Compressed closed circuit circularly polarized omni-directional antenna

Compressed closed circuit circularly polarized (CLCP) omni-directional antennas and methods of fabrication are described. Such an antenna reduces the size of conventional circularly polarized antennas while also allowing increased axial ratio. An antenna comprises a plurality of conductive elements at an angle of between 5 and 52 degrees spaced radially around a multi-element feed system. The multi-element feed system may be made from a PCB and fed from a coaxial cable. The plurality of conductive elements may contain between 2 and 8 individual conductive elements. Each element in the plurality of conductive elements is a closed loop. The antenna may be covered by a protective housing which may also further reduce the size of the antenna.

TECHNICAL FIELD

The present disclosure relates generally to antenna systems, and more specifically to circularly polarized omni-directional antennas for use in video piloting, drone vehicles (aircraft and ground), mesh networking, and Wi-Fi applications.

BACKGROUND

Antennas are electrical devices which convert electric power into radio waves, and vice versa. They are usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce an electric current at its terminals, and is applied to a receiver to be amplified.

Typically an antenna consists of an arrangement of metallic conductors (elements), electrically connected (often through a transmission line) to the receiver or transmitter. Antennas may also include additional elements or surfaces with no electrical connection to the transmitter or receiver, such as parasitic elements, parabolic reflectors or horns, which serve to direct the radio waves into a beam or other desired radiation pattern.

Antennas can be designed to transmit and receive radio waves in all horizontal directions equally (omnidirectional antennas), or preferentially in a particular direction (directional or high gain antennas). An omnidirectional antenna is a class of antenna which radiates radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. Omnidirectional antennas oriented vertically are widely used for nondirectional antennas on the surface of the Earth because they radiate equally in all horizontal directions, while the power radiated drops off with elevation angle so little radio energy is aimed into the sky or down toward the earth and wasted. Omnidirectional antennas are widely used for radio broadcasting antennas, and in mobile devices that use radio such as cell phones, FM radios, walkie-talkies, wireless computer networks, cordless phones, GPS as well as for base stations that communicate with mobile radios, such as police and taxi dispatchers and aircraft communications.

Typically omnidirectional circularly polarized antennas are much larger than linearly polarized antennas of the same frequency. Therefore, reducing their size to fit smaller devices such as WiFi systems or unmanned aerial vehicles is often desirable.

Various types of circularly polarized antennas have been developed. One is described in U.S. Pat. No. 3,656,166 titled “Broadband circularly polarized omnidirectional antenna” utilizing a plurality of passive elements surrounding a biconical dipole. It would be beneficial to not have to utilize a central dipole.

Another form of circularly polarized omnidirectional antennas may be found in Korean Patent KR101315546B1 titled “Dual-band omnidirectional circularly polarized wave antenna using metamaterial” which utilizes flat PCB s or stamped material to achieve an omni-directional circular pattern. It would be beneficial if the radiating elements in an antenna are turned upward and do not lay flat on a single plane.

Other forms of compressed circularly polarized omnidirectional antennas may be found in U.S. Published Patent App. 2017/0346194 titled “Compact Polarized omnidirectional helical antenna” in which an antenna has dipoles curved around a central axis fed by a micro-strip made from PCB material. It would be beneficial to have an antenna where the elements are closed-loop conductive elements and not open type dipoles. The closed loop elements allow for fewer electrical connections as well as allow a smaller form factor for the antenna.

SUMMARY

Provided are examples of compressed closed circuit circularly polarized omni-directional antennas and methods of fabricating such antennas. In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, an antenna comprises a plurality of conductive elements are curved or bent around the center. The number of individual elements in the plurality of conductive elements may be between 2 and 8 elements. Each element in the plurality of conductive elements is a closed loop where the element is electrically connected on both ends.

Each element in the plurality of conductive elements is tilted from horizontal. This tilt angle varies depending on the number of elements and the distance of each element to the center of the antenna. The elements are tilted upward to the right for a right-hand circularly polarized (RHCP) pattern or upward to the left for a left-hand circularly polarized pattern when viewing the antenna from the side. This tilt angle may be between 5 and 52 degrees from horizontal.

The antenna further comprises a feedline system which is electrically connected to each element in the plurality of conductive elements. In certain embodiments, this feedline system is a printed circuit board (PCB).

The antenna further comprises a cable connecting to the feedline system. The cable may be aligned with a center axis of the antenna. In some embodiments, the cable is a coaxial cable. The second end of the cable may include a coaxial radio frequency (RF) connector.

In various embodiments, the antenna is made from stamped metal such as copper or brass which comprises the plurality of conductive elements and the feedline system. In other embodiments, the feedline system and the plurality of conductive elements are made from a stamped or laser cut metal sheet in which the plurality of conductive elements is bent upward from the feedline system and then electrically bonded to a ground plane such as a copper disc.

In another aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, a method for constructing an antenna is provided. A cable is inserted into multi-element feed system on a printed circuit board (PCB). The center conductor of the cable is electrically bonded to one side of the PCB and the shield of the cable is electrically bonded to the opposite side of the PCB. The plurality of conductive elements is installed onto the edges of the multi-element feed system. One end of each element in the plurality of conductive elements is electrically bonded to a trace in the multi-element feed PCB. The opposite end of each element is electrically bonded to the opposite side of the PCB.

Other implementations of this disclosure include corresponding devices, systems, and computer programs, configured to perform the actions of the described method. For instance, a system is provided comprising a receiver and an antenna as previously described. In some embodiments, the antenna is coupled to the receiver via a coaxial radio frequency (RF) connector that is coupled to the second end of the cable. In some embodiments, the antenna is directly coupled to a circuit board of a receiver or transmitter. These other implementations may each optionally include one or more of the following features.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

For example, the techniques of the present invention will be described in the context of particular machines, such as drones. However, it should be noted that the techniques of the present invention apply to a wide variety of different machines that may require remote wireless control. As another example, the techniques of the present invention will be described in the context of particular wireless signals, such as Wi-Fi. However, it should be noted that the techniques of the present invention apply to a wide variety of different wireless signals, including Bluetooth, line of sight transmission mechanisms, beyond line of sight systems, satellite communications, as well as various other networking protocols.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Particular example embodiments of the present invention may be implemented without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

Various techniques and mechanisms of the present invention will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise. For example, a system uses a processor in a variety of contexts. However, it will be appreciated that a system can use multiple processors while remaining within the scope of the present invention unless otherwise noted. Furthermore, the techniques and mechanisms of the present invention will sometimes describe a connection between two entities. It should be noted that a connection between two entities does not necessarily mean a direct, unimpeded connection, as a variety of other entities may reside between the two entities. For example, a processor may be connected to memory, but it will be appreciated that a variety of bridges and controllers may reside between the processor and memory. Consequently, a connection does not necessarily mean a direct, unimpeded connection unless otherwise noted.

Various embodiments are provided which describe a circularly polarized omni-directional antenna. Antennas as described herein may be referred to herein as a miniature CLCP (closed loop circularly polarized) antenna. Such antennas may have implementations in a variety of fields, including, but not limited to video piloting, drone vehicles (aircraft and ground, mesh networking, and Wi-Fi applications. In various embodiments, the antenna uses a plurality of conductive elements curved or bent around a central multi-element feed system. Such elements may be wire or printed on a printed circuit board (PCB). The multi-element feed system may be a coaxial cable, PCB, or a combination of both.

In various embodiments, the CLCP antenna uses a PCB microstrip to feed multiple closed loop conductive elements. These elements are bent or curved around the center of the antenna. These elements may be a made of a wire or printed on a PCB (printed circuit board). The entire antenna may be encapsulated with a cover and filled with a dielectric such as expanding foam for protection. Accordingly, various embodiments described in the present disclosure provide a lightweight omni-directional antenna that includes reduced sizing with greater durability and ease of assembly that may be implemented in a variety of systems.

With reference toFIGS. 1A, 1B, 1C, 1D, and 1Eshown are perspective views of a multi-element feed system100in accordance with one or more embodiments. In various embodiments, the multi-element feed system100is comprised of multiple microstrip traces122above a ground plane125. The microstrip traces122may connect to exposed soldering pads123on the edges of the PCB121which are electrically bonded to the plurality of conductive elements150. For example,FIG. 1Eis a printed circuit board layout of a three element version of a compressed closed circuit circularly polarized omni-directional antenna.FIG. 2Dis the corresponding antenna PCB layout for the 3 element version of the antenna.

In some embodiments the multi-element feed system120is comprised of multiple microstrip traces122within a printed circuit board121(PCB). The microstrip traces122may be straight or curved and may change width to achieve the desired electrical characteristics. The PCB121may be a multiple layer board made from FR4 or from a flexible PCB with the microstrip traces122on one side and a conductive ground plane125on the opposite side. The conductive ground plane125may cover the entire side of the PCB or may only cover a portion of the PCB. A hole124may be drilled in the center of the PCB121to pass a portion of cable201through.

With reference toFIGS. 2A, 2B, 2C, and 2Dshown is a perspective view of the plurality of conductive elements in accordance with one or more embodiments. In various embodiments, the plurality of conductive elements is comprised of a printed circuit board (PCB)153with individual conductive elements151printed on one side of the PCB153. In various embodiments the PCB153in the plurality of conductive elements is made from FR4. In other embodiments the PCB153in the plurality of conductive elements is made from a flexible PCB.

In various embodiments, each end of the individual conductive elements151may be terminated by an exposed soldering pad152. The plurality of conductive elements may also contain stress relief points154where the plurality of conductive elements may be bent at a sharp angle to fit within an angular cover. In various embodiments, there are no stress relief points154within the PCB153for structures such as a round or cylindrical antenna.

With reference toFIG. 2Cshown is a perspective view of the plurality of conductive elements200without stress relief points154. In various embodiments, each end of the individual conductive elements151may be terminated by an exposed soldering pad152which may be located on one or both sides of the PCB153.

With reference toFIGS. 3A, 3B, 3C and 3D, shown are perspective views of an example assembled CLCP omni-directional antenna300, in accordance with one or more embodiments. In various embodiments, antenna300includes a multi-element feed system100which connects a cable201with the plurality of conductive elements. Each element in the plurality of conductive elements200is fed by a microstrip trace122in the multi-element feed system100.

In various embodiments the exposed soldering pads152of the multielement feed system100are bonded to the exposed soldering pads123on the plurality of conductive elements. The soldering pads123on the plurality of conductive elements may be bonded on one or both sides of the PCB121.

In various embodiments, cable201comprises a coaxial cable, such as an RG142 coaxial cable, for example. In other embodiments, cable201may comprise any other type of cable with the appropriate electromagnetic characteristics. In some embodiments, the cable may include a characteristic impedance between 25 and 200 Ohms. Such other cables may include an RG402 coaxial cable. In various embodiments, cable102may include several layers. The outermost layer may be a jacket, such as a 4.95 mm PTFE jacket. The next layer may be an outer conductor or shield, such as a 4 mm layer of copper plated steel or silver coated copper clad steel. The next layer may be an insulation layer, such as a 2.95 mm layer of solid extruded PTFE. The innermost layer may be an inner conductor, such as a 0.8 mm silver plated copper wire. In various embodiments, cable102may comprise a combination of one or more of the aforementioned layers.

The second end of cable201may be coupled to a coaxial radiofrequency (RF) connector203. For example, coaxial RF connector203may be a SubMiniature version A (SMA) connector. As another example, coaxial RF connector203may be an MMCX connector, or any other suitable miniature RF connector for high-frequency signals. In some embodiments, coaxial RF connector203may be an integral part of cable201. In various embodiments, various types of connectors203may be implemented to electrically connect antenna300with a circuit board of a transceiver or other device. In some embodiments, cable201may be directly coupled to a circuit board without using a connector203. For example, second end of cable201may be directly soldered to a circuit board of a transmitter.

In various embodiments, the frequency of operation (f) of antenna100may depend on the length of the conductive elements151as well as the placement of the plurality of conductive elements. For example, for a given arrangement of components, the length of each conductive element151in inches may be approximated by the following equation:

Where f is the desired frequency in GHz. The radiation pattern may also depend on the distance of the conductive elements151from the center of the antenna. The equations above may be approximations and may include a margins of error. For example, the frequency measurements based on the length of the element may vary by +/−68%.

With reference toFIGS. 3A and 3Bin some embodiments, the distance from the center of each conductive element151in the plurality of conductive elements150to the center of the antenna may be approximated by the equation:

where ri is the distance in inches from the center of each conductive element to the center of the antenna and f is the frequency in GHz. This distance may vary by as much as +/−54%.

With reference toFIGS. 3C and 3Din some embodiments, the distance from the center of each conductive element151in the plurality of conductive elements150to the center of the antenna may be approximated by the equation:

where ri is the distance in inches from the center of each conductive element to the center of the antenna and f is the frequency in GHz. This distance may vary by as much as −41% to +105% depending on the desired characteristics of the antenna.

With reference toFIG. 4, show is an example single element151wherein the element151is a copper wire. In various embodiments the single element151is an uninsulated bare copper wire. In specific embodiments, the single element is covered partially by insulation. In specific embodiments the insulation is removed to exposed a soldering pad152in the element151.

FIG. 5is an example radiation pattern graph500of an omni-directional antenna, in accordance with one or more embodiments. The graph shows radiation pattern of an example of a right hand circular polarization configuration of antenna100. The graph shows the total gain502(outermost pattern), dominant rotation pattern504(middle pattern), and recessive pattern506(innermost pattern). The plurality of conductive elements may be reversed in direction to change the recessive and dominant antenna patterns from RHCP to LHCP and LHCP to RHCP. Additionally, the location of the plurality of conductive elements will change the pattern of the antenna.

FIG. 6is an example non-conductive protective cover600in accordance with one or more embodiments. The cover comprises a top portion601and a bottom portion602. The bottom portion may contain a hole for the cable to extend through. This hole may be in the bottom of the lower portion602or may be in the side of the upper portion601. The cover may be filled with protective foam603such as poly-urethane expanding foam.

FIG. 7is a flow diagram of a method of assembling a closed-circuit circularly polarized antenna omni-directional antenna in accordance with one or more embodiments. At step702a cable201is inserted through the bottom cover602and into the multi-element feed system100. At step704the center element of the cable201is electrically bonded to the microstrip traces122and the shield of the cable201is electrically bonded to the ground plane125. At step706, the plurality of conductive elements200is bent around the multi-element feed system100. At step708each solder pad152of each element in the plurality of conductive elements200is electrically bonded via the exposed solder pads152to the solder pads123of the multi-element feed system100. At step710, the CLCP antenna is bent and pressed inside of the top portion601of the non-conductive cover600. At step712, the top cover portion601is bonded to the lower cover portion602encapsulating the plurality of conductive elements200and the multi-element feed system100into an assembled CLCP antenna300.