Communications: radio wave antennas – Antennas – Antenna components
Reexamination Certificate
2000-11-13
2002-01-22
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Antenna components
C343S840000, C343SDIG002
Reexamination Certificate
active
06340956
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention (Technical Field)
The present invention relates to the field of impulse radiating antennas, specifically to wideband collapsible and portable impulse radiating antennas for ease of transport and deployment in the field.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
The present invention is a collapsible impulse radiating antenna (“CIRA”), which is a compact and lightweight implementation of the general class of antennas known as impulse radiating antennas (IRAs). IRAs are well suited for radiating an extremely broad band of signal frequencies at reasonable gain throughout the band. While the antenna gain is not optimal at any one frequency, it is sufficient for many applications over frequency ranges of around two decades (100:1 frequency ratio). Such devices also provide the ability to radiate an impulse-like electric field, when driven by a step-like voltage. Furthermore such devices are typically well matched to a 50-ohm impedance, so there is little power lost due to reflection from the antenna back into the source. Reflector IRAs generally consist of a parabolic reflector with a transverse electromagnetic (TEM) feed resulting in very broadband performance (2 decades) with a very narrow beam.
IRAs are useful in a wide variety of applications, including broadband communications and broadband radar. Broadband communications may include two distinct types of communication. First, broadband communications include conventional narrowband communications that are swept in frequency over large bandwidths. As an example, one may wish to listen to a very broad range of frequencies (or radio channels) without changing antennas. Second, broadband communications may include the radiation or reception of instantaneously broadband signals, which are often impulse-like in shape. This mode of communication is primarily digital, and is commonly implemented with pulse position modulation. In this form of modulation, a one or a zero is interpreted based on the time of arrival of an impulse relative to some time standard.
Broadband radar, like broadband communications, can encompass methods that require the use of either narrowband signals that are swept over a broad frequency band, or the use of signals that are instantaneously broadband or impulse-like. Broadband radar can have applications in the detection of mines or unexploded ordnance. It can also have application in the detection of cracks in road beds or in bridges. Furthermore, it can have applications in target identification, where the broad bandwidth is utilized to provide more information than what is normally generated by a narrowband radar system. Finally, broadband radar can be useful in Synthetic Aperture Radar (SAR), which can be used to map out ground features from the air.
An IRA enables a single antenna to perform multiple narrowband missions on a platform, such as a ship or satellite, with limited space available for antennas. While each of the missions may be intrinsically narrowband, the combined mission of the platform may require each of them to share a single broadband antenna.
Any of the IRA applications described above may, at times, require a portable version of the IRA to enable practical system development. This will occur if a system requires both high gain and portability. High gain forces one to use a large antenna, while portability suggests a small design. IRAs are generally fabricated from a solid reflector, which is clumsy to deploy and transport particularly when it reaches a certain size.
Several issued patents address the need for portable antennas and describe various collapsible configurations, some of which allow for stowing and deploying a paraboloidal reflector. None of these patents include the features of a broadband feed enabling a broad bandwidth for the antenna, collapsibility, and portability. U.S. Pat. No. 3,707,720 entitled, “Erectable Space Antenna” to Staehlin et al. describes a collapsible antenna for use in space. The antenna described is not applicable for a large bandwidth or for ultra-wide band use; the reflector is flat and cannot achieve a paraboloidal shape thereby compromising the available gain.
U.S. Pat. No. 4,642,652 to Herbig et al., entitled, “Unfoldable Antenna Reflector” discloses a collapsible antenna wherein bracing wires placed behind the antenna are used to provide the tension force to maintain the antenna's shape. U.S. Pat. No. 5,963,182 to Bassily entitled, “Edge-Supported Umbrella Reflector with Low Stowage Profile” discloses an umbrella-type antenna for use on a spacecraft where the ribs of the antenna are fixed in a parabolic shape using a rigid truss structure. U.S. Pat. No. 5,635,946 to Francis entitled, “Stowable, Deployable, Retractable Antenna” discloses a retractable and deployable antenna wherein cables are used to deploy as well as support the reflector. U.S. Pat. No. 4,899,167 to Westphal entitled, “Collapsible Antenna” discloses a collapsible antenna where rigid saw-tooth shaped segments collapse into one another to collapse the reflector. U.S. Pat. No. 3,618,111 to Vaughan entitled, “Expandable Truss Paraboloidal Antenna” discloses a collapsible antenna made up of a plurality of interconnecting hinged solid triangular supports making up a truss antenna structure. U.S. Pat. No. 3,982,248 to Archer entitled, “Compliant Mesh Structure for Collapsible Reflector” discloses a collapsible antenna made of a wire mesh structure with spring-loaded wires that expand to a certain shape when deployed. The elasticity of the mesh allows the material to take shape when deployed. U.S. Pat. No. 4,295,143 to Winegard et al. entitled, “Low Wind Load Modified Parabolic Antenna” discloses a collapsible reflector boom having two parabolic reflectors mounted thereon. Solid reflector elements make up the two symmetrical parabolic reflectors.
None of the antennas described in the above patents provide a lightweight, portable, ultra-wideband collapsible antenna. The present invention for a collapsible impulse radiating antenna overcomes the deficiencies in the prior art patents by providing a high gain, ultra-wideband antenna that comprises a reflector made of a conductive mesh fabric that is lightweight and collapsible in an easy umbrella-like fashion. The present invention enables all of the applications discussed above and many others, because it is more portable and lightweight than conventional IRAs. In the preferred embodiment, the present invention for a collapsible IRA (“CIRA”) weighs only five pounds and is about the size of a typical umbrella, making it easily transportable by an individual, and easily deployable in the field.
In a second embodiment, the CIRA includes expandable seams between adjacent panels of the reflector, enabling the reflector surface curvature to be adjusted from a more focused to a less focused mode. The flexibility of this embodiment provides a collapsible multifunction IRA (“CMIRA”).
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
The present invention is a broadband collapsible impulse radiating antenna having a reflector and feed arms made from a flexible conductive material. The antenna is operational over a broad bandwidth, in a range from below 50 MHz to above 8 GHz. When driven by a step function, the antenna can radiate an impulse on boresight having a full-width-half-maximum of less than one-fifth the time required for light to travel a distance of one reflector diameter in free space. An umbrella-like support mechanism is used to collapse and deploy the reflector. The umbrella-like mechanism consists of a plurality of support ribs, a center support rod, center push
Bowen Leland H.
Farr Everett G.
Mays Andrea L.
Nguyen Hoang
Wong Don
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