This application is a National Stage Application of PCT/IB2020/056300, filed Jul. 3, 2020, which claims benefit of Patent Application No. 2019/04391, filed Jul. 4, 2019 in South Africa, and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above-disclosed applications.
This invention relates to an antenna, more particularly a helical antenna.
A helical antenna is an antenna comprising of one or more conducting wires wound in the form of a helix. One known family of helical antennas is the family of axial mode helices where the antenna diameter is more or less 1 wavelength at the frequency of operation and the helix is typically several wavelengths in length. Such antennas have a main axis, a front end and a back end and radiate in axial or end-fire mode with a main beam along the main axis.
Known embodiments of such helical antennas include a uniform diameter helical antenna comprising of a single (unifiliar) helical conductor which is fed at the back end of the antenna and radiates a main beam. Such helical antennas exhibit good gain dependent on the length of the helix, while bandwidth is typically limited to about 20% of a centre frequency of a frequency band of operation. Unifiliar back end fed helices with a tapering helix diameter, but constant inter-turn spacing along the length have also been described. These antennas achieve some marginal increase in bandwidth. Helices with a step change in both diameter and inter-turn spacing are also known, but performance across the operational frequency band is unsatisfactory. Uniform diameter helixes with both a taper in diameter and decrease in inter-turn spacing for the last few turns towards the front end are also known, but once again, give only a small improvement in antenna bandwidth.
Bifiliar helical antennas comprising two helical conductors spaced 180 degrees are a different family of helical antennas in that the excitation is applied between the two helical conductors, typically at the front end of the antenna. These antennas often are tapered in diameter and the inter-turn spacing decreases. These antennas cover large bandwidths. They are often referred to as log-spiral or log conical spiral helices. These antennas hence achieve a bandwidth extension, but their gain, when configured as electrically long helices, are much lower than comparable back fed helical antennas. They are also more complex due to the two conductors and require a balanced feed-point at the front end of the antenna.
It is an object of the present invention to provide an alternative helical antenna with which the applicant believes the above problems may at least be alleviated or which would provide a useful alternative for the known helical antennas.
According to the invention there is provided a unifiliar axial mode helical antenna comprising:
The turns may be substantially circular, each having a respective diameter and wherein the respective diameters decrease from the back end to the front end.
The antenna may have a frequency band of operation or interest having a first lower frequency, a second higher frequency and a centre frequency, and the helix may have a length which is at least two wavelengths of a signal at the centre frequency.
The antenna may comprise p turns comprising a 1st turn at the back end through to a pth turn at the front end. A ratio between the diameter of the 1st turn at the back end with the largest diameter and the pth turn at the front end with the smallest diameter may be larger than 1.2:1 and smaller than 3:1.
In one embodiment, a relationship defining the diameter of the turns and their inter-turn spacing is:
where Dn is the diameter of the nth turn, Dn+1 is the diameter of the turn immediately adjacent turn n towards the front end 16 and Sn is the spacing between turns n and n+1. Sn+1 has a corresponding meaning.
A relationship between the diameter of a turn n and its spacing from a next successive turn n+1 is given by:
The diameter of the 1st and largest turn at the back end may be chosen such that:
πD1=C1=K1λmax
Similarly, the diameter of the pth or smallest turn at the front end is given by
πDp=Cp=K2λmin
The antenna may be driven at the feed-point at the back end between a ground plane and the largest or 1st turn.
The invention will now be described, by way of example only, with reference to the accompanying diagrams wherein:
An example embodiment of a unifiliar axial mode helical antenna is generally designated by the reference numeral 10 in the diagrams.
The antenna 10 comprises a single wire wound in a helix 12 comprising a plurality of turns 1, 2, 3, n, n+1, . . . p around a main axis 11 with immediately adjacent turns having an inter-turn spacing between them. The helix having a back end 14 and a front end 16 and the main axis defines a main beam direction.
A transverse cross-sectional area of the helix monotonously decreases from the back end 14 to the front end 16. The inter-turn spacing S1 . . . Sn . . . monotonously decreases from the backend 14 to the front end 16. A feed-point 13 (shown in
The antenna 10 comprises a ground plane 18 and a pillar 20 for supporting the arrangement.
Each turn has a respective transverse cross-sectional area and an inter-turn spacing Sn between a turn n and an immediately adjacent turn n+1 in a direction towards the front end 16. In a presently preferred embodiment, the turns are substantially circular, each having a respective diameter D1, . . . Dn, Dn+1, . . . Dp.
In this preferred embodiment, a relationship defining the diameter of the turns and their spacing is:
where Dn is the diameter of the nth turn, Dn+1 is the diameter of the turn immediately adjacent turn n towards the front end 16 and Sn is the spacing between turns n and n+1. Sn+1 has a corresponding meaning.
A relationship between the diameter of a turn n and its spacing from a next successive turn n+1 is given by:
In an example embodiment, it may be desired to cover a frequency band extending from fmin to fmax and having a centre frequency fc.
The diameter of the a 1st or largest turn at the back end 14 is chosen such that:
πD1=C1=K1λmax
Similarly, the diameter of the pth or smallest turn at the front end 16 is given by
πDp=Cp=K2λmin
The antenna may be driven at feed-point 13. In
In
The prior art antenna is 250 mm in length, the constant inter-turn spacing is 10 mm, the radius of the 1st turn is 21 mm and the radius of the last turn (or turn at the front end) is 1 mm. The example embodiment of the antenna according to the invention has a length of 250 mm, the inter-turn spacing decreases logarithmically from 22 mm to 0.5 mm, the radius of the 1st turn is 15 mm and the radius of the last turn is 2.5 mm.
As can be seen in
Number | Date | Country | Kind |
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2019/04391 | Jul 2019 | ZA | national |
Filing Document | Filing Date | Country | Kind |
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PCT/IB2020/056300 | 7/3/2020 | WO |
Publishing Document | Publishing Date | Country | Kind |
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WO2021/001799 | 1/7/2021 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
5216436 | Hall | Jun 1993 | A |
5329287 | Strickland | Jul 1994 | A |
7286099 | Lier | Oct 2007 | B1 |
9923266 | Casperson | Mar 2018 | B1 |
20030028095 | Tulley | Feb 2003 | A1 |
Number | Date | Country |
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FI20130071 | Sep 2014 | IT |
Entry |
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N. Padros et al., “Comparative Study of High-Performance GPD Receiving Antenna Designs”, IEEE Transactions on Antennas and Propagation 45(4): 698-706 (1997). |
K. Kholotov et al., “3D Antenna for GHz Application and Vibration Energy Harvesting”, IEEE 65th Electronic Components and Technology Conference (ECTC): 2018-2023 (2013). |
International Search Report and Written Opinion for PCT/IB2020/056300 (Sep. 18, 2020). |
Number | Date | Country | |
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20220255231 A1 | Aug 2022 | US |