Martin & Minear Method: 1st operationally feasible widely spaced antenna coherent transmit
with continual self-calibration of ALL electronics, circuitry and optics
and real-time atmospheric mitigation
EIRP increase: Plot shows increase in EIRP as each of the three 12m antennas was turned on during the demonstration.
When the signals leaving identical antennas are coherently combined, the EIRP is increased by N squared where N is the number of antennas. Example: For N=2, the EIRP increased by 6 dB. (N squared is 4, which is 6dB). Similarly, for N=3 (three antennas), the EIRP increase is about 9.5 dB (see arrow pointing to 'All 3').
Martin & Minear Method for "Widely-Spaced, Large Reflector, Coherent Transmit Arraying"
Initial results were first presented at the 2010 AIAA Conference, 'Delivering on the Dream'Authors:
Final results are published here: AIAA SpaceOps 2011, Chapter 24
Held the phase (antennas remained coherent) for over 6 months without the need for periodic re-calibration, until the system was powered down using COTS antennas
Traditional time-transfer methods require periodic re-calibration after just hours (possibly days if custom, state-of-the-art temperature controlled antennas and hardware are used like DSN)
Installation of the 12m antennas at KSC: InterTronic Solutions moved the antennas from Palm Bay, Florida to KSC.
Determination of antenna locations: Specialized Arrays performed obscuration analysis to determine the optimal antenna placement. Due to severe environmental, available land, and line-of sight to target constraints, the dish locations had to be within a couple of meters of these positions.
Operations center configuration at KSC:
Specialized Arrays researched, located, and configured the trailer layout including power requirements.
Primary benefits: Overcomes the size and power limitation of a single reflector system. Able to use COTs vs. custom hardware. Dispersed near-field radiation. Enables precision electronic beam control
Examples: Potential system applications include deep space communications, high resolution imaging of distant objects, space situational awareness, off-shore platform communications, battlespace awareness
Definition: Adaptive combining of large widely-spaced antenna elements for simultaneous coherent transmission and reception of signals
Real time atmospheric mitigation: Click on thumbnail to see atmospheric mitigation algorithm working during a tropical depression.
Graph 1/3: The difference between the measured and modeled receive phase is due to the atmosphere. Note both cyan and magenta data would be nearly zero if the model were correct and without atmospheric phase effects.
Graph 3/3 With atmospheric mitigation algorithm turned on a signal variation of only 0.3 dB is evident. The signal variation is 2.2dB without the method.
NASA-funded TxACE: 2008 - 2010
Dr. G. Patrick Martin & Ms. Kathleen Andreozzi Minear were the Principal Investigators on the NASA-funded TxACE program from September 2008- September 2010.
In order to coherently combine signals leaving antennas that are widely spaced, three sources of phase error were addressed.
(1) Time -of-flight from each antenna to the target
(2) Different signal paths including circuitry, electronics, and fiber
(3) Each antenna 'sees' a different column of atmosphere. Water vapor 'slows' the signal down
The TxACE antennas were moved and reassembled at KSC by InterTronic Solutions: The KaBOOM program mission was to implement a ground RADAR system using the 3-12m antennas used on TxACE for COMM. New algorithms and hardware were required to go from the X-band demonstration to Ka-band (~32GHz). The goal was high-resolution imaging and characterization of space objects.
NASA's interest in asteroids continues but with funding issues, citizen science and commercially led efforts are encouraged.
A request For Information (RFI) was issued by Dr. Christopher Moore of NASA HQ June 18, 2013.
"NASA is interested in concepts for augmenting and accelerating ground and space-based capabilities for detecting all near-Earth asteroids (NEAs) including those less than 10 meters in size that are in retrievable orbits, determining their orbits, and characterizing their shape, rotation state, mass, and composition as accurately as possible."
* Handling of RF carrier and information content (bits) separately. 1st demonstrated on NASA TxACE 2008-2010
Benefits of large reflector arrays
(1) Precision electronic beamsteering: mitigates large single antenna mechanical pointing limitations
(2) Beams & Nulls: Adaptive beamforming maximizes signals of interest while minimizing interferers
(3) Commodities: Cost per reflector (12m or smaller) has decreased. (InterTronic Solutions Inc)
(4) Power: High power amplifiers are not required.
(5) Transmit: EIRP increases as number of elements squared ; G/T increases linearly
(6) Dynamically reconfigurable, expandable, flexible allocation of resources - random placement
(7) Graceful degradation in the event of element failure or maintenance; scheduled maintenance
(8) Can control radiated power in unwanted directions
There have been three widely-spaced transmit arraying demonstrations indicating the viability of this new technology and its potential to solve a wide range of mission problems
Three uplink methods summary
IEEE "Uplink Arraying for Solar System Radar and Radio Science" by Davarian F. JPL
This document contains images of the installation of the antennas and configuration of the operations center at KSC as appeared on June 5, 2013.
Site credit: Dr. Geldzahler, NASA HQ, and Mark Seibert, KSC
Transmit array demonstration: In 2010 the first operationally feasible widely-spaced, large reflector transmit array was demonstrated on NASA-funding in Palm Bay, Florida. Specialized Arrays principals, Martin & Minear were the inventors and principal investigators. The modulated signals from three 12m diameter widely-spaced reflectors were combined during transmissions to the geosynchronous DSCS B13 (Defense Satellite Communications System) with less than 0.5dB combining loss. The antennas were about 60 meters apart which is over 2000 wavelengths at X-band. Atmospheric and all signal path phase variations were mitigated autonomously in real-time.
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