The present invention relates generally to radio frequency antennas, and more particularly to a low-profile axial mode helical antenna to be used in live entertainment production that has an improved and simplified impedance matching technique.
Axial mode helical antennas have been used for years in many wireless communication applications including the live entertainment industry for reception and transmission of wireless microphones, in-ear monitors, communications and cue control systems. This is due to the advantages of axial mode helical antennas such as circular polarization, large operational bandwidth and forward gain. Their construction is simple. There is a conductive ground plane, usually circular, but can be other shapes, where the connector for the antenna is located and where the shield of the connector makes contact to the ground plane. Perpendicular to the ground plane is a conductor wound in the shape of a helix which looks like a spring with progressing coils with varying or fixed pitch. One end of the helix terminates to the center conductor of the connector and the other end open or in “free space”. This helix forms the radiating element of the antenna. However, axial mode helical antennas naturally have an impedance of approximately 140 ohms and need to be matched to the transmission or reception system's characteristic impedance that is commonly 50 ohms. If not matched, power will be reflected, which is detrimental to any radio frequency system the antenna is connected to. This impedance match is commonly done using a conductive metal strip that is either flat and parallel to the ground plane, tapered and included in the first ¼ turn of the helix or a microstrip transmission line of varying shape, possibly with electrical components such as capacitors or resistors. Alternately, using a ¼ wavelength piece of higher impedance transmission line (in relation to the wavelength of the operating frequency of the antenna) for the first ¼ turn of the helix is also possible. While the latter of these techniques has the advantage of simplicity, and most previously mentioned techniques can be cost effective, none of them offer a very consistent impedance match throughout the majority of the antenna's bandwidth. The average reflected power throughout the tuning bandwidth of the previously mentioned matching techniques, especially those used in live entertainment helical antennas, can be approximately 5.5-11 percent or more. This leaves room for improvement. This can become a notable problem when many in-ear monitor transmission systems are frequency modulated. This analog frequency modulated systems can benefit from a lower audible noise floor when implemented in a radio frequency system using antennas with a better impedance match of approximately 1% average reflected power. In addition to an improved impedance match, there is another area in helical antennas that can be improved upon. With the use of axial mode helical type antennae in live event production, small form and portability is greatly desired. This can be difficult to achieve while satisfying the criteria of the traditional helical formula wherein a minimum of 3 to 4 turns for the helix radiating element and a minimum pitch angle of 12 to 14 degrees is electrically ideal. This, however, can make the axial length too long to be considered portable or small form. In conclusion, it is undoubtable that an antenna with lower reflected power across its entire tuning bandwidth is a better antenna than those with higher levels of reflected power in their tuning bandwidths. It is also undoubtable that in a portable application, it would be beneficial to have the helical antenna's axial length shortened if the electrical and radiating characteristics of the antenna are not compromised.
Axial mode helical antennas have been used for years in the music industry for reception and transmission of wireless microphones, in-ear monitors, communications and cue control systems. This is due to the advantages of circular polarity, large bandwidth and forward gain that are inherent to axial mode helical antennas. However, axial mode helical antennas have an impedance around 140 ohms and need to be matched to the transmission or reception system's characteristic impedance of 50 ohms. This impedance match is commonly done using a conductive metal strip that is either flat and parallel to the ground plane, tapered and included in the first ¼ turn of the helix or a microstrip transmission line of varying shape, possibly with electrical components such as capacitors or resistors. Alternately, using a ¼ wavelength piece of higher impedance transmission line (in relation to the wavelength of the operating frequency of the antenna) for the first ¼ turn of the helix is also possible These impedance matching techniques have a few short falls such as the geometry of these strips can be complex, many times it has a tapered cut adding challenges to the R&D and cost of manufacturing for this type of impedance match. The same is true regarding complexity with a microstrip type impedance match. More crucial is the fact that these impedance matches are generally not consistent throughout the entire tuning bandwidth of the antenna. They fluctuate many times between a good match and a mediocre match throughout the bandwidth of the antenna, leaving room for improvement.
Prior arts and devices used for the previous scenario do not effectively provide solutions to the above-mentioned problem. Much effort has been made to maximize specific functions of axial mode helical antennas such as gain, bandwidth and axial ratio in respect to the physical dimensions of the antenna. This is seen heavily in prior art such as helices with variable pitch angles, different diameter helices in one assembly, multiple helixes wrapped in the same axis, as well as a more straight-forward approach consisting of a tapered design such as antennae utilizing a conical or hemispheric type helix element. These designs can help with portability by reducing the size of the antenna. However, very few make mention of their impedance match and in the case that one does, it is of prior knowledge or still suffers from an inconsistent and fluctuating impedance match across the antenna's operating bandwidth.
U.S. Pat. No. 6,239,760B1 An electrically small broadband antenna comprises a plurality generalized contra wound toroidal helical antenna elements, each made from a single continuous conductor divided into two length portions each of which are substantially the same length and which have a generalized helical pattern, wherein the helical pitch senses the two length portions are opposite to one another, and the two length portions are insulated from one another and overlap one another on the surface of a generalized toroid. Each antenna element incorporates a signal coupler with an impedance matching network, wherein the first ports of the plurality of signal couplers are in proximate location to one another and are connected together to a common signal input port, and the second ports of the respective signal couplers are connected to the respective signal feed ports at the node locations where the respective length portions join one another, or at a diametrically opposite location.
U.S. Pat. No. 5,892,480A Optimization of the exchange of energy between a free space wave and current flowing in the conductive helix of an axial mode, helical antenna is achieved by varying the pitch angle of successive turns of the antenna along the axis of the antenna, from a relatively small pitch angle at the base, feed location of the antenna, to a relatively large value at the distal end of the antenna. Pitch angles of successive turns of the antenna are varied in a non-linear manner to correspond to the non-linear manner in which the phase velocity of a wave propagating through the antenna varies relative to the phase velocity of a free space electromagnetic wave. For the case of an axial mode, helical antenna operating at C-band, the pitch angle of said antenna may be varied between 3-8 degrees at the antenna feed point to 20-30 degrees at its free space-interfacing distal end. The variable pitch angle antenna has a gain versus bandwidth characteristic that contains a plurality of spaced apart peak regions, one of which has a peak gain slightly less than the other. This dual peak gain behavior permits application design tradeoff between a smaller sized antenna with slightly reduced performance versus a larger sized antenna with slightly higher performance.
U.S. Pat. No. 8,436,784B2 Novel reconfigurable antennas are provided which may be used to accommodate the requirements for wideband multi-standard handheld communication devices. It is shown that using a shape memory alloy spring actuator, the height of a helical antenna and therefore the pitch spacing and angle can be varied. This can in turn tune the far-field radiation pattern and gain of the antenna dynamically to adjust to new operating conditions. The radiation pattern can further be directed using a two-helix array. Finally, a helical antenna embodiment is implemented and measured using a shape memory alloy actuator. Measurement results confirm that while keeping the center frequency constant, gain tunability can be attained using this structure.
U.S. Pat. No. 4,935,747A An axial mode helical antenna includes a metal belt member disposed around the reflector of the antenna in order to permit use of reduced diameter reflectors and, therefore, to produce a small helical antenna having increased directivity.
U.S. Pat. No. 7,038,636B2 A helical antenna having a helix supported by a helix support. The helix support includes at least one piece of flexible sheet having its two surfaces covered with a layer antistatic material. The flexible sheet is curl able into a revolution surface configuration to form a revolution surface-shaped support section for at least partially supporting a portion of the helix component there around. A grounding mechanism electrically grounds the external sheet surface to the helix and the two sheet surfaces to one another when in the revolution surface configuration while a locking mechanism locks the flexible sheet in the revolution surface configuration. The combination of the helix and the flexible support renders the antenna structurally relatively rigid in all directions.
U.S. Pat. No. 4,772,895A An antenna is provided which includes first and second helical elements which are separated by a dielectric spacer. The first helical element is fed a radio frequency driving signal and the remaining second element is coupled to ground. The first and second elements are coupled together in a fashion which results in a dramatic increase in antenna bandwidth in comparison to prior helical antennas.
U.S. Pat. No. 9,142,882B2 A spiral, helical antenna is configured to produce a generally circular polarized radiation pattern covering a range of frequencies, over a ground plane. The antenna is comprised of a spring-like spiral conductor that may be held in compression by a size and shape regulating outer nonconductive membrane. The assembly may be compressed and or extended to adjust the antenna for best performance in a particular situation. The assembly may be compressed into a generally flattened state for storage and or transportation, and extended at a later time for use. Accurate antenna dimensions and good performance are afforded by the use of high-quality spring materials in conjunction with precise membrane dimensions.
U.S. Pat. No. 7,714,796B1 A hemispherical helical antenna employs a support frame assembly. The support frame assembly is configured to align and stabilize the turns of the helical antenna element above the ground plane. The support frame assembly includes a plurality of panels manufactured from a dielectric material. The panels are disposed at a fixed angular orientation that defines a central axis and form a series of supports for the element.
The present invention is very similar to already existing Helical antenna, but with a unique configuration. The main feature of the present invention is the impedance match of the antenna. Using an open wire parallel to the first quarter turn creates a “new” type of impedance match that is somewhere between the physical properties of the flat copper strip and a tapered copper strip or microstrip. The open wire impedance match should, in theory, be the same diameter of the element of the helix. However, in this particular antenna, the open wire impedance match diameter was lowered for multiple reasons. The helix is constructed with a 6.35 mm diameter copper tube. This helps with the bandwidth of the antenna and impedance match. However, it is large and difficult to bend which will become necessary for fine tuning. By lowering the open wire impedance match to 2.05 mm diameter solid copper wire (12 AWG), many benefits are realized. 1: Cost;12 AWG is cheap and readily available. 2; Flexibility, the impedance match will inevitably be bent in relation to the ground plane to control the capacitive/inductive reactance and fine tune the impedance match. This allows the combination of a potentially similar geometry to that of the tapered match as well as the flexibility of controlling the reactance of the copper strip match making a wideband, smooth and extremely efficient impedance match using simple and affordable materials.
The following summary is provided to facilitate an understanding of some of the innovative features unique to the present invention, this is not intended to be a full description. A full description of the various aspects of the invention can be gained by taking the entire specification, claims, and abstract as a whole.
The present invention comprises an axial mode helical type antenna assembly that utilizes a hollow copper tube for the radiating element which is wound to form a helix. This helix is shortened below the standard pitch angles as stated in the classic helical formula to be 12 to 14 degrees to a new pitch angle of 5.5 degrees. This helix is supported by an FDM 3D printed cross type dielectric structure with an octagonal base which is perpendicular to and mounted to a conductive circular ground plane. The dielectric structure is semi hollow aiding in maintaining a low relative permittivity to reduce dielectric losses. There is an N type connector that is mounted to the ground plane. For the invention's feed point, between the helix and the ground plane, is a smaller diameter solid copper wire. This wire is connected to the beginning of the helix, passes through the center conductor of the N type connector, travels parallel above the ground plane but below the first ⅛turn of the helix then gradually slopes up toward the helix and eventually meets the helix near the location of the first ¼ turn of the helix. These feeds point configuration, along with the diameter of the helix's hollow copper tube, creates an impedance match with an average reflected power of approximately 1% across the invention's operational bandwidth. This invention operates from 470 MHz to 663 MHz, creating a wide, radiating pattern while still maintaining a high forward gain and is circularly polarized. This invention has an axial length that is approximately 40% smaller than a standard axial mode helical type antenna utilizing similar operational characteristics. The invention has a dielectric protective covering sometimes referred to as a radome.
In
In
This application claims the benefit of U.S. Provisional Patent Application No. 63/183,454, filed May 3, 2021, which is incorporated by reference herein in its entirety.
Number | Date | Country | |
---|---|---|---|
63183454 | May 2021 | US |