Patent Application
20140232611
1. Field
This invention relates generally to a helical antenna and, more particularly, to a helical antenna that can be folded both axially and radially into a compact configuration suitable to be stowed on and deployed from a nano-satellite.
2. Discussion
Satellites orbiting the Earth, and other spacecraft, have many purposes, and come in a variety shapes and sizes. One known satellite type is referred to as a cubed nano-satellite (cubesat) that is typically used solely for communications purposes. Cubesats are modular structures where each module (1U) has a dimension of 10 cm×10 cm×10 cm, and where two or more of the modules can be attached together to provide satellites for different uses.
Satellites typically employ various types of structures, such as reflectors, antenna arrays, ground planes, sensors, etc., that are confined within a stowed orientation into the satellite envelope or fairing during launch, and then unfolded or deployed into the useable position once the satellite is in orbit. For example, satellites may require one or more antennas that have a size and configuration suitable for the frequency band used by the satellite. Cubesats typically operate in the VHF or UHF bands. Because cubesats are limited in size, their antennas are required to also be of a small size, especially when in the stowed position for launch. Cubesats have typically been limited to using dipole antennas having the appropriate size for the particular frequency band being used. However, other types of antennas, such as helical antennas, have a larger size, and as thus offer greater signal gain, which requires less signal power for use.
It is known in the art to deploy helical antennas on various types of satellites other than cubesats. Known satellites that employ helical antennas typically have been of a large enough size where the antenna can readily be stowed in a reduced area for launch. However, these helical antennas have typically been confined only in an axial direction, i.e., in a lengthwise direction, for subsequent deployment. For a cubesat, this level of confinement and reduced size for stowing of a helical antenna is unsatisfactory.
The following discussion of the embodiments of the invention directed to a helical antenna capable of being folded in both an axial and radial direction for stowing and launch on a rocket is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, the helical antenna described herein has particular application for a cubesat. However, as will be appreciated by those skilled in the art, the helical antenna may have other applications.
As will be discussed in detail below, in order for the helical antenna 16 to be of the size discussed herein to provide the desired antenna performance, and to allow the antenna 16 to be confined and stowed within the deployment box 14 for launch also of the size discussed herein, and for the antenna 16 to properly deploy to the shape shown in
When the antenna 16 is collapsed and confined within the deployment box 14 it has some amount of strain energy so that when the antenna 16 becomes “free” it will “open” using its own stored energy to its deployed orientation as shown in
The helical antenna 16 includes a number of elements that are secured together to provide the working antenna element and the structure necessary to support the antenna 16. Particularly, the antenna 16 includes two helical elements 22 and 24 that are wound and intertwined relative to each other to form an antenna column 26, where the helical element 22 is wound in a clockwise direction and the helical element 24 is wound in a counter-clockwise direction. In this non-limiting design, only the helical element 22 is an antenna element that receives and transmits the communications signal, where the helical element 24 is a support element. To provide the necessary electrical conductivity, the helical antenna element 22 is covered with or enclosed within an electrically conductive material, such as a copper tape 34 to provide the conductivity to propagate the signals. In other embodiments, the helical element 22 can be made conductive in other suitable ways. Also, in an alternate embodiment, both of the helical elements 22 and 24 can be antenna elements.
The column 26 formed by the helical elements 22 and 24 is reinforced by a series of vertical stiffeners 28, eight in this non-limiting example, circumferentially disposed around the column 26 and being equally spaced apart to provide axial stiffness. In this non-limiting embodiment, the helical elements 22 and 24 are wound outside of the stiffeners 28. At each location where one of the helical elements 22 or 24 crosses one of the vertical stiffeners 28, those elements are attached to each other so that they retain their desired shape and configuration. Likewise, at those locations where each of the helical elements 22 and 24 cross each other they are attached together. The stiffeners 28 and the elements 22 and 24 can be secured together in any suitable manner, such as by a suitable adhesive or by using heat to bond or weld the stiffeners 28 and the elements 22 and 24. The vertical stiffeners 28 and the helical elements 22 and 24 are configured and mounted together so that a mounting end 30 of the antenna 16 at the deployment box 14 has the same diameter as the column 26 and an opposite deployed end 32 of the antenna 16 has a rounded and tapered configuration.
In one non-limiting embodiment, the length of the vertical stiffeners 28 and the helical elements 22 and 24 is selected and the helical elements 22 and 24 are wound to have about five coils and a 12° pitch so that the length of the column 28 is about 138 cm to provide the desired antenna performance. In one embodiment, all of the helical elements 22 and 24 and the vertical stiffeners 28 are formed of a fiberglass, such as S-2, that is impregnated with a thermoplastic, such as PEEK, that is pultruded to form a material having a thickness of about 5 mils. These materials give the desired flexibility and rigidity necessary to collapse the antenna 16 as discussed herein, and give the collapsed antenna 16 the necessary spring energy to return to the desired deployed shape. However, as will be appreciated by those skilled in the art, other materials may also be applicable to provide these features. Further, in this non-limiting embodiment, the width of the helical elements 22 and 24 is about ¼ of an inch and the width of the vertical stiffeners 28 is about ⅝ of an inch. Also, the copper tape 34 has a thickness of about 3.5 mils.
Once the antenna 16 is held in the radially folded position as shown in
The foregoing discussion disclosed and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.
