TECHNOLOGY AREA(S): Weapons
OBJECTIVE: Develop, prototype and prove out a repeatable and cost effective means of readily measuring W-Band RF field strengths (two ranges) while in field conditions and to a traceable control/reference baseline.
DESCRIPTION: Making accurate & traceable (calibrated) measurements of W-Band RF fields is challenging and time-consuming, even in a controlled laboratory, as it requires expensive instrumentation and procedures, with meticulous controls for assuring calibration and experimental repeat-ability. Performing these same system performance measures in less controlled environments (particularly outdoors) compounds these challenges. The core need is for a means of RF telemetry instrumentation which is inexpensive to acquire and operate, particularly for conditions outside of a benign laboratory environment, which will facilitate an automated self-calibration system that can be designed into an RF transmitter system. The data collected is commonly used to verify basic RF transmitter function (output power, RF field strength (power density), RF field directionality/antenna beam focus) which has needs to be applied both "in beam" (achieving the design intent at target performance levels) as well as "out of beam" (for establishing RF field safety boundaries). The intended application can include highly directional high gain antennas (50+dB) which can result in peak field strengths as high as 100W/cm2, while the RF safety measures are low as 0.1mW/cm2 to 100mW/cm2 (traces to IEEE C95.1 Safety Values for Zone 0 / Zone 1 / Zone 2). Similarly, the application of the collected data may need to be expressed as instantaneous power and/or time-averaged power (or both), with an eventual goal of a real time data stream. Challenges can be illustrated in current RF measurement methods. A collecting horn is good for increasing low field strengths, but are overwhelmed at high field strengths. Similarly, they are sensitive to polarity, physical positioning (misalignment) as well as field gradients (particularly in near field). Time-averaging using IR thermography on Carbon Loaded Teflon (CLT) sheets is simple, effective and polarity insensitive for high field strengths, but aren't capable of the low (safety-centric) field strengths, plus their trace-ability path back to a calibrated control values is indirect, and the hardware itself is prone to questions on if adequate calibration is being maintained, even before contemplation of effects of ambient temperature, humidity/moisture, winds, solar loads, or literal "wear". Note: the primary W-Band target frequency is 95 +/- 3 GHz, and in two general field strength (power) ranges: (1): 0.1mW/cm2 to 100mW/cm2 (traces to IEEE C95.1 Safety Values for Zone 0 / Zone 1 / Zone 2) and (2): ~1W/cm2 to ~100W/cm2 (represents in-beam (focused) lower/upper engineering limits). While these field strength ranges contain a gap (between 100mW/cm2 and 1W/cm2), the solution should have no telemetry gap, but would incorporate an overlap. Similarly, because of the steep field gradient from high gain antennas, the solution for the lower power field range should not be prone to damage if/when it is unintentionally exposed to the higher power field.
PHASE I: During Phase I effort, the plan is to explore the specific requirements in greater depth & understanding, conduct baseline analysis & trades, calibration concepts & outline plans, and provide a pilot ‘breadboard’ concept demonstrator(s) for a feasibility check using a Government-supplied W-Band transmitter. Deliverables shall be final report (highlighting the pros/cons of various approaches), the breadboard, and recommended Phase II path forward. Deliverables should include consideration of unit costs on the concepts explored, such as to address having multiple sensors to collect multiple locations simultaneously (application of developing measurements for Safety Zones).
PHASE II: Develop the approach developed during phase I, with emphasis on the instrumentation requirements and calibration methodology; perform discrete feasibility experiments & provide data reduction & conclusions; initiate fabrication of system demonstrator. Conduct a series of tests as detailed which will prove out the technology and the fidelity of the calibration methods being used. The phase II final delivery should include the following: • Robust demonstrator system – turnkey solution (hardware/software); • Full system design, with calibration processes and resources (Executable and source code as developed); • Test Report, detailing the key factors for calibration & maintenance of same; • Operator’s Manual for use of demonstrator; • White Paper on future technology growth into a fully automated self-calibrating RF system.
PHASE III: Refined and matured technology solution for a subsystem which will allow for RF transmitter systems to have automated self-calibration control of RF power /field strengths and of antenna field patterns (directionality/alignment, uniformity, focus/aiming). Commercial & Military applications will be able to integrate these telemetry systems to employ automated feedback loops for enhancing control over net total output power, power density, antenna alignment & focus for W-Band weapons & mm-W radars, and be an enabler for dynamic real time directional syncing of two way narrow-beam communications.
1: Hati, A., Nelson, C.W., Nava, J.F. Garcia, Howe, D.A., Walls, F.L., Ascarrunz, H., Lanfranchi, J., Riddle, B., "W-Band Dual Channel AM/PM Noise Measurement System " An Update," Proceedings of the 37th Annual Precise Time and Time Interval Systems and Applications Meeting, Vancouver, Canada, August 2005, pp. 503-50
2: Fralick, Dion T. "W-band free space permittivity measurement setup for candidate radome materials." (1997).
3: Scheiblauer, Stefan. "W-band for CubeSat Applications." https://artes.esa.int/funding/cubesat-based-w-band-channel-measurements-artes-51-3b033 (2016).
KEYWORDS: W-Band, RF, Measurement, Instrumentation, Calibration, Carbon Loaded Teflon, FLIR, Thermal Imaging