N251-001 TITLE: Directional High Front to Back Ratio Low Frequency (< 90 MHz) Antenna

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials;Microelectronics

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a compact lower frequency communications antenna in the High Frequency (HF) (3MHz – 90MHz) spectrum with the ability to direct gain in a desired direction and minimize the gain in the opposing direction. The antenna is to be lightweight, compact, and tactically relevant. The antenna should be employed near enemy forces such that it can transmit in the direction of friendly forces and in the opposing direction minimize the power radiated.

DESCRIPTION: The Marine Corps seeks a compact (less than 6ft long), lightweight, lower communications frequency antenna (High Frequency (HF)/Very High Frequency (VHF) Range). The ability to adjust the frequency (microelectronics or physically) is required to maintain a minimum size. The antenna must operate in the 1.5MHz to 90MHz range (Threshold) and it is desired to operate slightly below the HF and in the HF/VHF/Ultra High Frequency (UHF)/Extremely High Frequency (EHF) ranges (Objective). Antennas as described above are already available at larger lengths (10’ Whip and Vertical Dipole 12’ to 18’). It is required to use such an antenna connector that is already fielded/used antenna in HF radios. See references for HF radios and links for associated antenna.

Directional gain should be maximized in a given direction, and in the opposing direction minimized (180 degrees). A drop of 30dB in the opposing direction (Threshold), 60+dB in the opposing direction (Objective) is desired. Low frequency Radio Frequency (RF) has a low directivity making the drop in gain difficult. Adaptive structures are sought that would allow non-hazardous materials (Threshold) to be used. Materials used typically in anechoic chambers are hazardous (Absorptive Foam) and usually pyramidal, which is too large for tactical use. Therefore, it is desired that alternate materials or active structures be used to ground the RF energy. References discuss the types of material absorption that may work and current research into this area.

Antenna form factors are usually vertical polarized using a dipole antenna. Thus, a structure suited to controlling energy in a compact (6ft or less) antenna are desired. The thickness of the material required should be less than 2" to reduce the operational impact (Threshold) and less than 0.25" is desired (Objective) and could be some type of antenna coating or grounded shielding that allows directional radiation. Thin materials that can absorb or ground the RF energy in a certain direction while minimizing the effect on the dipole antenna are required. The use of a directive low frequency antenna use case is limited to military use thus very little research has been done to provide directive HF antennas.

Advanced material research is deemed necessary, partnership with a university or research institution on advanced materials is encouraged.

PHASE I: Define and develop concepts for a device to absorb RF energy in the opposing direction of the directive gain for a compact antenna. Using modeling and simulation, determine the technical feasibility of the design of such a device. Describe the method and recommended materials required to build a structure and how it can be used tactically with HF radio antennae. Provide a Phase II development plan with performance goals and key technical milestones that will address technical risk reduction and includes development of a prototype.

PHASE II: Develop a scaled prototype integrated with a representative RF antenna that covers the frequency range and provides the required directivity and front to back (180 degree) power drop in a desired direction. Evaluate the prototype to determine its capability in meeting the performance goals defined in the Phase II development plan and Marine Corps requirements for HF transmission with a military radio. Demonstrate radio performance in the desired direction, and drop in detectability in the undesired direction in a prototype demonstration. Use evaluation results to refine the prototype into an initial design that will meet Marine Corps (tactical use) requirements and satisfies MIL-STD-810 environmental factors. Prepare a Phase III development plan to transition the technology to Marine Corps use.

PHASE III DUAL USE APPLICATIONS: Support the Marine Corps in transitioning the technology for their use. Develop the antenna directivity solution for evaluation to determine its effectiveness in an operationally relevant environment. Support the Marine Corps for testing and validation to certify and qualify the system for Marine Corps use.

The compact antenna has use in the commercial and amateur radio market based on its ease of use. The directivity capability could be used to improve communications (reduce interference) in a particular direction.

REFERENCES:

1. "Radiation-absorbent material." https://en.wikipedia.org/wiki/Radiation-absorbent_material

2. Ruiz Perez, Fernando. "Carbon-based, radar absorbing materials: A critical review." Journal of Science Advanced Materials and Devices 7(3):100454, April 2022. DOI:10.1016/j.jsamd.2022.100454.

https://www.researchgate.net/publication/359886052_Carbon-based_radar_absorbing_materials_A_critical_review

3. "AN/PRC-160(V) Wideband Hf/Vhf Manpack Radio." L3Harris. https://www.l3harris.com/all-capabilities/an-prc-160v-wideband-hf-vhf-manpack-radio

4. "L3Harris’High-frequency Radio Solutions Provide On-the-Move Communications in Satellite-denied Environments." L3Harris Spectrum Magazine, October 2020. https://issuu.com/l3harrisspectrum/docs/spectrum_magazine_ausa_2020_9oct2020/s/11138710

KEYWORDS: High Frequency (HF); Advanced Materials; Radiation absorbent materials (RAM); Radio Frequency (RF); absorption of RF; Directivity; Very High Frequency (VHF); Ultra High Frequency (UHF); Extremely High Frequency (EHF)

TPOC 1: Bradford Crane
Email: [email protected]

TPOC 2: Roger Kulbeth
Email: [email protected]

---