Development of a Novel Ultra-Wideband Antenna, 10-9176Printer Friendly Version
Inclusive Dates: 01/01/00 - 01/01/01
Background - Several antenna configurations can be designed to cover one or more octaves. Some configurations, such as the conical spiral and log periodic, are inherently directional, while other configurations, such as the bicone and tapered-blade antennas, are omni-directional. Most broadband antenna configurations are difficult to design for low-voltage standing wave ratio (VSWR) for more than one octave. Low VSWR is not a design necessity as long as the antenna is an efficient radiator; however, if the VSWR is high (greater than 3:1), some form of matching network must be placed between the transmitter and antenna to minimize mismatch loss. Such designs are costly and make automation of the matching function much slower than is possible with lower power, solid-state tuning elements. SwRI began investigation of a simple antenna configuration that exhibits low VSWR over a wide bandwidth while providing linear and circular polarization at certain frequencies. This configuration may be suitable for many military and commercial requirements.
This antenna configuration can be described as a tapered area small helix (TASH). Physically, the TASH antenna can be constructed by rolling a right-triangle-shaped conductive material into a spiral having a specific length and diameter. The key physical parameters affecting antenna performance are the height-to-base ratio, base feed point, turns spacing, and spacing above a ground plane. A three-turn TASH monopole above a ground plane with simulated current distribution (color pattern) is shown in the illustration below
Approach - The primary objectives of this research and development effort are to: determine the parameters that affect the characteristics of the TASH antenna by simulation; determine the limitations on bandwidth, radiation efficiency, and antenna pattern; develop design tools and aids that will allow design of a TASH antenna with particular characteristics; and assemble and test a practical prototype TASH antenna to validate the simulations and design tools and aids.
The TASH antenna configuration is being investigated using simulations based on method-of-moments analysis of the tapered area. The simulations allow optimization of the antenna configuration (turns spacing, taper, and height-to-diameter ratio) and development of aids and tools usable for design of practical antennas. Assembly and test of a prototype TASH antenna will follow as a verification of the simulation and a test of the design aids and tools. The tests will be structured to verify the radiation efficiency, pattern, and VSWR characteristics of various TASH antenna configurations as simulated and designed.
As a result of the simulations, nomographs or empirical equations will be developed for use as design tools and aids. The tools will be developed to determine VSWR, pattern, and material characteristics for a particular TASH antenna configuration. This development will be followed by verification of nomographs and equations. Verification will be via design, assembly, and test of a TASH antenna using the tools and aids for a specific application.
Accomplishments - To date, the program has simulated the TASH monopole and other single-element monopoles for comparison. Physical models were then assembled and verification tests of VSWR performed to determine the validity of the simulations. The verification tests showed excellent correlation with the simulated antennas. A large series of simulation runs were then performed on variants of the TASH monopole to establish design guidelines for TASH monopoles with low VSWR over at least one octave above first resonance. Several TASH prototypes were assembled and tested in accordance with the design guidelines. A patent disclosure also resulted from work performed in this project.