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Energy Efficient HF Transmit Antennas


OBJECTIVE: Current HF antennas are resonant and single function. Given the 10 to 1000's of meters of wavelengths at these frequencies, the antennas thus add substantial weight, radar cross section, and thermal signature to the platforms that carry them even as they cover a very narrow spectral range. Most man-pack scale platforms thus omit their functionality. Several approaches (superconducting SQIF, metamaterials, and plasmmonics) are attempting to build electrically small HF receive antennas, but their functionality in transmit mode appears more limited. The idea of this topic is to accept the idea that Tx requires substantial area and try to include the radiation function with some other function. For example, combine HF Tx with solar collectors (also produce power used), hull plates,walls and roof tops and armor. Moreover, there is the appealing idea of distributed production of RF energy of directional beams at the intended frequency. This could be done via strongly sub-wavelength phase arrays (ala a Hyugens wavelets construction of the interference pattern of multiple slits). Another idea which could be explored under this topic is that of sparse arrays in 3D of such arrays. Finally thermoelectric energy harvesting off hot amplifiers could both lower thermal signatures and improve energy efficiency. DESCRIPTION: The military is as desirous of reducing the weight, size and power consumption of military platforms as is the consumer electronics world since large SWaP impedes mobility and raises maneuvering costs. However, some wireless frequency bands such as HF have such long wavelengths (300m at 1 MHz) that transmitting it efficiently off any platform smaller than a 747 plane is difficult. Thus it is desirable to figure out how to utilize another, more essential and not necessarily planar part of the platform to do double duty as an energy efficient HF antenna, possibly using optical phased array techniques to coordinate multiple discrete non-resonant transmission elements into producing quasi-plane waves in the far field. Proposals for phase 1 need to present a definite design concept to be worked with a specific class of platform in mind, not propose to do a paper study of several approaches that could be considered. A concept of antennas that facilitate energy efficiency via co-utilization by multiple functions, optimal placement, use of untapped energy sources and energy and area effective design is to be reflected in the proposal. PHASE I: This phase should elaborate and refine the design concept defined in the proposal. If the approach requires layering, e.g. of photo-voltaics with antenna elements or antennas in structural members, issues of shadowing/field distortion and strength of the composite should be assessed. Small experimental efforts might be tried if the required parts have a short lead time. Furthermore, directionality must be considered to leverage gain to mitigate the power requirement. Arrays should be considered for optimal location and creating a real estate trade space. Multiple functionally needs to be addressed for receive, transmit, and geolocation, simultaneously. Design concepts that could be utilized for expendable, off board antennas would be acceptable as would antennas suitable only for naval combatants. Critical performance parameters include radiation patterns, gain and power handling for the antenna and power produced and cost efficiency for the alternate energy sources. By the end of phase 1 base, a clear image should have formed for the phase 2 proof of concept demonstration and the technical risk of the approach be strongly reduced. PHASE II: Execute the proof of concept developed in phase 1 first at small scale in a lab and then, after iterating the design, on an antenna range or in an anechoic chamber using a representative example of the platforms of interest. This prototype phase might be included, if suitable, a fleet experiment and exercise. PHASE III: Transition to a program responsible for the focused on platform demonstrating its increased performance would be expected. Production of an advanced prototype, further integration and limited production is anticipated. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: While HF is decreasingly of interest to the wireless community due to its lack of locality and congestion, the dual functionality approaches to antennas developed here should also be applicable in shrinking higher frequency systems. For example, having the antenna for a cell phone be spread over the entire package will help increase the antenna gain and lengthen battery life, especially if the power distribution is adaptive and thus turns off segments under the human's supporting hand.
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