1. Distributed Adaptive Control and Metrology for Large Radar Apertures Principal Investigator: James Lux, P.E. (337) Dr. Elaine Chapin (334), Samuel Li (337), Luis Amaro(337), Ofelia Quintero(337) Poster No. 05 - 003 Project Objective: Develop and demonstrate method of self-calibrating large (>100 m 2 ) phased array radar antennas without requiring a centralized metrology system. FY05 Results: Defined set of validated radar performance requirements Significant driving requirement is sidelobe performance Sidelobes < -30dB requires overall phase control to 1° rms Performance budget requires calibration to 0.1° rms Developed distributed calibration technique Uses mutual coupling between elements and beacon(s) for synchronization and frequency/phase reference. Demonstrated calibration technique with 3 active elements. Extended FY04 breadboard to 1.26 GHz radar frequencies “Antenna simulator” simulates interelement coupling Breadboard captures data, postprocessed with Matlab ® Produced 25 element antenna array for testing Square array (5x5) dual polarization patches Configuration allows testing nearest neighbor, cross polarized, 2 elements away, etc. Benefits to NASA and JPL: Future Earth Science missions contemplate the use of radar antennas tens of meters in extent and hundreds of square meters in area with tens of thousands of active elements. Accurate control of phase and amplitude for each element is required to meet overall performance requirements, particularly for sidelobes. Effects such as aging, radiation, and temperature change the phase & amplitude characteristics of the element electronics. The changes must be measured and calibrated out, after the radar is deployed in orbit. The method developed here is very scalable, without the limitations imposed by the use of centralized metrology systems, which have limits on the number of elements that can be calibrated at once. Self calibration may allow relaxed component performance specifications, reducing parts, ground testing and calibration cost. 5x5 patch array for testing (3 elements used, others terminated) Power Spectrum of Received Signals from Self, Beacon, & Other Elements Time (sec) Node 2Node 3Node 4 Tx Node 2 Node 3 Node 4 Coupling between elements is quite stable, can be modeled accurately, and “factored out” Measuring a calibration signal transmitted from one element and received by adjacent elements can be used to calculate the properties of the electronics. Need >2 elements in “Cal group” to be able to distinguish between Tx side and Rx side. Cal signals are low power and compatible with radar waveforms, so many groups can calibrate simultaneously, and will not interfere with the radar operation. E.g. 1% of elements are calibrated at any given time, and the other 99% do the radar work. Self Calibration Method PC Server for control and data collection Breadboard with 3 Elements Synchronization “pulse” All nodes reset. Signal from Node 4Signal from Node 32 Beacon Tones Net RF signal generator as beacon Own transmitter 1.26 GHz RF section Single-board PC + IF radio 5x5 Test Array Relative Power (dB) 1.26 GHz RF section Single-board PC & IF radio Single- board PC Wireless Network DDS IF Radio 1.26GHz Rx 1.26GHz Tx 10 MHz Ref Osc T/R switch