohms). According to illustrative embodiments, once the half-angle θhc is determined, that can provide an impedance Zin that can be close to the desired input impedance n, the constant angle θ1 of the inner portions 115A, 115B of the respective conical surfaces 115, 125 is selected as θ1=90°−θhc. For example, to achieve an impedance Zin of 48.3 Ohms, θhc may be set at 67.5°, resulting in θ1=22.5°.
Referring again to
f(x)=B*ln(A*X)−B (2)
where x is a radial distance along the horizontal axis x from the points PA, PB, f(x) can be the distance from the x-axis to the curved surface, and A and B can be constants that affect the shape of the logarithmically extending outer portions 115C, 125C with respect to the horizontal axis x and the vertical axis y. A and B can be chosen by an antenna designer to shape the logarithmically extending outer portion as desired.
As shown in
As noted above, the conical surfaces 115, 125 also can include respective transition portions 115B, 125B between the respective inner portions 115A, 125A and the respective outer portions 115C, 115C. The transition portions 115B, 125B are indicated in
In operation, RF energy arrives at the bicone antenna 100 via a cable fed into the feed portion 105. The RF energy starts transitioning from an input impedance (e.g., 50 Ohms) at the inner portions 115A, 125A of the respective conical surfaces 115, 125 to a lower impedance at the respective first ends of the outer portions 115C, 125C, due to the angles θ2A and θ2B being less than θ1. The RF energy then transitions into a higher impedance at the respective second ends of the outer portions 115C, 125C, due to the angles θ3A and θ3B being greater than the angles θ2A and θ2B, respectively. As the outer portions 115C, 125C of the respective conical surfaces 115, 125 extend logarithmically outward with respect to the horizontal axis, the RF energy exiting the bicone antenna 100 acts as a travelling wave, thus improving gain and allowing a narrower elevation beam width to be achieved.
As can be seen from
Additionally, the shapes and sizes of the top section 110 and bottom section 120 may be adjusted by adjusting the logarithmically extending outer portions 115C, 125C. Also, the length and shape of the transition portions 115B, 125B of the top section 110 and the bottom section 120 may be adjusted to accommodate a desired volume. Further, the shape and the roundness of the edges of the top cap 130 of the top section 110 may be adjusted.
Adjustments of the size and shape of the top section and bottom section of a bicone antenna are described in more detail below with reference to
As noted above, the bicone antenna with logarithmically extending conical surfaces can provide improved gain. As those skilled in the art will appreciate, the gain G of an antenna can be given by:
G=E·D (3)
where E=efficiency and D=directivity. The efficiency E can refer to the ability of an antenna to transfer energy from an RF feed cable to the antenna, including the energy internally absorbed by the antenna from resistive and dielectric losses. The directivity D refers to the ability of an antenna to focus energy in a particular direction. According to illustrative embodiments, directivity and efficiency can be maximized by allowing the RF energy to act as a travelling wave due to the logarithmically extending outer portions of the conical surfaces. By maximizing the directivity and the efficiency, the gain is maximized.
According to illustrative embodiments, gain can be improved while maintaining return loss. As those skilled in the art will appreciate, return loss is given by:
RL(dB)=10 log10(Pi/Pr) (4)
where RL(dB) is the return loss in dB, Pi is the incident power and Pr is the reflected power.
According to illustrative embodiments, the size and shape of a bicone antenna may be adjusted as desired while improving antenna gain and the electrical size of the antenna. For example, the shapes of the top section and the bottom section of a bicone antenna may be adjusted such that the top section and the bottom potion fit within an available volume (the space constraints could of course be balanced against desired gain and frequency range design criteria). This may be understood with reference to
As shown in
There are tradeoffs in adjusting the antenna size and shape to fit within a desired volume. For example, an excessive extension of the logarithmically extending outer portions of a bicone antenna could increase the capacitive reactance on the bicone antenna, diminishing the efficiency and bandwidth. Further, adjustment of the size of the bicone antenna may affect reflections for the edges of the top section. Accordingly, an antenna designer should be careful in adjusting the shape and size of a bicone antenna.
At step 520, a top cone with a top conical surface can be attached to the feed portion. This step can include the steps of extending a top inner portion of the top conical surface outwardly from the feed portion at a constant angle θ1 with respect to a horizontal axis of the bicone antenna at step 522. Step 520 can further include merging the top inner portion outwardly into a top outer portion at step 524, so that the top outer portion of the top conical surface can have a profile like logarithmic graph, when the antenna can be viewed in side profile. Step 520 can optionally include providing a top transition portion at step 526. As described above, the top transition portion may be provided by chamfering a portion of top conical surface where the top inner portion and the top outer portion would meet.
As shown in
Because of the complex, bulbous curvature of the top cone and bottom cone, one way to accomplish the methods can be to use additive manufacturing techniques to provide the top section (cone), bottom section (cone) and feed portion as a unitary structure, using additive manufacturing techniques. This could result in a single integrated structure, and allows for top and bottom cones with different radii or logarithmic curvature, should such a configuration be desired. Additive manufacture using metal materials could be accomplished, or additive manufacturing of a non-metallic, dielectric materials, followed by coating the dielectric with a metallic material could be used. In sum, additive manufacturing techniques could result in a unitary, integral structure, which would require a minimum of assembly, and which could afford great flexibility in cone geometry, according to the systems and methods of the present invention. It should be appreciated that fewer, additional, or alternative steps may also be involved in the method 500 and/or some steps may occur in a different order and/or that additional or fewer steps may be involved.
As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. Additionally, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the invention. This detailed description should be read to include one or at least one and the singular also includes the plural unless it is obviously meant otherwise.
The language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, the disclosure of the inventive subject matter is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims. Many modifications and variations of the embodiments disclosed herein are possible in light of the above description. Within the scope of the appended claims, the disclosed embodiments may be practiced otherwise than as specifically described. Further, the scope of the claims is not limited to the implementations and embodiments disclosed herein, but extends to other implementations and embodiments as may be contemplated by those having ordinary skill in the art.
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: sssc_pac_t2@navy.mil, referencing Navy Case 104087.
