The present invention is drawn to an expandible antenna.
Traditionally, antennas have been defined as metallic devices for radiating or receiving radio waves. Therefore, the paradigm for antenna design has traditionally been focused on antenna geometry, physical dimensions, material selection, electrical coupling configurations, multi-array design, and/or electromagnetic waveform characteristics such as transmission wavelength, transmission efficiency, transmission waveform reflection, etc. As such, technology has advanced to provide many unique antenna designs for applications ranging from general broadcast of RF signals to weapon systems of a highly complex nature.
Conductive wire antennas are generally sized to emit radiation at one or more selected frequencies. To maximize effective radiation of such energy, the antenna is adjusted in length to correspond to a resonating multiplier of the wavelength of frequency to be transmitted. Accordingly, typical antenna configurations will be represented by quarter, half, and full wavelengths of the desired frequency.
Efficient transfer of RF energy is achieved when the maximum amount of signal strength sent to the antenna is expended into the propagated wave, and not wasted in antenna reflection. This efficient transfer occurs when the antenna length is an appreciable fraction of transmitted frequency wavelength. The antenna will then resonate with RF radiation at some multiple of the length of the antenna. Due to this traditional length requirement, rigid metal antennas can be somewhat limited in breadth as to the frequency bands that they may radiate or receive. Frequency bands representing long wavelengths necessitate large antennas which are especially limited in mobility.
Supports for antennas have also evolved over time. Inflatable structures have been effectively used to suspend and support radar reflectors and antennas in various environments. For example, an inflatable radar reflector incorporated within a life raft has been described in U.S. Pat. No. 3,130,406. Specifically, this patent discloses a circular sheet of flexible material having at least one circular central section reflective of radio waves and an inflatable endless tube which encircles the sheet to hold the center section taut and flat when the tube is inflated.
U.S. Pat. No. 4,475,109 discloses an inflatable antenna for use with a buoy at sea that provides hemispherical coverage including sufficient gain at the horizon. The inflatable compartment contains webs that are metalized to form the feed portions of the radiating elements. Additionally, areas of the top inner surface of the inflatable compartment are also metalized to form capacitive loading portions of the radiating elements. A ground is formed by conductive inner and outer surfaces of the bottom of the inflatable compartment which are coupled to the sea water.
Inflatable antennas have also been used to support land radar antennas and reflectors for radio waves. Such an antenna was disclosed in U.S. Pat. No. 2,913,726. Specifically, this patent discloses an inflatable antenna structure that comprises two paraboloids joined at their rims to form an inflatable housing. The housing is supported in an upright position on a rotatable base. One of the paraboloids has its inner surface coated with reflective material so that when the housing is inflated, the coated paraboloid assumes the configuration of a parabolic antenna reflector.
U.S. Pat. No. 3,005,987 discloses an inflatable antenna assembly comprising an elliptical tubular member having sheets of flexible nonconducting material fastened to opposite sides of the tube to form an enclosure.
U.S. Pat. No. 3,115,631 discloses an inflatable reflector for radio waves comprising a base of double pile textile fabric having outer sheets which are rendered substantially impermeable to gas and are tied together in a parallel-spaced relation by pile threads. The threads are woven through the fabric and form a chamber which can be inflated. Upon inflation, sheets of flexible radio reflecting material which are secured therein become taut and held flat in a mutually perpendicular relation.
U.S. Pat. No. 3,170,471 discloses an inflatable honey-comb element for use in making up structures which are foldable and inflatable. The element comprises a collapsible, inflatable structure which has flexible outer skin members and flexible inner core members which are perpendicularly disposed to divide the element into a plurality of cells. The panel structure may be fabricated of a thin, lightweight flexible plastic film or sheet which may further have a thin layer of metal placed thereon to strengthen the plastic and to reflect the light and radio wave.
U.S. Pat. No. 3,176,302 discloses an inflatable variable band with antenna having an inflatable tubular ring which supports a flexible diaphragm. The diaphragm comprises nonconductive fabric and parallel, spaced elastic flexible conductive strips secured by their ends to the periphery of the housing.
U.S. Pat. No. 3,811,127 discloses an antenna suitable for airborne satellite communications. That antenna has four metal blades orthogonally positioned on a support base, which includes a ground plane. Each blade has at the upper edge thereof a metal capacitive loading portion which is formed roughly into the shape of a section of a sphere. The capacitive loading portions define at least approximately a spherical section.
U.S. Pat. No. 5,132,699 discloses a collapsible antenna formed of one or more generally planar and vertically inclined inflatable panels. Each of the panels has a continuous outer wall, a continuous inner wall, and a plurality of web partitions extending between the inner and outer walls to form a series of tubular members. The inner wall of the collapsible antenna is at least partially covered by a metallic material and a plurality of dipole elements are affixed to the web partitions and spaced from the inner wall in a predetermined relationship such that the antenna will operate at a preselected frequency when inflated.
U.S. Pat. No. 5,739,738 discloses an inflatable high Q toroidal inductor which is fabricated from a flexible toroidal-shaped shell. The shell is coupled to a source of pressurized gas which inflates the flexible shell to assume a toroidal shape. One or two flexible annular bands are secured at intervals to the toroidal shell to hold at least one flexible inductor in a toroidal-shaped winding configuration on the toroidal-shaped shell. The inductor itself is preferably comprised of flexible litz wire windings that are held in place by flexible bands on the inside and outside of the inflated toroidal-shaped shell.
Though some of the aforementioned patents describe various types of inflatable antennas, none describe a radially expandible antenna apparatus (and associated method) as disclosed or claimed hereafter that allows for rapid deployment and retraction as would be desirable for use with submarines and/or other underwater vessels. Thus, it would be useful to provide such an apparatus and associated method.
The present invention is drawn to an expandable antenna device comprising an expandible shell defining an interior chamber, wherein the shell is radially expandible from a compacted configuration with respect to a central axis within the chamber. An elongated support structure is disposed along the central axis and at least partially within the chamber. An antenna element is coupled to the shell such that the antenna is dimensionally stable when the shell is in an expanded position for operation. Any type of antenna that is flexible, pivotable, retractactable, expandible, etc., can be used. In one embodiment, the antenna element can be comprised of two conductive elements, and a fluid, e.g., gas or vapor, filled bulb or tube wherein the fluid is capable of ionization positioned between the conductive elements such that when the fluid in the bulb or tube is energized, the conductive elements electrically communicate with one another, and when the fluid is not energized, the conductive elements do not electrically communicate with one another.
Additionally, a method of deploying and operating an antenna element from a collapsed and protected configuration to a desired expanded and operational position is disclosed. This method comprises the steps of locating the antenna element having an expandible shell which surrounds an elongated axis at a desired location for deployment; radially expanding the shell such that the antenna element deploys from the central axis to a radially expanded position; and processing an electromagnetic wave through the antenna element.